Measurement of the branching ratio for β-delayed α decay of 16N

While the C12(α,γ)16O reaction plays a central role in nuclear astrophysics, the cross section at energies relevant to hydrostatic helium burning is too small to be directly measured in the laboratory. The β-delayed α spectrum of 16N can be used to constrain the extrapolation of the E1 component of the S-factor; however, with this approach the resulting S-factor becomes strongly correlated with the assumed βα branching ratio. We have remeasured the βα branching ratio by implanting 16N ions in a segmented Si detector and counting the number of βα decays relative to the number of implantations. Our result, 1.49(5)×10−5, represents a 24% increase compared to the accepted value and implies an increase of ≈10% in the extrapolated S-factor.