Collective structural evolution in neutron-rich Yb, Hf, W, Os, and Pt isotopes

An interacting-boson-model Hamiltonian determined from Hartree-Fock-Bogoliubov calculations with the microscopic Gogny energy density functional D1M is applied to the spectroscopic analysis of neutron-rich Yb, Hf, W, Os, and Pt isotopes with mass A∼180-200. Excitation energies and transition rates for the relevant low-lying quadrupole collective states are calculated by this method. Transitions from prolate to oblate ground-state shapes are analyzed as a function of neutron number N in a given isotopic chain by calculating excitation energies, B(E2) ratios, and correlation energies in the ground state. It is shown that such transitions tend to occur more rapidly for the isotopes with lower proton number Z when departing from the proton shell closure Z=82. The triaxial degrees of freedom turn out to play an important role in describing the considered mass region. Predicted low-lying spectra for the neutron-rich exotic Hf and Yb isotopes are presented. The approximations used in the model and the possibilities to refine its predictive power are addressed.