Health and radiation-dosimetry data from survivors of the Hiroshima and Nagasaki bombings are the primary basis for radiation risk calculations worldwide. After the release of dosimetry system 1986 (DS86), validation measurements of thermal-neutron activation products seemed to indicate that neutron fluences had been significantly underestimated in Hiroshima at distances most relevant to survivor studies. More importantly, there were no methods available at the time DS86 was developed to validate fast neutrons, which were responsible for almost the entire neutron dose to survivors in Hiroshima. For that reason, a search was conducted to identify fast-neutron activation products that could be measured using current sensitive techniques such as AMS. The reaction 63Cu(n,p)63Ni was recognized as a good candidate, but measuring 63Ni in copper samples presented difficult technical challenges largely due to isobar interference from the matrix (63Cu, 69%). Here we present AMS measurements of 63Ni in copper samples from Hiroshima, including new samples from the A-bomb Dome, and compare them to estimates based on neutron fluences from DS86 and the new dosimetry system, DS02. The A-bomb Dome is one of a few buildings near the hypocenter that partly survived the nuclear blast and was set aside for preservation as a monument.
Part of this work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48. This work was supported in large part by the U.S. Department of Energy (grant #DEFG0300ER62963 and contract #DEFC0397SF21354).
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