Japanese Journal of Health Physics

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Explosive yields of Hiroshima and Nagasaki bombs are important factors for the reassessment of radiation doses due to atomic bombings. Although the yield of Nagasaki bomb has been established as 22±2kt, that of Hiroshima bomb still remains uncertain. We estimated the yield of Hiroshima bomb by using comparative method which needs only relative figures of relevant parameters that can be obtained by comparing effects produced by a bomb of unknown yield with those produced by a bomb of known yield. In this study, the yield of Hiroshima bomb relative to that of Nagasaki bomb was estimated based on 9 comparative data of distances for equal thermal radiation effects in both cities. Results ranged from 10.8 to 18.6kt with no correction for incidence angle of thermal ray. After making correction for angle of incidence, the yield became 11.8-17.9kt. It was suggested that the longer the distance at which a data for calculation was observed, the smaller the estimated yield of Hiroshima bomb due to some unidentified reasons.

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In liquid scintillation measurement, counting rate is affected not only by the quenching but also by other causes such as nonhomogeneity of specimen and chemiluminescence. In this work, a method is presented to detect the affected samples automatically by using the double ratio technique of which standard curve is approximated with a polynomial of the external standard ratio. The deviation was calculated as the minimum distance from the standard curve to a plot of measured sample, which shows a discrepancy of a sample in the pulse height spectrum of beta-decay nuclides. When the discriminating level was set at 0.02 in the deviation, adsorption of specimen or chemiluminescence could be detected practically. Reliability of the presented method and setting of discriminating level were discussed.

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