Radiation Detection and Interdiction at U.s. Borders

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Radiation Detection and Interdiction at U.S. Borders

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Radiation Detection and Interdiction at U.S. Borders Edited by Richard T. Kouzes Joseph C. McDonald Denis M. Strachan Sonya M. Bowyer

1

1 Oxford University Press, Inc., publishes works that further Oxford University’s objective of excellence in research, scholarship, and education. Oxford New York Auckland Cape Town Dar es Salaam Hong Kong Karachi Kuala Lumpur Madrid Melbourne Mexico City Nairobi New Delhi Shanghai Taipei Toronto With offices in Argentina Austria Brazil Chile Czech Republic France Greece Guatemala Hungary Italy Japan Poland Portugal Singapore South Korea Switzerland Thailand Turkey Ukraine Vietnam

Copyright © 2011 by Oxford University Press Published by Oxford University Press, Inc. 198 Madison Avenue, New York, New York 10016 www.oup.com Oxford is a registered trademark of Oxford University Press All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior permission of Oxford University Press. Library of Congress Cataloging-in-Publication Data Radiation detection and interdiction at U.S. borders / edited by Richard T. Kouzes ... [et al.]. p. cm. ISBN 978-0-19-975450-2 (hardcover : alk. paper) 1. U.S. Customs and Border Protection. Radiation Portal Monitor Project. 2. Nuclear terrorism—United States—Prevention. 3. Radiation—Measurement. 4. Terrorism—Government policy—United States. I. Kouzes, Richard. II. Title. HV6433.86.R23 2011 363.325’564—dc22 2010046709 1 3 5 7 9 8 6 4 2 Printed in the United States of America on acid-free paper

DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor Battelle Memorial Institute, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or Battelle Memorial Institute. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

{ contents } List of Illustrations Preface Acknowledgments Introduction Acronyms and Abbreviations Units

xi xix xxi xxiii xxvii xxix

1 Overview of Radiation Interdiction 1.1 Radiation Portal Monitor Project History 4 1.1.1 Interdiction Goals and Objectives 5 1.1.2 Radiation Portal Monitor Project Mission 6 1.1.3 Initial Radiation Portal Monitor Project Activities 7 1.1.4 The Beginning of Radiation Portal Monitor Deployment 1.1.5 Deployment Advances 11 1.1.6 Moving Toward Project Completion 13 1.2 Detecting Threats 14 1.2.1 Threats 15 1.2.2 Example Incidents 16 1.2.3 Instrumentation to Counter the Threat 17 1.2.4 Specifications and Standards 19 1.2.5 The Multilayer Defense 20 1.3 The Necessity of Interdiction 21 1.4 References 24

3

8

2 Radiation Sources 2.1 Physics and Statistics of Radiation Sources 26 2.1.1 Gamma-Ray Interactions with Matter 27 2.1.2 Neutron Interactions with Matter 29 2.1.3 Neutron and Gamma-Ray Spectroscopy 31 2.1.4 Statistics 33 2.2 Background Radiation Sources 35 2.2.1 Cosmic Background 36 2.2.2 Earth–Terrestrial Background 46 2.2.3 Construction Materials 48 2.2.4 Weather-Related Variations 49 2.3 Naturally Occurring Radioactive Materials 57 2.3.1 Radioactive Sources of Concern and Common Legitimate Sources 2.3.2 Photon Emission Spectra from Cargo 61 2.4 Scope and Impact of Medical Radioisotopes 64

26

58

vi

Contents 2.4.1 Medical Radionuclide Use 65 2.4.2 Medical Radionuclide Survey Results 67 2.4.3 Medical Radionuclide Decay Properties 68 2.4.4 Detector Response Calculation Configurations 69 2.4.5 Detector Response Modeling Method 72 2.4.6 Detector Response Modeling Results 72 2.4.7 Expected Occurrence of Radionuclide Alarm Events 74 2.5 Industrial Radiation Sources and Special Nuclear Materials 77 2.5.1 Common Industrial Radiation Sources 78 2.5.2 Special Nuclear Materials 80 2.6 Electromagnetic Interference Effects 81 2.6.1 Sources of Radio Frequency Interference 83 2.6.2 Radio Frequency Interference 84 2.6.3 Electromagnetic Pulse Effects 85 2.6.4 Summary 86 2.7 References 86

3 U.S. Customs and Border Protection Radiation Interdiction Approach 3.1 Radiation Detection Mechanisms 91 3.1.1 Gamma-Ray Detection Mechanisms 92 3.1.2 Neutron Detection Mechanisms 96 3.2 Interdiction Options 97 3.2.1 Radiation Detection for Interdiction 98 3.2.2 Instrumentation Options 98 3.2.3 General Instrument Requirements 99 3.2.4 Options Considered for Scanning at Mail and Express Consignment Courier Facilities 101 3.2.5 Options Considered for Scanning at Land Border and Rail Crossings 101 3.2.6 Options Considered for Airport Cargo Scanning 102 3.2.7 Options Considered for Seaport Scanning 102 3.2.8 Radiation Portal Monitor Specifications 104 3.3 Instruments and Capabilities 106 3.3.1 Detection Technologies 106 3.3.2 Radiation Portal and Area Monitors 110 3.4 Imaging Systems 135 3.4.1 Nonionizing Radiation Technologies for Imaging and Identification 137 3.4.2 Ionizing Radiation Imaging Technologies 139 3.4.3 Future of Cargo Scanning 154 3.4.4 Future of Scanning People 155 3.5 Active Interrogation Techniques 155 3.5.1 Interrogation Techniques 156 3.5.2 Signature Detection 159 3.5.3 Active Interrogation Requirements 159 3.6 References 161

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Contents

4 Enhancing the Effectiveness of Radiation Portal Monitor Systems

vii

163

4.1 Modeling and Simulation 163 4.1.1 Photon Detection Efficiency 165 4.1.2 Specific Detector Simulations 168 4.1.3 Unshielded-Source Results 171 4.1.4 Spectral Distributions 172 4.1.5 Vehicle Modeling 175 4.1.6 Model Results for Simulated Drive-Through Scenarios 178 4.1.7 Observations 180 4.2 Intelligent Algorithms for Plastic Scintillator Gamma-Ray Detectors: Energy Windowing 181 4.2.1 Thresholds and Nuisance Alarms 182 4.2.2 Description of Naturally Occurring Radioactive Material and Special Nuclear Material Signatures 184 4.2.3 Algorithms for Radiation Detection 185 4.2.4 Summary of Energy Windowing Studies 203 4.3 Other Intelligent Algorithms for Plastic Scintillator Gamma-Ray Detectors 203 4.3.1 Absolute Threshold Algorithm 203 4.3.2 Cross-Talk Suppression in Multilane Deployments 204 4.3.3 Vehicle Speed and Detector Measurement Time 204 4.3.4 Tracking Algorithms for Background Suppression from Vehicles 205 4.3.5 Spatial Distribution of Naturally Occurring Radioactive Material Versus Point Sources 206 4.3.6 Spatial Distributions for Passenger (Noncommercial)Vehicles 206 4.3.7 Spatial Optimization 207 4.4 Baseline Suppression 218 4.4.1 Vehicle Profiles 220 4.4.2 Observations on Baseline Suppression 223 4.4.3 Baseline Suppression for Energy Window Ratios 224 4.4.4 Summary 226 4.5 Spectroscopic Portal Monitors (SPMs) 226 4.5.1 Drivers and Requirements for Deploying Spectroscopic Portal Monitor Systems 228 4.5.2 Prototype Spectroscopic Portal System 229 4.5.3 Specification for Spectroscopic Portal Monitors 232 4.5.4 Comparison of Thallium-Doped Sodium Iodide and High-Purity Germanium Detector Materials 234 4.5.5 Advanced Spectroscopic Portal (ASP) Program 235 4.5.6 Deployment Strategy 236 4.6 Human Factors in Radiation Portal Monitoring Systems 237 4.6.1 Human Role in Radiation Portal Monitor Security Decision Making 237 4.6.2 System Trust 239 4.6.3 False and Nuisance Alarms 240 4.6.4 Situational Awareness 242

viii

Contents 4.6.5 Applications to Radiation Portal Monitor Systems: The Likelihood Display Concept 243 4.6.6 Distinguishing between Illicit Material and Naturally Occurring Radioactive Material: Human Factors Applications 244 4.6.7 Human Factors Impact 246 4.7 References 246

5 Radiation Portal Monitor Project Deployment Summary 5.1 5.2 5.3 5.4

5.5

5.6

5.7

5.8

5.9

Introduction 249 Deployment Approach 251 Deployment Process Flow 251 Northern and Southern Land Borders 252 5.4.1 Primary Scanning 252 5.4.2 Secondary Scanning 256 5.4.3 Ancillary Equipment 257 Seaports 258 5.5.1 Primary Scanning 259 5.5.2 Secondary Scanning 261 5.5.3 Ancillary Equipment 261 International Mail/Express Consignment Courier Facilities 5.6.1 Primary Scanning 263 5.6.2 Secondary Scanning 266 5.6.3 Ancillary Equipment 268 International Airports 268 5.7.1 Primary Scanning 269 5.7.2 Secondary Scanning 269 5.7.3 Ancillary Equipment 269 Rail Crossings 270 5.8.1 Primary Scanning 270 5.8.2 Secondary Scanning 271 5.8.3 Ancillary Equipment 272 References 272

6 Operational Considerations for Radiation Interdiction 6.1 6.2 6.3 6.4 6.5

249

263

273

Overview of Operations for Radiation Interdiction 273 Operational Impacts of Gamma-Ray Alarms 276 Operational Impact of Neutron Alarms 281 National Integration of Radiation Portal Monitor Data 283 References 285

7 Related Work 7.1 Testing, Evaluation, and Standards 287 7.2 International Atomic Energy Agency Activities 291 7.3 Second Line of Defense Program 294 7.3.1 Second Line of Defense Core Program 295 7.3.2 Second Line of Defense Megaports Initiative 296 7.3.3 United States Interagency Relationships 297

287

Contents

ix

7.4 Department of Defense Programs 297 7.4.1 Joint Service Installation Pilot Project and Unconventional Nuclear Warfare Defense 298 7.4.2 Installation Protection Program “Guardian” 299 7.5 U.S. Department of Homeland Security’s Science and Technology, and Domestic Nuclear Detection Office Efforts 301 7.6 References 304

8 The Future for Interdiction of Radiological and Nuclear Threats at Borders 8.1 Detection Technologies 307 8.1.1 Signatures 307 8.1.2 Detectors 308 8.1.3 Passive Detection 309 8.2 Alarm Algorithms 309 8.3 Signal Processing and Alarm Criteria 310 8.4 Radioactive Isotope Identification 311 8.5 Vehicle Geometry Recording 312 8.6 Identification and Tracking Subsystems 312 8.7 Smaller Radiation Detection Systems 312 8.8 Imaging and Other Active Probes 313 8.8.1 Imaging 313 8.8.2 Interrogation 314 8.8.3 Interrogation and Detection with Imaging 314 8.9 Data Handling and System Control 315 8.10 Automatic Triage with Smart Alerts to Remote Centers 8.11 Data Fusion 316 8.12 Communication Standards 316 8.13 Modularization (Both Hardware and Software) 317 8.14 Multithreat Interdiction Technology Integration 317 8.15 Remote State-of-Health Monitoring 317 8.16 Control 317 8.17 Instruments for the Port of the Future 318 8.18 Away from U.S. Ports of Entry 318 8.18.1 Advance Scanning and Container Security 318 8.18.2 Small-Boat Scanning 318 8.18.3 Automation Aids 319 8.19 Summary 319 8.20 References 320

Contributors Index

306

315

323 325


{ list of illustrations } Figures 1.1 1.2

The 307 U.S. ports of entry representing 621 crossings Primary portal at Fort Street Cargo Facility, Detroit, Michigan, showing the first installed radiation portal monitor system commissioned in October 2002 1.3 Examples of Soviet nuclear weapons displayed in a Russian museum 1.4 Soviet 90Sr orphaned source recovered in the former Soviet Republic of Georgia 1.5 Orphaned radioactive well logging sources 1.6 An example of the total gamma-ray counting rates in counts per second from a typical scintillating plastic used in vehicle radiation portal monitor systems showing the mean distribution of 5,000 cargo vehicles with and without naturally occurring radioactive material plus background, the distribution of background alone, and a simulated test source 2.1 Graph of the Z of the absorber and the energy of the gamma ray 2.2 Neutron elastic scattering cross sections for three common elements 2.3 Neutron spectrum from a 252Cf spontaneous fission source 2.4 Energy spectrum produced by gamma rays from 60Co and displayed by a multichannel analyzer 2.5 Illustrative example of Gaussian distribution 2.6 Forbush decrease as seen with the four neutron monitors over the course of 13 days in late October and early November 2003 2.7 Process of primary cosmic particles entering the upper atmosphere and producing secondary particles as they strike air molecules along the way 2.8 Relationship between magnetic rigidity and the minimum particle energy necessary for a cosmic particle to reach the surface of the Earth excluding absorption effects in the atmosphere 2.9 Lines of magnetic rigidity cutoff that relate to the minimum energies that can be observed at locations shown in Figure 2.10 2.10 Map illustrating the location of some of the 52 cosmic-ray neutron monitors used to examine the relationship between cosmic background and the background measured at the radiation portal monitor locations

10

11 15 17 17

19 28 30 32 33 34 37

38

39 40

42

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List of Illustrations

2.11 The neutron count rate measured at the Newark Neutron Monitor in Newark, Delaware, with the neutron count rate measured at four radiation portal monitor locations shown as the lower four traces 44 2.12 The neutron count rate at the Newark Neutron Monitor against the total gamma-ray background count at four radiation portal monitor locations during a major solar flare in late October 2003 44 2.13 The neutron count rate measured at the Newark Neutron Monitor in Newark, Delaware, with the neutron count rate measured at four radiation portal monitor locations shown as the lower four traces 45 2.14 Maps based on the U.S. Department of Energy National Uranium Resource Evaluation program and extracted from the U.S. Geological Survey in Digital Data Series DDS 9. The top map shows the abundance of potassium (40K). The middle map shows the abundance of thorium 47 (232Th). The lower map shows the abundance of uranium (238U). 2.15 Map illustrating the locations of weather stations around the conterminous United States and the surrounding border regions that were available for examining the relationship between weather and the background measured at the radiation portal monitor locations 50 2.16 Average diurnal response of total gamma-ray, low-energy gamma-ray, high-energy gamma-ray, and neutron background as a function of time of day 55 2.17 High-purity germanium spectrum of marble tile 62 2.18 High-purity germanium spectrum of typical kitty litter 63 2.19 High-purity germanium spectrum of typical snow and ice melt salt, dominated by 40K 63 201 2.20 Gamma-ray spectrum emitted by a patient who had a Tl stress test weeks earlier 65 2.21 Energy distribution of dominant gammas emitted from selected medical radioisotopes 70 2.22 Front-view scale drawing of Lane 1 71 2.23 Top view of Lane 1 showing optical zones of detection 71 2.24 Low-energy responses of Lane 1 panels to 99mTc for the back-to-back configuration 73 2.25 Time in days for medical radioisotopes to decay below the alarm threshold 75 2.26 Photograph of two types of industrial radiography sources assemblies 79 60 2.27 Photograph of Co source that may have been used for cancer radiation therapy or other applications mentioned in the text 79 2.28 Replicas of the “Little Boy” and “Fat Man” atomic bombs 81 2.29 Radio frequency energy spectrum taken in New York City 82 3.1 Schematic diagram showing basic components of photomultiplierbased scintillation detector 92 3.2 Mass attenuation, transfer, and absorption coefficients for NaI 94


3.3 3.4

3.5

3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 3.20 3.21 3.22 3.23 3.24 3.25 3.26 3.27 3.28 3.29 3.30 3.31 3.32 3.33

Comparison of three gamma-ray spectra of natural background radiation in Southeastern Washington using three types of detectors The mass attenuation and mass energy-absorption coefficients, μ/ρ and μen/ρ, respectively, as a function of gamma-ray energy for CsI from XCOM tables Neutron total absorption cross sections for the 6Li(n,α)3H, 10B(n, α)7Li, and 3He(n,p)3H interactions from the Korea Atomic Energy Research Institute Cross-Section Plotter Polyvinyl toluene plastic scintillator with photomultiplier tubes attached at the right Measured spectra from polyvinyl toluene plastic scintillator detector Measured spectra from NaI(Tl) detector Two large-volume NaI(Tl) detectors with photomultiplier tubes attached and enclosed in metal shielding Layout of radiation sensor panel components within the environmental enclosure Alarm view scan, supervisory computer shown at a test facility Radiation portal monitor concept for cargo portals with existing U.S. Customs and Border Protection kiosks Basic architecture of a radiation portal monitor system with limited ancillary equipment Inside an NaI(Tl)-based prototype radiation sensor panel developed by Pacific Northwest National Laboratory Mobile radiation portal monitors in two-sided configuration Concept for a rail radiation portal monitor system Remotely operated radiation portal monitor Artist’s image of a straddle carrier portal concept Prototype mobile straddle carrier radiation portal monitor Concept for a portable source identification device Example personal radiation detector: Radiation Pager® Example radioisotope identifier device Bank of monitors for viewing area surveillance system imagery Auto dialer Modular booth Gate arm deployment Representative inductive loop presence sensor Lane speaker box and booth master unit for wireless intercom Optical character recognition reconciliation tool interface shown at a test facility Optical break-beam presence sensors typically used on radiation portal monitors Example programmable logic controller module Rail identification system components Strobe/siren unit installed at mail/ECCF deployment

xiii

95

95

97 107 108 108 109 111 113 114 114 116 117 118 119 120 122 122 124 124 126 126 127 128 128 129 132 132 133 133 134

xiv


3.34 Visual identification system images displayed at a test facility 3.35 Visual identification system camera and lighting attached to a radiation portal monitor 3.36 The Acoustic Inspection Device is a handheld gun that transmits ultrasonic pulses and detects return echoes to determine the contents of sealed containers 3.37 An example of the PNNL radio frequency imaging system installed at a security gate 3.38 Nonintrusive weapons detection using millimeter waves reveals hidden objects of metal and plastic 3.39 Transmission of a radiographic image using a 3.8 MV linear accelerator 3.40 Schematic of imaging system incorporating simultaneous backscatter and transmission of X-ray images from a single source 3.41 Backscatter image of stowaways in a cargo container 3.42 Computed tomographic image of a suitcase taken with an airport luggage scanner 3.43 The X-ray spectrum is hardened after passing through filters of aluminum, copper, and tin 3.44 A transmission image with a 3.5-MeV beam of a 0.46-mdiameter object with alternating lead and aluminum spokes 3.45 Mass attenuation coefficients for photons in various materials 3.46 Isometric drawing of a relocatable vehicle and cargo inspection system for truck inspection at a border 3.47 Sectional view of the relocatable vehicle and cargo inspection system truck inspection station 3.48 Two examples of a large-footprint system employing a high-energy linac 3.49 Example of a high-resolution backscatter X-ray image of automobiles 3.50 Transmission image of a truckload of durians, a spiny Southeast Asian fruit 3.51 A backscatter X-ray image of the same truckload of durians, showing an anomaly 3.52 A backscatter X-ray imager for checking people for contraband 3.53 Image from a scan with a BodySearch “Z-Backscatter™” scanner 3.54 Image taken with a transmission system during trials (plastic knife on the hip); this individual received 0.25 μSv 3.55 A typical accelerator to produce a neutron beam 3.56 A typical electron accelerator used to produce bremsstrahlung photons for imaging; in this case, a pallet of plywood 3.57 Large panels of 6Li glass fiber thermal neutron detectors 4.1 Calculated intrinsic detection efficiency for PVT and NaI(Tl) 4.2 Calculated absolute detection efficiency for polyvinyl toluene and NaI(Tl)

135 136

137 138 139 140 142 143 143 144 144 145 148 148 150 151 152 152 153 154 155 157 158 160 165 168


4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11 4.12 4.13

4.14

4.15

4.16 4.17 4.18 4.19 4.20

xv

Measured 133Ba spectrum from Na(Tl) and PVT detectors 171 Calculated photon flux and spectra for polyvinyl toluene and NaI(Tl) for 241Am 172 Calculated photon flux and spectra for polyvinyl toluene and NaI(Tl) for 133Ba 173 Calculated photon flux and spectra for polyvinyl toluene and NaI(Tl) for 232Th 174 A photo of a 20 ft (6 m) “dry van” trailer and the three-dimensional screen model representation of the trailer vehicle 176 A three-dimensional rendering of the cargo as a “cutaway” of the trailer shown in Figure 4.7 176 Model-to-data ratio for 133Ba source locations within intermodal cargo container without cargo 177 Source locations used with the trailer model for validation 178 Simulated drive-through profile showing dense cargo suppression of background 179 Simulated drive-through profile for naturally occurring radioactive material cargo 180 Example of the total gamma-ray counting rates in counts-per-second from a typical polyvinyl toluene used in vehicle radiation portal monitor systems showing the distribution of cargo vehicles with or without naturally occurring radioactive material plus background, the distribution of background alone, and a simulated test source. The vehicle distribution is seen to be downshifted relative to the background distribution, showing the effect of shadow shielding 183 Spectra from polyvinyl toluene for (A) naturally occurring radioactive material radiation and background, and (B) highly enriched uranium, weapons grade plutonium, and background to illustrate the differences in the spectra at low energies 186 Count rates in counts per second per energy window in the three energy bins for background, highly enriched uranium, weapons-grade plutonium, fertilizer, and tile obtained by summing the spectra in Figure 4.3 192 The ratio of counts in the (A) low- and (B) medium-energy windows to the counts in the high-energy window 193 Typical naturally occurring radioactive material alarm vehicle profile from a cargo radiation portal monitor 195 Typical nonradioactive cargo vehicle profile showing background suppression due to shadow shielding 196 Total count profiles for each of 700 vehicles passing through a 4-panel radiation portal monitor 197 The channel-by-channel ratio of counts in a net source spectrum to counts from a background spectrum for spectra from 57Co, highly enriched uranium, 133Ba, weapons-grade plutonium, and depleted uranium 198

xvi


4.21 Detection probability versus number of injected counts for 57Co 4.22 Detection probability versus number of injected counts for 133Ba 4.23 Detection probability versus number of injected counts for depleted uranium 4.24 Results from a single measurement with 2 kg (4.4 lb) of depleted uranium walked through a radiation portal monitor, displayed as the standard deviations above or below zero for four delta statistics versus sample observation time 4.25 Schematic of radiation portal monitor background count rate during a commercial vehicle passage, illustrating the dense-load background suppression effect 4.26 Schematic of count rate of two commercial vehicle passages, illustrating the difference in the profiles of a uniform source and a point-like source 4.27 Radiation portal monitor geometry 4.28 Effect of limiting position on m values 4.29 Comparison of spatial profile model 4.30 Example of a measured temporal profile 4.31 Comparison of simulated and measured spatial profile 4.32 Effect of source strength on optimal limiting position, which is the distance over which the signal is integrated 4.33 Optimal sum intervals 4.34 Signal-to-noise ratio for constant sources 4.35 Figure of merit for point source sensitivity 4.36 Comparison of (a) spatial profiles and (b) MDAs for varying d values 4.37 Ensemble plots from 979 vehicles showing vehicle percent baseline suppression profiles for all four radiation portal monitor panels at Site (A), with all narrow lanes pooled 4.38 Typical vehicle percent baseline suppression profiles 4.39 Profiles of percent ratio suppression based on vehicle energy window ratios vis à vis background energy window ratios for the narrow lanes at Site (A) 4.40 Spectroscopic portal monitor prototype utilizing four NaI(Tl) logs 4.41 The measured spectral shape of a 228Th source as a function of lead-shielding thickness 4.42 Background and alarming stationary vehicle spectra for an NaI(Tl) portal 4.43 Drive-by spectra from 60Co and UO2 cargo 4.44 Timeline for the introduction of advanced spectroscopic portal systems into the U.S. Customs and Border Protection environment 4.45 General model of human element in radiation portal monitor security systems

201 201 202

202

206

207 208 210 211 213 213 214 215 216 217 218

221 222

225 229 231 232 233 236 238


4.46 Two general classes of human-mediated inspection systems 4.47 Two-state radiation portal monitor alarm system involves four postalarm steps 4.48 Likelihood alarm radiation portal monitor system provides more information to officers through green, yellow, and red indications 5.1 Radiation portal monitors in privately owned vehicle lanes 5.2 Standard four-panel cargo radiation portal monitors 5.3 Eight-panel wide cargo radiation portal monitor at secondary 5.4 Dual-use radiation portal monitor 5.5 Cantilever cargo portal 5.6 Secondary and bus portal 5.7 Ship at dock at a seaport terminal 5.8 Radiation portal monitors at a seaport terminal 5.9 Seaport terminal exit gate 5.10 Primary and secondary truck exit gate portals 5.11 Small conveyer belt radiation portal monitor configuration in an international mail facility 5.12 Typical radiation sensor panel configuration for a doorway in an international mail facility 5.13 Tug portal for scanning packages and mail while in transit to an international express consignment courier facility 5.14 Cart-mounted, portable radiation portal monitor system for international mail/express consignment courier facility 5.15 Truck portal at an international mail facility 5.16 Airport tug radiation portal monitor prototype at test bed facility 5.17 Rail radiation portal monitor prototype 6.1 A record of the gamma-ray signal observed for the passage of vehicles through a radiation portal monitor over a period of about 6 hours 6.2 Record of the observed gamma-ray signal from a number of vehicles passing through a radiation portal monitor 6.3 Shipments of smoke detectors can cause radiation portal monitor alarms due to the presence of 241Am sources in most units 6.4 Radiation source used as a density gauge for liquids flowing through the vertical cylinder 6.5 Depleted uranium is used in a number of commercial applications, including shipping shields for strong commercial radiation sources, military munitions and armor, and airplane counterweights 6.6 An example of a gauge used to measure concrete dryness and soil density; such gauges can contain both gamma and neutron sources 6.7 Nuclear fuel assembly containing thousands of fuel pellets 6.8 Neutron spike event induced by a cosmic ray as seen at channel 31 6.9 Radiation portal monitor response to a vehicle containing a neutron and gamma-ray source; the center curve is the neutron response

xvii

239 243

244 254 254 255 255 256 257 258 259 260 262 264 265 266 267 267 269 271 278 278 279 280

280 281 282 283 283

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Tables 2.1 2.2

2.3 2.4

2.5

2.6 2.7 2.8 2.9 3.1

3.2 4.1 4.2 4.3 4.4

4.5 5.1 7.1 7.2 7.3 7.4

Average Correlation Between Radiation Portal Monitor Locations and Similar Cosmic Ray Observatory Locations 46 Average Correlation of the Low-Energy, High-Energy, and Neutron Background from Nine Radiation Portal Monitor Locations with Nine Weather Parameters 49 Average Correlation between Seasonal Cycle and the Measured Radiation Portal Monitor Background 56 Naturally Occurring Radioactive Material and Technologically Enhanced Naturally Occurring Radioactive Material Activity in Bq/kg for Various Materials and Foods 60 Other Cargo Items Known to Contain Significant Levels of Naturally Occurring Radioactive Material and Technologically Enhanced Naturally Occurring Radioactive Material 61 Approximate Relative Percentage of Alarming Cargo Loads Containing the Listed Radioactive Materials Observed at Some Border Crossings 62 Summary of Survey Results for Medical Radionuclide Use 67 Intrinsic Decay Properties of Medical Isotopes 69 Frequencies of Interest 83 Absolute Gamma-Ray Detection Efficiency for a Radiation Portal Monitor Detector with the Sources 2 m (6.5 ft) from the Detector Face 106 Ancillary Equipment Applications 125 Photon Emission Data for Model Sources Used in MCNP Simulations; Dominant Gamma Rays Are Shown in the Shaded Boxes 169 Power Values for Various Source Shield Configurations 212 Vehicle Profile Summary Statistics for a Single Vehicle from Four Portal Panels at Site (A) as Shown in Figure 4.38 223 Absolute Detection Efficiency Comparison for a PVT-Based System Versus a NaI(Tl) System Consisting of Four 10 cm × 10 cm × 40 cm (4 in. × 4 in. × 16 in.) Crystals 230 Detection Efficiencies for Radionuclides 234 Ancillary Equipment Available for Deployment with Radiation Portal Monitor Systems 250 Description of Scope and Purpose of American National Standards Institute Standards for Homeland Security Applications 290 Personal Radiation Detectors 292 Vehicle Portal Monitors 293 Some Properties of Scintillator Materials 294

{ preface } U.S. Customs and Border Protection (CBP) is the agency within the U.S. Department of Homeland Security with primary responsibility for interdiction of terrorist threats at U.S. borders. Events in recent years have resulted in a dramatic change to CBP’s scope of responsibility. In early 2002, as part of its response to the events of September 11, 2001, and the heightened threat of nuclear or radiological terrorism, CBP created the Radiation Portal Monitor Project (RPMP). Through the deployment of sophisticated radiation detection technology at U.S. ports of entry, the objective of the RPMP is to significantly enhance CBP’s ability to scan for illicit trafficking of radiological threats at our nation’s legal ports of entry (POEs). In this book, we provide a wide range of information from multiple authors on applicable radiation detection and interdiction methods, and reports on the approach taken in the first several years of the project by CBP, and on its behalf, by the Pacific Northwest National Laboratory RPMP team in deploying equipment and establishing operational procedures to effectively interdict nuclear and other radioactive material threats. While concentrating on the efforts of the RPMP, this information is placed into the context of broader security efforts taking place around the world. The terrorist threat is an international concern and efforts to prevent terrorist acts are found within many sectors of the U.S. government, other governments around the world, and international organizations. Only through a coordinated multinational effort can we hope to counter threats from those who would seek to harm others through nuclear or radiological means. Through its technical and deployment efforts, the RPMP has generated a large body of scientific work. This document describes most of the project and significant technical results of the first several years of this effort, including introduction to the radiation interdiction problem, description of technical approaches and possible enhancements, discussion of lessons learned to date from technology deployments, overview of related work, and future considerations of radiation interdiction for border security. We have chosen to focus this document on the time frame from the inception of the RPMP in January 2002 through September 2005, the first several years of the project. In October 2005, the RPMP became a joint program that was comanaged by CBP and the newly created Domestic Nuclear Detection Office. We felt that it would be beneficial to take the opportunity provided by this natural transition to document many of the technical and operational aspects developed and observed in this first stage of the project. Therefore, this document primarily covers the time frame prior to the RPMP becoming a joint program in October

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Preface

2005. Because of the sensitive nature of any such U.S. Department of Homeland Security program, we have been careful to share only certain information and data so that this book may be made more widely available. This book is not intended to represent a broad consensus on all methods and approaches for interdiction of radiological materials. Rather, it represents the expansive knowledge base of the RPMP team and the approach taken by this project. The RPMP balanced several factors in defining a viable and effective plan for interdiction of radioactive materials at POEs. Characteristic of any large effort of national importance, there have been varied opinions expressed about the best approach to protect our POEs. We have always considered such a debate to be invaluable to vetting and defining the RPMP. This book is primarily the product of a small group of authors at Pacific Northwest National Laboratory, but it represents the body of work done by many individuals at the laboratory and CBP, as well as many external contractors. We, the editors, are privileged to represent this collaborative work. Richard T. Kouzes Joseph C. McDonald Denis M. Strachan Sonya M. Bowyer Editors January 2007

{ acknowledgments } The technical work described herein was produced by the individual contributions of many staff members at Pacific Northwest National Laboratory who have worked on the Radiation Portal Monitor Project. Our gratitude goes to each individual whose dedication and time have contributed to the progress of the project. Of special note are the early project leaders who established the foundation of the project: Randy Hansen, James Hartley, Richard Kouzes, John Schmidt, Robert Thompson, and Ray Warner. We wish to thank Hope Matthews and Lynn Roeder for their assistance in preparing this book. We also want to express our appreciation to the leaders at U.S. Customs and Border Protection who directed and supported the efforts described here over the first several years of the project. Of particular note is Mr. John Pennella, who initiated the Radiation Portal Monitor Project; Mr. Christopher Milowic, who oversaw the project at its beginning; Ms. Sharon Sharp-Harrison, who dealt with the dayto-day activities of the project since its inception; Mr. Ira Reese, a constant supporter of the project through his role as director of Laboratories and Scientific Services; and Mr. Todd Hoffman, the Office of Field Operations sponsor of the project. Our thanks to Tracy Mustin for her assistance. This work was sponsored by the U.S. Department of Homeland Security’s U.S. Customs and Border Protection. The Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.


