SPS Outstanding Student Award for Undergraduate Research Talk: Lifetime Measurements and Deformation in 79Sr

High-spin states in $^{79}$Sr were produced following the $^{54}$Fe($^{28}$Si, 2\textit{pn}) fusion-evaporation reaction using a beam kinetic energy of 90 MeV at the Florida State University (FSU) Tandem-Linac particle accelerator facility, and the resulting de-exciting $\gamma $ rays were detected with the FSU array of 10 Compton-suppressed high-purity Ge detectors comprised of three Clover detectors and seven single-crystal detectors.~ The synthesized nuclei were stopped completely in the target, resulting in Doppler-shifted $\gamma $-ray line shapes that could be analyzed using the Doppler-shift attenuation method. The experimental line shapes were acquired at detection angles of 35\r{ } and 145\r{ }, and the resulting Doppler-shifted peaks were analyzed to extract the lifetime of their parent states.~ In all, 23 lifetimes were measured in three separate band structures using this method, and then used to infer transition quadrupole moments ($Q_{t})$ and quadrupole deformations ($\beta _{2})$ using the rotational model. The resulting $Q_{t}$ values indicated a high degree of collectivity and deformation in all three observed sequences of excited states (bands) with only a modest decline in collectivity with increasing angular momentum.~ The results show good qualitative agreement with the predictions of both cranked Woods-Saxon (CWS) and projected shell model (PSM) calculations.~ In addition, the pattern of excited energy states and their de-exciting gamma-ray transitions (level scheme) was re-examined and compared to the most recent study of $^{79}$Sr using $\gamma -\gamma $ coincidence measurements, intensity measurements, and directional correlation of oriented nuclei (DCO) ratios in addition to the lifetime measurements.~ Overall, the level scheme was verified, with the exception of the re-arrangement of one transition.~ The band based on the intrinsic $d_{5/2}$ single-particle orbital from the shell model, was found to have the largest average deformation ($\beta _{2}$,ave = 0.41) among the three observed bands, in agreement with the CWS and PSM theoretical predictions