C-12(ALPHA,GAMMA)O-16 CROSS-SECTIONS AT STELLAR ENERGIES

The excitation function of the C-12(alpha,gamma)O-16 reaction and the angular distribution of its gamma rays were measured at nine center-of -mass energies ranging from E = 1.37 to 2.98 MeV. These measurements a llowed the separation of the E1 and E2 contributions and their extrapo lation to the region of astrophysical interest. The analysis of ail th e available El cross sections with the K-matrix method and with a thre e-level R-matrix method yields a consistent prediction of 79 +/- 16 ke V b for the E1 S factor at 300 keV. The E2 contribution at the same en ergy is 36 +/- 6 keV b from a cluster model analysis of the present da ta. The best estimate of the total S factor at 300 keV is 120 keV b, a nd it is unlikely that it will fall outside the range of 80-160 keV b.