{ introduction } Events on September 11, 2001, changed the way Americans think about threats and defense. New defense approaches to reduce terrorist threats must now include scanning of cargo and passenger transportation modes for terrorist weapons and components. The radiological threats of most concern include acquired or stolen weapons, improvised nuclear devices, special nuclear material for weapons construction (including plutonium and highly enriched uranium), and material or assemblies for radiological dispersal devices (also known as “dirty bombs”). All of these radiological threats produce gamma ray or photon radiation, while plutonium, unique in its role as part of a weapon of mass destruction, also emits neutron radiation. What follows is an outline of the topics in this document. Chapter 1 focuses on the motivation for radiation interdiction at borders. Radiological scanning instrumentation is being broadly deployed at U.S. and foreign borders to search for nuclear and radiological contraband with passive and active sensing techniques. Although very few threatening radioactive cargos are expected, it is necessary to survey every vehicle and conveyance entering the country so these rare radionuclide threat items can be intercepted. This is a different requirement than that used for narcotics interdiction where the consequences of something escaping detection are less consequential. At the same time, such activity for the interdiction of radiological threats cannot impact the flow of commerce. Following the tragic events in 2001, the U.S. government emphasized the need for the U.S. Customs and Border Protection (CBP) to quickly and effectively deploy interdiction systems to combat the increasing threat of terrorists who might attempt to smuggle radioactive material into the U.S. through its ports of entry. To fulfill this requirement, the Radiation Portal Monitor Project (RPMP) was established in January 2002 at Pacific Northwest National Laboratory (PNNL). The primary objective of the RPMP is to quickly and effectively deploy radiation portal monitor (RPM) systems, as funding permits, at all U.S. ports of entry sites (i.e., international mail, express consignment courier facilities, land and rail border crossings, seaport terminals, and international airport terminals) that are selected by CBP on a prioritized basis. The design and operation of radiation detection systems for the interdiction of radiological materials at U.S. borders must be appropriately matched to the detection of a specified set of threats. In the case of

 A threat is a circumstance or event that could lead to the creation and/or exploitation of a flaw in a system.

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Introduction

RPM systems, this requirement for an operationally viable approach amounts to having a specified target for a detectable quantity of radioactive material under a specified geometry. Chapter 2 discusses sources of radiation and possible interferences for radiation detection. An introduction to the physics and statistics of ionizing radiation is covered with the purpose of introducing the terms used throughout this book. After this introduction, four sources of ionizing radiation are discussed: • Ubiquitous background radiation from soil, construction materials, and cosmic rays • Naturally occurring radioactive materials • Medical sources of radiation • Industrial and special nuclear materials

This is followed by a discussion of nonionizing radiation used for telecommunication that can interfere with the operation of an ionizing radiation detection device. Chapter 3 discusses interdiction of targeted materials, a difficult task intensified by the need for increasingly sophisticated technology. In this section, interdiction technologies are discussed, along with new developments, especially in areas such as active interrogation techniques and imaging. After a brief review of radiation detection basics, the operational realities under which detection must be performed at ports of entry are provided. This is followed by a discussion of current instrumentation and capabilities, and by information about more advanced instrumentation and techniques being developed. Chapter 4 discusses enhancing the effectiveness of RPM systems. Plastic detector–based RPM systems have many advantages, which includes their simplicity and low cost. However, they also have significant limitations under normal operation. For example, the use of gross counts to trigger alarms can lead to burdensome naturally occurring radioactive material–related alarms in some operating environments. Efforts to enhance the effectiveness of RPM systems are discussed, principally via changes to the software analysis of the count rate data. These changes allow more information to be gleaned from the collected data, and in combination with gross counts, allow better discrimination between normal commerce and materials of concern. An important element of this discussion is the use of modeling and simulation to better understand how count rate data are collected, how background count rates are suppressed by such phenomena as shadow shielding, and what suppression means to the count rate alarm levels. In addition, information is presented about how the data might be manipulated to gain more discrimination. The chapter then discusses the future role of spectroscopic detectors as RPMs. Lastly, the discussion focuses on the role of humans in making RPM systems more effective tools for detecting materials of concern. Chapter 5 discusses RPM deployments. The RPMP was initiated to provide CBP with technical advice on the interdiction of radiological and nuclear materials,

Introduction

xxv

and it grew into a deployment project to specify, procure, and deploy equipment targeted at the interdiction of illicit radioactive materials at U.S. ports of entry. The project thus hinged upon the fundamental technologies and tools capable of detecting radioactive materials. Chapter 6 discusses operational considerations for interdiction. Radiation interdiction equipment is deployed into the complex and busy operational environment of border crossings. Customs and Border Protection officers are responsible for enforcing hundreds of laws, and their new major role of protection against terrorism has added to their workload. This section considers some of the specific operational problems encountered. Border crossings were operated long before radiation detection devices were needed. Therefore, the installation of radiation detectors required that the devices fit within the physical confines of the existing facilities, and, once installed, have a minimal impact on facility operations. At border crossings, the impact on operations is minimized by incorporating the radiation scanning program into the existing standard operating procedures as much as possible. Chapter 7 discusses activities related to the interdiction of nuclear and radiological material that are underway around the world. Some of these activities include standards and testing that are important aspects of any instrumentation planned for field deployment. For equipment that is deployed for radiation interdiction purposes, standards provide vendors with the minimum requirements that the equipment must meet. Significant efforts are made both domestically and internationally in developing instrument standards for border security equipment and testing equipment of all types against these standards. For the last decade, the U.S. Department of Energy has worked to interdict illicit materials around the world, notably under the Second Line of Defense Program. The U.S. Department of Defense has also had an active program for force protection against radioactive threats, most notably the Guardian Project. Within the U.S. Department of Homeland Security, other major efforts (beyond the RPMP) largely relate to future requirements for interdiction. In the international arena, several nations have undertaken programs similar to those in the United States, and the International Atomic Energy Agency has been an important leader internationally. Chapter 8 discusses the future for interdiction of radiological and nuclear threats at borders. Radiation detection systems currently deployed at ports of entry and the additional systems being deployed are tailored in various ways to serve specific roles. These systems have been designed with precise dimensions and packaging and include newly specified user interfaces, electronics, alarm algorithms, and communication capabilities. Nonetheless, these systems rely on principles that had previously been demonstrated in field applications. In most—if not all—cases there is no presumption that current instruments are the most effective, efficient, or economical instruments that can ultimately be obtained. Continuing research and development activities are essential to ensure that U.S. ports of entry

xxvi

Introduction

are equipped with increasingly capable, yet affordable, radiation detection technology that remains highly effective against a dynamic terrorist threat. This book mainly covers the first several years of the RPMP from its inception by CBP in January 2002 to the time it became a joint program comanaged by CBP and the Domestic Nuclear Detection Office in October 2005. Since October 2005, the RPMP has continued to improve and press forward in effectively providing the protection needed at our nation’s ports of entry.

{ acronyms and abbreviations } BF ANSI ASP CBP CBRNE DB DHS DNDO DoD DOE DT DTRA DU ECCF EMP FOM FWHM HEU HPGe HSARPA IAEA IEC IGY IMCC IND IPP JPM JSIPP LSS MCNP MDA NaI(Tl) NIS NNSA NORM NRC NRF NURE OCR PB PBS

percent branching fraction American National Standards Institute Advanced Spectroscopic Portal U.S. Customs and Border Protection chemical, biological, radiological, nuclear, and explosive driver bottom Department of Homeland Security Domestic Nuclear Detection Office U.S. Department of Defense U.S. Department of Energy driver top Defense Threat Reduction Agency depleted uranium express consignment courier facility electromagnetic pulse figure of merit full width at half maximum highly enriched uranium high-purity germanium Homeland Security Advanced Research Projects Agency International Atomic Energy Agency International Electrotechnical Commission International Geophysical Year intermodal cargo container improvised nuclear device Installation Protection Program Joint Program Manager Joint Service Installation Pilot Project Laboratories and Scientific Services Monte Carlo N-Particle Minimum detectable amount thallium-doped sodium iodide National Integration System National Nuclear Security Administration naturally occurring radioactive material U.S. Nuclear Regulatory Commission nuclear resonance fluorescence National Uranium Resource Evaluation optical character recognition passenger bottom percent baseline suppression

xxviii

PLC PNNL POE POV PRD PRIDE PRS PSID PT PVT Rad/Nuc RDD RDT&E RFI RIID RO-RPM RPM RPMP RSP SAIC SLD SNM SPM TENORM UNSCEAR UNWD VACIS VIS WGPu WMD

Acronyms and Abbreviations

programmable logic controller Pacific Northwest National Laboratory port of entry privately owned vehicle personal radiation detectors Port Radiation Inspection, Detection, and Evaluation percent (window) ratio suppression portable source identification device passenger top polyvinyl toluene radiological/nuclear radiation dispersal device research, development, testing, and evaluation radio frequency interference radiation isotope identifier device remotely operated radiation portal monitor radiation portal monitor Radiation Portal Monitor Project radiation sensor panel Science Applications International Corporation Second Line of Defense (within DOE) special nuclear material spectroscopic portal monitor technologically enhanced NORM United Nations Scientific Committee on the Effects of Atomic Radiation Unconventional Nuclear Warfare Defense Vehicle and Cargo Inspection System Visual Identification System weapons grade plutonium weapons of mass destruction or disruption

{ units } per mm-Hg μR/hr μrem μSv Bq Ci cm cps cps/ng eV ft GB GeV GV in kCi keV kg MBq MV MeV MHz mph mrem m/s mSv Pa pC Sv V/m ZeV

percent change per millimeter of mercury microroentgen per hour microrem microsievert becquerel curie centimeters counts per second counts per second per nanogram electron volt foot gigabyte giga-electron-volt gigavolt inch kilocurie kilo-electron volt kilogram megabecquerel megavolt megaelectron volt megahertz miles per hour millirem meters per second milliseivert pascal picocoulomb seivert volts per meter zepta electron volts




{1}

Overview of Radiation Interdiction Richard Kouzes

September 11, 2001, changed the way Americans think about threats to the homeland and national defense. Terrorists are more concerned with instilling fear than destroying or deterring the use of military capability. The psychological and economic disruption caused by a terrorist attack does not necessarily require the spatial precision or timing of sophisticated military delivery systems. Consequently, the means by which an adversary’s weapon might reach its target has expanded from conventional military systems, such as missiles, to include common means of transport such as pedestrians, cars, trains, planes, and ships. New approaches to reduce the terrorist threat by these means must now include scanning of cargo and passenger for potential weapons.

terrorist weapons: two types of weapons Weapons of mass destruction: Nuclear, biological, or chemical weapons that cause catastrophic loss of life and/or property. Weapons of mass disruption: Any weapon that causes catastrophic consequences to a way of life, either through economic, social, or health impacts.

Radiological threats of most concern include acquired or stolen nuclear weapons such as improvised nuclear devices (INDs), special nuclear material (SNM) for weapons construction (including plutonium and highly enriched uranium [HEU]), and material or assemblies for radiological dispersal devices (RDDs), also known as dirty bombs. All these threats are comprised of radioactive materials that produce a gamma radiation signature. Some—most importantly plutonium— also emit neutron radiation. Detection of these threats is critical. Radiological scanning instrumentation is undergoing broad deployment globally with passive and active–sensing techniques to search for nuclear, radiological, and other contraband. Active techniques are defined here to include X-ray or gamma-ray radiography, and neutron or gamma-ray-induced signatures for the detection of explosives and SNM. Passive detection techniques include gamma-ray or neutron signature detection for radiological materials.




While very few conveyances are expected to contain threatening radioactive material, it is still necessary to scan all vehicles, cargo, mail, and packages at ports of entry (POEs) because of the very serious consequences of illicit nuclear materials being smuggled into the country. This is in stark contrast to the scanning process for drugs or other contraband where one can have effective enforcement while only surveying a statistical sample of vehicles, especially when intelligent targeting can increase detection probabilities. Because many ports of entry process a huge volume of cargo, scanning must be performed within a limited time frame to reduce the impact on the flow of legitimate trade and travel. If this efficiency is not achieved, and legitimate trade and travel is delayed, terrorists will have succeeded in achieving negative economic impact from reduced trade. To reliably intercept threats, a layered approach to defense must be taken in which each layer is comprised of a unique combination of technology along with human capabilities. As an example, intelligence information may lead to targeting certain vessels or cargo, and then passive scanning methods (such as radiation portal monitors [RPMs] and handheld or belt-worn radiation detectors) can be used for radiological interdiction. Radiography systems can also be used to look within cargo containers or packages to scan for hidden areas or suspect commodities, while acoustic techniques can be used to scan bulk liquid carriers for hidden material or structures. With available technology, vehicle surveys for radioactive materials have been implemented in an operationally acceptable manner at U.S. ports of entry (Kouzes 2004, 2005). Highly trained U.S. Customs and Border Protection (CBP) officers evaluate the attitude and behavior of people passing through control points and evaluate the input from all detection mechanisms to arrive at a probability-of-threat decision. The highly complementary nature of technology and human skill combined in this example results in effective detection of radiological and nuclear threats. This chapter provides an introduction to the port-of-entry radiation interdiction scenario, the history leading up to technologies deployed for interdiction, and some of the policy concerns that affect technical solutions for interdicting nuclear and radiological materials of concern.

1.1 Radiation Portal Monitor Project History Megan Lerchen, Richard Kouzes, and Robert Thompson Following the events of September 11, 2001, the U.S. government emphasized the need for CBP to quickly and effectively deploy radiation interdiction systems to  A POE is a legal entry point across an international border and may consist of multiple physical sites or crossings.  In 2001, the U.S. Customs Service was part of the Department of Treasury. With the creation of the Department of Homeland Security, the name was changed to U.S. Customs and Border Protection.

Overview of Radiation Interdiction

5

combat the increasing threat of terrorists penetrating the United States at ports of entry. Deployment of these systems required specialized science and technology support to detect and identify radioactive materials and components associated with the development and delivery of nuclear weapons and other radiological contraband. The Applied Technology Division at CBP, as part of its Radiation Monitoring Support Program, required a broad range of technical support in identifying and understanding the fundamental nature of the nuclear interdiction mission, evaluating and testing commercially available threat interdiction technologies, and deploying a nationwide network of radiological and nuclear material interdiction systems. To fulfill this requirement, the Radiation Portal Monitor Project (RPMP) was established in January 2002 at Pacific Northwest National Laboratory (PNNL). The term “RPM” refers to the primary radiation detection technology and configuration used in the project.

1.1.1 interdiction goals and objectives Customs and Border Protection deploys and operates the best available technology to (1) prevent smuggling of nuclear and radiological materials into the United States consistent with its strategic plan to prevent entry of illicit materials by terrorists at U.S. ports of entry, (2) balance legitimate trade and travel with security, and (3) modernize technology. To further strengthen its prevention capabilities, CBP developed near-term, midterm, and long-term strategic goals that address technology gaps and limitations with currently deployed detection technologies. The CBP continues to identify emerging technologies and plans to use both passive detection and active interrogation methods. Working in complex border environments, CBP effectively and efficiently scans all passengers, vehicles, and cargo, while maintaining the steady flow of legitimate trade and travel. Secondary scanning is conducted, when needed, to resolve primary scanning alarms and investigate suspect items. Customs and Border Protection applies a layered defense of radiation sensors, each with specific capabilities and defined applications, consisting of RPMs, radionuclide identifiers, and personal radiation detectors (PRDs). The intent of terrorists, criminal organizations, and rogue nations to cause damage to people and property, and to disrupt the economy of the United States, is widely known from well–documented prior attempts. Failure to deter and interdict radiological and nuclear materials and weapons entering the United States could result in serious loss of life, disruption of commerce, and the destruction and/or

Herein, whether a time before or after the creation of Department of Homeland Security is being referred to, the name CBP is used.  PNNL is a U.S. Department of Energy multiprogram national laboratory operated by Battelle Memorial Institute.




“U.S. Customs and Border Protection is addressing the terrorist threat -hours a day. We have a multi-layered approach that encompasses working with our foreign counterparts, employing intelligence, technology, advanced information in the field and the most professional workforce worldwide. We are aware of the terrorist threat and are evolving hourly to face it and keep America safe.” Robert C. Bonner, CBP Commissioner September , 

contamination of property beyond any event previously experienced (Reichmuth 2005). To minimize this threat, CBP develops and deploys highly integrated countermeasure systems that increase the ability to detect, identify, and deter the import of illicit radiological materials and improvised or stolen nuclear devices. These systems serve to complement other CBP targeting and data systems used for passenger and cargo scanning under such measures as the Container Security Initiative and the Customs-Trade Partnership Against Terrorism. Radiological and nuclear interdiction activities directed by CBP also work in harmony with international efforts, such as the U.S. Department of Energy (DOE) Second Line of Defense (SLD) and Megaports Initiative programs (see Chapter 7).

1.1.2 radiation portal monitor project mission The RPMP provides scientific and technical expertise on radiation detection and materials to support the CBP mission of radioactive materials interdiction at U.S. land, sea, and air ports of entry. This is accomplished through the expertise of PNNL staff in developing, identifying, testing, and deploying radiation detection tools that meet international detection standards, have minimal impact to the legitimate flow of trade and travel, are cost effective, and are (or can be made) commercially available. Critical responsibilities of CBP include detecting, identifying, and interdicting illicit radiological and nuclear materials at U.S. ports of entry. These responsibilities are closely aligned with the overall mission of the Department of Homeland Security (DHS) to strengthen border security against terrorist threats. The Science and Technology Directorate at DHS oversees research conducted to improve general detection and interdiction capabilities, while the Domestic Nuclear Detection Office (DNDO), created at DHS in 2005, now conducts research and development of advanced detection systems, and tests and procures these systems for scanning and interrogating vehicles and containerized cargo for radiological and nuclear threats. Together, these DHS organizations share the overall accountability for developing, deploying, and operating effective technologies to detect and identify smuggled threat materials at international mail facilities and express consignment courier facilities (ECCFs), land and rail border crossings, seaport and international airport terminals, and areas between the ports of entry. These organizations also


7

have the broader responsibility to coordinate detection and interdiction activities with other agencies, both domestically and internationally. One of the primary objectives of the RPMP is to deploy RPM systems quickly and effectively at all sites selected by CBP on a prioritized basis. These systems must provide effective interdiction capabilities for radiological items associated with weapons of mass destruction (WMDs) and other radiological threats. If other scanning technologies become available that can accomplish CBP objectives more effectively, efficiently, or economically, they may replace the RPM systems in accordance with CBP direction. Solutions to scanning problems at a particular site must address several factors, including current and future traffic volumes, site layout, type of cargo, radiation detection equipment performance, and defined threats. These and other factors may change over time. The second objective of the RPMP is to provide the scientific and technical expertise needed to design and support the deployment of RPM systems, and to interpret the acquired data. This includes specific expertise in radiation detection systems and their field application, operational simulation modeling, computational analysis, and evaluation of the transport phenomena associated with radioactive materials.

1.1.3 initial radiation portal monitor project activities In late autumn 2001, CBP was faced with an increased need to understand the threats and vulnerabilities posed by potential materials and components associated with the development and delivery of nuclear weapons and other radiological contraband. This extended to the problem of scanning inbound traffic for elevated radiation signatures—a potential indicator of a WMD or RDD—and identifying tools that could be used in the field for routine scanning. To meet this need, starting from initial tasking in January 2002, the CBP Applied Technology Division eventually enlisted PNNL for its expertise in radiation detection physics. Thus, the staff at PNNL began to provide broad technical support to identify and understand the fundamental nature of the nuclear and radiological materials interdiction mission, evaluate and test commercially available threat interdiction technologies, and deploy a nationwide network of nuclear and radiological materials interdiction systems. Customs and Border Protection requested consultation in these areas because PNNL staff had been providing science and technology support to CPB since the early 1990s in areas such as WMD interdiction considerations, WMD interdiction training to field operations and international inspectors, and nonintrusive inspection system evaluation. Consequently, as part of the CBP Radiation Monitoring Support Program, the RPMP was established. Initially consulted by CBP to focus on determining the radiological threat, PNNL staff was also asked to identify functional requirements for RPMs and suitable commercially available technologies that could be immediately deployed. A PNNL project manager and a small team of scientists and engineers advised CBP




on radiation interdiction. These early activities led to an understanding of CBP project needs, followed by instituting the RPMP to support these needs. Potential nuclear and radiological materials that could be used in nuclear weapons or RDDs were identified as plutonium, HEU, and several alpha-, beta-, and gamma-emitting radioisotopes. Various detection technologies were identified as capable of sensing these materials, including commercial devices ranging from handheld instruments to radiation portal systems for scanning vehicles. Efforts toward specifying a primary detection technology soon focused on RPMs capable of scanning cargo and entire vehicles. The conclusion of these efforts was a recommendation that CBP deploy RPMs as the main tool for interdiction of radiological and nuclear materials at border crossings. Portal monitors used to detect SNM and other radioactive sources in vehicles had been studied for decades, including extensive work conducted at the Los Alamos National Laboratory (Fehlau 1986, 1987; Fehlau et al. 1983) in New Mexico dating back to the 1970s. Unfortunately, commercially available systems were not ideally suited to the needs of CBP for scanning incoming cargo or traffic. In 2002, available commercial portal monitors were designed for one of two purposes: to prevent SNM from being smuggled or accidentally transported out of SNM facilities, or to detect radioactive sources entering steel scrap-reprocessing facilities. In the SNM case, the photon emissions are relatively low energy. In the steel scrap case, the photon emissions are relatively high-energy gamma rays but could be substantially shielded in a truck bed full of steel scrap. The portal monitors required by CBP needed capabilities similar to those used for both SNM and steel scrap applications. In addition, the potential for another type of threat—RDD material that only emits bremsstrahlung continuum gamma rays (such as Sr or Y)—also needed to be addressed. The PNNL staff analyzed portal monitor detector capabilities under various threat scenarios and conditions based on these broad radiation interdiction needs. Because the requirement to secure U.S. borders must be balanced by the need to maintain the flow of legitimate trade and travel, operational and cost constraints at ports of entry are generally different from those at steel scrap facilities and SNM facilities. To acknowledge this, an analysis of the measurement time required to confidently detect each source material in a variety of shielding configurations was useful in choosing technologies for deployment. For example, the specific technology solution for scanning intermodal containers at a seaport terminal could be markedly different from the solution for scanning mail and packages at an international mail facility. The staff identified effective technologies and devices that could be relatively quickly configured to a variety of deployment sites.

1.1.4 the beginning of radiation portal monitor deployment In July 2002, the director of CBP’s Applied Technology Division requested that PNNL expand its services to include deployment of radiation detection systems at


9

CBP ports of entry. Because the timeline for RPM deployment remained immediate and urgent, initial efforts focused on fielding RPM systems as quickly as possible. This urgency drove the early, rapid installation of temporary RPM systems without the benefit of complete infrastructure modifications needed to support permanent systems. It soon became evident that such an approach did not yield the benefits initially desired (i.e., rapid, low-cost deployments). The time to deploy a permanent system was found to be only somewhat longer than a temporary system deployment, and the cost savings of performing the permanent installation rather than a temporary deployment followed by a permanent deployment could, therefore, not be justified. Thus, the conceptual approach of temporary installations was quickly abandoned in favor of permanent installations. In evaluating its initial approach, the RPMP recognized that RPM deployments would not be a small effort. Therefore, the RPMP received its first significant funding increase, with the intent that RPM deployments begin immediately. Thus, over six short months, the RPMP grew from a relatively small advisory role into a significant, deployment-driven national effort. With the new infusion of funding, the RPMP began efforts in earnest to place RPMs at U.S. borders, resulting in large demands on staffing and contracting. The change from providing advice to deploying RPM systems represented a significant change in project focus; PNNL was now being appointed to execute its own advice given to CBP. To ensure success in placing RPMs at the ports of entry specified by CBP, PNNL produced a schedule and budget to be spent over several years of deployment. In August 2002, the RPMP plans included deployment of RPM systems at selected international mail facilities and ECCFs, land border crossings, seaport terminals, international airports, and rail crossings at CBP ports of entry. Figure 1.1 shows the U.S. ports of entry, including where the RPMP has deployed equipment. By September 2002, numerous tests had been completed on portal monitor systems purchased from several vendors, and a specification was completed for the purchase of RPM systems for deployment (Stromswold et al. 2005). The DOE Radiation Detection Panel performed a review of the RPMP deployment plans. The result was a recommendation from DOE to the U.S. Customs Service that existing commercial equipment met the needs for border scanning and should be deployed immediately. As a result, a brief specification for procurement of commercial off–the-shelf equipment was written and released. This procurement resulted in an award to Ludlum Measurements, Inc., for the first large-scale deployment of RPMs. While awaiting delivery of equipment on this contract, initial deployments began with equipment that had been purchased in spring 2002 from various manufacturers for testing. These deployment activities focused on

ECCF deployments did not include United Parcel Service™and FedExs® because these companies had stated to Congress that they would perform their own deployments; subsequently, CBP agreed with this arrangement.  This panel is a collection of experts assembled by DOE from the national laboratories that advise on matters of radiation detection. 




Mail/ECCF Land border Maritime Air cargo

figure 1.1 The  U.S. ports of entry representing  crossings ( data). Over , vehicles, , aircraft, and  ships pass through these ports every day.

international mail facilities, ECCFs, and northern land border crossings. By the fall quarter of 2002, the RPMP began its initial sequence of successful deployments at Detroit, Michigan.

The First Deployment: Fort Street Cargo Facility, Detroit, Michigan The RPMP was directed to conduct its first RPM deployment at the Fort Street Cargo Facility in Detroit, Michigan. This port is the busiest commercial land crossing in the nation, averaging approximately 8,000 to 12,000 trucks per day. To add to this complexity, the only access to the port is over the privately owned Ambassador Bridge. The RPMP was requested to fully implement the RPM system without impeding the traffic volume or flow of revenue-generating traffic over the bridge. In late August 2002, the RPMP team was requested by CBP to design and install the first-ever operational portal system at a U.S. legal border crossing and, subsequently, train local CBP officers and supervisors on how to use the system. The aggressive schedule called for the portal system to be fully operational by midOctober 2002. This effort required bringing together multiple stakeholders, including DOE Headquarters, local and Headquarters U.S. Customs Service officials, local and Headquarters Government Services Administration officials, Detroit International Bridge Company management, vendors, craftsmen, subcontractors, and PNNL staff, to reach agreement on an acceptable design, acquiring and assembling all necessary equipment, installing the equipment, supporting CBP in developing its operational procedures, and training CBP officers on how to use the system, all in the span of about 30 days.


11

figure 1.2 Primary portal at Fort Street Cargo Facility, Detroit, Michigan, showing the first installed radiation portal monitor system commissioned in October .

The portal system became operational just before midnight on October 17, 2002, meeting the aggressive schedule established by CBP. Great strides have been made in the RPMP since this early, expedited installation, but many of the founding principles established through this first deployment effort remain. Figure 1.2 shows the first RPM deployment at the Fort Street Cargo facility in Detroit.

1.1.5 deployment advances In the ensuing years, the strategy to deploy RPM systems was refined, and much progress was made and still continues. As more was learned and needs were better understood, additional ancillary equipment was identified to better enable CBP operations. Although initially viewed as a large, but straightforward project, the RPMP eventually became more attuned to the adage, “when you’ve seen one port, you’ve seen one port.” During this period, while the basic RPM system was well defined, the equipment toolset available for RPM deployments expanded to meet individual port needs for efficient operations.




In 2003, a memorandum of understanding between the newly formed DHS and DOE established that DHS work could be performed at PNNL on equal footing with DOE work. In July 2003, the project scope was expanded as a result of identifying additional sites requiring RPM systems. The revised scope, schedule, and cost baselines included implementing some additionally capable systems including thallium-doped sodium iodide [NaI(Tl)]-based spectroscopic portal monitor (SPM) systems. The revised scope also included establishing a detailed deployment schedule based on the current, best knowledge of the time frame when required funding could be provided. Deployment of the relatively small number of SPM systems added a substantial cost to the RPMP, with the total required funding estimated to be about $1.3 billion. This funding supported a scheduled completion of RPM system deployments and final project closeout in 2009. The full RPMP specification for procurement of RPMs was released in spring 2003 and resulted in a contract being placed for systems with Scientific Applications International Corporation (SAIC), which had purchased ExploraniumTM, a manufacturer of radiation portal monitors. The SAIC RPM systems were first deployed in 2004. The RPMP shares several common goals with the SLD program, including the Megaports Initiative within DOE (see Chapter 7). The RPMP also cooperates closely with two other organizations—the American National Standards Institute (ANSI) and the International Atomic Energy Agency (IAEA). The IAEA has been deploying radiation detection equipment under the Safeguards Program since the 1990s; as part of this effort, a specification was developed for radiation detection equipment to be used at border crossings. The SLD program and several DOE national laboratories had active participation in the IAEA standards development effort. The RPMP became similarly involved with the IAEA standards development effort in 2003, assisting with the development of the equipment standards and bringing that information back to similar U.S. efforts (IAEA 2005). When DHS was formed in 2003, part of the Science and Technology organization included a standards effort and produced standards for border security equipment (as well as other types of equipment) under the auspices of ANSI. The RPMP played a very active role in the writing of ANSI standards for border security equipment that were first released in 2004, and it continues with the development of new standards. Much of the work performed by the RPMP in writing specifications preceded the ANSI work, and these RPMP documents contributed significantly to the products produced by ANSI. The RPMP staff learned quickly that deployments required more than just standard equipment. While land border deployments were the most consistent, with

 The RPMP has undergone a number of changes in scope, schedule, and priority that have produced multiple changes in budget estimates. As this document covers the period only up to October 1, 2005, the figures and schedules given here are not current for the project.  Exploranium™ is a registered trademark of Science Applications International Corporation.


13

similar requirements for infrastructure at existing CBP installations, international mail and ECCF deployments were each unique and required smaller RPM models for installation at conveyor belts, as well as the use of area mode monitoring. Rail systems were larger and required the integration of complex, industry-specific railcar identification systems. Seaport deployments introduced the use of relocatable systems and required installing infrastructure where CBP had no prior permanent physical presence. Seaports also introduced the requirement for the RPMP to develop the concepts of remotely operated RPM (RO-RPM) systems that integrate multiple technologies, straddle-carrier based systems, and mobile RPM systems. Since the beginning of the RPMP, improvements were sought in the radioisotope identifier device (RIID) used for identification in secondary processing. The RPMP performed experimental work to test and define the capabilities of various RIID replacement devices. An outgrowth of this effort were specifications for several new devices for given applications. These included specifications for a portable source identification device (PSID), which called for a large NaI(Tl) detector to be mounted on a small truck. This PSID was intended for use in scanning cargo containers, especially at seaport terminals and rail crossings. The CBP staff modified some of the mechanical capabilities and renamed this device the mobile radiation identification system. The mobile radiation identification system has not been deployed. Another very significant technology that was considered to meet multiple drivers was the SPM system based on NaI(Tl) detectors (Kouzes et al. 2005; Milbrath et al. 2005). This technology was intended to address the need for improved sensitivity to potential threats in high-volume scanning situations, the need for improved identification in secondary processing, the operational need for primary identification on rail lines, and the need for mobile identification capability with better sensitivity than a handheld RIID. With high-level government recognition of the need for such systems, development of the SPM specification began in September 2003. Within the newly created DHS, responsibility for this system fell under the Science and Technology organization, which elected to issue a broad area announcement that incorporated many of the requirements spelled out in the CBP specification. This bid process, now transitioned to DNDO, should lead to systems for deployment in 2007.

