Exclusion of natural radioisotopes for measurements of ¹⁵²Eu in granites exposed to the Hiroshima atomic bomb

Abstract

  Precise ¹⁵²Eu gamma-ray measurements in the granite samples exposed to the Hiroshima atomic bomb require concentrating the europium (Eu) and excluding natural radioisotopes. In this study, an ion exchange method was applied for isolating Eu ions from granite samples at 56 m, 502 m and 818 m distances from the hypocenter. Although the Eu samples included ²³²Th atoms, the ¹⁵²Eu 344 keV gamma-ray full energy peaks were scarcely affected by the gamma rays from the radioisotopes of the thorium series. Almost all of the radioisotopes in the uranium and actinium series were removed. The Eu contents were determined by atomic absorption spectrometry. The ¹⁵²Eu specific radioactivities in the samples at 56 m and 502 m were higher than those inferred from the DS02 calculations. In the sample at 818 m, the measured value was in agreement with the calculated value based on the DS02. Estimations of the atomic bomb radiation doses are necessary for many investigations which attempt to decide the acceptable levels of radiation risk to the public and workers. The results in the present study will be useful for studying the uncertainties of the estimated atomic bomb radiation doses.