Particle-hole configurations in reaction mechanisms for single-particle level densities for target nuclei in (n ,p ) reactions at 14.8 MeV energy

Earlier, single-particle level densities were obtained for a large number of target nuclei from the analysis of experimental data on a (n ,p ) reaction at 14.8 MeV neutron energy using the Kalbach model. Recently, we obtained theoretical values of excitation energy ɛ_c for unbound states and Fermi energies (ɛ_f) for bound states for these single-particle level densities for many target nuclei by using Shlomo's theory, which leads to a shell structure, when ɛ_c was plotted as a function of the atomic weight A . This indicates support to the concept of multiple statistical direct (MSD) and multiple statistical compound preequilibrium processes that involves unbound and bound states. We have now calculated the particle-hole configurations which are dominantly involved in the reaction mechanism for creating the single-particle level densities for all target nuclei, including "spikes" and "dips" obtained in the data analysis earlier using the formulation given by Kalbach [Phys. Rev. C 23, 124 (1981), 10.1103/PhysRevC.23.124] and Shlomo [Nucl. Phys. A 539, 17 (1992), 10.1016/0375-9474(92)90233-A]. It seems that h =2 , p =0 is the dominant configuration for most of the targets in the preequilibrium process, whereas spikes seem to correspond to the h =1 , p =1 dominant configuration, corresponding to the direct reaction mechanism; and dips seem to belong to the h =2 , p =0 configuration and h =1 , p =1 and h =0 , p =2 configurations somewhat equally giving compound nucleus formation due to quantum statistical fluctuations and MSD. The implication of these calculations and results is discussed.