Alternating-Parity Collective States of Heavy Nonaxial Even-Even Nuclei with Quadrupole and Octupole Deformations

A nonadiabatic collective model is developed for nonaxial even-even nuclei featuring quadrupole and octupole deformations. Asymmetric quadrupole and octupolemodes are taken into account effectively. Analytic expressions for the energies of levels are obtained on the basis of the developed model. These expressions contain five adjustable parameters that are determined from a comparison of theoretical and experimental data. The angular part of polar coordinates is used as one of the parameters of the equilibrium state of the even-even nucleus being considered. A good description is obtained for the collective states of the alternating-parity yrast and first non-yrast bands of the following heavy nonaxial even-even nuclei: Nd-150, Sm-152,Sm-154, Yb-172, Th-228,Th-230,Th-232, U-232,U-234,U-236,U-238, and Pu-240. In the Appendix, the kinetic energy of octupole vibrations is quantized in curvilinear coordinates.