A measurement of Γ rad/Γ for the 7.654 MeV state of 12C and the rate of the stellar 3α reaction

Abstract

The branching ratio Γ rad/Γ for the radiative de-excitation of the 7.654 MeV, 0 + state in 12C has been measured. Coincidences between α-particles from 12C(α, α') 12C(7.654 MeV) and recoil 12C ions at the proper energy and angle were the signature of radiative decay. Conservative techniques were used throughout to avoid the need for large corrections. A value, of Γ rad/ Γ = (3.87±0.25) × 10 −4 was obtained in good agreement with other recent results but substantially higher than the previously accepted value of (2.9±0.3) × 10 −4. Available results are reviewed and a recommended value of Γ rad/ gG is presented. The implication of this result for the rate of the 3α process in stellar helium burning is discussed and a recommended reaction rate is presented.