The ground state mass of $^{73}$Rb from the $\beta$-delayed proton emission of $^{73}$Sr

Nuclear structure along the proton dripline has a significant impact on the rapid-proton capture process. In particular, the nuclear flow is heavily influenced by waiting-points, e.g. $^{72}$Kr, where proton captures are limited by the proton-unbound daughter nucleus. To determine the proton separation energy of $^{73}$Rb, and thus the strength of the $^{72}$Kr waiting point, the beta-delayed proton emission of $^{73}$Sr was studied. $^{73}$Sr was produced by the fragmentation of a $^{92}$Mo primary beam on a Be target and subsequent decays measured via ion implantation-decay correlations at the NSCL. Improvements in the analysis have reduced the low-energy charged-particle background and with a Bayesian analysis the proton separation energy of $^{73}$Rb was determined to be $S_p = -640(40)$ keV. With previous $^{73}$Rb non-observation measurements constraining the mass, our measurement provides a firm determination of $S_p$.