Symmetry and order in nuclear structure originating from the proton-neutron degree of freedom

Abstract

Nuclear states of mixed proton-neutron symmetry represent an entire class of nuclear valence shell excitations. We briefly discuss a few milestones in the experimental research on mixed-symmetry states before we present recent progress. The F-spin mixing matrix element has recently been measured for nuclei in the vicinity of the double closed-shell nucleus 208Pb. First assignments of vibrational MSSs in the A ≈ 140 mass region have recently been made by using radioactive ion beams. Moreover, the E2 decay strength of the scissors mode of deformed nuclei has been measured for the first time and an excited member of the K = 1 rotational scissors mode band has been identified for the first time based on transition rates.