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

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.

6 pages, 8 figures, 2 tables. Submitted to proceedings of International Conference on Nuclear Structure and Related Topics - NSRT18 (Bulgaria, Bourgas, June 3-9, 2018). The paper was resubmitted to enlarge the reference list