Measurement of the 232Th(n,2n)231Th reaction cross section with 14.5 MeV neutrons

The cross section of the 232Th(n,2n)231Th reaction for D-T neutrons was measured using a neutron generator at the Kyoto University Critical Assemblies (KUCA). The neutron energy was determined by the Zr/Nb ratio method. Irradiated thorium nitrate samples were chemically purified, and their γ-rays were measured with a high-purity germanium detector. The cross section was normalized to the 27Al(n,α)24Na reaction cross section of 119.36 mb, which is the evaluated value in ENDF/B-VI at 14.5 MeV. The result was (1198±65) mb for (14.5±0.2) MeV neutrons, and this agrees with the evaluated values in ENDF/B-VI and ENDL-86 within an experimental uncertainty, but is more than 20% larger than the newly evaluated value in JENDL-3. (author)