Developments in sub-barrier reactions

Abstract

The study of sub-barrier reactions has developed in recent years to include a broad range of interconnected phenomena. The initial discoveries of enhanced sub-barrier fusion cross sections and the attempts to understand them in terms of couplings to other reactions channels have stimulated investigations into all aspects of heavy-ion collisions at low bombarding energies. As a result, new effects have been observed and new ideas are being put forward. The present talk gives an overview of some current themes in this field. Perhaps the most encompassing development is that one can no longer think of the low energy fusion reaction as an isolated phenomenon, since the fusion rates depend crucially on the presence of other reaction channels. Thus, one wants to know what are the properties of these channels and then how to use this knowledge to explain the fusion rates quantitatively. Generally speaking, quite a number of sub-barrier fusion reactions have been measured but the other reactions which occur have been isolated in a relatively few cases. It is also generally true that theoretical sub-barrier fusion calculations have been successful for a limited range of fairly light mass systems. Thus, the field continues to be a challenging area ofmore » research. Going beyond the problem of understanding the fusion mechanism, there have been interesting new developments in all of the reaction classes that have been studied at sub-barrier energies, namely, elastic scattering, inelastic excitation, transfer reactions and deep inelastic collisions. A brief discussion of each of these subjects and how they relate to fusion will be given below. In addition, the important subject of compound nuclear spin distributions produced in fusion reactions will be noted. 20 refs., 9 figs.« less