Glow discharge spectrometry for the characterization of nuclear and radioactively contaminated environmental samples

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<ul><li><p>Keywords: Glow discharge spectrometry; Contaminants; Radionuclides</p><p>Spectrochimica Acta Part B 59 (2004) 13591376</p><p>www.elsevier.com/locate/sabContents</p><p>1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1360</p><p>2. General processes and instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1361</p><p>3. Instrumentation requirements for radioactive samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1362</p><p>4. Quantification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1364</p><p>5. Trace and bulk analysis in nuclear samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1364</p><p>5.1. Conducting nuclear samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1364</p><p>5.1.1. Metallic alloy nuclear fuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1364</p><p>5.1.2. Zircaloy cladding materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1365</p><p>5.2. Non-conducting nuclear samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1365Review</p><p>Glow discharge spectrometry for the characterization of nuclear and</p><p>radioactively contaminated environmental samples</p><p>Maria Betti*, Laura Aldave de las Heras</p><p>European Commission, Joint Research Centre, Institute for Transuranium Elements, P.O. Box 2340, 76125 Karlsruhe, Germany</p><p>Received 28 May 2004; accepted 14 July 2004</p><p>Abstract</p><p>Glow discharge (GD) spectrometry as applied to characterize nuclear samples as well as for the determination of radionuclides in</p><p>environmental samples is reviewed.</p><p>The use of instrumentation for direct current (d.c.) glow discharge mass spectrometry (GDMS) and radio frequency glow discharge optical</p><p>emission spectrometry (rf GDOES), installed inside a glove-box for the handling of radioactive samples as well as the two installations and</p><p>their analytical possibilities, is described in detail.</p><p>The applications of GD techniques for the characterization of samples of nuclear concern both with respect to their major and trace</p><p>elements, as well as to the matrix isotopic composition are presented.</p><p>Procedures for quantitative determination of major, minor, and trace elements in conductive samples are reported. As for non-conductive</p><p>samples three different approaches for their measurement can be followed. Namely, the use of rf sources, the mixing of the sample with a</p><p>binder conducting host matrix, and the use of a secondary cathode. In the case of oxide-based samples, the employment of a tantalum</p><p>secondary cathode, acting as an oxygen getter, reduces the availability of oxygen to form polyatomic species and to produce quenching.</p><p>Considerations on the use of the relative sensitivity factors (RSFs) in different matrices are reported.</p><p>The analytical capabilities of GDMS are compared with ICP-MS in terms of accuracy, precision, and detection limit for the determination</p><p>of trace elements in uranium oxide specimens. As for the determination of isotopic composition, GDMS was found to be competitive with</p><p>thermal ionisation mass spectrometry (TIMS) as well as for bulk determinations of major elements with titration methods. Applications of</p><p>GDMS to the determination of radioisotopes in environmental samples, as well for depth profiling of trace elements in oxide layers, are</p><p>discussed.</p><p>D 2004 Elsevier B.V. All rights reserved.0584-8547/$ - s</p><p>doi:10.1016/j.sa</p><p>* Correspon</p><p>E-mail addree front matter D 2004 Elsevier B.V. All rights reserved.</p><p>b.2004.07.006</p><p>ding author. Tel.: +49 7247 951 363; fax: +49 7247 951 186.</p><p>ess: betti@itu.fzk.de (M. Betti).</p></li><li><p>. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1366</p><p>. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1367</p><p>f nuclear interest . . . . . . . . . . . . . . . . . . . . . . . 1368</p><p>ronmental samples . . . . . . . . . . . . . . . . . . . . . . . 1371</p><p>fuel cladding material . . . . . . . . . . . . . . . . . . . . . 1373</p><p>. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1374</p><p>. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1374</p><p>traces, impurities and depth profiling of solids [13]. Glow composition, is of great importance. These materials can</p><p>rochimica Acta Part B 59 (2004) 13591376Discharge Optical Emission Spectrometry (GDOES) is</p><p>recognised to be a rapid method for depth profiling, capable</p><p>of surface analysis [47], interface and bulk qualitative and</p><p>quantitative analysis of solids [8]. Glow Discharge Mass</p><p>Spectrometry (GDMS) is one of the most powerful solid</p><p>state analytical methods for the direct determination of</p><p>impurities and depth profiling of solids [911]. Glow</p><p>discharge mass spectrometers, which are commercially</p><p>be analysed using several techniques based on nuclear and</p><p>Table 1</p><p>Type of radioactive samples</p><p>Oxide-based nuclear fuels</p><p>Metallic alloy nuclear fuels</p><p>Vitrified wastes</p><p>Zircaloy nuclear cladding materials</p><p>Forensic6. Simfuels . . . . . . . . . . . . . . . . . . . . . . . . . . . .</p><p>7. Nuclear waste glasses . . . . . . . . . . . . . . . . . . . . .