C12(α,γ)O16: The Key Reaction in Stellar Nucleosynthesis

The angular distributions of $\gamma$ rays from the ${}^{12}\mathrm{C}(\alpha ,\gamma {)}^{16}\mathrm{O}$ reaction have been measured at 20 energy points in the energy range $E_{\mathrm{cm}}=0.95\mathrm{}$ 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 $500\mu \mathrm{A}$ that were provided by the Stuttgart Dynamitron accelerator. The $S_{E1\mathrm{}}$ and $S_{E2\mathrm{}}$ factors deduced from the $\gamma$ angular distributions have been extrapolated to the range of helium burning temperatures applying the $R$-matrix method, which yielded $S_{E1\mathrm{}}^{300}=(76\pm 20)\mathrm{keV}\mathrm{b}$ and $S_{E2\mathrm{}}^{300}=(85\pm 30)\mathrm{keV}\mathrm{b}$.