Production of ternary events in 4He+U, Bi and Au reactions at 8.8Â GeV

Events with three fragments with Z⩾8 in the interactions of 8.8 GeV 4He with U, Bi and Au nuclei are examined using the Makrofol polycarbonate track detector. The sandwich technique is used to enable a direct observation of the multiply charged fragment emission by a single nucleus. Fragments produced in these events are identified and an event-by-event model-free analysis is performed in order to separate different production mechanisms. A classification scheme based on the multiplicity of intermediate-mass fragments 8⩽Z⩽20 is used in order to identify events belonging to the different reaction channels. In the interactions of 4He with U, about 70% of ternary events are registered with the multiplicity of intermediate-mass fragments MIMFobs=0,1, while in the interactions of 4He with Au, about 60% of ternary events are registered with MIMFobs=2,3. The analysis shows that these two groups of ternary events are produced by different reaction mechanisms. The cross-sections and experimental features are determined for the various reaction mechanisms, and their variation with the target mass has been investigated.