Odd-Even Effects in Pre-Equilibrium Processes

Neutron spectra produced by the ($p,n$) reaction at 12 and 14 MeV on targets of ${}_{}{}^{112}{}_{}{}^{}\mathrm{Cd}$, ${}_{}{}^{113}{}_{}{}^{}\mathrm{Cd}$, ${}_{}{}^{114}{}_{}{}^{}\mathrm{Cd}$, and ${}_{}{}^{115}{}_{}{}^{}\mathrm{In}$ are compared with the predictions of the exciton model for pre-equilibrium reactions. It is concluded that although the shape of the spectra for even-$A$ targets differs from that for odd-$A$ targets, the differences are not entirely consistent with the analysis of Lee and Griffin for ($p,n$) reactions on the Sn isotopes. The possible explanations for deviations from model calculations include effects due to shells, pairing, and angular momentum.