Evolution of octupole deformation and collectivity in neutron-rich lanthanides
K. Nomura, R. Rodrı́guez-Guzmán, L. M. Robledo, J. E. García-Ramos, Norge Cruz Hernández
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 $86\ensuremath{\leqslant}N\ensuremath{\leqslant}94$. 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 $Z\ensuremath{\approx}56$ and $N\ensuremath{\approx}88$ nuclei.