Proton Scattering byNi64andZn64at 9.6 and 11.7 MeV

Differential cross sections for elastic scattering of protons from ${\mathrm{Ni}}^{64}$ and ${\mathrm{Zn}}^{64}$ were measured and compared. The observed shift in the positions of the maxima and minima of the differential cross sections is shown to be consistent with the presence of a symmetry energy term [$\frac{C(N-Z)\mathrm{}}{A}$] in the real nuclear potential of the optical model. It is found that $C\approx 40$ MeV, in reasonable agreement with the results of other observations.