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LASERS AND ELECTRO-OPTICS RESEARCH AND TECHNOLOGY

LASER ABLATION: EFFECTS AND APPLICATIONS

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LASERS AND ELECTRO-OPTICS RESEARCH AND TECHNOLOGY

LASER ABLATION: EFFECTS AND APPLICATIONS

SHARON E. BLACK EDITOR

Nova Science Publishers, Inc. New York

Copyright © 2011 by Nova Science Publishers, Inc. All rights reserved. No part of this book may be reproduced, stored in a retrieval system or transmitted in any form or by any means: electronic, electrostatic, magnetic, tape, mechanical photocopying, recording or otherwise without the written permission of the Publisher. For permission to use material from this book please contact us: Telephone 631-231-7269; Fax 631-231-8175 Web Site: http://www.novapublishers.com

NOTICE TO THE READER The Publisher has taken reasonable care in the preparation of this book, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained in this book. The Publisher shall not be liable for any special, consequential, or exemplary damages resulting, in whole or in part, from the readers’ use of, or reliance upon, this material. Any parts of this book based on government reports are so indicated and copyright is claimed for those parts to the extent applicable to compilations of such works. Independent verification should be sought for any data, advice or recommendations contained in this book. In addition, no responsibility is assumed by the publisher for any injury and/or damage to persons or property arising from any methods, products, instructions, ideas or otherwise contained in this publication. This publication is designed to provide accurate and authoritative information with regard to the subject matter covered herein. It is sold with the clear understanding that the Publisher is not engaged in rendering legal or any other professional services. If legal or any other expert assistance is required, the services of a competent person should be sought. FROM A DECLARATION OF PARTICIPANTS JOINTLY ADOPTED BY A COMMITTEE OF THE AMERICAN BAR ASSOCIATION AND A COMMITTEE OF PUBLISHERS. Additional color graphics may be available in the e-book version of this book.

LIBRARY OF CONGRESS CATALOGING-IN-PUBLICATION DATA Laser ablation : effects and applications / editor, Sharon E. Black. p. cm. Includes index. ISBN 978-1-61209-189-1 (eBook) 1. Laser ablation. I. Black, Sharon E. TA1715.L367 2010 621.36'6--dc22 2010041370

Published by Nova Science Publishers, Inc. © New York

CONTENTS Preface Chapter 1

Chapter 2

Chapter 3

Chapter 4

vii Double-Pulse Laser Ablation of Solid Targets in Ambient Gas: Mechanisms and Effects G. Cristoforetti and V. Palleschi Assessing Hunter-Gatherer Mobility in Cis-Baikal, Siberia Using LA-ICP-MS: Methodological Correction for Laser Interactions with Calcium Phosphate Matrices and the Potential for Integrated LA-ICP-MS Sampling of Archaeological Skeletal Materials Ian Scharlotta, Andrzej Weber, S. Andy DuFrane, Olga I. Goriunova and Robert Creaser Modeling of Laser Ablation Induced by Nanosecond and Femtosecond Laser Pulses Tatiana E. Itina, Mikhail E. Povarnitsyn and Konstantin V. Khishchenko Fabrication of Silicon Nanocrystal Based Structures with Nanosecond Laser Ablation Processings in Liquid Media V. Švrček

1

45

99

127

Chapter 5

Ho:YAG Laser Lithotripsy Jinze Qiu, Thomas E. Milner and Joel M. H. Teichman

Chapter 6

Computer Modelling of Femtosecond Laser Ablation of Semiconductors and Dielectrics D. P. Korfiatis and K.-A. Th. Thoma

153

Thermophysical Effects of Femtosecond Laser Ablation of Metal Target Ranran Fang and Hua Wei

163

Chapter 7

143

vi Chapter 8

Chapter 9 Index

Contents Formation of Nanoparticles under Laser Ablation of Solids in Liquids G. A. Shafeev Nanodiamonds from Laser Ablation in Liquid G. W. Yang

191 227 267

PREFACE Laser ablation is the process of removing material from a solid (or occasionally liquid) surface by irradiating it with a laser beam. At low laser flux, the material is heated by the absorbed laser energy and evaporates or sublimates. At high laser flux, the material is typically converted to a plasma. Usually, laser ablation refers to removing material with a pulsed laser, but it is possible to ablate material with a continuous wave laser beam if the laser intensity is high enough. This book presents current research in the study of laser ablation from across the globe. Topics discussed herein include double-pulse laser ablation of solid targets in ambient gas; using laser ablation ICP-MS and its potential in sampling archaeological skeletal materials; and numerical modeling of laser-matter interactions. Chapter 1 - Laser Ablation (LA) is used in a widespread range of applications, among them it is employed as sampling procedure for the elementary chemical analysis of materials. With this aim, many analytical techniques makes use of LA - such as LA Ion Mobility Spectrometry, Resonant LA, LA-Atomic Fluorescence Spectrometry and LA-Microwave Induced Plasma-Atomic Emission Spectrometry – among them the most popular ones are probably the Laser-Ablation Inductively Coupled Plasma (LA-ICP) techniques and the Laser Induced Breakdown Spectroscopy (LIBS). In all these cases, it is desirable to attain the largest possible mass removal from the target in order to lower the Limit Of Detection (LOD) of the technique. Such intent is particularly true in the LIBS case, where LODs for solid samples are usually in the range of ppm or tens of ppm, which are often inadequate for many applications. One of the possible ways to overcome this problem is the use of two laser pulses, temporally separated by a suitable delay, for the laser ablation. In this scheme, the laser beams can be arranged in a collinear geometry, where both the beams are aligned normally to the target and are focused on its surface, or in an orthogonal geometry (pre-ablation configuration), where the first pulse runs parallel to the target surface and is focused in the ambient gas in front of it, while the latter is aligned perpendicularly and ablates the target. In case of ns-laser ablation, in both these configurations, a substantial enhancement of mass removal and of its atomization with respect to the case where a single pulse with equal total energy has been observed, where these phenomena lead to an improvement of both the LODs and the reproducibility of measurements. Such experimental configurations lead also to a different thermodynamic and dynamic evolution of the plasma, which can be useful in case of LIBS analysis.

viii

Sharon E. Black

Many works have been dedicated to Double Pulse (DP) Laser ablation, aimed to establish the optimal experimental conditions to be used in different applications and to understand the physical mechanisms, still not clear, leading to the observed mass removal enhancement [1]. The aim of the present chapter is presenting and resuming the ns-ns DP state of art, discussing the occurring physical processes. Experimental results of the authors, as well as of other scientists, will be shown and discussed to validate and run down hypotheses on the mechanisms involved. In particular, the interpretation of the lower plasma shielding, due to a rarefied ambient environment, experienced by the second laser pulse will be presented. The reduction of plasma shielding allows a larger part of the laser energy to reach the target surface, resulting in an enhancement of the mass removal. Besides, such an improved laser-matter coupling produces a stronger heating, which could lead the molten pool near the thermodynamic critical temperature and drive the onset of phase explosion mechanism. A summary of the effects produced in DP configuration by using short and ultrashort laser pulses is also mentioned, together with a brief discussion of the mechanisms involved. Chapter 2 - Micro-sampling and analysis of tooth enamel from faunal samples in the archaeological record has enabled research into the mobility and seasonality of animals in prehistory. However, studies on human tooth samples have failed to yield similar results. It is well understood that human tooth enamel does not fully mineralize in a strictly linear fashion, but rather entails five recognizable stages of mineralization. Until the enamel matrix fully crystallizes, the matrix remains an open chemical system, thus at each stage of mineralization, the geochemical composition of the enamel matrix can be altered. At present it is unclear if failure to mirror the results from faunal teeth with human teeth is a factor of mineralization rates or simply the result of the difference in enamel volume and formation time between human and herbivore teeth. Therefore, the applicability of chemical analyses to human teeth is a balance between micro-sampling analytical techniques and generating archaeologically relevant data. Yet limited case studies have been performed to examine the scale and extent of this problem in human teeth using laser-ablation ICP-MS. Five human molars from an Early Bronze Age cemetery on the shores of Lake Baikal, Siberia were serially sampled and analyzed by means of laser-ablation quadrupole and multicollector ICP-MS in order to examine the nature of geochemical changes within the enamel matrix. This sampling was performed in order to generate a statistically significant dataset to assess the effectiveness of two approaches along with published methodologies to counter known problems with attempts to assess Sr87. Recent research has demonstrated that among the methodological problems, there is isobaric interference at mass 87 caused by the formation of calcium phosphate (Ca40PO) in response to interaction between the laser and the enamel matrix. Correction procedures using Zr91 in tandem with Ba/Sr ratios are examined. Additionally, serial sampling of teeth from hypothesized mobile hunter-gatherers provides useful insight into the dynamic interplay between physical sampling limitations and the scale at which useful geochemical data can be recovered from organic minerals. Traditional utilization of geochemical data for mobility has relied on a local/non-local dichotomy in population level analyses; however, this approach is of limited utility with regard to mobile populations. The authors’ ability to effectively analyze skeletal materials at a micro scale provides their best hope at addressing the rift between recognition of an indirect relationship between biological intakes, mineral formation and being able to generate relevant analytical data.

Preface

ix

Chapter 3 - The chapter considers the problem of numerical modeling of laser-matter interactions. The main objective is to clarify the mechanisms of this extremely complex process. Comparison of femtosecond and nanosecond laser ablation is first presented. Thermal model is used for nanosecond ablation. The physical phenomena involved into the interaction of a laser-generated plasma plume with a background environment are furthermore studied. A three-dimensional combined model is developed to describe the plasma plume formation and its expansion in vacuum or into a background gas. The proposed approach takes advantages of both continuous and microscopic descriptions. The simulation technique is suitable for the simulation of high-rate laser ablation for a wide range of the background pressure. The model takes into account the mass diffusion and the energy exchange between the ablated and background species, as well as the collective motion of the ablated species and the background gas particles. The developed approach is used to investigate the ablation of aluminum in the presence of a background gas. The influence of the background gas on the expansion dynamics of the laser-generated plume is examined. Experimental density distributions are explained based on the simulation results. A detailed analysis of material decomposition in femtosecond regime is then performed by using a hydrodynamic model with a thermodynamically complete equation of state. As a result, several ablation mechanisms are observed. A major fraction of the ablated material is found to originate from the metastable liquid region, which is decomposed either thermally in the vicinity of the critical point into a liquid-gas-mixture or mechanically at high strain rate and negative pressure into liquid droplets and chunks. The calculation results agree with the results of previous molecular dynamics simulations and explain recent experimental findings. In addition, effects of the ultra-short laser excitations of wide band gap materials need a particular attention. In this case, material ionization through multi-photon excitation and electron-impact ionization should be considered. Laser interactions are simulated with a particular focus on the control over laser plume expansion process. The properties of the laser-generated plasma plume are shown to be strongly affected by the laser-mater interaction mechanism Chapter 4 - In this chapter a nanosecond (ns) laser ablation and fragmentation processing in water, pure and doped spin on glass (SOG) polymer-based solutions are discussed. The confinement of laser-generated plasma in liquids allows the silicon nanocrystals (Si-ncs) formation with a quantum confinement size effects. The author demonstrates that ns laser processes in liquid can be efficiently applied for the fabrication and tuning the optoelectronic properties of Si-ncs based nanostructures. The laser fragmentation in water induces the selfassembly and allows formation of closely-packed stable luminescent Si-ncs over ~ 200 μm. Contrary to the water, the laser ablation and fragmentation in pure and doped SOG solutions inhibit aglomeration and enhance the Si-ncs luminescence properties. Finally, the authior disccusses physics and dynamics of Si-ncs formation through the serial growth processes that occurred in liquid media confined ns laser generated plasma. Chapter 5 - The long-pulse Ho:YAG laser has been used for intracorporeal laser lithotripsy of urinary calculi since the mid-1990’s and is considered the “gold standard” modality for endoscopic laser lithotripsy. The authors present an overview of Ho:YAG laser lithotripsy. They begin with an introduction of the ablative mechanism of Ho:YAG laser lithotripsy, and compare to short-pulse (< 10 usec) laser lithotripsy. Ablative properties of

x

Sharon E. Black

Ho:YAG laser lithotripsy are reviewed and the authors summarize several practical problems and safety issues of existing optical fibers for Ho:YAG lithotripsy. Chapter 6 - Ultrafast laser ablation has proved to be a powerful tool for material processing. Combination of both experimental and theoretical efforts can lead to the determination of optimum values of laser parameters for the improvement of accuracy which is a most crucial aspect in micromachining. Besides experiment and theory, numerical simulation can also provide a significant research tool in the field for the calculation of parameters of great importance which influence the micromachining process. Such parameters are ablation threshold as a function of the laser wavelength, pulse duration and the properties of the particular material. Especially, the prediction through numerical simulation of the geometry and the dimensions of the craters formed and the damaged surrounding surface for known laser and material properties can lead to control and optimization of the micromachining process. Furthermore, numerical simulation can drop light to the microscopic processes through which femtosecond laser damage occurs. In this chapter, the numerical techniques currently used for the simulation of femtosecond laser ablation of semiconductors and dielectrics are presented and discussed. These techniques include molecular dynamics simulation, the Fokker-Planck approach and two temperature models. Chapter 7 - The electron-phonon relaxation time as a function of pulse width and fluence of femtosecond laser is studied based on the two-temperature model. The satisfactory agreement between our numerical results and experimental data indicates that the electronphonon relaxation time is reasonably accurate with the influences of pulse width and fluence of femtosecond laser. An improved two-temperature model to describe femtosecond laser ablation of metal target is also presented. The temperature-dependent heat capacity and thermal conductivity of the electron, as well as electron temperature-dependent absorption coefficient and absorptivity are all considered in this tailored two-temperature model. The satisfactory agreement between our numerical results and experimental data indicates that the temperature dependence of heat capacity, thermal conductivity, absorption coefficient and absorptivity in femtosecond laser ablation of metal target must not be neglected. This chapter finally presents a unified thermal model, which can describe the thermophysical effects with laser pulse width ranges from nanosecond to femtosecond. The satisfactory agreement between the authors’ numerical results and experimental results of vaporization threshold indicates that the unified thermal model is correct and reasonable. Chapter 8 - The process of nanoparticle formation under laser ablation of solids in liquids is described. Critical parameters are discussed that govern the properties of nanoparticles ejected into the surrounding liquid. These parameters are laser wavelength, pulse duration, interaction of individual nanoparticles with laser beam inside the liquid. A review of previous results is presented on the properties of nanoparticles of noble metals. Recent data on laserassisted generation of other metals is given, including the formation of alloyed nanoparticles. Micro- and nanostructuring of the target upon its laser ablation in liquid environment is discussed. Examples are given of the influence of the surrounding liquid on the chemical composition of generated nanoparticles. The laser control over the size distribution of nanoparticles in liquids is demonstrated either by spatial profiling of laser beam intensity or proper tuning of laser wavelength into plasmon resonance of nanoparticles. Recent results are

Preface

xi

given on excitation of high energy levels of media under laser exposure to laser pulses of picosecond range of duration. Chapter 9 - Laser ablation in liquid, i.e. pulsed-laser induced liquid-solid interface reaction (PLIIR) has been developed to synthesize diamond nanocrystals. Chemical and physical mechanisms of the nanodiamonds synthesis upon PLIIR are addressed based on the nucleation thermodynamics and growth kinetics. The author’s studies showed that PLIIR could be expected to be a general route to synthesize the nanocrystals with the metastable phases.

In: Laser Ablation: Effects and Applications Editor: Sharon E. Black

ISBN: 978-1-61122-466-5 © 2011 Nova Science Publishers, Inc.

Chapter 1

DOUBLE-PULSE LASER ABLATION OF SOLID TARGETS IN AMBIENT GAS: MECHANISMS AND EFFECTS G. Cristoforetti1 and V. Palleschi2 1

National Institute of Optics, Research Area of National Research Council, Via G.Moruzzi, 1 – 56124 Pisa (ITALY) 2 Applied Laser Spectroscopy Laboratory, Institute of Chemistry of Organometallic Compounds, Research Area of National Research Council, Via G.Moruzzi, 1 – 56124 Pisa (ITALY)

ABSTRACT Laser Ablation (LA) is used in a widespread range of applications, among them it is employed as sampling procedure for the elementary chemical analysis of materials. With this aim, many analytical techniques makes use of LA - such as LA Ion Mobility Spectrometry, Resonant LA, LA-Atomic Fluorescence Spectrometry and LA-Microwave Induced Plasma-Atomic Emission Spectrometry – among them the most popular ones are probably the Laser-Ablation Inductively Coupled Plasma (LA-ICP) techniques and the Laser Induced Breakdown Spectroscopy (LIBS). In all these cases, it is desirable to attain the largest possible mass removal from the target in order to lower the Limit Of Detection (LOD) of the technique. Such intent is particularly true in the LIBS case, where LODs for solid samples are usually in the range of ppm or tens of ppm, which are often inadequate for many applications. One of the possible ways to overcome this problem is the use of two laser pulses, temporally separated by a suitable delay, for the laser ablation. In this scheme, the laser beams can be arranged in a collinear geometry, where both the beams are aligned normally to the target and are focused on its surface, or in an orthogonal geometry (preablation configuration), where the first pulse runs parallel to the target surface and is focused in the ambient gas in front of it, while the latter is aligned perpendicularly and ablates the target. In case of ns-laser ablation, in both these configurations, a substantial enhancement of mass removal and of its atomization with respect to the case where a single pulse with equal total energy has been observed, where these phenomena lead to

2

G. Cristoforetti and V. Palleschi an improvement of both the LODs and the reproducibility of measurements. Such experimental configurations lead also to a different thermodynamic and dynamic evolution of the plasma, which can be useful in case of LIBS analysis. Many works have been dedicated to Double Pulse (DP) Laser ablation, aimed to establish the optimal experimental conditions to be used in different applications and to understand the physical mechanisms, still not clear, leading to the observed mass removal enhancement [1]. The aim of the present chapter is presenting and resuming the ns-ns DP state of art, discussing the occurring physical processes. Experimental results of the authors, as well as of other scientists, will be shown and discussed to validate and run down hypotheses on the mechanisms involved. In particular, the interpretation of the lower plasma shielding, due to a rarefied ambient environment, experienced by the second laser pulse will be presented. The reduction of plasma shielding allows a larger part of the laser energy to reach the target surface, resulting in an enhancement of the mass removal. Besides, such an improved laser-matter coupling produces a stronger heating, which could lead the molten pool near the thermodynamic critical temperature and drive the onset of phase explosion mechanism. A summary of the effects produced in DP configuration by using short and ultrashort laser pulses is also mentioned, together with a brief discussion of the mechanisms involved.

1. INTRODUCTION In the last decade, many papers, especially aimed at improving LIBS and LA-ICP figures of merit, focussed their attention on Double Pulse Laser Ablation [1]. However, the pioneering works on the subject go back to the seventies, where effects similar to those recently investigated had been already observed and discussed. The double pulse approach was firstly studied by Piepmeier and Malmstadt [2,3]. In both works a multiple spikes irradiation over an aluminium target in air from a Q-switched ruby laser (λ = 694.3 nm, τ ≈ 50 ns), with a separation between the pulses of 500 ns, was performed. The observed enhancement of Al II and Al III lines was associated to the absorption of the second pulse by the plasma ignited by the first pulse, resulting in a further excitation of the aluminium species. Maher and Hall [4] studied the effects produced by focussing two CO2 laser pulses, separated by a suitable temporal delay, on the same spot on different targets. When the delay between the pulses was in the 30-70 μs window, they observed a pulse-target coupling stronger with respect to that produced by a single pulse, resulting in a higher impulse delivered onto the target surface. In order to understand the reasons of such effect, the focal spots were slightly moved, so that they did not overlap; also in that case, the results obtained were very similar to the ones observed with overlapping spots, suggesting that a possible thermal explanation of the observed phenomena, based on the pre-heating of the target surface, could be ruled out. High-speed photographs, interferometric observations, target damage evaluations and impulse measurements led the authors to conclude that the stronger laser-target coupling is produced by a pronounced reduction in local medium density caused by shocks expanding from the first laser pulse interaction resulting in a more difficult ignition

Double-Pulse Laser Ablation of Solid Targets in Ambient Gas

3

of Laser Supported Detonation (LSD) regime and then in a weaker shielding of the second laser pulse. Pershin and coworkers [5-7] in the eighties studied the effects produced by focussing two Q-switched Nd:YAG pulses of 20 ns-duration, separated by 25 μs, on an aluminium target and on laser glasses in air, observing an intensity enhancement of target element lines and, at the same time, a reduction of line intensity from atmospheric species with respect to the signal obtained with a single laser pulse. The authors suggested that by an appropriate spatial selection of plasma emission acquisition should then be possible to enhance the spectral line signal-to-background and improve the limits of detections (LODs) of the analysis. The formation of a plasma mirror and/or of self-focussing of the radiation in the plasma, which both could be possible causes of the observed effects, were excluded by the experimental results. Scattering and transmission coefficients were measured for the plasmas produced by the first and the second pulse, finding a much lower intensity of scattered light in the latter case [6]. Such results, together with the lower emission from atmospheric species [7], led the author to the conclusion that double-pulse effects are produced by a reduction in the gas density following the interaction with the first laser pulse, allowing the radiation of the second pulse to reach the heated surface of the target and generate a more efficient breakdown. An interesting variant of the method, consisting of DP ablation of samples immersed in a liquid environment, was introduced by Nyga and Neu [8] and developed by Pichahchy et al. [9]. In this case, the first laser pulse produces a cavitation bubble on the target surface which expands, reaching the maximum extension after about 400 μs, and then collapses again; the plasma produced inside the bubble is rapidly quenched and the emitted lines are considerably broadened by pressure effects. If a second pulse is focussed onto the target in the correspondence of the cavitation bubble, a plasma plume is ignited and expands into the bubble vapour environment, in a condition similar to that of plasmas generated in ambient gas, resulting in emission lines much narrower and in a strong line intensity enhancement, which can reach up to two orders of magnitude. Such method was proposed for the elementary analysis of samples submerged in water (e.g. for geological samples located under water). From the nineties up to now, different experimental configurations for the double and multiple pulses approach have been tested and a large amount of papers have been published on the topic, modifying the geometry of the laser pulses; the duration, energy and wavelength of the pulses, including combinations between femtosecond, picosecond and nanosecond lasers, and the delay between them; the environment where the ablation is ignited and finally the target composition. Many of such works were devoted to a better understanding of the mechanisms underlying the DP effects, by means of a large variety of techniques for plasma diagnostics and for the examination of laser crater on the target, including spectroscopic analysis of plasma emission, direct or shadowgraphic imaging of the plume, interferometric analysis, microscopic target analysis, etc. Many other works focussed their attention on the possible applications of DP benefits, and most of them pointed to the improvement of reproducibility and sensitivity of LIBS and LA-ICP techniques. Such works were devoted mainly to the description of DP effects and to the determination of the most suitable experimental conditions and apparatus for their application. However, other applications were proposed, as for example the production of

4

G. Cristoforetti and V. Palleschi

nanoparticles by means of DP laser ablation of metal targets in liquid environment. Burakov et al. [10] showed that DP-LA provides a more effective ablation, and then a larger amount of nanoparticles with respect to SP-LA. Moreover, the mean size and the stability of nanoparticles could be controlled by a proper selection of the temporal delay between the laser pulses, which affects the decay time of the plasma plume and then the temporal window where the nucleation and growth of nanocrystals occur. Basically, three different laser beam geometries have been up to now investigated in the literature and will be considered here, despite other, more exotic configurations, have been also tested [11]. Most research efforts have been focused on the collinear configuration, which is certainly the easiest to arrange experimentally. In this configurations both beams are aligned normally to the target and are focused on its surface (Figure 1a). However, a large amount of works have been published dealing with an orthogonal arrangement of the beams; here, the first pulse (pre-ablation scheme) (Figure 1b) or the second one (reheating scheme) (Figure 1c) is directed parallel to the target surface and focused in the atmosphere in front of it, while the other is perpendicular and ablates the target. All such configurations, when utilized with a proper choice of experimental conditions, may result in an enhancement of plasma emission, which can be fruitfully used for the improvement of LIBS technique figures of merit. However, while the first two arrangements, with appropriate choice of experimental parameters, produce also a substantial increment of the mass ablated, the last one turns out only in a re-heating of the plasma produced by the absorption of the first laser pulse, so that, strictly speaking, it can not be classified as DP-LA method. Nevertheless, also the results obtained by such configuration will be rapidly summarized in the following for the completeness of the subject. Another important criterion of classification between the experimental configurations is the duration of the laser pulses, since the mechanisms occurring during the DP-LA are noticeably different depending on the pulse length. In most of the works, two nanoseconds pulses are used, whose utilization is certainly more accessible for portable instruments and stand-off applications; however, also combinations of nanosecond with ultrashort pulses have been tested [12,13]. A summary of the effects produced by DP-LA in the different experimental configurations and a critical review of the mechanisms proposed in the corresponding cases are reported in the following sections. Particular emphasis will be given to the ‘lower shielding’ mechanism, which is in our opinion the main reason of signal and mass removal enhancement in case of nanosecond-nanosecond pulses. The attention will be focussed mainly on the nanosecond-nanosecond laser ablation, which appears to be more accessible for applications, and whose mechanisms are noticeably different from those occurring in femtosecond and picosend DP-LA; however, a brief description of results, mechanisms and references related to combinations of laser pulses with different duration will also be given.


5

Figure 1. experimental geometries used in DP experiments

Finally, the present chapter is focussed to the case of DP-LA of solid targets, mainly metals, in ambient gas, although the technique has been successfully applied to solid targets immersed in a liquid environment [14,15], with important potential applications going from the target sampling and analysis to the synthesis of nanoparticles of controllable size distribution. DP-LA of liquids, gases and aerosols is not treated in the present chapter.

2. NANOSECOND-NANOSECOND PULSES COMBINATION: EFFECTS OF DP-LA a) Collinear Beams Configuration The collinear configuration, where both laser beams are aligned perpendicularly to the target surface, has been widely tested and studied and, from a practical point of view, is the most suitable for standoff applications [16,17]. Some works published in literature utilize also slightly different configurations, where the laser beams hit the target at non-normal angles of incidence [11]; however, since both the laser pulses produce the ablation of the sample and the physical processes involved are similar to those occurring in the collinear perpendicular configuration, such cases are included in the present section. The paragraph is subdivided in four parts, dealing with the effects of collinear DP-LA on the plasma emission, on the plasma dynamics, on the ablation mechanisms and on the relationship between ambient gas conditions and DP effects.

Effects on plasma emission All the works dealing with the spectroscopic analysis of plasmas induced by a ns-ns laser pulses combination evidence a large enhancement, depending on the matrix of the target, of the line intensities produced both by target atoms and ions, which can reach two orders of magnitude [18-23]. At the opposite, the intensity of spectral lines emitted by atoms and ions deriving from ambient gas (e.g. N and O species in ambient air) is markedly reduced. An example of plasma spectra in the range 250-400 nm obtained in SP and in collinear DP configuration by a Fe-Mn alloy is shown in Figure 2, taken from Ref.[25]; all the lines in the spectral range shown in the figure belong to Fe and Mn atomic and ionic species and exhibit an evident enhancement of 1-2 orders of magnitude.

6


It is worth to emphasize, however, that the signal enhancement found in collinear DP-LA is dependent on the detector field of view [24], that can be easily explained by the different plasma volume and dynamics obtained in SP and DP configuration. It is also important to note that, usually, the enhancement is obtained by calculating the ratio of the line intensities observed in the same temporal acquisition window both in SP and in DP configurations; clearly, the value so-calculated depends strongly on the different dynamical and thermodynamic evolution of the SP and DP plumes which can be very different, so that such method is, to some extent, arbitrary and misleading. This should be taken into account for example when the comparison of plasma temperature and electron density values in the two cases is done. The observed enhancement results in a marked improvement of the LIBS LODs, which can reach a few ppm or lower depending on the element analysed and on the matrix where it is embedded. Sturm et al. [26] found detection limits below 10 μg g-1 for C, P, S, Al, Cr, Cu, Mn and Mo in steel samples. Piscitelli et al. [23] found an improvement of LIBS sensitivity for Pb embedded in several metal targets of about an order of magnitude. In a previous work [27], we calculated the limits of detection for several elements in aluminium and steel alloys using both the single and the collinear double pulse configurations of laser-induced breakdown spectroscopy. We used a dual-pulse Nd:YAG laser (λ=1064 nm, Δτ=12 ns), where the energy per pulse was set to 30 mJ (~3 GW cm-2) for the ablation, and an echelle spectrometer coupled to an intensified CCD camera (λ/Δλ=5000) for the spectral acquisition. Calibration plots were constructed for Mg, Al, Si, Ti, Cr, Mn, Fe, Ni, and Cu using a set of certified aluminium alloy samples and a set of certified steel samples. The investigation included the optimization of the experimental conditions, where the temporal separation between the pulses, the delay time and the gate of acquisition were varied, to furnish the best signal-to noise ratio in both geometries. The final LODs are reported in Table 1, evidencing that the improvement obtained in DP configuration depends on the matrix of the target, being much higher for aluminium alloys than for steel alloys.

Figure 2. LIBS spectra obtained from the SP ablation (black line) and the collinear DP ablation (grey line) of a Fe-Mn alloy target. The figure has been taken from Ref.[25]


7

Table 1. Comparison of LIBS detection limits obtained in SP and DP collinear geometries for aluminium and steel alloys Element Aluminium alloys Mg Ti Cr Mn Fe Ni Cu Steel alloys Al Si Ti Cr Mn Ni Cu

Wavelength (Å) utilized

Single-pulse LOD

Double-pulse LOD

2852.13 3349.41 4254.33 2949.20 3719.93 3414.76 3247.54

30 ppm 100 ppm 100 ppm 0.1% 400 ppm 600 ppm 150 ppm

4 ppm 10 ppm 10 ppm 90 ppm 50 ppm 100 ppm 80 ppm

3961.52 2881.58 3088.02 4254.33 4823.52 3414.76 3247.54



Figure 3. ranges of enhancements RI1 and RI2 for a) ionic lines and b) neutral lines observed in the spectral range 200–900 nm at an inter-pulse delay of 1 μs. RI1 and RI2 indicate the enhancement values obtained in DP (pulse energies 60+60 mJ) with respect to the SP configuration with pulse energy of 60 mJ and of 120 mJ (corresponding to a zero interpulse delay), respectively. Taken from Ref. [28]

8


In a subsequent work [28], where the same apparatus described above (but an energy per pulse of 60 mJ) was used, we studied more in detail the effect of the matrix composition on the emission enhancement observed in DP collinear LIBS for several pure metal targets (Al, Au, Co, Cu, Fe, Mn, Mo, Ni, Pb, Pt, Si and W). In Figure 3 the range of enhancement of line intensities for the different targets are reported; RI1 and RI2 indicate the enhancement values obtained in DP (pulse energies 60+60 mJ) with respect to the SP configuration with pulse energy of 60 mJ and of 120 mJ (corresponding to a zero interpulse delay), respectively. The measurement of the emission enhancement for neutral and ionic lines of all the samples showed a wide range of results, going from the lowest observed for Pb, Ni and Mn to the highest values obtained for Cu, Al and Au. It is then clear that the matrix of the target plays an important role in determining the effects produced by DP configuration, as will be discussed successively. A large amount of papers have been published to evidence in detail the dependence of line intensity enhancement on many parameters – e.g. the interpulse delay, the energy of the pulses, the ionization stage of the emitting species, the energy of the upper level of the transition, the properties of the target and of the environment gas, etc. It is clear that line intensity enhancement is affected by two factors, which are the increase of ablated mass in the plume – related to the mechanisms of mass removal from the target, and thus to the material and ambient gas properties – and the variation of thermodynamic parameters of the plasma, e.g. temperature and electron density, related to the ignition process of the plasma and to its dynamical evolution. In fact, assuming the Local Thermal Equilibrium (LTE) of the plasmas, the intensity enhancement R of a generic line in DP configuration with respect to single pulse can be written:

R=

N DP n DP Z (TSP ) 1 1 exp(− E k ( )) − N SP n SP Z (TDP ) k B TDP k B TSP

(1)

where N is the absolute total number of atoms of the chemical element considered, n is the fraction of these atoms corresponding to the emitting species (atomic or ionic), Z is the partition function, Ek is the upper energy level of the transition and kB is the Boltzmann constant. In turn, the ratio n DP n SP can be expressed in terms of the temperature and electron density values via the Saha equation. So, the variation of experimental parameters results in a variation of the emission enhancement via the increase of the ablated mass (NDP/NSP) or via the enhancement of plasma temperature (terms nDP/nSP and exp(-Ek(1/kBTDP1/kBTSP)) ). A collection of the main results, dealing with the variation of experimental parameters, which can be useful to understand the DP effects and causes, is reported in the following. The emission enhancement depends strongly on the separation between the laser pulses, as shown in Figure 4 for gold line intensities (λ=1064 nm, τ=12 ns), where the maximum value is obtained for an interpulse delay going from hundreds of nanoseconds up to a few microseconds, depending on the other experimental parameters and on the ionization state of the emitting species. At separation delays shorter than ~100 ns a depressive effect on the LIBS signal can be obtained, mainly due to the laser shielding of the second laser pulse by the plasma formed by the first pulse, as clearly shown by Mao et al. [29] (Si target, λ= 1064 nm,


9

Line intensity enhancement

τ = 4 ns). The enhancement of plasma emission persists up to interpulse delays of tens of microseconds, often being still significant at 80-100 μs. In general, the optimal interpulse delay is larger for ionic than for atomic lines, as visible in Figure 4 where the largest enhancement for the Au I and Au II lines is obtained for interpulse delays of 1-2 μs and 4 μs, respectively. Just to make some examples, in a previous work [30] (brass target, λ=1064 nm τ=10 ns), we found an optimum interpulse delay of about 0.7 μs for neutral copper lines and of approximately 2 μs for ionic copper lines. In a successive work [31], where an aluminium target was used, we found the largest enhancement for interpulse delays in the range of 1-4 μs, both from neutral and ionic lines. St-Onge et al. [18,20], operating on an aluminium target, found that the optimum delay is less than 1 μs for Al I lines and between 2 and 5 μs for Al II lines.

Au I 312.2 Au II 291.3

25

20

15

10

5

0 0

10

20

30

40

50

interpulse delay (μs) Figure 4. Dependence of line intensity enhancement on the separation between laser pulses for a gold target

Gautier et al. [32] (Al target, λ=532 nm) found that the optimum interpulse delay Δτ depends on the excitation energy of the transition, where for low-energy atomic lines the highest improvement is obtained for Δτ = 0.2 μs, while for ionic lines and atomic lines with excitation energy higher than 6 eV the largest emission enhancement is obtained for Δτ higher than 1 μs. Other works evidenced that, in most of the cases, the emission enhancement is higher for ionic than for atomic lines, as visible in Figure 3, and for high excitation energy than for low excitation energy lines. Such features are well evident in Figure 5, taken from Ref.[31], where several aluminium atomic and ionic lines were observed and their enhancement was plotted versus the energy of the transition upper level.

10


By looking at Eq.(1), it is evident that the increasing trend of emission enhancement with the excitation energy of the upper level of the transition is due to an increase of plasma temperature. In Ref.[31], we calculated the plasma temperature in both SP and DP-LA plumes, finding a slight increase of the order of 10% in the latter case; it was then verified that such increment is compatible with the slope of the points plotted in Figure 5. It was also showed that the absolute values of emission enhancement can not be only attributable to such slight temperature increase but must be caused by a concomitant growth of the ablated mass by a factor of ~7, as will be discussed later. An increase of plasma temperature was also found in other works, i.e. by Sattmann et al. [22] (steel target, λ=1064 nm, τ = 20 ns) and De Giacomo et al. [33] (Ti target, λ1= 532 nm,λ2 = 1064 nm, τ = 8 ns). In Ref.[28] (acquisition delay = acquisition gate= 1 μs) we found an increase of plasma temperature in DP collinear geometry with respect to SP with half-energy for most of the targets analysed up to 1200K, where such enhancement was larger for targets showing a higher emission enhancement; at the opposite, no evident growth of plasma temperature with respect to SP with equivalent total energy was found. Other works evidenced no substantial change or even a slight decrease of plasma temperature [21,29]. It is then clear that the main contribution of the observed emission enhancement is not caused by the higher temperature of the plasma.

Figure 5. Emission enhancement obtained in DP collinear configuration for Al I at 265.3, 305.0, 308.2 nm and Al II at 281.6, 385.6, 466.3 nm lines, for an interpulse delay time of 4 μs. Taken from Ref.[31]

In Ref.[28] (acquisition delay = acquisition gate= 1 μs), we calculated the plasma electron density in DP and in SP configuration for a large quantity of metal targets, showing in all the cases a marked decrease in DP with respect to SP configuration at equivalent total


11

energy; on the other hand, the electron density found in SP at half energy and DP cases are comparable. Colao et al. [19] (Al target, λ=1064 nm, τ = 8 ns) and St. Onge et al. [20] (Al target, λ=1064 nm, τ = 6-12 ns) demonstrated that the electron density in plasmas induced by DPLA is consistently lower at early times of plasma evolution with respect to SP-LA at equivalent total energy, but exhibits a slower decay with time, so that the values in the two configurations approach, or electron density in DP plasma even becomes higher, at late times (e.g. 700 ns in Ref.[20] and after 1.2 μs in Ref. [19] after plasma ignition). The lower electron density found in DP-LA at short acquisition times can explain the largest emission enhancement observed for ionic lines with respect to neutral lines; in fact, if we assume LTE and consider the Saha-Eggert equation, a lower electron density results in a higher ionization degree of plasma species.

Plasma dynamics The expansion dynamics and the consequent morphology of plasmas induced in collinear DP configuration are noticeably different from those of plasmas produced by a single laser pulse. In Figure 6, time-resolved images (acquisition delay = 700 ns, gate = 400 ns) of plasmas from a brass target in air (λ=1064 nm, τ=12 ns), spectrally filtered around the Zn I @ 520 nm line, induced by a single pulse, two coincident pulses, and two delayed pulses (Δτ = 10 μs) and acquired by an Intensified CCD camera, are shown. Both from the experiments performed at atmospheric pressure and at 100 torr pressure, it is evident that the dimensions of plasmas induced by the DP configuration are much larger than those of plasmas produced by a single pulse and even by two coincident pulses. Moreover, the DP plasma tends to detach from the target much more than SP plasmas, denoting a very different expansion dynamic in the two cases. Two sequences of frames, describing the evolution of the plasma from a brass target in air produced by a single laser pulse and by two laser pulses delayed by 2 μs, are shown in Figure 7, taken from Ref.[34] (λ=1064 nm, τ=12 ns). The images are obtained by shadowgraphic technique, using a white flash light to back-illuminate the region of the plume. The exposure time of the single frame is 100 ns and the frames are separated by 500 ns. In SP-LA, the generation, evolution and decay of the plasma at the surface of the sample, together with the formation of a shock wave propagating in the surrounding atmosphere, are visible. According to Figure 6, the plasma plume is near the surface of the target during all its life. The shadowgrams of the plasma obtained in DP mode reveal that the second laser pulse, coming 2 μs after the first pulse, initiates a new plasma at the sample surface (frame 4), which very rapidly propagates, moving away from the target and almost fills the region encompassed by the shock wave front formed by the first pulse, resulting in a plume wider than in SP configuration. Rapid expansion is caused by the rarefied ambient gas, formed by the first laser pulse, where DP plasmas are generated and expand. Gas rarefaction is evidenced also by the failure of detecting the shock wave formed by the second laser pulse, because of the lower jump in density at the shock front [34].

12


Figure 6. Time-resolved images of plasmas obtained from a brass target by a single pulse (SP), two coincident pulses (CP) and two delayed pulses (DP) obtained at atmospheric (a-c) and 100 torr (d-f) pressure. The emission is spectrally filtered around the Zn I @ 520 nm line. Delay time of acquisition is 700 ns and gate is 400 ns

Figure 7. Shadowgrams of the laser induced plasmas in single pulse (on the left) and double pulse configuration (on the right). In both sequences, the first photograph (left bottom) has been taken at a delay time of ~500 ns with respect to the first laser pulse, while the temporal delay between photographs is 500 ns. Taken from Ref.[34]


13

A detailed study on the different dynamics of plasmas induced in SP and DP configuration was presented by De Giacomo et al. [33] (Ti target, λ1= 532 nm, λ2 = 1064 nm). In their experimental work (sided by a LIP expansion model), it was shown that the SP plasma expands up to ~ 1 μs and then stops, due to the counterpressure of the cold unperturbed ambient gas, at a distance of ~ 1.1 mm; differently, the DP plasma rapidly expands in the hot rarefied gas up to ~ 400 ns and then stops at a distance of about 1.7 mm from the target. De Giacomo et al. stress that the DP plasma expansion during the early hundreds of nanoseconds resembles a free expansion; however, the expansion inside a hot environment and the confinement produced by the shock wave formed after the first laser ablation, lead also to a smaller loss of plasma energy and then to a slower decay time of plasma temperature. Similar results and conclusions were also presented by Noll et al.[35], using a high-speed electro-optic camera to observe the spatial and temporal development of the plasma morphology and a Mach–Zehnder interferometer to detect the spatio-temporal changes of the refractive index of the plasma. They also showed that the second laser pulse interacts predominantly with the sample surface while the laser absorption by the residual plasma causing its re-heating is marginal. So, in conclusion, both the wider volume of plasma emission and the longer plasma lifetime obtained in DP configuration produce a situation more suitable for LIBS analysis than SP geometry.

