V. V. Kirakosyan

Critical temperature for the nuclear liquid-gas phase transition (from multifragmentation and fission)

Critical temperature Tc for the nuclear liquid-gas phase transition is estimated from both the multifragmentation and fission data. In the first case, the critical temperature is obtained by analysis of the intermediate-mass-fragment yields in p(8.1 GeV) + Au collisions within the statistical model of multifragmentation. In the second case, the experimental fission probability for excited 188Os is compared with the calculated one with Tc as a free parameter. It is concluded for both cases that the critical temperature is higher than 15 MeV.

Multifragmentation and nuclear phase transitions (liquid-fog and liquid-gas)

Abstract Thermal multifragmentation of hot nuclei is interpreted as the nuclear liquid-fog phase transition. The charge distributions of the intermediate mass fragments produced in p (3.6 GeV) + Au and p (8.1 GeV) + Au collisions are analyzed with in the statistical multifragmentation model with the critical temperature for the nuclear liquid-gas phase transition T c as a free parameter. The analysis presented here provides strong support for a value of T c > 15MeV.

Nuclear multifragmentation and fission: Similarity and differences

Thermal multifragmentation of hot nuclei is interpreted as the nuclear liquid–fog phase transition inside the spinodal region. The experimental data for p(8.1GeV)+Au collisions are analyzed. It is concluded that the decay process of hot nuclei is characterized by two size parameters: one density at the transition state and one at the kinetic freeze-out. The similarity between the dynamics of fragmentation and ordinary fission is discussed. The IMF emission time is related to the mean rupture time at the multiscission point, which corresponds to the kinetic freeze-out configuration.

The upgraded FASA setup for studying nuclear multifragmentation

The upgraded FASA 4π setup for studying target multifragmentation induced by relativistic light ions on the Nuclotron superconducting accelerator at the Joint Institute for Nuclear Research is described. Basic attention is concentrated on a new detector module composed of 25 telescope-spectrometers. This detector array is used to measure correlations between the relative velocities of fragments with intermediate masses, which is necessary for investigation of multifragmentation dynamics.

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.

Emission time of the intermediate mass fragments in collisions of relativistic deuterons with the gold target

The relative velocity correlation function of pairs of intermediate mass fragments has been studied for d + Au collisions at 4.4 GeV. Experimental correlation functions are compared to that obtained by multi-body Coulomb trajectory calculations under the assumption of various decay times of the fragmenting system. The combined approach with the empirically modified intranuclear cascade code followed by the statistical multifragmentation model was used to generate the starting conditions for these calculations. The fragment emission time is found to be less than 40 fm c−1.

Expansion time of hot nuclei produced by a relativistic deuteron beam

The multifragmentation time scale is measured for d(4.4 GeV) + Au collisions by the analysis of the relative angle correlation function for the intermediate-mass fragments. The experiment was performed with the FASA 4π setup installed at the external beam of the superconducting accelerator Nuclotron. A combined approach of intranuclear cascade prescription followed by the Statistical Model of Multifragmentation is used for the analysis of the data. Multifragmentation of a target spectator is measured to be 100 fm/c (CL > 99.5%) delayed in relation to the collision moment. The latter is fixed by the registration of the fast fragment with Z = 4, produced at the collisionmoment.

Time scale of nuclear multifragmentation induced by light relativistic ions

Nuclear fragmentation in a d (4.4 GeV) + Au collision was studied with a 4π setup FASA on the external beam of the Dubna Nuclotron. The IMF–IMF relative angle correlation function was analyzed using the statistical model of multifragmentation (SMM) with the main goal of estimating the total time scale of the process. It was found that the fragmentation of the hot nucleus was ∼100 fm/c delayed in respect to the collision moment. (Some figures may appear in colour only in the online journal)

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 Vt = (2.6 ± 0.3)V0. The freeze-out volume is found to be twice as large: Vf = (5 ± 1)V0. The similarity between multifragmentation and ordinary fission is discussed.

Source velocity at relativistic beams of 4He

The source velocities (β = ν/c) extracted from rapidity plots of the fragment invariant probability distribution in terms of the longitudinal versus transversal velocity components has been studied for 4He + Au collisions at 4 and 14.6 GeV. It was found transition from broad range source velocities distribution in case of 4He(4 GeV) + Au to fixed source velocity in case of 4He(14.6 GeV) + Au.