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. 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, anda 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.