Fission and ternary cluster decay of hyper - deformed 56 Ni

Coincidences between two heavy fragments have been measured from the fission of Ni compound nuclei formed in the S + Mg reaction at Elab( S) = 165.4 MeV. A unique experimental set-up consisting of two large-area position-sensitive (x, y) gas detector telescopes has been used allowing the complete determination of the observed fragments and their momentum vectors. In addition to binary fission events with subsequent particle evaporation, narrow out-of-plane correlations are observed for two fragments emitted in purely binary events and in events with a missing charge consisting of 2αand 3αparticles (C). These events are interpreted as ternary cluster decay from Ni nuclei at high angular momenta through hyper-deformed shapes. PACS. 25.70.Jj Fusion and fusion-fission reactions – 25.70.Pq Multifragment emission and correlations – 24.60.Dr Statistical compound-nucleus reactions