SPECTRAL ANOMALIES OF EVEN-MASS HG ISOTOPES

The Hg-184-200 isotopes are studied in the interacting-boson-approximation-plus-fermion-pair model. In general, energy levels up to I=22 can be reproduced quite well. In the low excitation energy region both the shape evolution and the (8+, 10+, 12+) triplet structure can be reproduced. The (8+,10+,12+) triplet structure can be understood as the saturation of isospin 1 fermion-pair interaction at the high spin end. The termination of triplet structure at I=12 strongly supports the (i13/2)2 band crossing. Striking agreements between the observed energy gaps of (14(1)+,12(1)+) and (2(1)+,0(1)+) states are considered as an indication of weak coupling between the boson core and the fermion pair. The B(E2,1-->I-2) are calculated and the spin dependence of the B(E2) values can be reproduced qualitatively. However, the detailed mass dependence is not correctly reproduced.