Nuclear Lifetimes in $^{79}$Sr

Lifetimes of eight discrete energy states in the $^{79}$Sr nucleus were measured using the Doppler-shift attenuation method. These states were populated at high angular momentum using the $^{28}$Si + $^{54}$Fe fusion-evaporation reaction at 90 MeV, with a thick 14 mg/cm$^{2}$ $^{54}$Fe target used to stop all recoiling nuclei. The de-exciting $\gamma$ rays were measured in prompt coincidence using a Compton-suppressed Ge array consisting of three Clover detectors and seven single-crystal detectors. Lifetimes were determined from experimental line shapes measured at 145$^\circ$ relative to the beam direction. Quadrupole deformations $\beta_2$ inferred from the lifetimes in the two lowest-energy positive-parity state sequences indicate highly deformed structures, in agreement with theoretical predictions from total Routhian surface calculations. Of these two sequences, the one built upon a higher intrinsic energy may have a larger average deformation, in agreement with the theoretical calculations.