Universality of spectator fragmentation at relativistic bombarding energies

摘要

Multi-fragment decays of Xe-129, Au-197, and U-238 projectiles in collisions with Be, C, Al, Cu, In, Au, and U targets at energies between E/A=400 MeV and 1000 MeV have been studied with the ALADIN forward-spectrometer at SIS. By adding an array of 84 Si-CsI(Tl) telescopes, the solid-angle coverage of the setup was extended to theta(sub lab)=16 . This permitted the complete detection of fragments from the projectile-spectator source. The dominant feature of the systematic set of data is the Z(sub bound) universality that is obeyed by the fragment multiplicities and correlations. These observables are invariant with respect to the entrance channel if plotted as a function of Z(sub bound), where Z(sub bound) is the sum of the atomic numbers Z(sub i) of all projectile fragments with Z(sub i) >= 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 scaling law. The reasons for and the limits of the observed universality of spectator fragmentation are explored within the realm of the available data and with model studies. It is found that the universal properties should persist up to much higher bombarding energies than explored in this work and that they are consistent with universal features exhibited by the intranuclear cascade and statistical multifragmentation models. (orig.)