Indirect study of ¹²C(α,γ)¹⁶O reaction

The radiative capture reaction ¹²C(α,γ)¹⁶O 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∼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 ¹⁶O. Hence, to further investigate the contribution of these two-subthreshold resonances to the ¹²C(α,γ)¹⁶O cross section, a new determination of their a-reduced widths and so their a- spectroscopic-factors was performed using ¹²C(⁷Li,t)¹⁶O 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 a- reduced widths as well as the assymptotic normalization constants (ANC) for the 2+ and 1⁻ subthreshold states. Finally, the results obtained from the R-matrix calculations of the ¹²C(α,γ)¹⁶O cross section using our obtained a-reduced widths for the two sub-threshold resonances are presented and discussed.