12C+12C Fusion Reactions near the Gamow Energy

The fusion reactions C-12(C-12, alpha)Ne-20 and C-12 (C-12, p)Na-23 have been studied from E = 2.10 to 4.75 MeV by gamma-ray spectroscopy using a C target with ultralow hydrogen contamination. The deduced astrophysical S(E)* factor exhibits new resonances at E <= 3.0 MeV, in particular, a strong resonance at E = 2.14 MeV, which lies at the high-energy tail of the Gamow peak. The resonance increases the present nonresonant reaction rate of the alpha channel by a factor of 5 near T = 8 x 10(8) K. Because of the resonance structure, extrapolation to the Gamow energy E-G = 1.5 MeV is quite uncertain. An experimental approach based on an underground accelerator placed in a salt mine in combination with a high efficiency detection setup could provide data over the full E-G energy range.