The nuclei ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$, ${}_{}{}^{15}{}_{}{}^{}\mathrm{O}$, and ${}_{}{}^{19}{}_{}{}^{}\mathrm{Ne}$ are examined in terms of the appearance of $\alpha$-particle core-excited threshold states. It is shown that this simple model can account for most of the $\alpha$-particle states seen above the threshold for $\alpha$-particle emission. We discuss the most striking features of these states.

• Received 6 December 1971

DOI:https://doi.org/10.1103/PhysRevLett.28.247