Microscopic origin of reflection-asymmetric nuclear shapes

Mengzhi Chen, Tong Li, Jacek Jan Dobaczewski, Witold Nazarewicz

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The presence of nuclear ground states with stable reflection-asymmetric shapes is supported by rich experimental evidence. Theoretical surveys of odd-multipolarity deformations predict the existence of pear-shaped isotopes in several fairly localized regions of the nuclear landscape in the vicinity of near-lying single-particle shells with Delta_ell=Delta_j=3.

We analyze the role of isoscalar, isovector, neutron-proton, neutron-neutron, and proton-proton multipole interaction energies in inducing the onset of reflection-asymmetric ground-state deformations.

The calculations are performed in the framework of axial reflection-asymmetric Hartree-Fock-Bogoliubov theory using two Skyrme energy density functionals and density-dependent pairing force.

We show that reflection-asymmetric ground-state shapes of atomic nuclei are driven by the odd-multipolarity neutron-proton (or isoscalar) part of the nuclear interaction energy. This result is consistent with the particle-vibration picture, in which the main driver of octupole instability is the isoscalar octupole-octupole interaction giving rise to large E3 polarizability.

The necessary condition for the appearance of localized regions of pear-shaped nuclei in the nuclear landscape is the presence
of parity doublets involving Delta_ell=Delta_j=3 proton or neutron single-particle shells. This condition alone is, however, not sufficient to determine whether pear shapes actually appear, and -- if so -- what the corresponding reflection-asymmetric deformation energies are.
The predicted small reflection-asymmetric deformation energies result from dramatic
cancellations between even- and odd-multipolarity components of the nuclear binding energy.
Original languageEnglish
Article number034303
JournalPhysical Review C - Nuclear Physics
Issue number3
Publication statusPublished - 3 Mar 2021

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