Evolution of octupole deformation and collectivity in neutron-rich lanthanides

TL;DR

This study investigates the emergence of octupole deformation in neutron-rich lanthanide isotopes using microscopic and bosonic models, revealing significant octupolarity around specific neutron and proton numbers.

Contribution

It combines mean-field calculations with the interacting boson model to predict octupole deformation and spectroscopic properties in lanthanides, a novel integrated approach.

Findings

Reflection asymmetric ground states predicted around N=88.

Pronounced octupolarity observed at Z≈56 and N≈88.

Spectroscopic properties align with experimental trends.

Abstract

The onset of octupole deformation and its impact on related spectroscopic properties is studied in even-even neutron-rich lanthanide isotopes Xe, Ba, Ce, and Nd with neutron number $86\leqslant N\leqslant 94$. Microscopic input comes from the Hartree-Fock-Bogoliubov approximation with constrains on the axially symmetric quadrupole and octupole operators using the Gogny-D1M interaction. At the mean-field level, reflection asymmetric ground states are predicted for isotopes with neutron number around $N=88$. Spectroscopic properties are studied by diagonalizing the interacting boson model Hamiltonian, with the parameters obtained via the mapping of the mean-field potential energy surface onto the expectation value of the Hamiltonian in the $s$, $d$, and $f$ boson condensate state. The results obtained for low-energy positive- and negative-parity excitation spectra as well as the electric dipole, quadrupole, and octupole transition probabilities indicate the onset of pronounced octupolarity for $Z\approx 56$ and $N\approx 88$ nuclei.