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

Abstract

  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.