DOES EXCHANGE PRODUCE L DEPENDENCE IN THE OPTICAL-MODEL POTENTIAL

We obtain a local but angular momentum dependent potential V(L) which is phase equivalent to a Hartree-Fock nonlocal potential for the descr iption of nucleon-nucleus scattering. We first identify two different pieces of the microscopic effective nucleon-nucleon interaction, guide d by an analysis of the L-dependent properties of the conventional mic roscopic direct and exchange matrix elements of the n-n interaction. B y separately folding these two pieces of the effective n-n interaction over the nucleons in the target nucleus we obtain two different micro scopic local potentials. We finally obtain V(L) from the superposition of these two potentials with L-dependent coefficients, determined suc h that the deviation of the scattering wave function from the exact so lution of the nonlocal Schrodinger equation, with the Hartree-Fock pot ential, is as small as possible. We provide a numerical example for n- O-16 scattering at 20 and 50 MeV. We find that the deviation of the wa ve functions for V(L) is only a little smaller than the deviation for a local L-independent potential obtained by inversion of the scatterin g phase shifts. Hence the latter provides a nearly optimum local descr iption of the exchange nonlocality.