The effect of the partial subshell closure near Z=64 is studied by introducing the effective boson number in the framework of the interacting boson model. The energy spectra and the B(E2) values of the Sm, Gd, and Dy isotope series are calculated. It is found that the agreements between the theoretical results and the observed data are very satisfactory when the partial closure effect is taken into account by a smooth variation of the effective proton-boson numbers.

• Received 21 November 1989

DOI:https://doi.org/10.1103/PhysRevC.42.280