Microscopic analysis of low-energy spin and orbital magnetic dipole excitations in deformed nuclei

Nesterenko V.O. Vishnevskiy P.I. Kvasil J. Repko A. Kleinig W.
June 2021 American Physical Society

Physical Review C
2021 #103 Issue 6

A low-energy magnetic dipole (M1) spin-scissors resonance (SSR) located just below the ordinary orbital scissors resonance (OSR) was recently predicted in deformed nuclei within the Wigner function moments (WFM) approach. We analyze this prediction using fully self-consistent Skyrme quasiparticle random phase approximation (QRPA) method. Skyrme forces SkM∗, SVbas, and SG2 are implemented to explore SSR and OSR in Dy160,162,164 and Th232. Accuracy of the method is justified by a good description of M1 spin-flip giant resonance. The calculations show that isotopes Dy160,162,164 indeed have at 1.5-2.4 MeV (below OSR) IπK=1+1 states with a large M1 spin strength (K is the projection of the total nuclear moment to the symmetry z axis). These states are almost fully exhausted by pp[411↑,411↓] and nn[521↑,521↓] spin-flip configurations corresponding to pp[2d3/2,2d5/2] and nn[2f5/2,2f7/2] structures in the spherical limit. So the predicted SSR is actually reduced to low-orbital (l=2,3) spin-flip states. Following our analysis and in contradiction with WFM spin-scissors picture, deformation is not the principle origin of the low-energy spin M1 states but only a factor affecting their features. The spin and orbital strengths are generally mixed and exhibit interference: weakly destructive in SSR range and strongly constructive in OSR range. In Th232, the M1 spin strength is very small. Two groups of Iπ=1+ states observed experimentally at 2.4-4 MeV in Dy160,162,164 and at 2-4 MeV in Th232 are mainly explained by fragmentation of the orbital strength. Distributions of nuclear currents in QRPA states partly correspond to the isovector orbital-scissors flow but not to the spin-scissors one.

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Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, Dubna, Moscow Region, 141980, Russian Federation
State University Dubna, Moscow Region, Dubna, 141980, Russian Federation
Moscow Institute of Physics and Technology, Moscow Region, Dolgoprudny, 141701, Russian Federation
Institute of Nuclear Physics, Almaty, 050032, Kazakhstan
Institute of Particle and Nuclear Physics, Charles University, Praha 8, CZ-18000, Czech Republic
Institute of Physics, Slovak Academy of Sciences, Bratislava, 84511, Slovakia

Laboratory of Theoretical Physics
State University Dubna
Moscow Institute of Physics and Technology
Institute of Nuclear Physics
Institute of Particle and Nuclear Physics
Institute of Physics

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