Transition Strengths and Degee of Deformation in 79Sr

High-spin states in 79Sr were studied using the 54Fe(28Si,2pn) reaction at 90 MeV, with a thick 14-mg/cm2 54Fe target used to stop all recoils. Prompt γ−γ coincidences were detected using the Florida State University Compton-suppressed Ge array consisting of three Clover detectors and seven single-crystal detectors. The most recent 79Sr level scheme has been confirmed in three separate band structures up to a spin as high as the (372+) yrast state based on γ-ray coincidence relations, intensity and effective lifetime measurements, and directional correlation of oriented nuclei ratios. Lifetimes of 33 excited states were measured using the Doppler-shift attenuation method, with the experimental line shapes obtained at two separate observation angles and by gating from above the transitions of interest whenever possible. Transition quadrupole moments Qt inferred from the lifetimes indicate a high degree of collectivity and deformation over a rather wide range of spins in all three observed bands, with evidence for modest reductions in the values with increasing spin. The changes in Qt are attributed to the onset of quasiproton alignment and are supported qualitatively by the predictions of the projected shell model and cranked Woods-Saxon calculations in conjunction with the cranked shell model. Lifetimes measured in a band based on the [431]12+ intrinsic Nilsson configuration suggest a large quadrupole deformation (β2≈0.41) associated with this band, providing another example of the strong deformation-driving properties of the d5/2 intruder orbital in the mass 80 region