First Accurate Normalization of the β -delayed α Decay of N16 and Implications for the C12(α,γ)O16 Astrophysical Reaction Rate

Le résumé fourni par la source

The $^{12}\mathrm{C}(\ensuremath{\alpha},\ensuremath{\gamma})^{16}\mathrm{O}$ reaction plays a central role in astrophysics, but its cross section at energies relevant for astrophysical applications is only poorly constrained by laboratory data. The reduced $\ensuremath{\alpha}$ width, ${\ensuremath{\gamma}}_{11}$, of the bound ${1}^{\ensuremath{-}}$ level in $^{16}\mathrm{O}$ is particularly important to determine the cross section. The magnitude of ${\ensuremath{\gamma}}_{11}$ is determined via sub-Coulomb $\ensuremath{\alpha}$-transfer reactions or the $\ensuremath{\beta}$-delayed $\ensuremath{\alpha}$ decay of $^{16}\mathrm{N}$, but the latter approach is presently hampered by the lack of sufficiently precise data on the $\ensuremath{\beta}$-decay branching ratios. Here we report improved branching ratios for the bound ${1}^{\ensuremath{-}}$ level [${b}_{\ensuremath{\beta},11}=(5.02\ifmmode\pm\else\textpm\fi{}0.10)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$] and for $\ensuremath{\beta}$-delayed $\ensuremath{\alpha}$ emission [${b}_{\ensuremath{\beta}\ensuremath{\alpha}}=(1.59\ifmmode\pm\else\textpm\fi{}0.06)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$]. Our value for ${b}_{\ensuremath{\beta}\ensuremath{\alpha}}$ is 33% larger than previously held, leading to a substantial increase in ${\ensuremath{\gamma}}_{11}$. Our revised value for ${\ensuremath{\gamma}}_{11}$ is in good agreement with the value obtained in $\ensuremath{\alpha}$-transfer studies and the weighted average of the two gives a robust and precise determination of ${\ensuremath{\gamma}}_{11}$, which provides significantly improved constraints on the $^{12}\mathrm{C}(\ensuremath{\alpha},\ensuremath{\gamma})$ cross section in the energy range relevant to hydrostatic He burning.

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