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

• Published in: Physics letters. B 2022-06, Vol.829
• Main Authors: Saxena, M., Ong, W.-J, Meisel, Z., Hoff, D.E.M., Smirnova, N., Bender, P.C., Burcher, S.P., Carpenter, M.P., Carroll, J.J., Chester, A., Chiara, C.J., Conaway, R., Copp, P.A., Crider, B.P., Derkin, J., Estradé, A., Hamad, G., Harke, J.T., Jain, R., Jayatissa, H., Liddick, S.N., Longfellow, B., Mogannam, M., Montes, F., Nepal, N., Ogunbeku, T.H., Richard, A.L., Schatz, H., Soltesz, D., Subedi, S.K., Sultana, I., Tamashiro, A.S., Tripathi, V., Xiao, Y., Zink, R.
• Format: Article
• Language: English
• Subjects: Astrophysics; Nuclear Theory; Physics
• ISSN: 0370-2693
• DOI: 10.1016/j.physletb.2022.137059

•In our letter, we address the dominant uncertainty regarding the extent of the rp-process flow bypass around Ni 56 waiting point for astrophysical conditions relevant to Type-1 X-ray bursts.•We removed the final significant uncertainty, the beta-delayed proton branching ratio for Zn 57 , definitively determining that there is a Ni 56 bypass.•In addition, we also identified the second case of the exotic β − γ − p decay mode in the fp-shell. We measured the Zn 57 β-delayed proton (βp) and γ emission at the National Superconducting Cyclotron Laboratory. We find a Zn 57 half-life of 43.6±0.2 ms, βp 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 fp-shell. The p/γ 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.