Microscopic analysis of dipole electric and magnetic strengths in $^{156}$Gd

TL;DR

This paper uses a self-consistent QRPA approach with Skyrme forces to analyze electric and magnetic dipole strengths in deformed $^{156}$Gd, exploring various resonances and modes, and comparing results with experimental data.

Contribution

It provides a comprehensive theoretical analysis of dipole excitations in $^{156}$Gd, including new insights into the origin of resonances and the effects of residual interactions.

Findings

Good agreement with most experimental data

Identification of the origin of the SFGR structure

Demonstration of the impact of the $ extbf{J}^2$-term

Abstract

The dipole electric ($E1$) and magnetic ($M1$) strengths in strongly deformed $^{156}$Gd are investigated within a fully self-consistent Quasiparticle Random Phase Approximation (QRPA) with Skyrme forces SVbas, SLy6 and SG2. We inspect, on the same theoretical footing, low-lying dipole states and the isovector giant dipole resonance in $E1$ channel and the orbital scissors resonance as well as the spin-flip giant resonance (SFGR) in $M1$ channel. Besides, $E1$ toroidal mode and low-energy spin-flip $M1$ excitations are considered. The deformation splitting and dipole-octupole coupling of electric excitations are analyzed. The origin of SFGR gross structure, impact of the residual interaction and interference of orbital and spin contributions to SFGR are discussed. The effect of the central exchange $\textbf{J}^2$-term from the Skyrme functional is demonstrated. The calculations show a satisfactory agreement with available experimental data, except for the recent NRF measurements of M. Tamkas et al for $M1$ strength at 4-6 MeV, where, in contradiction with our calculations and previous $(p,p')$ data, almost no $M1$ strength was observed.