Exchange terms in the optical model

Abstract

A number of existing proton elastic scattering differential cross section and polarisation angular distributions for 16O, 28Si, 40Ca, 58Ni, 66, 68Zn, 120Sn and 208Pb at several incident energies have been analyzed using an optical-model potential in which the real central and absorptive potentials are multiplied by “exchange terms” of the form [1+ C r ,(−1) l ] and [1+ C i (−1) l ] respectively. Since the major effect of these terms is to be found at backward angles, a number of differential cross section angular distributions for 16O, 66,68Zn and 208Pb have been extended to θ lab = 175°. Small improvements in the quality of the fits to experimental data were obtained with C r, C i ≠ 0. The behaviour of the coefficients C r and C i as functions of incident proton energy is discussed.