Differential cross sections have been measured for the mirror reactions ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}(\alpha ,n_0){}_{}{}^{15}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}(\alpha ,p_0){}_{}{}^{15}{}_{}{}^{}\mathrm{N}$ for incident energies between 13 and 16 MeV. A striking feature of the data is the existence of a pair of states in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$; One (17.63 MeV) appears to emit protons and not neutrons, the other (18.10 MeV) appears to emit neutrons and not protons. The total lab widths of these levels are ∼180 keV for the 17.63-MeV level and ∼250 keV for the 18.10-MeV level. The ($\alpha ,p$) angular distribution near the center of the 17.63-MeV state is similar to the ($\alpha ,n$) angular distribution near the center of the 18.10-MeV state. The results indicate large isospin mixing in the 18.10-MeV state. Evidence that the two states comprise an isospin-mixed doublet formed by strong mixing of a $T=0\mathrm{}$ and $T=1\mathrm{}$ state is presented.

• Received 1 July 1970

DOI:https://doi.org/10.1103/PhysRevC.3.427