Particulates of Ag and Pu radioisotopes released from Fukushima Daiichi Nuclear Power Plants

Massive radionuclides were released into environment due to the Fukushima Daiichi Nuclear Power Plant accident (DNPP). The volatile fission products, such as ¹³⁷Cs, ¹³⁴Cs, ¹³²I, ¹³¹I were found to be distributed in Fukushima and its adjacent prefectures. On the other hand, it is predicted that the non-volatile radionuclides, such as Pu isotopes and ^110mAg nuclide were distributed unlike with volatile radionuclides. Related to the size of particulates with the nuclides, their radioactivity concentrations vary over a wide range even if soil samples are collected in a same place. So, in this work, we tried to research for the particulate behavior of these radionuclides. Soil samples were collected in the area located at 4 km and 20 km north-west of Fukushima DNPP. Ten portions of 1.0 g were taken from each sample, and activities of ¹³⁷Cs, ¹³⁴Cs, and ^110mAg were determined by a Ge detector for each portion. For the sample at 4 km area, the coefficients of variation of ¹³⁷Cs, ¹³⁴Cs and ^110mAg were 14%, 13%, and 35%, respectively. We also found that the ^110mAg atoms were eluted from the soil samples with 0.5 M HCl and roughly separated from Cs atoms. These results suggest that the radioactivities of observed nuclides are correlated with the element property and relevant particulates. (author)