Measurements of 152Eu/Eu ratios in surfaces of rock samples near the hypocenter of the Hiroshima atomic bomb

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The 152Eu/Eu ratios were measured at various surface positions of two granite samples (gravestones) in the vicinities of the hypocenter of the Hiroshima atomic bomb. The sample pieces were dissolved and the europium elements were chemically isolated. The radioisotopes of Actinium series in the rock samples were excluded from the europium samples. The measured 152Eu/Eu ratio was not constant in each surface, and was low at the surface positions close to neighbor gravestone. The 152Eu/Eu ratios were high at the positions that were largely open for the scattered neutrons from the soil ground. This suggests that the rock materials between sample and soil ground reduced thermal neutron fluence to the sample.