New γ-ray measurements for 12C+12C sub-Coulomb fusion:: Toward data unification

Fusion excitation functions are measured for the alpha,p, and n evaporation channels in the fusion of the C-12+C-12 system at center-of-mass energies between 4.42 and 6.48 MeV, with energy steps of 75 keV. The gamma-ray technique is used with a new absolute normalization method which is independent of charge collection, allowing one to monitor at the same time the carbon buildup at the target. Discrepancies between previous works are discussed and a simple unification is proposed. Barrier penetration model (BPM) calculations are consistent with a belly-to-belly orientation of the oblate deformed C-12 nuclei at the touching point. As in previous works, much structure is seen in the excitation function which is nearly consistent with the positions of resonances reported in the literature for this system. Using BPM predictions for the background excitation function and doing a simultaneous fit of the relevant Breit-Wigner terms in the measured energy region produced a modified set of resonance parameters. The extrapolation of the astrophysical S factor to lower energies is discussed on the basis of the unified data.