Nuclear and astrophysical aspects of 18O(p, γ) 19F

Abstract

The capture reaction 18O(p, γ) 19F has been investigated in the energy range E p = 80–2200 keV. The seven known resonances have been studied in detail and twelve new resonances have been found. The resonances at E R = 680, 977 and 1670 keV correspond to new states in 19F. The known resonance at E R = 631 keV is observed to consist of a doublet ( ΔE p = 7 keV). Information on resonance energies, total and partial widths, branching and mixing ratios and ωγ values is reported. Transition strength arguments as well as analyses of γ-ray angular distribution data combined with results from previous work resulted in J π assignments for some of the resonances and low-lying states in 19F. The assignment of several states in 19F as T = 3 2 analogue states of 19O is discussed. A direct capture process to several final states in 19F up to E x = 8.8 MeV has been observed revealing information on the orbital momenta of the captured protons in the final states, their spectroscopic factors and J π assignments for interfering resonances. Special efforts were made to detect this process to states near the proton threshold, which are of importance to stellar hydrogen burning of 18O. The results are compared with corresponding information from other reactions. The investigated energy range of the 18O(p, γ) 19F reaction corresponds to the important stellar temperature range of T = 0.01 to 5 × 10 9 K. The energy-averaged astrophysical reaction rates determined from the present data are compared with previous estimates for this reaction. The data permit reliable conclusions to be drawn concerning the final termination of the CNO tri-cycle.