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Quality assurance in accelerator mass spectrometry: Results from international round-robin exercises for 10Be and 36Cl
Merchel, S.; Bremser, W.
Driven by the overall progress in the field of accelerator mass spectrometry (AMS) and its spreading application within the geosciences, measurements of increasing numbers of samples with low isotopic ratios of 10Be/9Be and 36Cl/Cl will be required in the future. In order to check the quality of measurements at low 10Be concentrations, we have examined the linearity of 10Be/9Be as a function of isotope ratio. For this purpose we have prepared small quantities of three secondary standards and distributed these to nine AMS laboratories. Ratios can be calculated relative to the diluted NIST SRM 4325 after taking account of the 10Be contribution of the 9Be carrier (10Be/9Be=(1.24±0.23)x10-14) @ ASTER, Gif, VERA). As the initial 10Be/9Be of the primary standard is under discussion, results of the secondary standards (~3x10-12/-13/-14) will be discussed relatively to the primary standard ratio only.
The problem of low ratio samples is even more crucial for 36Cl due to the high volatility of chlorine. Thus, we have prepared large quantities of three 36Cl/Cl solutions from a certified 36Cl activity (NIST SRM 4943) by step-wise dilution with NaCl (MERCK CertiPUR®, Cl traceable to NIST SRM 999a). AgCl precipitated from these solutions has been distributed to nine AMS laboratories. Calculated 36Cl/Cl ratios are 1x10-11/-12/-13.
Results for each nuclide show that these interlaboratory exercises are very valuable, as they show maximum differences between individual AMS labs up to 35% for 10Be, and 25% for 25Cl, respectively. Possible reasons for these discrepancies are standard-like materials in use for calibration and cross-contamination in the ion sputter source. A full statistical data evaluation is in preparation and might help to identify more clearly error sources at individual AMS facilities. Thus, we are taking a step forward on the long way of improving quality assurance systems in the AMS community.
Acknowledgments: This round-robin could not have taken place without the interest and team effort of the participating AMS laboratories, as there are: Laboratory for Ion Beam Physics/ETH Zurich, PRIME Lab/Purdue University, The Australian National University/Canberra, CAMS/Lawrence Livermore National Laboratory, Scottish Universities Environmental Research Centre/East Kilbride, Centro Nacional de Aceleradores/University of Seville, University of Tsukuba/Ibaraki, Vienna Environmental Research Accelerator/Universität Wien. This work was partially funded by CRONUS-EU (Marie-Curie Action, 6th FP #511927).
Keywords: AMS; QM; cosmogenic nuclides; reference materials
19th International Conference on Ion Beam Analysis, 07.-11.09.2009, Cambridge, UK