Proton optical model potential at sub-Coulomb energies for medium weight nuclei

The ($p$,$n$) reaction excitation functions for eleven nuclei from $A=45\mathrm{} \mathrm{to} 80$ measured at proton energies below ∼5 MeV have been analyzed utilizing the optical model. The real potential parameters used in the present work have been obtained by suitably combining the proton optical model parameters determined between 3 and 60 MeV. Large energy dependence of the real potential at energies below 5 MeV has been observed. The imaginary potential depths determined in the present analysis exhibit an anomalous behavior when plotted as a function of mass number $A$. By utilizing the low and intermediate energy proton data, an attempt has been made to obtain a "global" set of optical parameters in the proton energy range between 4 and 180 MeV, for medium weight nuclei.