Mixed-Symmetry Multiphonon Structures and First Evidence for F-Vector e1 Transitions

Recent gamma-ray spectroscopy of off-yrast low-spin states of Mo-94 yielded evidence for one-phonon and two-phonon states with mixed proton-neutron symmetry, a phenomenon anticipated by Franco Iachello and collaborators in the framework of the interacting boson model (IBM-2). The mixed-symmetry assignments are based on the measurement of absolute M1 matrix elements, approximate to 1 mu(N) in size. Corresponding structures were lateron found in other soft nuclei. We give a brief overview over the recent investigations of mixed-symmetry multiphonon structures and we discuss for the first time the observation of F-vector El transitions involving mixed-symmetry states.