First searches for the coherent dissociation of relativistic oxygen nuclei into four a particles are reported. It is shown that reactions of this type are characterized by a significantly lower decay temperature than the conventional multifragmentati
on of residual projectile nuclei. The momentum spectra and correlations of a panicles are not reproduced by the simple statistical model of direct fragmentation. The possibility that the oxygen nucleus undergoing fragmentation acquires a nonzero angular momentum in the collision process is discussed.
The transverse-momentum distributions and correlation characteristics of relativistic $alpha$ particles from the coherent dissociation of a carbon nucleus into three $alpha$ particles at 4.5 GeV/$c$ are studied in lead-enriched emulsion. Comparative
analysis of data obtained in ordinary and lead-enriched emulsion stacks is performed. It is shown that the statistical model of rapid fragmentation does not describe the momentum and correlation characteristics of a $alpha$ particles in the rest frame of the carbon nucleus. The estimated decay temperature of $^{12}$C is weakly dependent on the target atomic mass. It is shown that the carbon nucleus undergoing fragmentation acquires angular momentum in the collision.
The dissociation features in nuclear track emulsion of $^9$Be, $^{9,10}$C, and $^{12}$N nuclei of 1.2 A GeV energy are presented. The data presented for the nucleus $^9$Be can be considered as evidence that there is a core in its structure in the for
m of 0$^+$ and 2$^+$ states of the $^8$Be nucleus having roughly equal weights. Events of coherent dissociation $^9$C$rightarrow 3^3$He associated with the rearrangement of the nucleons outside the $alpha$-clustering are identified. A pattern of the charge fragment topology in the dissociation of $^{10}$C and $^{12}$N nuclei is obtained for the first time. Contribution of the unbound nucleus decays to the cascade process $^{10}$C$rightarrow ^9$B$rightarrow ^8$Be is identified.
Nuclear track emulsion is exposed to 1.2 A $^9$C GeV nuclei. Pairs of 2$^3$He nuclei having unusually narrow opening angles are observed in channel $^9$C $rightarrow$ 3$^3$He pointing to the possible 2$^3$He resonance near the production threshold.
A nuclear track emulsion was exposed to a mixed beam of relativistic $^{12}$N, $^{10}$C, and $^7$Be nuclei having a momentum of 2 GeV/$c$ per nucleon. The beam was formed upon charge exchange processes involving $^{12}$C primary nuclei and their frag
mentation. An analysis indicates that $^{10}$C nuclei are dominant in the beam and that $^{12}$N nuclei are present in it. The charge topology of relativistic fragments in the coherent dissociation of these nuclei is presented.
