STUDY OF THE TH-232 FISSION BARRIER BY ELECTRON-INDUCED FISSION

Fission fragment angular distributions and the electrofission cross se ction of Th-232 were measured in the electron energy region 4.5-7.9 Me V. Below 5.20 MeV two distinct shelves were observed in the isotropic component of the total electrofission cross section, indicating the pr esence of resonances in the photofission cross section at 4.55 [(2(+), 0) channel] and at 4.95 MeV [(1(-), 0) channel]. These resonances are interpreted as associated to vibrational levels in the second well of the Th-232 fission barrier Moreover, a resonance observed at 5.65 MeV in both channels is interpreted as a signature for a vibrational leve l in the third well of the triple-humped fission barrier deduced for t his nucleus.