Measurements of branching ratios from the 7.12-MeV state inO16and theC12(α,γ)O16reaction cross section

Abstract

Gamma-ray branching ratios of the 7.12-MeV state in {sup 16}O have been measured using the {gamma}-{gamma} coincidence technique. The extrapolations of several components of the important {sup 12}C({alpha},{gamma}){sup 16}O cross section to helium-burning energies are dependent upon the 7.12{yields}6.92 MeV branching ratio. An experimental upper limit has been placed on this transition; the 7.12{yields}6.13 MeV branching ratio has also been measured. Relative cross sections and {gamma}-ray angular distributions have been measured for the {sup 19}F(p,{alpha}{gamma}) reaction at several energies near E{sub p}=2 MeV, leading to the 6.13-, 6.92-, and 7.12-MeV states of {sup 16}O. Monte Carlo simulations of the various detectors have been developed and the simulated detector efficiencies have been compared and adjusted to experimental measurements. The available experimental data relating to the {sup 12}C({alpha},{gamma}){sup 16}O cross section have been fitted with the R-matrix formalism. The new upper limit on the 7.12{yields}6.92 MeV branching ratio impacts the extrapolation of both the E2 ground-state cross section and the cascade cross section through the 6.92-MeV state.