Spin-Dependent Nucleon-Nucleus Interactions Constrained by Neutron Observables and Their Impact on Near-Barrier Proton Fusion

Abstract

We investigate the role of spin-dependent nucleon--nucleus interactions in nuclear reactions. To this end, we use neutron spin observables to constrain the dominant central spin-spin form factors and then apply the corresponding like-channel interactions to near-barrier fusion in the $p+{}^{93}$Nb system. The interactions are constructed within a folding framework based on a finite-range effective nucleon-nucleon force and organized in terms of radial form factors associated with their spin-spin, tensor, and spin-orbit components. Neutron spin observables in the $n$ + ${}^{27}$Al, ${}^{59}$Co, and ${}^{93}$Nb target systems are analyzed within a distorted-wave Born approximation (DWBA) framework {to examine the sign and scale of the central spin-spin contribution and the assembled operator conventions.} The calculation reproduces the observed sign systematics of the neutron spin observables for the three targets, consistent with the dominant central spin-spin contribution in the adopted model. The unlike-channel (neutron--proton) interaction constrained by neutron scattering is then reconstructed for the corresponding like-channel (proton--proton) interaction and applied to a coupled-channels description of near-barrier fusion for the $p+{}^{93}$Nb system. The retained real spin-dependent interactions lead only to a weak modification of the effective barrier and a very small change in the unpolarized fusion cross section within the present model. The present work thus connects the neutron-scattering constraints on the operator conventions with the fusion calculation in the proton channel, and estimates the scale of the corresponding real spin-dependent correction in near-barrier fusion.

arXiv comment16 pages, 6 figures, 5 tables