Semi-monoenergetic neutron field for activation experiments up to 40 MeV

Abstract

A semi-monoenergetic high-energy neutron field for activation experiments was developed at the SF cyclotron of the Institute for Nuclear Study, the University of Tokyo, using a simple Be target system bombarded by 20, 25, 30, 35 and 40 MeV protons. The 1 and 2 mm thick Be targets were cooled by a water flow of 12 and 11 mm thick layers, respectively, which works as a proton beam stopper at the same time. The neutron spectra were measured with an NE213 scintillation counter and the energy resolution at their high energy peaks was corrected by calculations. The intensity was 4×10 15 to 1.6×10 16 [n sr −1 C −1] for the total neutrons of energy above 3 MeV, and 2×10 15 to 7×10 15 [n sr −1 C −1] for the high-energy peak neutrons. The irradiation point for the activation experiment is at 20 cm from the target, and the beam current is about 5 μA. The 27Al(n, α), 197Au(n, 2n) and 197Au(n, 4n) reaction rates at the irradiation point were measured and they were compared with the calculation performed with the corrected neutron spectra and the cross sections in references. For the former two reactions, the measured and calculated data agreed well with each other, and the 197Au(n, 4n) reaction cross section data in the reference were found to be overestimated.