Pickup coupling contribution to the optical model potential for 30.3 MeV protons and neutrons on⁴⁰Ca

Keeley, N. and Mackintosh, R. S. (2019). Pickup coupling contribution to the optical model potential for 30.3 MeV protons and neutrons on⁴⁰Ca. Physical Review C, 99(3), article no. 034614.

DOI: https://doi.org/10.1103/PhysRevC.99.034614

Abstract

We study the dynamic polarization potentials (DPPs) for 30.3 MeV protons and neutrons scattering from⁴⁰Ca that are generated by the coupling to deuteron channels. In this way we resolve unexpected differences from the general properties of such DPPs found in similar cases for lighter targets. It turns out that the contribution of particular states to the real part can change considerably with Q value, coming close to changing sign. One consequence is the surprising result presented in Mackintosh and Keeley [Phys. Rev. C 97, 069901(E) (2018)], which is investigated here. The Q-value dependence of the DPPs also contributes to a substantial difference between the optical model potential for protons and neutrons, there being substantially different Q values for ⁴⁰Ca (n, d) and ⁴⁰Ca (p, d) pickup reactions. The DPP calculations also enable a study of the dynamical nonlocality (distinct from exchange nonlocality) arising from pickup coupling. The characteristic properties of the DPPs for both protons and neutrons arising from nucleon pickup are also presented for incident nucleons at 25, 35, 40, and 45 MeV. All these properties vary with energy in a consistent way, including a change in the rms radius of the real potential, which, together with the general undularity of the DPP, shows that the pickup contributions cannot be represented by renormalizing a folding model potential.

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