1.1.6 moving toward project completion The RPMP continues to make significant positive impacts on the national security of the United States. As the project matures and takes on greater diversity of deployment configurations, the RPM systems—including supporting subsystems—have also diversified to meet individual site needs. Despite this increased complexity, the increasing number of RPM systems in operation at ports of entry has led to a recognized need for standardization and the use of robust, cost-effective, and




low-maintenance equipment. To the extent possible, RPM systems are based on standardized reference designs for each site type (vector) but are tailored to meet individual site needs and constraints. In fiscal year 2006, RPMP funding was moved from CBP to the new DNDO organization. Continuous progress has been made so that by July 2008, RPMs were routinely scanning 100% of international mail and express courier packages, 92% of cargo and 82% of privately owned vehicles (POVs) transported across northern land border crossings, 100% of cargo and 95% of POVs transported across southern land border crossings, and 98% of containerized seaport cargo, by volume.

1.2 Detecting Threats Richard Kouzes The design and operation of radiation detection systems for the interdiction of radiological materials must be appropriately matched to threats that are to be detected. A threat is a circumstance or event that could lead to the creation and/or exploitation of a flaw in a system. A threat has an associated radiological object referred to as a threat object. Since radiological and nuclear threats and threat objects span a great spectrum, it is necessary to reduce the number of threat objects to a manageable and highly relevant set that can be more effectively used to design, test, and constrain deployment and operating parameters. While operating characteristics and parameters, including thresholds, for the instrumentation are typically adjustable, the capability of equipment is limited on the low end by its inherent sensitivity, the environment in which it is used, and the implemented operational procedures. Measurement parameters are often set to detect a specified threat but may also be set to be less sensitive to accommodate individualized operating limitations at specific locations. Such factors that affect the detection capability of a deployed system create the need for a policy and approach to systematically and consistently set system operations across a broad range of deployed venues. In the case of RPM systems, this requirement for an operationally viable approach amounts to having a specified target for a detectable quantity of radioactive material under a specified geometry. Given these constraints, the size of the neutron and gamma-ray detection elements, and other components of the RPM system, can be designed. The size of the detector systems then fixes the inherent sensitivity (absolute efficiency) of the system. The systems must then be deployed at an existing site and still retain their sensitivity to the threats given this inherent sensitivity. The ANSI standard N42.35 (ANSI 2006a) embodies this approach, setting minimum standards for RPM equipment for border security purposes (see Chapter 7). This standard sets requirements for the response of RPM systems to a variety of different sources by stating amounts of specific sources that must produce alarms in specified geometries.


15

1.2.1 threats For border security applications, the threats of most concern for detection are conventional nuclear WMDs originating from a nation state, INDs, such as might be built by sophisticated and well-funded terrorists, SNM that could be used for making nuclear weapons, and other radioactive materials that might be used for an RDD and/or weapons of mass disruption built by terrorists organizations or individuals. Detection equipment may also be used to detect other types of illicit trafficking, such as contaminated products or non-manifested items, but these are not specifically targeted. For non-border applications, the targeted threats might be different; for example, detection at major public event, such as at a public stadium, might focus only on RDD materials, as that threat seems more probable for such a venue than does material for making a nuclear weapon. Decisions by policy makers about the targeted threat can have a large bearing on the cost and complexity of detection equipment. Figure 1.3 shows a photograph of three Soviet nuclear weapons. Of greatest concern would be an attempt to smuggle the smallest of these examples, the artillery shell weapon in the foreground. For SNM, an upper bound on the minimum quantity that would need to be detected would be those amounts designated by DOE as sufficient for creating a nuclear explosive device: 25 kg of U or 4 kg of Pu (CG-SMG-2 2003). These quantities are similar to those designated by the IAEA as significant quantities: 25 kg of HEU or 8 kg of plutonium (IAEA 2009). Because these materials could be transported in multiple shipments of smaller amounts, and shielding could be used, the deployed radiation detection equipment must be

figure 1.3 Examples of Soviet nuclear weapons displayed in a Russian museum.




sensitive to much smaller masses of material than these quantities. Radioactive materials that might be used for an RDD would be reasonably assumed to have larger radiation signatures than the targeted SNM quantities. Exceptions to this might be that the material may be shielded, or it may be used by a terrorist who simply wants to make a “statement” by exploding a small amount of radioactive material resulting in little consequence other than the disruption of daily activities.

1.2.2 example incidents The IAEA maintains a database of incidents of illicit trafficking of radiological sources (IAEA 2004). This database includes 18 incidents involving the smuggling of weapons-grade nuclear materials between 1993 and 2004. Some examples of radiological incidents include the following: • : Police at the Munich airport intercepted a suitcase from Moscow, Russia, containing approximately one-half kilogram of nuclear reactor fuel ( g of weapons-grade plutonium). • : In the Czech Republic, Prague police seized . kg of HEU from a former Russian nuclear institute worker. • : In the Chechen Republic, Chechen rebels buried a small amount of  Cs in a Moscow park and notified a Russian television crew. • : Radioactive material with explosives and an antitamper device were found near a railway east of Grozny, Russia. • : Three woodsmen in the former Soviet Republic of Georgia suffered radiation burns after handling the ~ kCi Sr core from an abandoned radiothermal generator, seen in Figure .. Such electrical generators are widely used to power remote locations, such as lighthouses. • : Russian customs officials said they had uncovered some  attempts to smuggle nuclear or radiological materials. • : Litvinenko was poisoned with ~ mCi of Po in London and died on November , . As many as , people were exposed in  countries, with  having an increased cancer risk from an exposure of over  mSv.

Another notable incident occurred in 1987 in Goiania, Brazil, when a container of Cs was scavenged from a defunct medical clinic. This was not a terrorist act, but simply the mishandling of an “orphaned” source. By the time the 1.4 kCi source was identified 11 days later, it had been tracked up to 100 miles away, killed 4 people from radiation doses of 4 to 6 Sv, burned 28 people, and contaminated 249 people, including children that had played with the glowing powder. Over 110,000 people requested medical screening, and the cleanup cost was about $20 million, with 275 truckloads of waste left in a large repository requiring long-term protection. An RDD incident might produce a similar result. Figure 1.5 shows an example of orphaned U.S. radiological sources found in a field under a water bucket.




17

figure 1.4 Soviet Sr orphaned source recovered in the former Soviet Republic of Georgia.

figure 1.5 Orphaned radioactive well logging sources.

1.2.3 instrumentation to counter the threat Whenever radiation detection equipment is to be deployed, a policy decision is made about the detection requirements for threats, which drives the detector design and thus the inherent sensitivity of the instrument. Once the equipment is procured and deployed, another decision must be made regarding where to set the alarm threshold; that is, the level of radiation at which the instrument will generate




an alarm. In 2002, DOE provided CBP with a targeted threat definition to be used in deploying radiation detection equipment at ports of entry. The alarm algorithm used in an RPM system is complex, so only a simple example of a gross-count instrument is presented here. Consideration of more complex algorithms will be discussed in later chapters. One approach to operating detection equipment is simply to set the threshold at the lowest value such that an acceptable rate of “false” alarms occurs. False alarms are defined as instrument alarms produced by statistical fluctuations in the background radiation or by some sort of malfunction of the instrument itself. These false alarms are unrelated to the additional alarms resulting from actual radioactive material in commerce that are actually true alarms. The acceptable false alarm rate must be determined operationally for each location, but it is typically less than 1 in 10,000 measurements. This approach utilizes the maximum capability of any specific deployed instrument but may cause significant operational problems by requiring CBP officers to resolve both false and true alarms. Designing RPM systems for this approach leaves no “excess capacity” of detection should there be a desire to detect a smaller source. This approach, operating on the edge of capability for an instrument, also means that a different threat is targeted at each deployment site, since the signal of interest rides on top of a site-dependent background. Variable site deployment and environmental factors impact the signal. An alternate approach to determine the threshold is to use measurements from a “targeted” radioactive source value that is directly related to the threat. Because a series of radiation level measurements (e.g., counts per second or dose rate) tends to produce a normal distribution, the threshold might be determined by setting it at the peak of the distribution from a series of measurements in a standard geometry from one specific source. This implies that the instrument should alarm about 50% of the time when that source is again presented in the same geometry relative to the detector. To detect the source 100% of the time, the threshold would need to be set lower than this value. This “targeted” source approach is commonly used. Generally, one specific radioisotope and source strength is used in a fixed, stationary position. The source strength is determined from the threat and is used as a surrogate for the threat. Results of static measurements from a given radioactive source for a deployed system can be scaled to the response to a targeted quantity of that source, as well as apply other correction factors. Once “calibrated” with the radioactive source, the hundreds of RPM operating parameters are set to detect the threat with a specified probability of detection. Figure 1.6 shows an example of the total gamma-ray counting rates, in counts per second, from a typical plastic scintillation detector used in a vehicle RPM system. The dash-dotted curve plot shows an unnormalized distribution of background count rate alone. This skewed-Gaussian-like distribution shows a width due to statistical variations, weather, and other effects from the surrounding

S gna probab ty d str but ons


Background suppresion

19

Background Vehicles Test source

NORM

1000

2000

3000 4000 Counts/second

5000

6000

figure 1.6 An example of the total gamma-ray counting rates in counts per second from a typical scintillating plastic used in vehicle radiation portal monitor systems showing the mean distribution of , cargo vehicles with and without naturally occurring radioactive material plus background (dashed curve), the distribution of background alone (dash-dotted curve), and a simulated test source (solid curve). The normalization is arbitrary.

environment. The tail toward higher energy is due to increases in background based on these factors, especially weather effects and the movement of cargo in the surrounding environment (but not directly within the RPM). The dashed curve distribution is the response to measurements of about 5,400 cargo vehicles with and without naturally occurring radioactive material (NORM), plus the observed background count rate. This vehicle distribution is also a skewed-Gaussian-like curve with an extended high count-rate tail from various NORM-bearing cargos (see Section 2.3 of Chapter 2 for a full discussion of NORM). The peak of this curve is downshifted relative to the background distribution, showing the effect of shadow shielding of the environmental background radiation by the vehicle (discussed in Chapter 4). The solid curve is from a simulated test source, which might, for example, represent a targeted threat source driven through an RPM. A set of repeated measurements generates a narrower Gaussian-like distribution with a centroid at the average count rate. A gross-count threshold set at the peak of this distribution would, on average, generate an alarm 50% of the time when this source was exposed to the RPM under similar conditions. A threshold set at a lower count rate than the peak could alarm on every observation of this source. Typically, a 99.9% probability of detection, or better, is desired.

1.2.4 specifications and standards The specification developed at PNNL for the procurement of RPM systems (Stromswold et al., 2005) to be deployed at U.S. borders used a similar approach to




that discussed in the last section. It specified that RPM systems must have minimum count rates in response to a variety of sources of different energies in a specific geometry. This requirement translated into a minimum area and thickness for the detector systems. Absolute detection efficiency was given in net count rate above background per microcurie of source activity. The ANSI N42.35 (ANSI 2006a) is the RPM standard that specifies the systems that must generate alarms in response to certain prescribed sources when the threshold is set for a given false alarm rate. The intent of this ANSI standard is to provide minimum requirements and allow the comparison of systems against an absolute; it is not directly tied to any specific threat definition. It is common practice for procurements to require that systems meet the ANSI standard, as well as additional, more stringent, radiological constraints. The RPM specification developed at the IAEA is similar to the ANSI standard in setting minimum detection requirements (IAEA 2005). This latter document provides a set of technical specifications that can be used in design, testing, qualifying, and purchasing radiation-monitoring equipment for border crossings. Because of continual advances in the field of border radiation-monitoring equipment, the specifications represent a consensus on the minimum detection requirements presently achievable. This specification is based on work undertaken through multiple meetings of the IAEA-coordinated research project entitled “Improvement of Technical Measures to Detect and Respond to Illicit Trafficking of Nuclear and other Radioactive Material.”

1.2.5 the multilayer defense The goal of deploying radiation detection equipment is to interdict specified threats. Several factors may impact the realization of this goal, including a general requirement for noninterference with the legitimate flow of trade and travel. This means that the equipment needs to be automated so that it only requires action (such as stop and search) for a small percentage of scanned commerce. Because of the presence of natural and man-made radioactive materials in normal commerce, an operational limitation may be imposed that requires either an increase in personnel resources or a reduction in operational sensitivity. The potential presence of shielding of a threat must also be considered, since shielding can have a significant effect on the observed signal from a source. Radiation detection instruments, like RPMs, are just one component of a multilayer defense against illicit trafficking. The first layer is located at the potential source point for a threat, such as facilities in the former Soviet Union that store large quantities of plutonium and HEU. Starting in the 1990s (as a result of the  Coordinated IAEA research project, “Improvement of Technical Measures to Detect and Respond to Illicit Trafficking of Nuclear and Other Radioactive Materials,” Consultants’ Meeting in Vienna, Austria, March 17–21, 2003.


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Nunn-Lugar Cooperative Threat Reduction Program), the United States established several projects to help secure radioactive source material in the former Soviet Union. For example, the Material Protection, Control and Accountability Program within the U.S. National Nuclear Security Administration helped establish improved physical security and accounting practices at many of the former Soviet Union’s weapons facilities. At the same time, radiation detection equipment was being deployed as the second line of defense along the border of the former Soviet Union by the SLD program to interdict radioactive materials leaving these countries (see Section 7.3 of Chapter 7 for a full discussion of SLD). Another recent program beyond the SLD is the effort to scan cargo at foreign seaports before it disembarks for U.S. ports. Once commerce arrives at the U.S. border, it is scanned for radioactivity and subjected to a wide range of additional examinations, including X-ray imaging, evaluation of manifests and other paperwork, and the scrutiny of highly trained personnel. The combination of these defense layers provides protection and deterrence greater than individual components. Additional material related to threats and detection can be found in the collection of papers presented at the 2004 Health Physics Society Summer School (Brodsky and Johnson 2004).

1.3 The Necessity of Interdiction Joseph McDonald Transportation and commerce go hand in hand, and it is necessary to ensure that any measures taken to uncover unlawful or dangerous materials do not severely impact the normal, legitimate flow of vehicles transporting goods and passengers. It is difficult to achieve an optimum balance between the actions necessary to prevent the transport of illicit materials and the free movement of legal materials. Being more restrictive in prevention necessarily impacts the efficiency of the movement of legitimate material. The legal responsibility for detecting and interdicting illicit materials rests with CBP and other law enforcement agencies, and their goal is to prevent the smuggling of radioactive and nuclear material and a variety of other illicit items into the Unites States. Therefore, officials from these agencies collaborate with their counterparts in other countries to detect and prevent the movement of illicit materials before they appear at the U.S. border. Sophisticated detection devices have been developed to survey for the presence of even minute amounts of radioactive material; these methods are discussed in 

See http://lugar.senate.gov/nunnlugar/. The term “first line of defense” is applied to the security surrounding a location where nuclear material is stored. Thus, the “second line of defense” is a perimeter farther away (such as at a country’s border) that is the next ring of protection against material being removed from a country. 




the following paragraphs. However, the deployment of advanced technology is not the complete solution to the complex problem of effectively uncovering illicit materials among vast quantities of legally transported goods. The interdiction system is comprised of regulatory requirements that control materials of concern. Radioactive materials fall under the jurisdiction of national agencies such as the U.S. Nuclear Regulatory Commission or DOE, who have the responsibility for controlling the possession and use of a wide variety of radioactive materials. The Department of Transportation controls the shipment of radioactive materials. The Nuclear Regulatory Commission, DOE, and Department of Transportation also have law enforcement powers enabling them to take action against the improper use or transport of radioactive materials. The process of registration or licensing of materials also aids in controlling illicit transport of radionuclides. Periodic inspections of facilities with licensed radioactive materials and requirements to report the loss of control of those materials further increases the safety and security of these materials. In addition, one of the most effective weapons in the campaign to limit the trafficking of illicit radioactive materials is the deployment of well-trained and experienced customs officers, police, and other law enforcement personnel. Successful interdiction is aided by radiation detection equipment, but another invaluable factor in that success is the intuition of the experienced agent who perceives illegal activity that a machine cannot. The illicit trafficking of radioactive materials has been a concern of the United States for a number of years. One of the events that highlighted the importance of radiation interdiction was the breakup of the Soviet Union. International concerns increased when the transport of radioactive materials was uncovered in countries, such as Austria, that have been pathways from Eastern to Western countries for quite some time. Radiation detection instruments were placed at strategically located border crossings in several European countries, and U.S. safeguard activities increased as well. Given the security at the U.S. sites that manufactured or stored nuclear weapons, it was determined that the likelihood of a stolen U.S. weapon was small, but finite. The task of detecting and interdicting illicit radioactive materials is simple to describe, but its implementation is daunting because of the inherent scale of the problem. Radiation detectors had to be developed that had the capability for scanning all vehicles and passengers that could be transporting illicit radioactive material. This scanning would also have to take place without substantially affecting the legitimate flow of trade or travel. A later section on “Interdiction Options” describes the details of radiation detection, identification, and the subsequent actions after a radiation source has been found (see Section 3.2 in Chapter 3). The approach to prevent the trafficking in illicit radioactive materials is similar to what would be used to prevent crimes in other areas. Law enforcement officials have long recognized that crimes can take place when there are opportunities, means, motives, and criminals to carry out the acts. Therefore, it is to be expected


23

that law enforcement personnel would work toward limiting the opportunities to obtain radioactive materials. As mentioned earlier, administrative controls, licensing, inspections, and required reporting from those legally using radiation sources are effective methods for controlling the misuse, loss, or theft of sources that could result in those sources finding their way to terrorists. Physical control, barriers, locks, and tags also serve to restrict the means that criminals might use to obtain illicit radioactive sources. In the case of ordinary criminals, it may be possible to make theft of radioactive materials so difficult and dangerous that any monetary rewards for stealing a source might not be worth the risk. Reducing or removing the motive in the case of terrorists may be considerably more difficult if the motivation is political, philosophical, or religious. Finding and arresting criminals or terrorists before they are able to complete their plots is probably the most difficult task, and there cannot be any hope for success in this area without significant investigation by intelligence agencies. Obviously, such intelligence is difficult to obtain in a timely manner. Officials charged with the task of interdicting illicit radioactive materials face a difficult problem because of the inherent scope of the problem. More than 330 thousand vehicles, 57 thousand containers, approximately 2,500 aircraft, and nearly 600 ships pass through U.S. ports of entry each day. There are more than 600 border crossings to protect, and scanning for illicit radioactive material on this massive scale requires a large number of searches conducted in part with radiation detection and identification equipment. In order not to delay the flow of legitimate trade and travel, rapid scanning is necessary; however, less time taken to scan vehicles or passengers means less time is available for counting with radiation detectors. Shorter counting times often limit the effectiveness of the radiation detection and identification equipment. Radiation detection equipment, being quite sensitive to low levels of radioactivity, will also detect NORM present in common commercial items such as roof tiles, porcelain fixtures, camera lenses, welding rods, and even cat litter. Many of these items are manufactured from materials that contain natural uranium, thorium, or other elements whose isotopes can be radioactive. Radioactive materials are also found in radiopharmaceuticals used to diagnose and treat various diseases. If a patient has recently received a nuclear medicine treatment, it is likely that person will trigger an alarm when passing through a radiation detector at a port of entry. These events, which are referred to as innocent or nuisance alarms, must be addressed, and decisions are made many times daily as to whether a radiation alarm has resulted from a naturally radioactive item, a patient with radioactive material in his or her body, a man-made legitimate source, or from an illicit radioactive source. Customs officers have experience in dealing with the types of decisions that must be made when a person is suspected of transporting an illegal substance or when a package or container might contain an illicit shipment. Determining whether the capsules a person is carrying in a prescription bottle are legally




obtained medicines or illegal drugs may be as difficult, or in some cases more difficult, than determining whether a radiation alarm is innocent. Customs officers have an array of tools to help them with such decisions, and radiation detection and identification equipment represent some of these tools. But, as mentioned earlier, the most effective weapon against smugglers and potential terrorists attempting to cross U.S. borders is the well-trained and experienced officer performing an evaluation. Ultimately, how effective this combination of technological and human interdiction factors can be is an open question. The actions taken after a radioactive source has been detected are as important, or in some ways more important, than the steps taken beforehand. If an illicit radioactive source is found, it may represent a radiation hazard to customs officer as well as others in the immediate vicinity. If the material is part of an RDD, explosives may be present and the hazard is thereby increased. The port of entry at which a source is found may have to be temporarily shut down until the hazard is addressed. This potentiality must be considered in planning for emergencies. If a radioactive source such as an RDD has been detected, there is also a possibility that the device might be detonated, which would make the port of entry area a radioactively contaminated zone. After dealing with the initial impact of such an occurrence, it would be necessary to decontaminate the area by removing, or otherwise dealing with, the dispersed radioactive material. If the radioactive material is a type that decays rapidly, it might be possible to quarantine the area until that radioactivity has decayed to innocuous levels. Preparing for the possibility of events, such as the detonation of an RDD, is an essential element of an emergency preparedness plan for federal, state, and local officials. Emergency exercises or disaster drills have been and are continuing to be carried out to prepare for expected threats from illicit radioactive materials. Resources and guidance documents are available from agencies such as the National Council on Radiation Protection and Measurements (NCRP 2001), the National Memorial Institute for the Prevention of Terrorism (MIPT 2006), and the American National Standards Institute Homeland Security Standards Panel (ANSI 2006b).

1.4 References ANSI. a. Evaluation and Performance of Radiation Detection Portal Monitors for Use in Homeland Security. ANSI N., American National Institute of Standards, Washington, DC. ANSI. b. The American National Standards Institute Homeland Security Standards Panel. Accessed April  at www.ansi.org (last updated November ). Brodsky A and RH Johnson Jr. (eds.). . Public Protection from Nuclear, Chemical, and Biological Terrorism. ISBN ---, The  Health Physics Society Summer School, Medical Physics Publishing, Madison, WI.


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CG-SMG-. . Joint CBP/DOE, Classification Guide for Nuclear Smuggling Information, U.S. Department of Energy, Office of Security, Washington, DC. Fehlau PE. . An Applications Guide to Pedestrian SNM Monitors. LA--MS, Los Alamos National Laboratory, Los Alamos, NM. Fehlau PE. . An Applications Guide to Vehicle SNM Monitors. LA--MS RP, Los Alamos National Laboratory, Los Alamos, NM. Fehlau PE, C Garcia, RA Payne, and ER Shunk. . Vehicle Monitors for Domestic Perimeter Safeguards. LA--MS, Los Alamos National Laboratory, Los Alamos, NM. IAEA. . IAEA Illicit Trafficking Database. Office of Nuclear Security, International Atomic Energy Agency, Vienna, Austria. Accessed on October , , at http:// www.iaea.org/NewsCenter/Features/RadSources/PDF/itdb_.pdf. IAEA. . Technical/Functional Specifications for Border Radiation Monitoring Equipment. IAEA-SVS-X, International Atomic Energy Agency, Vienna, Austria. IAEA. . IAEA Annual Report . International Atomic Energy Agency, Vienna, Austria. Kouzes RT. . Radiation Detection and Interdiction for Public Protection from Terrorism. In Public Protection from Nuclear, Chemical, and Biological Terrorism, eds. A Brodsky and J Johnson, R.H. Madison, WI: Medical Physics Publishing. pp. –. Kouzes RT. . Detecting Illicit Nuclear Materials. American Scientist (): –. Kouzes RT, JH Ely, BD Milbrath, JE Schweppe, ER Siciliano, DC Stromswold. . Spectroscopic And Non-Spectroscopic Radiation Portal Applications To Border Security. IEEE Transactions on Nuclear Science NSS San Juan Conference Record N- -. Milbrath BD, DC Stromswold, J Darkoch, J Ely, RR Hansen, RT Kouzes, RC Runkle, WA Sliger, JE Smart, DL Stephens, LC Todd, and ML Woodring. . Field Tests of a NaI(Tl)-Based Vehicle Portal Monitor at Border Crossings. PNNL-SA-, Pacific Northwest National Laboratory, Richland, WA. MIPT. . The MIPT Responder Knowledge Base Website. Accessed April , , at http://www.rkb.mipt.org (last updated November ). NCRP. . Management of Terrorist Events Involving Radioactive Material. NCRP Report , National Council on Radiation Protection, Bethesda, MD. Reichmuth B, S Short, and T Wood. . Economic Consequences of a Rad/Nuc Attack. Presented at the  IEEE–DHS R&D Conference, Boston, Massachusetts, April –, . Stromswold DC, JH Ely, RT Kouzes, JE Schweppe, and BS Carlisle. . Performance Specifications for Portal Monitors (Rev .). Pacific Northwest National Laboratory, Richland, WA.

{2}

Radiation Sources

In this section, sources of radiation and possible interferences with threat detection are discussed. The radiation emanating from these sources is both ionizing and nonionizing. Ionizing radiation can impart enough energy to release an electron from an atom, thus creating an ion. Nonionizing radiation has less energy and can take the form of visible, ultraviolet and infrared light, radio-frequency waves, or microwaves. First, an introduction to the physics and statistics of ionizing radiation is provided so that terms used throughout this book are introduced. This section, while basic for some, provides information for others who are less familiar with the terminology and science of radiation and statistics associated with radiological processes and detection. After this introduction, four sources of ionizing radiation are discussed: the ubiquitous background radiation from soil, construction materials, and cosmic rays; naturally occurring radioactive materials (NORM); medical sources of radiation (radiopharmaceuticals); and industrial and special nuclear materials. This is followed by a discussion of nonionizing radiation used for telecommunication that can interfere with the operation of an ionizing radiation detection device. The sources of interference fall into two broad categories—electromagnetic and radio frequency-generating devices. Of the sources of ionizing radiation, the special nuclear materials and a number of specific radionuclides are the radioactive materials of most concern at border crossings. Their detection is the primary focus of the remainder of this document.

2.1 Physics and Statistics of Radiation Sources Joseph McDonald There are hundreds of radioactive elements with unstable nuclei from which gamma rays, charged particles, and neutrons are emitted. A specific radioactive isotope of an element is referred to as a radionuclide. Three representative radionuclides that emit gamma rays are Am, Cs, and Co. These radionuclides are used for legitimate purposes, but they may also be used for illicit purposes. If any of these three radionuclides were to be dispersed by an RDD, they would

Radiation Sources

27

remain hazardous for a long period because of their long half-lives. The half-life of a radionuclide is the time required for one half of the initial number of nuclei to disintegrate. This results in the radioactivity decreasing by one half. The halflife of Am is 432 years, and it decays with the emission of both gamma rays and alpha particles. Two primary gamma rays are emitted with energies of 59.5 kilo-electron volts (keV) and 26.3 keV, while the alpha particles have energies of about 5 MeV. This radionuclide is used in various commercially available devices such as smoke detectors, thickness gauges, and medical diagnostic instruments. A second radionuclide that also has several legitimate applications is Cs, which has a half-life of 30.2 years and emits a gamma ray with an energy of 662 keV. This isotope had been used for cancer radiation therapy; however, the 662 keV gamma rays have a limited ability to penetrate the body, and therefore, this isotope is generally no longer used for external-beam radiation therapy. It has been used as an implant source for brachytherapy where the source is placed near the tumor, and it has been used to reduce the restenosis or reclosure of coronary arteries that have undergone balloon angioplasty. In addition to medical uses, Cs is used in industrial sources for radiography, in various industrial gauges, and for food irradiation to sterilize pathogens, such as E. coli. A radionuclide that emits fairly high-energy gamma rays is Co, which has a half-life of 5.27 years and emits two gamma rays with energies of 1.17 and 1.33 megaelectron volts (MeV). These penetrating gamma rays have been and are still being used in external–beam radiation therapy. There are several other uses for Co in radiation research, but its relatively short half-life means the source must be replaced fairly often. In addition to medical applications, Co is used in industrial sources for radiography and for food irradiation. Neutron sources are rarely encountered but may include Cf or Am-Be sources that are used in moisture gauges and devices for examining oil wells. In addition, cosmic rays produce a background of neutrons that varies at different geographical locations, is dependent upon weather conditions, and changes with the solar activity cycle (see Section 2.2). Several radionuclides have been identified as being potential candidates for use in an RDD; among them are Co, Sr, Cs, Ir, Pu, and Am. As mentioned earlier, some of these sources emit gamma rays with energies high enough to travel long distances in air and penetrate into the human body, causing damage. Both  Pu and Am emit alpha particles that can produce neutrons when they interact with certain materials.

2.1.1 gamma-ray interactions with matter When gamma-ray photons interact with materials, they deposit energy by means of several mechanisms that depend on their energy and the characteristics of the




material in which the energy is absorbed (See Section 3.1 of Chapter 3). These mechanisms include the following • • • • •

Photoelectric effect Rayleigh (coherent) scattering Compton effect Pair production Photonuclear interactions

These mechanisms are dependent on the atomic number, Z, of the element acting as an absorber and are also dependent upon the energy, E, of the gamma rays. As can be seen in Figure 2.1, for a low Z absorber like aluminum, the photoelectric effect is the dominant means of absorption for low-energy gamma-ray photons, while Compton scattering is important at intermediate energies, and pair production becomes important at high energies. The symbols, hn, refer to the photon energy given here in units of MeV. As shown in Equation (2.1), the cross section, s, for these various effects is a measure of the probability, P, of an interaction per unit fluence. Gamma-ray fluence (F) is the number of photons incident per unit area.

s=

P F

(2.1)

The photoelectric cross section is strongly dependent on the Z of the absorber— it is proportional to Z. The incoming gamma ray interacts with an electron of an

120

Z of absorber

100 80 60

Photoelectric effect dominant

Compton effect dominant

Pair production dominant

40 20 0 0.01

0.1

1 10 Photon energy hν, in MeV

100

figure 2.1 Graph of the Z of the absorber and the energy of the gamma ray. The two curves indicate the energy and Z for which the respective effects, photoelectric-Compton or Compton pair production, are equal.

Radiation Sources

29

atom and vanishes (all its energy is absorbed), producing a free electron with an energy that is the difference between the energy of the incoming gamma ray and the binding energy of the original electron. The binding energy is the energy needed to release the electron from the atom. The result of this removal of an electron, such as those from the inner shells of a high-Z atom, is that another electron may fill that vacancy and generate an X-ray that is characteristic of that atom. The Compton effect is a scattering interaction where the incoming gamma-ray photon transfers some of its energy to an electron and both continue traveling along different trajectories. The Compton scattering cross section is proportional to Z, and the energy deposited by the incoming gamma ray is shared with the electron after the interaction. Rayleigh scattering is the result of a less important interaction in which the incident gamma ray collides with a tightly bound electron and the gamma ray is scattered without an energy loss. Compton scattering is most prevalent for the gamma rays from radionuclides that may be encountered in the search for illicit radioactive materials, with an impact on the source spectrum and on the detection process. When the energy of the gamma ray exceeds 1.02 MeV, it can interact with the nucleus of an atom in which all of its energy is converted to mass and kinetic energy of the two resulting particles that are an electron and a positron (the antiparticle of the electron). Above 1.02 MeV, the pair production cross section increases approximately as Z. Soon after the creation of the electron–positron pair, these two particles can interact and annihilate each other, resulting in the creation of two gamma rays traveling in opposite directions, each with an energy of 0.51 MeV. Another process, relatively unimportant in the present context, is the photonuclear effect. It occurs when a gamma ray interacts with the nucleus of an atom that subsequently emits neutrons or protons. This effect occurs in many materials when the photon energies exceed 10 MeV, but the cross sections for the photonuclear effect are only a few percent of those for the three major cross sections (photoelectric effect, Compton scattering, and pair production).

