The nucleon optical potential

Abstract

We use the impulse approximation, the Tabakin internucleon potential and a Fermi gas model for the nucleus to calculate the low energy nucleon-nucleus optical potential. The real and imaginary parts are calculated simultaneously but it is found to be an extremely good approximation to calculate them separately as is usually done. The main features of the real part of the isospin independent potential are reproduced by our calculation. We also estimate the size and shape of the asymmetry term in the real part of the potential. The size is in agreement with empirical analyses and the predicted shape may be useful as a guide when fitting data. Our calculations for the imaginary part are much less satisfactory. In particular we cannot reproduce the large surface peaking of the empirical potentials perhaps reflecting our neglect of collective states. We find that the observed difference between the imaginary parts for protons and neutrons cannot be explained as a consequence of a reasonable difference between the proton and neutron distributions in nuclei.