W. Karcz

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 of gold nuclei by light relativistic ions: Thermal breakup versus dynamical disintegration

The multiple emission of intermediate-mass fragments (IMF) is studied for collisions of p, 4He, and 12C on Au with the 4π FASA setup. The mean multiplicities of IMF saturate at a value of around 2 for incident energies above 6 GeV. An attempt at describing the observed IMF multiplicities in the two-stage scenario, a fast cascade followed by a statistical multifragmentation, fails. Agreement with the measured IMF multiplicities is obtained by introducing an intermediate expansion phase and modifying empirically the excitation energies and masses of remnants. The angular distributions and energy spectra from p-induced collisions are in agreement with the scenario of “thermal” multifragmentation of a hot and expanded target spectator. In the case of 12C + Au(22.4 GeV) and 4He (14.6 GeV) + Au collisions, deviations from a pure thermal breakup are seen in the fragment energy spectra, which are harder than those both from model calculations and from the measured ones for p-induced collisions. This difference is attributed to a collective flow with the expansion velocity at the surface of about 0.1c (for 12C + Au collisions).

Thermal Multifragmentation of Hot Nuclei and Liquid-Fog Phase Transition *

Multiple emission of intermediate-mass fragments (IMF) in the collisions of protons (up to 8.1 GeV), 4He (4 and 14.6 GeV), and 12C (22.4 GeV) on Au has been studied with the 4π setup FASA. In all the cases, thermal multifragmentation of the hot and diluted target spectator takes place. The fragment multiplicity and charge distributions are well described by the combined model including the modified intranuclear cascade followed by the statistical multibody decay of the hot system. IMF-IMF-correlation study supports this picture, giving a very short time scale of the process (≤70 fm/c). This decay process can be interpreted as the first-order nuclear “liquid-fog” phase transition inside the spinodal region. The evolution of the mechanism of thermal multifragmentation with increasing projectile mass was investigated. The onset of the radial collective flow was observed for heavier projectiles. The analysis reveals information on the fragment space distribution inside the breakup volume: heavier IMFs are formed predominantly in the interior of the fragmenting nucleus possibly due to the density gradient.

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.

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.

Electromagnetic properties of sapphire, ruby, and irradiated ruby at frequencies of 30–40 GHz

Permittivity and electromagnetic losses of sapphire, ruby, and irradiated ruby samples were examined at frequencies of 30–40 GHz and temperatures of 4–300 K employing the whispering gallery mode technique. At room temperature, the dielectric properties of the sapphire, ruby, and irradiated ruby samples were similar. Significant differences in electromagnetic losses took place at cryogenic temperatures. Losses were related to the imaginary part of the susceptibility associated with the presence of paramagnetic Cr3+ ions as well as those introduced by structural defects caused by the irradiation of ruby samples. The presence of impurities and the structural defects result in the dielectric losses being larger than those of pure sapphire.