2.1.2 neutron interactions with matter Processes that occur in neutron interactions are also basically similar in nature to those for gamma rays. For instance, the processes can be classified as either scattering or absorption interactions with cross sections being defined for neutron interactions. Nuclear cross sections are generally expressed in barns, which are equal to 10– m. A barn is a unit of area, and it corresponds to the probability of interaction mentioned above and in Section 3.1 of Chapter 3. The smaller the area, or cross section, the lower the likelihood is of an interaction, and vice versa. The values of neutron cross sections vary over a wide range depending on the material in which the neutron is traveling and the energy of the neutron.




One of the neutron interactions with a large cross section is elastic scattering. This interaction is similar to billiard balls colliding. The energy transferred to a nucleus and the angles of recoil of the neutron and nucleus are given by expressions similar to those for colliding billiard balls. As illustrated in Figure 2.2, the elastic scattering cross section for hydrogen, H, is almost a factor of 10 larger than the corresponding cross section for C over most of the energy range shown. In an elastic scattering event, the collision is most effective in the transfer of energy if the mass of the atom is very close to the mass of the neutron. This occurs in the case of the hydrogen atom, whose nucleus is a proton, because the masses of the neutron and proton are nearly equal. Materials containing a large amount of hydrogen (such as water, paraffin, and polyethylene) are very efficient at scattering, slowing down, and absorbing neutrons. In such materials, the neutron collision results in energy loss until it eventually has approximately the same thermal energy as the material itself. Neutrons with energies equivalent to the thermal energy of a material at room temperature are referred to as thermal neutrons; their energy is approximately 0.025 eV at 20°C (68°F). There are additional neutron-scattering interactions that are not as simple as billiard ball collisions; they are known as inelastic or nonelastic interactions, depending on the type of particles or energy resulting from the collision. These interactions take place when the incoming neutron enters the nucleus of the

103

Cross sect on - barns

102

1H

16O

12C

101

1

10−1 10−8

10−7

10−6

10−5 10−4 10−3 Neutron energy - MeV

10−2

10−1

1

10 20

figure 2.2 Neutron elastic scattering cross sections for three common elements. Above a neutron energy of about 0.1 MeV, the O cross section becomes complex due to the presence of sharp increases or decreases (resonances) in the cross section (data from KAERI 2006).

Radiation Sources

31

atom and forms a compound nucleus with added energy. This nucleus can return to its ground state energy by emitting neutrons, other nuclear particles, and possibly gamma rays. An interaction where the incident neutron enters the nucleus and then is reemitted is known as inelastic scattering. When the neutron is absorbed and another lower-energy neutron and perhaps an alpha particle or proton is emitted, this process is known as a nonelastic scattering interaction. When a neutron has lost most of its energy through elastic or inelastic scattering interactions and is at thermal energy, it can easily be captured by a nucleus with the resulting emission of a gamma ray. This can be written symbolically as  H(n,γ)H. The thermal neutron, n, incident on a hydrogen nucleus (a proton), H, is captured (with a cross section of tens of barns) to form a deuterium atom, H, that consists of a neutron and a proton. The process is called radiative capture, and a gamma ray with an energy of 2.223 MeV is emitted. Low-energy and thermal neutrons can initiate the process of fission in heavy nuclei, such as U or Pu. This interaction results in the splitting of the nucleus into two roughly equal parts along with the emission of additional neutrons, charged particles, and a large amount of energy in the form of gamma rays and other photons. High-energy neutron interactions are generally more complex and can produce fragments of nuclei, multiple neutron, charged particle, and gamma-ray emissions. These interactions are not normally produced by radionuclides that are of concern at border crossings. However, cosmic-ray interactions in the Earth’s atmosphere represent a background radiation that can be detected with RPMs. The neutrons produced by cosmic-ray interactions can have energies high enough to cause spallation, or the breaking off of parts of nuclei. These processes can, in turn, result in additional radiations that may be detected. In some interactions, subatomic particles such as pi and mu mesons are released.

2.1.3 neutron and gamma-ray spectroscopy 2.1.3.1 Neutron Spectra Radionuclide-based sources of neutrons emit broad spectra that have few features. These spectra are normally characterized by their average energies. An example of a neutron energy spectrum is shown in Figure 2.3. The quantity BE∙E in the figure is proportional to the number of neutrons incident per unit area, per unit time. Narrow neutron spectra that are approximately monoenergetic are not produced from radionuclide sources. These narrow spectra can be produced in accelerator laboratories and will not normally be encountered by RPM detectors. The energy spectra of radionuclide-based neutron sources are usually determined with organic scintillation detectors (Section 3.1 of Chapter 3). Organic liquids and He gas-filled proportional counters are also used for neutron spectroscopy.



Radiation Detection and Interdiction at U.S. Borders 0.6

BEE (s−1)

0.5 0.4 0.3 0.2 0.1 0 0.01

0.1

1 Energy (MeV)

10

figure 2.3 Neutron spectrum from a 252Cf spontaneous fission source. The average energy of this spectrum is approximately 2.2 MeV, and the maximum energy is approximately 20 MeV (data from ISO 2001).

2.1.3.2 Gamma-Ray Spectra Radionuclide sources emitting gamma rays are fairly common, and these sources emit gamma-ray photons that are nearly monoenergetic. The interactions of gamma rays with detector materials, such as NaI(Tl), produce light pulses that are proportional to the energy deposited and can be detected with a photomultiplier tube (Chapter 3, Section 3.1). The electronic pulses produced from the photomultiplier can then be counted with a multichannel analyzer. These pulses result in the production of narrow distributions of counts, known as photopeaks. The NaI(Tl) detector has to be large enough so that the gamma-ray photon can deposit its full energy in the detector. As mentioned above, gamma-ray interactions are dependent on the atomic number, Z, of the detector material. Since NaI has a relatively large, effective Z, gamma rays having energies up to a few MeV deposit their full energy in a detector having dimensions of about 100 mm (3.9 in.). An energy spectrum produced by the gamma rays emitted from Co is shown in Figure 2.4. The two main emissions at 1.17 and 1.33 MeV are shown as photopeaks. Additional features of spectra are described in ORTEC® (2006). Figure 2.1 shows the energy regions where the three predominant gamma-ray interactions occur. These interactions are dependent on the Z of the material in which the gamma-ray deposits its energy. At low energies, the photoelectric effect is dominant and the peak (referred to as a photopeak) of such a low-energy photon interaction in NaI(Tl) results in a very narrow distribution. But, as the energy of the gamma-ray increases to the point where Compton scattering is predominant, there is a range of energy depositions that can occur depending on the scattering angle and the number and energy of photons that escape the crystal. These interactions give rise to a range of pulses of varying heights that make up the region up to about channel 400 in Figure 2.4; this is called the Compton continuum. Compton scattering of gamma-ray photons by electrons results in a scattered electron with a maximum energy dictated by the mechanics of the “billiard



ORTEC is a registered trademark of AMETEK Advanced Measurement Technology, Inc.

Radiation Sources

33

350 1.17 MeV 300

Count/channe

1.33 MeV

Compton edge for 1.33 MeV

250 Backscatter

200 150 100 50 0 0

80

160

240 320 Channel

400

480

540

640

figure 2.4 Energy spectrum produced by gamma rays from Co and displayed by a multichannel analyzer.

ball”–like scattering of the electrons and the photons (Knoll 1989). This maximum energy is known as the “Compton edge” and is shown in Figure 2.4 at approximately channel number 390. Ionizing photons are also produced in continuous spectra called “bremsstrahlung.” These photons are usually referred to as X-rays, and are generated when electrons bombard heavy metals such as tungsten in X-ray tubes. Bremsstrahlung, a German word, means braking radiation, and it describes the deceleration of the electrons as they transfer their energy to tungsten atoms. Characteristic X-rays appear as line spectra and are produced by transitions of atomic electrons (see Section 3.1, Chapter 3).

2.1.4 statistics If large numbers of 1-second measurements of the radiation emitted from a radionuclide source are taken and the number of detected counts is plotted versus the value of the radiation intensity, a distribution is obtained that is similar to a Gaussian or normal distribution (Figure 2.5). The measured values are plotted as differences from the mean value, so the most probable value for the measurement occurs at the midpoint (zero on the horizontal axis). The distribution takes the form of a bell-shaped curve with its maximum at the value of the quantity of radiation that was measured most often. This value is also the mean or average value for such a distribution. As more and more readings are taken, the curve becomes narrower and taller, still approximately centered on the mean or average value of the quantity of radiation. The width of the distribution is proportional to a quantity known as the standard deviation, σ.




0.4

0.3

0.2

0.1

0 −4

−3

−2

−1

0

1

2

3

figure 2.5 Illustrative example of Gaussian distribution.

4

The mean or average value, x , can be calculated with Equation (2.2): N

x=

∑x i =1

N

i

=

x1 x 2 + .... x N N

(2.2)

The standard deviation, σ, is given in Equation (2.3): 1 N ∑ (xi − x )2 N i =1

s=

(2.3)

From this equation, it can be seen that s is proportional to the difference between measurements and the mean value x ; therefore, s is a measure of the width of the distribution. It is often found that one quantity, such as the measured amount of radiation, shows a dependence on another quantity, such as the amount of material between the source and the radiation detector. As an example, the intensity of cosmic rays at sea level is dependent on the barometric pressure because the pressure is proportional to the number of air molecules that are above the point of measurement. More particles mean more absorption of the cosmic rays. For two variables, x and y, a quantity known as the correlation coefficient, r, can be defined: N

r=

∑ (x

x )( y

i

y)

i =1

N

∑x i =1

N

i

x

∑( y i =1

y )2

(2.4)

Radiation Sources

35

The correlation coefficient approaches one if x is strongly dependent on y, and approaches zero if there is no connection. Gamma rays and neutrons are emitted as a result of nuclear interactions, and radionuclides with short half-lives emit photons or particles more frequently than those with long half-lives. A radionuclide such as Na has a half-life of approximately 15 hours and emits large numbers of 2.75 MeV gamma-ray photons. The count distribution registered by a gamma-ray detector exposed to this source would be one where the number of gamma rays detected as a function of their energy forms an approximately Gaussian distribution about a mean value. Gaussian distributions are normally found for measurements in which there are a large number of random events. The neutrons emitted by the spontaneous fission that occurs in a Pu source occur far less frequently than the gamma rays from Na because the half-life of  Pu, at 88 years, is much longer than the half-life of Na (t/ = 15 h). When events occur relatively infrequently, their distribution may be characterized by a different type of distribution called a Poisson distribution. In a Poisson distribution, the standard deviation is given by the square root of the number of counts in the distribution as seen in Equation (2.5):

s Poisson = n

(2.5)

where n is the number of counts measured. Differences in the types of distributions of counts for neutron and gamma rays detected can be useful in the analysis of these radiations. For instance, detection circuits often calculate the standard deviation of electronic pulses from a detector that has been irradiated with gamma rays arising from natural background radiation on the assumption they follow a Poisson distribution. When a source is detected, an increase in the number of pulses is registered, and that increase can be expressed in terms of the standard deviation of the background. The difference between the background distribution of pulse counts and the measured amount from an illicit radioactive source may be expressed as a multiple of standard deviations, or sigmas, as discussed in Chapter 4. It is important to have analysis techniques to examine the pulse count distributions because the detection of an illicit radioactive source often depends on identifying a small increase in counts as compared with counts from natural background radiation.

2.2 Background Radiation Sources Paul Keller Sources of background radiation include cosmic sources, terrestrial sources, and man-made sources. Cosmic sources can vary with the solar cycle and solar




activity, such as solar flares. The measured cosmic background at the surface of the Earth is influenced by latitude, barometric pressure (including altitude), solar activity, diurnal cycle, and weather. Terrestrial background sources can vary spatially because of minerals in the soil and temporally by changes in the weather. Cosmic radiation was first discovered by Victor Hess in 1912 when he took a gold leaf electroscope radiation detector aboard a balloon and flew it to an altitude of 5300 m (17,389 ft). As the balloon climbed, he noted an increase in radiation and deduced that the radiation was coming from outside the Earth; therefore, he dubbed it cosmic radiation. Since then, cosmic radiation has been found to have two major components: galactic and solar. As their names suggest, galactic indicates sources other than the sun, and solar indicates radiation from the sun.

2.2.1 cosmic background The energy of cosmic particles ranges from MeV to 1 ZeV (10 eV). The highest energy particles likely originate from outside our galaxy, and with their high momentum, they are not deviated by the galactic magnetic field. Cosmic particles of this high energy are very rare and hit the Earth at a rate of one particle per square kilometer per century and preserve information about the direction of their origin. Lower-energy particles are much more prevalent and hit the surface of the Earth at a rate of many particles per square centimeter per second. Galactic cosmic radiation is fairly constant, so solar activity has a significant impact on the fluctuation in cosmic radiation that reaches the surface of the Earth and thus the measured background seen at RPM locations. There is a clear variation in cosmic radiation throughout the 11-year solar cycle, the yearly cycle, and even a noticeable variation in the diurnal cycle. All of these variations highlight the strong influence the sun has on cosmic radiation measured at the Earth. Solar activity influences the cosmic radiation at the surface of the Earth in two ways. First, solar activity contributes to cosmic radiation. Protons emitting from the sun are accelerated by solar flares and make their way to the Earth. High-energy neutrons are produced from nuclear reactions in the solar atmosphere during solar flares and also make their way to the Earth. Second, the propagation of cosmic radiation is affected by shock waves that originate on the sun and influence the interplanetary magnetic fields. Solar cosmic radiation intensity is a function of various solar activities including sunspots and heliospheric structure (Hess 1912). Rapid changes in cosmic-ray intensity are usually marked by a Forbush decrease, a term applied to the decrease in cosmic-radiation intensity immediately following a coronal mass ejection (Yanchukovsky and Philimonov 1999). During a coronal mass ejection, not only are a large number of charged particles ejected from the sun, but also the local magnetic field is greatly increased as these particles travel outward from the sun. This magnetic field sweeps away many of the charged particles that form cosmic radiation.

Radiation Sources

37

The net effect is a drop in the cosmic radiation arriving at the Earth. This decrease during solar activity was first described by Scott E. Forbush in 1937 (Forbush 1937). Figure 2.6 illustrates the recorded neutron flux at four locations on the surface of the Earth during a Forbush decrease in late October 2003. This event began with an × 17.2 magnitude solar flare that started on the sun at 09:51 Greenwich Mean Time on October 28, 2003. Within 20 hours, the pulse of energy from the flare arrived at the Earth, producing a rapid change in the magnetic field that resulted in nearly a 20% drop in cosmic particle flux recorded at the surface of the Earth. Cosmic radiation incident upon the upper atmosphere primarily consists of charged particles with energies typically above 300 MeV. Lower-energy cosmic particles usually do not penetrate the upper atmosphere. Primary cosmic particles are about 90% protons, but other charged particles with masses up to iron nuclei are common with traces of heavier element nuclei, possibly including U (Cronin 1999). Charged particles, such as protons, take a more indirect path from the sun to the Earth than do neutrons because of interplanetary magnetic fields. Cosmic radiation also consists of about 0.1% gamma radiation. Gamma radiation is important in determining the origin of a cosmic ray burst as it is deviated by neither the magnetic field of the Earth nor the interplanetary magnetic field. Upon arrival at the Earth’s atmosphere, the primary cosmic radiation particles undergo nuclear interactions through collisions with atmospheric nuclei to produce secondary particles. Some of these secondary particles reach the surface of

6000

Count rate (counts/m nute)

5600 5200 4800 4400 4000 3600

6-Nov

5-Nov

4-Nov

3-Nov

2-Nov

1-Nov

31-Oct

30-Oct

29-Oct

28-Oct

27-Oct

26-Oct

25-Oct

2800

24-Oct

3200

Start of each date (UT)

figure 2.6 Forbush decrease as seen with the four neutron monitors (from top to bottom: Oulu, Finland; Rome, Italy; Hermanus, South Africa; and Haleakala, United States) over the course of 13 days in late October and early November 2003.



Radiation Detection and Interdiction at U.S. Borders Primary cosmic particle π° π−

π±

γ

γ

e+

π

μ± N

N

p

n p

n N n p n

n N n

p

p n

P

Positron Electron Gamma ray Pion Muon High energy nucleon Disintegration product Nuclear disintegration

n

P

n

n

e±

Meson components

p n p

n

μ-

e−

Electromagnetic components

N

P

e+ e− γ π μ N, P n, p

n n

Secondary particles and emissions

pn p

Nucleonic components

figure 2.7 Process of primary cosmic particles entering the upper atmosphere and producing secondary particles as they strike air molecules along the way.

the Earth and contribute to the background radiation. Figure 2.7 illustrates this collision process. The number of secondary particles reaching the surface of the Earth is a function of five parameters: latitude, weather on the Earth, solar activity, diurnal cycle, and barometric pressure (including altitude effects). Because primary cosmic particles interact with the atmosphere, longer paths through the atmosphere reduce the flux reaching the ground, resulting in lower background radiation levels because of the reduction in the flux reaching the ground. Usually, only some energy is imparted to each secondary particle during collision and multiple collisions occur. This results in a cosmic ray shower of lowerenergy particles arriving at the surface of the Earth than are found in the outer atmosphere. Cosmic radiation is highly dependent on elevation with higher backgrounds at higher elevations. The most common radionuclide produced by cosmic radiation is C. Other radionuclides generated include H, Na, and Be. In addition, some cosmic radiation-induced neutrons reach the surface of the Earth. The amount of neutron background at the surface of the Earth is dependent upon atmospheric pressure; this is because pressure directly affects the interaction length for cosmic particles reaching the surface of the Earth. The important background components for RPMs resulting from cosmic rays are part of the low-energy gammaray flux observed in the gamma-ray detector arising from decay gamma rays from radionuclides produced by the cosmic rays, and the majority of the neutron background observed in the neutron detector from secondary neutrons. Arthur Compton first demonstrated that cosmic-ray intensity is dependent on magnetic latitude (Compton 1933). This is caused by the magnetic field of the Earth that creates complex trajectories for incoming particles and results in a

Radiation Sources

39

sorting of the particles by geography. This results in a variation in the portion of the cosmic-ray spectrum that reaches the Earth’s atmosphere. The spectrum is controlled by the geomagnetic cutoff that varies from a minimum at the magnetic poles, which is theoretically zero and where particles can easily penetrate, to a vertical geomagnetic rigidity cutoff of up to 17 GV at the magnetic equator. Geomagnetic rigidity is a relative measure of the ability for a cosmic particle to penetrate the magnetic field of the Earth and is the particle momentum per unit charge. It is the minimum electric potential, usually given in GV, that a charged particle arriving at the top of the Earth’s atmosphere must have to create a particle cascade that can reach sea level at that location. The rigidity, R, of a charged particle is given by Equation (2.6): R=

A 2 E Q

(2.6)

M0 E

where E = the kinetic energy of the particle given in GeV/nucleon A = mass number of the particle, Q = charge of the particle, and M0 = the atomic mass unit (0.9315016 GeV/c2). The relationship between the minimum particle energy per nucleon and the magnetic rigidity is shown in Figure 2.8 where the minimum particle energy in GeV is seen to be very similar to the magnetic rigidity in GV. The lines of magnetic rigidity cutoff around the Earth are illustrated in Figure 2.9. 20

M n mum part c e energy per nuc eon (GeV) E

18 16 14 12 10 8 6 4 2 0 0

2

4

6

8

10

12

14

16

18

20

Magnetic rigidity (GV). R

figure 2.8 Relationship between magnetic rigidity and the minimum particle energy necessary for a cosmic particle to reach the surface of the Earth excluding absorption effects in the atmosphere.

90°N

60°N

30°N

0°

30°S

60°S

90°S 180°W

150°W

120°W

90°W

60°W

30°W

0°

30°E

60°E

90°E

120°E

150°E

180°E

figure 2.9 Lines of magnetic rigidity cutoff that relate to the minimum energies that can be observed at locations shown in Figure 2.10. Magnetic rigidity cutoff lines are labeled as GV.

Radiation Sources

41

In high-latitude regions, the geomagnetic cutoff is low, so most particles present in the outer atmosphere produce secondary particles that make it to the surface of the Earth. For these high-latitude regions, the number of particles reaching the surface of the Earth is a function of the amount of air through which they must travel. In the polar regions at sea level, detected cosmic particles have an energy of at least 430 MeV. At the South Pole, which has an altitude of 2820 m (8600 ft) above sea level, the minimum detectable energy is about 300 MeV. Higher altitudes with the same magnetic rigidity will have a lower minimum detectable energy. From midlatitudes to the equatorial region, the minimum detectable energy is controlled fully by the geomagnetic cutoff and is independent of the altitude. At these locations, the intensity (count rate) is controlled at altitude through atmospheric absorption of the secondary particles generated in the outer regions of the atmosphere. Therefore, high-latitude neutron monitors are placed around the Earth to measure anisotropies in cosmic radiation and mid- to lowlatitude neutron monitors are placed to measure cosmic-ray densities and anisotropy components that exhibit anomalous behavior before the arrival of an interplanetary disturbance at the Earth (Belov et al. 2003).

2.2.1.1 Radiation Portal Monitor Locations in Cosmic Background Study Thirteen RPM locations were used to study the connection between cosmic background and measured background. These locations were spread across the entire United States and gave information on the variation of background radiation levels with location and elevation. Data were available over a range of 6 to 30 months for this study and include three noticeable solar events. The analysis results of cosmic effects at specific locations were used to form some general conclusions about cosmic radiation effects at all U.S. locations.

2.2.1.2 Cosmic Radiation Data Several external sources were used in this study to find the relationship between RPM location background and cosmic radiation. Cosmic-radiation data in the form of neutron flux measurements were obtained from 52 ground-based observatories around the Earth, some of which are shown in Figure 2.10. These groundbased observatories record neutrons arriving at the surface of the Earth and are operated by a variety of academic and research institutions where cosmic and solar activities are studied. There are two main types of ground-based neutron monitors used by the cosmic-ray research community, commonly called International Geophysical Year (IGY) monitors and NM64 monitors. The IGY monitors were the first series of neutron monitors to be developed for extensive cosmic ray research (Simpson 1957). These monitors came into use during a famous solar flare, IGY 23.02.1956, in 1957. They are small counters with low statistical accuracy, but at the time, the IGY monitor was one of the better instruments for detecting low-energy secondary neutrons that did not suffer ionization losses. Over time, most of the IGY neutron

90°N

60°N

30°N

0°

30°S

60°S

90°S 180°W

150°W

120°W

90°W

60°W

30°W

0°

30°E

60°E

90°E

120°E

150°E

180°E

figure 2.10 Map illustrating the location of some of the 52 cosmic-ray neutron monitors used to examine the relationship between cosmic background and the background measured at the radiation portal monitor locations.

Radiation Sources

43

monitors were replaced with NM-64 neutron monitors, although a few IGY monitors still exist. These ground-based neutron monitors detect secondary particles produced in the energy range of 500 MeV to 20 GeV and have a higher sensitivity at the lower part of that energy range (~500 MeV to 4 GeV). An improved monitor with a new counter and geometry was developed in the 1960s that offered higher statistical accuracy than the IGY monitor. This neutron monitor was developed for the International Quiet Sun Years of 1964–65, since greater counting capacity was required (Carmichael 1968). These monitors consist of boron trifluoride (BF), proportional counters surrounded by polyethylene, and lead. The boron is enriched in B to 90% of the total boron or greater; B has a greater cross section for neutrons than B. They are often designated as xx-NM-64 where xx is the number of tubes in the monitor. Secondary cosmic particles interact with the lead surrounding the counters, resulting in nuclear disintegrations of charged fragments and neutrons. These monitors are used to detect particles with energies in the range of 10 MeV to several GeV. The disintegration process from the interaction of neutrons produces a multiplication effect with more secondary fragments generated than incident particles. Finally, the neutrons are moderated by the polyethylene and then counted with BF proportional counters, which are efficient thermal neutron detectors. Many of the neutron observatories worldwide archive neutron counts at a rate of one per minute or one every 5 minutes, while others only archive at a rate of one per hour. A few are experimenting with recording counting rates on an interval of seconds. For this study, most analyses were done at the hourly rate and a few at the minute sampling rate. These observatories often provide the uncorrected rates, the atmospheric pressure, and the pressure-corrected count rates.

2.2.1.3 Major Solar Events The largest solar event during the 2-year span of data used in this study (2003 and 2004) occurred on October 29, 2003, with a 22% decrease in neutron background count rate at the surface of the Earth. Figure 2.6 shows this 13-day event as seen with four of the neutron monitors. Figure 2.11 shows this same event as seen at four RPM neutron monitors along the northern border and the Newark Neutron Monitor. This figure clearly shows that the Forbush decrease is not only visible in the cosmic-ray observatory data but also in the measured neutron background at all four RPM locations. Many of the minor peaks are coincident as well, though the RPM neutron data often contains more noise than the data from a cosmic-ray observatory. Figure 2.12 shows the gamma-ray background at these same four RPM locations during the solar flare and the Forbush decrease is clearly seen. There is much less similarity between plots and the measured neutron count rate at the Newark Neutron Monitor. However, there is a reduction in the gamma count fluctuation during the Forbush decrease, indicating a possible connection between some gamma-ray background and cosmic sources.

6.5 6

Average count rate

5.5 5 4.5 4 3.5 3 2.5 2 6-Nov

5-Nov

4-Nov

3-Nov

2-Nov

1-Nov

31-Oct

30-Oct

29-Oct

28-Oct

27-Oct

26-Oct

25-Oct

24-Oct

1.5

Start of each day (universal time)

figure 2.11 The neutron count rate measured at the Newark Neutron Monitor in Newark, Delaware (top solid trace), with the neutron count rate measured at four radiation portal monitor locations shown as the lower four traces.

3500 3300

Averaged count rate

3100 2900 2700 2500 2300 2100 1900 1700

Start of each day (UT)

figure 2.12 The neutron count rate at the Newark Neutron Monitor against the total gamma-ray background count at four radiation portal monitor locations during a major solar flare in late October 2003. The top solid trace shows the neutron count rate; the other four traces are gamma count rates at the RPM locations.

6-Nov

5-Nov

4-Nov

3-Nov

2-Nov

1-Nov

31-Oct

30-Oct

29-Oct

28-Oct

27-Oct

26-Oct

25-Oct

24-Oct

1500

Radiation Sources

45

Averaged count rate

6.5 5.5 4.5 3.5 2.5

1-Aug

31-Ju

30-Ju

29-Ju

28-Ju

27-Ju

26-Ju

25-Ju

24-Ju

23-Ju

22-Ju

21-Ju

20-Ju

1.5

Start of each day (UT)

figure 2.13 The neutron count rate measured at the Newark Neutron Monitor in Newark, Delaware (shown as the top solid trace), with the neutron count rate measured at four radiation portal monitor locations shown as the lower four traces (two solid and two dashed).

The second large solar flare event occurred on July 26, 2004, and caused a 10% drop in neutron background. Figure 2.13 shows this event as seen at the Newark Neutron Monitor and four RPM locations. This graph shows hourly counts covering the time period around the second largest solar flare and the subsequent Forbush decrease that occurred during this study. For each RPM location, the average count over an hour is used. This figure again shows that neutron background measured at the RPM locations is tied directly to the cosmic background. Some RPMs experience a greater decrease in count rate than others because of the variation in the RPM location.

2.2.1.4 Correlations Many of the cosmic radiation observatories record data at 1- to 5-minute intervals, while others record it at an hourly interval. They all supply data on an hourly count as well. The RPM data are generally recorded once a second, though there are often many gaps. For the correlation studies, all data were correlated on an hourly basis. For the RPM data, this involved summing up the counts over an hour and reweighting the hourly count for missing data. When most or all of the data are missing for a specific hour from either an RPM or a cosmic-ray observatory, that hour is not included in the correlation calculation. Table 2.1 shows the average correlations of the 13 RPM locations with 16 of the cosmic-ray observatory neutron monitors. A value of 1.0 would indicate perfect correlation, and lower values indicate poorer correlations. A correlation coefficient above 0.45 is considered a “strong” correlation, between 0.3 and 0.45 “good”, between 0.2 and 0.3 “moderate”, between 0.1 and 0.2 “weak”, and below




table 2.1 Average correlation between radiation portal monitor locations and similar cosmic-ray observatory locations Correlation with Cosmic Neutronsa

RPM Background

Neutron Low-energy gamma High-energy gamma Total gamma a

0.423 0.271 0.316 0.288

Correlation between cosmic neutrons and RPM neutron and gamma-ray background is shown.

0.1 insignificant. Chance has a correlation of zero. Correlation pairs were chosen between the RPM location and the cosmic ray observatory locations to approximately match the elevation and magnetic rigidity. Although this table shows average results, a relationship clearly exists between the cosmic background and both neutron and gamma-ray background recorded at the RPM locations. Stronger correlations exist between specific panels at RPM locations and specific cosmic-ray observatories.

