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, $n+{}^{59}$Co, and $n+{}^{93}$Nb target systems are analyzed within a distorted-wave Born approximation (DWBA) framework to constrain the sign and normalization in the central spin-spin parts of the radial form factors and to examine the assembled operator conventions. The calculation reproduces the observed sign systematics of the neutron spin observables for the three targets, indicating that the essential spin-dependent structure is properly incorporated. 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 resultant spin-dependent interactions lead only to a weak modification of the effective barrier and change the fusion cross section by about $0.01$-$0.03\%$ in the present calculation. These results show that the corresponding real spin-dependent correction in the like-channel is strongly suppressed in near-barrier fusion in $p+{}^{93}\mathrm{Nb}$. The present work thus connects the neutron-scattering constraints on the operator conventions with the fusion calculation in the proton channel, and quantifies the magnitude of the corresponding real spin-dependent correction in near-barrier fusion.