Neutron scattering from 28Si and 32S from 8.0 to 18.9 MeV, dispersive optical model analyses, and ground-state correlations

摘要

Background: The nucleon-nucleus dispersive optical model (DOM) has been successful in providing good fitsnto scattering data and in making valuable predictions for bound-state properties in single- and double-closed shellnnuclei. However, the generalizability of the DOM remains an ongoing issue.nPurpose: We investigate the DOM in the continuum and bound-state regions of the open-shell, self-conjugatennuclei 28Si and 32S. We collect new differential cross section and analyzing power data for elastic scattering atnincident neutron energies between 8.0 and 18.9 MeV.nMethods: The measurements were conducted using a pulsed deuteron beam, the 2He(d,n)3He source reaction,nand time-of-flight techniques. All data were corrected for finite-geometry effects. Phenomenological DOMnpotentials were tailored to fit the differential and total cross section data, and then extrapolated to the bound-statenregions. The DOM bound-state predictions were then compared to experimental data available for single-particlenenergies, occupation probabilities, root-mean-square radii, and spectroscopic factors.nResults: The DOM bound-state predictions are in only fair agreement with experimental data and with USDnshell-model predictions. Similar results are found after converting our neutron DOMs into proton DOMs.nWe investigate the separate effects of the dispersive surface and volume potential components on occupationnprobability and find that the volume component leads to a uniform depletion of the hole states, while thensurface component acts mainly to deplete the valence orbitals.We compare these results to those of a variationalnmultiparticle multihole configuration mixing (mp-mh CM) calculation using the Gogny D1S effective force.nConclusions: We find that the phenomenological DOM, which was originally designed for spherical nuclei,nshow certain deficiencies when applied to open-shell nuclei and suggest possible avenues of improvement. Wenalso find that the predictions of occupation probability by the DOM using the dispersive surface component arensimilar to those by the mp-mh CM. This lends support to the interpretation that the surface absorption in thenoptical model originates from particle-vibration couplings, that is, long-range correlations.