Behavior of Plutonium and Americium in Soils

Abstract

The depth profiles and the particle size dependencies of the distributions of ^{239, 240}Pu 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, 241}Pu 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, 240}Pu 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, 240}Pu and ¹³⁷Cs increase steadily with the particle size from coarse sand to clay fraction, while that of ²⁴¹Am doesn't show such a tendency. These facts suggest that the behavior of ²⁴¹Am in soil may be different from that of ^{239, 240}Pu and ¹³⁷Cs.