The 12C(a,g)16O Cross Section at Low Energies

Abstract

An R-matrix formula for the cross section for radiative capture reactions is developed and applied to fit recently measured 12C(oc,y)160 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 astrophysical S-factor appreciably larger than that adopted recently.