Limits of complete equilibration of fragments produced in central Au on Au collisions at intermediate energies

Experimental data related to fragment production in central Au on Au collisions were analysed in the framework of a modified statistical model which considers cluster production both prior and at the equilibrated stage. The analysis provides limits to the number of nucleons and to the temperature of the equilibrated source. The rather moderate temperatures obtained from experimental double-yield ratios of d, t, ³He and ⁴He are in agreement with the model calculations. A phenomenological relation was established between the collective flow and the chemical temperature in these reactions. It is shown that dynamical mechanisms of fragment production, e.g. coalescence, dominate at high energies. It is demonstrated that coalescence may be consistent with chemical equilibrium between the produced fragments. The different meaning of chemical and kinetic temperatures is discussed.Received: 14 November 2002, Published online: 8 July 2003PACS: 25.70.Mn Projectile and target fragmentation - 25.70.Pq Multifragment emission and correlations - 25.75.-q Relativistic heavy-ion collisions     

Thermal multifragmentation in p + Au interactions at 2.16, 3.6 and 8.1 GeV incident energies

Multiple emission of intermediate-mass fragments has been studied for the collisions p + Au at 2.16, 3.6 and 8.1 GeV with the FASA setup. The mean IMF multiplicities for events with at least one IMF are equal to 1.7, 1.9 and 2.1 (±0.2) respectively. The multiplicity, charge distributions and kinetic energy spectra of IMF are described in the framework of a intranuclear cascade model followed by the statistical multifragmentation model. However, between the two parts of the calculation the excitation energies and the residual masses and charges are modified to take into account the losses during expansion. The results support a scenario of true thermal multifragmentation of a hot and expanded target spectator. Received: 15 December 1997 / Revised version: 24 April 1998     

Mechanisms of fragment production in heavy-ion reactions at intermediate energies

Comparative analysis of three typical models of nuclear disintegration, the statistical multifragmentation model (SMM), the quantum statistical model (QSM) and a generalized evaporation model (GEM), is carried out. The thermodynamical properties of a decaying system as well as observable characteristics in heavy ion collisions predicted by the different models are discussed. It is shown that these models yield quite similar results for low charge yields at higher excitation energies (E/A>6 MeV per nucleon) and it is suggested that the coincidence measurements of the intermediate mass fragment multiplicity and the neutron and proton multiplicity (or alternatively, the total bound charge) may be very useful for deducing the decay mechanism. The GEM is shown to differ from the other models in predicting a high Z residue peak.     

Liquid-fog and liquid-gas phase transitions in hot nuclei

Thermal multifragmentation of hot nuclei is interpreted as the nuclear liquid-fog phase transition inside the spinodal region. The exclusive data for p(8.1 GeV) + Au collisions are analyzed within the framework of the statistical model SMM. It is found that the partition of hot nuclei is specified after expansion to a volume equal to V _t = (2.6 ± 0.3)V ₀. The freeze-out volume is found to be twice as large: V _f = (5 ± 1)V ₀. The similarity between multifragmentation and ordinary fission is discussed. The text was submitted by the authors in English.     

Collective flow in nuclear fragmentation induced by 4.4 GeV deuteron on gold target

Nuclear multifragmentation in d (4.4 GeV) + Au collision was studied with the 4π setup FASA installed at the external beam of the Dubna Nuclotron. Data obtained are analyzed within the statistical model of multifragmentation. It is found that the kinetic energy spectra of intermediate mass fragments deviate from the predicted ones. It is explained by the collective flow caused by the thermal expansion of fragmenting nucleus.     

Determination of the freeze-out temperature by the isospin thermometer

The high-resolution spectrometer FRS at GSI, Darmstadt, provides the full isotopic and kinematical identification of fragmentation residues in relativistic heavy-ion collisions. Recent measurements of the isotopic distribution of heavy projectile fragments led to a very surprising new physical finding: the residue production does not lose memory of the N/Z of the projectile ending up in a universal deexcitation corridor; an ordering of the residues in relation to the neutron excess of the projectile has been observed. These unexpected features can be interpreted as a new manifestation of multifragmentation. We have found that, at the last stage of the reaction, the temperature of the big clusters subjected to evaporation is limited to a universal value. The thermometer to measure this limiting temperature is the neutron excess of the residues.