Experimental study of beta-delayed proton decay of (23)Al for nucleosynthesis in novae

Abstract

The beta-delayed gamma and proton decay of (23)Al has been studied with an alternative detector setup at the focal plane of the momentum achromat recoil separator MARS at Texas AandM University. We could detect protons down to an energy of 200 keV and determine the corresponding branching ratios. Contrary to results of previous beta-decay studies, no strong proton intensity from the decay of the isobaric analog state (IAS) of the (23)Al ground state at E(x) = 7803 keV in (23)Mg was observed. Instead we assign the observed low-energy group E(p,c.m.) = 206 keV to the decay from a state that is 16 keV below the IAS. We measured both proton and gamma branches from the decay of this state at E(x) = 7787 keV in (23)Mg, which is a very rare case in the literature. Combining our data with its measured lifetime, we determine its resonance strength to be omega gamma = 1.4(-0.4)(+0.5) meV. The value is in agreement with older direct measurements, but disagrees with a recent direct measurement. This state is the most important resonance for the radiative proton capture (22)Na(p, gamma)(23)Mg in some astrophysical environments, such as novae.