Spallation products of 197Au induced by secondary particles from 12-GeV proton bombardment of a thick aluminum target

We measured the production rates of the spallation of 197Au, of which plates were attached on the wall of the neutrino target station of KEK, induced by the secondary particles emitted from the 12-GeV proton bombardment of a thick aluminum target. The spallation production rates of 197Au were also calculated using the newly issued MARS15 code system in order to compare the experimental and theoretical production rates. The calculated production rates agreed with the experimental ones. Products with mass numbers close to that of 197Au were produced by the prominent low-energy neutrons. Although, at energies higher than 300 MeV, the fluxes among neutrons, protons, π+ and π− were comparable, the pionic nuclear reactions were highly effective in producing lighter-mass products (<∼190) in Au plates placed at large-angle directions. At the forward angle positions, where particles with energies higher than 1 GeV were highly populated, the contribution of the lighter mass production from neutrons and protons becames comparable to that of pions, because the 140-MeV gain in the pionic nuclear reactions is not significant.