¹²C(α,γ)¹⁶O: The Key Reaction in Stellar Nucleosynthesis

The angular distributions of γ rays from the ¹²C(α,γ)¹⁶O reaction have been measured at 20 energy points in the energy range E_cm  =  0.95 to 2.8 MeV. The sensitivity of the present experiment compared to previous direct investigations was raised by 1–2 orders of magnitude, by using an array of highly efficient ( 100%) Ge detectors shielded actively with BGOs, as well as high beam currents of up to 500 μA that were provided by the Stuttgart dynamitron accelerator. The S_E1 and S_E2 factors deduced from the γ angular distributions have been extrapolated to the range of helium burning temperatures applying the R-matrix method, which yielded S_E1³⁰⁰  =  (76±20)  keV b and S_E2³⁰⁰  =  (85±30)  keV b.