First direct measurement of the ³⁴Ar(α,p)³⁷K reaction cross section for x-ray burst nucleosynthesis

As the final step in the αp process, the ³⁴Ar(α,p)³⁷K reaction has a considerable impact on the observable light curves of x-ray bursts and the isotopic abundance pattern of the ashes left behind on the neutron star crust. For many of the αp process cases for which some experimental constraint exists, statistical model predictions are found to differ substantially; in the case of ³⁴Ar(α,p), reaction rates derived from indirect techniques disagree with Hauser Feshbach calculations by nearly three orders of magnitude. We report the first direct measurement of the ³⁴Ar(α,p)³⁷K reaction cross section, utilizing the Jet Experiments in Nuclear Structure and Astrophysics (JENSA) gas jet target. JENSA is unique in providing a windowless, pure, and highly-localized target of helium for high-resolution spectroscopic studies of (α,p) reactions on proton-rich nuclei. The JENSA target was coupled to the superORRUBA and SIDAR silicon detector arrays and ANASEN position-sensitive ionization chamber and instrumented with a mixed digital/analog DAQ. Experimentally-derived cross sections for the (α,xp), (α,p0), and (α,2p) reactions are compared to HF predictions using TALYS. The impact of the direct measurement on various x-ray burst observational signatures will be discussed.