Analysis of octupole instability in medium-mass and heavy nuclei

Strutinsky-type potential-energy calculations are performed using various models for the microscopic as well as macroscopic energy terms. The following conclusions are nearly model-independent: Ra-Th nuclei around A {reversed tilde equals} 225 have ground-state equilibrium shapes with both quadrupole and octupole deformation; nuclei in the heavy barium region are just barely unstable with respect to octupole distortion of the quadrupole shape, while lighter nuclei are stable with respect to octupole deformation, albeit softness occurs e.g. in the region of the very light and the very heavy Z {reversed tilde equals} 34 isotopes. Tables of ground-state equilibrium shapes, calculated with the Woods-Saxon potential, are presented for doubly-even nuclei in the Ba and Ra-Th regions of octupole-deformed nuclei.