Shell effects in (n, p) and (n, α) cross-sections at about 14 MeV

Abstract

A comprehensive compilation of the available data on (n, p) and (n, α) reaction cross-sections, up to December 1969, for about 14 MeV neutrons is given. These data, suitably averaged, have been used in a search for shell effects by standard statistical methods. The analysis shows that the evaporation model is able to explain the experimental data when shell effects are included in the excitation energy in analogy with pairing corrections. This simple model gives the absolute value of a cross-section with a relative standard error of about 40% to be compared with an expectation value of about 10% as deduced from the errors (systematic plus random) with which the cross-sections have been measured. The most critical parameter in this model is that which takes roughly into account quantum penetration, while other approximations,i.e. neglecting secondary emission, considering independence of the temperature parameter on excitation energy and mass number, and so on, prove to be quite reasonable. However the temperature parameter mentioned above does not correspond to the nuclear temperature because it includes shell and Coulomb barrier effects; its value is about 2.1 MeV.