2.2.2 earth–terrestrial background Another major source of background radiation is terrestrial. Terrestrial background primarily comes from U, Th, and their progeny, and from K that occurs in rock and soil. Much of the actual gamma-radiation background measured at and just above the surface comes from radon gas transported to the surface through pores and cracks in the soil and rocks. Radon gas is the progeny of U and Th. For example, U decays to Pb through Rn in the U decay series. Uranium-235 decays to Pb through Rn in the actinium decay series. Thorium-232 decays to  Pb through Rn in the Th decay series. In the 1970s and 1980s, the DOE conducted an aerial radiometric survey of the conterminous United States as part of the National Uranium Resource Evaluation (DOE-NURE) program (DOE 1985). The survey data from this program have been integrated into contour maps of equivalent U, Th, K, and total gamma-radioactivity exposure for the conterminous United States. Figure 2.14 (located at the front of this book) shows four U.S. Geological Survey maps based on NURE data (Phillips 1993). The maps show concentrations of K,  Th, and U. The hottest (pinkish purple) zones (>57 picocoulomb [pC]/kg⋅s or > 8 μR/hr) show regions of the highest background gamma radiation and are generally from mineral deposits in the soil containing U, Th, and K. These regions include the Sierra Nevada mountains and parts of east-central California that have large deposits of granite, and southern Nevada and parts of Utah that have mountain ranges high in both granite and volcanic rock and basins filled with alluvium shed from the mountain ranges. Sporadic regions of the Rocky Mountains and nearby

Radiation Sources

47

3.8

K (%)

Potassium concentrations

0

21.6

eTh (ppm)

Thorium concentrations

0

5.4

eU (ppm)

Uranium concentrations

0

figure 2.14 Maps based on the U.S. Department of Energy National Uranium Resource Evaluation (NURE) program (DOE 1985) and extracted from the U.S. Geological Survey in Digital Data Series DDS-9 (Phillips 1993). The top map shows the abundance of potassium (K). The middle map shows the abundance of thorium (Th). The lower map shows the abundance of uranium (U).

mountain ranges within Colorado, Wyoming, and Montana have many deposits of granite and metamorphic rock that contain U and are part of this highest background zone. Other high background zones include southern Arizona, West Texas, and central and southern Idaho. The next hottest (red) zones (ca 57 pC/kg⋅s or 8 μR/hr) include regions of New Hampshire and Maine as well as the Black Hills of South Dakota. These regions are




predominately composed of granite and metamorphic rock that are high in radioactivity but surrounded by less radioactive sedimentary rock. Another red zone is the area surrounding Reading, Pennsylvania, which is composed of metamorphic rock high in U. The orange zones (ca 50 pC/kg⋅s or 7 μR/hr) include the Appalachian Mountains that are composed of granite with elevated amounts of U and Th, especially within its fault zones along black shale and soil that contain moderate to high levels of U. The yellow zones (ca 42 pC/kg⋅s or 6 μR/hr) include the Ohio shale found in northwest Ohio and northeast Indiana that contains U from a narrow outcrop and that was spread over this region by glacial action. Other U-bearing black shale (Chattanooga and New Albany shales) containing this general radioactivity level is found in Kentucky, Indiana, and other parts of Ohio. The green zones (28–36 pC/kg⋅s or 4–5 μR/hr) cover wide regions of the United States and include deposits of glacial Lake Agassiz in North Dakota that have some radioactive clay and silt, and the Mississippi River region that has sands containing U-bearing glauconite. The blue zones represent fairly low-exposure areas (ca 21 pC/kg⋅s or 3 μR/ hr) and include the southern states, various parts of Texas, and the Nebraska Sand Hills. These zones are composed of light quartz sand devoid of much Th and U. The violet zones represent very low-exposure areas ( 30 keV) Percent Branching Fractions (> 1.0%)

57

271

keV

d

%BF keV

51

Co

Cr

27.7 d

67

Ga

78.3 h

123

I

13.2 h

125

131

I

I

60.1 d 8.04 d

111

In

67.3 h

153

Sm

46.7 h

99m

Tc

6.01 h

201

Tl

73.1

Xe

85.54 320.0

136.4

–

–

–

–

10.69

–

–

–

–

–

–

–

–

–

–

–

–

–

–

93.31 184.5

208.9

300.2

393.5

0.0006 0.022

3.56 × 104

0.075

2.78

3.34 × 105

10.00

370

5.15 × 108

0.300

11.1

1.89 × 107

%BF keV

91.27

%BF keV

2.95

37.00 20.45

2.33

16.60

4.64

30.98

31.88 158.9

–

–

–

12.43

2.71

83.30

–

–

–

30.98 20.09

31.88 4.38

35.49 6.66

– –

– –

– –

N/A

N/A

N/A

636.9

722.8

–

41.80

1547

1.59 × 109

3.225

119

2.65 × 108

140.0

5180

5.47 × 109

16.91

626

5.85 × 108

20.00 740

1.07 × 109

10.00

3.18 × 108

%BF keV

9.83

%B keV

80.18 284.3

%BF keV

2.62

6.06

22.98

26.08

%BF keV

24.15

11.57

40.90

41.54

47.00

48.50

17.96

32.36

9.42

2.85

5.32

28.30

–

–

–

–

–

–

–

–

82.78 135.2

167.4

%BF keV %BF keV

140.4

364.4 81.25

7.27

26.80 171.2 2.40 90.24

87.20

–

–

68.89

70.82

80.12

1.80 245.3 94.00

– – –

69.67 103.1

%BF keV

26.89

45.67

16.08

4.39

2.67

5.25

30.63

30.97

34.97

36.01

80.99

–

d

%BF

14.06

25.98

7.10

1.74

36.97

–

h 133

122.0

Activity Activity Number of in mCi in MBq Photons Emitted Per Second

9.43 370

also be some RPM response in this high-energy (High E) region. However, these radionuclides have a larger fraction of photons below 250 keV than above, so the RPM response to Low E is important, as discussed below. Another feature seen in Figure 2.21 is the influence of the photons below 25 keV. This low-energy cutoff effect was studied by comparing the 5 keV–250 keV RPM responses to the 25 keV– 250 keV responses. The fractional number of photons shown in this graph helps to explain the fractional differences seen in the results for these two Low E responses.

2.4.4 detector response calculation configurations A computer model was constructed to simulate pairs of RPM panels, with one pair per lane. Only results for one traffic lane (Lane 1) are reported here. A twolane study is reported in Kouzes et al. (2006) where lane-to-lane cross talk alarms are discussed. Each pair of units has two identical towers facing each other, where



Radiation Detection and Interdiction at U.S. Borders Medical decay gamma rays with E > 5 keV and %BF > 1% 57Co

51Cr

67Ga

123I

131I

111In

153Sm

99Tc

201Tl

100 Percent branch ng fract on

90 80 70 60 50 40 30 20 10 0 1

10

25 Decay energy (keV)

100

250

1000

figure 2.21 Energy distribution of dominant gammas emitted from selected medical radioisotopes. The vertical axis is the percent branching fraction (%BF).

each tower consists of a steel support in which two detector enclosures are mounted. A schematic of the model RPM is shown in Figure 2.22. As indicated, the model coordinates are defined such that this view is in the y–z vertical plane, where the z direction is vertically upward. The key components shown in this figure are the four detector enclosures (shaded rectangles) and the steel supports to which the four enclosures are attached. For reference to these four locations in Lane 1, the notation 1Pb, 1Pt, 1Db, and 1Dt is introduced (P for passenger, D for driver, t for top, b for bottom). For the purposes of this calculation, a lane curb-to-curb width of 4.3 m (14 ft) is used. Also shown in Figure 2.22 is the y–z position of the sources (S). To roughly simulate the presence of a passenger who contains a medical isotope after having a heart or thyroid treatment, the sources in this study are taken as uniform spheres with 0.01 m radii, and with the y–z position of the centers fixed to give a 0.76 m (30 in.) off-center lane shift toward the 1Pb detector and a 1.5 m (60 in.) height from the pavement. This side-to-side and height position was chosen to be within the range of passenger vehicle profiles for subcompacts to large pickup trucks, indicated by the dashed rectangles (Ramsey and Sleeper 1994). Note that the asymmetric location of the sources should cause an asymmetric response in the detectors dictated approximately by the distances from the source to panel centers. By this reasoning, the count rates in the Lane 1 panels are expected to satisfy the inequality: 1Pb > 1Pt > 1Db > 1Dt. The steel-support structure acts as a blinder, or partial shield, for the RPM panels. The blinder gives rise to detection zones, A, B, C, D, and E, as illustrated in Figure 2.23.

Radiation Sources

71

Lane 1 passenger top (1Pt)

Lane 1 driver top (1Dt)

236cm Lane 1 passenger bottom (1Pb)

Lane center line

Lane 1 driver bottom (1Db)

206cm

S

155cm

Curb

Curb 4.27m Tower 1P

z

Tower 1D

y

figure 2.22 Front-view scale drawing of Lane 1 (S = Source).

1P Traffic flow Zone E

Zone D S Zone A

S

S

S

Zone C

Zone B

y x 1D

figure 2.23 Top view of Lane 1 showing optical zones of detection (S = Source).




2.4.5 detector response modeling method A series of MCNP (Briesmeister 2000) calculations was performed with the RPM model. The relative positions, surface geometries, and composition of the plasticpanel photon detectors were specified as input, as were all other components (e.g., aluminum doors, lead shielding, etc.) that could influence the photon responses. Additional input required for the MCNP calculations included the specific source type, its spatial distribution, and its position with respect to the gamma-ray and neutron detectors. The gamma-ray emission energies and %BF listed in Table 2.8 were used to specify the source types for the nine medical radionuclides evaluated in this modeling study. The third source position coordinate (x) was varied in 0.61 m (2 ft) increments from 8.6 m (28 ft) to 0 m (0 ft) (centerline of the portal panels). Thus, a total of 135 calculations were performed with 15 x values for 9 isotopes. The numerical output for these calculations was obtained from the MCNP photon pulse height output option (referred to as tally 8) taken separately for each of the plastic panels in the model. With 1 keV energy bins, this option provided an energy distribution of pulses created from the energy deposited by each photon entering the plastic. These counts-per-photon values were converted into countsper-second (cps) values with the photon-per-second factors for each isotope shown in Table 2.8. No additional reduction or rescaling of the output was performed. Thus, the cps results reported here represent a detector efficiency of 100% and therefore overestimate the actual detector responses that can be as low as 2% for photons below 25 keV. The models used to compute the detected signal include not only a large amount of detail on the physical systems but also simplifications that can affect the results. One simplification is the omission of shielding effects from the vehicle. Because a vehicle’s undercarriage, engine, and drive train provide a significant shielding effect, omission of shielding from these components leads to an overestimate of the counts seen in the lower detector of the RPM, but not in the upper detector. Another simplification is the discrete-step approximation to evaluating a moving source. In these calculations, the effects of vehicle motion were approximated with a static source over a series of equally spaced positions and equal simulation times. In reality, the movement of the vehicle through a portal limits the time available for detection and therefore could increase the statistical uncertainty.

2.4.6 detector response modeling results The complete set of results from these calculations was converted to figures representing the system response versus source position (distance from portal centerline in Lane 1). To simulate the data provided by the actual detectors, the energy

Radiation Sources

73

distribution output from MCNP is summed over two energy regions: the Low E from 5 keV to 250 keV, and the High E from 250 keV to 3.0 MeV. To illustrate some of the features from the results, Figure 2.24 shows the Low E region response to m Tc for the four panels in Lane 1. The asymmetric behavior of the responses seen in Figure 2.24 is characteristic of all Lane 1 results and is caused by the steel supports. Notable is the “left–right” asymmetry between the driver side (dashed lines) and passenger side (solid lines) detectors. For x > 7.5 m (24.5 ft), the source is beyond the optical field of view of both the 1D and 1P detectors, and their responses are small and essentially equal. Crossing this boundary, the 1D responses change slope, while the 1P responses do not. Recall that the source is closer to the 1P detectors, but for x > 3.7 m (12.3 ft) it is beyond the partial-panel field of view for that side. Thus, for those values of x, the 1D response is significantly larger than the 1P response. Crossing this second boundary, the source becomes exposed to the 1P detectors, and their responses rapidly increase, overtaking the 1D responses. For these small values of x, the closer proximity of the source to the 1Pb panel starts to become important and increases the difference between the top and bottom responses on each side. Note that at x = 0, the 1Pt value is just slightly greater than the 1Db value. This behavior is observed in all cases, reflecting the equality in source-to-panel distances for these two panels. The qualitative behavior discussed in the example for mTc is characteristic of the other isotopes evaluated in this study. The only significant difference among them is the scale of their values. Thus, the ratio of maximum values for any two

Lane-1 low-energy component response to 99mTc 1D bottom

1D top

1P bottom

1P top

Counts per second (0.35%) in the 100 keV to 400 keV energy region. Note that a simple, but misleading, estimate from the ratio of detector areas indicates it would take an array of approximately 15 NaI(Tl) detectors!




Abso ute detect on eff c ency (EAbs)

0.5%

0.4%

PVT, 3.8 cm, large PVT, 5.7 cm, medium PVT, two 3.8 cm, small

0.3%

0.2% NaI, 10 cm NaI, 5.7 cm NaI, 3.8 cm

0.1%

0.0% 101

102 103 Incident photon energy (keV)

104

figure 4.2 Calculated absolute detection efficiency for polyvinyl toluene (plastic scintillator) and NaI(Tl).

4.1.2 specific detector simulations The MCNP models discussed in this section were constructed to simulate actual PVT and NaI(Tl) detectors. The PVT model was constructed to the specifications of a commercial portal monitor, including the detector (38 mm × 360 mm × 1.73 m [1.4 in. × 14 in. × 5.6 ft]), shielding, insulation, and all enclosures. The NaI(Tl) model was constructed by replacing the PVT detector with a smaller NaI(Tl) crystal (100 mm × 100 mm × 410 mm [4 in. × 4 in. × 16 in.]) encased in a 1 mm (0.03 in.) stainless-steel shell, while retaining the same shielding, insulation, and enclosures as the PVT. In addition to the detailed detectors, the modeled sources were also constructed to simulate the actual sources in both physical extent and relative position. All of the modeled sources were single, small spheres at a distance of 2 m (6.5 ft) perpendicular from the face of the outer aluminum door and 1.63 m (5.3 ft) above a modeled pavement. This paved surface provided a reflector that accounts for ~10% of the total PVT responses for sources with gamma emissions above ~400 keV (e.g.,  Cs, Co, and Th). The 10% gain provided by the pavement was calculated relative to a spectrum with pavement replaced by a void. Gains for NaI(Tl) were somewhat less. The modeled sources included Am, Ba, Co, Co, Cs, and Th. The detailed values of the energies and percent branching fractions (%BFs) of the photons from these sources are listed in Table 4.1. Thorium was not one of the sources measured, but it is included here for reasons explained below. In the table, the entries for the dominant gamma rays are shaded.

table 4.1 Photon emission data for model sources used in MCNP simulations; dominant gamma rays are shown in the shaded boxes Source Isotope

Emitted Photon Energies ∗ Percent Branching Ratios (%BF) (∗Units for 232Th Are Gammas Emitted Per Second [gep] Per Gram)

Photons Emitted Per Second Per μCi 

keV %BF keV %BF

11.9 0.809

13.9 13.04

15.9 0.33

17.6 20.17

21 5.183

Am 26.3 2.4

32.2 0.017

33.2 0.12

42.6 0.001

55.5 0.02

59.5 35.7

69.8 0.024

97.1 0.001

98.9 0.02

101.1 0.002

102.9 0.019

122.9 0.001

125.3 0.004

43.4 0.073

28,800

36.01 4.40

53.15 2.17

102,000

14.41 9.54

122.06 85.54

59,900



keV %BF keV %BF

3.79 0.24

4.14 0.11

4.28 6.70

4.73 6.52

5.39 0.91

Ba 30.63 35.56

30.97 65.74

34.97 17.97

79.61 3.18

80.99 34.18

160.60 0.60

223.24 0.46

276.39 7.09

302.85 18.40

356.00 62.15

383.84 8.92



keV %BF keV %BF

0.62 0.07

0.63 0.05

0.70 0.65

0.73 0.4985

6.39 16.41

Co 6.4 32.5

7.06 5.842

7.17 2.2e-7

136.47 10.69

230.26 3.4e-4

339.66 4.6e-3

352.32 3.2e-3

366.74 6.1e-4

569.92 0.0146

691.98 0.1584

706.39 6.7e-3



keV %BF keV %BF

346.95 0.0076

826.33 0.0075

1173.2 99.90

1332.5 99.98

2158.9 0.0011

Co 2505.7 2.0e-6

3.95 0.01

4.33 0.01

4.46 0.3983

4.94 0.37

5.62 0.05

Cs-137 31.82 2.05

74,000

32.19 3.77

36.36 1.04

37.45 0.26

661.66 85.21

34,500

(Continued)

table 4.1 (Contd.) Source Isotope

keV geps/g keV geps/g keV geps/g keV geps/g keV geps/g keV geps/g keV geps/g

Emitted Photon Energies Percent Branching Ratios (%BF) (∗Units for 232Th Are Gammas Emitted Per Second [gep] Per Gram)

Photons Emitted Per Second Per μCi

∗

10.26 118 15.23 184 74.97 50.3 153.89 33.3 463.11 180 785.51 43.1 1496.0 41.5

10.83 256 15.38 44.2 77.11 691 209.39 163 510.61 302 794.79 181 1588.2 142

11.12 35.1 16.15 808 84.26 47.1 238.58 1700 562.65 39.9 835.60 68.5 1620.7 58.8

12.28 138 16.18 1780 87.19 244 240.76 152 581.53 59.4 840.44 37.1 1630.5 77.0

12.33 122 17.95 41.4 89.96 135 270.26 149 583.02 1200 860.30 168 2614.4 1400

 Th 12.76 750 18.80 513 90.13 72.5 277.28 95.0 677.07 33.8 904.29 35.2

12.95 596 19.11 183 93.35 220 300.03 130 726.63 34.4 911.16 1140

13.10 235 19.40 35.5 99.55 52.9 328.07 137 727.25 259 964.64 228

13.52 3950 39.85 42.8 105.36 79.5 338.42 491 755.28 52.1 968.97 688

15.15 395 74.81 411 129.04 116 409.63 86.9 772.28 43.0 1459.2 41.8

Enhancing the Effectiveness of RPM Systems

171

Although unshielded and shielded sources were modeled, for brevity only the results from the unshielded source are presented here. Results from the calculations for a source mixed with cargo are also presented. Calculations for the unshielded source were performed to simulate the real detector responses both qualitatively and quantitatively. Qualitative features of the simulated spectral distributions are discussed for the unshielded source, then the total-count values that result from evaluating the area under these distributions are tabulated (in units of counts per second per μ(Ci)) and, when available, compared to the measured values. Note that all numerical results presented here are net-signal values and not gross-signal (i.e., signal plus background) values.

4.1.3 unshielded-source results Figure 4.3 shows examples of experimentally measured spectra obtained with NaI(Tl) and PVT detectors for a Ba source. Figures 4.4, 4.5, and 4.6 show examples of computer-simulated net responses of the NaI(Tl) and PVT detector models for each of three individual sources (Ba, Am, and Th) with no intervening material (except air) between the sources and the detectors. In Figure 4.4 through Figure 4.6, the PVT results are depicted as solid lines, and the NaI(Tl) results as connected circles. Their values are given in counts per emitted source photon (the left-hand ordinate) as a function of the energy deposition. Also shown (filled triangles) in these figures are the distributions of photon flux incident on the detectors after passing through the aluminum door. These flux distributions are included to provide an unambiguous reference against which

Ba-133

Counts/sec/μC

101

PVT NaI

100

10−1

0.10

0.20

0.30

Approximate energy (MeV)

figure 4.3 Measured Ba spectrum from Na(Tl) and PVT detectors.

0.40




Re at ve to max

100 10−1

Am-241 Incident

10−2

Counts/em tted photon/keV

10−3

PVT response Nal response

10−4

10−5

10−6

10−7

0.02

0.04

0.06

0.08

0.10

0.12

0.14

Energy bins (MeV)

figure 4.4 Calculated photon flux and spectra for polyvinyl toluene (plastic scintillator) and NaI(Tl) for Am.

the detector responses can be compared. Although passage through the door spreads them somewhat, the flux shapes still appear as narrow spikes on the scale of energies plotted in the figures. For easy comparison, the values of the flux are given as relative values, normalized to their maximum and read from the righthand scale. Note that both the left-hand and right-hand ordinates cover four decades and, hence, can visually distort the relative importance of minor flux values.

4.1.4 spectral distributions One immediate observation about the model spectra displayed in Figure 4.4 is that they simulate well the two main features seen in the real spectra (e.g., Ba seen in Figure 4.3)—the presence of photo peaks in the NaI(Tl) responses, and the absence of peaks along with build-up of low-energy counts in the PVT responses. Note these are net spectra, excluding the background contribution. Nevertheless, these features are indeed characteristic of all the sources, and they underscore the need for PVT-based systems to have the lowest-possible energy threshold for maximizing signal collection.


173

Re at ve to max

100 Ba-133 Incident

10−1 10−2


10−3

PVT response Nal response

10−4

10−5

10−6

10−7

0.10

0.20

0.30

0.40

Energy bins (MeV)

figure 4.5 Calculated photon flux and spectra for polyvinyl toluene (plastic scintillator) and NaI(Tl) for Ba.

Comparing the position and relative strengths of the simulated photo peaks to the incident flux shows the extent to which NaI(Tl) is able to resolve the dominant gamma rays. From this comparison, it is obvious that the NaI(Tl) spectra are well correlated to the energy and amplitude of the incident flux. As with the measured spectra, however, this statement requires the caveat that the simulation is allowed to run for sufficient time to obtain good statistical results. Typically, each simulation run took >1900 seconds and tracked ~4 × 10 emitted photons. This corresponds to a real world “measurement time” of ~100 seconds with a 370 kBq (10 μCi) source. Much shorter detection times (~10 seconds) would be used in a simulation of the response of a source moving at speeds typical for vehicles passing through an RPM. In contrast to the NaI(Tl) results, a cursory comparison of the incident flux distributions to the simulated responses for PVT show little correlation, either in position or relative strength. As shown in Figure 4.3, the dominant PVT response is a shift of the high-energy intensity of the incident flux toward lower energies, due to the Compton scattering energy deposition process in the PVT material. For the sources with well-isolated flux below ~100 keV, a careful examination of




Re at ve to max

100 Th-232 Incident

10−1 10−2


10−3

PVT Nal

10−5

10−6

10−7

10−8 0.00

0.50

1.00

1.50

2.00

2.50

Energy bins (MeV)

figure 4.6 Calculated photon flux and spectra for polyvinyl toluene (plastic scintillator) and NaI(Tl) for Th.

the PVT spectra does show some hint of photo peak contributions, but these are mostly concealed by the Compton down-scatter contributions from higher-energy gamma rays. What can be seen, and roughly correlated in some of these PVT spectra, are the positions of the so-called Compton edge – the maximum energy deposited by back-scattered photons. These maxima single-scattering energy depositions create the broad bumps in the high-energy portions of the PVT spectra. In light of the above general comment about PVT response being poorly correlated in energy and amplitude to the incident flux, the results shown in Figure 4.4 for Am are discussed in detail. In that figure, the broad bump in the PVT response centered at 60 keV is indeed a broadened, and somewhat obscured, photo peak signal. This response is unique to this source for two reasons. First, the incident flux for this source is dominated by a single emission at ~60 keV, and thus, there are no higher-energy emissions to contribute Compton downscatter counts into this energy region. Second, although the photoelectric absorption process in PVT is not comparable to the Compton scattering process above ~20 keV, there is indeed a small (~4%) probability for photoelectric absorption in


175

the region of 60 keV. However, most of the energy deposited by the 60 keV flux is more likely to be distributed to lower energies by Compton scattering. A more common example of the NaI(Tl) and PVT spectral differences is shown in Figure 4.5 for Ba. For NaI(Tl), distinct photo peaks are apparent, although the ones centered at approximately 300 keV and 350 keV are rather broad because of the incident flux at nearby energies. On the other hand, PVT shows only a continuum, with no well-defined peaks and relatively few counts above 250 keV. However, a careful inspection of this simulated PVT spectrum does indicate the presence of a Compton-buried photo peak in the 30 keV to 40 keV region, and a high-energy Compton edge at ~200 keV from the ~350 keV flux. Most of these features are readily observed in the net experimentally measured spectra for this source shown in Figure 4.3. However, note that the energy locations for the data are approximate, where the low-energy values start at ~25 keV for PVT and ~50 keV for NaI(Tl). Again, the dominance of PVT counts at energies below ~50 keV in these results illustrates the importance of having a low discriminator threshold for PVT detectors. As a final example, the simulated NaI(Tl) and PVT responses to Th are shown in Figure 4.6. The gamma emission parameters used to model this source represent 1 gram of Th in equilibrium with its numerous decay products. The Th source is of interest because it and its daughters emit appreciable flux at energies both below 1 MeV (at 13.5 keV, 16 keV, 239 keV, 583 keV, and 911 keV) and above 2.5 MeV (at 2614 keV). The presence of the 2614 keV emission not only distinguishes Th from the other five sources, but it is also present in the natural background and in most NORM. In the energy region below 1 MeV, comparison of the NaI(Tl) to the PVT simulated spectra is the same as with the other sources, (i.e., well-defined, narrow photo peaks for NaI(Tl) and a low-energy-dominated continuum for PVT). The reason for these distinctions is the dominance of Compton scattering over photoelectric absorption in PVT for incident energies above ~20 keV. However, for energies above ~2 MeV, the probability of photoelectric interactions in NaI(Tl) has decreased to 4000 kg) produced a spectrum with high count-rates due primarily to 1001 keV and 767 keV gamma rays from m Pa, which is in the decay chain of U. These gamma rays are scattered in the uranium oxide, contributing to the large number oflow-energy counts.

4.5.3 specification for spectroscopic portal monitors In September 2003, the RPMP developed an initial specification for an SPM based upon the same requirements used in the PVT-based RPM specification. The concept was to allow the SPM system to be operationally similar to the deployed systems in every way but with the enhancement of spectroscopic identification from NaI(Tl) gamma-ray detectors. The specification includes the capability for filtering alarms based on user-defined criteria for rejection of NORM and radioisotopes utilized for medical procedures.


233

10000 4025;R20

UO2

Counts

1000

100 60Co

10

1 0

500

1000

1500 Energy (keV)

2000

2500

3000

figure 4.43 Drive-by spectra from Co and UO cargo.

Just as for the PVT-based RPM specification, the majority of the SPM specification dealt with operating requirements and environmental specifications. The SPM panels were required to fit into the existing support stands to allow easy implementation in deployed stands. The SPM had to be deployable to all of the same venues as the RPM systems. Compliance with the ANSI N42.35 standard for RPM systems was required, as was compliance with the ANSI N42.38 standard under development at that time. The list of isotopes to be identified with the SPM was based upon those listed in the ANSI N42.34 standard. These isotopes included: K, Co, Co, Ga, m Tc, Mo, I, I, Ba, Cs, Sm, Ir, Tl, Ra, Th, Th, U, U, U, U,  Pu (reactor grade plutonium [> 6% Pu]), and Am. The gamma-ray sensitivity for the SPM was specified to require an absolute detection efficiency for various sources, with similar sensitivity values used for the RPM specification, as shown in Table 4.5. The reason for this stringent requirement was to meet the basis outlined earlier in this chapter for detection of highly shielded sources. Based upon modeling studies by the RPMP, the configuration of detectors was specified as a specific arrangement of five 102 mm × 102 mm × 406 mm (4 in. × 4 in. × 16 in.) NaI(Tl) “logs,” which was known to meet the specified absolute detection criteria. The detectors were spaced vertically to allow for effective coverage of vehicles of all configurations. Several gamma-ray alarm algorithms were specified that could be applied to the individual detectors as well as groups of detectors. Complete data logging was required, along with state-of-health indicators to predict impending system failures. The software used to analyze the data is crucial to the success of an SPM. To date, the most promising analysis approach is known as “template matching,” in which a fit is made to the data from a library of actual spectra under a wide range of conditions. This method is used in some commercial products.




table 4.5 Detection efficiencies for radionuclides Radionuclide

Primary Emission Energies (keV)

Minimum Absolute Detection Efficiency (net cps/μCi)

241

60 122, 136 31, 356, 81, 302, 35, 383, 276 662 1173, 1333

20 100 200 110 220

Am Co 133 Ba 137 Cs 60 Co 57

4.5.4 comparison of thallium-doped sodium iodide and high-purity germanium detector materials Perhaps the most important consideration in a comparison of NaI(Tl) to HPGe for portal monitoring applications is the efficiency of the detectors themselves (Ely, Siciliano, and Kouzes 2004). Many comparisons of the efficiency of NaI(Tl) to HPGe have been conducted over the years, and in fact, the most common method of specifying a germanium detector is in terms of the relative efficiency compared to a 75 mm × 75 mm (3 × 3 inch) right cylindrical NaI(Tl) crystal. The relative efficiency is measured with a Co point source at a distance of 250 mm. The NaI(Tl) has greater gamma-ray absorption because of the higher effective Z compared to HPGe and, so, has a higher overall efficiency for the same size detector. For isotopic identification, full-energy peak efficiency is of considerable importance, and different analytical and semianalytical functions have been used to describe both HPGe and NaI(Tl) full-energy peak efficiencies (Sudarshan et al. 1992). For the same size detectors, the HPGe peak efficiency is less, but because of its superior energy resolution, the isotopic identification capability of HPGe is superior, and the MDA of source material is smaller. A recent investigation of the efficiencies, resolutions, and MDA of common-sized NaI(Tl) and HPGe detector systems has been made with regard to border security applications (Perez-Andujar and Pibida 2004) in which the NaI(Tl) system provided the most efficiency and lowest MDA. However, in this comparison the HPGe detector considered is a factor of 6 smaller than the NaI(Tl) detector. Other factors must also be considered in the comparison of NaI(Tl) to HPGe for vehicle RPM applications. The HPGe requires cooling, which is more expensive, but removes the problems related to ambient temperature changes that may cause instability in NaI(Tl) systems. Rapid temperature changes can crack large NaI(Tl) detectors, and the scintillation light output and resulting pulse-height spectra, are dependent on temperature. These problems can be overcome in NaI(Tl)-based systems either by providing constant temperature environments or by gain stabilization techniques with thermal insulation. Liquid nitrogen has traditionally been used for HPGe detectors, but for field applications, mechanical cooling provides a viable alternative (albeit with significant electrical power requirements). Investigation into more efficient and robust cooling for HPGe


235

detectors is a current priority with HPGe system manufacturers. Durability is a consideration; NaI(Tl) systems have been designed and used in many field applications, whereas HPGe has been used primarily in laboratory settings where the thin windows of the detection system can be protected. As they will typically be used in a fixed location, portal monitors of both NaI(Tl) and HPGe can be engineered to operate in a wide variety of environmental conditions for an extended period of time. Another factor for consideration is the need for a rapid real-time decision about the presence of any source of radiation above background while the vehicle transits a primary screening portal. Because of the very short time available for data collection, spectral identification may not be possible. Thus, HPGe systems with improved energy resolution may not have a significant advantage over NaI(Tl) systems for this real-time decision mode.

4.5.5 advanced spectroscopic portal (asp) program The HSARPA organization within DHS developed a specification for a class of SPM referred to as an ASP in 2004, for deployment starting in 2007. The development of these ASP systems is taking place under the program supported by the DHS DNDO. The HSARPA Broad Agency Announcement for the ASP program resulted in 10 contracts to vendors for prototype systems. These contracts were awarded in two groups of five vendors (the first five were redirected under a previous award, and five additional vendors were selected). The 10 vendors awarded contracts, under the two HSARPA Broad Agency Announcements, and the spectroscopic technology they used were: Ancore® (NaI); Applied Research Associates® (NaI); ORTEC (HPGe); Canberra Industries, Inc. (HPGe); Constellation Technology Corporation (high-pressure xenon); Corus (NaI); Northeastern University, Boston (NaI and liquid scintillator); NucSafe (NaI); SAIC/Exploranium (NaI); and Thermo Electron Corporation (NaI). Thus, the majority of the vendors used NaI(Tl) inorganic scintillator as the gamma-ray detector material. These systems were tested in the summer of 2005 at the Nevada Test Site, and the information obtained from those tests contributed to the process of down-selecting vendors in 2006 to manufacture limited-rate initial production (LRIP) systems. Like PVT-based systems, SPM systems are complex instruments requiring the integration of many component subsystems. Because NaI(Tl) gamma-ray detector material is only made by one large producer and a few small producers in the United States, one of the key challenges is to obtain sufficient amounts of the 

Ancore is a registered trademark of Rapiscan® Systems. Applied Research Associates is a registered trademark of Applied Research Associates, Inc.  Information regarding the Nevada Test Site is available at http://www.nv.doe.gov/main.aspx 




material for production of several hundred ASP units. Another major challenge is the development of the analysis and control software for the systems. This software needs to be effective in identifying radiation sources, and in providing this information to the operator in an easily understood interface.

4.5.6 deployment strategy The overall strategy for placement of the initial ASP systems into an operational environment should be consistent with several goals. Spectroscopic portals should be used to maintain, at a minimum, the existing level of interdiction capability while proving the operational suitability, capability, and reliability of the interdiction system. Deployment of ASPs, at least initially, should be done with the aim to gain knowledge of the enhanced capabilities when integrated into the interdiction system. This includes the ability to build conduct of operations and operational confidence centered around the ASPs integrated into the overall operation of ports of entry, which means that a plan for integration of this new technology into the overall border protection strategy would need to be developed. The systems to be initially deployed into the field will be placed at currently protected border crossings and ports in series with existing operational PVTbased detection systems. This will allow verification of ASP performance without affecting the existing screening capability of the port. The systems will be deployed at a cross section of ports-of-entry in order to sample the range of venues. As the reliability and operational readiness of the ASP is proven, and as production quantities become available, the systems will be widely deployed in a variety of venues. It is possible that some venues that have low amounts of NORM in commerce, such as mail facilities and POV lanes, will not require ASP systems. Figure 4.44 indicates a conceptual timeline of how ASP systems could be phased in and could replace many PVT-based RPM systems over a time period of

Dep oyed systems

Total systems

SPMs

PVT RPMs

Time

figure 4.44 Timeline for the introduction of advanced spectroscopic portal systems into the U.S. Customs and Border Protection environment.


237

approximately 5 years. The majority of initial ASP systems deployed may replace existing PVT-based systems, as the high-priority sites are already equipped with such RPM systems. As time passes, and more ASP systems are manufactured, they will replace more of the PVT-based systems. To date (2010), the ASP systems have not been deployed.

