Total Routhian surface calculations of triaxial or γ-soft properties in even-A N = 76 isotones with 54 ≤ Z ≤ 68

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 γ-soft asymmetry. (authors)