DETERMINATION OF I-129 AND I-127 IN ENVIRONMENTAL-SAMPLES BY NEUTRON-ACTIVATION ANALYSIS (NAA) AND INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY (ICP-MS)

In order to assess the levels and behavior of I-129 (half-life: 1.6 x 10(7) y) and I-127 (stable) in the environment, we have developed analytical procedures involving neutron activation analysis (NAA). Environmental samples collected around Tokaimura, Ibaraki Prefecture, Japan, have been analyzed using this method. Ranges of I-129 and I-127 concentrations in surface soil were 0.9-180 mBq kg(-1) and 1-60 mg kg(-1), respectively. Higher I-129 concentrations were found in soil sampler collected from coniferous forests, suggesting a contribution from tree canopies in the deposition of this nuclide. Most of the I-129 in soil was found to be retained in the first 10 cm. The I-129/I-127 ratios in wheat fields were lower than those in rice paddy fields. A soil sample collected by IAEA from an area contaminated by the Chernobyl accident was also determined. The I-129 concentration and the I-129/I-127 ratio were 1.6 mBq kg(-1) and 1.7 x 10(-7), respectively. The I-129 level in this sample was higher than the values obtained in areas far from nuclear facilities in Japan. It was suggested that the analysis of I-129 in soils in the Chernobyl area may be useful in evaluating the I-131 levels at the time of the accident. Analyses of I-129 and I-127 by ICP-MS in water samples were also made. The analytical speed of this method was very high, i.e., 3 minutes for a sample. However, there is a sensitivity limitation for I-129 detection due to interference from Xe-129 with the I-129 peak. The detection limits for I-129 and I-127 in water samples were about 0.5 mBq ml(-1) and 0.1 ng ml(-1), respectively.