241Am and Plutonium in Japanese Rice-field Surface Soils

概要

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Concentrations of ^<239,240>Pu, ^<241>Am and ^<137>Cs 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 ^<241>Am/^<239,240>Pu activity ratio with time could be followed well for the soil samples collected during the 24-year period, 1957-1980. Various plutonium isotopes have been introduced into the environment through the nuclear weapons tests performed in the atmosphere during the past three decades. Furthermore, the activity of ^<241>Am (T_<1/2> = 433 years) has been steadily growing in the environment through beta-decay of the short-lived ^<241>Pu (T_<1/2> = 14.4 years) produced simultaneously with other plutonium isotopes at the date of nuclear explosion.
日本放射線影響学会の論文