Linear polarization measurements and negative-parity states in ${}^{80}\mathrm{Sr}$

High-spin states in ${}^{80}\mathrm{Sr}$ were studied using the ${}^{54}\mathrm{Fe}({}^{28}\mathrm{Si},2p)$ reaction at 90 MeV and the ${}^{58}\mathrm{Ni}({}^{28}\mathrm{Si},\alpha 2p)$ reaction at 110 MeV. Prompt $\gamma \text{−}\gamma$ coincidences were measured from the ${}^{54}\mathrm{Fe}({}^{28}\mathrm{Si},2p)$ reaction using an array of 10 Compton-suppressed Ge detectors. $\gamma$-ray linear polarizations were measured in both reactions using three clover detectors as Compton polarimeters. Negative parity has been conclusively assigned to one band and is favored for two others based on the polarization measurements and the observation of six new linking transitions between the bands near their band heads. This evidence supports a picture of strong mixing between low-lying states with negative parity, similar to what has been observed in ${}^{82}\mathrm{Sr}$. Directional correlation of oriented nuclei ratios support the spin assignments made in the most recent in-beam study.

Figure 1

The level scheme of ${}^{80}\mathrm{Sr}$ below 5 MeV excitation energy as deduced from the present work. Transitions introduced in this work are indicated with asterisks. The energies of all other transitions as well as the labeling scheme of the decay sequences were taken from Ref.  [1].

Figure 2

The measured (dot-dashed line) and theoretically expected (solid and dashed curves) polarizations as a function of the multipole mixing ratio δ for the 1817-keV transition. The solid horizontal lines indicate the experimental uncertainty limits.

Figure 3

A portion of the background-corrected $\gamma$-ray coincidence spectrum projected from a gate on 1917 keV, as measured by all detectors in the ${}^{54}\mathrm{Fe}({}^{28}\mathrm{Si},2p)$ reaction. New transitions placed in the ${}^{80}\mathrm{Sr}$ level scheme are indicated with asterisks.