4.6 Human Factors in Radiation Portal Monitoring Systems Thomas Sanquist, Pamela Doctor, and Christian Richard Humans ultimately operate and administer the RPM systems, and their effective interaction with the technologies is a critical variable in overall system success. Human performance is influenced by many aspects of security system design, including the equipment with which personnel interface, the training they receive, the procedures used, and the teamwork needed for personnel to work with each other to perform their various roles. These aspects of security system design are addressed by human factors engineering—the systematic application of psychology and physiology to the design of equipment and systems. The objectives of human factors engineering are to ensure that the performance requirements of systems, in terms of staff, individual operators, and user interfaces, accommodate the capabilities and limitations of operations and maintenance personnel. Complex system design efforts involving systems as diverse as nuclear power plants, aircraft, and military command and control often engage human factors experts. The Department of Defense has institutionalized human factors through a Human-System Integration process that is part of the overall engineering development cycle (Booher 2003). A number of human-technology interfaces are part of RPM systems, as illustrated in Figure 4.45. The output of RPM systems is presented to inspection officers at various locations, depending on the transportation vector. For each alarm, the officer evaluates the nature of the signal, and other information, to resolve the alarm. Several important aspects of human factors engineering as they pertain to RPM systems are described in this chapter, including the role of the inspections officer, the variables influencing operator trust in systems, the impact of false or nuisance alarms and the base rate of threat events, and the methods of information display that can enhance situational awareness of true (legitimate) threat alarms.

4.6.1 human role in radiation portal monitor security decision making The most basic signal-processing systems, such as raw radar output, involve the human operator making fine sensory discriminations on system outputs (visual or acoustic displays) to determine the presence or absence of a signal of interest.



Radiation Detection and Interdiction at U.S. Borders Human decision & response

• Is it real? • Can I trust the sensor? • How do I respond? • What else do I need to know?

Threats exist in background of everyday human activity

Vulnerability vectors for potential threat manifestation

Sensors applied at vulnerability vectors to detect or amplify potential threats

Human operators administer and interpret sensor system data, and respond as appropriate

Security systems need to support the decision and response process

figure 4.45 General model of human element in radiation portal monitor security systems.

In these types of systems, the human decides when to issue an alert. A similar example is the use of a stethoscope by a physician—the instrument amplifies the physical signal, and the physician decides whether the resulting sounds represent normal or abnormal physiology. More sophisticated systems involve signal processing to determine the presence or absence of a condition of interest. These systems alert human operators when that condition is encountered. Alarm content may simply reflect a two-state “alarm/no-alarm” condition or may provide additional information in the alarm signal concerning the situation of interest. The human attendant’s job is to react to that information according to various procedures. This type of alerting system invariably involves elements of judgment and choice by the operator (Rankin et al. 1983). These two types of systems, visually represented in Figure 4.46, may be considered as the “amplifier model” and the “evaluator model” and are useful ways of conceptualizing the human decision process for purposes of developing decision aids. Most portal-monitoring systems deployed through the RPMP involve alerting officers by means of a two-state alarm when the radiation level at a sensor panel exceeds a threshold. The required response to alarms involves confirmation screening, more detailed isotope identification and, where applicable, examination of the manifest and inspection of the cargo contents. Once the source of the radiation alarm is resolved, the suspect vehicle or package is released. This process is best represented with the evaluator model. Because the principal job of the inspection officer is to evaluate RPM system output and render a case disposition, psychological processes involving system trust are at work. These, in turn, are influenced by the false or nuisance alarm rate of the system, and the base rate of threat events.


239

Physical signal Physical signal

Amplification & processing Amplification Decision criteria

Condition present or manual

Condition absent: no alarm

Condition present: alarm Evaluate

Final disposition

A Amplifier model

B Evaluator model

figure 4.46 Two general classes of human-mediated inspection systems. (A) The amplifier model involves the human deciding whether the target condition is present or absent. (B) The evaluator model involves a person assessing the system output.

In the following sections, the pertinent human factors findings and implications in these areas are discussed.

4.6.2 system trust Currently, RPM systems are based on technology elements used by inspection officers to directly detect threats or to obtain information that forms a basis for making judgments about the potential presence of threats. Through training, experience with the technology, and other means, officers will develop a sense of trust in the technology they use, and this trust impacts the degree to which they will be willing to rely on the information obtained from the system as a basis for making decisions. Lee and See (2004) define trust as “the attitude that an agent [technology] will help achieve an individual’s goals in a situation characterized by uncertainty and vulnerability.” In an applied context, trust is the attitude that a technology will provide some functional benefit (e.g., detecting a threat) even though there is potential uncertainty that the technology will function as expected and that relying on technology potentially leaves the user in a vulnerable situation (Johns 1996). Consequently, individuals will rely on automation they trust and likely reject automation that they do not trust.




Simply having trust in a technology is not the critical aspect of trust in automation. Rather, what is critical is that the level of trust is justified (i.e., valid) based on the actual capabilities and reliability of the technology (Lee and Moray 1994; Muir 1987). In other words, an individual’s level of trust in a system should be calibrated to match the degree to which it is safe to rely on that system to adequately perform as it should. For RPMs, a key issue in relation to the level of officer trust is the high rate of nuisance alarms; this is especially true for other systems like RPMs that are specifically designed to minimize the chance of missing a target event (Parasuraman and Riley 1997). For example, in early warning systems in aviation, excessive false alarm rates resulted in mistrust and lack of pilot usage, or pilots that found creative ways to disable alarm systems (Satchell 1993; Wiener 1988). Similar evidence is found in process control industries, where alarms from untrustworthy systems are more likely to be acknowledged (and turned off ) before their location and nature are determined (Hale and Glendon 1987; Zwaga and Veldkamp 1984). Thus, highly sensitive systems with excessive false or nuisance alarm rates eventually lead to a reduction of operator trust, and the development of various means to ignore, override, or disable alarms.

4.6.3 false and nuisance alarms The effectiveness of a warning or alerting system depends in large part on its credibility. The more credible an alarm, the more likely an operator is to take the potential threat seriously and to take action in response to the alarm. Unfortunately, the credibility of alarms can be significantly eroded by the excessive occurrence of false or nuisance alarms. This can result in an individual being less likely to respond with the same “intensity of conviction” to future alarms because of the potential that they may again represent a false alarm (Breznitz 1984). This attenuation in response or loss of credibility in a warning because of false alarms is called the “false alarm effect” (Breznitz 1984). High rates of nuisance alarms typically occur because detection sensitivity is set with a low threshold. This is a safe strategy when the costs of missing a signal or threat are very high, yet as mentioned above, the performance of operators in responding to the alarm may be less than optimal because they will likely suspect that it is just another false alarm (Breznitz 1984). It is also relatively safe when traffic volumes are very low. Even if operators are required to respond because of operating procedures, there is likely to be some incentive to “cut corners” in the investigation, especially if the search comes at a cost in terms of time and efficiency (Dzindolet et al. 2002). Thus, the strategy of trying to be sensitive to the presence of all potential threats is actually undermined somewhat by how the detection parameters influence the corresponding behaviors of individuals that respond to the alarms.


241

On the surface, one strategy for reducing false alarms may be to reduce the sensitivity of the system so that fewer false alarms are triggered, which means that operators will be responding to real threats more frequently and may do a better job at remaining vigilant in their responses. However, some research suggests that under low base rate conditions, lowering the system sensitivity, and thus the false alarm rate, may not result in any real improvement (Parasuraman et al. 1997). The problem is that with very low event base rates, the probability of a true alarm (known as the posterior probability) is still so low as to be effectively the same as with higher false alarm rates. Thus, not only is the system’s ability to capture potential threats diminished by reducing sensor sensitivity, but this cost is unlikely to lead to more vigilant behavior by security officers or a reduction in the false alarm effect. A critical aspect of designing effective detection and warning systems involving human operators is the availability of a base rate of target events of interest; in fact, this element underlies the entire philosophy of a routine inspection process designed to detect target events (Parasuraman et al. 1997). The base rate significantly affects the utility of any detection system. It has been found that extremely low base rates and high-consequence signals are associated with generalized operator mistrust of detection systems, leading to creative disabling or ignoring of alarms. Developing a hypothetical base rate for illicit nuclear smuggling in the United States can be done with data from sources such as the IAEA, which suggests approximately 450 nuclear smuggling incidents in Europe during the past 10 years (Orlov 2004). If we confine the analysis to cargo trucks entering the United States from Mexico or Canada, data from the U.S. Bureau of Transportation Statistics indicate that approximately 11 million transits occur on an annual basis. Thus, the base rate of occurrence would be Number of annual smuggling incidents/number of opportunities = 45/11⋅10 = 4.1⋅10– The probability of a true threat RPM alert with this base rate of occurrence is very nearly zero (obtained by applying Bayes Theorem): P ( threat alarm) =

P ( hit )

P ( hit ) + P ( nuisance alarm) ⎡⎣( −bbbase rate ) / bas a e rate ⎤⎦

= 3.9⋅10–

(4.22)

This quantity is otherwise known as the positive predictive value of the detection system, which is virtually nonexistent for the RPM as a threat detector. Instead, the RPM simply serves to alert the operators to the presence of some radioactive material and provides no additional information concerning the likelihood of a threat. Because the rate of alarms is generally considered between 0.5% and 1% of




vehicles, this base rate of occurrence would yield a true threat alarm on the order of every 2 to 4 years. However, because the actual base rate of occurrence of threats is probably substantially lower (because of a much larger denominator of transportation opportunities and a much smaller numerator of smuggling incidents), it is reasonable to question whether any true-threat alarms would be expected to occur over the life cycle of the system. At the present time, virtually all alarms from RPMs are a result of NORM or medical isotopes and are thus “nuisance” alarms. This situation is fraught with problems from a psychological standpoint (Sorkin 1988), because inspection officers are expected to carry out the same procedures regardless of their knowledge of the probable source and the frequency with which they see certain types of vehicles causing alarms. One method for improving the overall performance of a detection system with a low event base rate is to reduce false or nuisance alarms through a classification or response mapping procedure (Parasuraman et al. 1997) that assigns a likelihood value to specific instances of detected signals. Early experiments with this type of display (Sorkin et al. 1988) suggest that operator workload is reduced with signal classification. As described below, incorporating situational awareness information with energy spectrum and cargo data make it feasible to address alarm classification.

4.6.4 situational awareness The concept of situational awareness, which has migrated to human factors psychology from the military, is defined as “the perception of the elements in the environment within a volume of time and space, the comprehension of their meaning and the projection of their status in the near future” (Endsley 1997). Situational awareness is clearly an integrating concept that assembles basic elements of perception, interpretation, judgment, and forecasting. The definition is a reasonable description of the rapid cognitive activities performed, for example, by an inspection officer during a routine border crossing interview. They perceive the vehicle, its occupants, and their manner of interaction within the overall context of national security levels, prior history of smuggling or illegal entry at that particular location, along with any other intelligence information they may have available. A judgment is made regarding the relative safety or honesty of the vehicle occupants, and a course of action is determined. All of this happens within a span of 30 seconds or less in most instances. This type of cognition is often described as “pattern matching” since it appears that decision makers often rapidly assess critical cues and compare them to mental models. In the context of RPMs, situational awareness provides the inspection officer with the ability to interpret conflicting information and reach a conclusion.

The number of true threat alarms annually = (alarm rate × number of vehicles)(p(threat|alarm) < 0.5.




243

For example, should an isotope identification system suggest the presence of RDD material, but experience and all other data suggest that the source is a medical isotope, a decision would be made to resolve the alarm as a medical isotope. Because the isotope identification technology does make misclassifications, and inspection officers are aware of this, the flexibility of their decision process allows them to interpret the situation and respond accordingly.

4.6.5 applications to radiation portal monitor systems: the likelihood display concept The implications of the concepts described above for RPM system alarms and displays are best illustrated by example. Figure 4.47 shows the basic components of the most widely implemented RPM system design with the two-state threshold processor as the basis for alarms. In this design, the alarm status is all or none, and no distinction is made for NORM. Thus, secondary scanning is required, along with a prescribed isotopic identification and inspection protocol. Successful completion of these steps resolves the alarm. and the vehicle or package can be discharged. The secondary screening and inspection process can be relatively time consuming with cargo vehicles and can be especially problematic when traffic is heavy. The activity then becomes manpower limited. Because virtually all alarms are successfully resolved, a substantial human factors concern is the added workload to process alarms that have no security significance. An alternative approach to alarm display is shown in Figure 4.48. In this design, the primary signal from the RPM is processed with statistical templates

Primary signal

Threshold processor

Alarm status all-or-none

Inspect Secondary scan

Confirm

Resolve & discharge

figure 4.47 Two-state radiation portal monitor alarm system involves four postalarm steps.




Primary signal

Statistical processor: templates, spectra

Visual & meta-data

Alarm status calibrated to potential threat Resolve & discharge

Situational awareness

figure 4.48 Likelihood alarm radiation portal monitor system provides more information to officers through green, yellow, and red indications.

and/or energy spectra, and it is integrated with metadata concerning observed vehicle type and frequency and other salient information. This leads to a multistate output, color coded as green, yellow, and red to correspond to “no signal of concern,” “probable NORM—inspection optional,” and “unidentified signal—perform secondary inspection.” In this model, we have linked the alarm display to increasing levels of intervention. An unidentified signal that yields a red alarm requires additional inspection for resolution; a yellow alarm results from a signal that is highly probable NORM, so in this case inspection is left to the discretion of the inspection official. Addition of the intermediate alerting state of “probable NORM” significantly reduces the requirement for additional screening, while allowing the human operators to develop more complex and robust mental models of RPM system performance. The existence of the intermediate alarm state will lend credibility to the much lower frequency “unidentified signal” alarms. This basic approach has been termed a “likelihood display” as it presents alarm data in a probabilistic way. The need for classifying legitimate sources that generate RPM alarms is recognized as an important element by Kouzes et al. (2006), who stated: …it is necessary to anticipate and recognize the types of cargo that contain naturally occurring radioactive materials so that such “nuisance” alarms can be quickly dealt with. Clearly, any reduction in the time spent by [inspection] officers to determine that an alarm is not of concern will help in their search for actual illicit materials.

4.6.6 distinguishing between illicit material and naturally occurring radioactive material: human factors applications The physical signals underlying radiation detection in RPMs contain information that is potentially useful in developing a graded or likelihood display approach.


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The bulk of nuisance alarms are based on gamma-ray generated counts from PVTbased RPMs. Initially, alarms were based on gross-count thresholds established to determine the likely deviation of a particular signal over background radiation. However, this approach did not take into account any energy information available from the plastic scintillator (Ely et al. 2006). Application of energy windowing algorithms in PVT RPMs (see Section 4.2) to data collected in the field leads, in principle, to considerably reduced NORM alarms. This is shown in data from Weier et al. (2005), in which gross-count criteria resulted in 1731 alarms for NORM cargo, whereas energy window criteria resulted in 227 alarms—a reduction of 87%. The number of medical alarms was basically unaffected because their signatures are essentially indistinguishable from targeted materials when detected with PVT-based RPMs. While the energy windowing approach has been demonstrated in principle and has been activated in the field, practical issues related to implementation remain. The most significant of these is the need to retain a relatively low gross-count threshold in order to ensure that other threats not distinguished with energy windowing are detected. In practice, this leads to the same problem of inflated numbers of nuisance alarms. However, it is feasible to use energy windowing criteria in conjunction with metadata, such as cargo information, vehicle frequency, and other situational awareness factors to classify alarms as “highly likely NORM” or some similar designation to indicate the alarm does not imply a threat condition. Thus, with appropriate signal information mapped to alarm displays, RPM systems can be made to alert regarding the presence of a signal, inform the inspection officers regarding the likely content of the signal, and, thus, guide the intervention process. Depending on the complexity of the physical signal classification and metadata available, a considerable amount of information can be provided to the inspection officer to permit better judgment and choice regarding necessary intervention procedures. Existing data suggest that NORM can be classified with reasonable accuracy, while medical isotopes (which represent a surrogate for a radiation threat) are classified differentially based on energy spectrum ratios. Energy windowing and other statistical or logical classification rules based on various RPM signal data and metadata—such as rapidly obtained manifest information—could provide a much-needed enhancement to the current implementation of RPM systems in the field. At a minimum, the use of ratio data in the low-energy spectrum might form the basis for decision rules that can assign a probability (likelihood) that any specific RPM alarm signal is more like background (likely NORM), or more like SNM (likely threat). Coded logic for threat likelihood classification might take the following form: IF RPM gross counts > X, AND energy windowing ratio < 0.05 AND commodity = kitty litter THEN threat level = PROBABLE NORM, ELSE CHECK NEXT COMMODITY

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In order for this type of classification system to be developed for practical use in operational settings, a number of requirements must be met. The most important of these is the ability to rapidly capture and integrate metadata concerning the specific vehicle or cargo container being screened.

4.6.7 human factors impact The human factors discipline is concerned with enhancing the effectiveness of human–machine systems. With respect to the use of detection and warning systems, RPMs show a number of similarities to other technical domains. A substantial volume of literature suggests that detection systems for low-probability/high-consequence events can lead to system mistrust and lower alarm effectiveness if not properly designed. Bayesian analysis of alarm probabilities in RPM systems suggests that a true threat alarm may not occur during the life cycle of the system, because of the extremely low base rate of nuclear smuggling events and the large number of vehicles screened. To reduce the system mistrust that these circumstances are likely to engender, despite rigid response protocols, a likelihood display approach can provide additional RPM signal information to help classify alarm events. This method will enhance confidence that the system is actually working, while reducing the problems associated with high rates of nuisance alarms. Methods based on energy windowing represent one basis for this approach in PVT RPMs, which can be extended to advanced spectroscopic portals as they become available. To support the development of effective likelihood displays, collaborative research, development, and evaluation between human factors, statistics, and radiation physics specialists is required. The most likely near-term application of likelihood displays for RPMs is in cargo screening—an area where it is possible to obtain advance information concerning container contents, and where specific isotope signatures can be developed. Application of human factors principles to RPM design is an important area for continued focus, as system effectiveness is a function of both technical and human performance.

4.7 References ANSI. . American National Standard Performance Criteria for Spectroscopy-Based Portal Monitors Used for Homeland Security. ANSI Standard N ., American National Standards Institute, Washington, DC. Bevington PR. . Data reduction and error analysis for the physical sciences. McGraw Hill, New York. Booher HR. . Handbook of human systems integration. Wiley, Hoboken, NJ. Breznitz S. . Cry wolf: The psychology of false alarms. Erlbaum, Hillsdale, NJ. Briesmeister JF. . MCNP™: A General Monte Carlo N-Particle Transport Code, Version . LA--M, Los Alamos National Laboratory, Los Alamos, NM.


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Chambers WH, HF Atwater, PE Fehlau, RD Hastings, CN Henry, WE Kunz, TE Sampson, TH Whittlesey, and GM Worth. . Portal Monitor for Diversion Safeguards. LA-, Los Alamos Scientific Laboratory, Los Alamos, NM. Dzindolet MT, LG Pierce, HP Beck, and LA Dawe. . The perceived utility of human and automated aids in a visual detection task. Human Factors ():–. Ely JH, RT Kouzes, BD Geelhood, JE Schweppe, and RA Warner. . Discrimination of naturally occurring radioactive material in plastic scintillator material, IEEE Transactions on Nuclear Science ():–. Ely J, RT Kouzes, JE Schweppe, ER Siciliano, DM Strachan, and DR Weier. . The use of energy windowing to discriminate SNM from NORM in radiation portal monitors. Nuclear Instruments and Methods in Physics Research A ():–. Ely JH, ER Siciliano, and RT Kouzes. . Comparison of NaI(Tl) scintillators and high purity germanium for vehicle portal monitor applications, IEEE Nuclear Science Symposium Conference Record, Vol. , –, pp. –. Endsley MR. . The role of situational awareness in naturalistic decision making. In CE Zsambok and G Klein (eds.), Naturalistic Decision Making, –. Mahwah, NJ: Lawrence Earlbaum Associates. Fehlau PE, C Garcia, RA Payne, and ER Shunk. . Vehicle monitors for domestic perimeter safeguards. LA--MS, Los Alamos National Laboratory, Los Alamos, NM. Geelhood BD, JH Ely, R Hansen, RT Kouzes, JE Schweppe, and RA Warner. . Overview of portal monitoring at border crossings. In Nuclear Science Symposium Conference Record, Portland, OR, IEEE Transactions on Nuclear Science Volume , pp. –. Hale AR and AI Glendon. . Individual behaviour in the face of danger. Elsevier, Amsterdam, Netherlands. Iwatschenko-Borho M. . Schnellerkennung von Gammakontaminationen. International Magazine for Nuclear Energy :–. Iwatschenko-Borho M, L Dederichs, F Nürbechen, W Schiefer, and W Rieck. . Schnellerkennung von Künstlichen Gammastrahlern mit dem Nbr-Verfahren. Fachgespräch zur Überwachung der Umweltradioaktivität :–. Johns JL. . A concept analysis of trust. Journal of Advanced Nursing :–. Kouzes R, J Ely, J Evans, W Hensley, E Lepel, J McDonald, J Schweppe, E Siciliano, D Strom, and M Woodring. . Naturally occurring radioactive materials. Cargo at U.S. Borders, Packaging, Transport, Storage & Security of Radioactive Material ():–. Kouzes RT and ER Siciliano. . The response of radiation portal monitors to medical radionuclides in border applications. Radiation Measurements ():–. Lee JD and N Moray. . Trust, self-confidence, and operators’ adaptation to automation. International Journal of Human-Computer Studies ():–. Lee JD and KA See. . Trust in automation: Designing for appropriate reliance. Human Factors ():–. Lopresti CA, DR Weier, RT Kouzes, and JE Schweppe. . Baseline suppression of portal monitor vehicle gamma count profiles: A characterization study. Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment ():–. McCormick KR, DC Stromswold, J Ely, JE Schweppe, and RT Kouzes. . Spectroscopic Portal Monitor Prototype. PNNL-SA-, Pacific Northwest National Laboratory, Richland, WA.

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Muir BM. . Trust between humans and machines, and the design of decision aides. International Journal of Man-Machine Studies :–. Orlov VA. . Illicit nuclear trafficking and the new agenda. IAEA Bulletin ():–. Parasuraman R, PA Hancock, and O Olofinboba. . Alarm effectiveness in drivercentered collision-warning systems. Ergonomics ():–. Parasuraman R and V Riley. . Humans and automation: Use, misuse, disuse, abuse. Human Factors ():–. Perez-Andujar A and L Pibida. . Performance of CdTe, HPGe and NaI(Tl) detectors for radioactivity measurements. Applied Radiation and Isotopes ():–. Rankin WR, EG Duvernoy, KR Ames, MH Morgenstern, and RJ Eckinrode. . NearTerm Improvements for Nuclear Power Plant Control Room Annunciator Systems. NUREG-CR-, Nuclear Regulatory Commission, Washington, DC. Rieck W and M Iwatschenko. . Intelligent software solution for reliable high efficiency/ low false alarm border monitoring. In Measures to prevent, intercept and respond to illicit uses of nuclear material and radioactive sources, SNP Inspectorate (ed.), Vol. CSP--P, pp. –. International Atomic Energy Agency, Stockholm, Sweden. Satchell P. . Cockpit monitoring and alerting systems. Ashgate, Aldershot, England. Siciliano ER, JH Ely, RT Kouzes, BD Milbrath, JE Schweppe, and DC Stromswold. . Comparison of PVT and NaI(Tl) scintillators for vehicle portal monitor applications. Nuclear Instruments & Methods in Physics Research Section A - Accelerators Spectrometers Detectors and Associated Equipment ():–. Sorkin RD. . Why are people turning off our alarms? Journal of the Acoustical Society of America :–. Sorkin RD, BH Kantowitz, and SC Kantowitz. . Likelihood alarm displays. Human Factors :–. Stromswold DC, BD Milbrath, DL Stephens, LC Todd, RR Hansen, and RT Kouzes. . Field test of a NaI(Tl)-based vehicle portal monitor at a border crossing. Nuclear Science Symposium Conference Record, IEEE Vol. , –, pp. –. Stromswold DC, ER Siciliano, JE Schweppe, JH Ely, BD Milbrath, RT Kouzes, and BD Geelhood. . Comparison of plastic and NaI(Tl) scintillators for vehicle portal monitor applications. Nuclear Science Symposium Conference Record,  IEEE, Vol , pp. –. Sudarshan M, J Joseph, and R Singh. . Full energy peak efficiency of NaI(Tl) gamma detectors and its analytical and semi-empirical representations. Journal of Physics D: Applied Physics ():–. Trost N and M Iwatschenko. . Method and Device for Detecting Man-Made Radiation. ESM Eberline Instruments Strahlen- und Umwelmesstechnik GmbH: Patent Germany DE    C. Weier D, R Kouzes, J Ely, M Woodring, D Bates, and C LoPresti. . Performance of Energy Window Ratio Criteria at Radiation Portal Monitoring Sites. PNNL-SA-, Pacific Northwest National Laboratory, Richland, WA (Abstract). Wiener EL. . Human Factors in Aviation. Academic, San Diego, CA. Zwaga HJG and M Veldkamp. . Evaluation of integrated control and supervision in the process industries. Industrial and Chemical Engineering Symposium Series :–.

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Radiation Portal Monitor Project Deployment Summary Megan Lerchen

5.1 Introduction The RPMP was initiated to provide CBP with technical advice on the interdiction of radiological and nuclear materials, and it grew into a deployment project to specify, procure, and install equipment to interdict illicit radioactive materials at U.S. POEs. The project therefore hinged upon the fundamental technologies and tools capable of detecting radioactive materials (Kouzes 2004; 2005). As described in Chapter 3, the PVT-based RPM is the “workhorse” for most installations. A typical RPM system includes two or more RSPs, a control box, occupancy sensors, shielding/support stands, annunciator assemblies for each portal or lane, capability for a VIS, and analysis/control software components, as shown in Figure 3.13 from Chapter 3. This detection technology was deployed in a variety of configurations depending on the vector- and site-specific needs. The term “vector” refers to the type of port of entry, and they are international mail and express consignment courier facilities, land border crossings, seaports, international airports, and rail border crossings. In most deployments, each lane, gate, or other exit is monitored with at least one pair of RSPs. The exact system configuration for each deployment varies according to the infrastructure and daily operations at each deployment site. A concept of one possible configuration with RSPs located on both sides of multiple vehicle lanes is shown in Figure 3.12. The standard RPM system is typically augmented with a variety of ancillary equipment to meet individual site needs. Factors such as network and voice communication, traffic control, unacceptable impacts to staff presence, and other aspects in minimizing impacts to legitimate trade and travel are considered when establishing a need for additional equipment beyond the base RPM system.

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Examples of ancillary equipment include visual identification systems, surveillance, intercom, wireless, optical character recognition, rail identification, and traffic control systems. A synopsis of ancillary equipment used in RPMP deployments is presented in Table 5.1; more detailed information about this equipment is provided in Chapter 3.

table 5.1 Ancillary equipment available for deployment with radiation portal monitor systems Ancillary Equipment

Description

Area surveillance system Auto dialer

A remote free-running-type camera system with logging, alarm, and viewing capabilities Based on a system signal or alert, an auto dialer will transmit a number of prerecorded messages to preprogrammed telephone numbers for standard telephones, cellular phones, and voice and/or numeric pagers. Booths are provided where RPM systems have been installed in locations where there is no available structure for placing equipment (supervisory computer, annunciators, etc.) and CBP staff who will operate the system. Gate arms are available for additional traffic control in deployments that may be at some distance from a booth. The human machine interface is a touch screen control device for operating RPM systems over the local Ethernet network. Inductive-loop presence sensors detect the presence of a vehicle by inducing a current in the loop as vehicles transit the loop. These are used when optical break-beam presence sensors cannot be used. An intercom system provides communication between a CBP officer in the booth and a driver in the lane. There are two types of intercom systems: wired and network-based (required for wireless communications). Data communication within the RPM system and its ancillary equipment is by a local area network. Ethernet computer system network components are required for network communication on the RPM subsystem and the CBP wide area network. Network components may include such components as cabling, wireless bridges, antennas, managed switches, and data converters. Optical character recognition and reconciliation software convert optical images of identification numbers on intermodal containers into digital values suitable for computerized processing and tracking of containers. The container identification numbers are electronically reconciled with the shipping consist. Optical presence sensors detect the presence of a vehicle (road vehicles, train cars, etc.) that enters the field of view of the RPM with optical break-beam technology. Presence sensors generate signals that indicate when the vehicle enters or exits the RPM and provide a means to calculate vehicle speed. PRIDE will transfer specific data from the RPM system (RPM profile data, radiation spectral data, visual images, and other related information) at a particular POE site to a centralized data warehouse managed by CBP’s Enterprise Data Warehouse organization. PRIDE is under development. At the port, PRIDE will provide a tool to match vehicles from primary scanning to those in secondary scanning. Programmable logic controllers are hard-programmed devices used to ensure synchronized, consistent actions by the RPM system. The strobe/siren alarms with a single-tone siren with a warble sound output and a red strobe light. Traffic lights are used to provide traffic control information to drivers automatically or at CBP discretion. Records images of vehicles that pass through an RPM.

Booth

Gate arms Human machine interface Inductive-loop presence sensors Intercom

Network system

OCR/reconciliation software

Optical presence sensors

PRIDE

PLCs Strobe/siren Traffic lights VIS

Radiation Portal Monitor Project Deployment Summary

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5.2 Deployment Approach RPMs are deployed in conjunction with additional tools for radiation detection, such as PRDs and RIIDs. Furthermore, detection at U.S. ports of entry is part of a Department of Homeland Security multilayered approach for radioactive materials interdiction. Customs and Border Protection staff identified the ports of entry slated for RPM deployment and the priority scheme for these deployments. The deployment schedule was broken down into phases based on the vector locations (international mail and express consignment courier facilities, land border crossings, seaports, international airports, and rail border crossings). Within each phase, the deployment order was further prioritized on a port of entry basis.

5.3 Deployment Process Flow At each POE, deployments move through a standardized series of process steps from initiation through commissioning and postdeployment support. The work scope of a deployment generally consists of site surveys, design, procurement, subcontracting, construction, training, and other associated activities. Site surveys are needed to collect information from the site, identify specific local requirements, and provide an opportunity to establish initial deployment concepts. Infrastructure and RPM system designs, conceptual through final stages, need to be developed for each site. This includes holding meetings and providing needed information so all local stakeholders may review final design concepts and achieve consensus on the recommended approach. Systems and other required material and equipment need to be purchased, and subcontracts for site construction and installation need to be put in place. Then, the site and facilities to accommodate RPM system installation and operations need to be constructed and installed, including the infrastructure for communications within the site and to national centers. Since each facility is unique in many aspects, CBP officers and management need to be trained as part of the commissioning activities, during which time adjustments to operations and facilities are made and final acceptance testing and transfer the systems to CBP for sustained operation are performed. Lastly, technical and operational support to CBP is provided, as requested. The site survey is critical to the success of all subsequent steps in the process. The RPM system designs must be tailored to meet individual port infrastructure and operational requirements to effectively monitor all traffic and cargo without impeding commerce. Construction and installation activities are generally performed by local subcontractors but are managed by RPMP staff. The RPM systems are turned over (or commissioned) to the local port for operations only after CBP supervisory officers have been trained and the RPM system has been accepted, calibrated, and commissioned. In addition, a national data collection

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and integration system is under development to collect and integrate all RPM system data. The following sections present deployment strategies for each of the RPMP vectors.

