High-Precision Mass Measurement of Cu-56 and the Redirection of the rp-Process Flow

A. A. Valverde, Matthew Redshaw, Kerim Gulyuz

Research output: Contribution to journalArticlepeer-review


We report the mass measurement of Cu56, using the LEBIT 9.4 T Penning trap mass spectrometer at the National Superconducting Cyclotron Laboratory at Michigan State University. The mass of Cu56 is critical for constraining the reaction rates of the Ni55(p,γ) Cu56(p,γ) Zn57(β+) Cu57 bypass around the Ni56 waiting point. Previous recommended mass excess values have disagreed by several hundred keV. Our new value, ME=-38626.7(7.1) keV, is a factor of 30 more precise than the extrapolated value suggested in the 2012 atomic mass evaluation [Chin. Phys. C 36, 1603 (2012)CPCHCQ1674-113710.1088/1674-1137/36/12/003], and more than a factor of 12 more precise than values calculated using local mass extrapolations, while agreeing with the newest 2016 atomic mass evaluation value [Chin. Phys. C 41, 030003 (2017)CPCHCQ1674-113710.1088/1674-1137/41/3/030003]. The new experimental average, using our new mass and the value from AME2016, is used to calculate the astrophysical Ni55(p,γ) and Cu56(p,γ) forward and reverse rates and perform reaction network calculations of the rp process. These show that the rp-process flow redirects around the Ni56 waiting point through the Ni55(p,γ) route, allowing it to proceed to higher masses more quickly and resulting in a reduction in ashes around this waiting point and an enhancement to higher-mass ashes.

Original languageEnglish
Pages (from-to)032701
JournalPhysical Review Letters
StatePublished - Jan 19 2018


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