Non-Axial Octupole Deformations and Tetrahedral Symmetry in Heavy Nuclei

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The total energies of about 120 nuclei in the Thorium region have been calculated within the macroscopic‐microscopic method in the 5‐dimensional space of deformation parameters α20, α22, α30, α32 and α40. The macroscopic energy term contains the nuclear surface‐curvature dependence as proposed within the LSD approach. The microscopic energies are calculated with the Woods‐Saxon single particle potential employing the universal set of parameters.We study a possible presence of the octupole axial and non‐axial degrees of freedom all‐over in the (β, γ)‐plane focussing on the ground‐states, secondary minima and in the saddle points. In fact, a competition between axial and tri‐axial octupole deformation parameters is obtained at the saddle points and in the secondary minima for many isotones with N > 136. The presence of the tetrahedral symmetry minima is predicted in numerous nuclei in the discussed region, although most of the time at relatively high excitation energies.