Triaxial superdeformed bands in odd-odd Lu~(160~168) isotopes

摘要

The triaxial superdeformed rotational bands in the odd-odd Lu~(160~168) isotopes are investigated by performing the configuration dependent three-dimensional total routhian surface calculations. About fifty low lying triaxial superdeformed bands have been found for these odd-odd nuclei within the excitation energy of 3 MeV above the normal deformed yrast bands. The calculated equilibrium elongation, triaxial and hexadecapole deformations for these triaxial superdeformed bands are close to the values of ε_2~0.4, γ~20° and ε4~0.03, respectively. The configurations of calculated triaxial superdeformed bands have been assigned based on the total routhian surface calculations and the analysis of quasiparticle routhians in the rotating frame. The observed yrast triaxial superdeformed band of ~(164)Lu, where the linking transitions between superdeformed and normal deformed states are measured, have been reproduced by the present calculation in the relative energy to the normal deformed band. We show that the stability of superdeformed triaxial shapes in the odd-odd Lu isotopes is similar to that presented in odd-even Lu nuclei, and thus the wobbling excitations could be expected to occur in odd-odd Lu isotopes. The deformation driving effect of the proton high-j low-K orbit play an important role in the formation of the triaxial superdeformed states in both odd-odd and odd-even Lu isotopes, while the shell effect is a fundamental factor for the triaxial superdeformed shapes. The shell gaps and the positions of the deformation driving intruder orbits which are responsible for the triaxial superdeformed minima have been localized, particularly, the neutron N=94 gap and the position of the proton [660]1/2 orbit in the deformed single particle diagram provide the basis for a microscopic understanding of the observed triaxial superdeformed bands in the mass region.