Collective bands in the triaxial nucleus Xe

The nonyrast states of 124 Xe have been investigated with the 123 Te ( 3 He , 2 n ) reaction by means of in-beam γ -spectroscopy using a setup of 6 Compton-suppressed high-purity-germanium (HPGe) detectors. More than 65 new transitions, establishing 34 new levels, were observed. γγ -angular correlations were analyzed to assign spins and parities to the low-lying states, and to determine the multipolarities of the γ -transitions. In addition, the γ -excitation-function method was used for spin assignments. With these methods 10 (18) spin and parity assignments were made (some of them tentative) and 7 multipole mixing ratios could be determined. The excitation energies and B (E2) ratios of low-lying states are compared with predictions of the sd-IBM-1, giving rise to the identification of a 0 + state with O(6) quantum number σ=N−2 . Quadrupole shape invariants for the ground state and effective deformation parameters are calculated, showing an admixture of U(5) symmetry to the ground-state wave function.