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

Abstract

While the C 12 ( α , γ ) 16 O 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 16 N 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 16 N 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.