Cross section measurement for the 232Th(n, f ) reaction in the 4.50−5.40 MeV region using a time projection chamber* * This study was financially Supported by the National Natural Science Foundation of China (12075008), the Key Laboratory of Nuclear Data foundation (6142A08200103), the Basic and Applied Basic Research Foundation of Guangdong Province, China (2021B1515120027), and the State Key Laboratory of Nuclear Physics and Technology, Peking University (NPT2021KFJ57)

Accurate cross sections of neutron induced fission reactions are required in the design of advanced nuclear systems and the development of fission theory. Time projection chambers (TPCs), with their track reconstruction and particle identification capabilities, are considered the best detectors for high-precision fission cross section measurements. The TPC developed by the back-streaming white neutron source (Back-n) team of the China Spallation Neutron Source (CSNS) was used as the fission fragment detector in measurements. In this study, the cross sections of the ²³²Th(n, f) reaction at five neutron energies in the 4.50−5.40 MeV region were measured. The fission fragments and α particles were well identified using our TPC, which led to a higher detection efficiency of the fission fragments and smaller uncertainty of the measured cross sections. Ours is the first measurement of the ²³²Th(n, f) reaction using a TPC for the detection of fission fragments. With uncertainties less than 5%, our cross sections are consistent with the data in different evaluation libraries, including JENDL-4.0, ROSFOND-2010, CENDL-3.2, ENDF/B-VIII.0, and BROND-3.1, whose uncertainties can be reduced after future improvement of the measurement.