Fragmentation channels of relativistic 7Be nuclei in peripheral interactions

Abstract

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 *

Charge topology of the coherent dissociation of relativistic 11C and 12N nuclei

“…In addition, the nuclear-emulsion method should reveal multi-particle channels corresponding in charge topology to the coherent dissociation of the 7 Be [3,11] and 10 B [14] core nuclei in 11 C. An approximate equality of the probabilities for the He + He and He + 2H dominant channels of coherent dissociation is a special feature of the 7 Be nucleus (see Table 1). The respective branching ratio is 1 ± 0.2 according to data of a group from the Lebedev Physical Institute Moscow [3] and 0.7 0.1 according to vaster data sample obtained at JINR [11]. The 2He + H three-body channels are leading ones(of weight about 75%) among 10 B white stars (see Table 2).…”

“…Light nuclei can be represented as various superpositions of bound states of lighter nuclear cores, extremely light nuclear clusters (alpha particles, tritons, 3 He nuclei, and deuterons), and nucleons that coexist in dynamical equilibrium. Owing to this variety, the group of nuclei at the beginning of the table of isotopes provides a laboratory for studying the coexistence and evolution of cluster and shell degrees of freedom.…”

“…The 11 C nucleus, which exhibits a remarkable combination of cluster and shell features of the ground state, exemplify such nuclei. The isotope 11 C is a connecting link between light stable nuclei featuring a pronounced alpha-particle clustering of nucleons and light nuclei at the proton drip line, where clustering that involves the isotope 3 He is of importance. The interaction of virtual helium isotopes and neutron exchange between them in the 11 C nucleus lead to the formation of cluster structures, including the 2 4 He + 3 He configuration.…”

“…The interaction of virtual helium isotopes and neutron exchange between them in the 11 C nucleus lead to the formation of cluster structures, including the 2 4 He + 3 He configuration. Among them, configurations characterized by low binding energies, such as 7 Be + α (7.6 MeV), 10 B + p (8.7 MeV) and 3 He + 8 Be (9.2 MeV), are expected to be more probable than the 9 9 Be + 2p (15.3 MeV) and 8 Because of a wide variety of virtual cluster configurations that may exist in the structure of the 11 C nucleus, investigation of this nucleus becomes an interesting problem in and of itself.…”

Some peculiarities of formation of 4He nuclei in 16Op collisions at 3.25A GeV/c

“…[1][2][3][4][5][6] Information on existence of such cluster structures can be obtained by studying various correlations among final products of fragmentation, which can partly be formed from breakup of intermediate excited nuclear remnants (for example, 6 Li*, 7 Li*, 7 Be*, 9 Be*, 10 B*, 12 C*, 14 N*), 3,7,8 as well as from decay of unstable 8 Be and 9 B nuclei. 9 Besides it, the experimentally observed α particles can be the conserved constituents of the initial α cluster structure (especially at small excitations of the fragmenting nucleus).…”