The Ne22(p,γ)Na23 reaction, part of the neon-sodium cycle of hydrogen burning, may explain the observed anticorrelation between sodium and oxygen abundances in globular cluster stars. Its rate is controlled by a number of low-energy resonances and a slowly varying nonresonant component. Three new resonances at Ep=156.2, 189.5, and 259.7 keV have recently been observed and confirmed. However, significant uncertainty on the reaction rate remains due to the nonresonant process and to two suggested resonances at Ep=71 and 105 keV. Here, new Ne22(p,γ)Na23 data with high statistics and low background are reported. Stringent upper limits of 6×10-11 and 7×10-11 eV (90% confidence level), respectively, are placed on the two suggested resonances. In addition, the off-resonant S factor has been measured at unprecedented low energy, constraining the contributions from a subthreshold resonance and the direct capture process. As a result, at a temperature of 0.1 GK the error bar of the Ne22(p,γ)Na23 rate is now reduced by 3 orders of magnitude.

Direct Capture Cross Section and the Ep=71 and 105 keV Resonances in the Ne 22 (p,γ) Na 23 Reaction

D'Erasmo, G.;Fiore, E. M.;Mossa, V.;Pantaleo, F. R.;Paticchio, V.;Schiavulli, L.;
2018-01-01

Abstract

The Ne22(p,γ)Na23 reaction, part of the neon-sodium cycle of hydrogen burning, may explain the observed anticorrelation between sodium and oxygen abundances in globular cluster stars. Its rate is controlled by a number of low-energy resonances and a slowly varying nonresonant component. Three new resonances at Ep=156.2, 189.5, and 259.7 keV have recently been observed and confirmed. However, significant uncertainty on the reaction rate remains due to the nonresonant process and to two suggested resonances at Ep=71 and 105 keV. Here, new Ne22(p,γ)Na23 data with high statistics and low background are reported. Stringent upper limits of 6×10-11 and 7×10-11 eV (90% confidence level), respectively, are placed on the two suggested resonances. In addition, the off-resonant S factor has been measured at unprecedented low energy, constraining the contributions from a subthreshold resonance and the direct capture process. As a result, at a temperature of 0.1 GK the error bar of the Ne22(p,γ)Na23 rate is now reduced by 3 orders of magnitude.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11586/223699
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