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

TL;DR

This paper presents a new evaluation of the $^{232}$Th neutron-induced fission cross section from 500 keV to 200 MeV, integrating recent experimental data and ratios, resulting in a systematically lower cross section than previous libraries.

Contribution

The study introduces a comprehensive simultaneous evaluation of $^{232}$Th fission cross section using recent experimental ratios and data, refining previous evaluations and discrepancies.

Findings

The new evaluation yields a 4% lower cross section in the 2-6 MeV region.

It reduces the averaged cross section over the $^{252}$Cf spectrum by 4%.

The evaluation aligns closer to some libraries but underestimates certain measurements.

Abstract

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 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%.