5.4 Northern and Southern Land Borders The RPMP provides RPMs for radiation scanning of cargo, privately owned vehicles, and rail traffic. Each land crossing also has an RPM available for secondary scanning of vehicles that caused alarms during primary scanning. This secondary RPM may be an additional portal at most crossings, or a primary RPM through which vehicles pass a second time. This section describes the scanning for cargo and privately owned vehicles; rail crossings are sufficiently different to merit independent treatment and are described later in this section. Land crossing RPM systems for privately owned vehicles and cargo are based on a lane-by-lane RPM concept with limited exceptions. The privately owned vehicle deployments utilize standard RPM systems and typically operate with low alarm rates because there is generally no significant volume of NORM in privately owned vehicle traffic. The use of shielding walls may be necessary at some sites to prevent cross talk alarms from traffic in cargo lanes or pedestrians containing medical radionuclides (see Section 4.3). Bus lane deployments utilize standard cargo-type RPM systems. Cargo lane deployments utilize standard four-panel RPM systems as well as eight-panel wide lane systems, and a few cantilever designs where panels cannot be deployed on both sides of a road. Some cargo deployments utilize visual identification systems.

5.4.1 primary scanning The size and complexity of land border crossings vary considerably depending on the crossing configuration and traffic volume served. The RPM system complexity tends to increase with a greater number of lanes and traffic volumes. Primary radiation scanning at land crossings is with RPMs configured for the traffic and plausible threat in a particular lane (generally grouped into privately owned vehicle and commercial lanes). The privately owned vehicle lanes primarily handle cars, vans, pickup trucks, and sometimes recreational vehicles. Commercial lanes handle truck and cargo traffic but are also capable of handling other types of commercial road vehicles such as cars, light trucks, and buses. At some crossings, dual-use lanes are installed to handle both privately owned vehicle and commercial traffic. RPM designs are based on a lane-by-lane concept where RSPs are positioned on both sides of the lane. The privately owned vehicle RPMs typically have two RSPs deployed on opposite sides of the lane, while commercial traffic portals


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typically use four RSPs, with two vertically stacked panels on opposite sides of the commercial lane. Specific port conditions and operations ultimately determine the need for minor departures from these two main RPM geometries. For example, at ports with a commercial wide-cargo lane, the number of panels is doubled (four RSPs on each side of the lane) to ensure that sensitivity requirements are met despite the greater distance between RSPs. Land crossing RPM systems include infrastructure such as foundations, conduit, and cabling. In general, limited ancillary equipment is needed at land crossings for RPM system deployment as there is generally adequate infrastructure such as buildings, space, land, and devanning facilities. At some crossings, a visual identification system may also be deployed at CBP discretion. In addition to RPM systems, land crossings also have a considerable number of existing or planned technologies/programs to either improve the capabilities of CBP or to facilitate movement of traffic, such as license plate readers and the Free and Secure Trade program. Minimal, if any, interface is required with these technologies, although interference with their infrastructure and operation must be avoided. The following portal configurations represent the range of primary scanning options for land border crossings.

5.4.1.1 Privately Owned Vehicle Lanes Privately owned vehicle lanes have two panels per system, one on each side of the lane for standard spacing, as shown in Figure 5.1. Where a standard two-panel deployment is not feasible, an L-shaped cantilever configuration (with RPMs on one side and above the lane) is acceptable as long as efficiency requirements are met. A one-sided deployment is unacceptable. RPMs installed above the lane without an accompanying side panel are also unacceptable. Vehicles, such as a recreational vehicle, may pass through a privately owned vehicle deployment, but cargo trucks or car carriers must use dual-use or truck-configured lanes.

5.4.1.2 Commercial Lanes Commercial, or cargo, lanes typically have four panels per system, two on each side of the lane, placed vertically end-to-end for standard horizontal spacing, as shown in Figure 5.2.

5.4.1.3 Wide-Load Lanes Some commercial lanes must accommodate commercial wide-load traffic or a wider turning radius. The width of these lanes forces the RSP-to-RSP distance to exceed the maximum distance allowed to meet sensitivity requirements in a standard commercial lane RPM configuration. To mitigate this potential lack of operational sensitivity, the number of RSPs on each side of the lane is doubled so that for wide-lane installations, there are four panels for cars and eight panels for trucks, as shown in Figure 5.3.

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figure 5.1 Radiation portal monitors in privately owned vehicle lanes.

figure 5.2 Standard four-panel cargo radiation portal monitors.


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To further mitigate the loss of sensitivity, all vehicles that pass through wide RPMs proceed at a reduced speed, thereby increasing the detection time.

5.4.1.4 Dual-Use Radiation Portal Monitors Dual-use RPMs are used at lanes that have both commercial and privately owned vehicle traffic; the configuration is optimized for trucks. Like cargo RPMs, dualuse portals have four RSPs with two panels on each side of a monitored lane placed vertically end-to-end for standard horizontal spacing, as shown in Figure 5.4.

figure 5.3 Eight-panel wide-cargo radiation portal monitor at secondary.

figure 5.4 Dual-use radiation portal monitor.

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5.4.1.5 Dedicated Bus/Recreational Vehicle Lanes Like commercial cargo RPMs, dedicated bus/recreational vehicle RPMs have four RSPs deployed on both sides of a monitored lane, with two panels on each side of the lane placed vertically end-to-end, for standard horizontal spacing. Such lanes exist at ports where traffic volume requires it.

5.4.1.6 Cantilever Radiation Portal Monitors In a limited number of cases, port configurations and operations do not allow placement of RSPs on each side of the lane. In these instances, a cantilever RPM can be used, as shown in Figure 5.5. The RSP geometry is determined on a case-bycase basis for cantilever RPMs.

5.4.2 secondary scanning Each land crossing also has an RPM available for secondary scanning of vehicles that caused an alarm in primary scanning. This secondary RPM may be used as an additional RPM(s) at busier crossings. Vehicles may be redirected through a primary RPM a second time at low-volume sites. Crossings that accommodate privately owned vehicles only (no commercial truck traffic) use a two-panel secondary RPM; otherwise, a commercial RPM configuration is required for secondary scanning, as shown in Figure 5.6. When a vehicle passes through an RPM and sets off an alarm, the driver is directed to the secondary RPM for additional scanning. If the secondary scanning confirms the initial alarm, a further examination of the vehicle and cargo is

figure 5.5 Cantilever cargo portal.


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figure 5.6 Secondary and bus portal.

performed. Based on the secondary scanning, the alarm is either cleared or the vehicle is held for further examination and disposition. Most alarms are due to NORM and medical radioisotopes and are thus cleared relatively quickly through secondary scanning.

5.4.3 ancillary equipment Peripheral devices that may be needed for operations include auto dialers (equipment that automatically dials a telephone list, for when CBP is not present), flashing light alarm indicators, traffic control lights, portable detectors, and programmable logic controllers. The site configuration and needs of the local CBP operations determine which of these devices are deployed. Inductive-loop sensors are used only in a limited number of instances for land border crossings, generally in locations where the use of optical presence sensors is precluded for some reason. Land border crossings generally use optical break–beam presence sensors to trigger operation of the RPM system and some ancillary equipment, such as VIS cameras. Also at land border crossings, RPM systems use various programmable logic controllers to ensure consistent, logical operation. Typically, these are used to direct events for other ancillary equipment, such as VIS, based on signals from other system components, such as the presence sensor or RPM alarms. In limited cases, traffic lights are used as necessary for traffic control. Visual identification systems have been deployed to a limited number of locations to electronically provide vehicle identification. One version of VIS provides an image of vehicles passing through choke point RPMs that are out of the line-of-sight of CBP officers. More detailed information on each of these devices is provided in Chapter 3.

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In addition, the RPM systems deployed for land border crossings may be integrated into the system for national data collection and integration; more information about this system is provided in Chapter 6.

5.5 Seaports Seaports are comprised of individual, privately owned and operated terminals. Figure 5.7 shows one example of a seaport terminal. Nearly 95% of all foreign trade comes into the United States through seaports. Over 17 million cargo containers entered U.S. seaports in 2005 alone. The largest U.S. seaports each process over three million containers annually Imported goods entering through seaports are categorized as containerized cargo, bulk cargo (e.g., cement, coal), and break-bulk cargo (e.g., forest products, steel, and other loose cargo not containerized or shipped as bulk). Containerized cargo is shipped in a number of standard intermodal container configurations; bulk and break-bulk cargos are far more variable in configuration. Cargo received at seaports has considerable variability and includes significant amounts of NORM materials including tiles, granite, and other stone; ore; and consumer products like televisions. The bulk of imported goods exit seaports via truck and rail; a small fraction of the cargo is transshipped (off-loaded to another ship or barge) at a limited number of ports.

figure 5.7 Ship at dock at a seaport terminal.


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Radiation portal monitors are used at terminal exit gates and rail access gates for trucks or straddle carriers. Mobile RPMs and fixed dockside RPMs can be used for targeted cargo and transshipped cargo. Generally, there is limited room for secondary processing, and devanning space is limited. Seaport deployments utilize the widest range of ancillary equipment. Besides standard RPMs, some seaports have implemented RO-RPMs that include VIS, area surveillance, wireless communications, and intercom systems and may include optical character recognition, and manifest reconciliation systems. Mobile RPM systems are also largely deployed for use at seaports.

5.5.1 primary scanning The approach to radiation scanning at seaports is based on a “final exit gate” strategy with cargo RPMs deployed on a lane-by-lane basis, as seen in Figure 5.8. Also, mobile RPM systems are used for targeted cargo inspections at seaports. Primary and secondary RPMs are typically deployed in a manner to maintain the flow of commerce and provide a capability to detect and confirm the presence of radioactive materials. One or more primary RPMs are deployed at strategic locations on a terminal or port to provide a rapid pass/fail screen of cargo. A secondary RPM is typically deployed downstream from the primary RPMs to confirm alarms and to provide additional scanning capability. The secondary RPM is typically placed off the main traffic flow and is positioned in a protected area for conducting additional scanning of the alarm-producing truck. An extensive survey of the seaport environment is conducted prior to each RPM deployment. Based on data from terminal operators, local CBP, PNNL, and the port authority (as required), locations at seaport terminals, such as exit gates, seal check booths, natural choke points along the exit process, trailer interchange record gates, and access areas to on-dock rail yards, are considered as viable primary RPM deployment sites. Radiation portal monitors are deployed in standardand wide-cargo configurations in both permanent and relocatable configurations

figure 5.8 Radiation portal monitors at a seaport terminal.

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similar to those found at land crossings. In addition, truck-mounted mobile RPM systems are available where terminal operations may be more fluid. Seaport RPM installations typically include infrastructure, such as foundations, conduit, and cabling. Additional equipment and infrastructure, such as a booth for housing officers and equipment, network equipment, and traffic control equipment, are generally required to enable CBP operation of an RPM deployment at a seaport. Portable or handheld instruments, such as a RIIDs, are used by CBP officers to identify radioactive material that triggers alarms in primary and secondary RPMs. Because CBP staffing, space, and commercial needs are often limited, RPM systems installed at seaports require peripheral equipment and features beyond those strictly required for radiation monitoring. This additional equipment may include traffic lights and associated programmable logic controllers, seaport VIS and associated optical character recognition technology, surveillance video, and wireless communications networks. Seaport terminal exit gates are essentially commercial lanes similar to cargo lanes at land crossings (see Figure 5.9). These standard commercial cargo portals have four RSPs with two on each side of the lane placed vertically end-to-end and standard horizontal spacing. Rail access gates exist at some seaports. If the containers destined to leave the terminal by rail are transported between ship and rail yard on trucks, the rail access gate RPM is based on the standard commercial cargo RPM deployment.

figure 5.9 Seaport terminal exit gate.


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Often, these rail access gates have light usage and are only transited by vehicles operated by port or terminal employees. In these cases, additional ancillary equipment is added to result in an RO-RPM, which is operated from a remote location. In cases where there is a need for a fully functional RPM system that can be quickly deployed to different parts of the site or used in a mobile mode, seaports have mobile RPM systems available. Since some seaports have multiple terminal exit and rail access gates and these gates are rarely used, they do not warrant a continual CBP presence. In these cases, a remotely operated RPM is deployed to ensure scanning occurs while allowing optimal use of CBP officers at busier exits. Seaports are increasingly serving the needs of intermodal container transport and use specialized equipment for activity. At some ports, much of the on-dock handling and transport of containers is done with a straddle carrier, a tall vehicle that can straddle and move multiple containers in a stack. An RPM system tailored to straddle carrier operations has been designed, but none are currently commercially available. Further information on straddle carrier solutions is available in Chapter 3.

5.5.2 secondary scanning Secondary scanning of vehicles that caused an alarm in primary scanning is performed with a nearby secondary RPM. This secondary portal may be an additional portal (see Figure 5.10), or the vehicles may be redirected through a primary RPM a second time. When a vehicle that passes through a seaport RPM creates an alarm, the driver is directed by a CBP officer to the secondary RPM for additional scanning. If the secondary scanning confirms the initial alarm, further examination of the vehicle and cargo is conducted. Based on the secondary scanning, the alarm is either cleared or the vehicle is held for further examination and disposition. Most alarms are from NORM and medical radioisotopes.

5.5.3 ancillary equipment Peripheral devices that may be needed for seaport RPM operations include booths, presence sensors, network equipment, auto dialers for alarm notification, flashing light alarm indicators, and traffic control equipment. Site configurations and operational needs determine which and how these devices are deployed. Remotely operated RPMs are equipped with an area surveillance system tailored to the configuration of the port to allow CBP officers to maintain situational awareness and record events. In limited cases, the operating procedure for the use of an RO-RPM relies on designated CBP officers being informed by auto dialer or a visual and audible alert system, consisting of a strobe and siren in case of an alarm. Seaport RPM systems typically require installation of a booth, in which both operating

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figure 5.10 Primary and secondary truck exit gate portals.

equipment and the CBP officers are housed. Gate arms are used at RO–RPM installations to control traffic. In the case of multiple gates, the human machine interface unit is used for setting up, programming, operating, and reprogramming the programmable logic controller modules. This unit replaces the function of devices such as the annunciator and has audio capability for communicating programmable logic controller, network, and annunciator audio alarms to the CBP booth. In some cases, seaport configurations do not allow for installation of breakbeam presence sensors. In these cases, an inductive-loop presence sensor is used. Intercom systems are installed at RO-RPM systems to allow communication between the CBP officer in the main booth and a driver at the remote site. All RPM systems require a network for electronic communication between system components. The complexity and need for additional network components increases with the number and type of equipment. Typically, the most complex systems are installed at RO-RPM deployments with multiple gate locations. Optical character recognition and reconciliation software is used for RO-RPMs at rail exit gates to provide a tool for assuring that all containers leaving the seaport by rail have been screened. All of the RPM systems generally have optical break-beam presence sensors to trigger operation of the RPM system and various ancillary equipment, such as the VIS cameras. Various programmable logic controllers are used to ensure consistent, logical operation of ancillary equipment, such as traffic lights, strobe/ siren alarms, and VISs. Traffic lights are used where necessary for traffic control,


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typically at RO-RPM deployments. A VIS is typically deployed at RO-RPM systems where a clear record of traffic is required. A VIS is required for use of optical character recognition/reconciliation software at rail access gates. More detailed information about each of these devices is provided in Chapter 3. In addition, the RPM systems deployed at seaports may be integrated into the system for national data collection and integration; more information about this system is provided in Chapter 6.

5.6 International Mail/Express Consignment Courier Facilities International mail and ECCF are entry points into the United States for international mail and small cargo (letters, packages, air cargo containers) handled by organizations such as the U.S. Postal Service, DHL Express, Inc., and Emery Worldwide Freight Services. Handling of these materials is typically by conveyer belt, bulk mail cart, airport tug, or truck. The use of particular equipment and its configuration depends on the size and requirements of the operation in question. All RPM deployments at these facilities use systems of two sizes: a compact design for installation directly over or next to conveyer belts, and the standard larger systems for dock doors or roadways. International mail sites use systems configured for doorways, roadways, and smaller systems for belts. Some systems operate in area mode rather than being triggered by presence sensors, such as at doorways with bags moved by staff. Special needs arise for shielding from X-ray equipment. ECCF sites, generally similar to mail sites, use VIS equipment to identify tug containers.

5.6.1 primary scanning Primary scanning is typically performed with an RPM tailored to the package transport systems and geometry (e.g., conveyer belt, door, tug portals, or area monitors). Equipment deployed during the initial stages of the RPMP included a large variety of detection equipment to meet project schedules and needs. A subsequent campaign to upgrade and standardize equipment resulted in standard RSPs in a variety of configurations, including a smaller RSP appropriate for the equipment used for letter and package handling. Retrofits were driven by frequent design changes to ECCF facilities for a variety of purposes, such as streamlining and automating package handling, expansion of offices to accommodate new technology, company mergers, and subsequent decommissioning of facilities. The variety of configuration challenges for international mail/ECCFs included triple-layer conveyor belts, supervisory rooms separately located, X-ray machines in small spaces, and seasonal fluctuations in package volumes and commodities. Each facility had a unique footprint, with the primary common denominator being minimal space for placing radiation detection equipment. The unique nature

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of each deployment resulted in the use of a variety of customized stands for the RPM system equipment. Two additional RPM systems with smaller RSPs than those used for vehicles were developed to meet the space limitations of conveyor belts and inside doorways. This design was further expanded to include an area monitor for nonstop operation (also known as continuous scanning) to differentiate from vehicle presence sensor mode. Enable/disable switches, locks, and surveillance cameras were also installed to give additional administrative controls in locations where the international mail/ECCF employees had direct access to the RPMs during unstaffed periods. The following RPM applications represent the range of primary scanning options for international mail/ECCFs.

5.6.1.1 Conveyor Belts International mail/ECCFs rely on conveyer belts to move letters and packages. The size of these belts varies based on the facility needs. For purposes of radiation scanning, these may be viewed as either small or large conveyer belt types. Because materials are constantly transported on the belts, RPMs for this application are left in area monitor mode to provide continuous scanning. Conveyor belt RPM deployments can use either two RSPs mounted on opposing sides of the belt (similar to other, standard portal geometries) or a single small RSP usually mounted overhead to monitor the area of interest, as shown in Figure 5.11. In some cases, conveyer belt RPM detector panels may be mounted in a one-sided configuration provided they can meet the RPMP threshold requirements. In all cases, the detector’s view of the belt must be unobstructed.

figure 5.11 Small conveyer belt radiation portal monitor configuration in an international mail facility.


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figure 5.12 Typical radiation sensor panel configuration for a doorway in an international mail facility.

5.6.1.2 Doorways Optimal placement of RPMs at international mail/ECCF facilities is often in building entryways or facility doorways from one handling area to another. The doorways range in size from standard interior doors for foot traffic to industrialtype roll-up doors suitable for truck transit or loading/unloading. The RSPs deployed at these locations are selected to assure that the area of interest is screened. Doorway deployments require two RSPs mounted on opposing sides, similar to other standard RPM geometries. Small doorways may require only a single RSP to monitor the area of interest. For any configuration, efficiency standards are met through RPM threshold adjustment. In all cases, the detectors must have an unobstructed view of items passing through the doorway. Radiation portal monitors deployed at a door are mounted as closely as possible to the door to minimize the room between the door and monitor, preventing the possibility of mail or packages slipping through unchecked. At a door where mail bags are unloaded from a truck and then dragged away, RPMs operate in continuous mode while mail bags are in the area, and revert to measuring background when the area is clear, with appropriate buffer times. A typical doorway configuration is presented in Figure 5.12.

5.6.1.3 Tug Portal Tug portal RPM systems may be placed for scanning packages and mail while in transit from an air cargo plane to a nearby processing facility. Tug portals use either one or two pairs of RSPs located on opposite sides of the tug lane, as shown in Figure 5.13. Cargo containers no more than 1.8 m (6 ft) tall can be checked in a two-panel tug RPM, while cargo containers greater than 1.8 m (6 ft) tall must pass

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figure 5.13 Tug portal for scanning packages and mail while in transit to an international express consignment courier facility.

through a four-panel cargo RPM to meet sensitivity requirements. The speed of tugs pulling air freight containers should be no more than 8 km/h (5 mph).

5.6.1.4 Cart Mounted Because the arrival of packages and mail at international mail/ECCF facilities may be intermittent, a cart mounted, portable RPM system with a small RSP was developed, as shown in Figure 5.14. The cart-mounted system operates in area mode and is equipped with a strobe/siren that is activated in the event of an alarm (i.e., does not require active attention from a CBP officer for operation). The cartmounted RPM must be placed so that the surveillance area is 3.4 m (11 ft) or less from the monitor to meet sensitivity requirements.

5.6.1.5 Truck A small amount of international mail arrives via commercial truck. RPMs that service air containers close to the size of cars are configured as RPMs for cars, while RPMs that service air containers close to the size of trucks are configured as RPMs for trucks, as shown in Figure 5.15.

5.6.2 secondary scanning Secondary scanning at mail/ECCF facilities is typically accomplished with handheld instruments and visual inspection. Gamma- or X-ray imaging systems are also used to allow nondestructive examination of letters and packages.


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figure 5.14 Cart-mounted, portable radiation portal monitor system for international mail/express consignment courier facility.

figure 5.15 Truck portal at an international mail facility.

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5.6.3 ancillary equipment At international mail and ECCFs, peripheral devices that may be needed for operations include auto dialers, VIS, flashing light alarm indicators, traffic control lights, and portable detectors. The operating procedure at many facilities does not rely on continual CBP presence at the RPM. Instead, designated CBP officers are informed by an auto dialer or audible alert of a strobe/siren in case of an alarm. Tug and truck portals that operate on a vehicle basis use optical break–beam presence sensors to trigger the RPM systems. Various programmable logic controllers ensure consistent, logical operation. Typically, programmable logic controllers are used to direct events for other ancillary equipment, such as traffic lights, strobe/ siren alarms, and VIS. Where needed for traffic control of motorized vehicles, such as at tug and truck portals, traffic lights have been included. Depending on local needs, some international mail/ECCF deployments are outfitted with VIS equipment that generates images corresponding with the alarm records to facilitate alarm processing. Site configurations and local operational needs determine which of these devices are deployed. More detailed information on each of these devices is provided in Chapter 3. In addition, the RPM systems deployed for international mail/ECCFs may be integrated into the PRIDE system for national data collection and integration; more information about this system is provided in Chapter 6.

5.7 International Airports At the national air cargo POEs, approximately 2,500 aircraft are processed each day. Air cargo facilities are located at international airports and generally have multiple carriers with individual, separate operations located some distance from each other. In contrast, CBP offices are in a centralized location at each airport. Consequently, although airport operations are widely distributed across each airport, there is a significant driver for a substantial communications network supporting efficient air cargo RPM deployments. Airport facilities must have the capability to monitor air cargo containers from multiple carriers in an efficient fashion. This requires multiple carrier portals on the tarmac with sufficient peripherals to control, assess, and process containers that cause alarms with remote monitoring systems. Peripheral equipment is expected to be similar to that for seaports. Although only initial pilot deployments have been conducted to date, airports must incorporate systems similar to international mail and ECCFs, plus tarmac-based systems that may operate as RO-RPM systems. These can include VIS equipment, area surveillance, wireless communications, and intercom systems.


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figure 5.16 Airport tug radiation portal monitor prototype at test bed facility.

5.7.1 primary scanning Primary scanning will occur in a manner similar to tarmac-based systems employed for ECCF deployments. A prototype airport tug RPM system has been constructed at a PNNL test bed facility, as seen in Figure 5.16. The RPM systems deployed for air will be integrated into a system for national data collection and integration (see Chapter 6).

5.7.2 secondary scanning Secondary scanning of alarming vehicles, such as tugs or containers, will be performed in a manner similar to that at land border crossings or seaports. Because air cargo RPMs will be sited at various locations throughout an airport as needed to scan incoming air cargo, control of cargo that has created an alarm is critical to the success of the deployments. This is accomplished through use of ancillary equipment. After identifying a container that has alarmed, a CBP officer will direct the tug driver to the designated secondary RPM for secondary scanning. Based on the secondary scanning, the alarm is either cleared or the vehicle is held for further examination and disposition.

5.7.3 ancillary equipment Peripheral devices that may be needed for operations include presence sensors, network equipment, auto dialers for alarm notification, flashing light alarm

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indicators, and traffic control equipment, much of which has been discussed in previous sections. Site configurations and operational needs determine which of these devices are deployed. More detailed information on each of these devices is provided in Chapter 3.

5.8 Rail Crossings Rail crossings are a type of land border crossing for railroad traffic. Traffic at rail crossings includes freight and passenger rail. Approximately 70 million metric tons of cargo with a value approaching $80 billion is transported each year through these rail crossings, including 2.5 million rail containers. The bulk of rail cargo is shipped on freight trains; some light cargo and parcels may be shipped by passenger rail. Freight rail cargo consists of a wide variety of containerized and bulk cargo. Rail crossings typically consist of one or two sets of railroad tracks crossing the border. Available track, access, and other facilities for secondary scannings vary between crossings. Further, in some cases, rail traffic enters the country in remote locations, some of which are miles distant from border and port facilities. Installation of rail RPM systems at a crossing is complicated by existing track layout, trackside equipment, urban infrastructure, remote locations, and the need to be located a distance from rail X-ray systems. The rail RPM system is currently under development. Because of the difficulty of separating train cars for secondary processing, rail RPMs must provide as much radiation scanning as possible during primary scanning. This implies the need for spectroscopic identification in primary scanning. Railcar identification is also required, which creates the need for complex, redundant presence-sensing systems that include wheel counters, radio frequency tag readers, and optical character recognition systems. Rail RPMs may also require a technology for matching radiation measurements with X-ray images.

5.8.1 primary scanning Rail border crossings will be monitored with a standardized rail RPM system. The rail RPM concept is based on a RPM with two substantial towers on opposite sides of the track. Initially developed prototype rail RPMs have 12 RSPs per system, 6 on each side of the track placed vertically end-to-end, in two towers of three panels each and with standard horizontal spacing for rail applications. Because of the greater height and increased number of panels, and subsequently the added weight, the rail towers have a more robust structure than other RPM systems. A rail RPM prototype installation at a rail RPM test bed facility (shown in Figure 5.17) relies on initial use of plastic scintillator-based RSPs, although the baseline technology for routine rail deployments is expected to be spectroscopic RPMs.


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figure 5.17 Rail radiation portal monitor prototype.

Prior to initiating radiation monitoring at a rail crossing, operational details must be addressed through development of a standard operating procedure. The procedure requires understanding and addressing such issues as generation of NORM alarms, current port operations, secondary inspection capabilities for radiation sources, and site-specific factors such as inspection capabilities and available facilities. As complementary systems, RPM and X-ray imaging systems facilitate the clearing of alarms. To better integrate these systems, they will be deployed with some shared, common rail identification infrastructure. Rail automated manifest system or hard copy train manifests are also available at rail crossings at least one hour prior to trains crossing the border. This information provides cargo information that will facilitate the clearing of alarms.

5.8.2 secondary scanning Secondary examination at rail crossings of individual cars will most likely have a considerable time impact, depending on the secondary examination process. Consequently, to facilitate the clearing of alarms early in the process, the primary rail RPM scanning process is planned to be spectroscopic. If a railcar requires further examination, the railcar will generally be removed from the train and transported elsewhere. Typically, this will occur at a secondary scanning dock located at a yard or a bonded warehouse.

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In addition to the gathering of spectroscopic information during primary scanning, the CBP officers at most rail crossings have access to handheld radiation detection equipment, such as PRDs and RIIDs. Generally, railcars are too large to achieve the sensitivity needed to conduct a close examination of an entire railcar with standard handheld detection devices. Various devices to solve these problems have been proposed and are under consideration.

5.8.3 ancillary equipment Rail RPM systems require a specialized rail identification system to identify each railcar and container on a train. The rail identification system is similar to the system used in the rail radiography program. This system has been demonstrated in standard railroad operations. The rail identification system is an integrated system of components that includes automated equipment identification, railcar imaging, wheel sensors, a radio frequency identification tag reader, area cameras, a line scan camera, a radar detector, and track circuit overlay. Data from this system can be correlated to the presence sensor data and the individual railcar radiation profiles. The imaging system, based either on area scan cameras or digital line scan cameras, produces a continuous image of an entire train. The area or site surveillance system provides a means to maintain situational awareness by monitoring the pedestrian and/or vehicle traffic surrounding the area of the RPM system. This system includes surveillance cameras, a digital video recorder, and a monitor. Infrastructure used to support RPM placement and operations of the rail identification system and site surveillance systems includes power, lighting (both area and camera-specific), foundations, structural towers, equipment enclosures, communications network(s), telephone network(s), and security fencing. All RPM systems require additional site infrastructure; however, the rail RPM systems require significantly more infrastructure because they are usually placed in remote or urban locations and have more and heavier duty RPM towers and other structures than land border crossings. The RPM systems deployed for rail will also be integrated into the national data collection and integration system (see Chapter 6).

5.9 References Kouzes RT. . Radiation Detection and Interdiction for Public Protection from Terrorism. In Public Protection from Nuclear, Chemical, and Biological Terrorism, eds. A Brodsky and J Johnson, R.H. Madison, WI: Medical Physics Publishing. pp. –. Kouzes RT. . Detecting Illicit Nuclear Materials. American Scientist ():–.

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http://www.saic.com/products/security/rr-vacis/index.html

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Operational Considerations for Radiation Interdiction James Ely, Richard Kouzes, Denis Strachan, Robert Bass, and Joseph McDonald

Radiation interdiction equipment is deployed into the complex and busy operational environment of border crossings. CBP officers are responsible for enforcing hundreds of laws, and their new major role of protecting against terrorism has added to their workload. This chapter includes some specific operational issues CBP officers encounter on a daily basis.

