Total Routhian surface calculations of triaxial orγ-soft propertiesin even-A N=76 isotones with 54≤Z≤68

Abstract：

Total Routhian surface (TRS) calculations for even-even N=76 isotones with 54≤ Z≤68 have been performed in three-dimensional ( β ₂, γ, β ₄) deformation space. Calculated results of the equilibrium deformations are presented and compared with other theoretical predictions and available experimental data. The behavior of collective angular momentum shows the neutron rotation-alignment is preferred in the lighter N=76 isotones, while for the heavier ones the proton alignment is favored. Moreover, multi-pair nucleon alignments and their competition (e.g., in ¹⁴⁴Er) are predicted. It is pointed out that these nuclei in the N=76 isotonic chain exhibit triaxiality or γsoftness in high-spin states as well as ground states. Based on deformation-energy curves with respect to axial and non-axial quadrupole deformations, the shape instabilities are evaluated in detail and predicted, particularly in γdirection. Such instabilities are also supported by the odd- and even-spin level staggering of the observed γbands, which is usually used to distinguish between γ-rigid and γ-soft asymmetry.