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

Abstract As a follow up of Bonneau et al (2024 Phys. Scr. 99 055305), where we studied axial octupole shapes in two-quasiparticle states of even–even nuclei, we investigate this type of shapes in well-deformed odd-mass and odd–odd 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 Bonneau et al (2024 Phys. Scr. 99 055305). We deduce selection rules which can predict, from the single-particle spectra at Q 30 = 0 , whether in a given multi-quasiparticle 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 fully selfconsistent 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 could, in certain cases, be limited by the role of pairing correlations and a strong octupole coupling between quasi-degenerate members of a single-particle parity doublet.