428 research outputs found
Isospin diffusion in semi-peripheral + collisions at intermediate energies (II): Dynamical simulations
We study isospin effects in semi-peripheral collisions above the Fermi energy
by considering the symmetric + and the asymmetric reactions
+ over the incident energy range 52-74 A MeV. A
microscopic transport model with two different parameterizations of the
symmetry energy term is used to investigate the isotopic content of
pre-equilibrium emission and the N/Z diffusion process. Simulations are also
compared to experimental data obtained with the INDRA array and bring
information on the degree of isospin equilibration observed in Ni + Au
collisions. A better overall agreement between data and simulations is obtained
when using a symmetry term which linearly increases with nuclear density
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
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/
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
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
Coulomb chronometry to probe the decay mechanism of hot nuclei
In 129 Xe+ nat Sn central collisions from 8 to 25 MeV/A, the three-fragment
exit channel occurs with a significant cross section. We show that these
fragments arise from two successive binary splittings of a heavy composite
system. The sequence of fragment production is determined. Strong Coulomb
proximity effects are observed in the three-fragment final state. A comparison
with Coulomb trajec-tory calculations shows that the time scale between the
consecutive break-ups decreases with increasing bombarding energy, becoming
quasi-simultaneous above excitation energy E * = 4.00.5 MeV/A. This
transition from sequential to simultaneous break-up was interpreted as the
signature of the onset of multifragmentation for the three-fragment exit
channel in this system.Comment: 12 pages; 13 Figures; 4 Table; Accepted for publication in Physical
Review
Signals of Bose Einstein condensation and Fermi quenching in the decay of hot nuclear systems
We report experimental signals of Bose-Einstein condensation in the decay of
hot Ca projectile-like sources produced in mid-peripheral collisions at
sub-Fermi energies. The experimental setup, constituted by the coupling of the
INDRA 4 detector array to the forward angle VAMOS magnetic spectrometer,
allowed us to reconstruct the mass, charge and excitation energy of the
decaying hot projectile-like sources. Furthermore, by means of quantum
fluctuation analysis techniques, temperatures and mean volumes per particle "as
seen by" bosons and fermions separately are correlated to the excitation energy
of the reconstructed system. The obtained results are consistent with the
production of dilute mixed (bosons/fermions) systems, where bosons experience a
smaller volume as compared to the surrounding fermionic gas. Our findings
recall similar phenomena observed in the study of boson condensates in atomic
traps.Comment: Submitted to Phys. Rev. Lett. (december 2014
Estimate of average freeze-out volume in multifragmentation events
An estimate of the average freeze-out volume for multifragmentation events is
presented. Values of volumes are obtained by means of a simulation using the
experimental charged product partitions measured by the 4pi multidetector INDRA
for 129Xe central collisions on Sn at 32 AMeV incident energy. The input
parameters of the simulation are tuned by means of the comparison between the
experimental and simulated velocity (or energy) spectra of particles and
fragments.Comment: To be published in Phys. Lett. B 12 pages, 5 figure
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