Fate of Plutonium Released from the Nagasaki A-Bomb, Japan

About 15 kg of plutonium was used in the Nagasaki A-bomb, but only 1 kg was fissioned and the rest (14 kg) was released into the environment. The fate of this plutonium was investigated at the east side of Nagasaki city where the local fallout was deposited. The four objectives investigated concerning the unfissioned ^239+240Pu were: (1) the geographical distribution up to 100 km from the hypocentre, (2) the vertical movement of the deposited plutonium within a soil core and a reservoir sediment core, (3) the ecological distribution, and (4) an estimation of the total mass deposited as local fallout. The highest concentration of ^239+240Pu 64.5 mBq/g, was found at a point 2.8 km from the hypocentre. The local fallout was observed over a limited area up to 18 km east from the hypocentre. Plutonium was mobile within the soils and reservoir sediments. For the former an amount of 10% moved downward during the last four decades and the rest (90%) remained within 10 cm from the surface. A considerable amount of plutonium was found in fish (0.0195 mBq/g dry), freshwater shellfish (0.0278 mBq/g dry), ginger root (0.0366 mBq/g dry), and sweet potato (0.0110 mBq/g dry). An estimation of plutonium deposited as local fallout from the A-bomb was 37.54 grams.