948 research outputs found
Universal fluctuations in heavy-ion collisions in the Fermi energy domain
We discuss the scaling laws of both the charged fragments multiplicity
fluctuations and the charge of the largest fragment fluctuations for Xe+Sn
collisions in the range of bombarding energies between 25 MeV/A and 50 MeV/A.
We show close to E_{lab}=32 MeV/A the transition in the fluctuation regime of
the charge of the largest fragment which is compatible with the transition from
the ordered to disordered phase of excited nuclear matter. The size (charge) of
the largest fragment is closely related to the order parameter characterizing
this process.Comment: 4 pages, 3 figure
Isospin diffusion in semi-peripheral + collisions at intermediate energies (I): Experimental results
Isospin diffusion in semi-peripheral collisions is probed as a function of
the dissipated energy by studying two systems + and
+ , over the incident energy range 52-74\AM. A close
examination of the multiplicities of light products in the forward part of
phase space clearly shows an influence of the isospin of the target on the
neutron richness of these products. A progressive isospin diffusion is observed
when collisions become more central, in connection with the interaction time
Negative heat capacity in the critical region of nuclear fragmentation: an experimental evidence of the liquid-gas phase transition
An experimental indication of negative heat capacity in excited nuclear
systems is inferred from the event by event study of energy fluctuations in
quasi-projectile sources formed in collisions at 35 A.MeV. The
excited source configuration is reconstructed through a calorimetric analysis
of its de-excitation products. Fragment partitions show signs of a critical
behavior at about 5 A.MeV excitation energy. In the same energy range the heat
capacity shows a negative branch providing a direct evidence of a first order
liquid gas phase transition.Comment: 4 Postscript figures, submitted to Phys. Rev. Lett. on 14-apr-199
Thermodynamical features of multifragmentation in peripheral Au + Au Collisions at 35 A.MeV
The distribution of fragments produced in events involving the
multifragmentation of excited sources is studied for peripheral Au + Au
reactions at 35 A.MeV.
The Quasi-Projectile has been reconstructed from its de-excitation products.
An isotropic emission in its rest frame has been observed, indicating that an
equilibrated system has been formed. The excitation energy of the
Quasi-Projectile has been determined via calorimetry.
A new event by event effective thermometer is proposed based on the energy
balance. A peak in the energy fluctuations is observed related to the heat
capacity, suggesting that the system undergoes a liquid-gas type phase
transition at an excitation energy about 5 A.MeV and a temperature 4 - 6 MeV,
dependent on the freeze-out hypothesis. By analyzing different regions of the
Campi-plot, the events associated with the liquid and gas phases as well as the
critical region are thermodynamically characterized.
The critical exponents, tau, beta,gamma, extracted from the high moments of
the charge distribution are consistent with a liquid-gas type phase transition.Comment: 44 pages, 16 Postscript figures, Fig14_nucl-ex.eps in colors, to be
published in Nucl.Phys.A (1999
Isospin Diffusion in Ni-Induced Reactions at Intermediate Energies
Isospin diffusion is probed as a function of the dissipated energy by
studying two systems Ni+Ni and Ni+Au, over the
incident energy range 52-74\AM. Experimental data are compared with the results
of a microscopic transport model with two different parameterizations of the
symmetry energy term. A better overall agreement between data and simulations
is obtained when using a symmetry term with a potential part linearly
increasing with nuclear density. The isospin equilibration time at 52 \AM{} is
estimated to 13010 fm/
The prominent role of the heaviest fragment in multifragmentation and phase transition for hot nuclei
The role played by the heaviest fragment in partitions of multifragmenting
hot nuclei is emphasized. Its size/charge distribution (mean value,
fluctuations and shape) gives information on properties of fragmenting nuclei
and on the associated phase transition.Comment: 11 pages, Proceedings of IWND09, August 23-25, Shanghai (China
Constrained caloric curves and phase transition for hot nuclei
Simulations based on experimental data obtained from multifragmenting
quasi-fused nuclei produced in central Xe + Sn collisions have
been used to deduce event by event freeze-out properties in the thermal
excitation energy range 4-12 AMeV [Nucl. Phys. A809 (2008) 111]. From these
properties and the temperatures deduced from proton transverse momentum
fluctuations, constrained caloric curves have been built. At constant average
volumes caloric curves exhibit a monotonic behaviour whereas for constrained
pressures a backbending is observed. Such results support the existence of a
first order phase transition for hot nuclei.Comment: 14 pages, 5 figures, accepted in Physics Letters
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