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RESEARCH PRODUCT

RADIOISOTOPE MASS SPECTROMETRY

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Mass spectrometric methods are very sensitive and enable in many cases a multielement determination of trace and ultratrace elements combined with a good isotopic analysis ( Bacon et al. , 2001 ). Therefore, these techniques are also applied for the detection of long-lived radionuclides ( Becker and Dietze, 2000 ) mainly in environmental samples ( Adriaens et al. , 1992 ; Bailey et al. , 1993 ; Bibler et al. , 1998 ; Eroglu et al. , 1998 ; Edmonds et al. , 1998 ; Becker and Dietze, 1999 ; Wendt et al. , 1999 ), nuclear materials ( Betti, 1997 ; Chartier et al. , 1999 ), glass and ceramics ( Rohr et al. , 1994 ; Fukuda and Sayama, 1997 ), and in high-purity substances ( Beer and Heumann, 1992 ; Herzner and Heumann, 1992 ). Radiometry, used as standard method for the determination of radionuclides, has some disadvantages for ultratrace analysis of long-lived nuclides because the detection limit depends on the half-life and the decay type of the isotope to be measured. Besides that, for beta measurements, as applied for trace analysis of pure β-emitters like 90,89 Sr or 99g Tc, careful and time consuming chemical separations are needed to remove other β-emitters while for α-spectroscopy with surface barrier detectors, carrier-free or almost carrier-free samples are a prerequisite for a good energy resolution, and even then, an unambiguous isotopic analysis is very difficult as, e.g., for 239 Pu/ 240 Pu due to the very similar α-energies. Here, mass spectrometric techniques, which apply direct atom counting and different experimental set-ups and ionization methods to achieve a good sensitivity and isotopic as well as isobaric selectivity, are superior. The sensitive and fast determination of long-lived radioisotopes is of great interest in many areas such as risk assessment, low-level surveillance of the environment, studies of biological effects, radioactive waste control, management of radioactive waste for disposal, or investigations of the migration behaviour of actinides etc. The most important radioisotope mass spectrometric techniques are thermal ionization mass spectrometry TIMS ( Callis and Abernathey, 1991 ; Platzner, 1997 ), glow discharge mass spectrometry GDMS ( Betti, 1996 ), secondary ion mass spectrometry SIMS ( Adriaens et al. , 1992 ; Betti et al. , 1999 ), inductively coupled plasma mass spectrometry ICP-MS or laser ablation inductively coupled plasma mass spectrometry LA-ICP-MS ( Kim et al. , 1991 ; Crain, 1996 ; Becker and Dietze, 1998 ; Becker and Dietze, 1999 ; Becker et al. , 2002 ), resonance ionization mass spectrometry RIMS ( Wendt et al. , 2000 ), and accelerator mass spectrometry AMS ( Rucklidge, 1995 ; Fifield et al. , 1996 ). RIMS and AMS are used for sensitive monoelemental ultratrace analysis and precise determination of isotopic ratios whereas the other mass spectrometric methods represent very sensitive multielemental techniques permitting the determination of the concentrations and isotopic abundances of trace and ultratrace elements. Their limits of detection (LOD) are in the concentrations range of ng/g to sub-ng/g for solids and down to sub-pg/L for aqueous solutions. A precision as low as 0.02% relative standard deviation (RSD) for isotope ratio measurements can be obtained ( Becker, 2002 ). With AMS, the precision is almost comparable whereas with RIMS, it is in the low percentage range. The detection limits for RIMS and AMS are 10 6− 10 7 (fg) and 10 4 atoms (atg) per sample, respectively.