CHARGE CORRELATIONS AS A PROBE OF NUCLEAR DISASSEMBLY

We have studied multi-fragment decays of Au projectiles after collisio ns with C, Al, Cu and Pb targets at a bombarding energy of 600 MeV/nuc leon. We examine the correlations between the charges emitted in these reactions. These correlations are given as a function of the total ch arge in bound fragments, Z(bound) at forward angles, which is a measur e of the violence of the collision and can be related to the impact pa rameter. The charge distributions have been fitted by a power law and the extracted tau parameter exhibits a minimum as a function of Z(boun d). We observe a strong reduction in the maximum charge, Z(max), of th e event with decreasing Z(bound). For those events where Z(max) is les s than half Z(bound), the relative sizes of the two largest charges wi thin the event cover the full spectrum of possibilities. The charge-Da litz plots indicate that the multi-fragmentation events are not an ext ension of symmetric fission reactions. The event-by-event charge momen ts are examined to measure the size of the charge fluctuations. All of the charge correlations are independent of the target when plotted as a function of Z(bound). The results are compared to both nuclear stat istical and percolation calculations. The model predictions differ fro m each other, establishing that the observables are sensitive to how t he available phase space is populated. The sequential nuclear model pr edicts too asymmetric a decay, while the simultaneous model predicts t oo symmetric a break-up. The percolation model, which was adjusted to reproduce the size of Z(max) correctly predicts the mean behaviour and the fluctuations of the lighter fragments.