Contributions of the direct and statistical reaction mechanisms in scattering of fast neutrons by low-lying levels of light and medium nuclei

The main features in the behavior of the functions for excitation of low-lying nuclear levels by neutrons are analyzed and the connection between these features and the parameters of the optical and statistical models used to describe them is discussed. The differences between the dynamical-deformation parameters of nuclei derived from direct inelastic scattering of nucleons and from Coulomb excitation of low-lying collective levels are considered. It is shown that direct transitions make an important contribution to the excitation functions of individual levels even at comparatively low neutron energies. The part played by structural changes in the neutron strength functions in explaining the observed energy dependence of the inelastic-scattering cross sections in the near-threshold region is elucidated.