First in-beam γ-ray spectroscopy study of 24Al and its implications for the astrophysical 23Mg(p,γ)24Al reaction rate in ONe novae

The first in-beam gamma-ray spectroscopy study of Al-24 is presented. A complete level structure of Al-24 incorporating all states below the proton-emission threshold, has been constructed. The first excited state above the proton threshold has also been identified as a 3(+) state at 2345.1 +/- 1.4 keV. This state, corresponding to a resonance energy of 473 +/- 3 keV, has been suggested to be the dominant resonance contributing to the Mg-23(p,gamma)Al-24 stellar reaction rate. The improved precision of the level energy and unambiguous assignment of the state has reduced the uncertainty of the Mg-23(p,gamma)Al-24 stellar reaction rate, which constrains the production of A>20 nuclei in ONe novae.