</p><p>7.1. Determination of the isotopic composition in samples o</p><p>8. Determination of traces of radioisotopes in contaminated envi</p><p>9. Depth profiling of ZrO2 layers deposited on Zircaloy nuclear</p><p>10. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . .</p><p>References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .</p><p>1. Introduction</p><p>Radionuclides, particularly the long-lived ones along</p><p>with trace elements, represent nowadays, an important</p><p>category of inorganic pollutant that need to be determined</p><p>not only in nuclear samples, like for instance nuclear fuels</p><p>but also in environmental samples, as soils and sediments as</p><p>well as waste materials.</p><p>Radionuclides containing samples can originate through</p><p>different systems and processes. Human activities involving</p><p>nuclear weapons and nuclear fuel cycle (including mining,</p><p>milling, fuel enrichment, fabrication, reactor operation,</p><p>spent fuel stores, reprocessing facilities, medical applica-</p><p>tions and waste storage) are important, and may lead to a</p><p>significant creation of this kind of samples. Human</p><p>technology also releases pre-existing natural radionuclides,</p><p>which would otherwise remain trapped in the earths crust.</p><p>For instance, burning of fossil fuel (oil and coal) dominates</p><p>direct atmospheric release at pre-existing natural radio-</p><p>activity.</p><p>The ability to develop adequate models for predicting the</p><p>fate of inorganic contaminants, including radionuclides, in</p><p>both surface and subsurface environments, is highly</p><p>dependent on the accurate knowledge of the partitioning</p><p>of these constituents between the solid and solutions phases</p><p>and ultimately on the capability to provide molecular-level</p><p>information on chemical species distributions in both of</p><p>theses phases. Furthermore, the development of environ-</p><p>mentally sound yet cost effective remediation strategies</p><p>requires an understanding of the chemical speciation of the</p><p>contaminants within the sediment, soil and waste material</p><p>matrices in which they are contained.</p><p>Glow discharge (GD) sources that have been widely</p><p>exploited in analytical chemistry for the direct analysis of</p><p>solid samples are, among the solid state analytical methods,</p><p>the most powerful tools for the direct determination of</p><p>M. Betti, L. Aldave de las Heras / Spect1360available with fast and sensitive electrical ion detection,</p><p>allow direct trace elemental determination in solid materialswith good sensitivity and precision in the concentration</p><p>range lower than ng g1 [12,13].Primarily employed for the determination of transition</p><p>elements in steels and metals, GD-based methods have also</p><p>been recently exploited for the characterization of nuclear</p><p>radioactive solid samples [14]. The direct analysis of solid</p><p>samples is very important in the nuclear field since operator</p><p>exposure time to radiation and the quantity of liquid nuclear</p><p>wastes can be strongly reduced. Moreover, a non-destructive</p><p>analysis allows the sample to be reused for further</p><p>investigation, to be reprocessed, or to be kept as an archival</p><p>sample. Nowadays, GDMS can be considered as one of the</p><p>most powerful solid-state analytical methods for the</p><p>determination of traces and depth profiling of solid samples</p><p>of nuclear concern as well as for the monitoring of long-</p><p>lived radioisotopes in radioactively contaminated environ-</p><p>mental samples [9,1417]. Its ability to measure isotope</p><p>ratios in solids has been also evaluated [18,19], and the</p><p>technique has proven to be a good choice for isotopic</p><p>analysis in nuclear and radioactive environmental samples</p><p>[9,2026]. In Tables 1 and 2, the different types of</p><p>radioactive samples and the measurements carried out on</p><p>them via GDMS are summarised, respectively.</p><p>As compared to wet chemistry-based methods, glow</p><p>discharge-based methods using optical emission spectrom-</p><p>etry and mass spectrometry have the advantage of simpler</p><p>sample preparation procedures, as results of carrying out</p><p>measurements directly on solid samples. Therefore, for</p><p>nuclear samples, they meet both requirements of reducing</p><p>time exposure of the operator, as well as the amount of</p><p>liquid wastes.</p><p>In the field of nuclear research and technology, the</p><p>chemical characterization of different types of nuclear</p><p>fuels, cladding materials, nuclear-waste glasses and</p><p>smuggled nuclear samples, from the point of view of</p><p>trace, major and minor elements as well as their isotopicEnvironmental</p></li><li><p>non-nuclear methods that can be, to a varying degree,</p><p>tedious and time-consuming. In the last year, non-nuclear</p><p>methods based on MS have become predominant for the</p><p>characterization of samples of nuclear concern. The</p><p>application of ICP-MS has been widely investigated [27</p><p>30] for fission products and actinide determination as well</p><p>as Thermal Ionisation Mass Spectrometry (TIMS) for the</p><p>routine analysis of isotopes in liquid samples [31]. GDMS,</p><p>when used for the chemical characterization of nuclear</p><p>samples, provides information on the chemical composi-</p><p>tion