Pairing effects in 232Th neutron-induced fission cross section Original Research Article

The fission cross section of 232Th(n,F) is calculated consistently with the 232Th(n,2n) reaction cross section up to 20 MeV. The fission probability of the 232Th nuclide, fissioning in 232Th(n,nf) reaction is shown to be compatible with the surrogate 230Th(t,pf) fission probability data. The 232Th(n,nf) reaction contribution to the observed 232Th(n,F) cross section up to En∼9 MeV is defined by the collective levels of the 232Th at saddle deformations, lying within the pairing gap. The importance of the negative parity octupole Kπ=0− band levels at saddle deformations is demonstrated. The shoulder or small step-like structure in the observed fission cross section of the 232Th(n,F) above En∼9 MeV is correlated with the excitation of the two-quasiparticle states at saddle deformations of the fissioning 232Th nuclide. Influence of the multiple-chance fission on the 232Th prompt fission neutron spectra is demonstrated.