57Zn β-delayed proton emission establishes the 56Ni rp-process waiting point bypass

We measured the 57 Zn β -delayed proton ( β p ) and γ emission at the National Superconducting Cyclotron Laboratory. We find a 57 Zn half-life of 43 . 6 ± 0 . 2 ms, β p branching ratio of (84 . 7 ± 1 . 4)%, and identify four transitions corresponding to the exotic β - γ - p decay mode, the second such identification in the f p -shell. The p / γ ratio was used to correct for isospin mixing while determining the 57 Zn mass via the isobaric multiplet mass equation. Previously, it was uncertain as to whether the rp -process flow could bypass the textbook waiting point 56 Ni for astrophysical conditions relevant to Type-I X-ray bursts. Our results definitively establish the existence of the 56 Ni bypass, with 14-17% of the rp -process flow taking this route.