much faster than other techniques, making it possible</p><p>to modify fuel production procedures and reactor con-</p><p>ditions or to quickly recognise smuggled materials. The</p><p>2. General processes and instrumentation</p><p>Glow discharge is a low-energy plasma (Fig. 1) sustained</p><p>between two electrodes that are immersed within a reduced</p><p>pressure, inert gas environment. The sample usually serves</p><p>as the more negatively charged electrode [i.e., the cathode in</p><p>a direct (d.c.) glow discharge system]. Common discharge</p><p>support gas pressures are in the range 0.11 Torr. For</p><p>analytical applications, argon is most commonly used</p><p>discharge support gas even though other gases are some-</p><p>times used. The plasma is created by inserting two electro-</p><p>des in a cell filled with the discharge gas at a low pressure</p><p>and is initiated when a high potential typically of the order</p><p>of 1 kV is established between the two electrodes. The</p><p>application of the high potential causes the bdischarge gasbreakdown electricallyQ, namely, the gas is being split upinto positive ions and electrons resulting in the formation of</p><p>plasma. The positive ions are attracted toward the sample</p><p>surface by electric fields within the plasma, and may reach</p><p>substantial kinetic energy. In a plasma of argon, the Ar+ ions</p><p>Table 2</p><p>Type of measurements performed on radioactive samples</p><p>Trace elements</p><p>Major and minor elements</p><p>Isotopic ratios</p><p>Depth profiling</p><p>M. Betti, L. Aldave de las Heras / Spectrochimica Acta Part B 59 (2004) 13591376 1361advantages of GDMS are low limits of detection, uniform</p><p>element sensibility and capability to measure all elements</p><p>and even isotopes. Clearly, for the handling of nuclear</p><p>materials, instruments need to be properly modified for</p><p>installation in glove-boxes for a- and h-radiation protec-tion [32,33].</p><p>In this work, the exploitation of GD sources for the</p><p>characterization of samples of nuclear concern as well as</p><p>radioactively contaminated environmental samples as for</p><p>trace elements and long-lived radioisotopes is reviewed.</p><p>Instrumentation requirements for radioactive samples as</p><p>well as the type of samples and analyses performed are</p><p>considered. Quantification issues and comparisons with</p><p>other solid state techniques are discussed.Fig. 1. Schematic picture of the main procformed in the glow discharge are accelerated toward the</p><p>sample cathode and the sample material is sputtered at the</p><p>cathode surface by ion bombardment. Sputtered atoms and</p><p>molecules are ionised in the glow discharge plasma</p><p>(negative glow) by Penning and/or electron impact ionisa-</p><p>tion and charge exchanges processes. Mathematical models</p><p>of processes in a direct current glow discharge have been</p><p>developed by Bogaerts et al. [3436]. GDOES is based</p><p>upon the measurement of photons emitted by excited state</p><p>species in the plasma. In GDMS, the positively charged ions</p><p>formed in the argon plasma of the glow discharge source are</p><p>extracted and accelerated into the mass spectrometer, where</p><p>the ion beams are separated according to their mass-to-</p><p>charge and energy-to-charge ratio. The separated ions areesses occurring in a glow discharge.</p></li><li><p>tions with such instrumentation have been recently</p><p>reviewed [62].</p><p>rochimthen, electrically detected by ion/electron/photon conversion</p><p>by ion counting and a Faraday cup for analog ion beam</p><p>measurement.</p><p>The glow discharge ion source has been interfaced to</p><p>most of the standard mass spectrometer types. The first</p><p>commercially available GDMS instrument used a double</p><p>focusing magnetic sector mass analysis system, permitting</p><p>the acquisition of high-resolution spectra with high</p><p>sensitivity [37]. Quadrupole mass spectrometers are</p><p>typically more compact and less expensive than magnetic</p><p>sectors. As a consequence, quadrupoles have been</p><p>employed for fundamental and development research of</p><p>GDMS [38], finally resulting in the commercial avail-</p><p>ability of a quadrupole GDMS system [39]. At present,</p><p>quadrupole glow discharge mass spectrometers are mostly</p><p>in-house built instruments. Promising results have also</p><p>been obtained from the coupling of glow discharge ion</p><p>trap mass spectrometric systems [40], double and triple</p><p>quadrupole instruments [41], time-of-flight mass spec-</p><p>trometers [42,43], Fourier transform mass spectrometers</p><p>[44,45] and a MattauchHerzog double focusing sector</p><p>spectrometer [46]. However, the commercially available</p><p>GD mass spectrometers presently only employ inverse</p><p>NierJohnson double-focusing and quadrupole-based mass</p><p>spectrometers.</p><p>One of the main challenges for glow discharge</p><p>spectroscopy to overcome is the intrinsic requirement of</p><p>the sample to be electrically conducting. Nevertheless,</p><p>non-conducting solid samples can be directly analysed by</p><p>using a radio-frequency powered source [47], and their</p><p>applications have been recently reviewed [14], with direct</p><p>current device plasma using the secondary cathode</p><p>t...</p></li></ul>

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