Hydrogen burning of 20Ne and 22Ne in stars

Abstract

Abstract The 20 Ne(p, γ) 21 Na capture reaction has been studied in the energy range E p = 0.37–2.10 MeV. Direct-capture transitions to the 332 ( 5 2 + ) and 2425 keV ( 1 2 + ) states have been found with spectroscopic factors of C 2 S (1d) = 0.77±0.13 and C 2 S (2s) = 0.90±0.12, respectively. The high-energy tail of the 2425 keV state, bound by 7 keV against proton decay, has also been observed in the above energy range as a subthreshold resonance. The excitation function for this tail is consistent with a single-level Breit-Wigner shape for a γ-width of Γ γ = 0.31±0.07 eV at E x = 2425 keV. The extrapolation of these data to stellar energies gives an astrophysical S -factor of S (0) = 3500 keV · b. Two new resonances at E p = 384±5 and 417± 5 keV have been observed with strengths of ωγ = 0.11±0.02 and 0.06±0.01 meV, corresponding to the known states at E x (J π) = 2798 ( 1 2 − ) and 2829 keV (presumably 9 2 + ), respectively. For the known E p = 1830 keV resonance, a strength of ωγ = 1.0± 0.3 eV and a total width of Γ = 180± 15 keV were found. Branching ratios as well as transition strengths have been obtained for these three states. The Q -value for the 20 Ne(p, γ ) 21 Na reaction ( Q = 2432.3 ± 0.5 keV) as well as excitation energies for many low-lying states in 21 Na have been measured. No evidence was found for the existence of the state reported at E x = 4308±4 keV. In the case of 22 Ne(p, γ) 23 Na, direct-capture transitions to six final bound states have been observed revealing sizeable spectroscopic factors for these states. The astrophysical S -factor extrapolated from these data to stellar energies, is S (0) = 67 ± 12 keV · b. The astrophysical as well as the nuclear structure aspects of the present results are discussed.