Our high-resolution study of near-threshold states in 40Ca was recently published in Physical Review Letters! It was the first study to determine the proton spectroscopic factors of states important for potassium burning through the 39K(p,γ)40Ca reaction.
Led by Dr. Will Fox, we performed a high-resolution study of proton-unbound states in 40Ca that are important for potassium destruction in globular clusters. Previous astronomical studies have found that the globular cluster NGC 2419 exhibits a strong anticorrelation between potassium and magnesium that is hard to understand through standard chemical evolution models in these clusters. However, stellar models used to model this chemical evolution are poorly constrained because the nuclear reaction cross section inputs are highly uncertain. The $^{39}$K(p,$\gamma$)$^{40}$Ca reaction is one such reaction, which was found to be uncertain by about two orders of magnitude.
Our differential cross section data for key states in 40Ca. These are overlaid with the Distorted Wave Born Approximation reaction model results used to constrain the rate of the $^{39}$K($^3$He,d)$^{40}$Ca reaction.
In our work, we performed a $^{39}$K($^3$He,d)$^{40}$Ca proton transfer reaction measurement to populate proton-unbound states in $^{40}$Ca. We resolved the key excited state corresponding to the 154-keV resonance for the first time, increasing the recommended reaction rate by a factor of 13 and reducing its uncertainty by a factor of 42. We also performed nucleosynthesis calculations, showing that the temperatures at which potassium is destroyed in stars may be lower than previously assumed.
