INTERACTING-BOSON-FERMION-APPROXIMATION DESCRIPTION OF NEGATIVE-PARITY STATES IN EVEN-ODD YB ISOTOPES

The negative-parity energy levels of the even-odd Yb isotopes, 163Yb, 165Yb, Yb-169, Yb-171, and Yb-173, are studied systematically within the framework of the extended interacting-boson-fermion-approximation (IBFA) model in which one odd fermion is couplied with a boson core. The boson core is described with the IBA model but allowing one boson to break into a quasifermion pair. The odd fermion is assumed to be in one of the f7/2 and p3/2 single-particle orbitals while the fermion pair is allowed to occupy the single-particle orbit i13/2. It was found that the negative-parity energy levels of these even-odd Yb isotopes and the values of transition quadrupole moments for the ground-state rotational band of Yb-173 can be reproduced in fairly good agreement with the observed data.