Microscopic Calculation of Fission-Fragment Anisotropies for Nuclei Exhibiting a Double Barrier

Publisher Website
Google Scholar
Abstract
At moderate excitation energies fragment angular distributions are determined by an effective moment of inertia characteristic of the saddle-point deformation. We have performed a microscopic calculation which shows that at low excitation energy the experimentally deduced effective moment of inertia corresponds to the outer barrier. This is consistent with recent theoretical calculations showing that the inner barrier is unstable with respect to distortions destroying axial symmetry of the nuclear shape. At higher excitation energies the effective moment of inertia becomes characteristic of the liquid-drop-model saddle deformation. The transition is expected to occur at a fairly high excitation energy and may provide an explanation for the observation that the effective moment of inertia continues to increase at excitation energies well above that where pairing effects have disappeared.