Proton-decaying states in Mg-22 and the nucleosynthesis of Na-22 in novae

Populating states in Mg-22 via the (p,t) reaction in inverse kinematics with a 55-MeV /nucleon Mg-24 beam, we have measured the proton-decay branching ratios of the levels at 5.96 MeV and 6.05 MeV and obtained an experimental upper limit on the branching ratio of the 5.71-MeV state. On the basis of the present and previous measurements, we assign spins and parities to the 5.96-MeV and 6.05-MeV states. We combine our branching ratios with independent measurements of the lifetimes of these states or their Ne-22 analogs to compute the resonance strengths and thereby the astrophysical rate of the Na-21(p,gamma)Mg-22 reaction. We perform hydrodynamic calculations of nova outbursts with this new rate and analyze its impact on Na-22 yields.