Background: In presolar low-density graphite grains, an extraordinarily large ${}^{22}$Ne/${}^{20}$Ne ratio or even nearly pure ${}^{22}$Ne is found, pointing to the condensation of radioactive ${}^{22}$Na in grains. Supernovae and neon-rich novae are the main events that produce ${}^{22}$Na via the explosive hydrogen burning process. The ${}^{22}$Na($p$, $\gamma$)${}^{23}$Mg reaction is one of the key reactions that influences the ${}^{22}$Na abundance in ejecta.

Purpose:The present work aims to explore the proton resonant states in ${}^{23}$Mg relevant to the astrophysical ${}^{22}$Na($p$, $\gamma$)${}^{23}$Mg reaction. The determined ${}^{23}$Mg resonant parameters can be used to evaluate the ${}^{22}$Na($p$, $\gamma$)${}^{23}$Mg reaction rate.

Method:A low-energy ${}^{22}$Na radioactive ion beam is produced via the ${}^1$H(${}^{22}$Ne, ${}^{22}$Na)$n$ reaction, and used to measure the experimental excitation function of the ${}^{22}$Na + $p$ resonant scattering with a conventional thick-target inverse kinematic method. $R$-matrix analysis is applied to deduce the ${}^{23}$Mg resonance parameters from the experimental excitation function.

Results: Three proton resonance states in ${}^{23}$Mg are observed. Spins/parities and the proton partial widths are determined. The deduced excitation energies agree with the compiled values.

Conclusions: The new spin and parity assignments allow us to perform a shell-model calculation of the $\gamma$ widths of the ${}^{23}$Mg resonant states for the evaluation of the ${}^{22}$Na($p$, $\gamma$)${}^{23}$Mg astrophysical reaction rate. The two $s$-wave resonant states established in this work at 8.793 and 8.916 MeV in ${}^{23}$Mg, respectively, increase the total reaction rate by about 5% at a temperature greater than 2 GK.

• Received 17 May 2013

DOI:https://doi.org/10.1103/PhysRevC.88.035801