Semiclassical origin of nuclear ground-state octupole deformations

Abstract

Background: Ground-state octupole deformations are suggested in nuclei located in the north-east neighbor of the doubly magic nuclei on the nuclear chart (N,Z), such as those in Ba and Ra-Th regions. This systematics has been attributed to the parity mixing of the approximately degenerate Delta l=3 pair of single-particle levels near the Fermi surface. Purpose: Nuclear deformations are governed in most cases by the gross shell structures of the single-particle spectra. I will consider the systematics in octupole deformation from the view point of the gross shell structure, and investigate the mechanism of its manifestation using the semiclassical periodic-orbit theory (POT), which describes the quantum shell effect by means of the periodic orbits (POs) in the corresponding classical system. Methods: To focus on the role of deformation, simplified infinite-well (cavity) and radial power-law potential models are employed taking account of quadrupole and octupole shape degrees of freedom. Nuclear ground-state deformations are investigated over the nuclear chart, and the properties of the deformed shell structures are analyzed by means of the semiclassical POT. Results and conclusions: The systematics in nuclear ground-state octupole deformations are reproduced in simplified mean-field potential models either with or without parity mixing between Delta l=3 pair of levels. The strong octupole deformed shell effect at above the spherical shell closures are explained simply and clearly using the semiclassical POT. They are associated with the local restoration of dynamical symmetry, which enhance the contribution of classical POs to the gross shell effect.

arXiv comment13 pages, 20 figures

References in corpus (21)

• Global systematics of octupole excitations in even-even nuclei
• Octupole deformation in the ground states of even-even nuclei: a global analysis within the covariant density functional theory
• Nuclear Tetrahedral Symmetry: Possibly Present Throughout the Periodic Table
• Effect of shell structure on the fission of sub-lead nuclei
• Bifurcations of Periodic Orbits and Uniform Approximations
• Landscape of pear-shaped even-even nuclei
• Fission modes of mercury isotopes
• Cluster Radioactivity in Super Heavy Nuclei
• Cluster radioactivity of ${}_{118}^{294}$Og${}_{176}$
• Octupole deformation in the nuclear chart based on the 3D Skyrme Hartree-Fock plus BCS model
• Spectroscopic Criteria for Identification of Nuclear Tetrahedral and Octahedral Symmetries: Illustration on a Rare Earth Nucleus
• Symmetry Breaking and Bifurcations in the Periodic Orbit Theory: II -- Spheroidal Cavity --
• Periodic orbits near bifurcations of codimension two: Classical mechanics, semiclassics, and Stokes transitions
• Classcial Bifurcation and Enhancement of Quantum Shells --- Systematic Analysis of Reflection-Asymmetric Deformed Oscillator ---
• Nuclear prolate-shape dominance with the Woods-Saxon potential
• Periodic-orbit approach to the nuclear shell structures with power-law potential models: Bridge orbits and prolate-oblate asymmetry
• Semiclassical origin of anomalous shell effect for tetrahedral deformation in radial power-law potential model
• Nuclear shell structures in terms of classical periodic orbits
• Periodic-Orbit Bifurcation and Shell Structure in Reflection-Asymmetric Deformed Cavity
• Anomalous shell effect in the transition from a circular to a triangular billiard
• Octupole deformation of nuclei near the spherical closed-shell configurations