Description of the evolution of mixed-symmetry states in the N = 78 isotonic chain with IBM2**Supported by National Natural Science Foundation of China (11475062) and Natural Science Foundation of Zhejiang Province, China (KY6100135)

Abstract

The characteristics of the lowest mixed-symmetry states 2+ms and 1+ms for 132Xe, 134Ba and 136Ce in the even-even N = 78 isotones are investigated within the framework of the IBM2 model. The lowest mixed-symmetry state 2+ms levels for both a single isolated state in 132Xe and 136Ce and a fragmented state in 134Ba are reproduced by the predictions. The agreement between the IBM2 calculation and the experimental values is good for the B(E2) and B(M1) transition probabilities both quantitatively and qualitatively. The predicted summed B(M1) strength follows the experimental data, remaining nearly constant as a function of proton number along the chain of the N = 78 isotones.