Threshold resonances in relativistic ${}^{16}$O and ${}^{22}$Ne dissociation

The nuclear emulsion method is applied to study binary dissociation leading to the formation of $\alpha$-particles from ${}^{16}$O nuclei at 3.65 GeV per nucleon and ${}^{22}$Ne nuclei at 3.22 GeV per nucleon. The invariant mass distribution for the ${}^{16}$O$\to$${}^{12}$C(0${}_1^{+}$)+$\alpha$ channel indicates decays of the ${}^{16}$O(0${}_6^{+}$) excitation, whose probability exceeds the estimate for the ${}^{12}$C(0${}_2^{+}$)+$\alpha$ channel by a factor of 20. The invariant mass distribution for ${}^{22}$Ne$\to$${}^{18}$O+$\alpha$ exhibits a peak corresponding to ${}^{22}$Ne excitations around 11.6 MeV.