Heavy-ion fusion revisited

Heavy-ion fusion cross sections are presented for a selected number of reactions covering a wide range of Z/sub T/Z/sub p/ values (60 to 3000). For the lighter systems emphasis is placed on the high-energy part of the fusion-evaporation excitation functions. These experimental data are compared with several fusion models in order to test the validity of the various models over a large energy interval. For lighter systems and not too high energies, the fusion process is experimentally rather well distinguishable because of the dominance of compound-nucleus formation. At higher energies and, in particular, for heavier systems, the experimental situation is considerably more intricate. For example, for intermediate systems, fusion-fission competition begins to dominate over fusion-evaporation for angular momenta of approximately 65 h-bar. In addition, there may be a qualitatively distinguished type of fission of partially equilibrated, symmetric or non-symmetric intermediate systems. The experimental fusion-fission cross sections of the very heavy systems are smaller than predicted by a one-dimensional classical dynamical model, indicating that the topology of the underlying potential energy surface of relevance for the fusion process is not well approximated by a barrier in a one-dimensional picture. A simple model description of fusion inhibition induced by the dynamical evolution along a neck-degree of freedom proposed by Swiatecki is successfully applied to a variety of fusion-fission excitation functions. Detailed dynamical calculations have been performed to study the dependence of dynamical fusion inhibition on pertinent features of the multi-dimensional potential energy surface. 85 references