Abstract
IAEA-375 reference material is only IAEA reference material for 129I. The recommended value was published firstly in 1996 from an intercomparison in 1991. The value listed in the IAEA AQCS reference material catalogue (2004-2005) is 2 (1.3-2.1) mBq·kg-1 at 95% confidence level. Under an IAEA project for upgrading of reference materials, a new determination of 129I concentration in IAEA-375 reference material was performed at China Institute of Atomic Energy (CIAE). Seven AgI samples were prepared from IAEA-375 soil, and the atom ratio of 129I/127I in the samples was measured with IsoTrace Tandetron AMS facility at the University of Toronto, Canada. Five measurements were carried out for each of the samples. The results show the reproducibility in determining the relative 129I/127I ratio of the sample was less than 1% over a four months period. The activity concentration (CA) of 129I in the IAEA-375 reference material was determined to be 1.59 ± 0.08 mBq·kg-1 at 95% confidence level. The present value agrees within 2.5% with the result of a previous analysis of the IAEA-375 soil by IsoTrace laboratory in the last IAEA intercomparison run (1990) [1]. The agreements of AMS measurements were obtained largely independently of the chemical preparation. In the present measurement the AgI sample was prepared at CIAE, but in the last IsoTrace measurement the sample was prepared at IsoTrace laboratory. The chemical procedures were quite different in the both laboratories. The 129I concentration of IAEA-375 reference material measured by AMS, including the result obtained from an interlaboratory comparison run organized by Lawrence Livemore National Laboratory [2], are all systematically lower than the IAEA evaluated value, which mainly depended on the data measured by radiochemical neutron activation analysis (RNAA). The conclusion has been drawn that IAEA evaluated value of 129I concentration in the IAEA-375 soil has a large uncertainty as a reference material recently. Our result might be useful in upgrading of the recommended value, and the 129I-AMS method should be more reliable than RNAA.
References
[1] V. Strachnov, J. Larosa, R. Dekner, R. Zeisler, A Fajgelj, Determination of Radionuclides in Soil Sample IAEA-375, IAEA, Vienna, 1996. [2] M. L. Roberts, M.W. Caffee, I.D. Proctor, Nucl. Instr. Meth. B172(2000)388.
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See more of The 10th International Conference on Accelerator Mass Spectrometry (September 5-10, 2005)