The existence of two close-lying nuclear states in ${}^{73}\mathrm{Ga}$ has recently been experimentally determined: a $1/2^{-}$ spin-parity for the ground state was measured in a laser spectroscopy experiment, while a ${\mathrm{J}}^{\pi }=3/2^{-}$ level was observed in transfer reactions. This scenario is supported by Coulomb excitation studies, which set a limit for the energy splitting of 0.8 keV. In this work, we report on the study of the excited structure of ${}^{73}\mathrm{Ga}$ populated in the $\beta$ decay of ${}^{73}\mathrm{Zn}$ produced at ISOLDE, CERN. Using $\beta$-gated, $\gamma$-ray singles, and $\gamma -\gamma$ coincidences, we have searched for energy differences to try to delimit the ground-state energy splitting, providing a more stringent energy difference limit. Three new half-lives of excited states in ${}^{73}\mathrm{Ga}$ have been measured using the fast-timing method with ${\mathrm{LaBr}}_3$(Ce) detectors. From our study, we help clarify the excited structure of ${}^{73}\mathrm{Ga}$ and we extend the existing ${}^{73}\mathrm{Zn}$ decay to ${}^{73}\mathrm{Ga}$ with 8 new energy levels and 35 $\gamma$ transitions. We observe a 195-keV transition consistent with a $\gamma$ ray de-exciting a short-lived state in the $\beta$-decay parent ${}^{73}\mathrm{Zn}$.

• Received 25 April 2017

DOI:https://doi.org/10.1103/PhysRevC.96.034311