Plutonium Content of Soil at Nagasaki

Abstract

THE explosion of a plutonium atomic bomb over Nagasaki city in Japan took place at 1100 h on August 9, 1945. The bomb was detonated at a height of about 500 m above the place indicated in Fig. 1; the direction of the wind was from the west. In July 1969, samples of surface soils (each 10 cm deep) were taken from the less disturbed surface of the ground, such as graveyards or grassland, so that the amount of plutonium remaining in the soil after 24 yr could be determined. The sampling locations are shown in Fig. 1; three different samples (N1, N2, N3) were taken from Nishiyama area where high radioactivities due to fission products had been detected after the explosion The contour of the radioactivity dose rate in air in the autumn of 1945 is shown in Fig. 2.