Light charged-particle production from neutron bombardment of silicon up to 60 MeV: Role of level densities and isospin

Abstract

Inclusive light charged-particle emission spectra and cross sections from neutron bombardment of silicon were measured at $30\ifmmode^\circ\else\textdegree\fi{},$ $60\ifmmode^\circ\else\textdegree\fi{},$ $90\ifmmode^\circ\else\textdegree\fi{},$ and $135\ifmmode^\circ\else\textdegree\fi{}$ over the neutron energy range from threshold to approximately 60 MeV. Source neutrons, continuous in energy, were provided by the spallation neutron source of the Los Alamos Weapons Neutron Research facility. Comparisons of our alpha-particle data with Hauser-Feshbach calculations, which include multistage emission processes and preequilibrium particle emission, indicate that the majority of alpha particles result from compound nuclear reactions. For proton and deuteron emission, direct and preequilibrium processes contribute significantly to the emission cross section. These data provide rigorous tests for the calculations while helping to guide the selection of input parameters such as nuclear level densities. The effects of assuming partial or complete isospin conservation are shown to be important for these reactions.