Proton Branching Ratios of Mg23 Levels

Background: The anomalous Ne-22 abundance measured in certain presolar graphite grains is thought to arise from the decay of Na-22 that was synthesized at high temperatures in core-collapse supernovas. To better interpret this abundance anomaly, the primary destruction mechanism of Na-22, the Na-22(p, gamma)Mg-23 reaction, must be better understood. Purpose: Determine proton branching ratios of several Mg-23 excited states that play a role in the hightemperature Na-22(p, gamma)Mg-23 reaction rate. Methods: Particle decays of Mg-23 excited states populated with the previously reported Mg-24(p, d)Mg-23 transfer reaction measurement [Kwag et al., Fur. Phys. J. A 56. 108 (2020)] were analyzed to extract proton branching ratios. The reaction was studied using a 31-MeV proton beam from the Holifield Radioactive Ion Beam Facility of Oak Ridge National Laboratory and Mg-24 solid targets. Results: Proton branching ratios of several Mg-23 excited states in the energy range E-x = 8.044-9.642 MeV were experimentally determined for the first time for the p0 and p1' (p1 + p2 + p3) decay channels. Conclusions: These new branching ratios for Mg-23 levels can provide an experimental foundation for an improved high-temperature rate of the Na-22(p, gamma)Mg-23 reaction needed to understand production of anomalously high Ne-22 abundance in core-collapse supernovas.