Fragmentation channels of relativistic ${}^7$Be 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 $\lambda$=14.0$\pm$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+pchannels 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$\pm$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.

10 pages, 3 figures, 3 tables, conference: Conference on Physics of Fundamental Interactions, Moscow, Russia, 5-9 Dec 2005