SYSTEMATICS OF PREEQUILIBRIUM CONTRIBUTIONS IN (N,P) REACTIONS AT 14 MEV

The existing up to date 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 analyz ed to develop systematics in relative preequilibrium contributions (RP C). The experimental estimates of RPC were obtained either from asymme tric 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 wi th those expected from recent Feshbach-Kerman-Koonin theory as extende d by Kalbach et al. as well as with theoretical predictions by Brown a nd Muirhead. The mass number systematics of RPC manifest shell and eve n-odd effects. The fraction of the precompound nucleus decays obtained from RPC, using the Blann-Griffin model, is constant and small for A greater-than-or-equal-to 72, and increases to about 1 for small A's. T he analysis with the Kalbach model yields the dependence of the level density parameters a1 and a2 on A; also values of a1 and a2 manifest p rominent structures near closed shell nuclei. The values of a1 for com pound nucleus are systematically higher than a2, for the residual nucl ei by an amount much larger than expected by usual A dependence, indic ating excitation energy dependence of the single particle level densit y g. The excitation energy dependence of g when explored in the light of Rosenzweig's positive power law, with parameters n and k, reveals t hat for most cases 1.2 less-than-or-equal-to n less-than-or-equal-to 1 .5, with no systematic dependence of n on A, compared to reported theo retical values Of n congruent-to 1.6 by Rosenzweig, and 0.8 less-than- or-equal-to k less-than-or-equal-to 3.8 with a trend of slow increase of k with A.