The13C(α,n)reaction and its role as a neutron source for thesprocess

Abstract

The ${}^{13}C(\ensuremath{\alpha},n){}^{16}O$ reaction constitutes the dominant neutron source for the main $s$ process, which operates at a thermal energy of $\mathit{kT}=8$ keV. Since the cross section at stellar energies is very small, the reaction rate cannot be directly determined and has to be extrapolated from cross section results obtained at higher energies. To remove various discrepancies in the normalization of previous data sets and to subsequently improve the reliability of the extrapolation, we performed measurements of the ${}^{13}C(\ensuremath{\alpha},n){}^{16}O$ reaction in the energy range ${E}_{\mathrm{c}.\mathrm{m}.}=320\text{\ensuremath{-}}700$ keV. In addition, the double differential scattering cross section ${}^{13}C(\ensuremath{\alpha},\ensuremath{\alpha}){}^{13}C$ was measured in the energy range ${E}_{\mathrm{lab}}=2.6\text{\ensuremath{-}}6.2$ MeV for 28 angles. These data were used to constrain possible contributions from background resonances for a reliable extrapolation with the multichannel $R$-matrix code SAMMY. As a result, the uncertainties were significantly reduced, and a reaction rate of $(4.6\ifmmode\pm\else\textpm\fi{}1.0)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}$ ${\mathrm{cm}}^{3}$/moles at $\mathit{kT}=8$ keV ($T=0.1\ifmmode\times\else\texttimes\fi{}{10}^{9}$ K) was determined.