Sub-Coulomb {alpha} Transfers on C{sup 12} and the C{sup 12}({alpha}, {gamma})O{sup 16} S Factor

The {sup 12}C( {alpha}, {gamma}){sup 16}O reaction is crucial for the understanding of He burning in massive stars, but the low-energy cross section is highly uncertain. To address this problem we have measured at sub-Coulomb energies total cross sections for the {sup 12}C( {sup 6}Li, d){sup 16}O and {sup 12}C( {sup 7}Li, t) {sup 16}O reactions to the bound 2{sup +} and 1{sup -} states of {sup 16}O . The data are analyzed to obtain the reduced {alpha} widths of these states. Together with capture and phase-shift data, these results provide for a more accurate determination of the low-energy 12C({alpha}, {gamma}){sup 16}O S factor: S{sub E1}(0.3 MeV) =101{+-}17 keV b and S{sub E2}(0.3 MeV) =42{sup +16}{sub -23} keV b for the E1 and E2 multipole components of the reaction. (c) 1999 The American Physical Society.