36Cl measurements in hiroshima granite samples as part of an international intercomparison study

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Abstract
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. 36Cl and 152Eu 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, 36Cl concentrations were measured by accelerator mass spectrometry. Measured 36Cl/Cl ratios ranged from 1,670×10−13 (at a distance of 146 m from the hypocenter) to 2.2×10−13 (at a distance of 1,163 m from the hypocenter). One granite sample not exposed to A-bomb neutrons was measured as a control, and a 36Cl/Cl ratio of 2.6×10−13 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 36Cl, 60Co, and 152Eu 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 m.