Nearside-farside analysis of inelastic heavy-ion scattering

Abstract

Using a 'turning-wave' decomposition of the inelastic scattering amplitude, analogous to that employed in the elastic scattering of spin-zero nuclei, the authors give a qualitative interpretation of various properties of inelastic reactions. As in the elastic case, amplitudes of various dynamical origins exist, though they do not discuss here the effect of internal waves or of Coulomb excitation. Many of the arguments are based on the form of the DWBA radial integral and show how the concept of an angular momentum mismatch, due to the nonadiabaticity of the reaction, may be applied directly at the level of the entrance- and exit-channel wavefunctions. The authors discuss particularly a 'quasiclassical' limit in which the populations of the various magnetic substates are related in a simple way to one basic amplitude. At a given scattering angle these populations are essentially proportional to the angular part of the excited state's wavefunction evaluated at the points of closest approach for the corresponding nearside and farside 'trajectories'. It is shown that it is the relative sign of these wavefunctions for points on opposite sides of the nucleus which gives rise to the Blair phase rule. In this quasiclassical limit the spin of the excited state is left precessing about the recoil direction. In order to quantify some of the results the authors derive an analytic expression based on the Hahne prescription for the inelastic radial integrals in which they employ the McIntyre parametrisation of the elastic S matrix. The consequences of an angular momentum mismatch on the polarisation of the excited state and on the symmetry angle for its subsequent gamma decay are discussed in terms of nearside and farside components and they study in particular the phenomenon of the rapid reverse rotation of this symmetry angle.