Toroidal, compression, and vortical dipole strengths in 124Sn

TL;DR

This paper analyzes the toroidal, compression, and vortical dipole strengths in semi-magic 124Sn using the random-phase-approximation with various Skyrme forces, revealing the dominance of different nuclear currents in each mode and linking the toroidal mode to the pygmy resonance region.

Contribution

It provides a detailed analysis of dipole strength functions in 124Sn, highlighting the roles of convection and magnetization currents across different channels and forces, extending previous work on 208Pb.

Findings

Vortical and toroidal strengths are dominated by convection current in T=0 and by magnetization current in T=1 and 'elm' channels.

Compression strength is always determined by convection current.

The 'elm' strength is similar to T=1 strength and the toroidal mode is associated with the pygmy resonance region.

Abstract

The toroidal, compression and vortical dipole strength functions in semi-magic $^{124}$Sn (and partly in doubly-magic $^{100,132}$Sn) are analyzed within the random-phase-approximation method with the SkT6, SkI3, SLy6, SV-bas, and SkM* Skyrme forces. The isoscalar (T=0), isovector (T=1), and electromagnetic ('elm') channels are considered. Both convection $j_c$ and magnetization $j_m$ nuclear currents are taken into account. The calculations basically confirm the previous results obtained for $^{208}$Pb with the force SLy6. In particular, it is shown that the vortical and toroidal strengths are dominated by $j_c$ in T=0 channel and by $j_m$ in T=1 and 'elm' channels. The compression strength is always determined by $j_c$. It is also shown that the 'elm' strength (relevant for (e,e') reaction) is very similar to T=1 one. The toroidal mode resides in the region of the pygmy resonance. So, perhaps, this region embraces both irrotational (pygmy) and vortical (toroidal) flows.