Effect of configuration mixing on quadrupole and octupole collective states of transitional nuclei

TL;DR

This paper develops a nuclear model combining density functional theory and the interacting boson model to study shape coexistence and collective excitations, emphasizing configuration mixing effects on energy levels and nuclear shapes.

Contribution

It introduces an optimal Hamiltonian incorporating configuration mixing and octupole degrees of freedom, derived from self-consistent mean-field calculations for transitional nuclei.

Findings

Configuration mixing lowers excited 0+ energy levels.

Low-lying positive-parity states show shape admixture.

Negative-parity states are dominated by intruder configurations.

Abstract

A model is presented that simultaneously describes shape coexistence and quadrupole and octupole collective excitations within a theoretical framework based on the nuclear density functional theory and the interacting boson model. An optimal interacting-boson Hamiltonian that incorporates the configuration mixing between normal and intruder states, as well as the octupole degrees of freedom, is identified by means of self-consistent mean-field calculations using a universal energy density functional and a pairing interaction, with constraints on the triaxial quadrupole and the axially-symmetric quadrupole and octupole shape degrees of freedom. An illustrative application to the transitional nuclei $^{72}$Ge, $^{74}$Se, $^{74}$Kr, and $^{76}$Kr shows that the inclusion of the intruder states and the configuration mixing significantly lower the energy levels of the excited $0^+$ states, and that the predicted low-lying positive-parity states are characterized by the strong admixture of nearly spherical, weakly deformed oblate, and strongly deformed prolate shapes. The low-lying negative-parity states are shown to be dominated by the deformed intruder configurations.