Uranium isotopes were studied to clarify the fallout from the Hiroshima atomic bomb. The ²³⁴U/²³⁸U activity ratios of uranium leached from the soil in the Hiroshima fallout area were significantly higher than those of other areas according to alpha ray spectrometry. The correlation of specific activity of the fission product ¹³⁷Cs and the ²³⁴U/²³⁸U activity ratios was studied. Two different correlations were established inside and outside the fallout area. The results of this study suggest that manifestations of fallout from the Hiroshima atomic bomb are still detectable in the “black rain” area.

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