The E1 capture amplitude in ¹²C(α,γ₀) ¹⁶O

Abstract.

An excitation function of the ground-state γ₀-ray capture transition in ¹²C (α,γ)¹⁶O at θ_γ = 90^° was obtained in far geometry using six Ge detectors, where the study of the reaction was initiated in inverse kinematics involving a windowless gas target. The detectors observed predominantly the E1 capture amplitude. The data at E = 1.32 to 2.99 MeV lead to an extrapolated astrophysical S factor S _E1(E ₀) = 90±15 keV b at E ₀ = 0.3 MeV (for the case of constructive interference between the two lowest E1 sources), in good agreement with previous works. However, a novel Monte Carlo approach in the data extrapolation reveals systematic differences between the various data sets such that a combined analysis of all available data sets could produce a biased estimate of the S _E1(E ₀) value. As a consequence, the case of destructive interference between the two lowest E1 sources with S _E1(E ₀) = 8±3 keV b cannot be ruled out rigorously.