Dependence upon mass number and neutron excess of the real part of the proton optical potential for mass numbers44≤A≤72

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Abstract
We perform detailed theoretical and empirical investigations of the real part of the optical-model potential for protons with energy 9≤E≤12 MeV and targets with mass number 44≤A≤72, in order to clarify earlier claims that in this domain the potential depth presents a peculiar dependence upon the target mass number A, asymmetry parameter α, and isospin T. We compile several radial moments of the empirical potentials and compare them with those predicted by a nuclear matter approach based on Reid’s hard core nucleon-nucleon interaction. We find that this theoretical model is in good agreement with the empirical properties. In particular, the theoretical potential depends upon T for fixed α. This is due to the dependence upon A of its isoscalar component. The calculated potential is found to have approximately a Woods-Saxon shape with a fixed geometry, except in the surface tail where the theoretical model is, in any case, unreliable.