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In 1953, David Noel Ferguson Dunbar and collaborators used accelerated deuterons on nitrogen-14, populating carbon-12 through ${}^{14}\mathrm{N}(d,\alpha ){}^{12}\mathrm{C}$. Magnetic analysis resolved outgoing alpha particle groups. At $620\mathrm{keV}$ incident energy and laboratory angle $90$ degrees, they reported excitation $7.68\pm 0.03\mathrm{MeV}$, with yield $6\%$ of the $4.43\mathrm{MeV}$ group's yield. The stronger group supplied an internal comparison. The paper's opening explicitly relates the search to Fred Hoyle's abundance argument. This is evidence for a nuclear level from a different entrance reaction than stellar fusion.^[ref]

The inference uses energy and momentum conservation: at fixed incident energy and observation angle, more energy retained as carbon-12 excitation leaves less outgoing kinetic energy. A resolved particle group therefore identifies a nuclear level. This laboratory nuclear line supports an input required by a stellar synthesis model. It does not reproduce core helium burning, measure a complete stellar carbon yield, or by itself determine the stabilizing decay probability.