Thermodynamic Variables from Spectator Decay

New results for the masses, excitation energies, temperatures, and densities of excited spectator systems at breakup are presented. They were obtained in two recent experiments with the ALADIN spectrometer at SIS in which reactions of Au-197 on Au-197 in the regime of relativistic energies up to 1 GeV per nucleon were studied. The methods used to extract these thermodynamic variables are discussed.Comment: 17 pages, TeX with 10 included figures; To appear in the proceedings of the 14th Winter Workshop on Nuclear Dynamics, Snowbird, Utah, January 31 - February 7, 1998; also available from http://www-kp3.gsi.de/www/kp3/aladin_publications.htm

Determination of Critical Exponents in Nuclear Systems

Signatures of critical behaviour in nuclear fragmentation are often based on arguments from percolation theory. We demonstrate with general thermodynamic considerations and studies of the Ising model that the reliance on percolation as a reference model bears the risk of missing parts of the essential physics.Comment: 10 pages, TeX with 1 included figure; Proceedings of the 1st Catania Relativistic Ion Studies: Critical Phenomena and Collective Observables, Acicastello, May 27-31, 1996, to be published by World Scientific Publ. Co.; also available from http://www-kp3.gsi.de/www/kp3/aladin_publications.htm

Fragment Kinetic Energies and Modes of Fragment Formation

Kinetic energies of light fragments A <= 10 from the decay of target spectators in 197Au 197Au collisions at 1000 MeV per nucleon have been measured with high-resolution telescopes at backward angles. Except for protons and apart from the observed evaporation components, the kinetic-energy spectra exhibit slope temperatures of about 17 MeV, independent of the particle species, but not corresponding to the thermal or chemical degrees of freedom at breakup. It is suggested that these slope temperatures may reflect the intrinsic Fermi motion and thus the bulk density of the spectator system at the instant of becoming unstable. PACS numbers: 25.70.Pq, 21.65.+f, 25.70.M