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

Valentin Nesterenko,Jan Kvasil,Paul-Gerhard Reinhard,Anton Repko,N Arsenyev,A Vdovin,I Rogov,T Shneidman,A Bezbakh

doi:10.1051/epjconf/201819403005

Abstract

The existence of individual low-energy E1 toroidal and compression states (TS and CS) in 24Mg 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 24Mg 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, 24Mg and 20Ne, we show that the lowest TS is not a universal phenomenon but rather a peculiarity of 24Mg. The spectroscopy of TS and CS is analyzed and some additional interpretation of these states is suggested.

Highlights

In a recent publication [1], we have predicted the occurence of individual low-energy E1 toroidal and compressional states (TS and CS) in 24Mg
The calculations were performed within the quasiparticle random phase approximation (QRPA) method using several Skyrme forces
Eq (1), for K=1 dipole states are depicted for different deformations [1], including the calculated equilibrium deformation β=0.536

Summary

Introduction

In a recent publication [1], we have predicted the occurence of individual low-energy E1 toroidal and compressional states (TS and CS) in 24Mg. Note that (α, α′) is determined by the transition density while TDR is produced by the vortical nuclear current In this respect, the individual low-energy E1(T =0) TS in light nuclei have significant advantages over the TDR. [1], the TS in axially deformed 24Mg appears as the lowest (E=7.92 MeV) dipole state with K=1 (K is the projection of the total angular momentum to the symmetry z-axis) It is well separated from the neighbouring dipole states, which simplifies its experimental identification and exploration as compared to the TDR. Just the large axial quadrupole deformation makes the TS an individual mode, well separated from other states We consider spectroscopic properties of TS and CS and suggest their interpretation in terms of lowenergy T =0 dipole states with isospin-forbidden E1 transition (for TS) and octupole mode (for CS)

Calculation scheme

Results and discussion

Conclusions