Mass removal mechanisms, atomized ablated mass and effects of the matrix target Many works [18,29,36-39] report that DP collinear laser ablation produces deeper craters with respect to the SP ablation, where the ablation rate can increase from 2 to 20-fold. It was also observed that the crater rims are lower in DP case or, however, the ratio of volumes occupied by the rims (Volumeup) and that of the hole (Volumedown) is noticeably smaller than in SP. Caneve et al. [36] (copper-based alloy target, λ=1064 nm, τ = 8 ns) found ablation rates in the range 0.08-0.11 μm/shot and 1.78-3.2 μm/shot, for single and double pulse schemes respectively; moreover, the presence of rims is well visible in the former scheme and negligible in the latter. 3D reconstructions and 2D profiles of craters induced on an aluminium target in both configurations (λ=1064 nm, τ=12 ns, Δτ= 4 μs, pulses energy = 78 mJ), obtained by video-confocal microscopy and taken from Ref.[31], are reported in Figure 8. In such a paper, we reported an increase of crater volume (measured as the volume of the drilled hole) of 4-6 times in DP-LA, and a ratio Volumeup/Volumedown decreasing from the range 1.8-2.5 in SP-LA to 0.8-1.1 in DP-LA. Here, it is necessary to bear in mind that values larger than 1 of the ratio Volumeup/Volumedown are possible because the density of molten and re-solidified material can be lower than that of the target. Such observations demonstrate that DP-LA improves the laser-target coupling, reducing undesired thermal effects and phenomena produced by plasma-target interaction, such as melt displacement and splashing of the molten pool.

14


Figure 8. 3D reconstructions and profiles of craters produced in SP (on the left) and in DP configuration (on the right). Taken from Figure [31]

The increase of mass removal is certainly one of the major contributions to the LIBS signal emission and one of the reasons for which DP-LA is investigated for LA-ICP application. However, the increase of the ablation rate and the reduction of thermal effects deserved attention also in the field of micro-machining of materials [39,40]. Usually, for such applications, thermal effects and re-deposition of debris on the surface are avoided by using ultrashort laser pulses, which are able to produce high-quality large aspect-ratio holes; however, fs laser pulses have several drawbacks, as the low ablation rate, the need for reduced pressure to avoid air breakdown due to the high irradiance and the high cost of instrumentation, which limited their commercial exploitation. Forsman et al.[40] (steel and Al targets, λ=532 nm) and Wang et al. [39] (steel target, λ=1047 nm, τ = 21 ns) observed significant enhancements of the drilling rate (3-10 times in Ref.[40] and more than one order of magnitude in Ref.[39] depending on the experimental parameters) by using markedly smaller energy (fractions of mJ), tighter focussing (tens of μm) and smaller interpulse delays (tens of nanoseconds) with respect to the values usually utilized in LIBS experiments. Wang et al. showed that the drilling enhancement strongly increases with the thickness of the sample, since SP drilling rate tends to saturate at depths larger than 400 μm while DP performance remains stable with depth.


15

For applications as LIBS or LA-ICP, where quantifying the enhancement of atomized ablated mass in the plume rather than the drilling rate is important, the analysis of craters depth and morphology is not directly informative about the effectiveness of the laser ablation process. In fact, crater analysis does not provide the measure of the mass atomized in the plasma because the volume of the laser induced crater is often comparable to that of the rim around the hole, so that the calculation of the removed mass as the difference between such volumes leads to large uncertainties. Furthermore, even a precise measure of the removed mass would not be able to discriminate between the mass atomized in the plasma and that ejected (and spectroscopically lost) in particles or large clusters. A more direct measurement of the ablated mass could be obtained by weighing the target before and after the ablation process, even if also this method does not discriminate molten droplets and clusters; however, such approach is hindered by the low effective ablation rate, which can be much lower than a μg per pulse, so that it implies the weighing of the sample after a large number of laser shots, as in Ref. [41]. Because of these disadvantages, in Ref.[28,31,42-44] we estimated the atomized mass in the plasma, scaled by an arbitrary factor, directly from the analysis of emission spectra, even if this approach is strongly affected by the uncertainties in the determination on the thermodynamic parameters and by the geometry of signal collection in the experimental setup. In Figure 9, where the same notation of Figure 3 is used, the enhancement of atomized ablated mass for several metal targets is shown. By a rapid comparison with Figure 3, it is evident that there is a strong relationship between the enhancements of LIBS signal and of ablated mass, suggesting that the main contribution of DP-LA benefits in LIBS is produced by the increase of mass in the plume, and, only in the second place, to the increase of plasma temperature. In Ref.[31], we calculated the contribution to lines intensity enhancement of both the variations of temperature and atomized ablated mass. We showed that the calculated small increment of temperature (~10%) resulted in a slightly higher population of higher energy levels and a slightly higher ionization, producing a negligible variation of the intensity of the neutral lines in the range 0.94-1.2 and an increase of the ionized lines in the range 2.3-3; the remaining enhancement, which was by a factor of ~7, was due the increase of mass into the plume. By comparing the measured crater enhancement with the enhancement of the ablated mass in the plume (measured via spectroscopic analysis or via ICP analysis), it is evident that the latter is usually much higher; even if such comparison is incorrect, since the measurements of crater dimensions can not be used to estimate the mass removed from the target (see above), such observation led some authors to infer that DP-LA produces also a higher atomization of the ablated mass and a finer aerosol. Such hypothesis seems also confirmed by the imaging of the plume (e.g. see Ref. [45]). Despite the evident dependence of emission and ablated mass enhancement on the matrix of the target (see Figures 3 and 9), very few works were devoted to correlate the effects of DP-LA with the composition and properties of the target. In a detailed work [21], Gautier et al. analysed the effectiveness of the DP LIBS for different materials (aluminium, synthetic glass, steel, rocks) separating the contribution of temperature and ablated mass increase. Their results suggested that the intensity enhancement tends to be higher for the matrices originating a cooler SP plasma.

16


Figure 9. Calculated enhancement of ablated atomized mass RM1 and RM2 for all the targets. The uncertainty is ~25–30%. RM1 and RM2 indicate the enhancement values obtained in DP (pulse energies 60+60 mJ) with respect to the SP configuration with pulse energy of 60 mJ and of 120 mJ (corresponding to a zero interpulse delay), respectively. Taken from Ref. [28]

30

Au Al

ablated mass 1 enhancement RM

25 Pt

20 Si

15 10 5

Cu

W Mo Fe Co NiPb

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 2

-1

thermal diffusivity at melting point (cm s )

Figure 10. Ablated mass enhancement in DP LIBS (pulse energies = 60 mJ + 60 mJ) with respect to SP configuration (energy = 60 mJ) vs. thermal diffusivity at melting point. Taken from Ref.[28]

In Ref.[28], the effect of DP-LA on several metals and semiconductors characterized by different thermal, electronic and optical properties was studied. Other materials such as insulators and polymers were not considered because of their different ablation mechanism (volumetric heating) with respect to metals (surface heating). In particular, we made an attempt to correlate the increase of ablated mass, as reported in Figure 3, with the melting point and heat, the boiling point and heat, the reflectivity and the ionization energy of the metal. However, no evident correlation was found. At the opposite, a correlation was observed between the ablated atomized mass enhancement and the thermal diffusivity of the metal, as shown in Figure 10; in order to explain such correlation, we proposed a simple picture that will be described in the following sections.


17

Dependence on ambient gas pressure As final paragraph, we report some results concerning the influence of the ambient gas on the DP-LA effects previously described, i.e. the plasma emission, the plume dynamics and the mass removal. Some DP-LA studies were conducted in ablation chambers and performed at ambient gas composition different from air, such as nitrogen, argon, helium or mixtures [45-47]. Some of such experiments were motivated by the application of DP-LA for ICP analysis [45]; some others, where gas was flushing the interaction region, were aimed to remove the particulate produced by precedent bursts [46]. The results obtained suggest that the gas density (at constant gas pressure) strongly affects the drilling rate of the ablation process, both in SP and in DP configurations, and that the magnitude of DP enhancement decreases with increasing the density of ambient gas. Here, however, we will focus our attention on the effects associated to the pressure of the ambient gas, which are stronger and more significant for the modelling of DP-LA process. In a previous paper [30], we studied the effect of DP configuration on plasma emission, by performing laser ablation at different air pressures, ranging from 0.1 Torr to atmospheric conditions. Two Nd:YAG laser pulses (λ=1064 nm, τ=12 ns) were separated by a time delay ranging from 0 (coincident pulses) up to 8 μs and focussed on the surface of a brass sample. Neutral and ionized lines originated both by species deriving from the target and from the air environment were analysed. The results, shown in Figure 11, evidenced a different behaviour of copper species emission versus air pressure value in single- and double-pulse- operation modes. The line intensity measured in SP case shows a maximum emission around 100 Torr pressure followed by a significant reduction at higher pressures. This effect can be explained, as discussed in literature, in terms of the laser shielding of the target operated by the plasma, which is strongly affected by the buffer gas. On the other hand, in DP scheme the emission signal from copper species do not decrease at higher pressures, so that an enhancement with respect to the SP case is present for pressures higher than 100 Torr. It is also noticeable the reduction of Cu emission obtained in DP configuration at pressures lower than 100 Torr. A similar behaviour, was also observed for other lines emitted by atoms originated from the sample (e.g., Zn I lines). The analysis of the O I 777.3 nm line, shown in Figure 12, reveals a completely different behaviour with respect to that of Cu I, Zn I, and Cu II lines. The signal obtained by using a single pulse or two coincident pulses (Δτ=0) does not reach a maximum, but, on the contrary, shows a monotone increasing trend with increasing the air pressure in the chamber up to 300 Torr followed by a slight saturation. Such results are easily explainable by considering that the oxygen atoms originate from the environment, so that their concentration in the plasma is not affected by the laser shielding effect. Therefore, the increasing trend of the emission of oxygen atoms versus pressure is due to the combined effect of the increase of their concentration and of the raise of plasma temperature produced by the laser-shielding effect. Similar results were obtained by Peter and Noll [47], which studied the ablation of material and the plasma emission induced by a single pulse and two pulses (λ = 1064 nm, SP 1x80 mJ, DP 2x40 mJ, Δτ = 6 μs, τ = 20-40 ns) on iron samples at different argon pressures. The measured ablation rate confirms the spectroscopic trends shown in Figure 11, i.e. the DP mass removal is much more efficient than SP one at pressures higher than 100 mbar (DP

18


ablation rate is larger by a factor 4 at 1 bar) but the enhancement vanishes at pressures lower than such a value. Wang et al. [39], operating on a steel target at quite different experimental conditions (laser energies in the order of the mJ, λ = 1047 nm, Δτ = 52 ns, τ = 21 ns), also investigated the effectiveness of drilling in SP and DP modes at different air pressures, finding that the SP ablation rate at the pressure of 8 mbar is close to that produced in DP configuration in the open air.

Figure 11. On the left, Cu I 521.5 nm line intensity versus the air pressure obtained by using a single pulse (triangles), two coincident pulses (squares), and two laser pulses separated by 700 ns (circles). The acquisition windows are delayed by 2 μs with respect to the single laser pulse and to the second pulse. On the right, enhancement factor of Cu I 521.5 nm line expressed as the ratio of emission signal obtained in double pulse configuration (Δτ=700 ns) over that obtained with two simultaneous pulses. Taken from Ref.[30]

Figure 12. O I 777.3 nm line intensity versus the air pressure obtained by using a single pulse (triangles), two coincident pulses (squares), and two laser pulses separated by 700 ns (circles). The acquisition window is delayed by 700 ns with respect to the single pulse and to the second pulse. Taken from Ref. [30]

Such results suggest that the effects produced by DP-LA are strongly correlated with the environmental gas density in which the plume forms and expands. SP-LA at atmospheric pressure is affected by a strong laser shielding, i.e. a large part of the laser energy is absorbed before reaching the target, resulting in less ablated mass and a proportionally lower emission;


19

a stronger laser-target coupling in SP-LA is obtained at reduced pressure, where the optimal situation is achieved at around 100 Torr. On the contrary, in DP case, the second laser pulse ablation occurs in a rarefied medium, where the laser shielding is reduced and consequently the mass removed and the plasma emission are higher. Results slightly contradicting this interpretation were obtained by Krstulovic et al. [48,49] (Ti target, λ = 1064 nm, τ = 5 ns), which showed a 2/3-fold enhancement of crater volume and particle number density in the plasma in collinear DP-LA in vacuum (where evidently the rarefaction effect of the first laser pulse is not present). Such results are observed for interpulse delays shorter than those obtained in DP-LA at atmospheric conditions, where the optimal delay Δτmax for increasing crater volume and plasma number density were 370 ns and 1 μs, respectively. The authors suggest that such effects are caused by a lowering of the target ablation threshold produced by the heating produced first laser pulse. These results thus suggest that the pre-heating of the target, causing a modification of its optical properties (reflectivity, absorption) and a decrease of its ablation threshold, might have a role, though maybe not dominant, also in the DP-LA at atmospheric pressure. A more accurate picture of the processes occurring in the collinear configuration will be given in next sections, since we believe the discussion will be also useful for the understanding of the pre-ablation orthogonal DP-LA configuration.

b) Orthogonal Beams Pre-Ablation Configuration In the orthogonal pre-ablation (or pre-spark) configuration (Figure 1b) the first laser pulse is sent parallel to the target surface and focussed in front of it, producing a plasma, while the second pulse passes through it and ablates the target. The plasma produced by the first pulse, thus, is just composed by species deriving from the ambient gas and only the second pulse removes mass from the target. In this way, the role of the first pulse is only that of preparing the environmental conditions in which the successive ablation is more effective, because of a stronger laser-target coupling. From a practical point of view, such configuration is probably less viable than the collinear one because of the higher complexity of the apparatus. However, it is more suitable for understanding the processes occurring in the DP-LA, due to the clear separation between the roles of the two pulses. From the following discussion it will become clear that the effects produced by this configuration are similar to the ones shown in the previous paragraph; this suggests that the primary cause of DP-LA effects in the two cases is the same, as will be discussed in section 3. The pre-ablation DP scheme was proposed by the Angel’s group [50-53], who used two Q-switched Nd:YAG lasers (λ = 1064 nm, τ = 7 ns) both for producing the pre-spark (pulse energy = 210 mJ) and the ablation (pulse energy = 100 mJ). The first pulse was focussed 1-2 mm above the target and did not produce any appreciable ablation from the surface. Such configuration led to LIBS signal enhancement both in the case of metal target (11-fold and 33-fold for Cu and Pb, respectively [50], 16-fold for Zn [53]) and of non-conducting targets (from 11-fold to 20-fold for Ti, Al and Fe in glass [51]). The maximum enhancement was obtained for an interpulse delay of ~2.5 μs; however, the enhancement is strong for Δτ values up to ~100 μs and persists even at ~300 μs. An increase of plasma temperature up to ~5000 K was observed as well as an increase of crater volume up to ~30 times with respect to SP-LIBS

20


(in this case the comparison refers to the case where only the second pulse operates). Both these effects show a clear dependence on the interpulse delay similar to that obtained for signal enhancement; however, the authors suggest that the primary cause of line emission enhancement is the raise of ablated mass rather than the temperature increase [52]. The authors also noted that the largest enhancement was observed for lines originating from transitions departing from high energy levels; evidently, such effect is produced by the increase of plasma temperature from SP to DP configuration. Similar results were obtained by Gautier et al. [54] who performed DP pre-ablation LA on an Al target, using two Q-switched Nd:YAG lasers (λ = 1064 nm, τ = 9 ns for producing the pre-spark and λ = 532 nm, τ = 9 ns for the ablation). The largest line enhancements were obtained in an interpulse range going from 10 to 35 μs and for lines originating from high energy levels. Lindner et al. [55] (Cu-Zn target, λ = 1064 nm, τ = 8 ns) measured the size distribution and the composition of the particles generated in pre-ablation DP experiments performed in atmospheric argon. While in SP scheme the proportion of large particles (> 0.1 μm) was predominant, ultrafine aerosols particles (< 50 nm) were generated in DP configuration representing practically the total mass impacted. Since ultrafine particles form through vapour-phase condensation while large clusters points to a fragmentary mass removal mechanism, the authors conclude that the DP scheme provides a better atomization, close to 100%, of the ablated matter. According to the authors, thus, the signal emission enhancement is produced by the increase of both the ablated mass and its atomization. In the pre-ablation configuration, the value of the distance d of the pre-spark from the target surface can be adjusted, which constitutes an additional experimental parameter to be optimized, with respect to the collinear scheme. The influence of the d-value was studied by our group in a previous paper [56], where the effect of its variation in a range between 0.1 and 4.2 mm together with that of the variation of the interpulse delay, were investigated by spectroscopic and shadowgraphic approaches. The importance of studying the influence of the d-value resides in the information on the DP-LA mechanisms which can be disclosed; in particular, in the hypothesis that DP effects are produced by atmospheric effects, the effects in the pre-ablation scheme should reduce to those obtained in the collinear case when the dvalue approaches zero. In the work cited above, the emission spectra of the air spark could not evidence a detectable features from target species even in the case of d = 0.1 mm, indicating that the target ablation was negligible for all the values of the parameter d. The laser sources were two Nd:YAG lasers, each one emitting a laser pulse in 8 ns FWHM at the wavelength of 1064 nm. The energies of the first and second laser pulses were adjusted to 140 and 240 mJ, respectively. A brass target with ~60% Cu, ~ 40% Zn was used. Spectroscopic analysis of plasma emission reveals that a significant signal enhancement for the neutral and ionic lines is observed for distances d lower than 1 mm. This behaviour is highlighted by plotting the maximum enhancement (obtained at different interpulse delay values) vs. distance d, as shown in Figure 13 for neutral and ionic Zn lines, where a sharp reduction occurs around the value d = 1.0 mm.


21

Figure 13. Maximum signal enhancement of Zn I 472.2 nm and of Zn II 255.8 nm vs. the distance d between the air spark and the target surface. Taken from Ref.[56].

Figure 14. Intensity enhancement of Zn II 255.8 nm line vs. the interpulse delay time obtained at different values of the distance d. Taken from Ref.[56]

Other interesting information could be drawn from the behaviour of the signal enhancement with the interpulse delay time. It is evident from Figure 14 that the signal enhancement begins to increase already at a delay time of 100 ns for d=0.1 and 0.4 mm while

22


for increasing distances the signal enhancement occurs at progressively higher interpulse delay times. Moreover, for the higher values of the distance d, a reduction of the signal is visible (DP/SP signal ~0.35–0.6 for the Zn I 472.2 nm line and DP/SP signal ~0.10–0.4 for the Zn II 255.8 nm line) at values of the interpulse delay Δτ immediately before the onset of signal enhancement. A similar signal reduction was previously found by Stratis et al. [50] who hypothesized a shielding of the sample from the ablation laser pulse by the air plasma. The calculation of plasma thermodynamic parameters showed that signal enhancement is associated to a modest increment of the temperature (generally lower than 1000 K), when present, and to a marked decrease of the electron density. By hypothesizing Local Thermal Equilibrium and by considering Saha equation, such features lead to a higher plasma ionization, which is consistent with the larger enhancement observed for ionic lines with respect to atomic lines. In order to understand the origin of signal enhancement we estimated the increment in the total number of emitting atoms (as an indication of the ablated mass), from the intensity of the Zn 472.2 nm line and the calculated values of temperature and electron density. The socalculated ratio of mass ablated in DP over that in SP, is reported in Figure 15 for all the combinations of the interpulse delay Δτ and the distance d used. Again, a sharp reduction of the ablated mass enhancement for values of the distance d larger than 1 mm is evident. A comparison of Figure 15 with Figure 14 shows clearly that the general behaviour of the emission signal with the interpulse delay is the same of that of the ablated mass, suggesting that the origin of the signal enhancement is mainly the higher ablated mass in the DP configuration, as already observed in the collinear DP experiments. For studying the dynamic evolution of the plumes obtained by using different combinations of d-Δτ values, we acquired shadowgraphic images using a Hadland Photonics frame camera, back-illuminating the plasma during its evolution with a white light source. It was found that the plasma evolution is strongly dependent on the choice of the d-Δτ values, as can be observed from Figure 16 a–d.

Figure 15. Enhancement of the atomized ablated mass as a function of interpulse delay and at different values of the distance d. Taken from Ref. [56]


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Figure 16. Shadowgraphic images showing the evolution of the plume and of the first and second shock waves produced with an interpulse delay of 2 μs and a distance d of 4.2 mm (a), 2.8 mm (b) 1.9 mm (c), and with an interpulse delay of 4 μs and a distance d of 0.7 mm (d). The temporal delay between the frames is 500 ns. Taken from Ref.[56]

The four images nearly represent all the different situations which can occur in the orthogonal pre-ablation DP scheme. In all the cases, both the pre-spark and the ablation plasma produced near the surface by the second laser pulse are clearly visible, as well as the two shock waves SW1 and SW2 departing from them. In case a) the ablation laser is fired before the shock wave SW1 generated by the air spark arrives on the target surface. The expansion of the ablation plume and of the shock wave SW2 shows a slow expansion in the direction perpendicular to the surface and a faster expansion in the radial direction. SW2 slows down because it expands in a medium flowing in the opposite direction and, at early times, with a higher gas density at SW1 front (Sedov self-similar solution predicts that the SW radius r and the ambient gas density ρ are related to each other by r ∝

ρ −1 / 5 ). It is then clear that the expansion of both the second plume and

SW2 is faster in the radial directions, where there is no density increase with respect to atmospheric conditions. As a result the ablation plume and SW2 expand assuming a flat shape similar to a disc and do not coalesce with the air spark. In case b), the second pulse is fired just after the arrival on the target surface of the shock wave SW1. As in the previous case, the ablation plume has initially a flat shape, probably due to a slowdown caused by the interaction with the SW1 front; however, in this case, SW2 and the ablation plume find soon the rarefied slow moving region located beyond the SW1 front and in the middle of the air spark and accelerate their motion, assuming an elongated shape. This results in the coalescence of the two plumes; the mixing of the two plumes leads to a reheating of the air spark, evident by the stronger brightness of air plume in frames 5,6,7,8 of Figure 16b with respect to Figure 16a.

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In case c), the ablation laser pulse is fired well after the time taken by SW1 to reach the target. Here, the situation is similar to case b) but the elongation is much less evident since the rarefied region of the first plume is nearer to the target. The two plumes rapidly coalesce and the two shock waves become almost concentric. Finally, in case d) the ablation laser is fired well after both SW1 and also the air plasma have reached the target. In this case, the evolution is similar to case c) but the final plume is larger and much brighter even for larger values of the interpulse delay (frames 8–10 in Figure 16d). A rough estimation of the maximum radius of the air spark from the shadowgraphic images (the bright region coincides with the continuum emission zone) gives a value ~1 mm. By comparing this value with the range of distances d, derived from spectroscopic analysis, for which a large signal enhancement is obtained, it is possible to conclude that the large signal enhancement corresponds to the case d). In other words the d-Δτ values result in a considerable signal enhancement if the target ablation occurs inside the region of the air spark (i.e. the air plasma has reached the surface) and not only in the region encompassed by the shock wave SW1. Such result is significant for understanding the causes leading to the signal and the mass removal enhancement observed in this DP scheme and, for the similarity of the results, in the case of collinear pulses and will be discussed in section 3.

c) Orthogonal Beams Re-Heating Configuration The orthogonal re-heating configuration (Figure 1c), strictly speaking, is not a DP-LA technique since it does not produce a raise of the mass removed from the target. In this case, the interaction of the second laser pulse with the plume produced by the first pulse leads to a re-heating of the plasma and thus to an emission enhancement, that can be exploited in LIBS measurements. The scheme was originally introduced by Uebbing et al. [57] (Al and Mn in glass matrix; Mg and Mn in glass, copper and aluminium matrices, λ = 1064 nm, E1= 13 mJ, E2 = 115 mJ, τ1 = 8 ns , τ2 = 5 ns), with the purpose of improving the internal standardization effectiveness for different matrix targets. Uebbing et al., aiming at obtaining reliable quantitative analyses by SP LIBS, noted that the usage of the same calibration curve, obtained by internal standardization, for different matrices lead to large errors because of the different temperatures of plasmas induced on different matrices and because of the selective volatilization of particles and droplets of different elements in the plasma (e.g. Cu and Zn in brass, which have very different values of vapour pressure). The second problem could be overcome by choosing a long delay time of signal acquisition (tens of μs) when the atomization process is ended; however, the plasma emission in that temporal range is often very low and scarcely useful for analytical measurements because of the decay of the temperature. The authors, thus, proposed the re-heating of the atomized mass by a second laser pulse for reducing the problems related to fractionation of materials; at the same time, the temperature differences in plasmas induced on different matrices should also reduce because the temperature of the second plasma is only affected by the second pulse features (energy, duration and wavelength) and not by the properties of the target (reflectivity, thermal conductivity, absorption, etc.). By using the re-heating DP scheme in an Ar rarefied


25

environment, with an interpulse time Δτ of 40 μs, Uebbing et al. demonstrated the validity of internal standard usage over three orders of magnitude of concentrations for metals embedded in different matrices (Cu and Zn in brass; Mg and Mn in glass, copper and aluminium matrix; Al and Mn in glass and steel). The effectiveness of DP re-heating configuration for enhancing LIBS signal was investigated by Gautier et al. [54,58] (Al target; ablation laser λ = 532 nm, τ = 9 ns; reheating laser λ = 1064 nm, τ = 9 ns), who studied the influence of the delay between the laser pulses and of the delay time of acquisition. The authors showed that the optimal value of the interpulse delay for enhancing ionic lines is ~200 ns, for which intensity enhancements up to 7 could be obtained. At that interpulse delay value, however, the intensity of neutral lines is reduced, except that of lines deriving from high energy levels which slightly increases. There is no experimental condition for which the intensity of neutral lines is significantly increased. Such results, together with the found increasing trend of line enhancement vs. the upper level energy, are evidently produced by the increase of plasma temperature resulting in the raise of the ionization degree and favouring the population of high-energy atomic levels. As a consequence, Gautier et al. show that the re-heating configuration leads to an improvement of LODs by 2-3 times, if ionic lines are used for the analysis. Despite the modest line enhancement, that is often lower than that obtained by other DP schemes, such configuration can be useful in LIBS technique in cases where it is necessary to reduce the damage on the sample or in case of re-heating of fs-plasmas, which have usually a low temperature and decay much faster than ns-plasmas; this second case, however, will be treated in section 4. A slightly different re-heating approach was proposed by Cheung and coworkers [59-62], where a second laser pulse intercepts and rekindles the ablation plume via resonantabsorption (Resonance-Enhanced LIBS or RELIPS). The technique was probed on different matrix targets (potassium iodate KIO3 pellets containing traces of Na as analyte; sodium bicarbonate NaHCO3 pellets doped with lithium as analyte; Al alloys with Cu, Mg, Pb and Si as analyte) where in all cases the resonant absorption was performed by tuning the wavelength of a dye laser on a particular transition of the major component of the matrix. The character of resonant-rekindling was evident by slightly detuning the wavelength of the dye laser, which resulted in a sharp reduction of the RELIPS signal. Both longitudinal and transversal interception of the second beam were probed, finding that the latter scheme provides signal 6 to 20-times larger signals and lower background noise. For LIBS to perform equally well, the sampling has to be ten times more destructive, which can be undesirable for some applications. The extent of the enhancement was found to depend on type and pressure of ambient gas, where an appropriate choice could result in the confinement and in the thermal insulation of the plasma, leading to a maximization of signal intensity. The sensitivity was found to depend critically also on the beam profile and on the spatial overlap of the laser beams. According to Cheung and coworkers, the primary mechanism of RELIPS enhancement reside in the large volume of re-heated plasma, where, at the opposite, in a classical re-heating DP mode (non-resonant) just the hot spots of the plasma, characterized by a large electron density (the mechanisms is in this case the inverse Bremsstrahlung process), tend to be reheated. The authors argue that this feature constitutes an advantage because it allows an

26


uniform and stable final heating since local absorption is automatically capped whenever the excited population of the resonant transition is saturated. To quantify the performance, a mass LOD of about 100 amol for Mg, and a detection sensitivity of about 0.3% of a monolayer of aluminium oxide over a 1 mm2 probed area, were demonstrated.

3. NANOSECOND-NANOSECOND PULSES COMBINATION: DISCUSSION ON THE MECHANISMS While the mechanisms leading to signal enhancement obtained in DP-reheating configuration (either resonant or non-resonant) are clear, the mechanisms operating in collinear and orthogonal pre-ablation DP configurations are still uncertain and need to be discussed [33]. Although the obvious differences in the experimental setups of these last two schemes, strong similarities in the produced effects are obtained, as listed in the previous section, such as the similar line intensity enhancement, the large increase of crater depth and atomized mass in the plume, the scarce increase of plasma temperature, the larger ionization associated to a reduction of the plasma electron density, the similar expansion dynamics of the plume (when the parameter d is lower than 1 mm). Such similarities suggest the working hypothesis that the primary mechanism in collinear and orthogonal pre-ablation is substantially the same, where the latter scheme approaches essentially to the former when the distance of the pre-spark to the target surface tends to zero. As will be discussed in the following, the ‘lower shielding’ mechanism can fit well and is able to explain the gross of the results obtained in both the configurations; on the other hand, a minor role can be played by the pre-heating of the target in the collinear DP scheme. In both collinear and orthogonal pre-ablation schemes, it was found that LIBS enhancement is produced by an increase of atomized ablated mass and by a different expansion dynamics rather than by an increase of plasma temperature. The larger ablated atomized mass results in a larger amount of emitting atoms, which is even higher in case of ions because of the higher ionization degree. At the same time the expansion of the plasma in SP and DP schemes is completely different as remarked by De Giacomo et al.[33]: while a SP plasma expands in a cold environment, exchanging energy with it, a DP plasma expands in a rarefied hot environment composed by the same species, so that it can be considered a ‘closed’ system. In fact the limited energy loss due to dissociation of ambient gas molecules and to excitation of ambient gas species, together to a spatial confinement of the plume at late times by the shock wave SW1 produced by the first laser pulse, results in a slower decay of the plasma and in a condition more favourable to LTE condition. The reduction of plasma electron density, driving a higher ionization of the plume can be explained by two different, probably interplaying, mechanisms. Firstly, the DP plasma expands very rapidly during the early 300-400 ns, due to the rarefied environment encountered, and successively stabilizes to dimensions corresponding to the region encompassed by the shock wave SW1. The expansion results in a geometric reduction of electron (and atom) density which drives a further ionization of the plume. Secondly, the reduction of electron density is due to the lower contribution from the ionization of ambient gas species due to the rarefied environment where the second plasma forms. The contribution


27

of electrons due to the ionization of ambient gas species is very uncertain, as well as the amount of the ambient gas species in the plume. However, recent papers suggest that their contribution is not negligible [63] and can be even dominant; in this case, the depletion of ambient gas species inside the bubble formed by the first laser pulse, which can be estimated of the order of 1/10 with respect to atmospheric conditions, results in a reduction of the electron density and thus, considering the Saha-Eggert equation, in a larger ionization of the plume. In both cases, the ionization is due to the fall of three-body recombination rate caused by the drop of electrons in the plasma. The effects produced by the different expansion dynamics of the plumes in the preablation orthogonal DP scheme, with respect to SP case, were analysed by Choi et al.[64]. In their experiment, pre-ablation and ablation laser pulses with significantly reduced energy were applied, so that the increase in ablated mass was negligible. In this condition, both the larger ionization of the plume and its prolonged lifetime, where both the effects are related to ambient gas rarefaction, were evidenced. At the same time, the results by Choi et al. suggest that the contribution to LIBS enhancement due to dynamic effects is modest except than at large acquisition time delays, leading to the conclusion that the primary cause of emission enhancement in DP-LA (operated at larger laser energies) is the increase of atomized ablated mass. At this point, it remains to understand why the DP schemes produce an increase of crater volume and a even higher enhancement of atomized ablated mass in the plume. Two main hypotheses have been suggested in literature, already quoted in the early work by Maher and Hall [4], i.e. the pre-heating of the target operated by the first laser pulse and the ‘lower shielding’ of the second laser pulse due to the environment rarefaction.

a) Target Heating Effects This hypothesis supposes that the second laser pulse hits the target surface when it is still hot and, for short interpulse delays, even melted, which results both in a sharp fall of target reflectivity and in a reduction of the energy to be supplied to reach the evaporation point. In the collinear scheme the heating of the target is evidently produced by the impact of the first laser pulse, which obviously can not apply to the orthogonal scheme. However, it is possible to imagine several other ways in which a LIP formation near a solid can heat the sample surface [65]. The most direct mechanism is the absorption of the broadband emission produced immediately after plasma formation, which can be very effective if there exists a significant overlapping between the absorption bands of the target and the radiative emission continuum. Other possible mechanisms are the target heating by the impact of the shock wave and by the plasma itself, which persists above the surface for several hundreds of microseconds. Bogaerts et al. [66], modelled the Double Pulse Laser Ablation in case of collinear configuration, taking into account the laser-solid interaction, the vapour plume expansion, the plasma formation and the laser-plasma interaction. Since the model was one-dimensional, the maximum interpulse delay considered was only 100 ns, after which the radial expansion of the plume could not more be neglected. By comparing the DP case with the case of SP with the same total energy (Cu target, λ=266 nm, τ = 5 ns, irradiance 0.5 GW cm-2 per pulse),

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Bogaerts et al. found that the surface temperature at the maximum is a bit lower in the DP configuration, because of the lower irradiance of one laser pulse, but it remains high during a longer time, because it rises again upon the second laser pulse. Also the calculated amount of vaporized material is somewhat lower in the DP configuration, which is attributed to the lower surface temperature. However, the only mass removal mechanism included in the model is target vaporization, while melt splashing and phase explosion are not taken in account. Noticing that evaporation depths are much lower than melt depths and even of measured crater drilled depths, the authors suggest that melt effects and phase explosion can bring a major contribution to the ablation process; such role could be enhanced in DP case where the target remains for a longer time in the molten state. The model of Bogaerts et al. shows also that at interpulse delay times larger than 70 ns the target material solidifies again in between the two pulses, which suggests that the preheating effects of the target become unimportant for delay times in the order of μs. This agrees with De Giacomo et al. [33], who noted that for interpulse delay times in the order of μs, the target surface has enough time to reach equilibrium. Dissonant results were obtained by Krstulovic and Milosevic [49] which showed a 3-fold drilling enhancement in case of ns-ns dual-pulse ablation of a titanium target in vacuum, where the pre-heating of the target is the only hypothesis to be applicable. The maximum enhancement was obtained for the interpulse delay of 370 ns, but a significant increase was obtained for delay times up to 20 μs. In order to reduce the effects of target pre-heating in the DP scheme, Maher and Hall [4], using two CO2 lasers (τ ~ 25 μs) tried to misalign one of the laser beams, so that the two spots in the surface did not overlap. When the spots on the target are tangent to one other, the temperature increase caused by the first laser pulse in the point where the second pulse is focussed is negligible. In fact, the thermal diffusion time is larger than the interpulse delay. Moreover, the target heating caused by the interaction with the first plasma is strongly reduced. At the same time, also in the case of non overlapping spots, the expansion of the preablation plume produces a depleted environment in front of the focusing spot of the second laser pulse, so that the presumed effect due to air rarefaction, such as a decrease of laser shielding, is still present. It means that in such geometry the pre-heating of the sample and the environmental rarefaction effects produced by the first laser pulse are separated. The experiment of Maher and Hall revealed that the damage on the target produced by nonoverlapping spots is similar to that produced by a collinear scheme, suggesting that the preheating effect in determining DP outcomes is scarce. In order to extend such results to the ns-ns case, we performed an experiment by using an apparatus similar to that used by Maher et al., by using two Nd:YAG lasers in the fundamental mode onto an Al target [67]. The energy of the first laser pulse was fixed to 90 mJ (fluence ~ 200 J cm-2), the interpulse delay to 1 μs and the energy of the second pulse was scanned in the range 3-125 mJ (fluence in the range 12-502 J cm-2). The enhancement of line intensity, the amount of ablated atomized mass in the plume and their trend vs. laser fluence obtained in the collinear and in the parallel non-collinear (non overlapping spots) schemes are the same, strongly detaching from the values obtained in SP configuration. However, an unexpected strong increase of crater drilling was found in the non-collinear configuration, which was explained by a hydrodynamic draining out from the crater of the aerosol and of the molten material, hindering its re-deposition (see Ref. [67]).


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The above results again confirm that the effects due to the target pre-heating are scarce unless, maybe, for short interpulse delays in the order of a few hundreds of nanoseconds.

b) Atmospheric Effects on Laser Shielding Laser supported detonation and laser ablation The works on the photoablation process begun in the seventies, driven by the need of optimizing material processing techniques. According to the notation used in the literature, laser-matter interaction is characterized by the figure of merit Cm, defined as the ablation pressure over the incident laser intensity or, which is the same, the momentum imparted to the target over the total laser energy, quantifying the mechanical coupling between laser and target [68]. During the photoablation process the momentum can be delivered to the target by the vaporization of material, by the shock wave produced over the surface and finally by spallation or boiling phenomena. By the experimental measurement of Cm parameter in vacuum, mainly by the ballistic pendulum method, it was observed initially by Gregg and Thomas [69], that the mechanical coupling Cm shows a maximum in correspondence of a determined laser irradiance Imax, typically between 108 and 109 W cm-2, and then noticeably decreases at higher laser irradiances. Such threshold is slightly higher than the laser irradiance Ip at which plasma ignition occurs and corresponds to the onset of a strong laser absorption in the plasma which establishes a plasma-mediated photoablation regime. The situation is more difficult to explain when laser ablation is performed in ambient gas environment where, for adequate laser irradiances, the Laser Supported Detonation (LSD) mechanism is ignited and a complex gasdynamic description must be included in the model [70]. In this case, a hot high-pressure plasma, which is initially composed by target species, is produced and drives a shock wave in the surrounding gas. When the laser irradiance is high enough to ignite the LSD mechanism, the passage of the shock wave heats and ionizes a new shell of ambient gas, allowing the laser absorption to occur in it until the plasma state is reached. In turn, laser absorption feeds a further expansion of the shock wave, resulting in a progressive propagation of the plasma plume in the surrounding gas [71]. A further problem arises for the description of LSD ignition in ns-regime laser pulses, since the initiation time of the laser-supported regime is comparable with the pulse duration, so that for a certain range of pulse durations and energies a stationary LSD regime cannot be reached, and a transient regime should be considered. Xu et al. [72] estimated that the LSD initiation time for a Nd:YAG 1064 nm, 10 ns laser pulse in the range of irradiance 108-109 W cm-2 is of the order of 3 ns, though such value is strongly dependent on laser irradiance [73]. Although different mechanisms of laser absorption waves (i.e. blast waves) can occur at irradiances lower than LSD threshold, it was shown by Hettche et al. [74] that the onset of LSD wave corresponds to the beginning of a strong plasma shielding. This occurs because most of the laser energy cannot pass through the high-absorbing region behind the SW front, so that the shielding of the surface can be nearly complete. Therefore, the onset of LSD corresponds to a maximum of impulse coupling Cm parameter which tends to decrease at large laser irradiances. The coincidence of the onset of LSD with strong plasma shielding was

30


observed more recently by shadowgraphy and laser drilling experiments by Gravel et al.[75], showing that the strong laser absorption associated to LSD drastically reduces the ablation rate. Moreover, it is expected that the variation of laser-target coupling due to the onset of strong shielding also influences the mechanisms of mass removal and their thresholds. On one hand, melt splashing is favoured by the formation of a hot high-pressure plasma, on the other, phase explosion is hindered by the reduction of the effective irradiance on the target. In a previous work [42], we studied the transitions between different mass removal regimes varying the laser irradiance (λ = 1064 nm, τ = 50 ns, 2.4·108 < Irradiance < 1.2·1010 W cm-2), during the laser ablation in atmospheric air of an Al target. In a subsequent work [43], the investigation was extended to the SP ablation in air at reduced pressures and to the ablation in orthogonal DP pre-ablation configuration. The intensity of atomic and ionic lines and the crater volumes were measured in the different experimental conditions; moreover, the calculation of spatially-averaged temperature and electron density allowed also the estimation of the atomized ablated mass in the plume (see Figure 17).

