High-precision 28Si(p,t)26Si reaction to determine 22Mg(α,p)25Al reaction rates

The rise time of stellar x-ray bursts is a signature of thermonuclear runaway processes in the atmosphere of neutron stars and is highly sensitive to a series of (α,p) reactions via high-lying resonances in sd-shell nuclei. Lacking data for the relevant resonance levels, the stellar reaction rates have been calculated using statistical, Hauser-Feshbach models, assuming a high-level density. This assumption may not be correct in view of the selectivity of the (α,p) reaction to natural parity states. We measured the 28Si(p,t)26Si reaction with a high-resolution spectrometer to identify resonance levels in 26Si above the α-emission threshold at 9.164 MeV excitation energy. These resonance levels are used to calculate the stellar reaction rate of the 22Mg(α,p)25Al reaction and to test the validity of the statistical assumption.