Elastic Scattering of 21-MeV Protons from Nitrogen-14, Oxygen-16, Argon-40, Nickel-58, and Tin-116

Abstract

Differential cross sections were measured for 21-MeV incident protons elastically scattered from ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$, ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$, and ${}_{}{}^{116}{}_{}{}^{}\mathrm{Sn}$. An optical-model analysis was performed on these data as well as on previously measured elastic polarizations of 21-MeV incident protons scattered from the same nuclei. The optical potential used in this analysis included a real central term, a surface absorption term, and a real spin-orbit term. Good fits to both the cross sections and polarizations for all nuclei except ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ were obtained by allowing the nine parameters of the optical potential to vary from nucleus to nucleus. The diffuseness parameters derived to fit the ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ data in general differ considerably from those derived to fit the scattering from the heavier nuclei. These results are compared with those of two other calculations in which two different sets of nonunique constant geometrical optical-model parameters were assumed and only the three potential strengths were obtained by searching. As expected, these constant-geometry calculations gave poorer agreement with the data. The disagreement with the polarizations of ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ was very pronounced.