Two deformation paths in proton-induced fission of 232Th

Velocities of complementary fission fragments have been accurately measured by a double velocity time-of-flight method in the proton-induced fission of 232Th with incident energies from 12.0 to 14.7 MeV. The results experimentally demonstrate for the first time the correlation among the threshold energy, the total fragment kinetic energy, and the mass division mode in fission: one type of the fission process has a lower threshold energy and leads to a compact scission configuration with reflection asymmetry, and the other type has a higher threshold energy and leads to a symmetric elongated scission configuration.