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't show such a tendency. These facts suggest that the behavior of
241Am in soil may be different from that of
239, 240Pu and
137Cs.
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