Heavy-ion-induced fission — experimental status

Abstract

The process of fission of a composite nucleus produced in heavy-ion collisions is characterized in terms of the experimental kinetic-energy, mass and angular distributions of the fission fragments. Measurements of associated particles, and possibly of γ-rays, emitted prior to scission demonstrate that heavy-ion fission is an inherently slow (~10 −20 – 10 −19 s) process that is dominated by overdamped collective motion in the exit channel. Experimental fission excitation functions are consistent with the fission barriers of the finite-range liquid-drop model. While fission fragment angular distributions are well described in terms of the transition-state model, for relatively small angular momenta and excitation energies, the model is inapplicable for composite nuclei with vanishing effective barriers and for high spins and excitation energies. Angular anisotropies for these latter systems suggest considerable relaxation of the tilting mode.