Identification of Excited States in the Tz=+1/2 Nucleus 75Rb: The Quest for Experimental Signatures of Collective Neutron-proton Correlations

Excited states in the T-z-1/2 nucleus Rb-75 were observed for the first time using the Ca-40(Ca-40,alpha p) reaction at 128 MeV. Identification was achieved using events detected by the Daresbury recoil separator in coincidence with gamma rays detected in the 45 element EUROGAM I Ge-detector array. Threefold events were used to build a decay scheme which consists of two rotational bands observed to I-pi=(45+/2) and I-pi=(33-/2). The positive parity band in Rb-75 behaves similarly to a negative-parity band in Kr-74 and contains a region of alignment at (h) over bar omega approximate to 0.75 MeV. These data, and those of Sr-77, be interpreted by treating protons and neutrons separately in a cranked shell model approach despite a recent suggestion for the presence of T=1 neutron-proton pairing correlations in the neighboring self-conjugate, odd-odd Rb-74 ground state band. Our study suggests that some experimental observables such as the energy levels and moments of inertia, may not be able to differentiate between different T=1 pairing phases in these T-z=1/2 nuclei. (Less)