New measurements of low-energy resonances in the Ne 22 (p,γ) Na 23 reaction
The Ne22(p,γ)Na23 reaction is one of the most uncertain reactions in the NeNa cycle and plays a crucial role in the creation of Na23, the only stable Na isotope. Uncertainties in the low-energy rates of this and other reactions in the NeNa cycle lead to ambiguities in the nucleosynthesis predicted from models of thermally pulsing asymptotic giant branch (AGB) stars. This in turn complicates the interpretation of anomalous Na-O trends in globular cluster evolutionary scenarios. Previous studies of the Ne22(p,γ)Na23, Ne22(He3,d)Na23, and C12(C12,p)Na23 reactions disagree on the strengths, spins, and parities of low-energy resonances in Na23 and the direct-capture Ne22(p,γ)Na23 reaction rate contains large uncertainties as well. In this work we present new measurements of resonances at Erc.m.=417, 178, and 151 keV and of the direct-capture process in the Ne22(p,γ)Na23 reaction. The resulting total Ne22(p,γ)Na23 rate is approximately a factor of 20 higher than the rate listed in a recent compilation at temperatures relevant to hot-bottom burning in AGB stars. Although our rate is close to that derived from a recent Ne22(p,γ)Na23 measurement by Cavanna et al. in 2015, we find that this large rate increase results in only a modest 18% increase in the Na23 abundance predicted from a 5 M thermally pulsing AGB star model from Ventura and D'Antona (2005). The estimated astrophysical impact of this rate increase is in marked contrast to the factor of ∼3 increase in Na23 abundance predicted by Cavanna et al. and is attributed to the interplay between the Na23(p,α)Ne20 and Ne20(p,γ)Na21 reactions, both of which remain fairly uncertain at the relevant temperature range.
Kelly, KJ; Champagne, AE; Downen, LN; Dermigny, JR; Hunt, S; Iliadis, C; Cooper, AL
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