Elastic scattering

Abstract

In most HI collisions the local wave length X(r) of relative motion is small as compared to the nuclear interaction region R. Therefore, classical approximations have become extremely useful in describing and understanding HI reactions. It is for this reason that the classical theory has been described separately in chapter 2. But according to section 2.4, the classical treatment is limited by quantal effects (interferences and |grad X(r)| = 1) and by absorption. The quantal effects on the classical scattering are described in the semi-classical approximation (section 5.1). The optical model (cf. section 4.1) is applied to the elastic HI scattering in section 5.2. The following three sections are concerned with various parametrizations of the scattering phase shifts (so-called parametrized phase-shift models). These may be viewed as simplifications of or approximations to the optical model. In the sharp cut-off diffraction model (section 5.3) the importance of strong absorption is stressed, leading to Fresnel and Fraunhofer diffraction patterns. This description is generalized in the smooth cut-off model (section 5.4). The Regge-pole model (section 5.5) can account for specific structures in HI scattering which are related to surface waves or potential resonances.