ANALYSIS OF THE TOTAL C-12(ALPHA,GAMMA)O-16 CROSS-SECTION BASED ON AVAILABLE ANGULAR-DISTRIBUTIONS AND OTHER PRIMARY DATA

Because a knowledge of the C-12/O-16 ratio is crucial to the understan ding of the later evolution of massive stars, new R- and K-matrix fits have been completed using the available angular distribution data fro m radiative a capture and elastic alpha Scattering on C-12. Estimates of the total C-12(alpha,gamma)O-16 rate at stellar energies are report ed In contrast with previous work, the analyses generally involve R- a nd K-matrix fits directly to the primary data, i.e., the energy- and a ngle-dependent differential yields, with all relevant partial waves fi tted simultaneously (referred to here as surface fits). It is shown th at, while the El part of the reaction is well constrained by a recent experiment on the beta-delayed alpha-particle decay of N-16, only uppe r limits can be placed on the E2 ground state cross section factor whi ch we take conservatively as S-E2(300)<140 keV b. Simulations were the n carried out to explore what kind of new data could lead to better re strictions on S-E2(300). We find that improved elastic scattering data may be the best short-term candidate for such restrictions while sign ificantly improving S(300) with new radiative capture data may require a longer-term effort. Theoretical models and estimates from a-transfe r reactions for the E2 part of C-12(alpha,gamma)O-16 are then discusse d for comparison with the R- and K-matrix fits of the present work.