Evolution of shape and rotational structure in neutron-deficient 118-128Ba nuclei

The evolution of shape and rotational structure along the yrast line in even–even 118−128 Ba isotopes has been systematically investigated by means of pairing self-consistent Woods–Saxon– Strutinsky calculations using the total Routhian surface approach in (β2, γ , β4) deformation space. Based on deformation Routhian curves at different rotational frequencies, the shape instability and softness are evaluated and/or predicted in detail, particularly in the γ direction. The backbending or upbending behavior due to the alignments of neutron or proton h11/2 orbitals in moments of inertia can be basically reproduced, indicating the necessity for the adjustment of the pairing force strength to the experimental data. It is found that the competition between the proton and neutron alignments may depend sensitively on nuclear shape (e.g., in 126 Ba). In addition, the evolution and transition between vibrational and rotational collective modes along the yrast line are investigated on the basis of the centipede-like E-GOS (E-gamma over spin) curves, showing that the existing disagreement between theory and experiment may be to some extent attributed to a lack of the vibration mechanism in the present model.