The study of the (α, α’f) reaction at 120 MeV on 232Th and 238U (I). Fission probabilities and angular distributions in the region of the giant quadrupole resonances

The fission decay channel of 232Th and 238U has been investigated, using the (α, α’f) reaction at 120 MeV bombarding energy. The angular distributions of the fission fragments and the fission probabilities up to around 15 MeV excitation have been measured. No evidence for the fission decay of the giant quadrupole resonance has been found, although for 238U, a weakly excited structure is seen in the (α, α'f) spectrum at about 9.5 MeV excitation at backward angles with respect to the recoil axis. This effect is similar to what has been found in a (6Li, 6Li’f) experiment reported recently. The over-all feature of the fission probability for excitation energies above the fission barrier are well reproduced by statistical calculations.