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

We measured the Zn-57 beta-delayed proton (beta p) and gamma emission at the National Superconducting Cyclotron Laboratory. We find a Zn-57 half-life of 43.6 +/- 0.2 ms, beta p branching ratio of (84.7 +/- 1.4)%, and identify four transitions corresponding to the exotic beta-gamma-p decay mode, the second such identification in the fp-shell. The p/gamma ratio was used to correct for isospin mixing while determining the Zn-57 mass via the isobaric multiplet mass equation. Previously, it was uncertain as to whether the rp-process flow could bypass the textbook waiting point Ni-56 for astrophysical conditions relevant to Type-I X-ray bursts. Our results definitively establish the existence of the Ni-56 bypass, with 14-17% of the rp-process flow taking this route. (C) 2022 The Author(s). Published by Elsevier B.V.

Automated summary

In this study, the beta-delayed proton and gamma emission of Zn-57 were measured at the National Superconducting Cyclotron Laboratory. The results include the half-life of Zn-57, the branching ratio of beta p, and the transitions corresponding to the beta-gamma-p decay mode. The study definitively establishes the existence of the Ni-56 bypass.