Behavior of Plutonium and Americium in Soils

金沢大学環日本海域環境研究センターThe depth profiles and the particle size dependencies of the distributions of 239, 240Pu and 241Am in soil have been studied in comparison with those of 137Cs to obtain information on clarifying their behaviors and fates under the natural conditions. It was found that the concentrations of 239, 241Pu and 137Cs in soil decrease exponentially with increasing the depth, and over 80% of these fall-out radionuclides is accumulated in the upper 10 cm of the soils. The concentration of 241Am was measured by non-destructive γ-spectrometry using Ge-LEPS up to the depth of 6.5cm for two soil cores. The activity ratios of 241Am/239, 240Pu were found to be in the range from 0.25 to 0.30 for one core sample, while rather high values, i. e., 0.63-0.75, were obtained for another one. The particle size discrimination of surface soil showed that the concentrations of 239, 240Pu and 137Cs increase steadily with the particle size from coarse sand to clay fraction, while that of 241Am doesn\u27t show such a tendency. These facts suggest that the behavior of 241Am in soil may be different from that of 239, 240Pu and 137Cs