The isospin-forbidden proton and $\alpha$-particle decay modes of the lowest $T=2\mathrm{}$ state in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$-($E_{\mathrm{exc}}=22.717\mathrm{}$ MeV) have been measured, using the reaction ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}\mathrm{}(p,t)\mathrm{}{}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ at $E_p=43\mathrm{}$ MeV. Decay protons and $\alpha$ particles to states in ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$ and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, respectively, were detected in coincidence with outgoing tritons. Proton branching ratios of (25 ± 6)%, and (22 ± 5)%, and (15 ± 5)% to the ground state, 5.27 + 5.30, and 6.32-MeV states were obtained. The total $\alpha$-particle branching ratio to the ground state and 4.44-MeV state in ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ is zero within the experimental uncertainties. These results thus indicate that a branch of about 37% is unaccounted for by proton and $\alpha$-particle decay to the low-lying states of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$.

• Received 19 June 1972

DOI:https://doi.org/10.1103/PhysRevC.7.50