Charged-particle spectra: 90 MeV protons onAl27,Ni58,Zr90, andBi209

Abstract

Complete charged light-particle ($Z\le 2$, $A\le 4$) energy spectra were measured for 90 MeV protons on ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$, ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$, and ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}$ and 100 MeV protons on ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$. The energy spectra show a strong angular dependence and the spectral shapes at a given angle for the same particle type are similar in the high-energy continuum for all target nuclei. The non-equilibrium, charged light-particle yields show an $A^{\frac{1}{3}}$ dependence and are approximately given by $(200\mathrm{}\pm 10)A^{\frac{1}{3}}$(mb). One striking feature is the similarity of the shapes of the $p$, $d$, and $t$ spectra, if the spectra are shifted by an appropriate binding energy. The relative intensity is approximately $p:d:t\frac{1:1}{\frac{10:1}{100}}$ at all angles. In the backward directions ($\theta \ge 140°$) the spectra exhibit characteristic evaporation behavior with approximately the same slope for each target nucleus for a given observed particle. The slopes of the evaporation peaks (corresponding to a temperature of 2-3 MeV) for the different particle type are also rather similar. The experimental results were analyzed within the framework of the pre-equilibrium exciton model together with the evaporation theory. The pre-equilibrium exciton model using a 2p-1h initial configuration generally reproduces the experimental angle-integrated energy spectra reasonably well in shape, but underestimates especially the proton yield in the region of high-energy continuums.