Single-particle effects in precompound reactions: Influence of the f/sub 7/2/ shell closure

We present angle integrated spectra for the (p,n) reaction with 25 MeV protons on targets of 50,52, 2453Cr, and on 2658Fe, 2759Co, 2860Ni, and 2963Cu. These spectra are compared with two-quasiparticle state densities for proton-particle--neutron-hole configurations, calculated using Nilsson-model single-particle energies. The influence of shell structure on the precompound spectra, previously shown for the g/sub 9/2/ neutron shell closure, is shown here for the f/sub 7/2/ neutron and proton shells. Semiquantitative agreement is shown between experimental results and calculated two-quasiparticle densities. The parameter space of pairing energy, deformation, and oscillator stiffness is explored. Precompound spectra near shell closures are in better agreement with partial state densities from Nilsson-model considerations than with results from more commonly used equidistant spacing models