Low-lying level structure of ${}^{56}$Cu and its implications on the rp process

Abstract

The low-lying energy levels of proton-rich ${}^{56}$Cu have been extracted using in-beam $\gamma$-ray spectroscopy with the state-of-the-art $\gamma$-ray tracking array GRETINA in conjunction with the S800 spectrograph at the National Superconducting Cyclotron Laboratory at Michigan State University. Excited states in ${}^{56}$Cu serve as resonances in the ${}^{55}$Ni(p,$\gamma$)${}^{56}$Cu reaction, which is a part of the rp-process in type I x-ray bursts. To resolve existing ambiguities in the reaction Q-value, a more localized IMME mass fit is used resulting in $Q=639\pm 82$~keV. We derive the first experimentally-constrained thermonuclear reaction rate for ${}^{55}$Ni(p,$\gamma$)${}^{56}$Cu. We find that, with this new rate, the rp-process may bypass the ${}^{56}$Ni waiting point via the ${}^{55}$Ni(p,$\gamma$) reaction for typical x-ray burst conditions with a branching of up to $\sim$40$\%$. We also identify additional nuclear physics uncertainties that need to be addressed before drawing final conclusions about the rp-process reaction flow in the ${}^{56}$Ni region.

8 pages, accepted for Phys. Rev. C

References in corpus (5)

• Proton Drip-Line Calculations and the Rp-process
• Evaluated Experimental Isobaric Analogue States from $T=1/2$ to $T=3$ and associated IMME coefficients
• Statistical Methods for Thermonuclear Reaction Rates and Nucleosynthesis Simulations
• 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

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• Horizons: Nuclear Astrophysics in the 2020s and Beyond
• High-precision mass measurement of ${}^{56}$Cu and the redirection of the rp-process flow
• The Regulated NiCu Cycles with the new ${}^{57}$Cu(p,$\gamma$)${}^{58}$Zn reaction rate and the Influence on Type-I X-Ray Bursts: GS 1826$-$24 Clocked Burster
• On the inversion of isobaric-analogue states in nuclei
• Burning in the tail: implications for a burst oscillation model
• ${}^{57}$Zn $\beta$-delayed proton emission establishes the ${}^{56}$Ni $rp$-process waiting point bypass
• Isospin Mixing and the Cubic Isobaric Multiplet Mass Equation in the Lowest T = 2, A = 32 Quintet
• Second T = 3/2 state in ${}^9$B and the isobaric multiplet mass equation
• Exploring Isospin Symmetry Breaking in Exotic Nuclei: High-Precision Mass Measurement of 23Si and Shell-Model Calculations of T = 5/2 Nuclei