Study of proton-unbound states in $^{24}{\rm Al}$ relevant for the $^{23}{\rm Mg}(p,\gamma)$ reaction in novae

Author:

E. C. Vyfers, V. Pesudo, S. Triambak, P. Adsley, B. A. Brown, H. Jivan, M. Kamil, D. J. Marin-Lambarri, R. Neveling, J. C. Nzobadila Ondze, P. Papka, L. Pellegri, B. M. Rebeiro, B. Singh, F. D. Smit, G. F. Steyn

Keyword:

Nuclear Experiment, Nuclear Experiment (nucl-ex)

journal:

date:

2023-11-27 00:00:00

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 $^{23}{\rm Mg}(p,\gamma)^{24}{\rm Al}$, which links the NeNa and MgAl cycles in oxygen-neon (ONe) novae. Purpose: To extract $^{23}{\rm Mg}(p,\gamma)^{24}{\rm Al}$ resonance strengths from a study of proton-unbound states in $^{24}{\rm Al}$, produced via the $^{24}$Mg($^{3}$He,$t$) reaction. Methods: A beam of $^3 {\rm He}^{2+}$ 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 $\Gamma_p/\Gamma$ values for these four states. Together with USD-C shell-model calculations of partial gamma widths, the experimental data are also used to determine resonance strengths for the three lowest $^{23}{\rm Mg}(p,\gamma)^{24}{\rm Al}$ resonances. Conclusions: The energy of the dominant first $^{23}{\rm Mg}(p,\gamma)$ resonance is determined to be $E_{r} = 481.4 \pm 1.1$ keV, with a resonance strength $\omega \gamma = 18 \pm 6$ meV.

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