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

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.

💡 Research Summary

In this work the authors extend the study of axial octupole deformation, previously performed for two‑quasiparticle (2‑qp) states in even‑even nuclei, to the much richer domain of odd‑mass (odd‑A) and odd‑odd nuclei. The calculations are carried out within the Skyrme‑Hartree‑Fock‑BCS (SHF‑BCS) framework using the SIII Skyrme functional, a constant‑pairing BCS scheme, and a self‑consistent blocking procedure that treats the unpaired nucleon(s) explicitly and thus breaks time‑reversal symmetry. The single‑particle basis is an axially deformed harmonic‑oscillator set (N₀=14–16, with appropriate oscillator lengths and deformation parameters) and the axial octupole moment operator

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