Unstable states in dissociation of relativistic nuclei. Recent findings and prospects of research

Results are presented on the identification of the unstable nuclei ${}^8$Be and ${}^9$B and the Hoyle state (HS) in the relativistic dissociation of the isotopes ${}^9$Be, ${}^{10}$B, ${}^{10}$C, ${}^{11}$C, ${}^{12}$C, and ${}^{16}$O in a nuclear track emulsion (NTE). The main motivation for the study is the prospect of using these states in the search for more complex unstable states that decay with their participation. The possibilities of the NTE method for studying the contribution of multiple ensembles of the lightest He and H nuclei to the fragmentation of relativistic nuclei are described in brief. It is shown that to identify relativistic decays ${}^8$Be and ${}^9$B and HS in NTE, it is sufficient to determine the invariant mass as a function of angles in pairs and triples of He and H fragments in the approximation of conservation of momentum per nucleon of the parent nucleus. The formation of HS in the dissociation ${}^{16}$O → 4α is observed. According to the criteria established in this way, the contribution of the unstable states to the relativistic fragmentation of ${}^{28}$Si and ${}^{197}$Au nuclei was estimated. Promising applications of the NTE method in the study of nuclear fragmentation are discussed.