UNIVERSALITY OF SPECTATOR FRAGMENTATION AT RELATIVISTIC BOMBARDING ENERGIES

Multi-fragment decays of Xe-129, Au-197 and U-238 projectiles in colli sions with Be, C, Al, Cu, In, Au and U targets at energies between E/A = 400 and 1000 MeV have been studied with the ALADIN fonvard-spectrom eter at SIS. By adding an array of 84 Si-CsI(Tl) telescopes the solid- angle coverage of the setup was extended to theta(lab) = 16 degrees. T his permitted the complete detection of fragments from the projectile- spectator source. The dominant feature of the systematic set of data i s the Z(bound) universality that is obeyed by the fragment multiplicit ies and correlations. These observables are invariant with respect to the entrance channel if plotted as a function of Z(bound), where Z(bou nd) is the sum of the atomic numbers Z(i) of all projectile fragments with Z(i) greater than or equal to 2. No significant dependence on the bombarding energy nor on the target mass is observed. The dependence of the fragment multiplicity on the projectile mass follows a linear s caling law. The reasons for and the limits of the observed universalit y of spectator fragmentation an explored within the realm of the avail able data and with model studies. It is found that the universal prope rties should persist up to much higher bombarding energies than explor ed in this work and that they are consistent with universal features e xhibited by the intranuclear cascade and statistical multifragmentatio n models.