Figure 17. Drilled volume of the crater and atomized ablated mass vs. laser irradiance used. Taken from Ref.[43]


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By looking at the data obtained in SP configuration at atmospheric pressure, the trends of line intensities (not reported here), atomized ablated mass and crater volume vs. laser irradiance evidence a significant change of regime at ~8-9·108 W cm-2. In a following work [44], where a shorter laser pulse (λ = 1064 nm, τ = 32 ns) was focused on an Al target, the discontinuity was found at a slightly lower irradiance value of ~7·108 W cm-2. At lower irradiances, line intensities, atomized mass and crater volume increases with increasing laser irradiance; on the contrary, above the threshold they markedly fall down, evidencing a less efficient ablation process. The observed discontinuity indicates that a transition occurs between a weak laser absorption in the plasma, beginning at the plasma ignition threshold, and a strong plasma shielding, where the larger part of the pulse energy is absorbed in the plume by inverse Bremsstrahlung processes or reflected at its surface. These latter effects result in a significant reduction of ablated mass. A similar discontinuity in crater drilling, although at larger irradiance values (~ 2.5 GW -2 cm ), was found by Gravel et al. [75], (brass target, λ = 1064 nm, τ = 22 ns) who also showed by shadowgraphic imaging that the threshold is associated to the onset of a Laser Supported wave mechanism. The thresholds obtained in our works [42-44] agree with the power density corresponding to the maximum impulse-coupling coefficient found by Xu et al. [72], calculated using the ballistic pendulum method in the ablation of an aluminium target by a 10 ns 1064 nm laser pulse. Such threshold was again successfully modelled by considering the occurrence of LSD wave with non-negligible initiation times. The morphology of the craters, reported in Ref.[42], suggests that the onset of strong shielding produces also a change in the mechanism of mass removal from the target. For irradiance values lower than LSD threshold, melt effects on the surface were negligible and phase explosion was the only mechanism able to justify the ablation rate (2–4 μm per pulse) found experimentally. This is possible because almost all the laser energy reaches the surface and is able to heat the target surface up to the critical temperature for phase explosion onset. Despite the extensive discussion that appeared in literature about the irradiance threshold of phase explosion, where often much larger threshold values were proposed, striking evidence of phase explosion occurrence in metals was found at values similar to the one obtained here. For example, Porneala and Willis [76] (Al target, λ = 1064 nm, τ = 5 ns), found evidence of phase explosion both by measuring a jump in the ablation rate and by observing a violent ejection of droplets with a shadowgraphic technique, at 1 GW cm-2. Differently, at laser irradiances above the LSD threshold, melt displacement and expulsion progressively become more relevant, as testified by the increase of crater rims formed by re-solidified material and by melt droplets splashed on the target surface around the crater. It is likely that the motion of molten material is the effect of a lateral pressure gradient induced by the high-pressure plasma above the target surface. Phase explosion could be inhibited or become less efficient since, in this range, the ablation rate strongly decreases, despite the increasing melt displacement and expulsion. It is then possible that above the LSD threshold the main mechanisms of mass removal are the melt splashing, which however produces mostly liquid droplets, and vaporization, which produces atomized mass in the plasma. Concluding the paragraph, we want to remark that the occurrence of Laser Supported Detonation mechanism during SP laser ablation in ambient gas strongly affects the process,

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reducing the mechanical coupling with the target and therefore the drilling and the LIBS signal on one hand, and modifying the mass removal mechanism inhibiting the phase explosion, on the other hand.

Laser supported detonation wave and ambient gas pressure Several parameters affect the occurrence of LSD during laser ablation, mainly the target properties and the ambient gas pressure. Maher et al. [77] noted that the laser ablation of samples that absorb much of the incident laser energy, such as SiO2 and Lucite, induces the formation of blast waves instead of LSD waves, resulting in a much lower plasma absorption. According to the authors, this occurs because of the large amount of vaporized matter that pushes and heats the ambient air, so that the absorption blast wave moves perpendicular to the target surface (note that, on the contrary, LSD moves toward the laser beam, an effect which is clearly observable for non normal incidence angles). Also the gas pressure affects both the LSD thresholds and their initiation times. Such behaviour is comprehensible, in view of the fact that the low air pressure corresponds to lowdensity gas, which makes less effective the absorption from air atoms and therefore the feeding of LSD mechanism. Maher et al. [77] calculated the LSD threshold varying the air pressures for different targets, showing that, for metal targets, the LSD ignition is more difficult at pressures lower than the atmospheric, resulting in a higher ignition threshold. This is in accordance with the trends of crater volume and atomized ablated matter obtained at reduced air pressures plotted in Figure 17, showing that the irradiance threshold of strong shielding, resulting in the discontinuity observed in the range 7·108-2·109 W cm-2, slightly increases when air pressure decreases. It is also evident from Figure 17 that the effectiveness of plasma shielding similarly decreases with air pressure, where the discontinuity in the plot is scarcely visible for pressures lower than 300 torr. As a result, the trends of crater volume, atomized matter in the plume, and plasma line intensities (not shown here) have a monotone increasing trend at 100 torr pressure. These results agree with the observation that, in single pulse LIBS, the emission and the ablation rate are maximum when the buffer gas density is lower than the atmospheric one, as shown in Figure 11 and found experimentally by Sdorra and Niemax [78] and by Iida [79]. The same result can be obtained in Figure 17 by choosing a laser irradiance above the LSD threshold and by progressively reducing the air pressure. The key mechanism that must be considered is again the laser shielding operated by the plasma, since a high buffer gas density favours the breakdown-cascade process, the formation of free electrons in the plasma and the absorption of laser radiation. It should also be noted that for irradiances lower than LSD threshold the values in Figure 17 are coincident in all the experimental configurations. This suggests a picture of laser ablation in 2-steps Step 1. From the beginning of the laser pulse to the time where the plasma electron density reaches a critical value, a weak laser absorption occurs in the plume mainly by IB processes. The ablation efficiency seems not to be severely affected by ambient gas density since the ablation rate and the plasma mass are the same in SP and in DP configurations. This agrees with the hypothesis that, at the beginning of laser-target interaction, the plume freely expands in ambient gas without being affected by background gas properties [44,80]; however, the progressive laser absorption in the plume increases the expansion speed of the


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plume and produces a pile-up of vapour atoms at the vapour-background gas interface, the socalled ‘snowplough effect’, which forms a shock wave. The following expansion of the plume and growing rate of electron density is progressively affected by the background density. Step 2. During the trailing part of laser pulse the electron density reaches a critical value producing avalanche ionization and electron cascade, driving a much stronger laser pulse absorption and reflection, and causing a drop of the ablation efficiency. The laser absorption feeds the shock wave expansion so that a Laser Supported wave mechanism begins. In this picture, if laser irradiance is lower than LSD threshold, only Step 1 occurs, and Step 2 is never reached, a condition which explains the similarities of results obtained at different gas pressures in Figure 17.

Laser absorption in double pulse configuration By comparing the plots in Figure 17, it is evident the strong similarity between the data obtained in SP at 100 torr air pressures and those obtained in DP configuration, suggesting that DP effects are mainly related to atmospheric effects. At this point, it is important to give a picture of the environmental situation found by the second laser pulse when it reaches the target. When the first laser pulse ends, the LSD mechanism clearly stops and a blast wave moves in the environment, progressively dissipating its energy for the expansion and for the heating-ionization of the ambient gas. As time elapses, the shock wave, initially in contact with the plasma region, detaches from it and continues to expand, while the plume stops at a radius of the order of 1 mm, depending on the experimental conditions. When all the available energy has been dissipated in the expansion and in the excitation/ionization processes, the pressure of the internal region equalizes with the external one and the shock wave becomes a sonic wave. At times larger than the laser pulse width, the situation can be well described by the point strong explosion theory, formulated by Sedov [81,82], which describes the effect of a large amount of energy delivered in a small volume of a homogeneous atmosphere during a short time interval. According to the theory, during the expansion of the shock wave produced by the sudden release of laser energy, most of the mass of the ambient gas is compressed in a thin layer near its front surface. Therefore, Sedov theory predicts that the shock wave front is characterised by a large mass density pileup, while beyond it the density steeply drops down to values much lower than that in the unperturbed medium. Unfortunately, the Sedov self-similar solution, while it can be effectively used to describe the shock wave radius and velocity, and the profiles of temperature and gas density in the region near the shock front, is unable to give quantitative and reliable values of such parameters in the core of the plasma. In fact, the basic theory of strong point explosion neglects internal heat transfer phenomena such as conduction, radiation as well as excitation and ionization of the gas, and predicts an infinite temperature and a null density in the core of the plume. To correct this problem, more sophisticated models [83,84] accounting for the internal heat transport have been developed. These models predict a finite temperature in the core of the plume. Moreover, considering the ideal gas state equation ρ ∝ P , a non-zero gas T density is also predicted.

34


Figure 18. Qualitative sketch of the profiles of pressure, temperature and gas density along the preablation plume and shock wave. Taken from Ref. [56]

A qualitative sketch of the thermodynamic profiles in the air spark region is reported in Figure 18, where the steep increase of temperature at the plume border leads to an abrupt decrease of gas density in the core. The profiles plotted in the figure can also qualitatively represent the situation produced by the ablation of a solid target in air, where evidently the plasma expands from the target surface. The density profile (accounting for both the air and plume atoms) is consistent with the predictions and results of the numerical model by Bogaerts and Chen [85], although it is limited only to the early hundreds of nanoseconds after the laser ablation. The gas rarefaction in the core of the plume can be evaluated from the ideal gas relation:

n plume n atmospheri c

=

Pplume

Tatmospheri c

Patmospheri c

T plume

(2)

According to strong explosion theory, the pressure reaches a maximum PSW at the SW front and then rapidly decreases behind it toward a value Pplume≈0.365 PSW (this value is substantially independent on the blast wave energy down to a SW velocity around Mach 1.5). The corrections to the Sedov model accounting for the internal heat transfer processes do not bring significant variations in pressure profiles, showing at most a slight decrease of the value of Pplume; this can be also perceived from the good agreement of the measured shock wave radius with the predicted one, since the driving force of the shock is essentially the pressure behind it. Moreover, the SW front pressure PSW and the unperturbed pressure Patmospheric are linked by the relation


PSW =

Patmospheric (2γM 2 − γ + 1)

γ +1

35

(3)

where M is the SW Mach number and γ=1.4 is the adiabatic coefficient of air [81]. Calculating the Mach number by fitting the shock radius derived from Figure 16, we obtain M~2.2 and then PSW~5.5Patmospheric. Finally, substituting this value in Eq. (2) and considering Tatmospheric=300 K and Tplume~15,000 K (a reasonable value of the spark temperature) we obtain nplume/natomspheric = 0.04 [56]. By considering the images in Figure 7, it is possible to make the same calculations, as in Ref.[86], obtaining the value nplume/natomspheric = 0.07. Such values suggest that the gas density inside the first laser plasma is similar to the density of the gas at room temperature and at 50 torr pressure. At this point, it becomes immediate to observe that the occurrence of LSD mechanism becomes more difficult and less efficient for the second laser pulse, since laser ablation occurs in rarefied gas, resulting in a much lower plasma shielding of the target. Then, the DPLA process is to be compared to a SP-LA at lower air pressure, around 50-100 torr, which explains the similarities of the trends in Figure 17 between DP and SP low pressures configurations. In this way, the DP configuration avoids the onset or, at least, reduces the effects of LSD wave, in particular the strong plasma shielding, resulting in a much larger laser-target coupling and mass removal. In some sense, the first laser pulse in DP-LA has the effect of producing a sort of low-pressure chamber, which optimizes the laser-target coupling, but without the experimental complications inherent to the use of such apparatus. This mechanism is effective if the interpulse delay is larger than ~200 ns [29], when the capability of the first LIP to absorb the second laser pulse becomes unimportant and the rarefaction effects of ambient gas become dominant. This mechanism thus agrees with the range of interpulse delays suitable for generating DP-LA effects (see Figure 4), which are of the order of the plasma decay time. The mechanism proposed also allows the modelling of the influence of the distance of the pre-spark from the target surface. If such distance is large (d>1mm in Figure 13-15), so that only SW1 arrives on the target, this leads initially to a density growth at the surface–gas boundary, but successively the wave reflection leads to a modest gas rarefaction, resulting in a modest line intensity enhancement. However, if the hot plasma region produced by the pre-ablation pulse is able to reach the target surface (d τei, the ablation rate of DP falls with increasing the interpulse delay. The main reasons are the lower temperature of the target surface and the absorption/scattering of laser radiation by ejecta or by the plasma. The onset and the relevance of such phenomena depend on the heat diffusion time τD and on the time τT needed for the ejecta or the plasma induced by the first pulse to interfere with the second pulse. Roberts et al. [96] showed that such decrease begins at interpulse values depending on the laser fluence, in a range between 10 ps at low fluences and 0.1 ps at large fluences. Moreover, the authors evidenced that a completely different behaviour is obtained at fluences larger than 16 J cm-2, probably because of the onset of a different mass removal mechanism. A similar decreasing trend was also found by Semerok and Dutouquet [88] (Al and Cu target, τ = 50 fs, 160 fs, 675 fs), in the range 1 < Δτ < 10 ps, and by Chowdhury et al. [98] (fused silica target, τ=90 fs), in the range 0.1 < Δτ < 10 ps. In all the above works the ablation rate obtained at the lowest point was even lower than that obtained in SP scheme. Chowdhury et al. [98] measured also the transmission of the second pulse varying Δτ. They showed that the observed decrease of ablation rate is due to the absorption of the laser pulse by the plasma in front of the target. A similar conclusion was reached by Semerok and Dutouquet [88], who imaged the plasma plume produced in this temporal range with an ICCD camera, finding a much higher intensity and a higher reproducibility of the plasma emission in DP scheme, where the intensity rises with increasing the interpulse delay. The authors argued that the effect was produced by the re-heating of the plume by the absorption of the second laser pulse. Such plasma re-heating, which is optimal for Δτ ~100-200 ps according to Ref.[88], can be fruitfully used for fs-LIBS applications which are known to suffer from a low plasma emission. An interesting phenomenon observed in this interpulse delay range is also the enhancement of the low-energy ion yield, which can be fruitfully utilized for ion implantation in microelectronics and optoelectronics. Koudoumas et al. [93] (Si target, λ1 = 800 nm, τ1 = 180 fs; λ2 = 248 nm, τ2 = 0.5 ps) showed that the utilization of two ultrashort pulses with and an interpulse delay larger than ~1 ps results in the enhancement of the production of Si+ ions and in the increase of their thermal energy. The authors suggest that the effect is associated to the creation of a melted zone exhibiting modified optical coupling properties, where the second pulse induces a much higher temperature in a thinner surface layer. Many papers concerning DP-approach are devoted to the enhancement of fs-LIBS emission. The fs-LIBS has the potential advantage of reducing the ‘matrix effect’ of the technique and to assure a better stoichiometry of the ablation process. However, it often results in a low sensitivity caused by the lower temperature of the plasma and by its faster decay. In order to overcome these drawbacks some authors probed a double pulse approach


39

where a combination of ns and fs pulses are used. Scaffidi et al. [12] (Fe target, λ = 800 nm, τ = 100 fs; λ = 1064 nm, τ = 5 ns) reported a study where a combination of fs-ns pulses in collinear scheme was used; they found an enhancement of atomic emission at different focus positions, suggesting that different reasons, i.e. plasma-plasma coupling and reduction of air density during the second breakdown event, are the primary causes of such effects. Other experiments devoted to fs-LIBS emission enhancement were performed in the orthogonal configuration, where the processes of laser ablation and plasma re-heating are temporally well separated. Scaffidi et al. [91] (Al and Cu target, λ = 800 nm, τ = 100 fs; λ = 1064 nm, τ = 7 ns) probed different configurations where a fs or ns pulse is used for the ablation and the other is used for re-heating the plasma or for inducing a pre-spark in front of the target. The combination where the fs-plasma is re-heated by a ns pulse shows the largest emission enhancement (~30–fold for the Cu I 501 nm line and ~80 for the Al I 396 nm line) at an interpulse delay of 5 μs. Significant line enhancements were obtained by Santagata et al. [92] (Ti target, λ1 = 527 nm, τ1 = 250 fs; λ2 = 532 nm, τ2 = 7 ns) by using a similar configuration where a fs-plasma is re-heated by a ns pulse; in this case, however, the optimal interpulse delay, depending on the fs pulse energy, is noticeably larger than that found by Scaffidi et al. (Δτ = 500 μs for Epulse = 0.8 mJ and Δτ = 250 μs for Epulse = 3 mJ). On the other hand, the combination where the fs pulse induces a pre-spark in front of the target and the ns pulse ablates the surface shows a modest line enhancement which appears associated to the reduction of air density [90] and then substantially similar to the effects already discussed in the ns-ns orthogonal scheme.

PERSPECTIVES AND FUTURE DEVELOPMENT The large number of papers dealing with DP-LA recently appeared in literature attests the increasing interest on the subject, motivated by its fruitful usage in many applications, among which laser micro-sampling and laser micro-drilling. The experimental and theoretical results reported in the present chapter allow for a quite clear picture of the mechanisms underlying the process of ns-ns Double-Pulse laser ablation of solid targets. However, the quantitative prediction of the enhancement in ablation rates and optical emissions, as well as the theoretical determination of the thresholds observed in varying the laser pulse properties and the environmental characteristics still call for a reliable theoretical model of DP laser ablation, valid for interpulse delays of the order of microseconds and including all the different mass removal mechanisms (vaporization, melt displacement, melt splashing, phase explosion, spallation). Most of the results reported in this chapter concerns the LA of metals in ambient gas, to which prevailingly the above considerations and modelling refer to. The utilization of the DP scheme for the ablation of solid targets immersed in liquid is also very promising for many applications, going from analytical analyses to nanoparticles formation; however, for the different characteristics of the LA process, the issue is not treated here, so that we suggest the interested reader to refer to other specialized publications [14,15]. The understanding of DP-LA of non-metals targets still needs accurate and dedicated works, because of the substantial differences of laser ablation processes, which result also in dissimilarities in DP effects. More works are also needed in the case of DP-LA with short-

40


ultrashort pulses, for the still scarce knowledge on the LA process obtained with fs and ps lasers.

ACKNOWLEDGMENTS The authors would like to acknowledge Elsevier B.V. for the use of excerpts and figures published in Spectrochimica Acta Part B. The authors acknowledge also IOP sciences for the use of excerpts taken from Journal of Physics D: Applied Physics.

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Chapter 2

ASSESSING HUNTER-GATHERER MOBILITY IN CIS-BAIKAL, SIBERIA USING LA-ICP-MS: METHODOLOGICAL CORRECTION FOR LASER INTERACTIONS WITH CALCIUM PHOSPHATE MATRICES AND THE POTENTIAL FOR INTEGRATED LA-ICP-MS SAMPLING OF ARCHAEOLOGICAL SKELETAL MATERIALS Ian Scharlotta, Andrzej Weber, S. Andy DuFane, Olga I. Goriunova and Robert Creaser University of Alberta, Edmonton, Alberta, Canada

ABSTRACT Micro-sampling and analysis of tooth enamel from faunal samples in the archaeological record has enabled research into the mobility and seasonality of animals in prehistory. However, studies on human tooth samples have failed to yield similar results. It is well understood that human tooth enamel does not fully mineralize in a strictly linear fashion, but rather entails five recognizable stages of mineralization. Until the enamel matrix fully crystallizes, the matrix remains an open chemical system, thus at each stage of mineralization, the geochemical composition of the enamel matrix can be altered. At present it is unclear if failure to mirror the results from faunal teeth with human teeth is a factor of mineralization rates or simply the result of the difference in enamel volume and formation time between human and herbivore teeth. Therefore, the applicability of chemical analyses to human teeth is a balance between micro-sampling analytical techniques and generating archaeologically relevant data. Yet limited case studies have been performed to examine the scale and extent of this problem in human teeth using laser-ablation ICP-MS. Five human molars from an Early Bronze Age cemetery on the shores of Lake Baikal, Siberia were serially sampled and analyzed by means of laser-ablation quadrupole and multicollector ICP-MS in order to examine the

46

Ian Scharlotta, Andrzej Weber, S. Andy Dufane et al. nature of geochemical changes within the enamel matrix. This sampling was performed in order to generate a statistically significant dataset to assess the effectiveness of two approaches along with published methodologies to counter known problems with attempts to assess Sr87. Recent research has demonstrated that among the methodological problems, there is isobaric interference at mass 87 caused by the formation of calcium phosphate (Ca40PO) in response to interaction between the laser and the enamel matrix. Correction procedures using Zr91 in tandem with Ba/Sr ratios are examined. Additionally, serial sampling of teeth from hypothesized mobile hunter-gatherers provides useful insight into the dynamic interplay between physical sampling limitations and the scale at which useful geochemical data can be recovered from organic minerals. Traditional utilization of geochemical data for mobility has relied on a local/non-local dichotomy in population level analyses; however, this approach is of limited utility with regard to mobile populations. Our ability to effectively analyze skeletal materials at a micro scale provides our best hope at addressing the rift between recognition of an indirect relationship between biological intakes, mineral formation and being able to generate relevant analytical data.

INTRODUCTION Strontium isotope analysis has traditionally relied on thermal ionization mass spectrometry (TIMS) due to its reliability and analytical precision. The advent of multicollector inductively-coupled-plasma mass-spectrometry (MC-ICP-MS) as an alternative to TIMS coupled with either a laser microdrill or a laser ablation (LA) unit for micro-sampling greatly expanded the possibilities for archaeometric research of Sr isotopes. Both laser microdrills and laser ablation are far less destructive and enable higher spatial resolution for analysis than traditional TIMS and MC-ICP-MS methodologies, however micro-sampling for solution preparation still requires significant lab handling for sample preparation whereas laser ablation requires virtually no special handling [1, 2]. In spite of several studies using LA on human bone and high-Sr apatites [3, 4], analysis of phosphate minerals by LA has not figured prominently in the scientific literature until recently [1, 5-10]. The goal of this study is to examine problems associated with the application of laser ablation as a sample introduction method for MC-ICP-MS on human skeletal materials. Previous research[1, 8, 10] has indicated a number of potential problems in gathering accurate strontium isotopic data from calcium phosphate matrices using LA-MC-ICP-MS. In addition to interference from rubidium (87Rb), doubly charged rare earth elements [11], and calcium dimers [10], there is the production of a polyatomic species of CaPO that interferes with the [87] Sr [1, 8, 9]. This polyatomic species is apparently unique to laser ablation as it is not apparent with solution mode (SM) MC-ICP-MS. The exact source of this polyatomic species is uncertain; however it is a relatively minor contributor of isobaric mass 87 to most geological samples. Unfortunately, many archaeological skeletal samples have very low concentrations of Sr and are thus susceptible to significant error terms as a result of this polyatomic species while using LA-MC-ICP-MS. Traditional Sr isotopic research has focused primarily on sedentary agrarian groups. With such groups, the focus of research is on identifying the local signature so that nonlocals (people, animals, etc.) can be recognized. Such an approach is perhaps of only limited utility for the broader study of hunter-gatherers, as many groups utilized large ranges of territory and

Assessing Hunter-Gatherer Mobility in Cis-Baikal, Siberia Using LA-ICP-MS

47

would thus have more complex (averaged over larger areas) isotopic signatures reflecting their lifetime mobility. Such complexity drives interest in micro sampling of skeletal materials to access greater chronologically refined insight into mobile individuals. However, further research is needed to fully understand the dynamic interaction between direct chemical interaction with the biologically available strontium, the formation of skeletal tissues, and data recovery from these tissues. This study is focused on the data recovery side of this problem, examining the range of variability in strontium isotope ratios and trace element composition found within human teeth.

HUNTER GATHERER MOBILITY IN CIS-BAIKAL The Cis-Baikal region of Siberia denotes the geographic region including the western coast of Lake Baikal, the upper sections of the Angara and Lena river drainages, and the Tunka region adjacent to the southwestern tip of Lake Baikal (approximately between 52° and 58° N and 101° and 110° E). The topographic complexity of the rift valley that formed Lake Baikal led to the formation of a large number of microhabitats, with a variety of seasonally available resources [12-14]. The thermal capacity of Lake Baikal itself moderates the local climate, resulting in generally milder temperatures during the winter and cooler temperatures during the summer. As a result, the Angara River Valley remains relatively free of snow during the long winter which attracts various species of ungulates looking for forage and less restricted mobility [15]. There is a variety of large game found in the region including moose (Alces alces), red deer (Cervus elaphus), roe deer (Capreolus capreolus pygarus), reindeer (Rangifer tarandus), and mountain goat (Capra sibirica). Smaller species such as hare (Lepus sp.), suslik (Spermophilus citellus), wild boar (Sus scrofa sibiricus), marmot (Marmota sibirica), geese, and other waterfowl are also abundant in many areas around the lake. During the summer, large runs of black grayling (Thymallus arcticus) are found in the first section of the Angara River, and several fish species enter the tributaries of the Angara in large numbers to spawn. The shallow coves and bays in the Little Sea region of Lake Baikal, between Ol’khon Island and the west coast of the lake, also provide excellent opportunities for fishing and during the late winter when the lake is frozen, nerpa, the Lake Baikal seal (Phoca sibirica) can be hunted [16-19]. Ethnographic studies of boreal forest populations highlight the use of mushrooms, berries, and pine nuts as other non-medicinal resources [15, 20, 21]. There is very limited evidence for plant use during the Neolithic, however there is sufficient ethnographic evidence for the role that plants play in boreal forager subsistence systems around the world to speculate upon their usage. Within the Cis-Baikal region there are four main geological zones that roughly overlap with archaeological micro-regions (Figure 1). The main zones are 1) the Baikal basin, including the lake itself, the coastal areas as well as the Little Sea area enclosed by Ol’khon Island; 2) the drainage of the upper and middle Angara River bounded by the Eastern Sayan Mountains to the west and the Central Siberian Plateau to the east and extending north towards Bratsk; 3) the upper Lena river basin cutting through the Central Siberian Plateau as it heads northwards; and 4) the Tunka region covering a sizeable valley running south of the Eastern Sayan Mountains and broadly connecting the southwestern tip of Lake Baikal to Lake Khovsgol in Mongolia. The upper and middle sections of the Angara River flow through

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Ian Scharlotta, Andrzej Weber, S. Andy Dufane et al.

Mesozoic and Quaternary deposits, with expected 87Sr/86Sr values in the range of 0.7050.712. The upper Lena watershed and the surrounding Central Siberian Plateau are dominated by Cambrian and Precambrian limestones, with expected values fairly tightly clustered around 0.709 [22, 23]. Overall values for Lake Baikal water are reported as 0.7085 [24]. The Baikal basin includes the Primorskii and Baikalskii mountain ranges and is characterized by relatively high 87Sr/86Sr (~0.720-0.735) due to the presence of Archean and Proterozoic granites [12]. Bedrock of similar ages occur around the southwestern shores of Lake Baikal and drainages adjacent to the Eastern Sayan Mountains, however our preliminary data for environmental sampling of biologically available strontium isotopes in the Cis-Baikal region indicate that these two regions have quite different 87Sr/86Sr values [25]. Both zones overlap 87 Sr/86Sr ranges of neighboring regions (e.g., Angara Drainage), while only the Little Sea area exhibits values above 0.720. Further clarifications of the distinction between these two zones of similar age will be possible upon completion of regional sampling efforts.

Figure 1. Lake Baikal, Siberia showing the location of the KN XIV cemetery, cultural micro regions, and the age of the dominant bedrock formations


49

KHUZHIR-NUGE XIV CEMETERY The KN XIV cemetery is located on the west coast of the Little Sea micro-region of the Lake Baikal basin, near the southern end of Ol’khon Island and c. 3 km southwest of the mouth of the Sarma River (53°04’58” N, 106°48’21” E). It occupies the southeast slope of a hill rising from a shallow bay. With 79 graves and a total of 89 individuals unearthed, KN XIV is the largest Early Bronze Age hunter-gatherer cemetery ever excavated in the entire Cis-Baikal region (Weber et al. 2007). All the graves were only c. 30-60 cm deep subrectangular pits filled with rocks and loamy sand, and covered by surface structures built of stone slabs still visible on the surface prior to archaeological excavation. Most graves contained single inhumations, seven were double, and two were triple interments. The north-south orientation of Grave 7 is consistent with the Late Neolithic Serovo culture of the Ol’khon region, while all the other graves show clear similarities with the mortuary tradition of the Early Bronze Age Glazkovo culture [22, 26, 27]. The most diagnostic Glazkovo characteristics include the generally west-east orientation of the burials and such grave goods as copper or bronze objects (rings, knives, needles, and bracelets), kaolinite beads, and rings and discs made of white nephrite or calcite [28]. A recent analysis of approximately 80 14C dates indicates that the KN XIV cemetery was used continuously by Glazkovo peoples for a maximum of 700 years between ~4650 and 3950 cal. BP but the majority of the burials (70%) date to between ~4450 and 4250 cal. BP [29]. Since the analysis did not reveal any obvious temporal trends in mortuary attributes, it seems to be justified to treat the cemetery with the exception of the much earlier Grave 7, as one analytical unit (McKenzie 2006; Weber et al. 2005). In previous studies [15, 22, 26] a sample of 25 individuals from KN XIV were analyzed for strontium isotope ratios and compared with 79 faunal samples collected throughout Lake Baikal and the Cis-Baikal region. Of these samples, there were 20 adult individuals for which all three molars and a femur sample were available, 5 subadult burials with only M1 and M2 crowns completed were included too. For the latter individuals (Burials 16, 35.2, 37.2, 39 and 45) the M3 was either not yet formed, or still forming. Partly developed crowns were not examined because such crowns are incompletely mineralized and this could have affected the isotope ratios. The five molar samples used for this research came from this pool of previously studied materials. Teeth from Burials 7, 12, 16, 35.1, and 35.2 were used in this study to provide continuity and comparability with previous studies on KN XIV. This previous work has helped to expand the possible applications of strontium isotope research and helped to identify an interesting general pattern with several mobility profiles within KN XIV individuals. Broadly speaking, it appears that there was a significant amount of movement of individuals during their lifetime, whereby people buried at KN XIV were frequently not born in the Little Sea region, but only migrated there as subadults or adults [15, 22]. There was significant variability within the cemetery itself as to the origin and age of migration to the Little Sea with indications of correlated mortuary patterning that is the subject of ongoing research.

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PRINCIPLE OF STRONTIUM CATCHMENT Strontium ratios in herbivore bone reflect the isotopic signatures in the plants that these animals eat and the water that they drink thus are a direct reflection of their bioavailable geochemical environment. An herbivore foraging range will therefore roughly equate to its Sr-catchment [30, 31]. The situation is slightly different for carnivores as their Sr-catchment will reflect their dietary intake rather than simply their geographical territory. The territory of a predator, human or otherwise, will intersect and contain portions of the territories of numerous prey animals, though will likely not encompass the full procurement ranges of these species. Therefore the strontium ratios of their prey animals may derive from geological regions outside of the predator’s geographic territory. This highlights the important concept of effective geochemistry as a step beyond bioavailable geochemical signatures. Herbivores provide direct translations of bioavailable geochemical values in plants, thus whatever portion of soil geochemistry can be mobilized into the food chain. Carnivores subsist largely or solely on other animals, thus their bioavailable geochemical values will not directly translate into either their actual movements on the landscape or their bounded procurement territory. The only evidence to directly relate carnivores with their physical territory is the water that they drink, any vegetal matter they may consume (e.g., berries), or small animals (e.g., rodents, lizards, etc.) whose entire range will be limited in scale and thus contained with the carnivore’s territory. Thus both human and animal predatory strontium signatures may reflect procurement ranges both larger and different from their actual territories. In geologically diverse regions, interpretation of bioavailable geochemistry can be complicated by the fact that animals with small home ranges (e.g., suslik) may have adjacent geographical territories but exist on different bedrock formations and thus have different strontium ratios. Larger species, such as moose and red deer frequently cross geologic boundaries during the course of an annual foraging cycle; averaging the 87Sr/86Sr ratios in their tissues. Thus interpretation of the bioavailable geochemistry can be unintentionally biased during sampling based on sample availability.

TOOTH MINERALIZATION Teeth are dynamic mineral structures whose complexities are still being unraveled. It has long been recognized that the incremental striae of Retzius represented some aspect of matrix deposition but that there is a disconnect between this matrix deposition and the final mineralization that will finalize the mineral matrix (e.g., [32]). At the time, microsampling of individual striae was not practical, thus the matter was largely ignored. However, there has recently been a resurgence of interest in the formation process of the incremental growth lines as reflections of the circadian rhythm of enamel matrix secretion with the advent of microsampling techniques such as laser ablation and microdrilling that could theoretically sample the enamel at such pertinent scales (e.g., [1, 4, 7, 33, 34]). Numerous hypotheses have been forwarded regarding the pattern and progression of enamel mineralization, however the common theme amongst all works is that the progression of mineralization of layers and/or maturation of matrices is patchy and effectively non-linear thus making the chronological relationship between incremental lines and geochemical signals rather tenuous [33-42]. Broad


51

trends whereby mineralization begins at the tooth cusp and finishes at the cingulum are still present, though the intermediate pathways are debatable. Montgomery and Evans, [39] and Fincham et al., [37] provide excellent discussion of the biomineralization of tooth enamel with respect to Sr isotope analysis. The process of mineralization spans a series of five distinct phases wherein an organic gel or protein superstructure is transformed into a mineral matrix: 1) secretion; 2) assembly; 3) matrix formation; 4) resorption prior to maturation; and 5) maturation (see Fincham et al. [37] Figure 8; Bentley [35] Figure 18). Following assembly, nanospheres of apatite will remain largely intact until maturation, however although these individual crystal structures are reflexive of their formation environment, they will mingle with other crystals to form a heterogeneous lattice of crystals in the mature matrix. Effectively, at all stages prior to maturation, the enamel matrix remains an open chemical system vulnerable to alteration, overprinting, or simply averaging of the matrix at the scale of modern recovery techniques. The practical ramifications of this open chemical system is that while the formation of tooth crowns progresses at a well known rate and there are incremental growth lines to further support the logical conception of enamel matrix as a progressive linear formation, all work to date demonstrates that there is a disjunction between enamel formation and matrix maturation. So while we know that calcification of M1 begins at birth and ends with maturation and root formation between 3 – 4 years of age, we are left with nearly three years of that molar remaining an open chemical system and a potential averaging effect [33, 43]. In spite of this theoretical difficulty, there is still some promise to the concept of microsampling tooth enamel. That incremental growth lines do not mineralize in a similar incremental fashion has been well demonstrated, however we still have some broad guidelines that remain true: 1) the crown of a tooth will fully mineralize before the root; and 2) though accomplished in a patchy or wave-like fashion, there are still broadly linear trends in mineralization progressing from crown to cingulum. Ongoing research into this problem with herbivore teeth has demonstrated that there are long-term mixing effects in action during the formation and maturation of tooth enamel [32, 42, 44-51]. Such research has highlighted a secondary problem with efforts to access the microstructure of teeth and thus provenance their formational period, that while formation of enamel proceeds using available mineral components within the body and that available components come from the diet, there is a gap between intake of the raw ionic components of the mineral structure and their incorporation into mineral tissues. Specifically this is the problem of residence time in the body for different elements. Water has a short residence time in the body of only 14 days; however strontium, calcium, and lead can remain in the body for 800–1600 days, with 10% of traceable doses remaining active after 400 days [51-53]. Recent works (e.g., [46, 51, 54]) have demonstrated that this residence time in the body has an intriguing effect on isotopic signatures of a linearly-sampled herbivore tooth. Namely that an abrupt change in geochemical geography and/or diet will not manifest as a sharp transition in isotopic signals, but rather that there will be a gradual sloping change as contributions from different geochemical end-members vary within the body-water average being accessed for ionic component material in enamel formation. At face value, this combination of lag time in mineral formation and maturation with body-water averaging of over a year should render discussions of microsampling human teeth for interim provenance information between the crown and cingulum, however it should be noted that there is an important difference between herbivore and human teeth. While it is quite likely that the same mineralization primers are in

52


effect for both human and herbivore teeth and that the non-linear progression of mineral maturation is effectively the same, the time spans involved are different. For example, each bovine molar will form and fully mineralize over a span of 12–18 months [51]. However, each human molar can theoretically span a time of 24–48 months between initial calcification and final mineral maturation, though it will likely occur in less than 36 months. Thus, we have a gap in comparative volumes and chronologies in discussing the differences between herbivore and human teeth. While many herbivore teeth are not good candidates for microsampling because their tooth formation rates will not outstrip uncertainties about residence time and mineralization rates, human teeth will likely exhibit some aspects of useful variability in isotopic signatures through formation time and thus through enamel mineral volume/geography. We still must keep in mind that at present it is impossible to overcome residence time for intake and maturation time for the mineral matrix, it may well be worth pursuing microsampling of human teeth in between cusp and cingulum.

LASER ABLATION OF TEETH The coupling of a laser ablation unit to either an ICP-MS or a MC-ICP-MS is no longer a novel concept to the fields of analytical chemistry and archaeology, and is rapidly becoming a mainstream tool for ongoing research and a key player in the advancement of microanalytical techniques (cf. [55-58]). Studies involving skeletal materials were fairly late additions to the field, in part due to latent concerns about the materials being analyzed and their potential for diagenetic alteration at the proposed scale of analysis. However, in the last decade or so, ICP-MS studies on teeth and bones have picked up significantly and are now part of a healthy academic field of research [1, 3-5, 7, 8, 51, 59-62]. Numerous studies have demonstrated the reliability of ICP-MS and MC-ICP-MS as compared to TIMS and INAA (cf. [57, 63-66]) using both laser ablation and solution mode sample introduction for both elemental composition and numerous isotopic series. ICP-MS and MC-ICP-MS are generally faster and less labor intensive than traditional analytical methods, however one of the tradeoffs is the tacit recognition of the need for corrections for a variety of interferences. The identification of and correction for the seemingly endless string of interferences across the mass spectrum is an extremely important part of researchers ability to use confidently ICPMS as an analytical tool. For single radiogenic isotopic series such as strontium, the list of potential problems includes known isobaric interferences (87Rb), doubly-charge rare earth ions [11], polyatomic species such as calcium dimers [10], calcium phosphate (CaPO) [1, 7-9, 67, 68], and other molecular species yet to be identified. While daunting and providing a divergence from the seemingly parsimonious relationship linking artifact and data via traditional analytical methodologies, identifying possible problems and monitoring for data quality are important parts of any analytical process and so should not be avoided. For Sr analysis, the largest if not most pernicious problems are isobaric interference from [87] Rb and a recently identified polyatomic interference from calcium phosphate, though an important distinction between the two should be made. Rubidium corrections are necessary for all ICP-MS and MC-ICP-MS analyses as the charged [87] Rb will carry the same masscharge ratio as its 87Sr counterpart, though this can be countered with accurate mass-bias calculations. This is not a problem associated with sample introduction methodology. On the


53

other hand, polyatomics such as Ca dimers and calcium phosphate species are notably absent in solution-mode analysis as sample ions are held in acid and thus prevented from recombining as they are free to do in the carrier-gas environment of laser ablation chambers. From the perspective of an end-user, that such interference only manifest, or are only apparent at significant levels via laser ablation introduction both with and without aspirated acids introduced, is both interesting and discouraging for microsampling potentials. It is intriguing that complex molecules manifest in the highly charged plasma environment when introduced by a carrier gas but not as an aspirated solution, as both are theoretically entering into the plasma chamber as ionized particles. Woodhead et al. [10], Simonetti et al. [8], Horstwood et al. [1], and Vroon et al. [9] have all discussed the presence of significant interference on mass 87 from a previously unidentified source, thus impinged on researchers’ ability to accurately assess the 87Sr/86Sr ratios of phosphate matrices with laser ablation. As all mammalian skeletal tissues are varieties of phosphate mineral matrices, this is a major problem for efforts to access the life signals contained therein and thus in archaeologists’ and paleontologists’ ability to accurately interpret these signals and thus reconstruct the movement histories of these animals. It appears that the root of the problem is the excess of Ca and P present in the charged environment coupling with the oxide production rates within the MC-ICP-MS. In theory, Ca and P levels should be proportional in all parts of skeletal tissues, thus mineral replacements such as Sr, Ba, and the incorporation of other trace elements should be proportional as well, and interferences will be related to the oxide operational conditions of the instrument itself. This leaves us with several important points to consider: do we have reason to question any of these starting assumptions? Can we monitor the formation of CaPO during analysis and thus correct for it in ways other than those outlined in previous works? Can we recover useful geochemical information from skeletal tissues using laser ablation as a microsampling technique?

