118 RADIATION RESEARCH 171, 118–122 (2009) 0033-7587/ 09 $15.00  2009 by Radiation Research Society. All rights of reproduction in any form reserved. SHORT COMMUNICATION Fast Neutrons Measured in Copper from the Hiroshima Atomic Bomb Dome A. A. Marchetti, a,1 J. E. McAninch, b G. Rugel, c W. Ru ¨hm, d G. Korschinek, c R. E. Martinelli, a T. Faestermann, c K. Knie, c S. D. Egbert, e A. Wallner, c C. Wallner, c K. Tanaka, f S. Endo, f M. Hoshi, f K. Shizuma, f S. Fujita, g,2 H. Hasai, h T. Imanaka i and T. Straume j a Lawrence Livermore National Laboratory, Livermore, California 94550; b Los Alamos National Laboratory, Los Alamos, New Mexico 87545; c Fakulta ¨t fu ¨r Physik, Technische Universita ¨t Mu ¨nchen, Garching, D85748, Germany; d Helmholtz Zentrum Mu ¨nchen – German Research Center for Environmental Health, 85764, Neuherberg, Germany; e Science Applications International Corporation, San Diego, California 92121; f Hiroshima University, Hiroshima, Japan; g Radiation Effects Research Foundation, Hiroshima, Japan; h Hiroshima Kokusai Gakuin University, Hiroshima, Japan; i Research Reactor Institute, Kyoto University, Japan; and j NASA Ames Research Center, Moffett Field, California 94035 Marchetti, A. A., McAninch, J. E., Rugel, G., Ru ¨hm, W., Korschinek, G., Martinelli, R. E., Faestermann, T., Knie, K., Egbert, S. D., Wallner, A., Wallner, C., Tanaka, K., Endo, S., Hoshi, M., Shizuma, K., Fujita, S., Hasai, H., Imanaka, T. and Straume, T. Fast Neutrons Measured in Copper from the Hi- roshima Atomic Bomb Dome. Radiat. Res. 171, 118–122 (2009). The first measurements of 63 Ni produced by A-bomb fast neutrons (above 1 MeV) in copper samples from Hiroshima encompassed distances from 380 to 5062 m from the hy- pocenter (the point on the ground directly under the bomb). They included the region of interest to survivor studies (900 to 1500 m) and provided the first direct validation of fast neutrons in that range. However, a significant measurement gap remained between the hypocenter and 380 m. Measure- ments close to the hypocenter are important as a high-value anchor for the slope of the curve for neutron activation as a function of distance. Here we report measurements of 63 Ni in copper samples from the historic Hiroshima Atomic Bomb Dome, which is located 150 m from the hypocenter. These measurements extend the range of our previously published data for 63 Ni providing a more comprehensive and consistent A-bomb activation curve. The results are also in good agree- ment with calculations based on the current dosimetry system (DS02) and give further experimental support to the accuracy of this system that forms the basis for radiation risk estimates worldwide.  2009 by Radiation Research Society INTRODUCTION After the release of the dosimetry system 1986 (DS86) (1), validation measurements of thermal-neutron activation 1 Address for correspondence; Lawrence Livermore National Labora- tory L-096, 7000 East Ave., Livermore, CA 94550; e-mail: marchetti1@llnl.gov. 2 Deceased. products appeared to indicate that neutron fluences had been underestimated in Hiroshima at distances most rele- vant to survivor studies (1–5). Furthermore, fast neutrons, which account for a major fraction of the neutron dose to survivors, could not be measured and validated directly at those distances. To resolve this discrepancy, the U.S. De- partment of Energy and the Japanese Ministry of Health, Labour and Welfare supported a major reassessment of all aspects of DS86, which resulted in a new revised dosimetry system for Hiroshima and Nagasaki called DS02 (6). Prior to and during the development of DS02, we developed an accelerator mass spectrometry (AMS) methodology to an- alyze trace amounts of 63 Ni (half-life, 100.1  2.0 years) produced by fast neutrons on copper via the reaction 63 Cu(n,p) 63 Ni and successfully measured 63 Ni in Hiroshima copper samples ranging from 380 to 5062 m from the hypocenter (7–10). The measurements, plotted as a function of distance to the hypocenter, were consistent with A-bomb fast-neutron activation. Here we extend these measurements to the central region near the hypocenter. The Hiroshima Atomic Bomb Dome was part of a build- ing formerly known as the Hiroshima Prefectural Industrial Promotion Hall and stood approximately 150 m northwest from the hypocenter (the A-bomb detonated at an altitude of 600 m). The force from the explosion caused extensive structural damage to buildings near the hypocenter. How- ever, some of the reinforced concrete walls and the steel frame of the dome itself were able to withstand the shock wave. An approximately 0.2-mm-thick copper plate cov- ered the roof of the dome, and it was mostly melted away by the thermal radiation. However, some remnants of the copper plate were located under a 10-cm brick and mortar overhang at the base of the dome, and two samples were made available for AMS analysis.