Polarization and differential-cross-section data are presented for the elastic scattering of 40-MeV protons from eleven targets: ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$, ${}_{}{}^{54}{}_{}{}^{}\mathrm{Fe}$, ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$, ${}_{}{}^{59}{}_{}{}^{}\mathrm{Co}$, ${}_{}{}^{60}{}_{}{}^{}\mathrm{Ni}$, ${}_{}{}^{68}{}_{}{}^{}\mathrm{Zn}$, ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$, ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sn}$, and ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$. These data were analyzed with a 10-parameter optical model from which "average parameters" were obtained. The average parameters provide a good fit to our data and lead to a value of about 26 MeV for the depth of the symmetry part of the real central potential. Satisfactory fits to existing 30-MeV data are also realized with these average parameters which, together with the fits to the 40-MeV data, result in an energy dependence of the real central potential of about —0.22 MeV per MeV increase in proton beam energy. Behavior of the $l=0\mathrm{}$ optical-model reflection coefficients is studied as a function of $A$ and appears to be consistent with a mean free path for a reaction in nuclear matter of about 7 F.

• Received 28 November 1966

DOI:https://doi.org/10.1103/PhysRev.156.1207