Helium burning of 18O

Abstract

The 18O(α, γ) 22Ne capture reaction has been studied at E α = 0.6−2.3 MeV. The known resonance at E α = 2.20 MeV has been established and fourteen new resonances have been found in the energy range covered. The E α = 1.16, 1.32, 1.45, 1.53, 1.87, 1.96 and 2.15 MeV resonances correspond to resonances observed previously in the 18O(α, n) 21Ne reaction. The E α = 0.77, 1.25 and 1.27 MeV resonances represent new compound states in 22Ne. Information on branching ratios, ωγ values and total widths is reported. Transition strength arguments and analyses of γ-ray angular distribution data together with results from previous work resulted in the most likely J π assignments for the resonances. The E α = 1.66 and 1.78 MeV resonances are good candidates for the two J π = 8 + states predicted at E x ≈ 11–12 MeV and are probably members of the K π = 0 + (ground state) and K π = 2 + rotational bands in 22Ne. The investigated energy range of E α together with that of previous work corresponds to stellar temperatures of T = (0.3−4.3) × 10 9 K. The astrophysical reaction rate determined from these data is compared with predictions based in part on the nuclear optical model. The rate is also compared with that of the competing 18O(α, n) 21Ne reaction.