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The differential cross section in the transverse momentum Q and a total cross section of (31 ± 4) mb for the coherent dissociation of a 3-A-GeV/c 7 Li nucleus through the 3 H+ 4 He channel have been measured on emulsion nuclei. The observed Q dependence of the cross section is explained by the predominant supposition of the nuclear diffraction patterns on light (C, N, O) and heavy (Br, Ag) emulsion nuclei. The contributions to the cross section from nuclear diffraction (Q ≤ 400 MeV/c) and Coulomb (Q ≤ 50 MeV/c) dissociations are calculated to be 40.7 and 4 mb, respectively. The properties of the nuclei and mechanisms of the reactions induced by the Coulomb and nuclear interactions in nucleus-nucleus collisions have been studied for more than five decades [1-4]. These investigations have been recently expanded to the relativistic energy range [5-8].It is known that the nuclear diffraction mechanism of the reactions at low momentum transfers Q (similar to optical diffraction), which was predicted as early as the 1950s [9][10][11][12], becomes significant at energies of about hundreds of MeVs and higher along with the Coulomb interaction. Diffraction is characterized by the observed oscillations of the cross sections for the elastic scattering of particles and nuclei, dσ/dQ, with the main maximum at small angles ϑ λ/R, where λ is the de Broglie wavelength of the incident particle and R is the radius of the nuclear interaction region. It is also known [12] that the diffraction mechanism can induce the coherent dissociation of the incident nucleus (without the excitation of the target nucleus) and the production of particles. The dissociation of the 12 C nucleus into three α particles was observed at relativistic energies [13,14]. However, the direct observation of the diffraction pattern with the counter technique (measurement of dσ/dQ) in the nuclear dissociation remains a sufficiently complex problem. The energy spectra of the charged particles at given angles [15,16] are normally used in such experiments.Among numerous reactions accompanying the collisions of relativistic nuclei (multifragmentation, meson production), we take a comparatively simple channel of coherent (elastic) dissociation of the 7 Li nucleus (λ 0.01 fm), which corresponds to the twocluster structure of the 7 Li nucleus and is convenient for the application of the developed theoretical approaches to the description of such reactions.The cross section dσ/dQ for the elastic dissociation of the 7 Li nucleus is measured in the experiment in order to analyze the diffraction pattern of the process and to determine the contribution from the electromagnetic dissociation. According to previous nuclear emulsion measurements [8], the chosen reaction is characterized by very small nucleus emission angles and correspondingly low values Q ≤ 0.45 GeV/c; under these conditions, the simultaneous manifestation of the Coulomb and nuclear diffraction mechanisms of the process can be expected [5]. The Q regions of the contributions from the Coulomb and nuclear intera...

Nuclei of 7 Li were accelerated at the JINR Nuclotron. After the charge-exchange reaction involving these nuclei at an external target a second 7 Be beam of energy 1.23A GeV was formed.This beam was used to expose photo-emulsion chambers. The mean free path for inelastic 7 Be interactions in emulsion λ=14.0±0.8 cm coincides within the errors with those for 6 Li and 7 Li nuclei.More than 10% of the 7 Be events are associated with the peripheral interactions in which the total charge of the relativistic fragments is equal to the charge of the 7 Be and in which charged mesons are not produced. An unusual ratio of the isotopes is revealed in the composition of the doubly charged 7 Be fragments: the number of 3 He fragments is twice as large as that of 4 He fragments.In 50% of peripheral interactions, a 7 Be nucleus decays to two doubly charged fragments. The present paper gives the channels of the 7 Be fragmentation to charged fragments. In 50% of events, the 7 Be fragmentation proceeds only to charged fragments involving no emission of neutrons. Of them, the 3 He+ 4 He channel dominates, the 4 He+d+p and 6 Li+p channels constitute 10% each.Two events involving no emission of neutrons are registered in the 3-body 3 He+t+p and 3 He+d+d channels. The mean free path for the coherent dissociation of relativistic 7 Be nuclei to 3 He+ 4 He is 7±1 m. The particular features of the relativistic 7 Be fragmentation in such peripheral interactions are explained by the 3 He+ 4 He 2-cluster structure of the 7 Be nucleus.PACS numbers: 21.45.+v, 23.60+e, 25.10.+s *