Residual plutonium migration in soil of Nagasaki

Abstract

The residual 239+240 Pu concentration in the Nagasaki soil was observed 36 years after the plutonium atomic bombing of Nagasaki in 1945. The highest level of 239+240 Pu contamination was discovered in the soil at the edge of the Nishiyama reservoir, a level about 10–30 times higher than in other areas of Nagasaki. In the Nishiyama district, 97% of the total plutonium in the soil was retained to a depth of 0.3 m, but the remaining 3% was dispersed over a 0.3‐ to 2.25‐m depth at approximately 0.037 Bq/kg of dry soil. The mean 239+240 Pu migration rate in the Nishiyama soil for 36 years was estimated at 1.25 mm yr −1 , compared to the infiltration rate of rainwater of 2500 mm yr −1 .