Optical-Model Analysis of Elastic Scattering of Protons on Carbon at Intermediate Energies

Differential cross sections and polarizations for the elastic scattering of protons by carbon at energies between 7 and 20 Mev have been analyzed according to the diffuse-surface optical model of the nucleus. The model parameters were varied systematically, the best fits to the experimental data being determined by a method of least squares. Various forms of the absorptive part of the potential were investigated, although the main part of the analysis was carried out with a surface-plus-volume absorption potential. It was found that the model could not account satisfactorily for the data below about 12 Mev, and the presentation of results is limited to the region $11.85 \mathrm{Mev}<~E_{\mathrm{lab}}<~19.4 \mathrm{Mev}$. Excellent fits can be obtained over the latter region with generally reasonable values of the model parameters, although some features of their behavior as a function of energy remain to be explained. The most striking of the results is the thin absorptive shell and small volume absorption which characterizes the potential. Although the predicted reaction cross sections appear generally too low, the experimental data are not sufficiently precise to warrant drawing a definite conclusion.