Single-particle effects in precompound reactions: Influence of the f7/2 shell closure.

We present angle integrated spectra for the (p,n) reaction with 25 MeV protons on targets of $_{{\mathrm{}}^{50}}$,52,${\mathrm{}}_{24}^{53}$Cr, and on $_{26}^{58}\mathrm{Fe}$, $_{27}^{59}\mathrm{Co}$, $_{28}^{60}\mathrm{Ni}$, and $_{29}^{63}\mathrm{Cu}$. These spectra are compared with two-quasiparticle state densities for proton-particle\char21{}neutron-hole configurations, calculated using Nilsson-model single-particle energies. The influence of shell structure on the precompound spectra, previously shown for the ${g}_{9/2}$ neutron shell closure, is shown here for the ${f}_{7/2}$ 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.