https://doi.org/10.1140/epja/i2003-10034-2
Original Paper
Cosmic-ray-induced 63Ni --A potential confounder of fast-neutron-induced 63Ni in copper samples from Hiroshima
1
Radiobiological Institute, University of Munich, Schillerstrasse 42, 80336, Munich, Germany
2
Maier-Leibnitz Laboratory, Faculty of Physics, Technical University of Munich, 85747, Garching, Germany
3
Lawrence Livermore National Laboratory, Livermore, USA
* e-mail: W.Ruehm@lrz.uni-muenchen.de
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 ($12.6 \pm 1.6$)% obtained. The cross-section for the cosmic-ray-induced production by fast muons was measured to be ($0.64 \pm 0.33$) 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 $(4 -5)\cdot 10^{3}$ 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.
© Società Italiana di Fisica and Springer-Verlag, 2003
