Indirect study of C-12(alpha, gamma)O-16 reaction

The radiative capture reaction C-12(alpha, gamma)O-16 plays an important role in helium burning in massive stars and their subsequent evolution [1]. However, despite various experimental studies, the cross section of this reaction at stellar energies remains highly uncertain. The extrapolation down to stellar energy (E-cm similar to 300 keV) of the measured cross sections at higher energies is made difficult by the overlap of various contributions of which some are badly known such as that of the 2(+) (E-x = 6.92 MeV) and 1(-) (E-x = 7.12 MeV) sub-threshold states of O-16. Hence, to further investigate the contribution of these two-subthreshold resonances to the C-12(alpha, gamma)O-16 cross section, a new determination of their alpha-reduced widths and so their alpha-spectroscopic-factors was performed using C-12(Li-7, t)O-16 transfer reaction measurements at two incident energies and a detailed DWBA analysis of the data [2]. The measured and calculated differential cross sections are presented as well as the obtained spectroscopic factors and the alpha-reduced widths as well as the assymptotic normalization constants (ANC) for the 2(+) and 1(-) sub-threshold states. Finally, the results obtained from the R-matrix calculations of the C-12(alpha, gamma)O-16 cross section using our obtained alpha-reduced widths for the two sub-threshold resonances are presented and discussed.