The 12C(α,γ)16O cross section at low energies

An R-matrix formula for the cross section for radiative capture reactions is developed and applied to fit recently measured 12C(α,γ)16O data, for both ground-state transitions and cascade transitions through the 6.92 and 7.12 MeV levels. The correct treatment of the channel contributions is significant for the E2 cascade transitions. Consistent fits of the cascade and ground-state data suggest a value of the channel radius larger than those previously used, and consequently a value of the low-energy S-factor appreciably larger than that adopted recently. 32 refs., 8 tabs., 13 figs