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 addressedThis work was supported in part by Grants-in-Aid for Scientific Research (A)No. 20244022 and No. 217368. Author K.N. acknowledges the support by the JSPS. The work of authors R.R., L.M.R, and P.Swas supported by MICINN (Spain) under Research Grants No. FIS2008-01301, No. FPA2009-08958, and No. FIS2009-07277, as well as by Consolider-Ingenio 2010 Programs CPAN CSD2007-00042 and MULTIDARK CSD2009-0006