Individual low-energy E1 toroidal and compression states in light nuclei: deformation effect, spectroscopy and interpretation

TL;DR

This paper investigates low-energy E1 toroidal and compression states in light nuclei, focusing on $^{24}$Mg, and explains how deformation influences their energy positioning and spectroscopic features.

Contribution

It provides a mean-field explanation for the deformation-induced low-energy E1 states in $^{24}$Mg and compares these states with those in $^{20}$Ne to highlight their non-universal nature.

Findings

Deformation shifts toroidal strength to low energies in $^{24}$Mg.

Lowest TS is specific to $^{24}$Mg, not universal.

Spectroscopic analysis offers new interpretation of these states.

Abstract

The existence of individual low-energy E1 toroidal and compression states (TS and CS) in $^{24}$Mg was predicted recently in the framework of quasiparticle random-phase-approximation (QRPA) model with Skyrme forces. It was shown that the strong axial deformation of $^{24}$Mg is crucial to downshift the toroidal strength to the low-energy region and thus make the TS the lowest E1(K=1) dipole state. In this study, we explain this result by simple mean-field arguments. Comparing TS in two strongly axial nuclei, $^{24}$Mg and $^{20}$Ne, we show that the lowest TS is not not a universal phenomenon but rather a peculiarity of $^{24}$Mg. The spectroscopy of TS and CS is analyzed and some additional interpretation of these states is suggested.