MATERIALS AND METHODS Tooth enamel samples consist of five human molars from the KN XIV cemetery that have previously been used for analytical work by the Baikal Archaeology Project. Samples included 4 second molars from graves 7 (Sample #1997.211), 16 (1997.217), 35-1 (1998.355), and 35-2 (1998.359), as well as 1 third molar from grave 12 (1997.225). All samples were previously analyzed by Haverkort et al. [22] and several were also analyzed via TIMS by Weber et al.[26]. All samples were analyzed for elemental composition using both SM-ICP-MS and LA-ICP-MS and likewise for 87Sr/86Sr ratios using SM-MC-ICP-MS and LA-MC-ICP-MS. All preparation and analyses were conducted at the Radiogenic Isotope Facility of the Department of Earth and Atmospheric Sciences at the University of Alberta. Solutions were prepared by extracting fragments of enamel (between ~0.020-0.060 g) as close to the cingulum as possible to provide comparability between teeth with various levels of wear. Fragments were mechanically removed using a diamond cutting disk (NTI Diamond disc, Interflex-double sided, 8 mm diameter, 0.15 mm thickness) fitted to a Dremel tool. If necessary, samples were abraded with the disk to remove any adhering dentine. Sample locations were not side-specific as these teeth have been previously sampled, thus samples

54


were taken where adequate materials remained, though largely stemming from areas immediately adjacent to previous sampling locations. Sample preparation occurred in a Class 100 clean room facility and followed procedures outlined in Simonetti et al. [8] and Haverkort et al.[22]. Samples were sonicated for 15 min in milliQ (MQ) de-ionized water and then in 5% acetic acid for 15 min. After an overnight leaching in 5% acetic acid, the acid was removed and samples were rinsed with MQ prior to transfer to clean Teflon vial. A known amount of 87Rb–84Sr spike was added, followed by 4 mL of 16 N HNO3 and 1 mL of 12 N HCl and capped to digest on an 80 C hotplate overnight. Digested samples were then dried overnight on the hotplate. Dried samples were dissolved in 3 mL of 0.75 N HCl and loaded into syringes with disposable filters. Filtered samples were loaded onto 10 cm cation exchange columns containing 1.42 mL of 200-400 mesh AG50W-X8 resin. Columns were rinsed with 3x1 mL of 0.75 N HCl, 3x1 mL of 2.5 N HCl and washed with 17 mL of 2.5 N HCl. Samples of 5 mL of 2.5 N HCl containing the purified Sr were collected into clean Teflon vials and left to dry overnight on the hotplate. Dried samples were dissolved with 1 mL of 2% HNO3 prior to necessary dilution for MC-ICP-MS analysis. Analysis was conducted on a Nu Plasma HR MC-ICP-MS with a DSN-100 nebulizer. Strontium isotope data were acquired in static, multicollection mode using five Faraday collectors for a total of 400 s, consisting of 40 scans of 10 s integrations. The ‘wash-out’ period following the analysis of a sample was approximately 5 min. Prior to the aspiration of a sample, a 30 s measurement of the gas (+acid) blank was conducted to correct for [86] Kr and [84] Kr isobaric interferences. The isobaric interference of [87] Rb was monitored and corrected online using the [85] Rb signal. Accuracy and reproducibility of the analytical protocol based on long-term repeated analysis of a 100 ppb solution of the NIST SRM 987 strontium isotope standard 0.710242 ± 0.000041. Elemental samples of similar size underwent similar handing, though without the [87] Rb–[84] Sr spike, and not loaded onto cation exchange columns. Digested samples were simply dissolved in 2% HNO3 prior to quadrupole-ICP-MS analysis. Sample solutions were analyzed for 57 elements (Li, Be, B, Na, Mg, Al, P, Ca, Ti, V, Cr, Mn, Fe, Cu, Zn, Ga, Ge, As, Rb, Sr, Y, [90] Zr, [91] Zr, Nb, Mo, Ru, Pd, Ag, Cd, Sn, Sb, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Os, Pt, Au, Tl, Pb, Th, and U) using a Perken Elmer Elan6000 quadrupole ICP-MS, and instrument operating conditions as follows: RF power = 1200 W; dual detector mode; blank subtraction performed subsequent to internal standard correction; unit of measurement is cps (counts per second); auto lens on; use of 4point calibration curves (0, 0.25, 0.50, and 1.00 ppm for Ca, Mg, and Fe; 0.005, 0.010, and 0.020 ppm for the remaining elements); sample uptake rate (using a peristaltic pump) was ~1 mL; sample analysis consisted of 35 sweeps/reading, 1 reading/replicate and 3 replicates; dwell times were 10 ms for Al, Mn, and U, and 20 ms for the remaining elements; total intergration times (dwell time x number of sweeps) were 350 ms for Al, Mn, and U, and 700 ms for the remaining elements (Table 1). External reproducibility, based on repeated analysis of international whole rock standards is 5-10% (2σ level) for most elements. Laser ablation for elemental analysis of samples was conducted using the Perken Elmer Elan6000 quadrupole ICP-MS coupled to a UP213 nm laser ablation system (New Wave Research, USA). The instrument was optimized using the NIST SRM 612 international glass standard reference material (RF power 1200 W, peak hopping acquisition, 50 ms dwell time). Teeth were serially sampled (Figure 2) using LA-ICP-MS to examine the nature and extent of useful intra-tooth geochemical variability in tandem with attempts to monitor the formation of


55

the CaPO polyatomic species. This sampling included 8 sampling locations or groups on each tooth, offset but approximately equally spaced between the bottom of the crown and the cingulum. Groups consisted of 5 lines each with a combination of laser spot size and laser power settings were employed to assess the impact of potential laser-matrix effects. Half of the sampling groups were conducted using 50% laser power, while the other half was run at 100% laser power. Line groups consisted of reducing laser spot sizes of 100, 80, 55, 40 and 25 µm in sequence, with a repetition rate of 20Hz and an energy density of ~13 J cm-2. Experiments were conducted in a mixed He/Ar atmosphere (ratio of 0.5:0.1 L min-1) within the ablation cell, and mixed with Ar (1.03 L min-1) prior to entering the torch assembly. The laser ablation cell was flushed with a higher flow rate of He (up to 0.9 L min-1) for approximately 1 min in-between laser ablation runs to ensure adequate particle washout. The NIST SRM 612 glass standard was used as the external calibration standard. Quantitative results for 57 elements (Li, Be, B, Na, Al, Si, P, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Ga, Ge, As, Rb, Sr, Y, [90] Zr, [91] Zr, Nb, Mo, Ag, Cd, In, Sn, Sb, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Re, Au, Tl, Pb, Bi, Th, and U) were obtained and normalized to 24Mg, as measured by solution analysis, as the internal standard using the GLITTER® (XP version, Macquarie University) laser ablation software (Table 2). Mg was used instead of Ca in order to assess variability in calcium in these teeth. Laser ablation for isotopic analysis was conducted using a UP213 nm laser system coupled to the Nu Plasma HR MC-ICP-MS with the sample-out line from the desolvating nebulizing introduction system (DSN-100 from Nu Instruments) to allow for simultaneous aspiration of a 2% HNO3 solution. At the beginning of each analytical session, parameters for the introduction system and the ion optics were optimized by aspirating a 100 ppb solution of the NIST SRM 987 Sr isotope standard. Based on the results of the elemental laser ablation analysis, a full replication of the line groups was not done. Instead, overlying each full powered elemental sampling site, three parallel lines were analyzed using 100 µm laser spot size; 100% laser power; 20 Hz repetition rate; ~15 J cm-2 energy density (Table 3). Half powered elemental sampling sites were not sampled for isotopic data as the elemental data were deemed to be of poor quality. Strontium isotope data were acquired in static, multicollection mode using five Faraday collectors for a total of 400 s, consisting of 40 scans of 10 s integrations, for data reported. Testing for potential collector setups included attempts at using eight collectors in order to extend the monitored mass range to include masses 90 and 91. Similar efforts were also attempted using dual-acquisition, static analysis to similar effect following Horstwood et al. 1. Laser data were partially monitored by repeated analysis of a specimen of Durango Apatite with a reported value of 0.706327 ± 0.000724 by TIMS 1. In one analytical session, an average value of 0.706118 ± 0.000035 were observed, and in a second, 0.706244 ± 0.000028. This sample is currently being intensively sampled for its ongoing use as a mineral standard for strontium analysis at the Radiogenic Isotopic Facility, however at present has been analyzed fewer than fifty times and thus can only be viewed with moderate confidence. As such, no attempts were made to standardize data for enamel samples to apatite values. Quantification of the oxide levels during analyses using UO+/U+ demonstrated levels of approximately 0.7%.

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Ian Scharlotta, Andrzej Weber, S. Andy Dufane et al. Table 1. Solution mode 87Sr/86Sr ratios and elemental data for KN XIV teeth. Local/Nonlocal determinations from Haverkort et al. 2008 Re

Os

Pt

Au

Tl

Pb

Th

U

0.001927

0.009514

0.001906

0.058862

0.001221

0.268555

2.340665

0.071605

Little Sea Origin Nonlocal

0.007496

0.043007

0.007412

0.298735

0.073691

0.079869

0.213768

0.015656

Local

0.005342

0.033591

0.007894

0.246172

0.04021

0.138083

0.198961

0.024269

Local

0.001878

0.028736

0.006105

0.186726

0.022941

0.054092

0.091068

0.005631

Nonlocal

0.002238

0.012796

0.002007

0.083647

0.007105

0.060767

0.030142

0.003889

Nonlocal

Figure 2. Sampling scheme used on sectioned teeth. Enlargement – laser ablation scars representing one sampling group

RESULTS AND DISCUSSION This research included a number of different aspects, beginning with efforts to demonstrate the value in trace element analysis of human teeth for provenance and/or mobility purposes. The treatment of organic minerals in a similar fashion to complex inorganic minerals for the purposes of provenance analysis is a fairly new and expanding area of research within the realm of provenance analysis (cf. [5, 69, 70]). The underlying concept is the same for any geochemical sourcing study, in that the range of variability must meet the strictures of the “Provenance Postulate” [71]. Though this has been demonstrated for populations on Rapa Nui [70], and in distinguishing African immigrants in a Mexican cemetery [5, 69]; the range of useful variability in trace element composition must be determined for each geographical region. Thus, for cemeteries in Cis-Baikal, a new database of locally useful elemental variability must be generated. This research consisted of only 5 samples, however still presents a beginning to the formation of such a database.

Table 2. Laser ablation elemental data for KN XIV teeth (Sample ID Laser Spot Size Sample Group) Sample ID_Spot Size_Group 97211_100_A 97211_80_A 97211_55_A 97211_40_A 97211_25_A 97211_100_B 97211_80_B 97211_55_B 97211_40_B 97211_25_B 97211_100_C 97211_80_C 97211_55_C 97211_40_C 97211_25_C 97211_100_D 97211_80_D 97211_55_D 97211_40_D 97211_25_D 97211_100_E 97211_80_E 97211_55_E 97211_40_E 97211_25_E 97211_100_F 97211_80_F

Li 0.364 0.49 0.65 0.3 1.08 0.452 0.41 0.44 0.28 1.44 0.5 0.36 0.4 0.67 0.19 0.342 0.52 0.32 0.6 1.56 1.1 1.37 3.13 5.44 25.95 0.35 1.2

Be 0.205 0.6 2.02 1.05 7.14 0.46 0.2 1.37 2.56 2.68 0.048 0.25 2.56 3.48 3.63 0.36 1.04 0.18 2.17 6.97 7.93 11.93 33.7 23.82 160.17 2.8 2.12

B 1.08 1.22 1.23 3.77 7.2 0.79 1.58 1.06 2.36 4.11 1.31 1.11 1.09 1.83 3.78 1.01 0.83 1.56 1.15 4.17 3.15 5.69 17.63 22.8 59.52 1.2 3.89

Na 3650.44 3547.81 3653.11 3716.37 3814.94 3657.98 3724.74 3741.95 3569.28 3175.41 3649.68 3641.77 3607.72 3416.2 3474.17 4132.01 4204.36 4010.44 4146.8 4206.67 3894.62 4215.7 3801.75 4827.18 5311.39 3803.64 3779.97

Al 241.22 43.92 6.41 47.85 18.7 21.52 25.71 39.4 75.03 265.42 14.92 21.53 35.86 43.02 94.97 19.07 37.76 51.79 62.98 148.6 10.1 392.19 1018.72 1198.29 2085.95 273.24 190.42

Si 207.24 117.65 104.64 146.62 403.09 104.25 55.41 120.28 83.01 476.86 101.74 69.43 135.81 129.46 287.02 101.29 95.69 129.55 156.79 272.57 154.08 403.74 850.41 1125.62 4583.92 75.26 323.51

P 64027.67 63294.82 61442.43 64486.52 65675.6 58902.48 61789.18 59194.78 59178.95 53285.48 55783.39 57419.32 55748.88 54201.63 55328.13 51666.73 58097.5 55033.9 56970.46 55208.66 48036.38 49273.86 49333.76 43452.75 48566.3 41278.58 41964.24

Ca 222294.11 237603.84 236211.53 234467.86 264530.88 218525.92 233481.7 230185.63 225280.58 195903.66 214245.89 228728.3 210288.25 203894.3 210873.78 201905.63 225548.22 214956.39 223171.36 202296.55 199831.05 190208.02 169428.05 166217.27 190663.23 155721.28 167564.7

Sc 0.09 0.163 0.38 0.44 1.99 0.083 0.158 0.33 0.45 1.37 0.076 0.154 0.257 0.45 1.48 0.099 0.193 0.29 0.43 1.41 0.88 1.95 4.42 5.23 20.43 0.44 1.28

Ti 4.27 1.69 4.81 5.07 21.41 0.85 1.47 4.78 5.9 15.23 0.66 1.82 2.65 4.25 17.57 0.82 1.53 2.74 4.14 17.12 8.08 15.33 33.18 57.2 242.12 4.44 18.32

V 2.88 2.99 3.11 2.47 3.5 2.6 2.39 2.81 1.69 1.9 2.25 2.37 2.11 2.1 1.53 2.2 1.94 1.94 2.28 2.01 3.12 1.96 4.45 5.8 23.43 3.33 2.6

Cr 1.01 0.72 1.62 2.11 9.87 0.88 1 1.52 2.12 7.14 1.05 1.44 1.18 2.28 7.03 0.93 0.75 1.7 2.25 6.81 4.24 8.88 22.43 26.83 116.43 1.91 7.42

Mn 35.32 9.61 4.16 12.8 9.85 5.81 5.95 9.29 14.62 31.62 5.91 7.58 11.68 16.71 23.61 10.03 9.76 15.9 43.31 214.22 1.51 26.38 444.45 205.11 829.46 12.23 48.77

Fe 112.83 57.92 42.41 52.47 44.14 55.75 58.15 50.59 65.95 128.41 54.41 53.47 50.49 59.75 78.31 51.05 49.51 65.86 83.66 161.45 41.3 122.1 247.13 193.95 611.92 99.04 126.33

Co 0.325 0.082 0.117 0.124 0.82 0.072 0.065 0.128 0.155 0.61 0.035 0.197 0.107 0.159 0.33 0.126 0.116 0.16 0.332 2.09 0.39 0.83 4.88 10.14 13.29 0.193 0.59

Cu 0.53 0.34 0.69 0.93 4.1 0.243 0.25 0.61 0.91 3.09 0.205 0.3 0.41 0.93 2.68 0.164 0.25 0.52 0.93 2.78 1.39 2.89 6.95 7.29 41.04 0.51 2.24

Zn 111.04 87.43 78.25 86.53 82.72 58.72 54.58 45.15 61.21 63.15 46.04 50.7 47.52 56.47 63.14 31.87 36.83 48.97 63.01 88.47 22.07 25.29 68.38 59.31 145.64 29.72 17.46

Table 2. (Continued) Sample ID_Spot Size_Group 97211_55_F 97211_40_F 97211_25_F 97211_100_G 97211_80_G 97211_55_G 97211_40_G 97211_25_G 97211_100_H 97211_80_H 97211_55_H 97211_40_H 97211_25_H 97217_100_A 97217_80_A 97217_55_A 97217_40_A 97217_25_A 97217_100_B 97217_80_B 97217_55_B 97217_40_B 97217_25_B 97217_100_C 97217_80_C 97217_55_C 97217_40_C 97217_25_C

Li 1.81 1.78 4.18 0.51 0.3 2.77 1.84 0.001 0.57 0.63 2.43 3.53 21.17 0.302 0.23 0.156 0.76 1.3 0.27 0.42 0.39 0.67 2.38 0.33 0.42 0.75 0.75 2.44

Be 0.001 5.31 17.92 1.31 0.45 12.88 0.001 19.03 0.28 5.88 12.35 67.22 92.14 0.049 0.25 2.23 4.03 9.3 0.57 1.03 3.77 5.33 3.59 0.51 1.81 2.2 0.55 5.37

B 9.57 6.65 12.3 1.58 1.18 6.89 6.83 6.33 1.17 3.18 10.22 42.16 72.65 1.25 1.3 2.63 3.13 4.74 1.55 1.61 1.87 3.21 7.52 1.2 2.14 1.95 1.75 9.74

Na 3236.03 2218.74 1287.24 3620.49 2540.82 2853.51 2510.86 2013.43 4636.57 5196.43 5194.39 4132.36 3925.68 5322.98 5153.04 5177.93 5336.97 5415.9 5164.93 5245.86 5329.83 5352.14 5516.12 5361.01 5488.83 5538.91 5787.83 5344.36

Al 452.1 460.72 357.72 176.83 275.93 332 281.65 1399.86 262.33 692.49 833.21 946.69 2336.83 4.03 2.83 0.84 1.83 4.69 4.97 5 13.07 8.4 6.8 7.6 21.42 27.02 42.73 70.34

Si 434.71 452.35 739.64 54.21 214.82 281.46 438.22 535.55 84.19 354.25 450.13 3006.45 3143.39 87.9 75.32 188.54 131.66 445.3 119.17 134.56 119.79 122.07 425.48 101.6 103.23 160.34 177.41 491.56

P 36926.37 25898.87 12963.16 37092.63 25102.88 31469.35 31199.55 16874.91 46825.67 53934.13 54286.59 46711.54 39578.45 73633.24 78360.02 76338.85 78017.85 79130.62 75013.55 79826.28 80309.66 81215.74 84018.63 72692.55 80016.89 79543.34 84828.95 83480.05

Ca 147313.73 100775.26 44549.54 147173.53 100285.7 129220.73 117070.11 56437.6 184185.75 205958.03 207796.53 206638.84 170792.42 288064.91 301801.22 301184.59 310309.25 312386.91 295278.63 316606.38 311098.38 313226.5 322509.84 287984.03 315531.25 305731.81 335817.41 322326.03

Sc 2.18 2.15 4.64 0.25 0.44 1.35 2.03 2.56 0.39 1.08 2.14 13.37 14.04 0.097 0.19 0.39 0.82 2.45 0.078 0.183 0.38 0.59 2.05 0.096 0.2 0.4 0.63 1.82

Ti 14.3 25.22 32.42 2.54 4.43 16.66 25.25 30.69 5.41 9.2 23.24 150.48 184.61 1.05 1.32 4.09 5.57 21.26 0.88 1.58 2.95 6.23 13.76 0.69 1.83 3.86 6.61 24.66

V 3.06 2.39 4.11 3.73 1.99 4.33 2.49 2.81 3.66 2.7 3.04 12.71 14.02 1.29 1.11 0.83 0.67 1.88 0.9 1 0.84 0.6 2.09 0.98 1.33 1.25 1.4 1.82

Cr 11.28 11.96 19.39 1.44 2.98 7.94 11.77 14.3 1.95 5.62 12.6 71.73 86 1.17 0.89 2.03 3.75 13.64 1.27 1.63 2.3 3.35 11.41 1.31 2.01 1.94 3.62 11.19

Mn 16.03 16.69 6.98 115.21 20.58 33.58 81.72 238.55 353.34 314.95 504.33 174.51 67.08 1.19 1.18 1.37 0.9 3.08 2.05 1.26 2.4 1.22 2.71 1.48 2.97 2.79 6.08 12.04

Fe 283.83 144.88 96.96 82.6 137.19 191.63 165.51 309.78 171.42 193.53 388.33 324.33 1350.36 86.75 81.11 67.95 77.8 97.92 74.66 73.82 58.88 61.34 108.25 67.52 72.63 54.57 97.04 64.64

Co 0.96 0.94 1.33 0.72 1.14 0.79 2.73 4.2 10.1 7.32 7.08 4.31 8.11 0.522 0.128 0.158 0.29 0.8 0.03 0.051 0.215 0.4 0.53 0.054 0.117 0.114 0.228 0.74

Cu 2.15 3.17 5.05 0.46 0.76 1.93 3.07 4.31 0.57 1.73 3.39 22.78 24.61 0.443 0.27 0.62 1.05 2.14 0.78 0.32 0.47 1.09 2.56 0.142 0.186 0.49 0.67 2.35

Zn 17.79 22.71 28.1 21.46 15.11 11.66 19.09 19.27 24.26 28.9 55.69 88.13 106.7 54.82 60.25 61.75 52.89 39.46 80.93 87.49 109.41 101.06 124.54 75.36 128.63 140 161.98 225.47

Table 2. (Continued) Sample ID_Spot Size_Group 97217_100_D 97217_80_D 97217_55_D 97217_40_D 97217_25_D 97217_100_E 97217_80_E 97217_55_E 97217_40_E 97217_25_E 97217_100_F 97217_80_F 97217_55_F 97217_40_F 97217_25_F 97217_100_G 97217_80_G 97217_55_G 97217_40_G 97217_25_G 97217_100_H 97217_80_H 97217_55_H 97217_40_H 97217_25_H 97225_100_A 97225_80_A 97225_55_A

Li 0.253 0.29 0.45 0.73 2.22 1.35 3.37 5.58 12.48 29.37 0.51 0.34 3.48 7.5 25.38 0.67 1.2 6.13 15.07 11.67 1.45 4.18 3.73 15.94 15.77 0.138 0.36 1.27

Be 0.15 1.12 2.44 3.93 7.97 0.73 12.55 29.31 46.07 340.96 5.72 11.48 25.14 38.1 90.59 4.74 20.96 9.41 60.66 185.76 5.01 28.56 23.31 43.94 49.86 0.21 0.81 0.88

B 1.16 0.83 3.84 1.3 8.81 3.36 8.4 13.91 38 89.22 3.36 9.56 13.56 15.21 53.91 1.63 10.35 12.93 25.88 112.51 2.94 15.91 11.66 27.01 73.04 2.15 2.79 2.69

Na 5927.98 6053.21 6359.43 6338.53 5876.09 4874.99 4940.43 4384.32 5117.52 6593.72 5447.38 4986.99 6080.22 5933.6 6416.94 5204.55 5310.13 5367.78 4478.11 5050.97 5566.45 4952.52 4308.03 6457.71 5397.13 7009.91 6991.29 7209.43

Al 17.49 17.32 49.05 43.1 25.42 1.95 4.08 8.34 18.48 46.4 1.32 8.92 96.24 15.44 30.51 1.22 5.06 7.75 19.24 65.11 1.24 8.03 6.13 16.53 54.8 11.65 5.8 11.45

Si 147.25 121.23 153.02 176.99 554.23 157.63 385.68 716.33 1674.86 5197.13 131.51 344.7 594.78 1192.35 2850.36 112.05 430.95 701.58 1402.86 6014.97 145.54 654.89 752.29 1401.29 4588.98 236.14 203.36 115.56

P 77479.99 82094.33 84394.7 83431.14 80796.29 74659.08 66046.16 62152.77 72106.77 73007.28 61558.16 56684.51 62864.18 59769.67 54528.75 61292.16 63336.43 63516.46 55760.45 71602.13 62848.21 64016.12 56822.76 63017.98 56168.67 118420.75 117615.88 115827.97

Ca 304195.91 330688.81 331941.84 331381.16 310824.81 288323.47 272802.16 253801.8 255346.58 252952.38 238079.16 229622.8 221898.14 229634.73 229070.47 230307.47 257116.75 232396.8 209294.88 211325.31 245832.11 269740.88 217050.23 239038.19 254952.69 547999.25 533000.56 534019.63

Sc 0.1 0.176 0.41 0.58 1.88 0.85 1.79 3.52 8.62 29.53 0.76 1.68 3.43 6.21 15.06 0.7 1.91 3.02 6.99 27.45 0.76 3.04 3.64 6.55 19.83 0.197 0.33 0.64

Ti 0.94 1.46 4.45 8.74 15.15 7.2 15.89 22.6 76.39 268.9 7.09 17.35 21.84 65.84 145.7 2.87 30.52 31.54 57.12 291.19 6.6 33.5 33.31 57.01 203.67 2.5 3.72 8.39

V 1.47 1.51 1.85 1.78 1.55 0.84 1.75 3.24 7.03 24.41 0.89 1.59 2.4 6.56 12.4 0.62 1.87 2.97 5.88 18.66 1.14 2.67 3.2 5.23 16.15 2.63 1.9 1.45

Cr 1.31 1.76 2.5 3.22 9.78 4.14 11.14 19.99 44.99 141.67 3.55 9.32 22.42 34.57 76.63 3.12 11.28 19.41 37.26 167 4.02 17.63 20.4 37.44 128.87 2.29 1.42 2.84

Mn 2.15 2.16 4.04 4.55 4.27 0.98 2.54 4.58 11.92 29.96 0.88 2.18 3.83 6.24 17.4 0.65 2.32 4.13 9.29 34.55 0.9 3.94 4.49 8.11 25.43 22.63 19.45 30.69

Fe 62.82 67.75 97.87 93.64 55.41 64.49 79.98 102.32 233.36 750.51 23.24 51.4 100.09 219.56 403.72 21.43 72.1 98.5 189.85 847.78 39.04 82.8 99 211.21 710.13 164.72 92.34 79.29

Co 0.054 0.088 0.134 0.215 0.31 0.39 0.83 1.12 3.91 7.09 0.215 0.61 1.33 3.17 5.81 0.197 0.77 2.23 1.56 9.54 0.256 1.03 1.67 2.33 7.25 0.267 0.203 0.29

Cu 0.166 0.32 0.48 2.99 1.91 1.05 2.72 5.22 11.55 45.08 0.9 1.92 8.17 9.38 22.22 0.87 3.09 5.71 10.36 48.97 1.2 5.71 7.16 10.75 42.1 0.54 0.41 0.74

Zn 89.66 133.34 161.51 171.33 213.6 18.04 15.44 31.78 44.87 157.48 29.97 39.49 30.27 63.28 77.88 27.64 16.15 22.12 41.25 146.95 25.61 20.12 24.28 39.32 127.89 233.38 197.71 180.02

Table 2. (Continued) Sample ID_Spot Size_Group 97225_40_A 97225_25_A 97225_100_B 97225_80_B 97225_55_B 97225_40_B 97225_25_B 97225_100_C 97225_80_C 97225_55_C 97225_40_C 97225_25_C 97225_100_D 97225_80_D 97225_55_D 97225_40_D 97225_25_D 97225_100_E 97225_80_E 97225_55_E 97225_40_E 97225_25_E 97225_100_F 97225_80_F 97225_55_F 97225_40_F 97225_25_F 97225_100_G

Li 1.3 2.1 0.26 0.39 0.53 0.35 6.26 0.21 0.14 0.82 0.94 5.34 0.34 0.12 1.63 1.23 1.83 2.38 6.32 0.001 54.37 65.04 2.36 5.63 13.96 20.93 41.89 2.66

Be 8.14 32.21 1.4 1.66 4.56 0.001 4.97 0.76 2.5 3.33 5.58 21.27 0.78 1.76 0.001 6.65 14.99 5.64 23.43 108.18 241.3 232.96 8.36 19.7 48.22 11.64 0.001 1.36

B 5.23 12.01 1.7 2.26 2.74 4.4 10 2.66 3.65 2.59 3.44 14.47 2.64 3.04 2.82 6.96 13.52 7.22 21.38 25.63 81.33 216.3 10.21 14.88 35.32 75.92 104.35 24.07

Na 7091.02 7298.59 7110.85 7101.9 7213.48 7262.51 6867.13 6903.09 6900.58 7091.58 6971.92 6917.97 7044.42 7369.27 7249.75 6012.49 6205.92 7142.03 6578.72 6918.53 7743.79 7593.37 6720.33 8880.7 7745.32 7110.64 13476.81 6693.77

Al 22.99 30.42 11.32 27.67 2.87 50.78 144.9 29.25 62.83 40.18 90.88 312.97 45.77 61.45 97.82 1168.06 1193.8 153.98 124.8 315.61 621.28 1749.5 112.88 485.34 780.71 855.26 1660.19 449.02

Si 406.28 969.63 188.03 173.43 221.78 334.47 1187.44 245.45 240.13 166.9 330.92 1007.41 252.37 193.14 324.94 2203.63 1523.9 717.12 729.19 1919.67 4511.08 7438.72 329.52 631.81 1511.97 2208.14 7062.54 196.77

P 116400.12 115523.09 105481.35 107869.02 103344.02 102750.77 99076.79 94364.73 96928.23 102025.57 98884.62 110471.86 87573.85 95663.72 95804.03 81548.66 81772.52 86554 80613.89 78710.49 102583.11 84279.17 78545.98 73909.46 85002.02 76997.26 73522.03 64489.92

Ca 528096.56 538233.38 486559.34 500983.44 493218.41 452287.69 433927.63 429419.22 447873.19 446393.53 439993.31 451093.31 407170.88 454880.19 437473.03 354900.31 382409.78 394904.47 377897.91 390870.03 454514.84 319535.22 347284.44 324531.34 358737.06 312071.31 303866.94 288153.59

Sc 1.06 3.77 0.231 0.46 0.61 0.89 2.96 0.23 0.27 0.58 0.85 3.48 0.278 0.31 0.56 0.65 2.3 1.44 3.66 7.92 20.08 35.12 1.24 2.91 7.42 11.41 38.06 0.72

Ti 15.75 49.6 3.32 4.6 6.87 22.02 32.24 1.82 4.24 5.72 9.97 40.78 2.47 2.81 5.18 199.39 41.36 67.73 32.64 129.8 287.86 436.9 11.31 31.28 134.15 308.31 324.19 30.89

V 2.51 3.75 1.52 1.73 1.37 1.63 2.44 1.91 2.29 2.15 1.55 3.03 1.75 1.48 1.56 3.84 3 2.46 3.34 6.66 17.18 26.82 2.58 2.7 5.78 7.37 28.36 4.19

Cr 5.28 19.59 2.09 1.84 3.04 4.32 15.95 2.16 1.63 2.63 4.42 17.02 2.08 1.38 2.79 3.44 12.07 6.6 17.86 48.22 112.72 185.53 6.04 14.9 36.92 55.22 181.28 3.44

Mn 51.46 70.57 72.05 116.74 41.39 139.16 191.49 90.3 114.56 117.72 133.45 165.93 66.22 71.25 96.46 198.46 317.94 25.13 55.97 417.99 47.27 252.2 215.38 324.34 5553.71 983.29 4583.88 995.24

Fe 105.56 115.7 89.8 101.37 72.48 129.37 255.37 108.12 195.85 124.74 246.59 284.82 154.96 104.73 162.87 1195.9 1467.85 183.52 122.69 525.76 554.84 1294.26 147.61 479.44 1667.19 465.53 3465.42 661.69

Co 0.34 0.91 0.361 0.57 0.24 0.36 1.72 0.94 0.62 0.34 0.61 1.11 1.71 0.43 0.82 1.45 4.88 0.69 2.54 10.67 7.48 14.38 2.67 3.26 111.06 18.13 94.51 10.7

Cu 1.62 6.09 0.4 0.67 0.72 1.29 14.63 0.59 1.16 0.7 1.16 3.99 0.56 0.53 0.63 2.29 4.52 24.17 12.67 28.57 49.34 166.2 5.66 22.62 34.72 23.08 63.43 7.49

Zn 148.62 160.13 110.46 133.36 136.73 137.3 121.88 63.11 83.93 100.05 127.31 159.73 50.85 82.18 109.97 147.13 209.36 44.22 43.21 46.12 191.91 175.58 32.93 38.32 45.03 58.93 166.3 49.91

Table 2. (Continued) Sample ID_Spot Size_Group 97225_80_G 97225_55_G 97225_40_G 97225_25_G 97225_100_H 97225_80_H 97225_55_H 97225_40_H 97225_25_H 98355_100_A 98355_80_A 98355_55_A 98355_40_A 98355_25_A 98355_100_B 98355_80_B 98355_55_B 98355_40_B 98355_25_B 98355_100_C 98355_80_C 98355_55_C 98355_40_C 98355_25_C 98355_100_D 98355_80_D 98355_55_D 98355_40_D

Li 6.55 22.54 22.79 97.52 3.32 7.57 13.67 13.86 13.25 0.54 1.01 2.44 2.97 14.16 1.19 0.98 1.47 3.55 1.27 0.6 0.9 1.93 2.61 2.72 0.95 1.58 1.29 3.25

Be 21.49 51.58 51.42 306.78 14.55 3.35 28.11 41.03 88.78 1.24 1.92 4.42 2.14 3.61 0.91 1.25 5.58 6.75 25.41 1.03 1.71 6.37 6.53 0.001 0.98 0.75 1.07 12.4

B 18.48 27.72 58.92 192.06 9.17 27.47 50.85 26.43 70.58 5.76 5.56 4.37 5.01 15.13 3.2 3.23 2.88 5.29 10.19 2.48 2.96 3.75 2.63 10.44 1.91 2.22 2.31 3.08

Na 6380.51 6193.42 5364.01 7696.5 6893.58 6836.5 8864.9 5652.05 5005.34 5715.82 5622.5 5663.76 5670.43 4686.16 5657.17 5615.04 5372.02 5249.11 6173.66 5582.27 5446.07 5575.09 5514.95 5778.55 6429.01 6421.12 6820.49 7765.45

Al 1021.31 859.05 1316.62 2135.23 1161.7 1539.04 1908.91 3108.64 5094.67 47.49 73.4 32.12 26.4 28.89 3.01 0.49 1.08 1.6 7.56 1.09 0.45 1.44 3.48 7.16 237.45 323.44 273.27 729.25

Si 1335.82 1466.06 1545.29 6449.39 905.22 1612.08 2008.06 3307.72 9918.99 160.44 147.51 171.84 237.2 588.75 148 126.5 191.85 142.09 527.63 105.88 57.24 191.56 132.94 483.09 1193.9 1267.38 1211.85 943.44

P 67508.48 70270.96 53421.58 58507.17 80838.57 87671.91 96971.75 65682.73 75493.9 76667.38 78834.41 77084.85 80196.4 75901.7 68496.59 68328.76 65910.07 68869.52 72705.4 62837.27 64233.39 63542.27 65848.53 71633.34 59013.73 60990.56 62857.28 70267

Ca 292432.97 350032.38 238860.69 299051.5 352329.72 401446.84 391857.13 304642.97 264445.81 416772.53 431454.03 409923.94 426649.38 387291.19 364693.19 369036.72 343270.53 350840.31 368005.75 323981.69 333070.44 319095 335529.44 355946.41 323913.41 341151.97 344753.59 347507.31

Sc 2.07 8.38 7.78 29.7 1.44 3.35 5.97 5.25 10.08 0.221 0.236 0.51 0.84 2.92 0.107 0.222 0.44 0.68 2.38 0.111 0.158 0.35 0.61 2.04 0.085 0.143 0.3 0.77

Ti 61.34 77 75.24 357.12 51.19 61.56 110.92 211.5 224.26 1.21 2.12 3.64 6.64 29.52 0.94 1.51 4.07 6.01 22.59 0.91 0.81 1.88 6.21 16 10.85 16.11 8.05 23.78

V 4.61 5.45 5.16 23.14 2.65 4.48 16.21 18.87 10.29 8.08 7.73 7.25 7.12 5.07 5.11 4.19 3.48 3.06 4.81 2.82 2.62 2.2 3.02 3.83 4.06 3.78 4.16 3.95

Cr 11.34 35.98 39.87 157.61 6.74 17.02 29.96 32.3 61.11 2.16 1.35 2.52 4.53 15.51 1.96 1.97 2.24 3.78 14 1.58 1.57 1.99 3.56 13.25 3.3 4.59 3.56 5.72

Mn 1122.96 146.26 587.92 76.04 714.47 2161.51 7760.16 11867.08 4544.06 30.84 27.08 20.22 15.82 13.3 10.49 5.33 3.39 4.13 4.17 2.88 3.19 2.66 3.05 4.09 28.16 54.91 30.31 23.01

Fe 1626.33 811.2 1544.88 1325.45 1753.68 2538.6 4277.3 5616.39 8637.84 96.47 65.61 74.58 48.68 85.65 48.69 34.46 45.33 43.18 64.66 58.47 30.25 39.47 36.14 67.77 245.76 369.97 306.27 456.15

Co 28.25 3.06 22.83 11.05 15.33 76.2 141.86 249.35 238.78 0.34 0.148 0.178 0.184 0.88 0.116 0.084 0.09 0.31 0.58 0.064 0.103 0.132 0.3 1.51 0.456 0.716 0.193 0.39

Cu 9.74 7.5 10.52 31.23 5.73 8.44 11.78 26.78 16.51 0.727 0.38 0.81 0.96 3.7 0.495 0.25 0.45 0.68 3.2 0.206 0.159 0.34 0.55 2.37 10.24 11.73 12.21 1.86

Zn 52.58 48.88 33.97 128.11 112.81 174.01 386.13 181.63 194.79 112.49 85.24 67.55 56.57 45.46 32.04 25.22 22.53 22.76 19.42 30.29 35.1 48.45 72.28 78.21 35.88 49.34 58.79 74.3

Table 2. (Continued) Sample ID_Spot Size_Group 98355_25_D 98355_100_E 98355_80_E 98355_55_E 98355_40_E 98355_25_E 98355_100_F 98355_80_F 98355_55_F 98355_40_F 98355_25_F 98355_100_G 98355_80_G 98355_55_G 98355_40_G 98355_25_G 98355_100_H 98355_80_H 98355_55_H 98355_40_H 98355_25_H 98359_100_A 98359_80_A 98359_55_A 98359_40_A 98359_25_A 98359_100_B 98359_80_B

Li 7.48 2.65 8.41 5.53 45.64 135.38 2.76 0.001 14.86 35.13 116.58 0.32 8.75 17.38 14.44 68.33 2.35 2.86 4.17 12.33 13.1 0.89 0.64 2.01 5.07 14.36 0.87 0.74

Be 28.57 7.15 12.24 7.48 123.51 518.4 2.74 34.52 57 67.4 206.26 1.72 16.82 33.42 55.57 0.001 6.39 27.29 23.26 21.93 0.001 0.28 3.05 6.43 5.39 7.48 0.28 2.87

B 10.06 7.09 9.7 27.77 43.72 106.08 4.8 10.28 26.19 43.86 159.77 4.2 9.83 21.87 23.03 44.58 3.47 8.03 18.14 8.09 90.89 1.97 2.62 2.34 5.68 18.51 1.78 1.58

Na 7226.71 7003.48 6643.06 6571.61 6222 7630.24 6357.18 6530.7 6482.76 5455.34 10722.04 6637.35 6358.15 6488.91 6861.44 6309.71 6866.28 6626.17 6971.95 5529.31 5899.21 5155.86 5219.42 5111.96 5250.39 4523.82 4936.14 5005.04

Al 816.36 451.6 164.06 110.82 51.48 80.32 17.83 31.94 29.75 49.25 100.66 9.56 14.6 12.41 16.2 74.92 233.88 472.36 577.83 2086.6 9426.62 83.85 41.29 1.61 1.49 5.66 23.98 2.6

Si 1445.24 304.93 450.82 1095.75 1935.38 7652.89 183.21 369.99 899.09 1417.57 6978.81 145.86 327.27 688.09 852.42 2313.8 124.11 370.88 1629.38 2253.96 16379.57 295.08 134.21 152.6 148.71 532.77 152.36 97.72

P 60617.42 73559.76 72134.31 77795.85 73093.86 67619.34 65250.62 69647.97 75102.91 57715.38 79516.3 62604.81 62025.96 59559.25 67326.55 61648.47 60993.12 61651.24 56879.88 48220.17 28831.54 71507.77 73027.66 69484.04 70842.09 69690.9 61188.7 64117.52

Ca 327554.84 387677.06 389539.25 403901.31 390653.22 390669.75 346684.97 371498.56 386510.13 302612.47 406200.09 323535.66 320332.09 312780.53 279488.56 272751.09 314303.63 316833.75 281299.06 201172.02 120600.91 375569.22 389421.38 366452.78 372658.91 341599.88 321109.91 331139.34

Sc 2.04 0.65 1.99 5.13 7.73 32.84 0.6 1.82 4.56 5.73 37.13 0.7 1.38 3.14 3.21 9.56 0.54 1.46 2.29 3.38 9.06 0.105 0.199 0.45 0.62 2.7 0.103 0.328

