The role of deformations, inertias, and wall friction in heavy ion fusion

The time evolution of the shapes of colliding heavy ions is determined using a full dynamical calculation which includes among other ingredients; deformations, deformation dependent inertias and wall dissipation. A carefully chosen criterion allows the determination of the critical angular momentum for fusion, Icr, as a function of bombarding energy. It is shown that the characteristics of the entrance channel, namely, deformations, deformation dependent inertias, and wall friction affect the fusion excitation function in a fundamental way. The fusion excitation functions for 16O, 28Si, 40Ca and 56Fe are calculated using the one-body wall friction and are compared with similar calculations using a weaker wall friction (surface friction). These dynamical calculations show that the experimental excitation functions are consistent with the wall friction but not with the smaller surface friction. Also, general non-dynamical considerations have been used to place upper bounds on the excitation function, which are very useful. (orig.)