MEASUREMENT OF THE TH-232(N,2N)TH-231 REACTION CROSS-SECTION WITH 14.5-MEV NEUTRONS

The cross section of the Th-232(n,2n)Th-232 reaction for the 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 gamma-rays were measured with a high-purity germanium detector. The cross section was normalized to the Al-27(n,alpha)Na-24 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.