Ti 34.46 7.17 22.75 39.24 81.43 223.27 4.91 8.55 44.54 52.55 220.29 3.14 13.03 30.57 30.32 110.94 6.67 13.23 27.08 79.21 438.55 1.96 2.63 4.35 6.05 20.95 2.07 1.52

V 3.85 7.29 6.89 8.59 9.83 25.21 4.88 4.9 4.45 5.27 16.19 3.57 3.9 3.25 3.39 8.52 2.68 2.72 2.87 5.01 20.38 3.85 3.5 3.32 2.29 3.02 3.65 3.04

Cr 11.1 3.96 11.84 29.63 52.67 204.87 3.35 9.88 24.29 37.58 181.6 3.23 8.88 18.31 22.44 60.58 3.34 9.55 13.16 19.37 63.91 2.3 1.7 2.34 3.91 13.66 1.8 1.19

Mn 15.73 281.81 187.55 783.73 376.86 328.08 20.55 3.77 5.97 9.16 44.79 1.99 2.86 5.73 5.09 15.53 8.33 47.32 642.65 35.12 3839.48 7.37 8.23 2.86 1.4 3.32 1.81 1.03

Fe 523.33 159.94 70.34 138.07 244.42 907.71 39.85 56.89 111.98 217.75 844.32 32.76 46.4 81.55 129.05 283.86 188.03 383.12 736.87 1438.3 7596.34 87.05 53.1 27.35 26.45 69.27 73.71 28.83

Co 0.78 3.34 1.95 13.7 5.11 8.08 0.48 0.85 2.16 2.08 11.95 0.139 0.36 1.77 1.47 3.27 0.34 0.92 18.4 1.24 127.47 0.16 0.16 0.235 0.136 0.58 0.044 0.06

Cu 1.78 1.23 2.24 4.13 6.48 33.26 0.52 1.8 3.64 6.08 30.78 0.52 1.07 3.46 3.21 10.36 0.7 1.33 2.57 2.73 12.61 0.389 2.34 1.96 3.33 8.1 0.207 0.38

Zn 82.64 35.97 30.44 26.03 50.53 124.6 19.58 19.08 23.78 36.41 159.19 25.05 28.27 21.33 21.62 58.73 28.24 40.54 33.35 29.19 63.06 99.1 64.81 50.85 41.51 29.85 54.9 42.41

Table 2. (Continued) Sample ID_Spot Size_Group 98359_55_B 98359_40_B 98359_25_B 98359_100_C 98359_80_C 98359_55_C 98359_40_C 98359_25_C 98359_100_D 98359_80_D 98359_55_D 98359_40_D 98359_25_D 98359_100_E 98359_80_E 98359_55_E 98359_40_E 98359_25_E 98359_100_F 98359_80_F 98359_55_F 98359_40_F 98359_25_F 98359_100_G 98359_80_G 98359_55_G 98359_40_G 98359_25_G

Li 0.85 2.72 9.34 0.35 0.28 2.13 2.44 8.56 0.85 0.96 1.37 1.94 1.06 2.28 2.68 27.73 4.03 88.56 0.34 10.43 12.91 36.32 132.88 0.99 5.82 16.32 12.99 26.59

Be 6.15 1 36.26 0.97 0.76 4.14 9.48 40.81 0.87 2.6 3.78 6.63 5.84 6.7 25.98 44.3 91.09 0.001 6.06 20.45 4.96 71.31 261.06 1.84 22.91 8.32 36.17 20.52

B 1.84 2.62 17.2 1.7 1.93 2.5 4.4 7.12 1.82 2.04 2.29 3.11 13.21 4.99 7.94 19.64 34.21 199.35 11.18 10.92 16.16 38.18 213.89 7.84 7.43 21.05 25.21 23.14

Na 4997.4 5108.13 4932.36 4903.19 4943.03 4978.02 4939.95 4685.97 5348.59 5498.72 5397.37 5637.41 5009.01 5693.73 5703.57 6335.57 5890.06 6135.47 5376.1 5545.46 5018.12 5154.94 4990.08 6065.3 6486.02 6366.62 7365.09 6516.75

Al 0.9 1.48 4.83 1.42 0.4 0.78 1.26 4.62 0.371 0.41 0.83 2.74 8.41 1.73 3.71 8.38 12.74 52.47 2.45 4.28 7.04 18.9 54.35 1.48 3.49 8.73 11.35 14.08

Si 193.66 138.25 536.52 131.86 75.48 174.13 160.23 424.1 108.87 74.36 138.84 119.24 385.34 120.81 359.4 845.04 1292.55 4619.15 117.25 369.16 777.74 1514.04 5214.77 122.57 306.39 607.2 721.1 1466.4

P 62665.92 65434.02 65240.82 57371.66 59334.29 60393.65 60888.34 60645.27 56437.51 59835.91 57691.97 62415.65 60288.12 61014.26 59933.54 65396.54 58709.2 51783.14 54854.95 56081.06 56912.63 61955.3 88965.34 58369.95 61152.07 64143.27 68626 54682.33

Ca 320117.16 336027.06 323575.19 297024.63 307361.75 307603.44 308996.72 302050.69 289109.75 313633.91 298639.34 315019.06 296060.66 294051.94 293452.13 319323.88 274251.97 220297.39 270489.22 283891.38 285265.88 298124.88 299012.84 283876.56 304762.22 284995.59 258389.66 183066.75

Sc 0.4 0.7 1.89 0.084 0.205 0.35 0.49 1.9 0.069 0.141 0.32 0.48 1.41 0.6 1.48 2.87 5.54 19.94 0.56 1.75 2.89 7.33 20.08 0.62 1.24 2.74 2.63 6.14

Ti 3.85 6.11 19.11 9.34 1.4 1.94 5.86 15.54 0.4 1.35 2.48 3.42 10 5.77 8.44 24.87 46.59 209.49 3.38 11.38 25.69 39.52 128.23 5.77 11.51 22.78 32.38 46.8

V 2.83 2.6 3.12 2.68 2.65 2.83 2.47 2.84 2.44 2.76 2.76 2.13 3.11 0.87 1.07 2.47 3.59 12.45 1.33 1.43 2.92 4.4 24.21 2.29 2.48 3.24 3.48 3.69

Cr 2.3 3.71 12.41 1.44 0.96 2.03 3.95 12.05 1.68 2.29 2.41 3.43 11.95 3.19 8.7 22.56 35.73 125.24 4.39 9.97 19 41.9 140.9 3.19 8.59 16.17 19.71 39.59

Mn 1.14 1.08 3.04 5.56 0.66 0.92 0.9 2.59 0.541 0.66 0.74 1.6 2.57 0.77 2.03 4.73 8.45 28.88 0.71 2.15 4.46 9.36 34.68 0.88 1.73 3.46 4.13 9.15

Fe 20.95 41.69 57.78 25.07 28.16 27.2 27.81 48.3 26.33 25.96 16.67 18 51.89 22.66 37.9 85.3 184.32 612.7 22.55 49.12 74.04 169.8 693.69 35.08 59.96 69.29 99.63 167

Co 0.157 0.126 0.75 0.034 0.078 0.046 0.074 0.68 0.035 0.038 0.114 0.27 0.62 0.235 0.64 2.19 1.29 6.96 0.171 0.41 1.43 2.83 10.34 0.109 0.105 0.25 1 2.9

Cu 0.52 0.65 2.23 0.144 0.28 0.6 1.06 2.76 0.153 0.204 0.35 0.62 2.15 0.97 2.48 4.88 5.93 26.93 0.56 1.87 4.11 8.52 24.89 0.67 5.64 4.12 5.21 9.47

Zn 37.53 38.11 32.91 32.56 30.94 33.48 34.83 46.73 39.78 54.79 68.81 95.38 143.8 18.37 23.36 28.19 24.78 78.4 23.29 16.37 35.53 35.4 110.36 24.71 25.48 26.7 36.11 62.63

Table 2. (Continued) Sample ID_Spot Size_Group 98359_100_H 98359_80_H 98359_55_H 98359_40_H 98359_25_H Ga 0.289 0.28 0.205 0.23 1.4 0.164 0.201 0.227 0.356 0.99 0.173 0.159 0.227 0.25 0.67 0.179 0.146 0.33 0.26 0.86 0.44

Li 3.75 2.82 6.31 22.02 0.001

Ge 0.059 0.115 0.35 0.43 2.42 0.06 0.178 0.36 0.37 1.82 0.066 0.112 0.31 0.5 1.15 0.057 0.158 0.235 0.51 1.58 0.69

Be 2.99 0.001 38.17 43.49 74.28

As 0.26 0.59 1.08 1.33 8.53 0.25 0.51 1.21 1.29 4.97 0.3 0.54 1.02 1.46 5.52 0.227 0.69 1.07 1.42 4.82 2.2

B 4.01 9.87 16.94 20.41 23.4

Rb 0.113 0.101 0.264 0.29 1.53 0.048 0.119 0.226 0.32 1.1 0.048 0.093 0.163 0.28 0.95 0.043 0.089 0.194 0.31 0.85 0.5

Na 6224.87 6294.9 6217.4 12534.47 7188.94

Sr 97.83 99.13 99.69 99.84 113.04 98.87 99.7 99.58 98.14 90.62 94.49 93.42 89.69 88.4 91.61 94.98 98.26 94.41 100.4 98.18 115.82

Y 0.637 0.202 0.03 0.249 0.206 0.095 0.093 0.136 0.473 1.46 0.0663 0.115 0.272 0.564 1.29 0.146 0.098 0.302 0.365 1.08 0.106

Al 12.51 7.55 47.8 79.04 52.02

Si 207.87 238.55 711.08 857.8 1536.63

Zr90 0.118 0.027 0.064 0.095 0.45 0.0166 0.058 0.024 0.136 0.4 0.0216 0.0181 0.045 0.037 0.54 0.031 0.031 0.11 0.085 0.29 0.162

Zr91 0.195 0.027 0.77 0.53 3.81 0.092 0.206 0.22 0.36 2.61 0.08 0.114 0.35 0.44 1.63 0.099 0.34 0.5 0.41 1.85 1.47

P 58702.38 61310.42 59534.62 71561.28 42252.8

Nb 0.0091 0.0101 0.088 0.047 0.31 0.014 0.04 0.058 0.025 0.28 0.0155 0.03 0.031 0.059 0.26 0.0123 0.0092 0.036 0.062 0.143 0.112

Mo 0.132 0.187 0.31 0.47 2.68 0.129 0.156 0.27 0.42 2.98 0.115 0.136 0.35 0.3 2.09 0.111 0.107 0.191 0.59 1 1.26

Ca 285996.91 263535.66 281567.31 280557.31 179132.05 Ag 0.046 0.026 0.035 0.146 0.69 0.026 0.033 0.131 0.107 0.51 0.027 0.055 0.057 0.108 0.34 0.028 0.039 0.038 0.162 0.64 0.29

Sc 0.6 0.98 3.06 3.93 6.78

Cd 0.119 0.118 0.35 0.65 0.76 0.046 0.143 0.23 0.43 2.47 0.096 0.096 0.38 0.65 1.78 0.026 0.202 0.36 0.76 1.88 1.22

Ti 6.59 9 58.95 27.23 51.88

In 0.0095 0.0181 0.0248 0.058 0.32 0.0091 0.0175 0.024 0.03 0.06 0.0084 0.0216 0.03 0.066 0.256 0.0098 0.0119 0.06 0.078 0.25 0.089

V 2.59 1.89 2.67 5.46 4.79

Sn 0.174 0.134 0.164 0.32 1.14 0.099 0.226 0.223 0.29 0.95 0.113 0.123 0.158 0.25 0.92 0.162 0.184 0.193 0.32 0.98 0.66

Cr 3.5 6.58 18.7 86.26 41.22

Sb 0.025 0.028 0.1 0.106 0.98 0.032 0.04 0.131 0.27 0.76 0.0157 0.054 0.105 0.225 0.58 0.0282 0.046 0.083 0.135 0.19 0.34

Mn 1.68 1.44 4.28 5.75 10.26

Cs 0.01 0.0226 0.039 0.048 0.26 0.0078 0.0261 0.0259 0.055 0.16 0.0093 0.0124 0.0222 0.042 0.149 0.0099 0.0132 0.043 0.038 0.235 0.144

Ba 31.86 27.73 26.19 29.06 28.33 26.24 25.92 27.05 28.35 32.27 23.09 23.17 25.15 25.52 28.06 23.15 23.85 25.99 29.78 33.55 27.56

Fe 45.43 32.42 83.31 109.72 199.94 La 2.48 1.112 0.08 1.06 0.47 0.376 0.453 0.778 1.9 6.98 0.478 0.568 1.1 1.96 3.11 0.762 0.389 1.44 2.28 6.87 0.273

Co 0.204 0.5 1.28 1.69 3.52 Ce 2.59 0.471 0.064 0.454 0.187 0.295 0.322 0.4 1.36 3.72 0.301 0.297 0.514 0.952 1.41 0.379 0.186 0.722 1.02 6.91 0.139

Cu 3 1.61 5.5 17.16 10.06

Zn 60.05 104.34 133.56 239.34 117.26

Pr 0.386 0.126 0.024 0.189 0.145 0.0577 0.086 0.123 0.277 1.45 0.0706 0.078 0.108 0.353 0.491 0.1098 0.061 0.198 0.513 0.96 0.06

Table 2. (Continued) Ga 1.32 2.29 2.61 10.95 0.448 0.74 0.84 1.49 2.29 0.27 0.34 0.98 1.45 1.3 0.35 0.77 1.13 7.62 9.57 0.621 0.471 0.43 0.38 1.34 0.547 0.68 0.84 0.51 1.31 0.73

Ge 2.24 5.01 5.47 25.87 0.42 0.93 2.42 2.28 4 0.26 0.42 1.58 2.56 2.43 0.41 1.19 2.39 15.65 14.68 0.081 0.179 0.37 0.79 2.38 0.072 0.191 0.35 0.77 2.43 0.069

As 6.29 13.02 19.01 93.03 0.86 4.22 5.82 6.6 13.63 1.37 2.25 4.6 6.75 9.05 1.45 3.52 5.99 43.8 65.94 0.222 0.7 1.27 2.15 6.35 0.25 0.43 0.89 2.05 6.35 0.36

Rb 1.14 2.81 3.94 15.15 0.266 0.81 1.5 1.54 2.81 0.164 0.32 0.96 1.38 1.86 0.246 0.7 1.56 8.79 9.98 0.114 0.096 0.28 0.4 1.73 0.081 0.105 0.217 0.37 1.49 0.052

Sr 114.88 108.6 102.1 124.85 98.78 110.75 111.94 87.97 65.19 103.57 83.64 108.29 102.31 92.34 101.59 108.49 108.61 131.1 199.86 113.4 113.59 113.71 113.51 110.88 120.11 123.23 122.05 124.06 121.92 126.72

Y 1.93 3.74 4.43 7.55 1.072 2.2 3.57 2.89 1.75 1.18 1.93 3.67 1.6 3.72 1.25 2.75 3.88 5.01 23.33 0.0071 0.0161 0.1 0.027 0.232 0.0202 0.0208 0.062 0.062 0.117 0.0145

Zr90 0.34 1.76 2.36 10.16 0.177 0.29 0.44 0.77 0.52 0.104 0.107 0.42 0.31 1.11 0.112 0.22 1.23 2.52 4.61 0.0415 0.0188 0.082 0.147 0.71 0.026 0.053 0.111 0.135 0.47 0.0182

Zr91 1.56 5.07 7.56 20.66 0.72 2.98 1.99 2.75 4.32 0.23 0.83 1.3 3.33 3.31 0.51 1.75 2.76 11.45 14.81 0.112 0.224 0.64 1.16 3.23 0.116 0.319 0.5 0.86 3.04 0.165

Nb 0.47 0.77 0.94 5.44 0.022 0.5 0.43 0.3 0.84 0.086 0.073 0.34 0.41 0.3 0.077 0.34 0.32 1.74 2.25 0.0098 0.034 0.098 0.144 0.49 0.0144 0.045 0.133 0.186 0.33 0.0085

Mo 1.2 3.88 4.73 22.39 0.55 1.03 0.47 1.94 4.07 0.31 0.64 1.74 1.64 1.8 0.55 1.56 4.31 8.83 19.79 0.099 0.238 0.29 0.73 1.9 0.09 0.106 0.33 0.49 1.66 0.066

Ag 0.76 1.01 2.77 10.16 0.145 0.76 0.57 0.55 2.24 0.078 0.137 0.53 0.78 0.67 0.146 0.41 1.06 4.69 6.99 0.034 0.025 0.188 0.34 1.17 0.028 0.02 0.119 0.254 1.1 0.034

Cd 2.23 2.96 6.23 24.01 0.66 1.54 3.26 2.24 2.6 0.188 0.55 1.41 4.02 1.89 0.41 0.52 1.7 15.91 11.86 0.072 0.127 0.51 1.19 3.63 0.052 0.134 0.071 0.96 1.37 0.067

In 0.267 0.43 0.83 2.5 0.0166 0.255 0.42 0.235 0.39 0.032 0.108 0.194 0.33 0.35 0.061 0.15 0.105 1.39 2.54 0.0096 0.0236 0.037 0.115 0.196 0.0115 0.0117 0.043 0.074 0.185 0.0071

Sn 0.97 2.11 3.45 13.34 0.28 1.24 1.48 1.98 2.14 0.202 0.38 1.26 1.39 2.22 0.33 0.88 2.5 7.67 11.67 0.231 0.142 0.33 0.57 1.75 0.216 0.144 0.255 0.42 1.49 0.189

Sb 1.02 2.34 1.09 11.62 0.078 0.43 0.91 1.4 1.45 0.074 0.051 0.42 1.06 1.05 0.107 0.55 0.94 3.61 4.65 0.04 0.07 0.285 0.42 0.38 0.029 0.074 0.155 0.266 1.14 0.025

Cs 0.239 0.51 0.82 3.15 0.051 0.258 0.34 0.31 0.42 0.026 0.062 0.121 0.23 0.33 0.051 0.124 0.25 1.49 2.36 0.0059 0.0222 0.052 0.087 0.36 0.01 0.02 0.062 0.091 0.28 0.0137

Ba 35.36 49.17 46.24 81.83 33.08 38.03 39.03 36.26 38.63 32.91 32.04 40.59 34.87 52.26 34.27 42.02 53.94 54.43 178.6 85.83 78.45 71.86 73.39 64.21 87.27 94.47 101.74 104.38 99.09 102.59

La 5.16 9.96 9.84 18.26 3.9 6.8 12.31 13.53 16.01 5.22 9.71 13.1 10.14 17.38 3.87 5.68 10.85 17.58 64.67 0.0104 0.0129 0.03 0.054 0.186 0.0284 0.034 0.029 0.049 0.117 0.0178

Ce 2.97 6.19 8.43 23.55 1.91 3.12 4.9 4.43 4.56 1.48 2.42 4.24 3.46 6.8 2.89 2.8 8.85 13.22 31.76 0.0439 0.0161 0.027 0.048 0.088 0.0251 0.0321 0.044 0.062 0.103 0.0299

Pr 1.26 1.51 2.6 2.48 0.805 1.22 2.28 1.98 2.37 0.693 1.52 2.35 1.81 2.94 0.549 1.36 1.86 5.65 14.75 0.0063 0.0126 0.036 0.053 0.181 0.0063 0.0164 0.028 0.034 0.207 0.0065

Table 2. (Continued Ga 0.78 0.97 1.38 1.27 1.24 1.12 1.21 1.51 1.11 0.54 1.13 1.99 4.95 15.88 0.77 1.08 2.71 4.11 8.42 1.11 1.36 2.16 3.5 11.52 1.35 1.82 1.87 3.91 12.77 1.81

Ge 0.148 0.33 0.61 2.18 0.097 0.198 0.46 0.5 1.98 1.03 2.54 3.68 11.7 29.5 0.8 1.92 3.94 6.78 18.06 0.82 2.12 3.75 7.68 37.92 0.67 3.45 3.82 8.13 22.53 0.216

As 0.38 1.26 1.89 5.65 0.33 0.43 1.43 1.35 5.93 1.87 5.05 14.72 22.35 84.77 2.13 2.56 8.82 16.77 44.23 1.45 4.51 7.95 20.3 103.24 2.45 9.34 7.56 20.01 74.21 0.45

Rb 0.108 0.212 0.43 1.14 0.103 0.117 0.222 0.35 1 0.46 1.02 2.1 4.47 15.29 0.32 1.1 1.64 2.79 8.29 0.28 0.98 1.96 3.52 17.55 0.35 1.65 2.13 3.55 12.26 0.232

Sr 129 128.36 138.29 124.89 142.7 147.03 150.12 148.55 141.15 107.97 99.03 94.71 84.06 133.39 121.7 106.33 109.06 121.88 131.03 108.09 127.42 117.05 103 131.44 118.94 114.98 95.27 91.21 100.22 206.73

Y 0.0205 0.048 0.114 0.143 0.0087 0.0209 0.0155 0.025 0.261 0.111 0.123 0.147 1.22 3.27 0.086 0.42 0.53 0.001 1.34 0.131 0.38 0.63 0.4 3.79 0.144 0.133 0.47 0.3 0.7 0.318

Zr90 0.052 0.109 0.019 0.25 0.0254 0.067 0.144 0.072 0.108 0.17 0.42 1.17 1.53 5.03 0.22 0.53 5.2 1.59 1.59 0.019 0.47 1.36 2.7 5.82 0.31 0.89 1.61 1.78 4.39 0.055

Zr91 0.288 0.33 0.65 3.62 0.086 0.175 0.102 0.86 3.15 0.77 1.45 3.37 6.92 32.21 0.6 4.16 6.15 9.65 13.18 0.97 2.13 3.08 10.58 45.6 1.41 4 4.6 6.09 39.75 0.177

Nb 0.0273 0.053 0.066 0.71 0.0035 0.0267 0.016 0.025 0.28 0.034 0.5 0.48 0.77 6.03 0.159 0.52 0.69 1.7 0.83 0.148 0.46 0.47 1.32 4.03 0.029 0.067 0.99 1.87 2.63 0.0157

Mo 0.122 0.27 0.5 1.62 0.131 0.192 0.41 0.47 2 0.6 2.96 3.44 10.78 17.75 0.46 2.96 4.56 12.3 17.83 0.76 1.67 4.17 6.76 15.84 0.55 4.43 4.41 6.75 15.57 0.292

Ag 0.049 0.146 0.33 0.88 0.036 0.074 0.195 0.25 0.54 0.33 0.57 0.94 3.6 16.76 0.181 0.31 0.76 3.77 3.27 0.208 0.65 0.82 3.22 11.34 0.215 1.22 1.72 1.22 8.62 0.063

Cd 0.185 0.27 0.61 2.31 0.067 0.236 0.34 1.05 2.82 1.04 2.08 6.83 9.24 24.8 0.65 1.84 2.83 7.39 10.07 0.64 2.82 4.06 9.28 19.97 0.76 4.28 3.47 6.5 12.95 0.431

In 0.0039 0.032 0.096 0.36 0.0104 0.037 0.056 0.052 0.31 0.066 0.43 0.6 1.46 1.96 0.104 0.253 0.39 0.48 1.61 0.072 0.184 0.59 0.91 1.4 0.149 0.35 0.4 1.05 2.98 0.0153

Sn 0.211 0.225 0.61 1.64 0.225 0.215 0.27 0.39 1.11 0.47 1.22 2.45 7.33 19.28 0.48 1.25 3.5 3.56 10.88 0.36 1.62 2.34 5.16 18.79 0.39 2.02 2.39 4.89 12.67 0.352

Sb 0.051 0.151 0.279 0.43 0.052 0.106 0.162 0.258 0.55 0.232 0.36 1.01 4.14 9.62 0.36 0.71 0.97 2.34 1.6 0.143 0.63 1.81 1.79 10.92 0.29 1.43 2.12 3.07 10 0.059

Cs 0.034 0.045 0.048 0.31 0.0126 0.0158 0.059 0.063 0.3 0.133 0.242 0.59 1.08 3.12 0.088 0.152 0.36 0.71 1.8 0.05 0.38 0.45 0.77 4.49 0.072 0.38 0.41 0.83 3.05 0.0156

Ba 123.08 137.93 177.35 160.01 154.58 160.86 179.69 184.3 191.44 93.47 82.7 86.54 90.61 126.97 140.69 143.84 376.5 193.63 195.51 119.4 152.91 141.88 124.83 165.22 157.4 115.34 104.97 113.29 88.85 163.9

La 0.07 0.075 0.159 0.168 0.0097 0.025 0.053 0.081 0.145 0.027 0.215 0.25 1.23 2.56 0.048 0.135 0.21 0.44 1.04 0.066 0.169 0.49 0.48 3.59 0.079 0.223 0.36 0.31 2.43 0.447

Ce 0.064 0.057 0.065 0.26 0.0212 0.0183 0.038 0.043 0.128 0.077 0.134 0.22 0.97 2.26 0.021 0.037 0.254 0.55 2.99 0.034 0.258 0.3 0.43 1.83 0.049 0.197 0.035 0.6 1.38 0.363

Pr 0.0131 0.028 0.051 0.164 0.0038 0.0039 0.036 0.036 0.068 0.06 0.04 0.244 0.38 1.77 0.033 0.09 0.35 0.31 1.02 0.032 0.165 0.098 0.58 1.44 0.067 0.31 0.218 0.33 2.16 0.0649


Ge 0.27 0.62 1 4.37 0.132 0.29 0.6 1.02 2.53 0.119 0.207 0.58 0.99 3.47 0.13 0.275 0.48 0.61 2.31 1.14 3.87 9.46 22.17 43.11 1.09 3.31 7.5 10.44 35.41 0.58

As 0.76 2.12 2.64 8.97 0.3 0.83 1.36 1.95 5.66 0.35 0.62 1.47 1.92 9.58 0.34 0.47 1.13 1.98 6.26 2.89 9.25 19.98 49.42 97.02 2.77 6.48 15.72 28.82 68.97 1.56

Rb 0.34 0.7 1.15 4.4 0.161 0.29 0.55 0.83 2.98 0.139 0.226 0.43 0.76 2.67 0.85 0.222 0.44 0.83 1.72 0.94 2.57 6.25 15.86 24.64 0.85 1.89 4.86 6.98 24.42 0.57

Sr 196.19 205.11 198.42 194.21 193.9 194.45 189.39 178.93 161.1 186.09 184.64 180.38 181.43 180.83 177.93 186.82 185.44 159.81 160.61 162.01 153.97 167.69 193.57 199.85 151.26 157.07 173.82 155.48 152.54 155.8

Y 0.139 0.201 0.605 1.29 0.176 0.324 0.059 0.68 1.67 0.527 1.09 0.571 0.83 1.82 0.635 0.73 0.602 1.9 6.99 1.08 2.06 6.31 9.23 15.14 2.82 9.13 12.57 12.15 15.98 10.67

Zr90 0.139 0.136 0.37 1.13 0.04 0.094 0.181 0.34 1.15 0.047 0.147 0.091 0.215 1 0.033 0.105 0.193 0.214 0.88 1.8 1.4 3.23 5.85 23.78 0.37 1.22 2.6 2.52 6.04 0.82

Zr91 0.34 1.05 0.2 5.12 0.234 0.3 0.58 0.97 4.01 0.095 0.219 0.41 1.19 5.19 0.095 0.212 0.76 0.79 1.78 2.1 1.59 7.28 27.95 46.47 0.96 3.17 10.91 9.16 54.48 0.7

Nb 0.03 0.053 0.163 0.64 0.0227 0.0157 0.14 0.149 0.5 0.0145 0.048 0.025 0.149 0.4 0.0145 0.033 0.054 0.172 0.27 0.163 0.31 1.58 1.72 3.81 0.208 0.49 1.45 2.47 8.38 0.169

Mo 0.52 0.39 0.84 3.29 0.388 0.31 0.53 0.22 1.83 0.241 0.319 0.61 0.77 2.9 0.219 0.168 0.32 1.17 1.73 0.83 3.07 8.15 18.08 21.26 0.76 1.78 6.12 6.38 30.58 0.42

Ag 0.76 0.229 0.23 0.87 0.056 0.094 0.181 0.37 1.78 0.042 0.069 0.017 0.204 0.82 0.055 0.134 0.138 0.252 0.98 1.27 0.87 3.28 4.46 14.85 0.33 1.02 3.03 2.99 15.18 0.32

Cd 0.26 0.53 1.31 7.81 0.248 0.158 0.74 0.41 1.15 0.65 0.161 0.43 0.87 1.9 0.069 0.27 0.45 0.86 1.83 1.79 10.95 9.13 23.34 33.56 0.98 0.84 6.8 8.67 33.86 0.76

In 0.0069 0.064 0.159 0.44 0.0091 0.025 0.071 0.119 0.45 0.0183 0.023 0.071 0.103 0.32 0.0164 0.037 0.1 0.084 0.22 0.129 0.24 1.41 2.43 5.21 0.144 0.44 1.06 1.4 2.75 0.096

Sn 0.333 0.32 0.59 2.24 0.32 0.296 0.46 0.44 1.7 0.262 0.308 0.27 0.55 2.07 0.379 0.437 0.32 0.47 1.26 1.91 2.01 5.16 14.76 23.53 0.71 1.42 4.46 6.23 18.62 0.48

Sb 0.139 0.122 0.3 2.39 0.042 0.121 0.145 0.276 0.65 0.038 0.087 0.231 0.38 1.45 0.026 0.102 0.211 0.221 0.7 0.111 1.52 2.01 7.72 10.46 0.263 0.87 2.99 3.81 7.45 0.134

Cs 0.036 0.084 0.148 0.45 0.121 0.042 0.051 0.06 0.234 0.0143 0.0221 0.055 0.134 0.37 0.0126 0.0238 0.062 0.069 0.27 0.158 0.51 0.89 2.28 1.89 0.151 0.223 0.81 1.44 3.03 0.073

Ba 148.62 171.93 164.96 182.34 142.54 158.96 136.55 156.83 160.34 163.42 174.71 166.84 180.55 179.16 123.46 125.96 131.01 159.81 264.05 190.43 192.38 217.35 268.64 375.55 177.84 227.77 737.75 276.48 742.59 307.13

La 0.267 0.459 0.705 1 0.281 0.544 0.085 1.15 2.37 0.83 1.94 0.98 1.63 3.14 0.782 1.03 0.722 4.38 12.94 1.4 2.4 6.41 9.73 18.25 2.25 6.31 9.57 7.38 13.73 10.27

Ce 0.177 0.353 0.501 1.25 0.342 0.419 0.172 1.05 2.81 0.93 1.4 1.03 1.49 2.86 1.74 0.702 0.97 3.84 13.27 1.23 2.2 5.17 9.64 16.68 2.75 9.1 56.14 14.34 104.21 10.94

Pr 0.0459 0.094 0.131 0.252 0.0523 0.101 0.024 0.074 0.41 0.165 0.395 0.232 0.301 0.71 0.18 0.174 0.201 0.781 2.72 0.195 0.62 1.57 2 4.18 0.713 2.13 2.05 2.86 6.49 2.51


Ge 2.42 6.68 7.5 32.33 1.56 3.66 5.16 4.94 9.31 0.105 0.209 0.51 0.89 3.1 0.089 0.206 0.47 0.75 3.59 0.067 0.217 0.25 0.67 2.52 0.073 0.161 0.36 0.89 3 0.72

As 4.8 20.86 14.09 80.38 2.57 8.1 14.87 10.8 19.6 0.25 0.59 0.98 1.88 5.17 0.238 0.41 1.24 1.76 4.46 0.198 0.4 0.76 1.53 3.9 0.203 0.32 0.77 1.18 4.17 1.93

Rb 1.45 4.56 4.63 19.07 0.85 1.88 3.39 3.5 6.67 0.09 0.182 0.38 0.59 2.26 0.071 0.163 0.26 0.52 2.1 0.052 0.108 0.258 0.7 1.44 0.615 1.5 0.69 0.42 1.12 0.43

Sr 156.39 181.93 132.64 148.55 186.2 201.28 208.04 208.2 222.18 164.29 168.34 168.1 170.07 155.8 167.05 160.26 152.23 151.87 160.76 146.77 145.79 137.35 137.33 139.54 210.62 221.73 217.34 165.43 145.39 192.06

Y 10.98 15.09 14.19 21.68 12.91 21.79 18.21 44.51 55.27 0.0442 0.041 0.072 0.075 0.135 0.0088 0.0162 0.052 0.088 0.234 0.0095 0.0169 0.048 0.084 0.29 0.452 0.43 0.435 0.769 0.75 1.05

2.44

1.62

6.13

1.18

194.28 0.202

Zr90 1.16 1.78 2.63 9.03 0.95 0.95 1.92 5.02 5.62 0.036 0.095 0.127 0.228 0.54 0.053 0.083 0.079 0.134 1.13 0.0144 0.059 0.102 0.128 0.44 0.29 0.395 0.479 0.366 0.39 0.238

Zr91 2.91 6.1 9.72 23.52 1.11 3.5 6.19 7.52 10.81 0.143 0.255 0.41 1.29 3.54 0.19 0.34 0.36 0.62 2.33 0.149 0.35 0.88 0.4 2.85 0.198 0.281 0.48 0.78 2.06 1.27

Nb 0.27 1.23 1.49 6.27 0.24 0.38 1.73 0.76 1.66 0.0216 0.047 0.089 0.225 0.53 0.0128 0.0175 0.078 0.038 0.61 0.0143 0.0237 0.0068 0.09 0.31 0.0184 0.081 0.047 0.145 0.39 0.039

Mo 2.31 4.5 4.46 18.71 1.53 1.97 3.48 3.46 7.44 0.152 0.186 0.128 0.31 0.78 0.097 0.191 0.56 0.48 1.8 0.089 0.121 0.26 0.92 0.26 0.084 0.156 0.26 0.75 1.4 0.4

Ag 1.08 3.66 2.56 6.59 0.95 1.39 2.01 2 3.04 0.04 0.088 0.166 0.211 1 0.013 0.085 0.18 0.143 0.67 0.027 0.089 0.135 0.169 0.82 0.0362 0.047 0.156 0.225 0.9 0.259

Cd 2.94 4.05 8.01 16.78 1.12 3.05 5.39 3.08 6.62 0.252 0.203 0.174 0.8 2.21 0.075 0.152 0.32 0.39 1.46 0.059 0.138 0.3 0.64 2.19 0.1 0.103 0.34 0.78 1.6 0.8

In 0.146 1.1 1.2 4.1 0.216 0.37 0.38 0.93 1.41 0.0059 0.0214 0.066 0.119 0.201 0.0136 0.04 0.034 0.071 0.202 0.0026 0.0085 0.027 0.117 0.28 0.0142 0.0209 0.056 0.077 0.251 0.089

Sn 1.35 4.39 4.69 17.17 0.7 2.26 3.19 3.07 7.8 0.252 0.158 0.29 0.4 1.64 0.157 0.131 0.3 0.32 1.54 0.238 0.145 0.235 0.43 1.37 0.167 0.323 0.2 0.37 1.44 0.45

Sb 0.125 1.54 1.53 7.74 0.3 1.5 1.67 1.17 5.63 0.035 0.044 0.175 0.123 0.87 0.036 0.06 0.127 0.153 0.81 0.033 0.077 0.033 0.147 0.87 0.031 0.076 0.135 0.111 0.63 0.159

Cs 0.22 0.6 0.96 4.04 0.134 0.25 0.43 0.71 1.13 0.0097 0.0229 0.066 0.095 0.32 0.0071 0.0185 0.0206 0.081 0.36 0.0093 0.02 0.054 0.081 0.32 0.0287 0.0423 0.034 0.08 0.28 0.069

Ba 354.16 250.35 256.57 274.65 249.58 437.42 1199.26 1671.06 1419.87 250.44 262.66 252.21 245.61 223.98 238.67 230.61 216.93 214.98 221.25 202.42 199.97 183.53 192.41 199.11 197.17 199.39 182.75 211.52 198.71 369.39

La 13.44 12.07 15.86 14.36 18.37 26.89 26.84 58 72.04 0.425 0.524 0.105 0.136 0.257 0.0503 0.0176 0.026 0.064 0.169 0.0368 0.029 0.045 0.064 0.207 0.663 1.024 0.771 1.55 1.76 6.69

Ce 25.84 5.77 10.76 16.65 18.96 52.44 163.57 186.59 301.29 0.212 0.105 0.027 0.048 0.162 0.427 0.0111 0.024 0.04 0.262 0.196 0.0273 0.031 0.038 0.198 0.599 1.148 0.789 1.48 1.98 1.81

Pr 3.47 2.63 3.54 5.86 3.55 6.68 6.77 12.35 17.47 0.0386 0.0209 0.03 0.038 0.179 0.0202 0.0219 0.0261 0.063 0.118 0.0089 0.0079 0.0169 0.03 0.102 0.14 0.191 0.141 0.413 0.389 0.453

0.45

0.27

0.164

1.57

0.82

0.34

0.28

1.42

0.41

0.218

348.85

0.206

0.184

0.041

Table 2. (Continued) Ga 3.09 5.39 16.58 2.3 3.29 2.46 4.01 21.01 2.01 2.13 2.48 2.37 5.64 2.15 2.78 3.18 2.05 12.52 1.397 1.48 1.06 0.9 1.56 1.178 1.095 0.94 1.22 1.45 1.044

Ge 6.52 11 43.92 0.57 2.01 4.15 6.7 38.44 0.74 1.26 3.84 3.58 10.9 0.58 2.08 2.9 4.79 7.97 0.081 0.193 0.44 1.01 1.89 0.124 0.243 0.4 0.8 1.95 0.107

As 9.67 29.6 90.07 1.48 4.83 10.83 13.82 73.54 1.98 2.66 10 8.03 26.22 1.56 2.58 5.67 8.97 19.99 0.253 0.49 0.92 1.5 3.69 0.21 0.41 1.15 0.99 5.88 0.223

Rb 3.32 5.97 25.02 0.38 1.16 2.7 3.98 23.54 0.42 0.85 1.83 2.23 6.47 0.35 1.13 1.4 2.43 7.77 0.087 0.114 0.273 0.4 1.57 0.099 0.101 0.228 0.34 1.49 0.156

Sr 214.18 195.33 186.24 183.41 201.3 206.12 161.84 257.53 192.01 199.72 172.15 173.45 170.76 147.27 153.53 138.43 110.57 116.7 110.03 113.44 110.51 111.12 103.01 100.03 99.25 99.12 104.09 95.76 99.42

Y 0.49 0.77 3.23 0.08 0.151 0.5 0.15 3.88 0.055 0.251 0.166 0.48 1.3 0.887 1.85 0.97 2.69 4.21 0.344 0.141 0.054 0.067 0.062 0.0223 0.029 0.051 0.061 0.209 0.0112

Zr90 2.37 4.07 12.05 0.108 0.16 1.52 3.1 10.26 0.119 0.31 0.62 1.45 3.96 0.117 0.61 0.74 1.3 4.87 0.038 0.039 0.164 0.144 0.067 0.038 0.036 0.031 0.089 0.45 0.0296

Zr91 6.91 10.83 32.04 0.46 1.5 6.04 8.22 47.15 0.29 1.44 4.03 8.17 12.85 0.76 1.62 1.95 4.58 9.68 0.086 0.178 0.53 1.14 1.84 0.122 0.233 0.095 0.85 3.58 0.078

Nb 1.05 1.65 0.71 0.036 0.228 0.75 1.25 5.87 0.118 0.028 0.38 0.078 1.96 0.044 0.35 0.194 0.35 0.46 0.0089 0.039 0.057 0.101 1.55 0.0264 0.0205 0.077 0.131 0.214 0.012

Mo 3.82 6 10.91 0.89 1.18 2.74 4.15 21.45 0.43 1.14 3.18 0.41 10.18 0.43 1.82 2.19 0.73 15.4 0.119 0.172 0.42 0.74 1.82 0.13 0.132 0.4 0.84 1.66 0.089

Ag 2.83 0.72 22.76 0.189 0.97 1.44 2.4 7.94 0.16 0.94 1.18 0.98 4.61 0.224 0.95 0.37 1.43 2.85 0.036 0.053 0.248 0.195 0.95 0.026 0.049 0.127 0.048 1.38 0.0233

Cd 4.35 10.79 20.2 0.41 1.34 4.41 2.86 24.33 0.49 0.91 2.55 3.66 9.98 0.59 2.06 2.47 1.78 8.69 0.079 0.16 0.193 0.84 2.9 0.055 0.105 0.23 0.54 1.32 0.086

In 0.69 0.88 2.6 0.065 0.243 0.49 0.82 3.6 0.063 0.165 0.33 0.54 1.28 0.062 0.264 0.225 0.46 0.79 0.0122 0.0291 0.053 0.076 0.186 0.0122 0.0135 0.0195 0.06 0.34 0.0128

Sn 3.13 6.57 21.29 0.37 1.12 3.23 4.36 20.77 0.34 0.93 2.19 2.48 7.01 0.34 1.28 1.59 2.12 7.67 0.193 0.222 0.31 0.5 1.53 0.229 0.137 0.25 0.53 1.44 0.181

