Fragmentation channels of relativistic 7Be nuclei in peripheral interactions

At the JINR Nuclotron, 7Li nuclei are accelerated. The charge-exchange reaction involving these nuclei at an external target provides a secondary 1.23-A-GeV 7Be beam. This beam is used to irradiate emulsion chambers. The mean free path λinel(7Be) = 14.0 ± 0.8 cm for inelastic 7Be interactions in an emulsion coincides within the errors with those for 6Li and 7Li nuclei. More than 10% of the 7Be events are associated with the peripheral interactions in which the total charge of the relativistic fragments is equal to the charge of the 7Be 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 7Be nuclei: the number of the 3He fragments is twice as large as that of the 4He fragments. Each of 50% of peripheral interaction events includes two doubly charged fragments. The channels of the 7Be fragmentation into charged fragments are presented. In 50% of events, the 7Be fragmentation occurs only into charged fragments without the emission of neutrons. The 4He + 3He channel dominates, whereas each of the 4He + d + p and 6Li + p channels constitutes 10%. Two events without neutron emission are observed in the 3He + t + p and 3He + d + d three-body channels. The mean free path for the coherent dissociation of relativistic 7Be nuclei into 4He + 3He is equal to 7 ± 1 m. The main features of the fragmentation of relativistic 7Be nuclei in such peripheral interactions are explained by the 3He + 4He two-cluster structure of the 7Be nucleus.