Octupole deformation for Ba isotopes in a reflection-asymmetric relativistic mean-field approach

The potential energy surfaces of even-even Ba142-156 are investigated in the constrained reflection-asymmetric relativistic mean-field approach with parameter set PK1. It is shown that for the ground states, Ba-142 is near spherical, Ba-156 well quadrupole-deformed, and in between Ba144-154 octupole deformed. In particular, the nuclei Ba-148,Ba-150 with N=92, 94 have the largest octupole deformations. By including the octupole degree of freedom, energy gaps N = 88, N = 94 and Z = 56 near Fermi surfaces for the single-particle levels in Ba-148 with beta(2) similar to 0.26 and beta(3) similar to 0.17 are found. Furthermore, the performance of the octupole deformation driving pairs (nu 2f(7/2), nu 1i(13/2)) and (pi 2d(5/2), pi 1h(11/2)) is demonstrated by analyzing the single-particle levels near Fermi surfaces in Ba-148.