241Am and plutonium in Japanese rice-field surface soils

Concentrations of sup(239,240)Pu, 241Am and 137Cs were determined for 30 rice-field surface soil samples in Japan collected from 15 locations mostly in 1963 and 1976, and for 15 soil samples periodically collected from 2 locations during 1957-1980. From the results, the amounts of these radionuclides in rice-field soils and their distribution patterns were made clear, showing that the integrated deposits of these radionuclides on the Japan Sea coast of Honshu is 2.5 to 3 times higher than those on the Pacific coast. Furthermore, the variation of 241Am/sup(239,240)Pu activity ratio with time could be followed well for the soil samples collected during the 24-year period, 1957-1980. (author)