Pu Isotopes, ²⁴¹Am and ¹³⁷Cs in Soils from the Atomic Bombed Areas in Nagasaki and Hiroshima

Abstract

Plutonium Isotopes, ²⁴¹Am and ¹³⁷Cs in soil samples collected from Nagasaki and Hiroshima were measured to evaluate the contribution of residual radioactivity derived from the atomic bombs dropped in 1945.
In the soils from Nishiyama area of Nagasaki City, activity ratios different from those of global fallout were found for the ²³⁸Pu/^{239, 240}Pu (0.05-0.06), ^{239, 240}Pu/¹³⁷Cs (0.2-0.3), ²⁴¹Am/^{239, 240}Pu (0.04-0.05) and ²⁴⁰Pu/²³⁹Pu (0.08-0.13), activity ratios indicating that a fair amount of plutonium derived from the atomic bomb had accumulated in this area. On the other hand, in the soils from the “Black-rain” area of Hiroshima, no significant difference from the global fallout was found for the activity ratios among the Pu isotopes, ²⁴¹Am and ¹³⁷Cs except for the soils collected at 10 km and 12 km in the NNW direction from the epicenter, where a factor 2 to 3 lower ²⁴¹Am/^{239, 240}Pu activity ratio was observed. However, no evidence of the contribution of the atomic bomb was found by the measurement of ²⁴⁰Pu/²³⁹Pu isotopic ratio.