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

While the C-12(alpha,gamma)O-16 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 beta-delayed alpha spectrum of N-16 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 beta alpha branching ratio. We have remeasured the beta alpha branching ratio by implanting N-16 ions in a segmented Si detector and counting the number of beta alpha decays relative to the number of implantations. Our result, 1.49(5) x 10(-5), represents a 24% increase compared to the accepted value and implies an increase of approximate to 10% in the extrapolated S-factor. (C) 2015 The Authors. Published by Elsevier B.V.