Polarization and Differential Cross Section for Elastic Scattering of 40-MeV Protons. II

Polarization and differential-cross-section data are presented for the elastic scattering of 40-MeV protons from eleven targets: ¹²C, ²⁸Si, ⁴⁰Ca, ⁵⁴Fe, ⁵⁸Ni, ⁵⁹Co, ⁶⁰Ni, ⁶⁸Zn, ⁹⁰Zr, ¹²⁰Sn, and ²⁰⁸Pb. 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 $l=0$ 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.