Studying the (α, p)-process in X-ray bursts using radioactive ion beams

In type I X-Ray Bursts (XRBs) the nuclear flow is driven towards the proton-drip line by the triple-α reaction, the (α, p)-process, and the rp-process. Along the nucleosynthetic path, the reaction flow can be stopped at so-called waiting-point nuclei. The low Qpγ value of a waiting-point nucleus leads to (p; γ)-(γ, p) equilibrium causing the flow to stall and await a β decay. However, if the temperature is high enough the competing (α, p) reaction can bypass the waiting point. This can have significant effects on the final elemental abundances, energy output, and observables such as double-peaked luminosity profiles. In the intermediate mass region 22Mg, 26Si, 30S, and 34Ar have been identified as possible candidates for waiting-point nuclei in XRBs. A method to study the (α, p)-process on intermediate mass waiting-point nuclei has been developed whereby the time-inverse reaction is studied in inverse kinematics using radioactive ion beams produced by the in-flight method at the ATLAS facility at Argonne National Laboratory. The three reactions p(29P,26Si)a, p(33Cl, 30S)a, and p(37K,34Ar)a have been studied for the first time to determine cross sections for 26Si(α, p) 29P, 30S(α, p)33Cl, and 34Ar(α, p)37K, respectively. The results and future plans will be discussed. © Copyright owned by the author(s)