Direct Measurement of Low-Energy Resonances in ^31P(p,α)^28Si and ^35Cl(p,α)^32S

Reaction cycles in explosive hydrogen burning in novae and X-ray bursts influence both the energy generation and the processing of material to higher masses. The ^31P(p,α)^28Si and ^35Cl(p,α)^32S reactions are thought to lead to the formation of reaction cycles in the Si-Ar region, but the strength of these cycles depends on the (p,γ)/(p,α) reaction rate ratio. Previous attempts to measure the strength of low-energy resonances in ^32S and ^36Ar have relied on indirect methods or resulted only in setting upper limits for a number of the resonances of interest. We have measured the strength of low-energy resonances in ^32S and ^36Ar at Oak Ridge National Laboratory by using stable ^31P and ^35Cl beams and a differentially pumped windowless hydrogen gas target to detect p-α coincidences in arrays of silicon strip detectors. Details of the experimental configuration and results will be presented. ^*This work is supported in part by the U.S. DOE and NSF.