The spectrum of low energy beta-delayed alpha-particle emission of ${}_{}{}^{16}{}_{}{}^{}\mathrm{N}$ was measured with high sensitivity; e.g., at ${\mathit{E}}_{\mathrm{\alpha }}^{\mathit{L}}$≊1 MeV, a sensitivity for a beta-decay branching ratio in the range of ${10}^{\mathrm{-}9}$ (to ${10}^{\mathrm{-}10}$) was achieved. We used previous theoretical work of Ji, Filippone, Humblet, and Koonin to extract from these data the astrophysical p-wave S factor for the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ (α,γ${)}^{16}$O capture reaction, and find ${\mathit{S}}_{\mathit{E}1}$(300)=95±6(stat)±28(syst) keV b. This result is crucial, for example, for understanding the last stages of a massive star before a supernova.

• Received 13 November 1992

DOI:https://doi.org/10.1103/PhysRevLett.70.2066