NUCLEAR PHOTOFISSILITY AT INTERMEDIATE AND HIGH-ENERGIES

The nuclear photofissility of actinides, at intermediate and high energies, was studied by means of a formalism which makes salient the aspects of preequilibrium emissions, compound nucleus formation, and fission decay of the equilibrated system. This formalism was applied in the interpretation of the recently measured photofissilities of Th232 and U238, in the energy range 300-1200 MeV, using (a) an intranuclear cascade Monte Carlo calculation to describe the preequilibrium and thermalization processes, and (b) the statistical model for the fission decay of the compound nucleus. It was found that the nonsaturation of the Th232 photofissility, even at energies up to 1200 MeV, could be explained as a consequence of its higher nuclear transparency, when compared with heavier actinides. Also, the question about a possible competition between statical and direct fission in Th232 and U238 was addressed. © 1995 The American Physical Society.