6.1 Overview of Operations for Radiation Interdiction Border crossings, seaport and airport terminals, mail facilities, and ECCFs operated long before radiation detection devices were needed. Therefore, the installation of radiation detectors required that these devices fit within the physical confines of the existing facilities, and, once installed, have minimal impact on facility operations. Unavoidably, there are impacts on operations from interdiction activities. However, the goal should be to minimize impacts. At border crossings, impact is minimized by incorporating the radiation scanning program into the existing standard operating procedures as much as possible. At land border crossings, this entails the use of pre-existing primary and secondary scanning approaches and the existing infrastructure. At seaports, radiation scanning is typically integrated with the exit gates, where paperwork and container numbers are verified. However, CBP generally does not have booths or other shelters for officers in place at every seaport terminal, and this makes it necessary to install facilities and infrastructure, along with the radiation detection and ancillary equipment. At high-volume crossings, it may be appealing to install RPMs where the least number would be required, such as at the entrance to a facility where a small number of traffic lanes (choke point) feed a large plaza with many booths. An alarming vehicle must then move to an inspection center. However, experience

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with this type of installation indicates that it is extremely difficult to reliably track a vehicle that causes an alarm from the RPM to the inspection gate without stopping all traffic and causing a significant impact on the traffic flow through the crossing. When each lane has an RPM, traffic flows better and the impact on commerce and CBP operations is minimized. At low-volume border crossings, it may seem practical not to install an RPM and, instead, scan cargo with a handheld radiation scanning device. This approach involves a lot of CBP personnel time because it can take several minutes to perform this task, during which time no other traffic can pass. Or, alternatively, another CBP officer must be available to monitor the other vehicles. Therefore, in both cases, it is almost always more cost effective and efficient to install RPMs at each lane of traffic at a border crossing independent of traffic volume. Primary and secondary radiation scanning stations are used to further minimize the impact on the flow of commerce because this type of action is a familiar part of preexisting operating procedures. Primary scanning takes place in the main lanes of traffic (see Chapter 3). If no radiation alarm is triggered, the vehicle is allowed to pass, subject to other conventional indicators that may lead a CBP officer to refer a vehicle for additional inspections. If a vehicle causes a radiation alarm, it is sent immediately to a secondary RPM where it is scanned again, but at a slower speed and under more control. Assuming that the radiation alarm is confirmed by the secondary RPM, a procedure is typically performed, guided by the RPM results, whereby an RIID is used to identify the specific radionuclide that produced the alarm. In the case where the radionuclide cannot be identified, or where an unusual situation produces uncertainty, further checks can be performed. Results can then be shared with a centralized site where radiation detection experts are available to review the information before the vehicle is released. At lowvolume crossings, where a secondary RPM may not be available, typically the cargo is scanned again with the primary RPM for confirmation. Installing new radiation interdiction equipment at an existing facility is challenging, especially when space is limited. At border crossings, space for operations is always at a premium. In the case of RPM installations, the challenge is to fit the extra equipment between the multiple existing traffic lanes. The least amount of space is taken with the back-to-back RPM configuration. In some situations, the RPMs must be staggered side-by-side to fit them into the existing lane spacing. This does not usually hinder the operation of the RPM, but it does increase the total length of the space where these primary scans are performed and in some cases creates operational limitations such as the need for traffic lights to moderate traffic flow. A few sites have such tight space constraints that cantilevered RPM configurations must be used because space does not allow two independent pillars. Shielding the backs of the RPMs minimizes the cross talk between adjacent lanes from radiation signals as well as the background radiation. Special lanes are required at some sites for extra-wide loads requiring larger RPM units containing up to 16 RSPs. Some RPM installations require configurations that are easily

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relocated for sites that frequently undergo reconfiguration, such as some seaport terminals. Mobile RPM systems are also used for interdiction, especially for targeted scanning. As might be expected, in an established international mail facility, an RPM must be adapted to the existing mail-handling equipment. Ideally, an RPM should be placed at a choke point through which all mail and packages pass; for example, as the tractor-trailer rig enters the facility. This is generally not always possible. Multiple systems must then be installed to guarantee that all commerce is scanned. Monitoring rail shipments is particularly difficult because the types of loads in a 2-mile long train can vary significantly. A train can easily contain a large number of cars carrying NORM, which requires time-consuming processing. The width of train cars and engines is limited by the presence of tunnels and the proximity of other tracks on which trains travel, but regulations limit the closest distance an RPM can be placed, thus requiring larger detection systems. The distance between RPM pillars and their proximity to other traffic has implications on the amount of cross talk that occurs. At some border crossings, the commercial traffic is well separated from noncommercial traffic. In these cases, there are a limited number of instances in which a vehicle that causes an alarm in its lane also causes one in a commercial lane. In cases where the commercial and noncommercial traffic lanes are in close proximity, a radioactive cargo in one lane could cause an alarm in any, or several, of the other neighboring lanes. In cases of multiple alarms, all affected vehicles report to secondary scanning—a potentially significant operational burden. A further possibility arises for the case where there is a space-constrained vehicle site and a nearby railway. Alarms can then be induced in the vehicle lanes by train cars containing NORM. When RPMs are installed (and periodically thereafter), the equipment must be calibrated to assure proper operation. This calibration operation requires trained staff and a period of time when a lane can be closed to traffic for approximately 1 hour for a typical PVT-based RPM. Calibration activities are usually performed during off-peak hours. Periodically during routine operation, data that are collected from the RPMs are downloaded to a central site where the data are further analyzed. The data sets can become quite large because of all the RPM data from four or more panels, each with their own data set, background information, metadata (information on the cargo) and, in some cases, pictures of the vehicle. At some of the high-volume border crossings, the size of the data set can be a few gigabytes per day. These data sets must be retained at a central location where terabyte disk storage capacity is required. Operationally, complications can arise before the vehicle arrives at the POE. Information on the cargo contents is needed at the port before the vehicle or ship arrives to determine which cargo will require extra processing. In the case of vehicles, this prenotification might be several hours; for ships, approximately 1 day is needed to process the hundreds of containers on the ship. Electronic manifests, or

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consists (lists of cargo contents), have to be matched to the vehicle or to individual containers on a ship. In cases where a vehicle or container causes an alarm, the consist can be examined to determine if it is reasonable to suspect that an alarm should arise. There are various reasons why a certain cargo type might cause an alarm: for example, NORM in the form of ceramic tile or TENORM such as welding rods containing thorium. If a vehicle or container causes an alarm, much of the information about the alarm and the following secondary examination must be manually entered. At some facilities, this is performed on hard copy or on computer systems. These data are potentially useful in a number of alarm analyses, such as the following: Development of load-specific alarm algorithms Examination of seasonal load variation effects on alarm trends Prediction of staff needs during certain time periods Identification of cargo (and events) that routinely and therefore predictably cause nuisance alarms • Long- or short-term forecasting of equipment functionality based on alarm descriptions and categorizations • • • •

Over the long term, the robustness of the RPM system is important. If a system has a very high mean–time-between-failure rate, there will be fewer times when lanes are removed from service; this is especially important at high-volume POEs. Additionally, at a low-volume border crossing where only a single RPM may be used, a failure might mean the entire crossing must be shut down. The RPM system must be able to perform over long time periods without failure withstanding extreme weather that ranges from hot to subzero temperatures and dry to rainy conditions. The PVT-based RPM systems currently in place are robust with a mean-time-to-failure rate of several years.

6.2 Operational Impacts of Gamma-Ray Alarms Gamma-ray detectors in RPMs are designed for detecting materials of interest with high efficiency, and consequently, they must be physically large systems. Typical plastic scintillator-based RPMs are sensitive to gamma-ray radiation sources over an energy range up to about 3 MeV, corresponding to emissions from most radionuclides of concern. Although beta particles could be detected with these devices, the short range of beta particles in materials means they are quickly absorbed. However, when beta particles are absorbed, they can raise to an energetic bremsstrahlung (X-ray) photon spectrum (see Chapter 2) that is also detectable. Energetic gamma rays (above 1 MeV) present in background radiation are extremely penetrating and require significant shielding with high-density metals. The need for high efficiency, as well as shielding, results in physically large RPMs that have a significant footprint where installed.


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At land border crossings, the main sources of RPM alarms are nuisance alarms from NORM and medical radionuclides. The alarm rate from medical radiopharmaceuticals is similar for both POV and cargo lanes, although there appear to be more alarms on the northern U.S. border than on the southern border. As described in Section 2.4, the most common medical radionuclide is mTc. Common NORM and TENORM that cause alarms include kitty litter, fertilizer, road salt, gravel, stone, ores, and ceramic tiles, as discussed in Section 2.3. Relatively few NORM alarms occur in POV lanes because only small quantities of NORM can be carried in passenger cars. Alarm rates at land border crossings vary greatly and can be in the range from 1 in 50 vehicles to 1 in 1,000 vehicles. Many ports have X-ray imaging systems that are used routinely in secondary inspections. If not positioned far enough away from the RPMs, these X-ray systems can produce primary alarms that must be resolved at secondary inspection locations. At seaport terminals, NORM commodities are encountered, but the cargo container loads tend to be more densely packed. This gives rise to a somewhat higher rate of alarms at some seaport terminals. The radioactive loads may not be equally distributed on a ship, giving rise to sporadic clusters of alarms from containers. Note that while food is transported in large quantities and some has high K content that could, in principle, produce alarms, the packing density of food is generally low. Thus, contrary to some reports, bananas do not actually produce RPM alarms. Mail handling and ECCFs have fewer alarms from NORM because the package sizes are smaller. Alarms tend to be items such as watches and instruments with radium-painted dials, pottery glazed with uranium-bearing materials, and stone countertops. The radiation background at mail handling and ECCF has less of an impact on the operation of RPMs, although nearby X-ray equipment can produce problems that need to be addressed with shielding. Operationally, alarms cause problems when the number of vehicles or containers to be handled exceeds the capacity of secondary processing. Because every alarm must be verified, and the source identified, a sufficient number of CBP officers must be available to process them to keep legitimate trade and travel flowing. Because cargos containing NORM are only weakly radioactive and only produce radiation alarms when present in large quantities, identification of NORM sources is one of the main challenges to the detection and identification of illicit radioactive materials. Strong sources of gamma radiation, such as medical radionuclides, are easily detected and can induce alarms in multiple lanes, causing several vehicles to be routed to secondary scanning areas for processing. This may mean that secondary processing must quickly clear a dozen vehicles. One approach to solving this problem is the development of intelligent data processing algorithms (as discussed in Section 4.3) that can help reduce the number of NORM alarms and thus reduce the burden in secondary scanning.




Counts/second

4000 3500 3000 2500 2000 8:30:00

9:42:00

10:54:00 12:06:00 13:18:00 14:30:00 Time

figure 6.1 A record of the gamma-ray signal observed for the passage of vehicles through a radiation portal monitor over a period of about  hours.

800 1000 600 400 200 0

Total counts (cps)

Figure 6.1 displays a record of the passages of many vehicles through an RPM over a 6-hour time period. Several observations can be made from this record. First, it is seen that the average background count rate decreases by about 7% over the 6-hour period due largely to changes in the natural radon background with increasing daytime temperature (Stranden et al. 1984). Such weather-related effects also vary depending on the season, and at times the background can change dramatically during a short period due to activity such as thunderstorms (Crozier 1969; Fujitaka et al. 1992; Gale and Peaple 1958; Miles and Algar 1988; Porstendorfer et al. 1994;). Secondly, when each vehicle transited the RPM, the background count rate was generally suppressed to a varying degree due to shadow shielding (Lopresti et al. 2005). Occasionally, the signal increases above the background, representing the passage of a radiation source. Figure 6.2 shows a 30-second time record of many vehicle passages through an RPM. The variety of temporal shapes can be seen. The majority of traces fall near the baseline, since the vehicles do not contain significant radioactivity. Some traces

0

5

10

15 20 Normalized time

25

30

figure 6.2 Record of the observed gamma-ray signal from a number of vehicles passing through a radiation portal monitor.


279

figure 6.3 Shipments of smoke detectors can cause radiation portal monitor alarms due to the presence of Am sources in most units.

have long durations of high-count rates. These are due to evenly distributed NORM loads. Other traces show short durations at high-count rates. These represent vehicles with point sources, such as medical radionuclides. In addition to gamma-ray alarms caused by NORM and medical sources, commercial products containing radiation sources produce some alarms. Figure 6.3 shows a smoke detector that contains a Am source. Only bulk shipments of such devices can produce radiation alarms because the radioactivity of an individual smoke alarm is very small. Industrial irradiation sources are used for such applications as the sterilization of surgical tools, medical supplies, food, inspection of welds (Figure 6.4), liquid-level gauges, curing of plastics, and many other processes. These sources, when they are shipped legally, have adequate paperwork and posting to enable status confirmation. Because of its very high density, depleted uranium (containing less than 0.7%  U) is used in a variety of applications such as shipping shields for commercial radiation sources, counterweights for elevators, sailboat keel weights, airplane components (Figure 6.5), military armor, and armor-piercing bullets. Nuclear reactor fuel and its precursors (yellowcake and uranium hexafluoride) cross the borders on a regular basis. These shipments produce large radiation signatures and need to be specially handled, although there is usually adequate paperwork and vehicle posting to verify the source of the alarms.




figure 6.4 Radiation source used as a density gauge for liquids flowing through the vertical cylinder. (Photo credit: Berthold Technologies, TN.)

figure 6.5 Depleted uranium is used in a number of commercial applications, including shipping shields for strong commercial radiation sources, military munitions and armor, and airplane counterweights. (Photo credit: Boeing Company, WA.)


281

6.3 Operational Impact of Neutron Alarms Neutron alarms observed at border crossings are caused most often by neutronemitting radionuclides in commercial material or instruments. Neutron sources are fairly rare in commerce, occurring in about one in 10,000 vehicles, and there is a huge range of alarm rates varying from port to port. These sources include welllogging probes (used to examine oil and gas wells), concrete dryness detectors (Figure 6.6), nuclear fuel (Figure 6.7), and uranium-bearing compounds in large quantities, such as yellowcake and uranium hexafluoride. Commercial instruments containing neutron sources principally use Cf or AmBe neutron sources. Although the neutrons emitted from these sources can be relatively energetic and penetrate many materials, their enclosures will reduce the energy of the neutrons. This energy reduction, or moderation, can make the detection of these neutrons somewhat easier because the neutron detectors used in RPMs are more sensitive to low-energy neutrons. Background count rates for neutrons are usually very low, with brief spikes in the count rate associated with cosmic rays. These cosmic ray–induced events are enhanced by the presence of large masses of material such as loads of steel with

figure 6.6 An example of a gauge used to measure concrete dryness and soil density; such gauges can contain both gamma and neutron sources. (Photo credit: Troxler Electronic Laboratories, Inc., Research Triangle Park, NC.)




figure 6.7 Nuclear fuel assembly (top) containing thousands of fuel pellets (bottom).

which cosmic rays can interact and produce multiple neutrons. This phenomenon is referred to as the “ship effect” (Kouzes et al. 2008). Figure 6.8 shows a brief neutron spike at channel 31 induced by cosmic rays. Such cosmic ray–induced neutron events are usually short spikes in the neutron count rate and thus can be differentiated from true neutron sources. Figure 6.9 shows the RPM response to a vehicle with both a neutron and a gamma-ray source. The trace shows a broad feature, rather than a spike, and this is characteristic of a neutron source being moved past the detector. All sustained neutron alarms are investigated thoroughly because they indicate a noncosmic source that may be of concern. Neutron sources of extreme concern include improvised nuclear weapons or actual state-produced nuclear weapons. The He proportional counters typically used for neutron detection in RPM systems are somewhat sensitive to vibration and radiofrequency interference. Alternative neutron detection technologies may have additional sensitivities to environmental factors. The neutron counters and electronics need to be designed and installed to have adequate radiofrequency shielding and to have vibration and shock isolation, as these systems can be sensitive to such effects. Requirements for these environmental factors are included in the ANSI standards used to test systems for adequate performance (ANSI 2006).


283

Profile (0.1 second samples)

Back

Counts in 0.1second

Front

0

10

20

Gamma

30

40 50 60 70 80 90 100 110 120 130 140 150 Total vehicle duration 15.5 seconds Neutron

figure 6.8 Neutron spike event induced by a cosmic ray as seen at channel .

Profile (0.1 second samples)

Back

Counts in o.1second

Front

0

5

10 15 20 25 30 35 40 Vehicle duration 28 samples = 2.8 seconds, speed: 7.38 MPH Gamma Lo Sum Number of pre sample: 10 Gamma Hi Sum Number of post sample: 10 Neutron Sum

45

figure 6.9 Radiation portal monitor response to a vehicle containing a neutron and gamma-ray source; the center curve is the neutron response.

Because the neutron background count rate is very stable, generally varying appreciably only with altitude, a sensitive alarm threshold can be used. Functional testing of the neutron detection system of an RPM must be performed with a known neutron source to verify its correct response to sources expected to be encountered at monitoring sites.

6.4 National Integration of Radiation Portal Monitor Data The amount of data generated by deployed RPMs and associated monitoring instrumentation is enormous. Each passage through an RPM produces from 10 kB to 100 kB of data, and there are hundreds of thousands of such passages each day. Beyond the immediate use of determining if a vehicle contains radioactive material, the archive of RPM data contains useful information to improve the




interdiction process and the RPM equipment. Information on some radiation alarms is communicated to a central site for further analysis. Both of these functions would be better served if the information were automatically communicated and made available electronically; however, it must be realized that the process of acquiring, storing, and analyzing large quantities of data is a problem that needs to be addressed. Early in the project, RPMP staff proposed the creation of a National Integration System (NIS) to perform this automated archive and notification process. The NIS is designed to deliver a compilation of radiation interdiction data to a central site to facilitate a variety of CBP data needs, including real-time resolution of unresolved alarms. It is the primary function of NIS to gather data generated from the RPMs, the RIID, video images, CBP officer notes, and other metadata from each of the ports and create data records that are stored in a central location and are accessible by appropriate authorities. The primary tool used in the NIS is the software program entitled PRIDE. Generally, the data flow at an RPM deployment site stems from the primary and secondary RPMs and video cameras to a site server where it is archived, along with metadata and RIID information. Information, such as the consist and commercial vehicle identification, are added during secondary inspection. Consist data and other information will eventually be merged electronically before the vehicle arrives at the POE. Railcars have electronic identification tags that make it easier to match a consist with a specific car. The PRIDE software allows the radiation profiles of all vehicles that pass through the RPM to be transmitted over a wide area network to the central data store. For those vehicles that cause an alarm at the RPM, a more complete data set is initiated. This set of data includes visual images, RIID scan, and any remaining data that are entered manually or electronically. Scans from the secondary RPM are automatically transmitted, whereas the RIID scans are entered electronically when the RIID is placed in its docking station. Because there may be more than one vehicle in secondary inspection, the secondary information must be matched to the primary data. All this information is transmitted to the centralized data store where it is added by the PRIDE software to the previously transmitted information on the vehicle. All of these data for the vehicle form a record for that vehicle. Another function of the PRIDE software is to gather information on the state-of-health of the RPMs. Information on manual events, such as RPM calibrations, and on automatic events that are part of the PRIDE system, is also transmitted. There are four CBP departments that make the greatest use of the data transmitted by PRIDE, including the following: 1. Laboratories and Scientific Services: This organization provides scientific support to the field and provides forensic capabilities. Use of the PRIDE software can enhance the quality and timeliness of the technical support that Laboratories and Scientific Services provides


285

to the POE. With the electronic availability of the information on vehicles, Laboratories and Scientific Services staff can have a real-time display of RPM, RIID, video images, CBP officer notes, and metadata accessible in their office. Laboratories and Scientific Services staff has available sophisticated analysis software to help resolve alarms, and the expertise to provide these analyses. Similarly, the staff has available information analytics software to analyze RPM data and national trend profiles. 2. National Enforcement Equipment Maintenance and Repair: National Enforcement Equipment Maintenance and Repair staff performs the maintenance and repair of the CBP radiation interdiction instrumentation. With these data, National Enforcement Equipment Maintenance and Repair staff can evaluate the state-of-health parameters for the equipment in the system. The system will support display of system errors, remote diagnosis of system failures, and predictive analyses to identify pending component failures. 3. National Command Center: This center can use real-time data from PRIDE to status alarm data and resolution information, system status information, system response control, and trend analyses. The latter includes much better ways of understanding seasonal variations in RPM operation and background radiation. Port alarm patterns can be identified and tracked. . National Targeting Center: This center can enhance operational capabilities, day, and season, targeting analysis by commodity and carrier, and feedback to targeting models and rules. National integration of the RPM systems provides a unique centralized data resource for operations, predictive maintenance, and counterterrorism.

6.5 References ANSI. . American National Standard for Evaluation and Performance of Radiation Detection Portal Monitors for Use in Homeland Security. ANSI ., American Nuclear Standards Institute, Washington, DC. Crozier WD. . Direct measurement of radon- (thoron) exhalation from ground. Journal of Geophysical Research :–. Fujitaka K, M Matsumoto, K Kaiho, and S Abe. . Effect of rain interval on wet deposition of radon daughters. Radiation Protection Dosimetry (–):–. Gale HJ and LHJ Peaple. . A study of radon content of ground-level air at Harwell. International Journal of Air Pollution :–. Kouzes RT, JH Ely, A Seifert, ER Siciliano, DR Weier, LK Windsor. . Cosmic-rayinduced ship-effect neutron measurements and implications for cargo scanning at borders. Nuclear Instruments and Methods A , –.




Lopresti CA, DR Weier, RT Kouzes, and JE Schweppe. . Baseline suppression of portal monitor vehicle gamma count profiles: A characterization study. Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment ():–. Miles JCH, and RA Algar. . Variations in radon- concentrations. Journal of Radiological Protection :–. Porstendorfer J, G Butterweck, and A Reineking. . Daily variation of the radon concentration indoors and outdoors and the influence of meteorological parameters. Health Physics ():–. Stranden E, AK Kolstad, and B Lind. . Radon exhalation – moisture and temperaturedependence. Health Physics ():–.

{7}

Related Work

Interdiction of nuclear and radiological materials is underway around the world. Activities include developing standards and testing equipment, two important aspects for any instrumentation planned for field deployment. For equipment that will be deployed for interdiction purposes, standards provide vendors with minimum requirements the equipment must meet. Significant efforts have been made (both domestically and internationally) in developing instrument standards for security equipment used at border crossings, and in testing this equipment against these standards. For the last decade, DOE has worked to interdict illicit radioactive and nuclear materials worldwide under the Second Line of Defense (SLD) program. The U.S. Department of Defense (DoD) is also executing the Joint Program Manager (JPM)-Guardian, an active program designed for force protection against radioactive threats. Within the U.S. Department of Homeland Security, other major efforts (beyond the RPMP) largely relate to future requirements for interdiction. In the international arena, several nations have undertaken programs similar to those in the United States, and the International Atomic Energy Agency (IAEA) has been an important leader in these international programs. This chapter summarizes selected efforts related to significant programs for interdiction of illicit trafficking in nuclear and other radioactive materials.

7.1 Testing, Evaluation, and Standards Joseph McDonald Equipment used for detection and identification of illicit radioactive sources became more widely available following September 11, 2001. Health physics instruments had been available for many years, and some of the tasks performed for radiation protection are similar to those used in radiation interdiction. However, the general purpose of radiation protection measurements is to determine the dose equivalent or dose equivalent rate produced by a source of radiation in a controlled environment, such as a research laboratory or a nuclear reactor.




Radiation detection equipment initially produced for homeland security purposes was not primarily designed to measure dose equivalent but, rather, provided a quick indication of the presence of unexpected radiation. Subsequent to radiation detection, additional measurements could then be conducted to identify the radiation source. These measurements would also need to be performed in public, commercial, and other relatively uncontrolled areas where portable, batteryoperated equipment and instruments would be required. The environmental conditions to which radiation detection and identification equipment was expected to be exposed included a wide range of temperatures, humidity, and ambient interferences. For example, a handheld device could be carried by an emergency responder who was also carrying a portable transmitter or cell phone, each of which might produce radio frequency electromagnetic radiation that could interfere with the operation of the radiation detection or identification equipment. In addition, emergency conditions may require responders to wear additional protective clothing, thus making it difficult to hear an alarm produced by radiation detection equipment, or to read its panel display of data. It was also anticipated that instruments would be dropped or otherwise shocked. Therefore, it was important to determine whether commercial instruments would operate correctly when challenged by environmental conditions and interferences that might be experienced during expected use. For many years, the performance of health physics instruments has been tested and evaluated prior to purchase or use. Some of this testing experience was used to develop appropriate tests for the newly developed radiation detection and identification equipment. Existing U.S. and international standards for testing health physics instruments were useful models for developing new testing standards for radiation detection equipment and devices intended for interdiction of illicit radioactive materials. However, because of the significantly different nature of the two different types of equipment, the health physics standards could not be directly applied to the new equipment. Health physics instruments are designed to measure dose equivalent or dose equivalent rate, so their response is relatively independent of the energy of the incident radiation. Such instruments are generally less sensitive than radiation interdiction devices. In addition, health physics instruments are often used indoors and may be subject to a narrower range of temperature and humidity fluctuations. These instruments may also be somewhat larger than the radiation detection devices, which may be carried by a CBP officer who requires an inconspicuous device that produces a silent, vibrating alarm. These features are not normally found in health physics instruments. The essential differences in function and design between health physics instruments and radiation detection and identification equipment required the development of new testing and evaluation procedures and standards. The organization most familiar with the development of testing standards for radiation-measuring instruments is the American National Standards Institute

Related Work

289

(ANSI) Committee N42 on Nuclear Instrumentation. An N42 subcommittee addresses radiation protection instrumentation; therefore, several committee members began developing testing standards specifically for radiation detection and identification equipment for interdiction applications. The purpose, and therefore the design, of radiation detection equipment can vary. Equipment can be placed in four general categories. First, there are the small PRDs that may be worn in a pocket or on a belt, or otherwise concealed. These devices may provide an indication of a person in possession of an illicit radiation source at an airport terminal or other public area. The second category is a handheld detector that may be used when a CBP officer conducts a search, and higher sensitivity to radiation is required. Detection of radiation sources in vehicles passing a checkpoint, such as a border crossing or port of entry, is performed with the third category of equipment, large RPMs usually mounted on either side of a vehicle lane. As the vehicles pass through this detector combination, measurements are performed in a few seconds, and small quantities of radiation can be detected. When a radioactive source has been located, an identification of the type of source can be performed with the fourth category, an identification instrument typically containing a small NaI(Tl) scintillator, phototube, and multichannel analyzer to perform a spectroscopic analysis of the photons emitted by the source. The new ANSI standards for homeland security applications released in 2003, and updated in 2006, drew from previous standards such as ANSI N42.17A, Performance Specifications for Health Physics Instrumentation–Portable Instrumentation for Use in Normal Environmental Conditions (ANSI 1994b) and ANSI N42.17C, Performance Specifications for Health Physics Instrumentation– Portable Instrumentation for Use in Extreme Environmental Conditions (ANSI 1994a). In addition, international standards were consulted, including International Electrotechnical Commission (IEC) standard IEC 60395, Portable X or Gamma Radiation Exposure Rate Meters and Monitors for Use in Radiological Protection (IEC 1972). Other international standards dealing with the performance of radiation detection instrumentation also provided information used in the new ANSI standards for homeland security applications (IEC 2004; ISO 1996, 2001). The four main ANSI standards developed for homeland security applications are 1. ANSI N42.32 (2006), American National Standard Performance Criteria for Alarming Personal Radiation Detectors for Homeland Security (ANSI 2006a). 2. ANSI N42.33 (2006), American National Standard for Portable Radiation Detection Instrumentation for Homeland Security (ANSI 2006b). 3. ANSI N42.34 (2006), American National Standard Performance Criteria for Hand-Held Instruments for the Detection and Identification of Radionuclides (ANSI 2006c).




4. ANSI N42.35 (2006), American National Standard for Evaluation and Performance of Radiation Detection Portal Monitors for Use in Homeland Security (ANSI 2006d). Table 7.1 provides a synopsis of the scope and purpose of these four ANSI standards and a few of the other standards developed for homeland security purposes.

table 7.1 Description of scope and purpose of American National Standards Institute standards for homeland security applications Standard

Description

ANSI N42.32 Performance Criteria for Alarming Personal Radiation Detectors for Homeland Security (ANSI 2006a)

This standard describes design and performance criteria, along with testing methods, for evaluating the performance of instruments for homeland security that are pocket sized and carried on the body for the purpose of detecting the presence and magnitude of radiation. This standard specifies the performance criteria for radiation detection and measurement instruments that may be used in a variety of environmental conditions. The performance criteria contained in this standard are meant to provide a means for verifying the capability of these instruments to reliably detect significant changes above background levels of radiation and alert the user to these changes. This standard establishes design and performance criteria, test and calibration requirements, and operating instruction requirements for portable radiation detection instruments. These instruments are used for detection and measurement of photon–emitting radioactive substances for the purposes of radiation detection and interdiction, and hazard assessment. The informative annexes of this standard provide reference information. This standard addresses instruments that can be used for homeland security applications to detect and identify radionuclides, for gamma-dose rate measurement, and for indication of neutron radiation. This standard specifies general requirements and test procedures; radiation response requirements; and electrical, mechanical, and environmental requirements. Successful completion of the tests described in this standard should not be construed as an ability to successfully identify all isotopes in all environments. This standard provides the testing and evaluation criteria for RPMs to detect radioactive materials that could be used for nuclear weapons or RDDs. RPMs may be used in permanent installations, in temporary installations for short-duration detection needs, or as a transportable system. These systems are used to provide monitoring of people, packages, and vehicles to detect illicit radioactive material transportation, or for emergency response to an event that releases radioactive material. This standard describes training requirements for homeland security personnel using radiation detection instruments.

ANSI N42.33: Portable Radiation Detection Instrumentation for Homeland Security (ANSI 2006c)

ANSI N42.34: Performance Criteria for Hand-Held Instruments for the Detection and Identification of Radionuclides (ANSI 2006b)

ANSI N42.35: Evaluation and Performance of Radiation Detection Portal Monitors for Use in Homeland Security (ANSI 2006d)

ANSI N42.37: Training Requirements for Homeland Security Personnel Using Radiation Detection Instruments (ANSI, 2006e)

(Continued)

Related Work

291

table 7.1 (Contd.) Standard

Description

ANSI N42.38: This standard describes the performance requirements for Performance Criteria for radionuclide identifying portal monitors, also referred to as Spectroscopy-Based Portal spectroscopic portal monitors. The requirements stated are Monitors Used for Homeland based on monitors used in support of DHS-related work. Security (ANSI, 2006f ) ANSI N42.41: This standard describes the performance criteria for Active Minimum Performance Criteria Interrogation Systems in Homeland Security applications. for Active Interrogation These systems are intended for nonintrusive inspection of Systems Used for closed containers, vehicles, and packages of a wide range of Homeland Security types and sizes. In these systems, the contents of an inspection (ANSI, 2007) zone are irradiated with penetrating ionizing radiation to determine the presence of a hidden substance of interest by the analysis of stimulated secondary radiations or nuclear resonance absorption spectra that are indicative of the chemical and/or nuclidic composition of the substance of interest. ANSI N42.42: This standard specifies the data format that shall be used for both Data Format Standard for required and optional data to be made available by radiation Radiation Detectors Used for instruments for U.S. Homeland Security applications. Homeland Security The performance for these types of instruments is described (ANSI, 2006g) in other standards.

7.2 International Atomic Energy Agency Activities Joseph McDonald and Richard Kouzes The IAEA provides recommendations for monitoring activities to member states and has developed performance specifications and test methods for radiation detection equipment used in monitoring border crossings. Beginning in 1997, a project to evaluate the performance of commercially available radiation detection and identification equipment was conducted jointly by the IAEA and the Austrian Research Centre Seibersdorf. This project was called the Illicit Trafficking Radiation Detection Assessment Program (ITRAP). Laboratory and field tests were conducted at Austrian Research Centre Seibersdorf, and as a result, significant improvements in the specifications evolved. Additional tests and specification improvements were made following a workshop on test procedures at the European Research Centre at Ispra, Italy. Additional tests and measurements were conducted at the IAEA laboratory and the Illicit Trafficking Radiation Detection Assessment Program test site at Austrian Research Centre Seibersdorf, and a final version of the specifications, Technical/Functional Specifications for Border Radiation Monitoring Equipment (IAEA 2005) was written. Because the ANSI standards were being developed at approximately the same time, members of the ANSI writing groups collaborated with the IAEA, which was helpful to both groups in synchronizing the standards.




The primary difference between the IAEA specifications document (IAEA 2005) and the ANSI standards is the purpose of the IAEA document is to be a deployment specification rather than purely a test specification, which is the purpose of ANSI standards. System parameters given in the document can be used as the specification for how the equipment will actually be deployed for border security applications rather than only for use during tests and evaluations of equipment from various manufacturers. For this reason, some system parameters may differ between the IAEA document (IAEA 2005) and the ANSI standards. Table 7.2 and Table 7.3 compare a few of the IAEA and ANSI specifications for personal radiation detectors and RPMs. As an example of the difference in approach between the ANSI standards and the IAEA specification, consider the entries in Table 7.3 for the gamma-ray sources. The IAEA specification requires that a particular count rate be observed per becquerel of activity for each source centered in the RPM. In contrast, the ANSI standard simply requires that the RPM alarm 90% of the time with 95% confidence for the indicated radioactive sources passing through the monitor at a specified distance and speed. The ANSI approach allows for pass and fail type–testing for comparison of the operation of different systems, while the IAEA approach table 7.2 Personal radiation detectors Specification

IAEA

Standard background

0.1 μSv⋅h ± 50%

20, 60, 100 μR⋅h–

False alarm rate

≤1 γ/60 min ≤1 n/60 min (≤2/1 h, 95% Confidence Level)

≤1/60 min

Test speed

0.5 m⋅s–

Static tests

γ - sensitivity

0.2 + 0.3 μGy.h– within 5 ± 1 s 0.5 μSv⋅h– at detector with source passing with speed of 0.5 m⋅s– alarms alarms within 30 min with continuous alarm “low” indicator for lifetime

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