Octupole deformation in quasiparticle states of odd-mass and odd-odd nuclei

TL;DR

This paper extends the study of octupole deformations to odd-mass and odd-odd nuclei using Skyrme-Hartree-Fock-BCS calculations, introducing a perturbative approach to predict deformation energy minima based on single-particle spectra.

Contribution

It develops a perturbative mechanism and selection rules to predict octupole deformation patterns in odd nuclei, expanding previous work on even-even nuclei.

Findings

Qualitative agreement between predictions and calculations

Quantitative predictions limited by pairing correlations

Strong octupole coupling affects deformation energy curves

Abstract

As a follow up of [Phys. Scr. 99 055305 (2024)], where we studied axial octupole shapes in two-quasiparticle states of even-even nuclei, we investigate this type of shapes in odd-mass and odd-odd well-deformed nuclei, using the Skyrme-Hartree-Fock-BCS approach with selfconsistent blocking and a constraint on the expectation value $Q_{30}$ of the axial octupole moment operator. To interprete the pattern of the resulting deformation energy curve as a function of $Q_{30}$, we extend the perturbative mechanism of Ref. [1]. We deduce selection rules which can predict, from the single-particle spectra at $Q_{30} = 0$, whether in a given multiquasiparticle state the deformation energy curve has a local minimum at a vanishing or a finite value of $Q_{30}$. The predictions of this perturbative mechanism are compared with actual Skyrme-Hartree-Fock-BCS calculations with a constraint on the expectation value $Q_{30}$. Overall we obtain a qualitative agreement and we show that quantitative predictions are limited by the role of pairing correlations and strong octupole coupling between quasi-degenerate members of a single-particle parity doublet.