Total Routhian surface calculations of triaxial or γ-soft properties in even- A N = 76 isotones with 54 ≤ Z ≤ 68**Supported by National Natural Science Foundation of China (10805040, 11175217), Foundation and Advanced Technology Research Program of Henan Province(132300410125), S & T Research Key Program of Henan Province Education Department (13A140667)

Abstract

Total Routhian surface (TRS) calculations for even–even N = 76 isotones with 54 ≤ Z ≤ 68 have been performed in three-dimensional (β2, γ, β4) 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 γ softness 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 γ direction. Such instabilities are also supported by the odd- and even-spin level staggering of the observed γ bands, which is usually used to distinguish between γ-rigid and γ7-soft asymmetry.