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 epsilon(c) for unbound states and Fermi energies (epsilon(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 epsilon(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)] and Shlomo [Nucl. Phys. A 539, 17 (1992)]. 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.