C12(α,γ)16O cross sections at stellar energies

The excitation function of the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$(α,γ${)}^{16}$O reaction and the angular distribution of its γ rays were measured at nine center-of-mass energies ranging from E=1.37 to 2.98 MeV. These measurements allowed the separation of the E1 and E2 contributions and their extrapolation to the region of astrophysical interest. The analysis of all the available E1 cross sections with the K-matrix method and with a three-level R-matrix method yields a consistent prediction of 79±16 keV b for the E1 S factor at 300 keV. The E2 contribution at the same energy is 36±6 keV b from a cluster model analysis of the present data. The best estimate of the total S factor at 300 keV is 120 keV b, and it is unlikely that it will fall outside the range of 80–160 keV b. © 1996 The American Physical Society.