675 research outputs found
Pseudo-critical clusterization in nuclear multifragmentation
In this contribution we show that the biggest fragment charge distribution in
central collisions of Xe+Sn leading to multifragmentation is an admixture of
two asymptotic distributions observed for the lowest and highest bombarding
energies. The evolution of the relative weights of the two components with
bombarding energy is shown to be analogous to that observed as a function of
time for the largest cluster produced in irreversible aggregation for a finite
system. We infer that the size distribution of the largest fragment in nuclear
multifragmentation is also characteristic of the time scale of the process,
which is largely determined by the onset of radial expansion in this energy
range.Comment: 4 pages, 3 figures, Contribution to conference proceedings of the
25th International Nuclear Physics Conference (INPC 2013
Sequential fissions of heavy nuclear systems
In Xe+Sn central collisions from 12 to 20 MeV/A measured with the INDRA
4 multidetector, the three-fragment exit channel occurs with a significant
cross section. In this contribution, we show that these fragments arise from
two successive binary splittings of a heavy composite system. Strong Coulomb
proximity effects are observed in the three-fragment final state. By comparison
with Coulomb trajectory calculations, we show that the time scale between the
consecutive break-ups decreases with increasing bombarding energy, becoming
compatible with quasi-simultaneous multifragmentation above 18 MeV/A.Comment: 6 pages, 5 figures, contribution to conference proceedings of the
Fifth International Workshop on Nuclear fission and Fission-Product
Spectroscop
Fusion excitation function revisited
We report on a comprehensive systematics of fusion-evaporation and/or
fusion-fission cross sections for a very large variety of systems over an
energy range 4-155 A.MeV. Scaled by the reaction cross sections, fusion cross
sections do not show a universal behavior valid for all systems although a high
degree of correlation is present when data are ordered by the system mass
asymmetry.For the rather light and close to mass-symmetric systems the main
characteristics of the complete and incomplete fusion excitation functions can
be precisely determined. Despite an evident lack of data above 15A.MeV for all
heavy systems the available data suggests that geometrical effects could
explain the persistence of incomplete fusion at incident energies as high as
155A.MeV.Comment: 8 pages, 5 figures, contribution to the NN2012 Proceeding
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/
Freeze-out volume in multifragmentation - dynamical simulations
Stochastic mean-field simulations for multifragmenting sources at the same
excitation energy per nucleon have been performed. The freeze-out volume, a
concept which needs to be precisely defined in this dynamical approach, was
shown to increase as a function of three parameters: freeze-out instant,
fragment multiplicity and system size.Comment: Submitted to Eur. Phys. J. A - march 200
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
- …