Matter distribution and spin-orbit force in spherical nuclei

TL;DR

This paper explores semi-bubble density structures in spherical nuclei and their impact on spin-orbit splitting and excitation spectra, using Hartree-Fock and RPA methods to analyze specific nuclear properties.

Contribution

It reveals a link between semi-bubble density profiles and reduced spin-orbit splitting, and examines how this affects low-lying excitation energies in nuclei.

Findings

Semi-bubble structures correlate with decreased spin-orbit splitting.

Presence of semi-bubbles influences low-lying 4+ excitation energies.

Study covers 37 spherical nuclei mainly in the s-d shell.

Abstract

We investigate the possibility that some nuclei show density distributions with a depletion in the center, a semi-bubble structure, by using a Hartree-Fock plus Bardeen-Cooper-Schrieffer approach. We separately study the proton, neutron and matter distributions in 37 spherical nuclei mainly in the $s - d$ shell region. We found a relation between the semi-bubble structure and the energy splitting of spin-orbit partner single particle levels. The presence of semi-bubble structure reduces this splitting, and we study its consequences on the excitation spectrum of the nuclei under investigation by using a quasi-particle random-phase-approximation approach. The excitation energies of the low-lying $4^+$ states can be related to the presence of semi-bubble structure in nuclei.