Angle-energy correlated model of preequilibrium angular distributions

In this paper a new version of the generalized exciton model of preequilibrium angular distributions is proposed to predict the energy dependence of inelastic neutron-scattering angular distributions. The Kikuchi-Kawai expression is used for the scattering of the followed ''fast particle'' in nuclear matter, whereby its full angle-energy correlation is taken into account to describe the emission at the first collision. For the higher steps an energy-averaged scattering kernel is employed for the description of the changes in direction of the fast particle on its way inside the nucleus. The refraction of the incident and outgoing beam is described by the approximation of geometrical optics. This model retains the simple mathematical structure previously introduced by Akkermans et al., providing an easy interpretation of the observed energy-dependence of angular-distribution coefficients without the use of fit parameters. A comparison with experimental neutron-emission data and with the empirical Kalbach-Mann systematics illustrates the predictive ability of the present physical model