Resonance effects in fusion and transfer reactions

Abstract

An impressive quantity of high quality experimental data has become available in the last five years and has now rather clearly defined the resonance behavior present in light nucleus-nucleus systems and has shown that “resonance” behaviors persist in heavier systems. It is found that for some light systems the nucleus-nucleus interaction is unexpectedly weakly absorbing for surface partial waves and this surface transparency manifests itself in “resonance” structures in the elastic scattering as well as the reaction channels. What has become clear from these studies is that it is only by carefully establishing the detailed behavior in all channels, the elastic scattering, the “direct” reaction channels, and the fusion reaction channels, that sufficient information becomes available to form a complete picture. The success of the band crossing model in reproducing many of the features observed in the data looks promising. In going to heavier systems,it is observed that the strengths of the elastic scattering cross sections at back angles for 12C and 16O on α-nucleus targets is significantly larger than expected with strong absorption potentials. The excitation functions for these cross sections, as well as those observed for (16O,12C) reactions at both forward and back angles, do not show a smooth energy dependence but rather exhibit “resonance” behaviors. Although the understanding of the behavior in these heavier systems is far from complete now, the smooth trend in the strength of the back angle elastic scattering cross sections as a function of the mass suggests a connection between the behaviors observed in the light and heavier systems exists. The next year or two should prove to be an exciting period of time during which these phenomena will be explored both experimentally and theoretically.