Effect of non-axial octupole shapes in heavy and superheavy nuclei

摘要

We search for effects of tetrahedral deformation β_(32) over a range of ～3000 heavy and superheavy nuclei, 82 ≤ Z ≤ 126, using a microscopic-macroscopic model based on the deformed Woods-Saxon potential, well tested in the region. We look for the energy minima with a nonzero tetrahedral distortion, both absolute and conditional-with the quadrupole distortion constrained to zero. In order to assure reliability of our results we include the ten most important deformation parameters in the energy minimization. We could not find any cases of stable tetrahedral shapes. The only sizable-up to 0.7 MeV-lowering of the ground state occurs in superheavy nuclei Z ≥ 120 for N = 173-188, as a result of a combined action of two octupole deformations: β_(32) and β_(30), in the ratio β_(32)/β_(30) ≈√3/5. The resulting shapes are moderately oblate, with the superimposed distortion β_(33) with respect to the oblate axis, which makes the equator of the oblate spheroid slightly triangular. Almost all found conditional minima are excited; a handful of them are degenerate with the axial minima.