Spectral anomalies of even-mass Hg isotopes.

Abstract

The $^{184--200}\mathrm{Hg}$ 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 (${\mathit{i}}_{13/2}$${)}^{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,I\ensuremath{\rightarrow}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.