Abstract
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 (Ecm∼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+ (Ex=6.92 MeV) and 1− (Ex=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.
Highlights
During He burning phase in massive stars, the two main and important reactions through which He is consumed are the triple-α reaction and 12C(α, γ)16O
The extrapolation down to stellar energy (Ecm ∼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+ (Ex=6.92 MeV) and 1− (Ex=7.12 MeV) sub-threshold states of 16O
In view of the importance of 12C(α, γ)16O reaction and the large uncertainties surrounding the Sα and the γα2 of the two sub-threshold states, we perfomed a new measurement of these quantities via the transfer reaction 12C(7Li,t)16O [3]
Summary
During He burning phase in massive stars, the two main and important reactions through which He is consumed are the triple-α reaction and 12C(α, γ)16O. The ratio of these two reaction rates determine the 12C/16O abundance ratio in stars at the end of their helium burning phase. This ratio has important consequences on further hydrostatic burning stages and so on nucleosynthsis in massive stars and has an effect on the final fate of the stars [1]. The low-energy cross section of the latter remains highly uncertain despite the various experiments
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