Universality of spectator fragmentation at relativistic bombarding energies

Abstract

Multi-fragment decays of 129 Xe, 197 Au, and 238 U 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 SiCsI(Tl) telescopes the solid-angle coverage of the setup was extended to θ 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 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 bound , where Z bound is the sum of the atomic numbers Z i of all projectile fragments with Z 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.

Analyzing fragmentation of simple fluids with percolation theory

“…), Darmstadt [13]. Beams of gold ions (Au, Z = 79) at 600 and 1000 MeV/nucleon incident energies were used to bombard targets made of thin copper foils.…”

Generalized isoscaling of isotopic distributions

“…It is important to note that there are problems with determining both the excitation energy [2,5,7,19] and the temperature [12][13][14][15][20][21][22][23][24][25][26] of multifragmenting systems. After correction for collective expansion, for example, calculated excitation energies for peripheral collisions at high energies must be further reduced by roughly 30% to reproduce experimental data and larger corrections are estimated for energetic central collisions [2,7,19,27]. Collective motion, pre-equilibrium emission and Coulomb barrier fluctuations increase significantly the temperatures deduced from kinetic energy spectra [1][2][3]12,19] while secondary decay modifies the temperatures deduced from excited state populations and isotope ratios [21,22].…”

Time scales in spectator fragmentation

“…The distance to the target was 60 cm. The products of the projectile decay were measured with the time-of-flight wall of the ALADIN spectrometer [6] and the quantity Z BOU N D was determined event-by-event. Z BOU N D is defined as the sum of the atomic numbers Z i of all fragments with Z i ≥ 2.…”