Proton–neutron structure of low lying collective quadrupole excitations in 126Xe Original Research Article

Low spin states of the nucleus 126Xe were studied by means of γ-spectroscopy using the fusion evaporation reaction 123Te(α,n)126Xe performed at the Cologne fn tandem accelerator. The γγ coincidence and singles spectra were measured with the osiris-cube spectrometer. Beside the ground and quasi-gamma bands many other low lying states were observed. γγ directional correlations from oriented states (DCO) were analyzed to determine the multipolarities of the γ-transitions. We observed dominant E2-transitions in the quasi-gamma band and from the gamma- to the ground band but also a large M1-fraction in the 6+2→61+ transition. We additionally found a strong M1-decay depopulating the 2+4-state at 2064 keV. The lifetime of this state was measured using the Doppler shift attenuation technique. The experimental data are compared with a calculation using the Proton–Neutron Interacting Boson Model (IBM-2). Good agreement is reached in the vicinity of the O(6)-limit. The observed M1-transition of the 2+4 state is interpreted as due to a fragment of the lowest 2+ mixed-symmetry state predicted by the IBM-2.