EXFOR-based simultaneous evaluation for fast neutron-induced fission cross section of thorium-232

The 232 Th neutron-induced fission cross section was evaluated from 500 keV to 200 MeV. The experimental 232 Th fission cross sections and their ratios to the 235,238 U fission cross sections in the EXFOR library were reviewed and analysed by using the least-squares method. The newly published 232 Th/ 235 U fission cross-section ratios from the time-of-flight measurements at the CERN n_TOF and CSNS Back-n facilities were compiled in EXFOR. Additional simultaneous evaluation was performed by including the experimental 233,238 U and 239,240,241 Pu fission cross sections and their ratios. The new evaluation provides the 232 Th fission cross section systematically lower than the JENDL-5 cross section. The reduction is 4% in the plateau region between 2 and 6 MeV and more significant in the subthreshold fission region. The present evaluation reduces the 232 Th fission cross section averaged over the 252 Cf spontaneous fission neutron spectrum from the JENDL-5 evaluation by 4%, which is closer to the other general purpose libraries but underestimates Grundl et al.'s measurement by 11%.