Proton-unbound states in ${}^{24}\mathrm{Al}$ relevant for the ${}^{23}\mathrm{Mg}(p,{\hat{I}}^3)$ reaction in novae

Abstract

Background: The nucleosynthesis of several proton-rich nuclei is determined by radiative proton-capture reactions on unstable nuclei in nova explosions. One such reaction is ${}^{23}\mathrm{Mg}(p,{\hat{I}}^3{)}^{24}\mathrm{Al}$, which links the NeNa and MgAl cycles in oxygen-neon (ONe) novae. Purpose: To extract ${}^{23}\mathrm{Mg}(p,{\hat{I}}^3)$ resonance strengths from a study of proton-unbound states in ${}^{24}\mathrm{Al}$, produced via the ${}^{24}$Mg(${}^3$He,$t$) reaction. Methods: A beam of ${}^3{\mathrm{He}}^{2+}$ ions at 50.7 MeV was used to produce the states of interest in ${}^{24}$Al. Proton-triton angular correlations were measured with a $K=600$ QDD magnetic spectrometer and a silicon detector array, located at iThemba LABS, South Africa. Results: We measured the excitation energies of the four lowest proton-unbound states in ${}^{24}$Al and place lower-limits on $\hat{I}{“}_p/\hat{I}“$ values for these four states. Together with shell-model calculations of partial gamma widths, the experimental data are also used to determine resonance strengths for the three lowest ${}^{23}\mathrm{Mg}(p,{\hat{I}}^3{)}^{24}\mathrm{Al}$ resonances. Conclusions: The energy of the dominant first ${}^{23}\mathrm{Mg}(p,{\hat{I}}^3)$ resonance is determined to be $E_r=478\pm 4$ keV, with a resonance strength $\ddot{I}‰{\hat{I}}^3=19\pm 9$ meV.

Accepted for Publication in Physical Review C