Al reaction in Type I X-ray bursts*

We have performed a direct measurement of the ²²Mg(α,p)²⁵Al reaction cross section in inverse kinematics for a center of mass energy range of 3.5 - 7 MeV using a ²²Mg beam from the Argonne In-Flight Radioactive Ion Separator (RAISOR) and the MUlti-Sampling Ionization Chamber (MUSIC) at Argonne National Laboratory. The dominant (p,γ) nucleosynthesis flow in Type I X-ray bursts (XRBs) is halted at several waiting point nuclei such as ²²Mg, ^24-26Si, ^28-30S and ³⁴Ar due to (p,γ)-(γ,p) equilibrium. It has been suggested that the flow can be bypassed by (α,p) reactions on these waiting point nuclei. However, the present uncertainties in the relevant (α,p) reaction rates at these waiting points hinder the ability to accurately predict the light curve and ash composition of XRBs. Among the reactions on the waiting point nuclei, the ²²Mg(α,p)²⁵Al reaction has been identified as an important reaction bypassing the waiting points for XRB nucleosynthesis. Thus, it is crucial to constrain the reaction rate of the ²²Mg(α,p)²⁵Al reaction at astrophysical energies.