Effects of fissioning nuclei distributions on fragment mass distributions for high energy fission

We study the effects of fissioning nuclei mass- and energy-distributions on the formation of fragments for fission induced by high energy probes. A Monte Carlo code called CRISP was used for obtaining mass distributions and spectra of the fissioning nuclei for reactions induced by 660 MeV protons on 241 Am and on 239 Np, by 500 MeV protons on 208 Pb, and by Bremsstrahlung photons with end-point energies at 50 MeV and 3500 MeV on 238 U. The results show that even at high excitation energies, asymmetric fission may still contribute significantly to the fission cross section of actinide nuclei, while it is the dominante mode in the case of lead. However, more precise data for high energy fission on actinide are necessary in order to allow definite conclusions.