The existing up to data global data on angle integrated energy spectra (AIES) and energy integrated angular distributions (EIAD) of protons from (n,p) reactions at 14 MeV nominal neutron energy have been analyzed to develop systematics in relative preequilibrium contributions (RPC). The experimental estimates of RPC were obtained either from asymmetric components of the extrapolated EIAD or from the analysis of AIES, by comparison with equilibrium contributions obtained from the Hauser-Feshbach model. The experimentally obtained RPC have been compared with those expected from recent Feschbach-Kerman-Koonin theory as extended by Kalbach et al. as well as with theoretical predictions by Brown and Muirhead. The mass number systematics of RPC manifest shell and even-odd effects. The fraction of the precompound nucleus decays obtained from RPC, using the Blann-Griffin model, is constant and small for A≥72, and increases to about 1 for small A’s. The analysis with the Kalbach model yields the dependence of the level density parameters ${\mathit{a}}_1$ and ${\mathit{a}}_2$ on A; also values of ${\mathit{a}}_1$ and ${\mathit{a}}_2$ manifest prominent structures near closed shell nuclei. The values of ${\mathit{a}}_1$ for compound nucleus are systematically higher than ${\mathit{a}}_2$, for the residual nuclei by an amount much larger than expected by usual A dependence, indicating excitation energy dependence of the single particle level density g. The excitation energy dependence of g when explored in the light of Rosenzweig’s positive power law, with parameters n and k, reveals that for most cases 1.2≤n≤1.5, with no systematic dependence of n on A, compared to reported theoretical values of n≃1.6 by Rosenzweig, and 0.8≤k≤3.8 with a trend of slow increase of k with A.

• Received 6 July 1993

DOI:https://doi.org/10.1103/PhysRevC.49.1066