[Show abstract][Hide abstract] ABSTRACT: Isotope temperatures from double ratios of hydrogen, helium, lithium, beryllium, and carbon isotopic yields, and excited-state temperatures from yield ratios of particle-unstable resonances in 4He, 5Li, and 8Be, were determined for spectator fragmentation, following collisions of 197Au with targets ranging from C to Au at incident energies of 600 and 1000 MeV per nucleon. A deviation of the isotopic from the excited-state temperatures is observed which coincides with the transition from residue formation to multi-fragment production, suggesting a chemical freeze-out prior to thermal freeze-out in bulk disintegrations.
Physical Review C 12/2007; 76(6). · 3.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: t, D-60486 Frankfurt, Germany e Forschungszentrum Rossendorf, D-1314 Dresden, Germany f Max-Planck-Institut fur Kernphysik, D-69117 Heidelberg, Germany g Soltan Institute for Nuclear Studies, 00-681 Warsaw, Hoza 69, Poland h NSCL, Michigan State University, East Lansing, MI 48824, USA Energy spectra of protons emitted by the target residue in Au+Au collisions at 1 GeV/u reveal two components with different slopes attributed to preequilibrium and equilibrium emission. The relative contribution of the latter decreases rapidly with excitation energy, so that its presence becomes not apparent for the highest energy bins. It is argued therefore, that equilibrium may not be reached on the gas branch of the caloric curve. The nuclear liquid-gas phase transition thus belongs to the category of nonequilibrium phase transitions for which the concepts developed in synergetics, such as self-organized criticality, provid
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: Proton–proton correlations and correlations of protons, deuterons and tritons with α particles from spectator decays following 197Au + 197Au collisions at 1000 MeV per nucleon have been measured with two highly efficient detector hodoscopes. The constructed correlation functions, interpreted within the approximation of a simultaneous volume decay, indicate a moderate expansion and low breakup densities, similar to assumptions made in statistical multifragmentation models.
[Show abstract][Hide abstract] ABSTRACT: Energy spectra of protons emitted by the target residue in Au + Au
collisions at 1 GeV/u were measured for different excitation energy
bins. They reveal two components with different slopes attributed to
preequilibrium and equilibrium emission. The relative contribution of
the latter decreases rapidly with excitation energy, so that its
presence becomes not apparent for the highest energy bins. It is argued
therefore, that equilibrium may not be reached on the gas branch of the
Acta Physica Polonica Series B 02/1999; 30:445. · 1.01 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Heavy-ion reactions at relativistic energies offer unique possibility for studying phase transitions in finite, hadronic systems. A general overview of this subject is given, emphasizing the most recent results on the liquid-gas transition obtained via nuclear calorimetry.
PROCEEDINGS OF THE EUROPEAN CONFERENCE ON ADVANCES IN NUCLEAR PHYSICS AND RELATED AREAS; 01/1999
[Show abstract][Hide abstract] ABSTRACT: Temperature-excitation energy correlation measurements on several systems at different incident energies are discussed in
the framework of the investigation on possible liquid-gas phase transition in nuclear matter. Results are compared to the
presently available experimental caloric curves. Moreover theisotope and theexcited states temperatures, extracted from double ratios of isotope yields and population ratios of fragment unbound states, respectively,
are compared. p ]The differences on the temperatures deduced from the two methods cannot be accounted for by the sequential
feeding corrections. Instead, they seem to be related to the space-time evolution of the fragmentation process.
[Show abstract][Hide abstract] ABSTRACT: Spectator decay was studied for the system Au + Au at an energy of 1000 A·MeV and the decay of the interaction region at energies between 50 and 200 A·MeV. In both cases temperatures were derived from several double-ratios of neighboring isotopes and from the population of excited states in 5Li and 4He. Agreement was found among the different isotope temperatures and also among the two excited state temperatures. The comparison of isotope and excited state temperatures, however, reveals large differences, which cannot be explained by feeding corrections.At incident energies between 600 and 1000 A·MeV the energy spectra of fragments and also neutrons of the decaying projectile spectator were measured. Whereas the slope parameters of the energy spectra and mean energies for fragments with Z ≥ 2 are independent of the incident energy, a strong dependence is found for the lightest particles, so that preequilibrium contributions to the spectator decay should be taken into account.
[Show abstract][Hide abstract] ABSTRACT: Breakup temperatures were deduced from double ratios of isotope yields for target spectators produced in the reaction 197Au + 197Au at 1000 MeV per nucleon. Pairs of 3,4He and 6,7Li isotopes and pairs of 3,4He and H isotopes (p, d and d, t) yield consistent temperatures after feeding corrections, based on the quantum statistical model, are applied. The temperatures rise with decreasing impact parameter from 4 MeV for peripheral to about 10 MeV for the most central collisions. The good agreement with the breakup temperatures measured previously for projectile spectators at an incident energy of 600 MeV per nucleon confirms the universality established for the spectator decay at relativistic bombarding energies. The measured temperatures also agree with the breakup temperatures predicted by the statistical multifragmentation model. For these calculations a relation between the initial excitation energy and mass was derived which gives good simultaneous agreement for the fragment charge correlations. The energy spectra of light charged particles, measured at /lab = 150o, exhibit Maxwellian shapes with inverse slope parameters much higher than the breakup temperatures. The statistical multifragmentation model, because Coulomb repulsion and sequential decay processes are included, yields light-particle spectra with inverse slope parameters higher than the breakup temperatures but considerably below the measured values. The systematic behavior of the differences suggests that they are caused by light-charged-particle emission prior to the final breakup stage.
Zeitschrift für Physik A Hadrons and Nuclei 11/1997; 359(4):397-406.