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AMS analysis of I in Japanese soil samples collected from background areas far from nuclear facilities |
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| Authors: | Yasuyuki Muramatsu Yukari Takada Hiroyuki Matsuzaki Satoshi Yoshida |
| Institution: | aDepartment of Chemistry, Gakushuin University, Mejiro 1-5-1, Toshima-ku, Tokyo 171-8588, Japan bDepartment of Nuclear Engineering and Management, The University of Tokyo, Yayoi 2-11-16, Bunkyo-ku, Tokyo 113-0032, Japan cEnvironmental Radiation Effects Research Group, National Institute of Radiological Sciences (NIRS), Anagawa 4-9-1, Inage-ku, Chiba-shi 263-8555, Japan |
| Abstract: | Analytical procedures in the determination of iodine-129 (half-life: 1.6×107 y) have been studied using accelerator mass spectrometry (AMS), with special references to the separation procedures of iodine from soil samples for the AMS measurement. Iodine was successfully volatilized from soil samples by pyrohydrolysis at 1000 °C and collected in a trap solution. Iodine was purified from the matrix by solvent extraction. Finally, it was precipitated as silver iodide to make a target for AMS. In order to obtain information on the 129I/127I ratio in a chemical blank (or iodine carrier), we have determined the ratios in several iodine reagents and found that the ratios fell in a narrow range around 1.7×10?13. The detection limit for soil sample (1 g material) by the present method was about 0.01 mBq/kg or 4×10?11 as the ratio of stable iodine (129I/127I ratio), i.e. these values were much better than that by neutron activation analysis (NAA) used in our previous studies. We have applied this method in the analysis of soil samples collected from different places in Japan. We could successfully determine 129I in soil samples with low 129I concentrations, which could not be detected by NAA. Sample size necessary for the soil analysis by AMS was only about 0.5 g or less, whereas about 100 g of the sample were required for NAA Muramatsu, Y., Ohmomo, Y., 1986. Iodine-129 and iodine-127 in environmental samples collected from Tokaimura/ Ibaraki, Japan. Sci. Total Environ. 48, 33-43]. Using this method, new data were obtained for the 129I levels in 20 soil samples collected from background areas far from nuclear facilities, and the ranges were 1.4×10?5?4.5×10?3 Bq/kg as 129I concentrations and 3.9×10?11?2.2×10?8 as 129I/127I ratios. These values are useful in understanding the 129I levels in Japanese environments. Higher 129I concentrations were observed in forest soils than those in field and rice paddy soils should be related to the interception effect of atmospheric 129I due to tree canopies. Relatively high 129I/127I ratios found in rice paddy soils could be explained by their low stable iodine concentrations which were caused by the desorption of stable iodine from the rice paddies during the cultivation. |
| Keywords: | I-129 Iodine Soil Japan |
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