Abstract
Dosimetry system; so-called DS86 and DS02 are used for dose estimation of the Hiroshima and Nagasaki Atomic bomb survivors. For the early entrance survivors, radiation doses came from activated materials induced by the atomic bomb neutrons. For estimation of such doses, element composition in soil is necessary. Especially Sc density is important for estimating radiation doses during the period after several ten days from the explosion. Scandium-46 which has the half-life of 84 days-, is induced by neutrons from stable 46Sc(abundance 100%). However, few data of Sc density in soil are available both of Hiroshima and Nagasaki (Hashizume 1967, DS86) cities. Purpose of this study is evaluation of Sc density in soil and its variation using neutron activation analysis.
Soil samples were taken from 11 locations within 4 km from the hypocenter of Hiroshima city. The soil samples were dried up in a condition of 120o for over night and grained in a mortar. The grained samples were activated by neutrons in Kyoto University Reactor (KUR). The activated soil samples are measured by Ge-detectors.
From gamma-ray spectrum, 23 element compositions including Al, Mn, Na and Sc are obtained. The obtained element compositions are roughly the same as the DS86-reported values. Sc density in Hiroshima soil was estimated to be 5.12(59) (ppm). It was found SD value of Sc density in soils for 11 location of Hiroshima city is about 12%.
Using element compositions obtained from the activation analysis, time variation of radiation exposure rate by activated soil were estimated. It was found that exposure rate in the few minutes was time dominated by 28Al, in the several days by 24Na, and then by 46Sc. This estimated result was compared with measured dose rate values after three months after the explosion by Pace and Smith (1959). The estimated dose rate was quite similar to the measured one.
