First direct measurement of the Mg23(p,γ)Al24 reaction

The lowest-energy resonance in the Mg23(p,γ)Al24 reaction, which is dominant at classical nova temperatures, has been measured directly for the first time using the DRAGON recoil spectrometer. The experiment used a radioactive Mg23 beam (mixed within a significantly stronger Na23 beam) of peak intensity 5×10⁷ s^-1, at the ISAC facility at TRIUMF. We extract values of E_R=485.7_-1.8^+1.3 keV and ωγ=38_-15⁺²¹ meV from our data (all values in the center-of-mass frame unless otherwise stated). In addition, the experiment prompted a recalculation of the Q value for this reaction based on a revision of the Al24 mass. The effect on the uncertainties in the quantities of ejected Na22 and Al26 from oxygen-neon classical novae is discussed.