Cosmic-ray-induced 63Ni - A potential confounder of fast-neutron-induced 63Ni in copper samples from Hiroshima

W. Rühm, G. Rugel, T. Faestermann, K. Knie, A. Wallner, B. Heisinger, E. Nolte, A. A. Marchetti, R. E. Martinelli, K. L. Carroll, G. Korschinek

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Recently, the determination of 63Ni in copper samples has been suggested as a means to assess fast-neutron fluences in Hiroshima and Nagasaki. In those samples, 63Ni (half-life: 100.07 years) was produced by MeV neutrons from the A-bomb explosions via the reaction 63Cu(n,p) 63Ni. For large distances from the hypocenters, cosmic-ray-induced production of 63Ni might also be important and, therefore, it is calculated here. The effective probability f* which is required to quantify the cosmic-ray-induced production by stopped muons, was measured, and a value of (12.6 ± 1.6)% obtained. The cross-section for the cosmic-ray-induced production by fast muons was measured to be (0.64 ± 0.33) mb, at a muon energy of 100 GeV. To validate the proposed method, cosmic-ray-induced production of 32P in sulfur and of 39Ar in granite was also calculated, and reasonable agreement with literature values was found. Our estimates indicate that as many as (4-5) · 103 63Ni nuclei per gram copper were produced in a sample that was exposed to cosmic radiation in Hiroshima for about 80 years. A similar concentration due to A-bomb neutrons would be expected in Hiroshima at a distance from the hypocenter of about 1900 m.

Original languageEnglish
Pages (from-to)633-639
Number of pages7
JournalEuropean Physical Journal A
Issue number4
StatePublished - Jul 2003


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