Proton-Induced Fission of 232Th at Low and Intermediate Energies

Mass–energy distributions of fission fragments are measured in the proton energy region of 7 to 55 MeV in order to study shell effects in the fissioning of 232Th nuclei induced by protons at low and intermediate energies. Experiments at proton energies of 13 to 55 MeV are performed using proton beams from the K-130 cyclotron at the University of Jyvaskyla (Finland) using the CORSET two-armed time-of-flight spectrometer. Experiments at proton energies of 7, 10, and 13 MeV are performed using the beam from the U‒150M cyclotron at the Institute of Nuclear Physics in Almaty (Kazakhstan) using a 2Е spectrometer for detecting fission fragments. It is found that the yield of symmetric fragments falls along with the proton energy, while the yield of asymmetric fragments rises. Deep below the Coulomb barrier at the lowest proton energy of 7 MeV, an increased yield of fission fragments is observed in the region of 60−70 a.m.u., which corresponds to the superasymmetric mode of fission.