New indirect study of the 12 C(α,γ) 16 O reaction via the 12 C( 7 Li,t) 16 O transfer reaction

Abstract

The radiative capture reaction 12 C(α, γ) 16 O plays a key role in stellar nucleosynthesis and evolution. However the cross section of this reaction at stellar energies remains highly uncertain despite various experimental studies. 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 16 O. Indeed, the α-reduced widths and so the α-spectroscopicfactors of these two sub-threshold states are spread over too-large a range of values. Accordingly, a new determination of these quantities through 12 C( 7 Li,t) 16 O transfer reaction measurements at two incident energies and a detailed DWBA analysis of the data was performed recently at Orsay. The measured and calculated differential cross sections are presented as well as the obtained spectroscopic factors and the α-reduced widths for the 2 + and 1 − sub-threshold states. The R-matrix calculations of the 12 C(α, γ) 16 O cross section using our obtained α-reduced widths for the two sub-threshold resonances are presented and discussed. 12th Symposium on Nuclei in the Cosmos