Proton elastic scattering on light nuclei. I. Energy dependence

Differential cross sections for proton elastic scattering by ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$, ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$, and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ were measured at several proton energies between 14 and 44 MeV. Previous data on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$, ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ have also been considered. Evidence has been found for a strong enhancement in proton emission at backward angles for scattering by spherical nuclei at incident energies higher than 26 MeV. A phase-shift analysis of all the differential cross sections showed that the partial waves involved are those near grazing. Optical-model fits of good quality have been obtained for collective nuclei, while for spherical nuclei the cross sections at backward angles are not reproduced. The disagreement is not substantially modified when nonstandard radial dependences are given to the optical potential.