Fragmentation channels of relativistic 7Be nuclei in peripheral interactions

At the JINR NUclotron, Li-7 nuclei are accelerated. The charge-exchange reaction involving these nuclei at an external target provides a secondary 1.23-A-GeV Be-7 beam. This beam is used to irradiate emulsion chambers. The mean free path lambda(inel) (Be-7) = 14.0 +/- 0.8 cm for inelastic Be-7 interactions in all emulsion coincides within the errors with those for Li-6 and Li-7 nuclei. More than 10% of the Be-7 events are associated with the peripheral interactions in which the total charge of the relativistic fragments is equal to the charge of the Be-7 nucleus and in which charged mesons are not produced. An unusual ratio of the helium isotopes is revealed in the composition of the doubly charged fragments of the Be-7 nuclei: the number of the He-3 fragments is twice as large as that of the He-4 fragments. Each of 50% of peripheral interaction events includes two doubly charged fragments. The channels of the Be-7 fragmentation into charged fragments are presented. In 50% of events, the Be-7 fragmentation occurs only into charged fragments without the emission of neutrons. The He-4 + He-3 channel dominates, whereas each of the He-4 + d + P and Li-6 + p channels constitutes 10%. Two events without neutron emission are observed in the :He-3 + t + P and He-3 + d + d three-body channels. The mean free path for the coherent dissociation of relativistic Be-7 nuclei into He-4 + He-3 is equal to 7 +/- 1 m. The main features of the fragmentation of relativistic 7 Be nuclei ill Such peripheral interactions are explained by the He-3 + 4 He two-cluster structure of the Be-7 nucleus.