Sb 1.74 2.2 8.07 0.232 0.38 1.25 1.47 11.96 0.278 0.37 1.03 1.2 4.64 0.195 0.112 0.87 1.25 4.31 0.031 0.046 0.097 0.241 0.59 0.012 0.043 0.159 0.272 0.54 0.029

Cs 0.82 1.24 3.12 0.055 0.273 0.48 0.7 3.52 0.097 0.172 0.37 0.46 1.41 0.079 0.211 0.29 0.44 1.17 0.0177 0.0277 0.049 0.079 0.225 0.0095 0.0141 0.039 0.099 0.29 0.0109

Ba 399.64 358.22 328.93 275.99 296.07 325.8 250.62 302.23 279.18 291.95 273.52 267.88 299 217.4 244.32 323 289.22 941.25 149.34 157.5 157.73 160.42 140.3 136.64 134.46 139.1 142.2 137.8 131.46

La 0.62 0.56 2.33 0.047 0.154 0.156 0.42 2.8 0.056 0.105 0.207 0.224 2.16 1.268 2.3 2.29 3.85 10.73 1.344 0.733 0.039 0.039 0.37 0.0099 0.0065 0.045 0.044 0.151 0.0169

Ce 0.45 1 2.08 0.03 0.016 0.39 0.69 0.58 0.05 0.162 0.186 0.234 1.06 0.949 1.75 6.69 3.44 57.26 0.95 0.287 0.04 0.061 0.149 0.0369 0.0108 0.0124 0.039 0.018 0.037

Pr 0.133 0.77 3.24 0.023 0.131 0.25 0.29 1.38 0.028 0.073 0.204 0.239 0.22 0.372 0.549 0.53 0.95 2.63 0.236 0.063 0.001 0.033 0.199 0.0044 0.0083 0.0252 0.031 0.104 0.0043

Table 2. (Continued) Ga 1.072 1.22 1.03 1.95 0.909 0.83 0.722 0.99 1.16 1.26 1.97 2.12 2.95 11.22 1.33 0.97 2.32 3.56 13 1.43 0.83 1.49 1.52 3.65 0.76 1.15 1.87 1.99 3.5

Ge 0.165 0.33 0.63 2.21 0.061 0.152 0.43 0.7 1.86 0.55 1.43 4.5 6.9 24.79 0.59 1.65 4.86 7.75 26.08 0.6 1.83 2.68 3.79 9.72 0.59 1.33 3.52 4 9.31

As 0.35 0.89 1.02 3.11 0.194 0.42 0.95 1.59 4.03 1.97 3.11 7.5 17.56 41.45 1.12 4.63 5.4 14.22 39.31 1.15 3.65 4.83 10.52 20.04 1.57 1.92 7.56 9.2 11.1

Rb 0.084 0.171 0.33 1.23 0.04 0.097 0.161 0.34 0.91 0.31 0.97 2.29 2.91 11.19 0.32 0.88 2.1 3.57 13.17 0.35 0.86 1.51 1.75 3.66 0.25 0.64 1.85 1.97 3.98

Sr 98.43 100.79 98.44 95.29 97.5 97.72 91.98 95.94 87.44 114.69 114.12 123.07 109.47 102.25 113.21 120.06 126.26 130.86 102 111.29 112.48 103.07 101.63 63.2 91.15 84.59 88.8 83.46 65.71

Y 0.0041 0.032 0.054 0.189 0.0028 0.0147 0.03 0.075 0.208 0.021 0.25 0.3 0.26 3.83 0.082 0.085 0.55 0.53 2.01 0.0071 0.02 0.35 0.48 1.12 0.079 0.096 0.57 0.135 0.78

Zr90 0.033 0.145 0.165 0.66 0.015 0.032 0.065 0.114 0.37 0.077 0.31 1.06 2.18 5.85 0.078 0.185 1.2 1.68 4.34 0.122 0.46 0.34 0.84 2.1 0.28 0.83 4.86 8.82 70.15

Zr91 0.214 0.33 0.53 1.87 0.068 0.145 0.42 1.47 0.91 0.74 2.47 4.84 9.93 32.64 0.46 2.7 2.73 12.09 19.73 0.73 1.22 1.87 4.67 5.51 0.86 1.02 4.87 6.39 10.87

Nb 0.0031 0.051 0.055 0.29 0.0043 0.0223 0.079 0.032 0.26 0.114 0.237 0.75 0.77 5.77 0.072 0.241 0.42 0.84 3.05 0.043 0.33 0.37 0.72 1.48 0.147 0.15 0.067 0.99 0.52

Mo 0.122 0.38 0.35 1.22 0.096 0.117 0.42 0.17 1.94 0.6 1.16 2.79 4.04 21.71 0.93 1.27 4.45 7.66 16.15 0.6 1 2.79 0.92 9.06 0.36 0.24 3.28 4.56 4.49

Ag 0.064 0.171 0.225 0.79 0.041 0.043 0.154 0.221 0.137 0.222 0.43 2.06 1.5 9.85 0.198 0.67 1.43 3.66 8.47 0.222 0.37 1.03 1.84 2.38 0.167 0.29 1.49 2.19 2.88

Cd 0.078 0.085 0.28 1.2 0.088 0.093 0.19 0.47 1.02 0.47 0.91 4.4 3.19 17.14 0.092 1.42 3.04 4.93 9.78 0.33 1.36 2.2 1.21 7.12 0.5 0.61 2.57 0.57 6.1

In 0.0215 0.027 0.062 0.46 0.0113 0.0238 0.024 0.043 0.139 0.061 0.166 0.63 0.71 2.2 0.077 0.258 0.5 0.45 3.26 0.074 0.3 0.206 0.39 1.02 0.045 0.085 0.23 0.46 0.64

Sn 0.235 0.251 0.48 1.22 0.222 0.123 0.249 0.27 1.32 0.31 0.97 2.16 3.48 16.52 0.35 1.02 1.97 3.8 18.68 0.38 0.91 1.85 1.65 4.23 0.41 0.62 2.11 5.73 5.17

Sb 0.056 0.087 0.075 0.98 0.036 0.054 0.078 0.137 0.77 0.037 0.53 0.91 2.28 7.08 0.214 0.59 1.26 1.11 6.5 0.093 0.46 0.65 1.03 2.57 0.153 0.44 0.76 0.86 2.55

Cs 0.0198 0.052 0.032 0.29 0.0113 0.0125 0.039 0.068 0.223 0.058 0.131 0.54 0.36 2.11 0.04 0.207 0.27 0.94 3.83 0.052 0.106 0.34 0.38 0.78 0.083 0.126 0.37 0.53 0.78

Ba 131.73 140.09 132.39 127.06 108.44 105.28 101.3 106.17 95.92 168.93 186.32 189.52 174.35 135.46 177.44 177.52 209.42 189.63 190.86 147.23 155.12 143.27 144.46 109.49 94.55 93.22 81.3 86.45 50.98

La 0.0191 0.059 0.055 0.136 0.0087 0.0085 0.025 0.054 0.123 0.026 0.147 0.5 0.72 1.38 0.021 0.228 0.282 0.56 1.33 0.03 0.044 0.249 0.34 0.4 0.097 0.266 0.158 0.097 0.56

Ce 0.0171 0.001 0.024 0.122 0.0045 0.0134 0.001 0.077 0.111 0.034 0.025 0.033 0.056 2.14 0.061 0.069 0.099 0.71 1.3 0.034 0.113 0.224 0.178 0.63 0.206 0.086 0.185 0.3 0.62

Pr 0.0108 0.0167 0.038 0.094 0.0049 0.0127 0.015 0.0212 0.148 0.046 0.144 0.3 0.217 1.9 0.033 0.079 0.195 0.61 1.41 0.037 0.087 0.172 0.193 0.39 0.029 0.068 0.142 0.228 0.48

Table 2. (Continued) Nd 1.35 0.541 0.099 0.38 0.67 0.129 0.23 0.39 1.1 4.66 0.154 0.362 0.451 0.63 1.62 0.404 0.21 0.77 1.42 3.91 0.36 4.82 5.06 10.96 24.06 2.7 4.08 7.68 8.7 9.83 2.82

Sm 0.183 0.092 0.282 0.33 1.39 0.065 0.153 0.117 0.31 1.25 0.053 0.119 0.174 0.51 1.29 0.106 0.119 0.262 0.39 1.25 0.48 1.88 4.03 4.54 16.18 0.57 1.54 1.69 2.32 2.7 0.31

Eu 0.0481 0.0174 0.044 0.046 0.37 0.0098 0.028 0.029 0.07 0.25 0.017 0.0187 0.03 0.041 0.224 0.0127 0.0255 0.042 0.043 0.194 0.109 0.166 0.75 0.79 1.52 0.13 0.197 0.42 0.37 0.33 0.08

Gd 0.127 0.058 0.084 0.129 0.41 0.022 0.048 0.073 0.266 0.55 0.0228 0.056 0.082 0.156 0.78 0.0277 0.04 0.083 0.124 0.58 0.46 0.76 1.42 1.73 5.8 0.254 0.59 1.03 0.44 1.26 0.434

Tb 0.0211 0.0075 0.0249 0.03 0.213 0.0046 0.0071 0.0284 0.0215 0.111 0.0034 0.0118 0.0225 0.04 0.164 0.0049 0.0118 0.015 0.046 0.135 0.062 0.093 0.37 0.37 1.23 0.061 0.112 0.2 0.163 0.27 0.031

Dy 0.108 0.045 0.15 0.189 0.23 0.027 0.068 0.099 0.169 0.58 0.033 0.058 0.088 0.199 0.31 0.03 0.051 0.091 0.148 0.192 0.33 0.8 2.24 1.93 6.48 0.199 0.48 1.71 1.1 1.62 0.282

Ho 0.0202 0.0122 0.053 0.047 0.13 0.0084 0.0132 0.025 0.039 0.083 0.0059 0.0177 0.0224 0.055 0.191 0.0089 0.0154 0.0159 0.058 0.144 0.124 0.129 0.68 0.64 2.27 0.046 0.084 0.25 0.3 0.57 0.05

Er 0.0345 0.024 0.111 0.083 0.27 0.0102 0.023 0.073 0.118 0.42 0.0159 0.047 0.036 0.104 0.232 0.0161 0.0287 0.047 0.134 0.177 0.197 0.42 0.68 0.82 1.37 0.089 0.5 0.52 0.48 0.6 0.097

Tm 0.0046 0.005 0.0258 0.038 0.156 0.0058 0.0105 0.017 0.0274 0.033 0.0058 0.0071 0.0253 0.034 0.132 0.005 0.0087 0.022 0.0254 0.023 0.102 0.168 0.39 0.54 1.81 0.039 0.024 0.214 0.208 0.28 0.029

Yb 0.0449 0.052 0.019 0.091 0.86 0.0159 0.029 0.081 0.106 0.39 0.0168 0.067 0.104 0.199 0.51 0.0206 0.041 0.04 0.121 0.22 0.31 0.2 0.49 2.58 6.1 0.143 0.39 1.17 0.28 1.04 0.118

Lu 0.0056 0.0082 0.0168 0.058 0.234 0.0061 0.0136 0.0255 0.024 0.149 0.0053 0.0106 0.0186 0.044 0.114 0.0053 0.013 0.0286 0.027 0.122 0.097 0.178 0.53 0.41 2.35 0.058 0.124 0.23 0.125 0.36 0.036

Hf 0.0164 0.0321 0.034 0.149 0.7 0.0201 0.036 0.102 0.134 0.28 0.0174 0.035 0.041 0.119 0.26 0.0276 0.03 0.108 0.088 0.49 0.275 0.34 1.54 1.44 11.74 0.109 0.29 1.05 0.42 1.18 0.121

Ta 0.0076 0.0192 0.045 0.062 0.18 0.0127 0.0106 0.055 0.05 0.165 0.0051 0.0144 0.031 0.069 0.021 0.0072 0.0215 0.039 0.073 0.033 0.093 0.31 0.39 0.67 4.48 0.034 0.236 0.25 0.3 0.4 0.046

W 0.029 0.083 0.098 0.179 0.84 0.04 0.039 0.049 0.17 0.62 0.0269 0.093 0.068 0.13 0.41 0.027 0.02 0.118 0.305 0.44 0.35 0.74 1.19 0.22 13.74 0.064 0.25 0.66 0.91 1.06 0.077

Re 0.0162 0.045 0.039 0.117 0.39 0.017 0.047 0.109 0.105 0.44 0.0118 0.033 0.069 0.081 0.42 0.0069 0.044 0.052 0.069 0.31 0.216 0.53 0.85 1.47 4.26 0.086 0.27 0.53 0.52 0.93 0.048

Au 0.029 0.116 0.3 0.45 1.32 0.034 0.108 0.302 0.56 1.66 0.036 0.088 0.127 0.34 0.41 0.056 0.086 0.154 0.25 0.8 0.63 0.94 1.52 1.85 15.1 0.34 0.97 0.83 0.81 3.97 0.166

Tl 0.0197 0.061 0.103 0.164 0.77 0.0242 0.051 0.106 0.138 0.5 0.0226 0.046 0.1 0.181 0.51 0.0233 0.049 0.104 0.178 0.47 0.29 0.58 1.59 2.35 9.89 0.11 0.44 0.75 0.82 1.4 0.099

Pb 0.335 0.122 0.086 0.105 0.67 0.072 0.049 0.079 0.12 0.35 0.062 0.068 0.086 0.208 0.48 0.102 0.037 0.066 0.126 0.4 0.192 0.57 1.25 1.13 5.04 0.167 0.6 0.73 0.77 0.97 0.053

Bi 0.009 0.0231 0.041 0.068 0.38 0.0053 0.0235 0.057 0.06 0.222 0.0125 0.0193 0.035 0.047 0.255 0.0112 0.0236 0.049 0.084 0.18 0.057 0.28 0.85 1.03 2.82 0.069 0.272 0.208 0.37 0.57 0.052

Th 0.0106 0.0142 0.047 0.025 0.115 0.0104 0.0077 0.0058 0.028 0.103 0.0077 0.0126 0.0158 0.043 0.134 0.0062 0.0152 0.027 0.044 0.115 0.04 0.167 0.38 0.33 3.1 0.027 0.1 0.148 0.144 0.24 0.024

U 0.0345 0.0112 0.0052 0.056 0.206 0.0095 0.0129 0.0335 0.027 0.327 0.006 0.0147 0.0214 0.035 0.064 0.0102 0.0047 0.0225 0.037 0.095 0.027 0.124 0.32 0.24 0.74 0.038 0.067 0.169 0.168 0.159 0.043

Table 2. (Continued) Nd 6.63 9.97 4.67 11.23 2.39 5.26 5.2 12.41 55.41 0.043 0.092 0.124 0.32 1.08 0.022 0.08 0.118 0.35 0.096 0.044 0.055 0.116 0.214 0.98 0.04 0.039 0.176 0.2 0.6 0.25 0.63

Sm 0.67 1.23 2.69 2.78 0.34 1.2 1.26 11.78 13.9 0.054 0.188 0.27 0.93 2.53 0.079 0.162 0.39 0.67 1.79 0.091 0.17 0.25 0.47 1.23 0.079 0.205 0.47 0.35 1.5 1.01 2.08

Eu 0.199 0.49 0.28 0.37 0.085 0.3 0.31 1.18 2.16 0.0076 0.0164 0.094 0.069 0.33 0.0119 0.03 0.052 0.034 0.44 0.0085 0.0069 0.029 0.094 0.144 0.0123 0.012 0.054 0.107 0.185 0.111 0.098

Gd 0.64 1.01 0.93 1.3 0.224 0.52 1.01 1.96 8.21 0.0253 0.024 0.014 0.32 0.89 0.0037 0.047 0.074 0.168 1.32 0.045 0.043 0.096 0.251 0.81 0.033 0.068 0.103 0.067 0.27 0.03 0.73

Tb 0.075 0.203 0.114 0.223 0.047 0.147 0.145 0.96 1.51 0.0066 0.001 0.049 0.039 0.269 0.0079 0.0141 0.0053 0.036 0.102 0.0048 0.0079 0.0205 0.0102 0.123 0.0034 0.0229 0.044 0.035 0.057 0.078 0.111

Dy 0.24 0.47 0.85 0.84 0.203 0.51 1.07 4.1 4.61 0.033 0.069 0.266 0.169 1 0.024 0.113 0.179 0.222 1.33 0.029 0.094 0.153 0.33 0.55 0.048 0.044 0.164 0.3 0.64 0.43 0.83

Ho 0.06 0.184 0.157 0.3 0.054 0.143 0.133 0.89 1.62 0.0041 0.01 0.052 0.073 0.287 0.0054 0.0213 0.039 0.066 0.3 0.0073 0.0181 0.054 0.041 0.262 0.0076 0.0109 0.053 0.066 0.3 0.118 0.119

Er 0.179 0.52 0.36 0.47 0.135 0.241 0.4 3.04 5.55 0.0092 0.03 0.121 0.125 0.6 0.025 0.045 0.034 0.046 0.57 0.0267 0.044 0.113 0.114 0.39 0.032 0.033 0.07 0.113 0.091 0.249 0.179

Tm 0.045 0.14 0.066 0.144 0.0222 0.125 0.187 1.22 0.91 0.008 0.0013 0.023 0.041 0.282 0.0058 0.0208 0.0218 0.0051 0.053 0.0051 0.0145 0.0215 0.04 0.128 0.0091 0.0107 0.023 0.052 0.03 0.047 0.117

Yb 0.31 0.25 0.98 0.44 0.128 0.3 0.99 2.07 2.29 0.019 0.047 0.109 0.34 1.77 0.0196 0.07 0.18 0.253 0.25 0.0242 0.069 0.145 0.189 1.37 0.0202 0.041 0.156 0.177 1.18 0.225 0.56

Lu 0.041 0.148 0.07 0.39 0.041 0.132 0.276 1.5 2.37 0.006 0.0103 0.0243 0.044 0.211 0.0062 0.0191 0.04 0.069 0.242 0.0076 0.0108 0.046 0.073 0.272 0.0056 0.0161 0.0245 0.088 0.016 0.087 0.174

Hf 0.144 0.28 0.58 0.71 0.077 0.31 0.78 4.23 4.46 0.0195 0.034 0.21 0.247 0.84 0.0246 0.062 0.13 0.07 0.64 0.0303 0.035 0.09 0.194 0.44 0.026 0.064 0.159 0.181 0.21 0.33 0.4

Ta 0.014 0.23 0.29 0.088 0.077 0.199 0.26 1.42 1.84 0.008 0.0197 0.057 0.083 0.53 0.0102 0.006 0.069 0.014 0.33 0.0072 0.0145 0.043 0.046 0.37 0.0129 0.0264 0.074 0.074 0.158 0.067 0.29

W 0.224 0.28 0.64 1.73 0.119 0.58 1.21 2.33 8.46 0.0135 0.052 0.017 0.38 0.41 0.031 0.056 0.117 0.108 1 0.0271 0.055 0.281 0.212 0.68 0.0188 0.081 0.123 0.28 0.84 0.36 0.88

Re 0.098 0.51 0.88 0.83 0.095 0.208 0.43 4.06 4.29 0.0076 0.045 0.076 0.158 0.6 0.0209 0.0188 0.093 0.144 0.67 0.0238 0.048 0.058 0.132 0.65 0.032 0.041 0.077 0.142 0.37 0.181 0.5

Au 0.39 0.93 1.11 2.75 0.206 0.92 1.21 7.97 5.93 0.0258 0.109 0.33 0.59 1.56 0.045 0.066 0.196 0.53 1.18 0.0129 0.091 0.134 0.5 1.79 0.033 0.094 0.247 0.276 1.93 0.41 0.71

Tl 0.163 0.45 0.91 0.83 0.108 0.41 0.74 4.53 4.25 0.0203 0.056 0.122 0.264 0.68 0.027 0.043 0.128 0.205 0.8 0.027 0.054 0.095 0.192 0.56 0.028 0.052 0.121 0.215 0.67 0.28 0.53

Pb 0.154 0.39 0.62 0.95 0.158 0.26 0.65 4.3 3.75 0.036 0.044 0.094 0.184 0.57 0.073 0.027 0.119 0.136 0.59 0.062 0.063 0.067 0.215 0.57 0.029 0.047 0.093 0.115 0.45 0.24 0.55

Bi 0.065 0.153 0.43 0.31 0.064 0.166 0.32 1.53 3.57 0.0097 0.0237 0.055 0.077 0.37 0.0096 0.028 0.033 0.099 0.167 0.0122 0.019 0.033 0.113 0.36 0.0138 0.03 0.065 0.027 0.31 0.071 0.3

Th 0.05 0.096 0.052 0.24 0.027 0.073 0.216 0.83 0.75 0.0065 0.0113 0.0143 0.048 0.162 0.0082 0.0169 0.0127 0.074 0.061 0.0047 0.0031 0.0243 0.063 0.205 0.004 0.012 0.0174 0.059 0.124 0.091 0.129

U 0.075 0.151 0.088 0.115 0.058 0.192 0.328 0.79 1.76 0.002 0.0076 0.0179 0.056 0.074 0.0064 0.0161 0.0238 0.029 0.027 0.0055 0.0078 0.0164 0.0163 0.138 0.004 0.014 0.0247 0.039 0.204 0.079 0.087

Table 2. (Continued) Nd 1.78 2.27 12.95 0.097 0.56 1.21 3.16 1.77 0.27 0.28 1.42 2.82 12.12 0.32 0.71 1.06 0.32 12.89 0.393 0.181 0.44 0.54 0.95 0.191 0.475 0.228 0.74 1.67 0.648 1.36

Sm 2.58 8.57 29.72 0.61 1.56 2.64 5.13 10.84 0.6 1.24 2.53 3.55 30.53 0.71 3.48 3.52 2.49 16.09 0.107 0.214 0.43 0.62 3.18 0.127 0.229 0.44 0.67 1.62 0.142 0.287

Eu 0.64 0.99 2.31 0.086 0.026 0.37 0.22 1.33 0.098 0.3 0.31 0.3 0.82 0.071 0.49 0.65 1.06 2 0.0148 0.0199 0.074 0.078 0.199 0.0181 0.021 0.091 0.119 0.33 0.0188 0.038

Gd 1.7 1.88 6.2 0.163 0.071 0.29 2.62 5.05 0.131 1 1.44 1.65 10.05 0.269 1.32 0.88 2.32 5.35 0.047 0.043 0.114 0.21 0.85 0.04 0.082 0.17 0.32 0.87 0.09 0.255

Tb 0.26 0.4 2.3 0.078 0.171 0.126 0.32 0.31 0.04 0.067 0.253 0.35 2.64 0.041 0.164 0.27 0.35 1.19 0.0069 0.0198 0.025 0.045 0.17 0.0104 0.0123 0.024 0.056 0.133 0.011 0.0178

Dy 2.35 4.59 8.07 0.37 0.74 1.13 3.12 3.49 0.32 0.79 1.33 3.05 9.29 0.3 1.41 1.4 3.04 8.57 0.044 0.07 0.237 0.46 1.04 0.052 0.106 0.3 0.3 0.93 0.057 0.202

Ho 0.52 0.61 2.84 0.053 0.259 0.23 0.6 0.98 0.03 0.33 0.192 0.66 3.66 0.075 0.47 0.45 0.54 2.14 0.0155 0.027 0.026 0.104 0.32 0.007 0.0264 0.057 0.095 0.25 0.0164 0.0298

Er 0.82 2.57 4.23 0.223 0.45 0.134 1.46 3.45 0.22 0.4 1.14 2.26 10.89 0.185 0.74 0.85 1.13 3.67 0.038 0.037 0.176 0.196 1.09 0.0181 0.088 0.13 0.219 0.43 0.06 0.084

Tm 0.192 0.6 1.39 0.064 0.104 0.226 0.34 1.61 0.03 0.184 0.188 0.53 2.78 0.023 0.299 0.2 0.53 2.71 0.0062 0.0121 0.037 0.065 0.254 0.0026 0.013 0.025 0.059 0.243 0.0054 0.0175

Yb 0.91 1.09 9.38 0.247 0.076 1.32 0.84 2.62 0.244 0.25 1.79 1.78 7.65 0.35 0.38 0.94 1.77 9.98 0.042 0.081 0.133 0.058 1.71 0.03 0.062 0.205 0.187 0.67 0.058 0.109

Lu 0.203 0.45 1.47 0.067 0.19 0.45 0.88 1.7 0.031 0.195 0.34 0.39 2.4 0.064 0.36 0.51 0.55 1.81 0.0066 0.018 0.047 0.068 0.077 0.0134 0.0193 0.0045 0.062 0.21 0.0079 0.0183

Hf 0.66 2.06 9.59 0.126 0.62 1.1 2.03 4.8 0.144 0.63 1.29 3.39 7.8 0.256 0.59 0.96 2.21 8.31 0.037 0.083 0.199 0.271 0.87 0.038 0.077 0.121 0.202 0.48 0.028 0.064

Ta 0.209 0.85 1.98 0.104 0.147 0.28 0.44 2.8 0.045 0.41 0.38 0.53 3.22 0.0082 0.35 0.4 0.74 2.97 0.0088 0.03 0.082 0.112 0.44 0.0127 0.037 0.078 0.102 0.44 0.0081 0.037

W 1.02 2.04 7.42 0.32 0.78 0.85 1.81 1.76 0.223 0.65 2.24 2.8 8.54 0.32 1.83 1.05 2.57 9.09 0.033 0.095 0.138 0.242 0.38 0.034 0.097 0.228 0.221 1.05 0.031 0.07

Re 0.63 1.62 4.61 0.107 0.34 1.01 1.45 3.44 0.126 0.43 0.67 1.01 7.51 0.217 0.57 0.53 1 3.6 0.031 0.061 0.121 0.275 0.45 0.03 0.065 0.134 0.159 0.53 0.03 0.044

Au 2.33 5.75 11.94 0.38 1.4 1.66 1.32 4.82 0.35 0.78 1.93 2.21 13.42 0.36 1.76 1.64 4.35 7.07 0.088 0.155 0.148 0.45 2.29 0.081 0.127 0.243 0.33 0.79 0.045 0.024

Tl 1.14 2.6 9.24 0.185 0.56 0.92 2.03 4.19 0.186 0.73 0.98 2.34 9.52 0.262 1.02 1.06 2.13 6.01 0.033 0.062 0.138 0.243 1.14 0.027 0.069 0.15 0.157 0.75 0.028 0.05

Pb 1.08 2.51 7.05 0.197 0.28 0.81 1.56 3.51 0.105 0.46 1 1.14 9.85 0.089 0.61 0.86 1.6 3.69 0.094 0.06 0.147 0.225 0.77 0.054 0.065 0.106 0.218 1.17 0.125 0.14

Bi 0.68 1.01 4.44 0.039 0.33 0.38 0.88 2.69 0.094 0.28 0.49 1.11 4.48 0.079 0.28 0.36 0.87 3.11 0.0226 0.031 0.086 0.135 0.46 0.0148 0.036 0.063 0.061 0.58 0.0133 0.0197

Th 0.3 0.81 1.54 0.04 0.11 0.248 0.37 0.88 0.032 0.142 0.35 0.7 3.48 0.081 0.263 0.21 0.13 0.22 0.0114 0.0069 0.039 0.071 0.189 0.0067 0.0192 0.037 0.062 0.253 0.0056 0.0134

U 0.247 0.45 1.79 0.047 0.171 0.118 0.35 0.59 0.0217 0.095 0.194 0.38 1.17 0.0084 0.125 0.143 0.46 1.74 0.0161 0.0121 0.0222 0.046 0.127 0.0094 0.0128 0.025 0.041 0.169 0.0305 0.065


Sm 0.47 0.55 3.14 0.129 0.255 0.46 0.64 1.76 0.84 2.47 5.85 19.43 26.36 0.87 2.2 7.57 8.51 24.65 1.21 3.6 4.52 5.48 22.98 3.01 2.97 6.02 9.13 9.83 0.101 0.12

Eu 0.071 0.118 0.257 0.0316 0.042 0.056 0.096 0.32 0.179 0.47 0.72 1.59 1.22 0.152 0.57 0.54 0.64 3.79 0.52 0.39 0.79 1.35 4.61 0.58 0.88 1.41 1.33 3.7 0.0136 0.0243

Gd 0.132 0.26 0.69 0.099 0.113 0.115 0.52 1.01 0.28 1.03 3.33 3.68 7.07 0.53 1.7 2.48 4.72 10.12 1.61 1.81 2.1 2.08 6.16 1.84 3.83 2.23 9.46 9.75 0.0215 0.066

Tb 0.033 0.096 0.21 0.0129 0.021 0.034 0.045 0.265 0.104 0.068 0.72 1.84 2.16 0.077 0.258 0.31 1.21 1.34 0.228 0.254 0.64 0.42 1.33 0.355 0.31 0.52 0.89 0.91 0.008 0.0143

Dy 0.176 0.45 0.91 0.077 0.082 0.241 0.34 1.08 0.37 1.35 1.79 5.81 11.43 0.48 1.46 3.28 4.84 13.38 1.1 1.07 2.35 3.37 9.99 1.62 2.48 2.4 6.25 5.92 0.027 0.107

Ho 0.072 0.073 0.23 0.0148 0.039 0.027 0.069 0.303 0.091 0.38 1 1.72 4.66 0.118 0.34 0.67 0.85 2.89 0.306 0.4 0.75 0.77 2.49 0.257 0.72 0.61 0.68 2.11 0.0071 0.0246

Er 0.13 0.31 0.32 0.041 0.061 0.113 0.145 0.75 0.271 0.87 2.66 4.17 4.52 0.32 0.58 2.3 2.93 8.6 0.84 0.73 1.43 1 3.71 1.07 2.74 1.38 2.99 4.15 0.0152 0.033

Tm 0.05 0.042 0.222 0.0081 0.0128 0.026 0.034 0.152 0.063 0.072 0.76 1.38 2.29 0.116 0.135 0.47 1.08 1.64 0.105 0.149 0.32 0.76 1.42 0.114 0.3 0.36 0.39 0.65 0.0099 0.0108

Yb 0.118 0.027 0.75 0.044 0.061 0.126 0.228 0.87 0.3 0.79 2.09 10.37 7.71 0.3 1.33 1.45 4.61 1.13 0.54 0.77 2.3 3.67 11.67 0.76 1.64 1.37 2.88 3.78 0.0183 0.074

Lu 0.045 0.044 0.235 0.0049 0.0135 0.056 0.051 0.196 0.095 0.175 0.8 1.45 3.42 0.086 0.32 0.6 0.33 2.45 0.101 0.151 0.62 0.5 1.49 0.122 0.27 0.28 0.48 0.86 0.0075 0.0231

Hf 0.12 0.246 0.76 0.0053 0.088 0.128 0.116 0.64 0.31 1.13 0.001 4.71 13.56 0.197 0.58 1.12 1.65 9.72 0.175 0.35 2.02 1.15 11.84 0.32 0.51 0.9 1.78 1.94 0.052 0.054

Ta 0.078 0.101 0.54 0.0081 0.036 0.064 0.107 0.214 0.126 0.33 0.88 1.94 2.46 0.115 0.269 0.93 1.36 3.27 0.059 0.142 0.48 1.06 3.45 0.163 0.36 0.35 0.52 1.12 0.0158 0.0145

W 0.263 0.118 0.83 0.043 0.096 0.14 0.179 1.14 0.127 0.88 3.29 7.28 8.56 0.123 1.24 1.74 2.56 12.26 0.169 0.75 2.55 3.09 12.94 0.28 0.79 2.41 2.75 0.86 0.027 0.055

Re 0.067 0.193 0.42 0.0218 0.0164 0.071 0.204 0.61 0.295 0.45 1.87 4.14 8.14 0.22 0.51 1.25 2.6 6.97 0.178 0.38 1.45 1.43 5.37 0.25 0.89 1.32 0.86 1.51 0.0249 0.036

Au 0.241 0.61 0.82 0.039 0.124 0.29 0.26 0.59 0.26 1.29 3.13 13.03 17.65 0.212 2.2 4.72 3.7 19.82 0.226 0.54 1.41 1.81 18.55 0.5 1.78 3.13 3.67 6.65 0.026 0.056

Tl 0.112 0.212 0.63 0.03 0.057 0.124 0.219 0.48 0.31 0.88 2.15 6.29 10.45 0.28 0.66 2.02 2.64 9.51 0.212 0.31 1.79 1.77 5.95 0.43 0.72 1.38 1.5 2.48 0.0217 0.04

Pb 0.105 1.13 0.77 0.12 0.063 0.102 0.202 0.54 1.79 0.7 1.49 5.01 10.01 0.312 1.24 1.38 2.19 7.93 0.335 0.84 1.7 1.72 8.68 0.79 1.1 3.57 1.43 3.15 0.063 0.041

Bi 0.063 0.096 0.51 0.0132 0.026 0.047 0.092 0.29 0.092 0.34 0.83 2.24 6.14 0.117 0.37 0.67 1.65 2.38 0.053 0.231 0.7 0.69 4.09 0.118 0.5 0.38 0.53 1.4 0.0059 0.0184

Th 0.031 0.061 0.229 0.0059 0.0132 0.061 0.119 0.101 0.129 0.169 0.32 0.99 1.64 0.024 0.237 0.47 0.49 1.65 0.041 0.135 0.34 0.48 1.41 0.134 0.258 0.37 0.59 0.95 0.0025 0.0106

U 0.03 0.051 0.156 0.0282 0.035 0.026 0.08 0.373 0.061 0.178 0.63 0.92 2.2 0.129 0.52 1.09 0.96 1.56 0.57 0.72 0.67 0.99 0.98 0.76 1.08 0.89 2.24 3.39 0.0032 0.0158

Table 2. (Continued) Nd 0.177 0.32 1.51 0.041 0.052 0.11 0.188 1 0.02 0.067 0.143 0.25 1.05 0.528 0.653 0.73 1.13 2.1 1.54 0.082 0.2 2.32 4.21 0.241 0.91 1.06 0.46 11.65 0.234 0.44

Sm 0.36 0.76 2.38 0.093 0.115 0.35 0.59 2.02 0.063 0.16 0.259 0.4 1.56 0.112 0.11 0.36 0.44 1.39 0.55 2.05 4.23 5.13 32.8 0.56 1.3 3.02 3.9 21.06 0.56 0.96

Eu 0.056 0.123 0.41 0.014 0.0163 0.023 0.084 0.31 0.0089 0.0149 0.045 0.056 0.283 0.0344 0.0235 0.042 0.053 0.3 0.085 0.43 0.46 0.73 5.28 0.076 0.202 0.33 1.11 3.66 0.021 0.137

Gd 0.087 0.078 1.13 0.0148 0.063 0.19 0.32 0.61 0.0028 0.041 0.123 0.154 0.086 0.056 0.077 0.115 0.194 0.47 0.311 0.52 0.17 1.3 2.42 0.208 0.68 0.91 2.62 7.09 0.143 0.53

Tb 0.0232 0.042 0.094 0.0082 0.0052 0.041 0.049 0.226 0.0037 0.0175 0.0187 0.033 0.195 0.0078 0.0112 0.0247 0.031 0.142 0.0191 0.112 0.037 0.43 2.53 0.026 0.069 0.48 0.29 2.63 0.053 0.08

Dy 0.142 0.256 0.86 0.041 0.083 0.089 0.261 0.8 0.028 0.066 0.141 0.38 1.47 0.063 0.06 0.107 0.253 0.62 0.38 0.84 2.91 3.72 15.58 0.224 0.73 0.85 2.45 17.52 0.27 0.177

Ho 0.036 0.12 0.43 0.0073 0.0148 0.029 0.066 0.201 0.0041 0.0213 0.0204 0.072 0.173 0.0113 0.0152 0.032 0.082 0.109 0.062 0.173 0.52 0.54 4.78 0.079 0.258 0.43 0.87 3.32 0.033 0.152

Er 0.108 0.237 0.65 0.0156 0.032 0.067 0.161 0.29 0.008 0.05 0.137 0.109 0.83 0.0258 0.043 0.081 0.123 0.47 0.172 0.64 0.48 3.44 3.4 0.189 0.55 0.64 1.07 7.05 0.1 0.263

Tm 0.0249 0.045 0.213 0.0072 0.0103 0.0219 0.053 0.038 0.0057 0.0188 0.035 0.05 0.121 0.0053 0.012 0.0087 0.047 0.108 0.026 0.12 0.29 1.13 1.92 0.0277 0.09 0.161 0.35 2.31 0.047 0.086

Yb 0.016 0.088 0.73 0.0033 0.05 0.106 0.181 0.46 0.0273 0.064 0.097 0.069 0.58 0.043 0.067 0.056 0.194 0.3 0.184 0.16 0.19 0.72 4.03 0.189 0.43 0.62 1.68 6.42 0.043 0.32

Lu 0.037 0.048 0.226 0.0077 0.0155 0.023 0.04 0.02 0.0074 0.0141 0.0213 0.065 0.182 0.0056 0.0128 0.034 0.035 0.162 0.057 0.256 0.29 1.2 2.04 0.029 0.096 0.222 0.52 2.26 0.06 0.13

Hf 0.088 0.223 0.75 0.031 0.073 0.109 0.227 0.49 0.0199 0.033 0.1 0.125 0.6 0.0132 0.0247 0.061 0.116 0.38 0.231 0.42 2.06 2.1 11.68 0.137 0.32 1.27 1.11 0.93 0.163 0.23

Ta 0.061 0.127 0.37 0.0145 0.0254 0.031 0.075 0.28 0.0057 0.0231 0.049 0.071 0.297 0.0075 0.0099 0.027 0.094 0.265 0.054 0.34 0.93 0.65 2.73 0.039 0.221 0.3 0.86 5.18 0.019 0.031

W 0.134 0.032 0.001 0.026 0.079 0.118 0.109 0.76 0.031 0.051 0.109 0.33 0.66 0.029 0.065 0.1 0.255 0.59 0.207 0.66 0.65 2.51 10.66 0.151 0.73 1.15 3.32 8.97 0.255 0.18

Re 0.116 0.269 0.4 0.0194 0.028 0.045 0.142 0.42 0.0108 0.04 0.077 0.096 0.39 0.0144 0.0231 0.088 0.143 0.35 0.18 0.46 0.8 1.78 5.39 0.142 0.58 0.81 1.35 4.13 0.064 0.29

Au 0.13 0.252 1.57 0.046 0.094 0.163 0.278 1.28 0.037 0.122 0.107 0.152 0.11 0.035 0.037 0.031 0.178 0.82 0.35 1.12 0.64 2.88 20.84 0.212 0.98 2.28 4.26 17.86 0.31 0.82

Tl 0.097 0.195 0.78 0.033 0.04 0.132 0.163 0.72 0.0206 0.041 0.096 0.11 0.5 0.022 0.038 0.093 0.178 0.58 0.139 0.58 1.57 2.46 9.6 0.143 0.47 0.77 1.87 10.37 0.151 0.32

Pb 0.104 0.202 0.77 0.114 0.05 0.092 0.143 0.72 0.0366 0.036 0.091 0.122 0.65 0.298 0.235 0.213 0.167 0.37 0.17 0.62 1.33 1.77 8.75 0.134 0.35 1.08 1.34 6.29 0.16 0.3

Bi 0.055 0.164 0.33 0.0132 0.0202 0.037 0.073 0.18 0.0079 0.0131 0.044 0.049 0.4 0.0083 0.0164 0.037 0.05 0.185 0.084 0.27 0.77 0.91 4.27 0.073 0.179 0.29 0.49 3.25 0.073 0.149

Th 0.042 0.0118 0.147 0.0053 0.0054 0.0115 0.073 0.136 0.00128 0.0129 0.0105 0.069 0.203 0.027 0.032 0.0168 0.056 0.104 0.052 0.117 0.115 0.45 0.54 0.027 0.087 0.203 0.89 1.58 0.045 0.032

U 0.0162 0.077 0.098 0.0033 0.0045 0.0077 0.035 0.092 0.0037 0.0123 0.0132 0.04 0.052 0.0143 0.0197 0.0247 0.029 0.1 0.0236 0.079 0.27 0.049 1.8 0.0258 0.059 0.138 0.231 2.42 0.0218 0.014


Sm 2.91 2.88 8.61 0.63 1.4 2.38 3.26 9.16 0.155 0.119 0.205 0.72 1.52 0.047 0.18 0.36 0.23 1.38 0.052 0.165 0.223 0.68 1.25 0.046 0.177 0.227 0.35 1.46 0.35 0.78

Eu 0.47 0.55 1.22 0.041 0.218 0.41 0.31 1.42 0.0218 0.0169 0.0144 0.108 0.31 0.0077 0.0222 0.034 0.015 0.106 0.0149 0.0116 0.0085 0.0137 0.36 0.0065 0.0195 0.04 0.0067 0.108 0.033 0.36

