Direct interaction effects in the fission of 238U with 63.5 MeV 4He ions

Abstract

Position-sensitive semiconductor detectors have been used to measure both in-plane and out-of-plane angular correlations for binary fission events from 63.5 MeV 4He ion-induced fission of 238U. From these data a value of 7.5±1.0% has been derived for the contribution of direct interaction mechanisms to the total fission cross section at 63.5 MeV. When this result is included with recent theoretical expressions, the interpretation of fission fragment angular distribution data is found to be consistent with both theory and low-energy results up to this energy. The most probable total kinetic energy release was found to be 173.3±5.4 MeV for the compound nucleus 242Pu. The measured variations in the average fission fragment kinetic energies and the widths of the fragment spectra as a function of correlation angle are interpreted in terms of effects arising from direct interactions, neutron evaporation and the reaction kinematics.