The even-mass Yb isotopes are studied in the boson-plus-fermion-pair model. The energy spectra of the ground-state bands, side bands, quasi-β bands, and quasi-γ bands can be reproduced quite well. It was found that the high-spin states between the second and the first backbends are mainly one-fermion-pair states while those states above the second backbends are mainly two-fermion-pair states. The effective moments of inertia and B(E2) values can be reproduced qualitatively. Some possible extensions of the model are discussed.

• Received 23 April 1990

DOI:https://doi.org/10.1103/PhysRevC.43.2205