Gd 1.48 1.23 3.35 0.24 0.44 0.72 1.04 5.64 0.096 0.046 0.196 0.172 0.59 0.0225 0.043 0.092 0.021 0.29 0.0204 0.0106 0.086 0.019 0.49 0.0179 0.025 0.11 0.192 0.88 0.193 0.53

Tb 0.159 0.32 1.13 0.052 0.085 0.188 0.22 0.54 0.0097 0.0141 0.036 0.037 0.127 0.0068 0.0092 0.034 0.034 0.163 0.0044 0.0045 0.0099 0.03 0.147 0.0038 0.0022 0.0234 0.05 0.133 0.0117 0.112

Dy 1.39 1.99 2.56 0.29 0.79 0.95 1.37 3.26 0.063 0.087 0.129 0.278 1.11 0.036 0.09 0.149 0.255 0.5 0.0026 0.0149 0.114 0.184 0.46 0.0236 0.05 0.072 0.31 0.92 0.18 0.6

Ho 0.49 0.2 0.96 0.066 0.14 0.196 0.3 1.18 0.0091 0.0243 0.032 0.08 0.196 0.0105 0.0225 0.0215 0.064 0.102 0.0082 0.013 0.029 0.046 0.114 0.0059 0.0153 0.036 0.084 0.206 0.032 0.15

Er 0.74 0.56 2.88 0.14 0.42 0.62 0.51 1.77 0.045 0.046 0.097 0.17 0.42 0.0222 0.06 0.064 0.045 0.53 0.0143 0.0186 0.085 0.097 0.48 0.0034 0.053 0.022 0.095 0.31 0.095 0.37

Tm 0.099 0.4 1.09 0.046 0.097 0.287 0.24 1.01 0.0096 0.0151 0.001 0.056 0.137 0.0052 0.014 0.0029 0.0097 0.175 0.0047 0.0091 0.034 0.0172 0.112 0.0058 0.0012 0.0178 0.0042 0.102 0.031 0.148

Yb 1.43 1.93 2.14 0.168 0.47 0.37 1.15 1.29 0.0269 0.073 0.029 0.051 0.66 0.0248 0.019 0.102 0.246 0.08 0.0091 0.044 0.064 0.154 0.001 0.0197 0.042 0.035 0.212 0.2 0.15 0.71

Lu 0.026 0.3 1.16 0.0139 0.103 0.124 0.179 0.62 0.0072 0.0092 0.041 0.042 0.145 0.0123 0.0257 0.0225 0.054 0.186 0.0067 0.0104 0.017 0.027 0.266 0.0062 0.0092 0.0189 0.057 0.152 0.074 0.091

Hf 1.04 1.57 1.87 0.16 0.68 0.82 0.59 2.03 0.0257 0.065 0.136 0.276 0.39 0.0255 0.035 0.181 0.179 0.43 0.0164 0.071 0.139 0.112 0.68 0.0143 0.052 0.088 0.109 0.61 0.109 0.42

Ta 0.34 0.28 1.09 0.065 0.239 0.166 0.48 1.17 0.0079 0.0143 0.032 0.079 0.052 0.0127 0.0199 0.001 0.073 0.176 0.0094 0.0257 0.028 0.045 0.159 0.0058 0.0123 0.0102 0.063 0.249 0.052 0.21

W 0.94 1.69 5.2 0.25 0.14 1.12 0.93 4.54 0.041 0.016 0.249 0.029 0.76 0.027 0.078 0.118 0.201 1.19 0.052 0.027 0.156 0.36 0.51 0.0154 0.049 0.199 0.07 0.57 0.303 0.83

Re 0.66 0.87 2.38 0.109 0.38 0.45 0.74 1.61 0.0096 0.042 0.117 0.155 0.66 0.0144 0.034 0.102 0.124 0.49 0.0185 0.031 0.067 0.141 0.31 0.0081 0.03 0.05 0.062 0.35 0.124 0.42

Au 1.33 1.1 2.94 0.179 0.76 0.86 1.87 2.98 0.0117 0.032 0.36 0.31 1.33 0.029 0.079 0.207 0.24 0.7 0.059 0.051 0.159 0.182 1.11 0.033 0.07 0.177 0.253 1.01 0.31 0.7

Tl 0.89 1.39 2.39 0.09 0.41 0.49 0.74 2.91 0.031 0.051 0.099 0.198 0.83 0.0238 0.048 0.083 0.133 0.55 0.0195 0.045 0.073 0.154 0.54 0.019 0.044 0.07 0.123 0.45 0.131 0.45

Pb 0.59 0.98 1.63 0.112 0.34 0.53 0.71 3.01 0.142 0.049 0.103 0.153 0.58 0.049 0.042 0.052 0.089 0.43 0.0215 0.047 0.109 0.056 0.55 0.0431 0.03 0.062 0.14 0.25 0.133 0.211

Bi 0.45 0.56 1.63 0.085 0.217 0.39 0.34 1.42 0.0241 0.0185 0.039 0.131 0.194 0.0073 0.0244 0.052 0.063 0.33 0.0082 0.0224 0.045 0.072 0.277 0.0083 0.0124 0.031 0.063 0.145 0.078 0.193

Th 0.165 0.193 0.91 0.025 0.188 0.129 0.23 0.77 0.0034 0.0103 0.0087 0.038 0.018 0.0027 0.0095 0.035 0.049 0.016 0.0064 0.0059 0.0269 0.031 0.108 0.0039 0.0118 0.0241 0.042 0.097 0.004 0.116

U 0.049 0.061 0.51 0.066 0.091 0.191 0.13 0.59 0.0056 0.0142 0.015 0.026 0.025 0.0049 0.0036 0.0057 0.024 0.219 0.0034 0.0105 0.0133 0.03 0.051 0.0028 0.0039 0.012 0.0141 0.037 0.021 0.081

Table 2. (Continued) Nd 0.15 1.5 9.89 0.141 0.47 1.17 2.84 3.68 0.156 0.64 0.73 0.82 1.67 0.134 0.29 1.21 0.13 0.34

Sm 4.18 6.35 10.28 0.4 1.2 2.97 5.11 18.64 0.28 1.24 2.27 1.8 2.13 0.52 0.89 3.07 2.46 4.19

Eu 0.24 0.67 1.79 0.044 0.257 0.37 0.3 1.88 0.069 0.232 0.46 0.57 0.52 0.104 0.09 0.041 0.3 0.52

Gd 0.13 1.83 4.92 0.242 0.71 0.71 2 5.16 0.135 0.001 1.09 1 1.44 0.143 0.076 1.04 1.18 2.46

Tb 0.191 0.39 1.05 0.037 0.151 0.34 0.6 1.1 0.029 0.068 0.035 0.261 0.43 0.0165 0.118 0.41 0.178 0.61

Dy 0.85 0.63 7.96 0.196 0.154 0.67 3.23 4.82 0.218 0.51 0.59 1.47 1.9 0.189 0.231 0.97 1.56 1.88

Ho 0.209 0.74 1.15 0.049 0.051 0.33 0.74 1.3 0.03 0.061 0.29 0.37 0.48 0.033 0.1 0.172 0.39 0.37

Er 0.27 1.28 3.44 0.12 0.49 0.5 2.2 9.51 0.094 0.31 0.88 0.98 1.74 0.04 0.172 0.72 0.16 1.71

Tm 0.06 0.155 0.62 0.039 0.162 0.164 0.46 2.37 0.0042 0.012 0.144 0.162 0.66 0.0177 0.0087 0.169 0.159 0.46

Yb 2.2 2.86 2.22 0.133 0.45 1.57 2.69 8.02 0.21 0.115 0.98 1.1 1.58 0.157 0.38 0.25 1.83 2.7

Lu 0.22 0.45 2.4 0.042 0.14 0.3 0.69 1.77 0.057 0.077 0.191 0.172 0.5 0.0188 0.12 0.36 0.203 0.85

Hf 0.1 1.8 6.83 0.119 0.33 0.81 3.2 10.1 0.152 0.25 0.87 0.98 1.99 0.162 0.28 1.02 0.94 1.6

Ta 0.41 0.42 3.21 0.056 0.107 0.33 1.3 1.03 0.024 0.103 0.35 0.4 0.47 0.025 0.114 0.26 0.77 0.8

W 0.17 1.67 6.35 0.221 0.14 0.92 3.16 6.67 0.3 0.41 0.32 1.29 1.87 0.186 0.148 0.59 1.08 1.85

Re 0.41 0.84 6.76 0.136 0.37 0.57 1.3 4.1 0.088 0.29 0.71 0.56 1.48 0.132 0.161 0.59 0.86 1.97

Au 1.68 2.44 16.04 0.32 0.77 1.65 2.69 11.98 0.188 0.74 0.85 1.9 3.37 0.194 0.75 1 1.61 3.87

Tl 0.81 1.55 3.86 0.11 0.37 0.91 1.57 5.72 0.122 0.27 0.83 0.7 2.06 0.129 0.31 0.53 0.75 1.88

Pb 0.51 1.16 3.41 0.119 0.33 0.81 1.7 5.06 0.108 0.31 0.71 0.85 1.21 0.404 0.3 1.77 2.3 2.64

Bi 0.29 0.43 3.24 0.08 0.213 0.33 0.49 3.8 0.104 0.149 0.36 0.23 0.83 0.075 0.1 0.34 0.44 0.74

Th 0.278 0.28 1.87 0.0164 0.127 0.156 0.3 1.96 0.004 0.139 0.138 0.309 0.32 0.044 0.05 0.099 0.182 0.54

U 0.196 0.35 1.32 0.042 0.063 0.156 0.38 1.38 0.0209 0.07 0.138 0.11 0.39 0.024 0.054 0.198 0.13 0.22

78

Ian Scharlotta, Andrzej Weber, S. Andy DuFrane et al. Table 3. Laser ablation 87Sr/86Sr ratio data for KN XIV teeth (Sample ID_Sample Group) Sample ID 97.211_A1 97.211_A2 97.211_A3 97.211_B1 97.211_B2 97.211_B3 97.211_C1 97.211_C2 97.211_C3 97.211_D1 97.211_D2 97.211_D3 97.217_A1 97.217_A2 97.217_A3 97.217_B1 97.217_B2 97.217_B3 97.217_C1 97.217_C2 97.217_C3 97.217_D1 97.217_D2 97.217_D3 97.225_A1 97.225_A2 97.225_A3 97.225_B1 97.225_B2 97.225_B3 97.225_C1 97.225_C2 97.225_C3 97.225_D1 97.225_D2 97.225_D3 98.355_A1 98.355_A2 98.355_B1 98.355_B2 98.355_B3 98.355_C1 98.355_C2

total Sr (V) 0.5155146 0.5160899 0.4953065 0.5237191 0.5002587 0.4872413 0.5060082 0.4307859 0.5063735 0.4994893 0.46193 0.540535 0.4115777 0.4041834 0.4004222 0.3322841 0.3403646 0.3680073 0.2988586 0.4335352 0.4269052 0.3627065 0.3776331 0.379205 0.2559062 0.2326417 0.2678432 0.2201758 0.2348739 0.2483402 0.2104877 0.2590772 0.2533799 0.1873117 0.2179966 0.1321271 0.2093049 0.1914608 0.17089 0.195499 0.2208219 0.170033 0.1643442

88Sr (V) 0.45866608 0.453345569 0.428867147 0.436220764 0.4155926 0.4048075 0.420384 0.3578929 0.4208142 0.4150779 0.3837917 0.4492097 0.3417825 0.3355515 0.3324746 0.2759177 0.2825703 0.3055199 0.2481763 0.359995 0.3544793 0.3011957 0.3135448 0.3147506 0.212446 0.1931096 0.2222689 0.182762 0.194932 0.206077 0.1746781 0.2149743 0.2102729 0.1554626 0.1808601 0.1097235 0.174305 0.1597384 0.1419118 0.1623537 0.1833904 0.1412572 0.1365448

85Rb (V) 2.89E-04 2.41E-04 2.70E-04 2.80E-04 1.92E-04 2.08E-04 1.77E-04 1.41E-04 1.77E-04 2.26E-04 1.12E-04 1.67E-04 3.00E-04 3.99E-04 4.29E-04 2.38E-04 2.91E-04 3.38E-04 2.15E-04 2.94E-04 2.86E-04 1.91E-04 2.07E-04 2.35E-04 3.16E-04 2.65E-04 3.13E-04 3.03E-04 3.21E-04 3.51E-04 3.30E-04 3.62E-04 3.90E-04 2.53E-04 3.44E-04 1.64E-04 5.31E-05 5.37E-05 5.08E-05 5.24E-05 6.25E-05 4.84E-05 6.00E-05

87Sr/86Sr 0.7123743 0.7125077 0.7125393 0.7122774 0.7120285 0.71261 0.7116353 0.7115308 0.7117711 0.712428 0.7119169 0.7114825 0.7158983 0.7170207 0.7172126 0.7163448 0.7168815 0.7174497 0.7153606 0.7158572 0.7151173 0.7151284 0.715732 0.7160216 0.7144163 0.7161518 0.7163261 0.7155843 0.716525 0.7161068 0.715738 0.7153563 0.7159872 0.7150012 0.7166502 0.7152321 0.7132161 0.7152994 0.7126116 0.7120714 0.7119601 0.7116431 0.7121804

2σ error 0.0001806 0.0001684 0.000204 0.000198 0.0001622 0.0001414 0.0001572 0.000202 0.000164 0.0001718 0.0001888 0.000214 0.0001974 0.000274 0.0002 0.00032 0.0001302 0.000204 0.000214 0.00024 0.000204 0.000234 0.000195 0.000236 0.000294 0.000312 0.000208 0.000296 0.000252 0.0003 0.0003 0.000252 0.00028 0.00032 0.000348 0.000672 0.000366 0.00042 0.00045 0.000302 0.000278 0.000414 0.000448

84Sr/86Sr 0.05591817 0.05651735 0.05614837 0.05598387 0.05664957 0.05541669 0.05709169 0.05717407 0.05517618 0.05474164 0.05678069 0.0562032 0.05696245 0.05821956 0.05708164 0.05776875 0.05858407 0.05726491 0.0579626 0.05737652 0.05757585 0.05827334 0.05776602 0.05894893 0.05954526 0.05905727 0.05987656 0.05914619 0.05998222 0.05992156 0.06010092 0.06026456 0.05949909 0.06019127 0.06077109 0.05440657 0.03778981 0.02281661 0.06041714 0.05998997 0.05933711 0.05909435 0.05917739

2σ error 0.000181 0.000202 0.000192 0.000182 0.000115 0.000272 0.000112 0.000116 0.000191 0.000404 0.000109 0.000262 0.000175 0.000114 0.000112 0.000196 0.000147 0.000129 0.000155 0.000145 0.000102 0.000167 0.000131 0.00015 0.000222 0.00019 0.000232 0.000166 0.000208 0.000216 0.000246 0.000159 0.000169 0.00026 0.00023 0.000842 0.001754 0.001328 0.00036 0.000192 0.00024 0.00024 0.000226


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Table 3. (Continued) Sample ID 98.355_C3 98.355_D1 98.355_D2 98.355_D3 98.359_A1 98.359_A2 98.359_A3 98.359_B1 98.359_B2 98.359_B3 98.359_C1 98.359_C2 98.359_C3 98.359_D1 98.359_D2 98.359_D3

total Sr (V) 0.1749326 0.1417553 0.1710117 0.154442 0.08855514 0.09535257 0.09603494 0.07893794 0.0850022 0.09881024 0.07774534 0.09139404 0.0969025 0.0784394 0.08522065 0.08934028

88Sr (V) 0.1453045 0.1177061 0.1420012 0.1282176 0.07353076 0.07918973 0.07977681 0.06555476 0.07058874 0.08204339 0.06454512 0.07587025 0.08046143 0.0651374 0.07078526 0.0742008

85Rb (V) 6.72E-05 5.70E-05 1.05E-04 6.71E-05 3.41E-05 3.17E-05 3.54E-05 2.82E-05 2.74E-05 2.92E-05 2.07E-05 1.97E-05 2.68E-05 1.65E-05 2.26E-05 3.15E-05

87Sr/86Sr 0.7126502 0.713514 0.7136801 0.7146961 0.7117397 0.7127162 0.7118754 0.7117544 0.7129407 0.7129047 0.7141845 0.7134008 0.7137356 0.7133296 0.7123873 0.7126201

2σ error 0.000346 0.000632 0.00039 0.000464 0.00069 0.00066 0.000672 0.00071 0.000916 0.000712 0.001052 0.00068 0.00061 0.00086 0.00088 0.0008

84Sr/86Sr 0.05839649 0.05987801 0.05868803 0.05890335 0.06180479 0.05925366 0.05880733 0.06094116 0.06024675 0.06003406 0.05964469 0.05944841 0.05919033 0.06141835 0.06142619 0.06015517

2σ error 0.000288 0.000342 0.000278 0.00024 0.00049 0.00047 0.000402 0.000444 0.000504 0.00044 0.000504 0.000456 0.000352 0.000484 0.000472 0.000414

We must first establish the veracity of hypothesized expectations for Cis-Baikal inhabitants. Within each sampling group, five lines of different sizes: 100, 80, 55, 40, and 25 µm, were drawn to demonstrate the impact that sample size has within a microsampling environmental. Figures 3 and 4 show the results of different laser spot sizes being used on strontium and rubidium at full laser power; rubidium being representative of elements of low concentration (below 20 ppm) and strontium of elements of higher concentration. The results are not surprising as the direct relationship between the physical amounts of sample introduced into the ICP-MS is integral to the functioning of the equipment; however it does provide a reminder that mass ranges with low concentrations are subject to significantly larger error terms as beam size is reduced. As such, the use of low concentration mass ranges (i.e., rubidium or zirconiuim) for correction factors must be taken carefully as the sampling methodology can have a major impact on the effectiveness of such a correction factor. The difference in variability is strictly the results of resultant signal strength, which can be equally altered by changes in the spot size and the laser power. This variability viewed as confidence ellipses on bivariate plots will yield relatively larger or smaller ellipses. Figure 5 demonstrates this as a compounded effect of both laser power and spot size as each ellipse represents one group of five laser lines of different size. The extent of variability related to laser effects was somewhat surprising, not in that the concentrations were more variable, but rather that these data formed significantly different shapes in statistical space. This could be interpreted as reflecting significant internal variability within a single tooth, greater than may actually be present, simply as an effect of the laser power. As these data came from prehistoric hunter-gatherer teeth, it is possible that such variability is reflective of provenance shifts during the life of the individual, however with the neat divide between groups measured with 50% and 100% laser power, it is reasonable to assume that the ranges seen are in fact the result of the laser settings and not fully reflective of internal variability within the enamel matrix.

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Figure 3. Rubidium values by spot size

Figure 4. Strontium values by spot size


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Figure 5. Impact of laser effects shown by groups’ variability clustering by laser power rather than by internal variability

Figure 6. Strontium and zinc bivariate plot, suggests a transitional period during the early period of molar formation followed by a period of relative stability in geography and diet and the beginning of another transition towards the end of molar formation

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Figure 7. Barium and manganese bivariate plot shows an intriguing separation between paired groups A-B and C-D demonstrating a clear shift in geography or diet between the first and second half of the molar growth period

The next question is whether there is adequate variability reflected in the geochemical data from serial sampling of a tooth to potentially address the underlying concern of the disjunction between enamel matrix formation and the supposed dietary source of these signals. Figures 6 and 7 demonstrate that there is significant variability within the span of a single tooth. As noted by Britton et al. [46] and Montgomery et al.[51], the incorporation of a sudden change in geochemical input signal will lead to a moderately sloped interchange reflecting both the old and new end-members of the geochemical signal, so any significant change in the elemental data is likely outstripping the visibility of this effect, or showing snapshots along the transition slope still reflecting different values and statistical morphology. This is highly suggestive of the presence of useful variability in trace element composition in the hunter-gatherer population of Cis-Baikal comparable to effects noted in agrarian groups by Cucina et al. [5, 69] and Dudgeon [70]. However, one interest aspect of the range of variability within a single tooth raises some concerns about the extent of the validity of the assumption that the hydroxyapatite matrix contains relatively stable quantities of Ca and P. Figures 8 and 9, show calcium and phosphorous projected against strontium, two elements that are supposed to be present in a fairly constant ratio throughout the tooth, should show similar patterning. The predictable nature of calcium phosphate matrices is the primary feature that enables geochemical research to be conducted on skeletal tissues. The range of variability visible in this one sample is still within the ranges to be expected for normal Ca:P ratios of teeth not significantly altered by diagenetic processes, however the distribution and differences in statistical morphology is intriguing.


Figure 8. Strontium and calcium are strongly correlated as expected as interchangeable mineral components

Figure 9. Surprising variability in the phosphorus values both in extent and direction with correlation not following suit of Sr/Ca ratios as is generally hypothesized

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After establishing that trace element analysis is a useful tool for analyzing huntergatherers from Cis-Baikal, we must identify elements that may mirror or enhance provenance information acquired from 87Sr/86Sr ratios. Strontium isotope ratio is a well developed analytical approach for provenancing skeletal tissues, however it has one major caveat in its ability to elucidate either origins or mobility of an individual; that it can only operate on the scale of the dominant bedrock formation and/or geologic zone. In some areas of the world, this is more than adequate to answer all of the current research questions relating to available cemetery populations. This is particularly true for agrarian groups, where questions are dominated by a local/nonlocal dichotomy where the primary goal is to establish the local signal and thus identify immigrants in a population, with the provenancing of the immigrants falling to secondary level of investigation. Geologically complex areas such as Cis-Baikal are broadly speaking, quite amenable to such a research approach as there are geologic formations spanning three major epochs in fairly well defined and non-overlapping geography, however we encounter several problems in this situation. Previous studies in CisBaikal have demonstrated that the 87Sr/86Sr technique works in the region, but also that there are two situations that cannot be clarified without further research: that there are some individuals who, though likely mobile, stayed within a single geological zone; and that there are two major zones of similar age and thus theoretically indistinguishable, leaving a rather difficult scenario where hypotheses regarding regional population exchange will inevitably be hampered by an inability to separate out individuals from these two regions. Two potential solutions to this problem are intensive environmental sampling in order to improve the comparison map available for samples, and the addition of another elemental and/or isotopic series to provide statistical depth to the data and enable multivariate analyses. Within CisBaikal, four elements appeared to meet the criteria for their ability to enhance the 87Sr/86Sr data: rubidium (Figure 10), cesium (Figure 11), barium (Figure 12), and rhenium (Figure 13). That Rb concentrations can mimic 87Sr/86Sr ratios is not too surprising as most radiogenic formations also contain higher levels of Rb and Sr, however this does not inhibit its value as an elemental signal in helping to elucidate further provenancing of samples within a radiogenic zone as there is still considerable variability in the raw concentrations of the element encountered in the environment. Rhenium functions in a similar fashion. Barium and cesium do not replicate 87Sr/86Sr data as effectively, demonstrating instead their usefulness in discriminating between groups within a single zone (Cs) or between individuals who all come from an area with similar 87Sr/86Sr values, but markedly different Ba concentrations, and thus likely from different areas within another zone. Examined more closely, rhenium and zinc values, for example, show a fair amount of variability throughout the geography of a single tooth (Figure 14), illustrating this individual’s continual presence within a single geologic zone, in this case the Little Sea, however also showing that they had notable variability in their interaction with rhenium through their environment via either dietary or mobility changes. Discussions over methodological approaches to obtaining accurate 87Sr/86Sr data using laser ablation frequently include debates over diagenetic alterations and the presence of various interferences. Doubly-charged rare earth elements frequently fall within the mass ranges monitored for 87Sr/86Sr analysis, thus their presence is of great concern. Theoretically, the presence of elements unable to make direct replacements in the mineral matrix strongly supports proponents of the view that all rare earth elements are diagenetic in origin and thus represent both contaminated samples and a dead end avenue for geochemical research.


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However, there are very often anomalies within any mineral matrix, especially so in organic matrices such as calcium hydroxyapatite, and these areas of imperfect mineral matrix are effectively traps for other mineral constituents, including trace elements in general. Furthermore, studies demonstrating the utility of trace elemental analysis on human teeth tend to overshadow concerns of diagenetic overprinting or alteration of samples preventing the recovery of useful compositional data from teeth. Following in light of this debate, we attempted to see if there were significant correlations between the strontium and barium values. Sr2+ replaces calcium within enamel at a rate not exceeding 1 in 10 ions, and so has a limited capability for accumulation within skeletal tissues even if abundant in the body water supply at the time of enamel formation. Similarly, Ba2+ sometimes substitutes strontium in the same position, again at a fraction of the potentially available positions in the matrix. So, significant shifts in the Sr:Ba ratios should hypothetically be a signal that there is diagenetic alterations that could render normal interference calculations for rare earth elements or other interferences inaccurate. However, in the teeth analyzed for this research, no significant correlations could be found linking Sr:Ba ratios with other forms of interference in 87Sr/86Sr analyses.

Figure 10. Rubidium replicates Sr isotope groupings

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Figure 11. Cesium values largely replicate Sr isotope groupings, however suggest greater internal variability for “local” groupings than is suggested by isotopic analysis

The last major goal of this research was to generate adequate data to test the potential for an online or in situ measurement of interference on mass 87 from the polyatomic molecule [40] Ca [31] P[16]O. Previous research has demonstrated that the formation of this polyatomic species is the source of significant interference for laser ablation analyses of strontium isotopes at such a scale that interpretations can be biased through methodological fault. As the [40] Ca [31] P [16] O is the result of interactions between the enamel surface, the laser and the charged oxidation environment of the plasma, however it remains unclear which element in the system is primarily responsible for this interference, or if it is truly an unavoidable consequence of having excess amounts of Ca, P and O in a charged environment. There are several uncertain variables in this equations, thus the easiest way to measure [40] Ca [31] P [16] O production during analysis would be to measure the related species [44] Ca [31] P [16] O that will skew values of mass 91 in relative proportion to the level of interference on mass 87. In order to measure the interference at mass 91, we need to compare the mass peaks of zirconium 90 and 91. A comparison of [90] Zr and [91] Zr between solution mode and laser ablation quadrupole-ICP-MS clearly shows the presence of the hypothesized offset between the two masses of Zr (Figure 15). The LA values include the data from small laser spot sizes as well as larger ones, so there is significantly more variability in the laser data than the solution data, though there is still a readily apparent offset and linear trend in the offset that can be used for a correction. Such a correction follows the logic that the visible offset in Zr values will correlate with the 87Sr/86Sr differences between laser and solution data.


87

Figure 12. Barium values suggest greater variability in “nonlocal” interpretation than is indicated by Sr isotope values.

As a test of this concept, we first utilized the published dataset from Simonetti et al.8 to see if using reported Sr concentrations we could “correct” the LA data and get results within the original error terms of the analysis. The published data contained Sr concentrations, but no information on Zr, so an added step was needed in this experiment. A linear relationship between the concentrations of Sr and Zr were drawn from the KN XIV analyses and applied to the reported Sr values in order to generate the expected offset of [91] Zr. This offset was then compared to the differences in 87Sr/86Sr data to gain a second linear relationship for the expected error from [40] Ca [31] P [16] O based on the levels of Sr and Zr (Figure 16). The dataset lacked information on specific corrections used, however the laboratory protocols from the time did not incorporate REE or Ca-dimer corrections, so additional blanket correction values were included in the process, however the correction procedure largely followed that outlined by Horstwood et al. 1. Due to the number of variables missing, there is a fair amount of uncertainty in the accuracy of the final “corrected” data, yet the new LA data largely fall on or near the SM data reported. Several of the values did not end within the original error terms, showing the difficulties in applying corrections to data with significant amounts of uncertainty attached and compounding concerns over the comparability of microsampling locations with the masses of enamel homogenized for solutions. The fact that the majority of samples fell surprisingly close to the SM values strongly supports the potential for this avenue of online correction. The difficulty with this situation is that these data were drawn from quadrupole-ICP-MS analysis that is equipped with different electronmultipliers and will have different operating oxide conditions than both another quadrupoleICP-MS and a MC-ICP-MS. This problem could theoretically be overcome if the quadrupole-

88


ICP-MS and the MC-ICP-MS were connected to the same ablation chamber and online correlations could be drawn between 87Sr/86Sr values and Zr concentrations, however the RIF laboratory is not set up in such a fashion.

Figure 13. Grouping via rheniuim replicates Sr isotope groupings

Figure 14. Rhenium values for a single “local” individual illustrate their continued residence within a geologic region, though with some smaller scale mobility


Figure 15. Comparison between 90Zr/91Zr between solution mode and laser ablation ICP-MS for KN XIV teeth

Figure 16. Zirconium difference extrapolated from strontium concentrations and compared with observed laser ablation– and solution mode–MC-ICP-MS differences for Simonetti et al.2008 data

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90

Ian Scharlotta, Andrzej Weber, S. Andy DuFrane et al. Table 4. Laser ablation 87Sr/86Sr ratio data for KN XIV teeth with correction results Sample ID 87Sr/86Sr 97.211_A1 0.7123743 97.211_A2 0.7125077 97.211_A3 0.7125393 97.211_B1 0.7122774 97.211_B2 0.7120285 97.211_B3 0.71261 97.211_C1 0.7116353 97.211_C2 0.7115308 97.211_C3 0.7117711 97.211_D1 0.712428 97.211_D2 0.7119169 97.211_D3 0.7114825 Standard Deviation 97.217_A1 0.7158983 97.217_A2 0.7170207 97.217_A3 0.7172126 97.217_B1 0.7163448 97.217_B2 0.7168815 97.217_B3 0.7174497 97.217_C1 0.7153606 97.217_C2 0.7158572 97.217_C3 0.7151173 97.217_D1 0.7151284 97.217_D2 0.715732 97.217_D3 0.7160216 Standard Deviation 97.225_A1 0.7144163 97.225_A2 0.7161518 97.225_A3 0.7163261 97.225_B1 0.7155843 97.225_B2 0.716525 97.225_B3 0.7161068 97.225_C1 0.715738 97.225_C2 0.7153563 97.225_C3 0.7159872 97.225_D1 0.7150012 97.225_D2 0.7166502 97.225_D3 0.7152321 Standard Deviation 98.355_A1 0.7132161 98.355_A2 0.7152994 98.355_B1 0.7126116 98.355_B2 0.7120714

Zr Corrected #1 0.708214083 0.708232427 0.708248213 0.708167282 0.708107142 0.708259837 0.707992527 0.707963213 0.708035033 0.708211639 0.708071365 0.707968825 0.000113406 0.709163308 0.709466918 0.709530354 0.709282721 0.709433961 0.709599039 0.709011616 0.709152765 0.70895875 0.708948668 0.709119498 0.709208743 0.000223459 0.708755271 0.709239481 0.709286307 0.709074139 0.709337331 0.709231976 0.709117164 0.709023225 0.709190372 0.708913961 0.709373185 0.708993929 0.000184104 0.708425491 0.709003086 0.708261768 0.708117652

Zr Corrected #2 0.711088326 0.7112217 0.711406978 0.711007949 0.710774713 0.711366711 0.710362712 0.710267076 0.710558893 0.711157536 0.71069914 0.710286141 0.000415611 0.714625791 0.715773901 0.716033087 0.71507506 0.715642341 0.716232863 0.714099739 0.714610899 0.713868661 0.713851615 0.71446194 0.714729529 0.000830401 0.713143106 0.714888032 0.715136798 0.714320011 0.715261989 0.714866517 0.714457597 0.714078762 0.714739576 0.713722761 0.715376629 0.71401245 0.000673628 0.711944233 0.714034025 0.711343396 0.710820199

Sr Corrected 0.710569148 0.710718353 0.710756634 0.710484925 0.710245952 0.710826027 0.709787549 0.709668758 0.709856572 0.710586686 0.710117022 0.709633692 0.00044487 0.714258617 0.715382757 0.715575752 0.7147632 0.715324752 0.715883702 0.713830202 0.714343247 0.71359879 0.713702191 0.714330123 0.714636228 0.000763181 0.713245991 0.714950852 0.715151286 0.714376255 0.715318674 0.714884275 0.714504436 0.71411776 0.71473358 0.71373858 0.715419111 0.713996315 0.000667163 0.711898467 0.713999032 0.711305823 0.71073572

2σ error 0.0001806 0.0001684 0.000204 0.000198 0.0001622 0.0001414 0.0001572 0.000202 0.000164 0.0001718 0.0001888 0.000214 0.0001974 0.000274 0.0002 0.00032 0.0001302 0.000204 0.000214 0.00024 0.000204 0.000234 0.000195 0.000236 0.000294 0.000312 0.000208 0.000296 0.000252 0.0003 0.0003 0.000252 0.00028 0.00032 0.000348 0.000672 0.000366 0.00042 0.00045 0.000302


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Table 4. (Continued) Sample ID 87Sr/86Sr 98.355_B3 0.7119601 98.355_C1 0.7116431 98.355_C2 0.7121804 98.355_C3 0.7126502 98.355_D1 0.713514 98.355_D2 0.7136801 98.355_D3 0.7146961 Standard Deviation 98.359_A1 0.7117397 98.359_A2 0.7127162 98.359_A3 0.7118754 98.359_B1 0.7117544 98.359_B2 0.7129407 98.359_B3 0.7129047 98.359_C1 0.7141845 98.359_C2 0.7134008 98.359_C3 0.7137356 98.359_D1 0.7133296 98.359_D2 0.7123873 98.359_D3 0.7126201 Standard Deviation

Zr Corrected #1 0.708087172 0.707992121 0.708145311 0.708280574 0.708529766 0.708583201 0.70886989 0.000328141 0.70802341 0.708290944 0.70808271 0.708028108 0.708352823 0.708341993 0.708692376 0.708478361 0.708591637 0.708455316 0.708200505 0.708271653 0.000214107

Zr Corrected #2 0.710714156 0.710377001 0.710937714 0.711487117 0.712218521 0.712382943 0.7134102 0.001154633 0.710463167 0.711456789 0.710661269 0.710486623 0.711697772 0.711632711 0.712909064 0.712154703 0.71248943 0.712055396 0.711126393 0.711417852 0.00077966

Sr Corrected 0.710585614 0.710239802 0.710771703 0.711191809 0.712354224 0.712548372 0.713553632 0.001243646 0.710068174 0.711076884 0.710208528 0.709975754 0.711152791 0.711115233 0.712398622 0.711602994 0.711965841 0.711520369 0.710580792 0.7107383 0.000759206

2σ error 0.000278 0.000414 0.000448 0.000346 0.000632 0.00039 0.000464 0.00069 0.00066 0.000672 0.00071 0.000916 0.000712 0.001052 0.00068 0.00061 0.00086 0.00088 0.0008

Figure 17. 87Sr/86Sr ratios by sample for SM, LA, and LA corrected for REE, calcium dimer and CaPO

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In order to enable in situ correction of mass 87 using mass 91 for 87Sr/86Sr analysis, the same machine must monitor both masses simultaneously. Unfortunately, the MC-ICP-MS used for this research was not sensitive enough to measure peaks at masses 90 or 91 without special tuning. It remains theoretically possible that this machine could be effectively used for LA 87Sr/86Sr analysis using a Zr offset correction; however the special tuning would render the procedure impractical and likely interfere with regular operations of the instrument. Thus at present, efforts to correct 87Sr/86Sr data for [40] Ca [31] P [16] O interference remain most ably demonstrated with the procedures used by Horstwood et al. 1. Without the same depth of suitable reference materials and sample runs, we can still examine new data, but must approach it with some measure of caution. Taking the LA data for the Cis-Baikal samples and applying several different approaches to correction, we find a significant amount of variability. Applying the correction equation used for the Simonetti et al. [8] directly, but with measured Zr concentrations, we clearly have an overcorrection (Table 4). There is likely to be a significant divergence of the laser data from the single solution datum as we realize the disconnect between internal variability of a tooth’s formation and the homogenizing effects of solution preparation, however are overcorrected by a 87Sr/86Sr ratio of approximately 0.002. A second attempt at using zirconium differences as a correction yield better results, which are well within the realm of uncertainty regarding internal variability relative to the solution data available. We find similar results from a correction drawn directly from strontium concentrations and bypassing zirconium offsets altogether. These later two corrections are difficult to assess without a coupled set of microsampled set of solutions. Given the added uncertainty of drawing these data from a different instrument, we were inclined to have greater faith in the strontium corrected laser data in this case. The strontium data are likely to be more similar between the two instruments and thus less prone to measurement errors within the scope of this experiment. These data also highlight a fair amount of internal variability regardless of which correction is used. Of the five teeth sampled, there is an average deviation of 0.000773 for 87Sr/86Sr ratios, with some individuals exhibiting significantly more variability than others. This is strongly suggestive of 87Sr/86Sr ratios indicative of mobility across geologic zones and/or changes in dietary geochemical interactions of these individuals.

CONCLUSION Microsampling of complex minerals is a delicate balance between microsampling methodology, analytical precision and the formation events responsible for the initial complexity. This will be true whether the mineral matrix is organic or inorganic. For skeletal materials, there is greater uncertainty attached to the formation process and the contributing ionic pool of resources used to form the final matrix. Dietary intakes will be averaged within the body, for over a year for elements such as strontium, and the forming mineral structure remains an open chemical system for weeks or months after the formation of the structures visible as Retzius lines. This makes progress difficult to impossible for efforts to generate useful provenance and/or dietary data for individuals at a temporal scale smaller than a tooth as a whole. Evidence from herbivore teeth strongly suggest that lag times can outstrip effective mineralization rates, making intensive microsampling an unnecessary effort as the


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same trend lines can be generated with a fraction of the total analyses involved in intensive microsampling. The same may or may not be true for human teeth as they take longer to form and in a smaller volume than herbivore teeth, thus potentially incorporating geochemical information at a temporal scale either within the body residence time of heavy elements or sufficiently long that changes in body averages can become visible using mixing models to interpret such data effectively. The data generated for this research strongly support two conclusions: 1) that trace element analysis can provide a useful contribution to understanding provenance/mobility data for skeletal tissues; and 2) that microsampling of human teeth is a worthwhile effort, with laser ablation being a reasonable option with appropriate corrections applied.

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Horstwood, MSA; Evans, JA; Montgomery, J. Determination of Sr isotopes in calcium phosphates using laser ablation inductively coupled plasma mass spectrometry and their application to archaeological tooth enamel. Geochimica et Cosmochimica Acta, 2008, 72(23), 5659-5674. Nowell, GM; Horstwood, MSA. Comments on Richards et al. Journal of Archaeological Science, 35, 2008. Strontium isotope evidence of Neanderthal mobility at the site of Lakonis, Greece using laser-ablation PIMMS. Journal of Archaeological Science, 2009, 36, 1334-1341. Bizarro, M; Simonetti, A; Stevenson, RK; Kurszlaukis, S. In situ 87Sr/86Sr investigations of igneous apatites and carbonates using laser-ablation MC-ICP-mS. Geochimica et Cosmochimica Acta, 2003, 67(2), 289-302. Prohaska, T; Latkoczy, C; Schultheis, G; Teschler-Nicola, M; Stingeder, G. Investigation of Sr isotope ratios in prehistoric human bones and teeth using laser ablation ICP-MS and ICP-MS after Rb/Sr separation. Journal of Analytical Atomic Spectrometry, 2002, 17, 887-891. Cucina, A; Dudgeon, J; Neff, H. Methodological strategy for the analysis of human dental enamel by LA-ICP-MS. Journal of Archaeological Science, 2007, 34(11), 18841888. Horstwood, MSA; Parrish, RR; Condon, DJ; Pashley, V. Laser ablation acquisition protocols and non-matrix matched standardisation of U-Pb data. Geochimica et Cosmochimica Acta, 2006, 70(18, Supplement 1), A264-A264. Richards, MP; Harvati, K; Grimes, V; Smith, C; Smith, T; Hublin, JJ. Strontium isotope evidence of Neanderthal mobility at the site of Lakonis, Greece using laser-ablation PIMMS. Journal of Archaeological Science, 2008, 35(5), 1251-1256. Simonetti, A; Buzon, MR; Creaser, RA. In-situ elemental and Sr isotope investigation of human tooth enamel by laser-ablation-(MC)-ICP-MS: successes and pitfalls. Archaeometry, 2008, 50(2), 371-385. Vroon, PZ; van der Wagt, B; Koornneef, JM. Problems in obtaining precise and accurate Sr isotope analysis from geological materials using laser ablation MC-ICPMS. Analytical and Bioanalytical Chemistry, 2008, 390(465-476).

