Measurement of the 232Th(n,f) cross-section in the 1–200 MeV range at the CSNS Back-n

摘要: The 232Th(n,f) cross-section is very important in basic nuclear physics and applications based on the Th/U fuel cycle. Using the time-of-flight method and a multi-cell fast fission ionization chamber, a novel measurement of the 232Th(n,f) cross-section relative to 235U in the 1–200 MeV range was performed at the China Spallation Neutron Source Back-n white neutron source (Back-n). The fission event-neutron energy spectra of 232Th and 235U fission cells were measured in the single-bunch mode. Corrected 232Th/235U fission cross-section ratios were obtained, and the measurement uncertainties were 2.5–3.7% for energies in the 2–20 MeV range and 3.6–6.2% for energies in the 20–200 MeV range. The 232Th(n,f) cross-section was obtained by introducing the standard cross-section of 235U(n,f). The results were compared with those of previous theoretical calculations, measurements, and evaluations. The measured 232Th fission cross-section agreed with the main evaluation results in terms of the experimental uncertainty, and 232Th fission resonances were observed in the 1–3 MeV range. The present results provide 232Th(n,f) cross-section data for the evaluation and design of Th/U cycle nuclear systems.