Residual Neutron-Induced Radionuclides in Samples Exposed to the Nuclear Explosion over Hiroshima: Comparison of the Measured Values with the Calculated Values

A Review of Forty-Five Years Study of Hiroshima and Nagasaki Atomic Bomb Survivors I. DOSIMETRY

Abstract

Residual radionuclides induced by neutrons from the Hiroshima atomic bomb have been measured at Kanazawa University for these 14 years. The results of ¹⁵²Eu, ¹⁵⁴Eu and ⁶⁰Co are reviewed in this paper. Where appropriate, an attempt is made to provide our new data with the aim of reinterpreting our published data. From the comparison of the measured values with the calculated values by DS86 methodology, we may point out here: (1) that close agreement was found between measured and calculated values for the specific radioactivity of ¹⁵²Eu in the samples exposed at ground ranges between 320 m and 720 m; (2) that the calculated/measured ratios for the specific radioactivity of ¹⁵²Eu were, however, larger than unity in the vicinity of ground zero and smaller than unity at locations more than 1000 m apart from ground zero; (3) that, in the vicinity of ground zero, epithermal neutron fluence evaluated from a set of measured specific radioactivities of ¹⁵²Eu, ¹⁵⁴Eu and ⁶⁰Co showed a close agreement with the calculated result, whereas thermal neutron fluence evaluated in the same way was different from the calculated result; and (4) that the depth distribution of the specific radioactivity of ¹⁵²Eu in a wall sample which was exposed at the location 320m from ground zero approximately agreed with the calculated result.