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[10] Woodhead, JD; Swearer, S; Hergt, J; Maas, R. In situ Sr-isotope analysis of carbonates by LA-MC-ICP-MS: interference corrections, high spatial resolution and an example from otolith studies. Journal of Analytical Atomic Spectrometry, 2005, 20, 22-27. [11] Paton, C; Woodhead, JD; Hergt, J; Phillips, D; Shee, S. Sr-isotope analysis of kimberlitic groundmass perovskite via LA-MC-ICP-MS. Geostandard Geoanalytical Research, 2007, 31(4), 321-330. [12] Galazii, GI. Baikal Atlas. Russian Academy of Sciences, Moscow, 1993. [13] Weber, AW; Link, DW; Katzenberg, MA. Hunter-Gatherer Culture Change and Continuity in the Middle Holocene of the Cis-Baikal, Siberia. Journal of Anthropological Archaeology, 2002, 21(2), 230-299. [14] Weber, AW. Biogeographic profile of the Lake Baikal region, Siberia. In Prehistoric Foragers of the Cis-Baikal, Siberia, Proceedings of the First Conference of the Baikal Archaeology Project, AW; Weber, H. McKenzie, Eds. Canadian Circumpolar Institute Press: Edmonton, 2003, 51-66. [15] Haverkort, CM; Bazaliiski, VI; Savel’ev, NA. Identifying hunter-gatherer mobility patterns using strontium isotopes. In Prehistoric Hunter-Gatherers of the Baikal Region, Siberia: Bioarchaeological Studies of Past Lifeways., AW; Weber, MA; Katzenberg, TG. Schurr, Eds. University of Pennsylvania Museum of Archaeology and Anthropology: Philadelphia, 2010, 217-239. [16] Levin, MG; Potapov, LP. The Peoples of Siberia. University of Chicago Press: Chicago, 1964. [17] Losey, RJ; Nomokonova, T; Goriunova, OI. Fishing ancient Lake Baikal, Siberia: inferences from the reconstruction of harvested perch (Perca fluviatilis) size. Journal of Archaeological Science, 2008, 35(3), 577-590. [18] Weber, AW. The neolithic and early bronze age of the Lake Baikal Region: A review of recent research. Journal of World Prehistory, 1995, 9(1), 99-165. [19] Weber, AW; Link, DW; Goriunova, OI; Konopatskii, AK. Patterns of Prehistoric Procurement of Seal at Lake Baikal: A Zooarchaeological Contribution to the Study of Past Foraging Economies in Siberia. Journal of Archaeological Science, 1998, 25(3), 215-227. [20] Katzenberg, MA; Weber, AW. Stable Isotope Ecology and Palaeodiet in the Lake Baikal Region of Siberia. Journal of Archaeological Science, 1999, 26(6), 651-659. [21] Lam, YM. Isotopic evidence for change in dietary patterns during the Baikal Neolithic. Current Anthropology, 1994, 35, 185-190. [22] Haverkort, CM; Weber, AW; Katzenberg, MA; Goriunova, OI; Simonetti, A; Creaser, RA. Hunter-gatherer mobility strategies and resource use based on strontium isotope (87Sr/86Sr) analysis: a case study from Middle Holocene Lake Baikal, Siberia. Journal of Archaeological Science, 2008, 35, 1265-1280. [23] Huh, Y; Coleman, D; Edmond, J. 87Sr/86Sr in Siberian Rivers, EOS. Transactions of the American Geophysical Union, 1994, 75(16), 142. [24] Kenison Falkner, K; Lebaron, G; Thouron, D; Jeandel, C; Minster, JF. Cr, V and Sr in Lake Baikal, EOS. Transactions of the American Geophysical Union, 1992, 73(14), 140. [25] Scharlotta, I. In Spatial variability of biologically available 87Sr/86Sr, rare earth and trace elements in the Cis Baikal region, Siberia: Evidence from environmental samples


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[41] Suga, S. Enamel hypomineralization viewed from the pattern of progressive mineralization of human and moneky developing enamel. Advances in Dental Research, 1989, 3, 188-98. [42] Tafforeau, P; Bentaleb, I; Jaeger, JJ; Martin, C. Nature of laminations and mineralization in rhinoceros enamel using histology and X-ray synchrotron microtomography: Potential implications for palaeoenvironmental isotopic studies. Palaeogeography, Palaeoclimatology, Palaeoecology, 2007, 246(2-4), 206-227. [43] Avery, JK. Essentials of Oral Histology and Embryology - A Clinical Approach. Mosby-Year Book, Inc.: St. Louis, 1992. [44] Balasse, M. Potential biases in sampling design and interpretation of intra-tooth isotope analysis. International Journal of Osteoarchaeology, 2003, 13, 3-10. [45] Balasse, M; Ambrose, SH; Smith, AB; Price, TD. The seasonal mobility model for prehistoric herders in the south-western Cape of South Africa assessed by isotopic analysis of sheep tooth enamel. Journal of Archaeological Science, 2002, 29, 917-932. [46] Britton, K; Grimes, V; Dau, J; Richards, MP. Reconstructing faunal migrations using intra-tooth sampling and strontium and oxygen isotope analyses: a case study of modern caribou (Rangifer tarandus granti). Journal of Archaeological Science, 2009, 36 (5), 1163-1172. [47] Hoppe, KA; Koch, PL; Carlson, RW; Webb, DS. Tracking mammoths and mastodons: Reconstruction of migratory behavior using strontium isotope ratios. Geology, 1999, 27, 439-442. [48] Hoppe, KA; Koch, PL; Furutani, TT. Assessing the preservation of biogenic strontium in fossil bones and tooth enamel. International Journal of Osteoarchaeology, 2003, 13, 20-28. [49] Hoppe, KA; Stover, SM; Pascoe, JR; Amundson, R. Tooth enamel biomineralization in extant horses: implications for isotopic microsampling. Palaeogeography, Palaeoclimatology, Palaeoecology, 2004, 206 (3-4), 355-365. [50] Koch, PL; Heisinger, J; Moss, C; Carlson, RW; Fogel, ML; Behrensmeyer, AK. Isotopic tracking of change in diet and habitat use in African elephants. Science, 1995, 267, 1340-1343. [51] Montgomery, J; Evans, JA; Horstwood, MSA. Evidence for long-term averaging of strontium in bovine enamel using TIMS and LA-MC-ICP-MS strontium isotope intramolar profiles. Environmental Archaeology, 2010, 15(1), 32-42. [52] Dahl, SG; Allain, P; Marie, PJ; Mauras, Y; Boivin, G; Ammann, P; Tsouderos, Y; Delmas, PD; Christiansen, C. Incorporation and distribution of strontium in bone. Bone, 2001, 28(4), 446-453. [53] Bowen, HJM. Evnironmental Chemistry of the Elements. Academic Press: London, 1979. [54] Montgomery, J; Evans, JA; Cooper, RE. Resolving archaeological populations with Srisotope mixing models. Applied Geochemistry, 2007, 22(7), 1502-1514. [55] Gratuze, B. Obsidian Characterization by Laser Ablation ICP-MS and Its Application to Prehistoric Trade in the Mediterranean and the Near East: Sources and Distribution of Obsidian within the Aegean and Anatolia. Journal of Archaeological Science, 1999, 26, 869-881. [56] Russo, RE; Mao, X; Liu, H; Gonzalez, J; Mao, SS. Laser ablation in analytical chemistry - a review. Talanta, 2002, 57(3), 425-451.


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[57] Speakman, RJ; Neff, H. Laser ablation-ICP-MS in archaeology research. University of New Mexico Press: Santa Fe, 2005. [58] Tykot, RH; Young, SMM. Archaeological Applications of Inductively Coupled Plasma - Mass Spectrometry. In Archaeological Chemistry, AM; Pollard, C. Heron, Eds. Royal Society of Chemistry: Cambridge, 1996, 116-130. [59] Budd, P; Montgomery, J; Cox, A; Krause, P; Barreiro, B; Thomas, RG. The distribution of lead within ancient and modern human teeth: implications for long-term and historical exposure monitoring. The Science of the Total Environment, 1998, 220, 12136. [60] Copeland, SR; Sponheimer, M; le Roux, PJ; Grimes, V; Lee-Thorp, JA; de Ruiter, DJ; Richards, MP. Strontium isotope ratios (87Sr/86Sr) of tooth enamel: a comparison of solution and laser ablation multicollector inductively coupled plasma mass spectrometry methods. Rapid Communications in Mass Spectrometry, 2008, 22(20), 3187-3194. [61] Copeland, SR; Sponheimer, M; Lee-Thorp, JA; Le Roux, PJ; De Ruiter, DJ; Richards, MP. Strontium isotope ratios in fossil teeth from South Africa: assessing laser ablation MC-ICP-MS analysis and the extent of diagenesis. Journal of Archaeological Science, 2010, 37(7), 1437-1446. [62] Trotter, JA; Eggins, SM. Chemical systematics of conodont apatite determined by laser ablation ICP-MS. Chemical Geology 2006, 233, 196-216. [63] Christensen, JN; Halliday, AN; Lee, DC; Hall, CM. In situ Sr isotopic analysis by laser ablation. Earth and Planetary Science Letters, 1995, 136, 79-85. [64] Kin, FD; Prudêncio, MI; Gouveia, MÂ; Magnusson, E. Determination of Rare Earth Elements in Geological Reference Materials: A Comparative Study by INAA and ICPMS. Geostandards and Geoanalytical Research, 1999, 23(1), 47-58. [65] James, WD; Dahlin, ES; Carlson, DL. Chemical compositional studies of archaeological artifacts: Comparison of LA-ICP-MS to INAA measurements. Journal of Radioanalytical and Nuclear Chemistry, 2005, 263(3), 697-702. [66] Revel, G; Ayrault, S. Comparative use of INAA and ICP-MS for Environmental Studies. Journal of Radioanalytical and Nuclear Chemistry, 2000, 244(1), 73-80. [67] Horstwood, MSA; Evans, JA. Complications of LA-MC-ICP-MS Sr isotope analysis of phosphate matrices. In Eighth International Conference on Plasma Source Mass Spectrometry, University of Durham, UK, 2002. [68] Horstwood, MSA; Nowell, GM. Multi-collector devices. In ICP-MS Handbook, Nelms, S., Ed. Blackwell Scientific Publications: Oxford, 2005, 54-68. [69] Cucina, A; Neff, H; Tiesler, V. Provenance of African-born individuals from the colonial cemetery of Campeche (Mexico) by means of trace element analysis. Dental Anthropology, 2005, 17, 65-69. [70] Dudgeon, J. The genetic architecture of the late prehistoric and protohistoric Rapa Nui. Doctoral Dissertation, University of Hawai'i, Manoa, 2008. [71] Weigand, PC; Harbottle, G; Sayre, EV. Turquoise Sources and Source Analysis: Mesoamerica and the Southwestern U.S.A. In Exchange Systems in Prehistory, TK; Earle, JE. Ericson, Eds. Academic Press: New York, 1977, 15-34.



Chapter 3

MODELING OF LASER ABLATION INDUCED BY NANOSECOND AND FEMTOSECOND LASER PULSES Tatiana E. Itina1*, Mikhail E. Povarnitsyn2 and Konstantin V. Khishchenko2 1

Hubert Curien’s Laboratory, CNRS 55216, 18 rue de Professeur Benoît Lauras, Bat. F, 42000, Saint-Etienne, France 2 Joint Institute for High Temperatures RAS, 13 Bd. 2, Izhorskaya street, Moscow, Russia

ABSTRACT The chapter considers the problem of numerical modeling of laser-matter interactions. The main objective is to clarify the mechanisms of this extremely complex process. Comparison of femtosecond and nanosecond laser ablation is first presented. Thermal model is used for nanosecond ablation. The physical phenomena involved into the interaction of a laser-generated plasma plume with a background environment are furthermore studied. A three-dimensional combined model is developed to describe the plasma plume formation and its expansion in vacuum or into a background gas. The proposed approach takes advantages of both continuous and microscopic descriptions. The simulation technique is suitable for the simulation of high-rate laser ablation for a wide range of the background pressure. The model takes into account the mass diffusion and the energy exchange between the ablated and background species, as well as the collective motion of the ablated species and the background gas particles. The developed approach is used to investigate the ablation of aluminum in the presence of a background gas. The influence of the background gas on the expansion dynamics of the lasergenerated plume is examined. Experimental density distributions are explained based on the simulation results. A detailed analysis of material decomposition in femtosecond regime is then performed by using a hydrodynamic model with a thermodynamically complete equation *

Corresponding author: Email: [email protected].

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Tatiana E. Itina, Mikhail E. Povarnitsyn and Konstantin V. Khishchenko of state. As a result, several ablation mechanisms are observed. A major fraction of the ablated material is found to originate from the metastable liquid region, which is decomposed either thermally in the vicinity of the critical point into a liquid-gas-mixture or mechanically at high strain rate and negative pressure into liquid droplets and chunks. The calculation results agree with the results of previous molecular dynamics simulations and explain recent experimental findings. In addition, effects of the ultra-short laser excitations of wide band gap materials need a particular attention. In this case, material ionization through multi-photon excitation and electron-impact ionization should be considered. Laser interactions are simulated with a particular focus on the control over laser plume expansion process. The properties of the laser-generated plasma plume are shown to be strongly affected by the laser-mater interaction mechanism

1. INTRODUCTION Shortly after the demonstration of the first laser, the most intensely studied theoretical topics dealt with laser-matter interactions. Many experiments were undertaken to clarify the mechanisms of this extremely complex process. At the same time, numerous models, both analytical and numerical, were proposed to describe these interactions. In these models, different experimental conditions were considered, and several terms were proposed to denote the processes occurring during laser action on different materials. Thus, "laser ablation", "evaporation", "desorption" or "sputtering" – all these terms are relevant to the interaction of a laser beam with a solid (or a liquid) surface that results into transition of the surface particles into a gas phase. For simplicity, here we will use only the term "laser ablation". Laser ablation has found a number of industrial applications, such as laser cleaning, micromachining, molecular mass spectrometry, plasma technology, laser surgery, etc. One of the main advantages of this technique is the simplicity of the experimental set-up. The other advantage is the possibility of adjusting the experimental conditions in order to obtain the desirable treatment quality. Among the important experimental parameters one should mention the followings • • • • •

laser pulse parameters (fluence, beam dimensions, duration, time-shape) target material target-substrate distance ambient gas (pressure, atomic mass, temperature) substrate characteristics

Recently, a particular attention has been attracted to various surface-treatment applications, such as laser micromachining, marking, modification of the surface properties, etc. One of the major problems that arise in the development of these applications is connected with prevention of collateral thermal damage of the treated material. One way of the minimization of the undesired thermal effects is the decrease of laser pulse duration. That is why starting from the beginning of 80th, the interest of researches turned to lasers with nanosecond pulse duration. After recent commercialization of laser systems with short (picosecond) and ultra-short (femtosecond) laser pulse duration, the attention of researches has been naturally focused on the advantages of these systems [1-7]. The rapid evolution in laser system development has opened new horizons for laser applications. Laser wavelength

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now varies from infrared to ultra-violet and starts to penetrate into X-ray. Laser power has grown considerably, so that smaller focusing is required. Among other important adjustable parameters, one can note laser pulse shape, polarization and beam quality. Therefore, lasers are currently used not only for surface treatment, cleaning, micro and nano-machining, structuring, but also for nanoparticle formation, surface analysis, optics and photonics, microelectronics, nanoplasmonics, nano-bio-technology, atomic physics, chemistry, medical applications, etc. In particular, femtosecond laser pulses provide unique opportunities for such applications as laser spectroscopy (LIBS), nanoparticle synthesis both in vacuum, in gas, and in liquid, laser surgery, nano-fabrication, etc. [8,9,10]. One one hand, cluster formation by laser ablation provides an attractive avenue for fabrication of nanostructured materials and for medicine [15,11,12,13,14]. The applications based on cluster deposition include fabrication of nano-crystalline or cluster-assembled films and coatings, deposition of metal particles for catalysis, or composite compound semiconductors for electro-optical applications. On the other hand, the presence of clusters or particulates in the ablation plume can be harmful for the quality of thin films grown in pulsed laser deposition (PLD) [15]. In addition, the formation of debris and re-deposition of ejected particulates can cause problems in manufacturing of surface microstructures. Clusters in the expanding plume can scatter the incident laser light and lead to a shielding of the target surface in the case of long laser pulses or in the multi-pulse irradiation regime. For all these reasons, it is crucial to be able to predict and control the parameters of clusters formed in laser ablation, such as particle size distributions, velocities, and temperature at the time of deposition. Despite rapid development in laser physics, one of the fundamental questions still concerns the definition of proper ablation mechanisms. Apparently, the progress in laser systems implies several important changes in these mechanisms, which depend on both laser parameters and material properties. Among the more studied ablation mechanisms there are thermal, photochemical and photomechanical ablation processes [11]. Frequently, however, the mechanisms are mixed, so that the existing analytical equations are hardly applicable. In this case, numerical simulation is needed to better understand and to optimize the ablation process [16,17,18]. So far, thermal models are commonly used to describe nanosecond (and longer) laser ablation [19, 20]. In these models, the laser-irradiated material experiences heating, melting, boiling and evaporation. Thermal effect plays therefore a major role, particularly in the case of metals with high thermal conductivity. In this case, the ablation flux can be described by a Hertz-Knudsen equation. The interaction of femtosecond pulses even with metals implies, however, a change in the ablation mechanism due to not only the absence of equilibrium between electrons and lattice-ions during the pulse, but also because the heating is too fast. The Hertz-Knudsen equation is inapplicable in this case and a numerical study is for the careful optimization of the laser processing of metals. Recently, many experimental and theoretical investigations of the mechanism of femtosecond (< 100 fs) ablation have been performed [21,22,23,24]. Evidently, the interest in femtosecond lasers was caused by numerous exciting laser applications listed above. Among the main advantages of these short pulses is the possibility of laser treatment of any materials, even these that were considered to be transparent, in a possibility of control over electronic excitations, and in the minimization of non-desirable thermal effects. However, the mechanisms of these interactions are often rather different from that of longer pulses, and many difficulties first arouse in the corresponding numerical modeling. The main point that

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Tatiana E. Itina, Mikhail E. Povarnitsyn and Konstantin V. Khishchenko

makes ultra-short interactions difficult to model, is that the pulse duration is shorter than the electron-phonon/ion relaxation time tei~1-10 ps. As a result of strong difference between the electron and ion mass, the mean electron energy rises much faster and higher that that of ion subsystem. The terms “electron and ion temperatures”, however, require equilibrium in each sub-system that also may take longer time to establish. If these terms can be applied, electron temperature is much larger that ion temperature during the interaction. The knowledge about the required equation of state (EOS) is also very limited. In addition, metastable matter states, such as superheated liquid one, seem to play a role. All these points limit the information about model parameters and make computer simulation rather difficult. In studies of femtosecond interactions with metals, new ablation mechanisms have been proposed both for metals and semiconductor materials [21,22,23,25-34]. In particular, for semiconductor and/or dielectric materials, such processes as multi-photon/tunneling ionization, electron-impact, or avalanche ionization, charge separation, optical breakdown, material damage and ablation have been investigated [35]. Previous theoretical studies used either the detailed Boltzmann’s equation [35,36] or simplified rate equations to describe laser excitation kinetics [37-41]. For metals, two-temperature model [42,43] has yielded information about electron and lattice temperature evolution. However, the validity of the classical TTM model is limited due to the conditions of equilibrium to be established in each of two sub-systems and because of the heat diffusion equations that do not describe the heat front. As a result, the general conclusion was that the conventional TTM can be used for a bulk metal target at relatively high intensities. At smaller laser intensities, there is no equilibrium in the electron sub-system. In addition, for metal films, the ballistic electron transport should be considered [44]. In general, even in the case of a bulk target, the heat diffusion equation disregards the finite time of the heat propagation. In addition, the calculation of model parameters represents a challenge because of the lack of knowledge of electron distribution and temperature-dependency of such parameters as heat capacity, thermal conductivity, electron-phonon coupling, etc in the absence of both thermal and electron-ion equilibrium. Only recently, ab-initio calculations were performed [45] to account for the excitation of d-band electrons [46] in some metals, such as gold, silver, nickel. However, these first results need more analysis and verification To calculate material motion (and not only its temperatures), three numerical approaches were used, such as •

•

Atomistic approach, based on such methods as molecular dynamics (MD) [25,47,48,49] and Direct Monte Carlo Simulation (DSMC) [50,51,52].Typical calculation results provide detailed information about atomic positions, velocities, kinetic and potential energy; Macroscopic approach based hydrodynamic models [18,53,54] This model allows the investigations of the role of the laser-induced pressure gradient, which is particularly important for ultra-short laser pulses. The models are based on a one fluid two-temperature approximation and a set of additional models (equation of state) that determines thermal properties of the target. Recently electron-phonon coupling parameter was calculated as a function of electron temperature by using abinitio quantum mechanical methods [45];

Modeling of Laser Ablation Induced by Nanosecond and Femtosecond… •

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Multi-scale approach based on the combination of two approaches cited above was developed by several groups and was shown to be particularly suitable for laser applications.

The ejection of liquid and/or solid particulates has been studied for metals [55,56,57,58], semiconductors [59,60,61,62], dielectrics [63,64], and organic materials [11,65]. The parameters of the ejected particles are found to have a strong dependence on the laser irradiation conditions and the background gas pressure. A number of scenarios of cluster formation in laser ablation have been discussed in the literature. In many cases, observation of small clusters is attributed to the collision-induced condensation in the dense regions of the ejected plume [62,64,66,67]. Some evidences of the direct ejection of nanoparticles by ultrashort laser pulses were also obtained. Before considering the modeling details, we would like to emphasize that the laser-target interaction is an extremely complex process involving more than one physical phenomenon. These phenomena include the absorption of laser radiation, the creation of a high pressure and temperature region in the solid, the propagation of the compression and thermal waves, phase transitions, material decomposition and ionization, the ejection of electrons, ions and/or neutrals, laser plume expansion, the interaction of the ablated species with background gas, chemical reactions, cluster formation, etc… That is why it is difficult to formulate a complete and self-consistent model to interpret all observations. In general, laser ablation models can be subdivided into two categories • •

modeling of the interaction of the laser beam with a surface, where attention is focused on the primary mechanisms of the material ejection; modeling of the formation of a laser plume (secondary mechanisms) and its expansion in vacuum or in a background gas.

These categories are closely connected, since the first one provides initial conditions for the second one. Models that describe all the ablation process self-consistently and combine both calculations are exceptional. Some models are based on approaches with considerable mathematical complexity, some rely on simple physical descriptions, and others are phenomenological. Most of the theoretical studies do not provide insights directly applicable to improve the experimental conditions. In addition, the calculations contain many parameters, some of which are unknown and most of them are temperature dependent. Nevertheless, as far as several particular characteristics of the process are concerned, the quantitative comparison with experimental data turns out to be possible. The latter is valid especially for the experiments with either very small or very large laser fluence. This former case is of a particular interest because of a number of technical and scientific applications. Herein, we examine the different approaches used in the modeling of laser ablation and the most interesting results that were obtained in this field.

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2. MODELING OF NANOSECOND LASER ABLATION In this section we consider the modeling of laser ablation induced by nanosecond laser pulses. The description consists of two parts that correspond to the two categories of the ablation models.

2.1. Primary Mechanisms of the Material Ejection under Nanosecond Laser Action As we have noted in the Introduction, the most common and simplest model that describes the laser-solid interaction under low power density is based on a “thermal effect”. The problem of the evaporation of a metal surface heated up to a certain temperature T0 was considered by a number of authors, for example, by Anisimov et al [68], and by Ready. A simplified one-dimensional model which neglected the presence of a liquid phase was used in the first papers. Later, more realistic models of target heating and evaporation were developed, where moving boundary conditions were used. One can note, for example, the model of Luikov et al [69]. More recently, temperature, pressure and density discontinuity across Knudsen layer were considered by Anisimov [70]. To describe the heat transport one can use the heat flow equation that can be written in one-dimensional form as follows [71]:

c(T ) ρ (T )

∂T ∂ ⎛ ∂T ⎞ = ⎜ K (z , T ) ⎟ + μ I (z , t ) , ∂t ∂z ⎝ ∂z ⎠

(1)

where I is the absorbed laser radiation given by (1.1). For simplicity, the quantities c, ρ and K are frequently assumed to be temperature and space independent. If one neglects, furthermore, surface melting and the movement of the evaporation front, the boundary conditions for a surface laser source and a semi-infinite solid target can be written as follows:

z = 0 I = (1 − R) I 0 ,

(2)

z = 0, t = 0 T = T0 , and the solution of Eq. (1.6) obtained analytically using Green function technique is

T ( z, t ) =

1

ρ c πχ

t

∫ 0

I 0 (t − ψ )

ψ

⎛ z2 ⎞ ⎟⎟dψ + T0 exp⎜⎜ − ⎝ 4 χψ ⎠

Then, the time-evolution of the surface temperature is given by the equation:

(3)

Modeling of Laser Ablation Induced by Nanosecond and Femtosecond…

T (z, t ) =

A

ρc

t

πχ ∫

I (t − ψ )

ψ

0

dψ + T0

105

(4)

where A=1-R is the absorption coefficient. This equation allows the calculation of the surface temperature for a given time-evolution of the laser intensity. Using the solution obtained one can estimate the minimum (threshold) laser intensity Ith for evaporation by using the equation Tmax= TVap, where Tmax is the maximum surface temperature obtained from Eq. (1.9), and TVap is the material vaporization temperature. For example, for a top-hat laser pulse it gives:

I th =

ρ c πχ 2A τ

(TVap − T0 ) .

(5)

If thermal desorption mechanism is assumed, the initial velocity distribution is halfMaxwelian with the surface temperature T(t). Since the desorbed current is cosine distributed, the ablated flow velocity U0(t)=VT(t)/2, where VT (t ) = 8kT (t ) / πm , k is a Boltzmann’s constant and m is the particle mass. The desorption flux Φ(t ) = n0 (t )U 0 (t ) , where n0(t) is the density of the desorbed material immediately in front of the surface. If surface melting takes place, phase transition must be considered. To consider solidliquid or liquid-solid transitions, two boundary conditions are required at the interface where the phase transition occurs. First of these is an energy balance:

ρΔH m (Ttr )υ int = K sol

∂T ∂z

z + int

− K liq

∂T ∂z

(6) z − int

where Ttr is the temperature at which the transition takes place, Ksol and Kliq are thermal conductivities of solid and liquid phase respectively, ΔHm is the heat of melting at T= Ttr , and

υ int is the solid-liquid interface velocity. Moreover, the thermodynamics of crystallization

(Pererlongo et al., Ref.71) requires that υ int should be a function of the supercooling Ttr- Tm,

υ int = f (Ttr − Tm ) .

(7)

During the vaporization the surface recedes with velocity υ r . It is, however, still possible to label its position with z=0 in the reference frame moving with a receding surface. Then, neglecting mass accumulation and temperature dependence, Eq. (1) becomes

cρ

∂ 2T ∂T ∂T + μ I (z, t ) = K 2 + cρυ r ∂z ∂t ∂z

(8)

106

Tatiana E. Itina, Mikhail E. Povarnitsyn and Konstantin V. Khishchenko A simple way to compute υ r is to consider that liquid is in thermal equilibrium with its

saturated pressure. In this case the number NV of particles vaporizing per unit time and area is

NV =

p

(2πkTm)1 / 2

CS ,

(9)

where p is the gas pressure, and CS is the sticking coefficient. If one assumes that this equation also holds in a nonequilibrium situation as when particles are emitted into vacuum, then the velocity

υr =

p

ρ (2πkT / m )1 / 2

CS

(10)

The relation between the equilibrium vapor pressure and the temperature may be obtained from the Clausius-Clapeyron equation in the limit VliqIth. At this intensity (here, ~5 × 1013 W/cm2), Ne overcomes the plasma critical density nc. Interestingly, the experimentally measured plasma radiation from the breakdown region was shown to increase similarly with laser intensity. These results confirm the validity of our model.

Figure 7. Maximum density of the conduction band electrons as a function of the peak laser intensity. Here, calculations are performed for 50 fs laser pulse at 800 nm

120


The calculated optical breakdown threshold as a function of the laser pulse width is shown in Figure 8. One can see that the threshold intensity rises for laser pulses shorter than 100 fs. This result is in good qualitative agreement with recent experimental observations, where similar pulse width dependency and intensities values were observed [105]. Larger threshold values that obtained in the experiments for ultra-short pulses (30 mV), which avoids agglomeration and results in high nanoparticles stability. Even more nanoparticles directly produced and dispersed in liquid media are not inhalable and thus leads to facilitating of the process safety requirements. Moreover, the chemical precursors are not necessary therefore compared to laser ablation in gas atmosphere enhanced purity of colloidal particles is widely reported [13, 14]. It has to be stress that nowadays besides element metal, alloying, and oxide nanocrystals also organic fullerene-like nanostructures have been produced by laser ablation in liquids [15, 16]. Silicon nanocrystals (Si-ncs), since the discovery of visible room-temperature photoluminescence (PL) from anodized porous silicon, have attracted much attention due to their potential application in many fields (i.e. optoelectronics, photovoltaics, biology). Laser ablation in liquid can be employed in producing of highly luminescent Si-ncs with strong quantum confinement effects [17-19]. As Si-based technology will keep playing an crucial role for device fabrication, also silicon dioxide (SiO2) will remain a fundamental interface material. Direct processing in water or oxide based liquid media might allow engineer Sidioxide interface at Si-ncs at superior quality by cost effective way. Thus might consent to control and even enhance overall Si-ncs properties. Environmental and human body compatible procedure based on laser processing in water can be another factor for producing non-toxic, room temperature luminescent Si-ncs, which might at the same time provide a further foundation for applications in biology or medicine. In this chapter cheap and scalable nanosecond-laser ablation and fragmentation processing in liquids is applied for the fabrication of Si-ncs based nanostructures. The confinement of laser-generated plasma in liquids allows the Si-ncs formation with quantum confinement size effects. Particularly, we discuss aspects of the Si-ncs preparations in water and liquid transparent polymers i.e. pure and doped spin on glass (SOG). We demonstrate that compared to the water the SiO2-based SOG inhibits aggregation and enhance the photoluminescence properties of Si-ncs. In order to enhance the Si-ncs rate formation, an effective way to prepare luminescent Si-ncs by pulsed laser-induced fragmentation of Si micrograins prepared by electrochemical etching in water and SOG is outlined. We demonstrate that nanosecond-pulsed laser fragmentation in water can be efficiently used to induce the self-assembly of closely-packed and stable luminescent nanocrystals. Finnaly, the mathematical description of dynamical Si-ncs formation within laser plasma confined by liquids is applied to describe obtained results.

Fabrication of Silicon Nanocrystal Based Structures with Nanosecond…

129

2. EXPERIMENTAL DETAILS 2.1. Laser Ablation Our experimental set-up for the synthesis of Si-ncs with strong quantum confinement effect is based on a recently developed nanosecond laser ablation technique described elsewhere [17,19]. In this approach the laser-produced plasma with high pressure (~GPa) is confined in liquid media [17,18]. Figure 1 represents schematic sketch of our experimental set-up. The Si-ncs are fabricated by using a single-crystal silicon wafer fixed in glass ware filled with liquid medium. Both types of (n-type, p-type, , resistivity 0.1 cm, thickness 0.525 mm) as a target could be used. To induce laser ablation and the Si-ncs formation a third-harmonic of Nd:YAG laser (Spectra Physics LAB-150-30, 355 nm, 30 Hz, τ = 8 ns) or KrF excimer laser ((KrF, 245 nm, 20 Hz, 10 ns).) are used to irradiate onto the target immersed in liquid media (water, SOG solution) at room temperature. It has to be noted that the SOG polymers solutions are commercially available (Si-59000 Tokyo Ohka Kogyo Co., Ltd.). The laser beam is focused on the target by a lens (f = 250 nm) [17, 18]. Relatively low laser fluences are used to obtain a spherical shape of the plume, to limit excessive bubble formation, and to avoid generation of strong shock waves in liquid [19, 20]. During the ablation process the container with liquid and immersed Si target was rotated. To observe visible PL the aging processes of Si-ncs in water was assured by keping them in aqeuos solution at ambient temperature [17, 18]. The colloidal suspension prepared by laser ablation in SOG was sonicated for 10 min and solidified in air atmosphere at 323 K for 24 h, resulting in the formation of self-supporting samples [21, 22].

Figure 1. Schematic sketch of the experimental set-up used for fabrication of silicon nanocrystals (Sincs) by laser ablation of crystalline silicon target in liquid media. In this work two types of ns lasers have been applied independently (Nd:Yag and excimer KrF laser)

130

V. Švrček

Figure 2. Sketch of the experimental set-up used for preparation of Si-ncs by ns laser fragmentation of silicon micrograins prepared by electrochemical etching

2.2. Laser Fragmentation Figure 2 shows sketch of experimental set-up used for preparation of Si-ncs by ns laser fragmentation method of Si-ncs micrograins prepared by electrochemical etching. The technique involves the etching of a silicon wafer (p-type boron doped, h1 0 0i, 0.1 X cm, thickness 0.525 mm) for 1 h at 1.6 mA/cm2 constant current in HF:ethanol electrolyte (1:4). After the etching process, the resulting porous silicon wafer has been subsequently mechanically pulverized [21]. After mechanical pulverization of several porous silicon wafers the powder with Si-ncs micrograins is collected. The fragmentation of Si-ncs micrograins have been proceed in water, pure and phosphorus doped SOG (Liquid pure and doped SOG are commercially available from Tokyo Ohka Kogyo Co., Ltd.)) [23-25]. Colloidal solutions were placed into a glass ware, and irradiated by ns pulsed lasers (Nd:YAG, or KrF) independantly at room temperature. The laser beam in both cases was focused on the liquid surface. During irradiation, the glass container with colloidal solutions was closed and rotated. Fragmentation by ns pulsed laser requires a homogenous dispersion of the Si-ncs micrograins [25], therefore in the case that the Si-ncs micrograins were observed to disperse poorly in water, a small amount of ethanol (20 drops) was used to wet the micrograins surface prior to the introduction of water. The color of homogenously dispersed aqueous and SOG Si micrograins solution is yellow. When the nanosecond pulsed laser irradiation is applied, fragmentation of the micrograins occurs and at prolonged laser irradiation, the solutions become almost transparent [25]. After fragmentation, the transparent colloidal dispersions were used to prepare two types of samples. Upon preparation in water the Si-ncs have shown to self-assemble in specific structures when let it dry on glass substrate. In the case of SOG after irradiation, the colloidal suspensions was dried for solidification [23] in air at 323 K for 24 h to obtain self-supporting SOG films.


131

Figure 3. Photos of blue luminescent Si-ncs prepared by excimer KrF laser in water and aged in water for 7 months. Image (a) represents Si-ncs prepared from p-type and photo (b) from n-type doped crystalline silicon wafer

3. SI-NCS AND SI-NCS BASED COMPOSITES PRODUCED BY LASER ABLATION IN LIQUID MEDIA Si-based technology keeps and most likely will keep playing a key role for electronics and photovoltaic industry. Due to the compatibility, non toxicity and most importantly purity of the nanoparticles surface highly luminescent Si-ncs with quantum confinement effects prepared by laser ablation in water with Si-dioxide surface termination might play an important role for development novel types of devices [17, 19, 20]. Surface passivation achieved by laser ablation in water leads to stable PL properties [19], that can facilitate the integration within existing Si based technologies. The employment of doped Si-ncs prepared by laser ablation can expand the possibilities of utilization of Si-ncs. Figure 3 represents photographs of room temperature luminescent Si-ncs prepared by excimer KrF laser in water and aged in water for 7 months. Image (a) represents Si-ncs prepared from p-type and photo (b) from n-type doped crystalline silicon wafer. Visible blue-room temperature PL is observed from both colloids under He:Cd laser excitation at 325 nm. At ambient conditions Si-ncs in colloidal solution show a stable blue-bands with maxima centered at ~420 nm. Compared to the Si-ncs made from p-type doped wafer, the PL band for n-type doped is stronger more than 2 times. Since for n-type doped silicon a smaller surface recombination velocity has been reported compared to p-type Si wafers [26], similar effects could be expected for Si-ncs and different surface termination due to the dopant most likely influences the PL intensity. In order to overcome aging process and allow to appear the PL ns laser ablation in SiO2 based polymer solution semms to be an effective way [18]. Our results showed that we can successfully prepare Si-ncs directly in SiO2 based polymers, which decreased the aging time from months to several hours [18]. The Figure 4 (a) shows the chemical formula of the polymer solution. The polymer consists of the mixture of thylpolysillicate (C2H5O(SiO)C2H5O)2n(C2H5), ethanol, and ethylacetate. The contents of these chemicals in SOG are 9%, 71%, and 20%, respectively. Such transparent solution has refractive index of 1.44, which allows ablation process directly in solution without considerable deterioration of polymer quality. The fabrication of Si-ncs directly in polymer solutions opens also flexibility

132

V. Švrček

for variety of sample structures. From Si-ncs/polymer colloidal solutions we can prepare thin films at low-cost (Figure 4 (b), either by spin coating or printing technique, in principle, on any type of the substrate. On the other hand, by simple solidification of the Si-ncs/polymer colloidal solution we can form self-supporting samples (Figure 4.c) with high concentrations of Si-ncs and different architectures. It has to be noted that this SOG polymers can be doped and doping level might help easy to control the PL properties of embedded Si-ncs [27]. It is observed that at low ablation intensities [28] irregular Si-nc fragments obtained by laser ablation in water are stabilized into regular-spherical particles. Figure 5 shows typical SEM images of Si-ncs prepared by laser ablation in water (a) by Nd:Yag and (b) by KrF excimer laser, respectively. In both cases SEM images shows that Si-ncs aggregates just after the preparation. As depicted, spherical aggregates reaching size distributions ranging from 2 to 100 nm, which is rather similar for both lasers. It was clearly observed that the smaller irregular aggregates of Si-ncs were obtained at higher laser fluences [28]. At higher fluences the formation of spheres is inhibited mostly because of enhanced fragmentation processes. Such fragmentation is induced by the increased density and intensity of shock waves that propagate through the liquid at higher laser fluence. Detailed structural analysis revealed that agglomerates contain Si-ncs with irregular shape smaller than the strong quantum confinement limit for silicon ( Chang, C; Gmit-ter, T; Bright, TB. Phys. Rev. Lett, 1986, 57, 249. Švrcek, V; Slaoui, A; Rehspringer, JL; Muller, JC. J. of Lumin, 2003, 101, 269. Švrcek, V; Sasaki, T; Shimizu, Y; Koshizaki, N. Journal of Laser Micro/Nanoengineering, 2007, 2, 15. Fauchet, PM. J. of Lumin., 1996, 70, 294. Švrček, V; Mariotti, D; Kalia, K; Kondo, M. Chem. Phys. Lett, 2009, 478, 224. Kanemitsu, Y; Uto, H; Masumoto, Y; Matsumoto, T; Futagi, T; Mimura, H. Phys. Rev. B, 1993, 48, 2827.


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[32] Deegan, RD; Bakajin, O; Dupont, TF; Huber, G; Nagel, SR; Witten, TA. Nature, 1997, 389, 827. [33] Tlusty, T; Safran, SA. Science, 2000, 290, 1328. [34] Tang, ZY; Kotov, NA; Giersig, M. Science, 2002, 297, 237. [35] Jackson, AM; Myerson, JW; Stellacci, F. Nat. Mater, 2004, 3, 330. [36] Oraevsky, AA; Letoshkov, VS; Esenafiev, RO. Pulsed LaserAblation of Biotissue: Review of Ablation Mechanisms, Springer, Berlin, 1991. [37] Geohegan, DB. Appl. Phys. Lett, 1992, 60, 2732 . [38] Zeldovich, YB; Raizer, YP. Physics of Shock Waves and High- Temperature Hydrodynamic Phenomena, Dover Publications, Inc, New York, 2001.



Chapter 5

HO:YAG LASER LITHOTRIPSY Jinze Qiu1, Thomas E. Milner1 and Joel M. H. Teichman2 1

Dept. of Biomedical Engineering, The Univ. of Texas at Austin, 107 W Dean Keeton, Austin TX, USA 78712 2 Dept. of Urologic Sciences, University of British Columbia, and St. Paul's Hospital, 1081 Burrard St., Burrard Bldg. C307, Vancouver BC, Canada V6Z 1Y6

ABSTRACT The long-pulse Ho:YAG laser has been used for intracorporeal laser lithotripsy of urinary calculi since the mid-1990’s and is considered the “gold standard” modality for endoscopic laser lithotripsy. We present an overview of Ho:YAG laser lithotripsy. We begin with an introduction of the ablative mechanism of Ho:YAG laser lithotripsy, and compare to short-pulse (< 10 usec) laser lithotripsy. Ablative properties of Ho:YAG laser lithotripsy are reviewed and we summarize several practical problems and safety issues of existing optical fibers for Ho:YAG lithotripsy.

INTRODUCTION Clinical application of intracorporeal laser lithotripsy to human urinary calculi began in the mid 1980s[1-3]. The surgical technique of visualizing a calculus in the urinary tract by inserting a ureteroscope and fragmenting the stone by fiber delivered laser energy has undergone significant advances over the past twenty years[4]. The principle advantage of intracorporeal laser lithotripsy over previous surgical techniques is the use of small diameter flexible optical fibers (

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