${}^{57}$Zn $\beta$-delayed proton emission establishes the ${}^{56}$Ni $rp$-process waiting point bypass

Abstract

We measured the ${}^{57}$Zn $\beta$-delayed proton ($\beta$p) and $\gamma$ emission at the National Superconducting Cyclotron Laboratory. We find a ${}^{57}$Zn half-life of 43.6 $\pm$ 0.2 ms, $\beta$p branching ratio of (84.7 $\pm$ 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 ${}^{57}$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.

References in corpus (17)

• A Unified Approach to the Classical Statistical Analysis of Small Signals
• New effective interaction for $pf$-shell nuclei and its implications for the stability of the $N$=$Z$=28 closed core
• Models for Type I X-Ray Bursts with Improved Nuclear Physics
• A Full $PF$ Shell Model Study of a~=~48 Nuclei
• Dependence of X-Ray Burst Models on Nuclear Reaction Rates
• The Effects of Variations in Nuclear Processes on Type I X-Ray Burst Nucleosynthesis
• Nucleosynthesis in Type I X-ray Bursts
• Nuclear Physics of the Outer Layers of Accreting Neutron Stars
• Evaluated Experimental Isobaric Analogue States from $T=1/2$ to $T=3$ and associated IMME coefficients
• Dependence of X-ray Burst Models on Nuclear Masses
• Influence of Nuclear Reaction Rate Uncertainties on Neutron Star Properties Extracted From X-ray Burst Model-Observation Comparisons
• Mass measurements in the vicinity of the doubly-magic waiting point 56Ni
• Observation of the $\beta$-delayed $\gamma$-proton decay of ${}^{56}$Zn and its impact on the Gamow Teller strength evaluation
• Beta decay of the exotic $T_z$ = -2 nuclei ${}^{48}$Fe, ${}^{52}$Ni and ${}^{56}$Zn
• High-precision mass measurement of ${}^{56}$Cu and the redirection of the rp-process flow
• Low-lying level structure of ${}^{56}$Cu and its implications on the rp process
• $\beta$-particle energy-summing correction for $\beta$-delayed proton emission measurements