Search

Triple and four-fold coincidences among fragments have been measured in the reaction 84 Kr+Au at 43 MeV/u. All events showing the projectile-like nucleus and fission fragments of the target-like nucleus, and all events with one additional intermediate-velocity fragment, were analysed in the frame of a dissipative collision and a participant-spectator model. The mechanism is basically that of a dissipative collision but the emission of the intermediate velocity fragment by the target differs from an equilibrated evaporation.

We have studied the transition from the evaporation to the vaporization regime in 197Au induced reactions on C, Al, and Cu targets at a beam energy of 600 MeV per nucleon. The experiment was performed with the ALADIN forward spectrometer at SIS. We find that with increasing violence of the collision the mean multiplicity of intermediate mass fragments first increases to a maximum ⋍ 3.5 and then decreases again. Calculations using the BUU model suggest that the fragmentation is governed by the energy Edep deposited into the Au nucleus and that the maximum of is reached around Edep = 8 MeV/nucleon.

Energy and angular distributions of products with 3⩽Z⩽22 from 32 S + 93 Nb reactions at 10 MeV/N were measured and the cross section for deep-inelastic reactions was deduced. Energy and angular correlations between α-particles and deep-inelastic fragments were measured and analysed in terms of sequential emission from the detected projectile-like fragment ( M α = 0.30± 0.06) and sequential emission from the target-like fragment α = 0.90±0.10). For sequential emission from the target-like fragment shadowing was observed due to the proximity of the two fragments at the time of emission. Three-body Coulomb trajectory (TBCT) calculations give a lifetime of (1–3)×10 −21 s for the target-like fragment, in good agreement with statistical-model calculations. It is shown that the shadow effect is sensitive to the charge/size of the projectile-like fragment as predicted by the TBCT calculations. In the forward hemisphere nonsequential emission of beam-velocity α-particles is observed α = 0.20±0.06). At backward angles another component is observed α = 0.05±0.01) which appears to be emission from the neck region of the scissioning fragments. It is shown that the two nonsequential emission processes have a different dependence on the exit-channel mass split.

Light charged particles and nuclei (1⩽Z⩽8) have been detected in a large forward plastic multidetector (3° < θ