Low-Energy M1 States in Deformed Nuclei: Spin Scissors or Spin-Flip?

Abstract

The low-energy $$M$$ 1 states in deformed $${}^{164}$$ Dy and spherical $${}^{58}$$ Ni are explored in the framework of fully self-consistent Quasiparticle Random-Phase Approximation (QRPA) with various Skyrme forces. The main attention is paid to orbital and spin $$M$$ 1 excitations. The obtained results are compared with the prediction of the low-energy spin-scissors $$M$$ 1 resonance suggested within Wigner Function Moments (WFM) approach. A possible relation of this resonance to low-energy spin-flip excitations is analyzed. In connection with recent WFM studies, we consider evolution of the low-energy spin-flip states in $${}^{164}$$ Dy with deformation (from the equilibrium value to the spherical limit). The effect of tensor forces is briefly discussed. It is shown that two groups of $$1^{+}$$ states observed at 2.4–4 MeV in $${}^{164}$$ Dy are rather explained by fragmentation of the orbital $$M$$ 1 strength than by the occurrence of the collective spin-scissors resonance. In general, our calculations do not confirm the existence of this resonance.