36Cl measurements in Hiroshima granite samples as part of an international intercomparison study -: Results from the Munich group

Within the effort to resolve the so-called Hiroshima neutron discrepancy, an international intercomparison study has been carried out on granite samples from Hiroshima, with participating institutions from Japan, the US, and Germany. Cl-36 and Eu-152 produced in these samples by thermal neutrons from the A-bomb explosion were assessed independently by means of different techniques. At the Maier-Leibnitz-Laboratory near Munich, Germany, Cl-36 concentrations were measured by accelerator mass spectrometry. Measured Cl-36/Cl ratios ranged from 1,670x10(-13) (at a distance of 146 in from the hypocenter) to 2.2x10(-13) (at a distance of 1,163 in from the hypocenter). One granite sample not exposed to A-bomb neutrons was measured as a control, and a Cl-36/Cl ratio of 2.6x10(-13) was obtained. On average, our experimental results are 20-30% lower than those provided by model calculations based on the dosimetry system DS86. The results presented here do not support previous assessments of Cl-36, Co-60, and Eu-152 which had suggested much larger thermal neutron fluences than those calculated on the basis of DS86 for distances from the hypocenter of more than 1,000 in.