Fermion dynamical symmetry model for the even-even and even-odd nuclei in the Xe-Ba region.

The even–even and even–odd nuclei Xe-Xe and Ba-Ba are shown to have a wellrealized SO8 ⊃ SO6 ⊃ SO3 fermion dynamical symmetry. Their low-lying energy levels can be described by a unified analytical expression with two (three) adjustable parameters for even–odd (even–even) nuclei that is derived from the fermion dynamical symmetry model. Analytical expressions are given for wavefunctions and for E2 transition rates that agree well with data. The distinction between the FDSM and IBM SO6 limits is discussed. The experimentally observed suppression of the the energy levels with increasing SO5 quantum number τ can be explained as a perturbation of the pairing interaction on the SO6 symmetry, which leads to an SO5 Pairing effect for SO6 nuclei. PACS number: 21.60.EV, 27.60.+j ∗Permanent address: Physics Department, Nanjing Normal University, Nanjing, 210097, P.R.