58 research outputs found
Effect of nucleon exchange on projectile multifragmentation in the reactions of 28Si + 112Sn and 124Sn at 30 and 50 MeV/nucleon
Multifragmentation of quasiprojectiles was studied in reactions of 28Si beam
with 112Sn and 124Sn targets at projectile energies 30 and 50 MeV/nucleon. The
quasiprojectile observables were reconstructed using isotopically identified
charged particles with Z_f <= 5 detected at forward angles. The nucleon
exchange between projectile and target was investigated using isospin and
excitation energy of reconstructed quasiprojectile. For events with total
reconstructed charge equal to the charge of the beam (Z_tot = 14) the influence
of beam energy and target isospin on neutron transfer was studied in detail.
Simulations employing subsequently model of deep inelastic transfer,
statistical model of multifragmentation and software replica of FAUST detector
array were carried out. A concept of deep inelastic transfer provides good
description of production of highly excited quasiprojectiles. The isospin and
excitation energy of quasiprojectile were described with good overall
agreement. The fragment multiplicity, charge and isospin were reproduced
satisfactorily. The range of contributing impact parameters was determined
using backtracing procedure.Comment: 11 pages, 8 Postscript figures, LaTeX, to appear in Phys. Rev. C (
Dec 2000
Critical Behavior in Light Nuclear Systems: Experimental Aspects
An extensive experimental survey of the features of the disassembly of a
small quasi-projectile system with 36, produced in the reactions of 47
MeV/nucleon Ar + Al, Ti and Ni, has been carried
out. Nuclei in the excitation energy range of 1-9 MeV/u have been investigated
employing a new method to reconstruct the quasi-projectile source. At an
excitation energy 5.6 MeV/nucleon many observables indicate the presence
of maximal fluctuations in the de-excitation processes. The fragment
topological structure shows that the rank sorted fragments obey Zipf's law at
the point of largest fluctuations providing another indication of a liquid gas
phase transition. The caloric curve for this system shows a monotonic increase
of temperature with excitation energy and no apparent plateau. The temperature
at the point of maximal fluctuations is MeV. Taking this
temperature as the critical temperature and employing the caloric curve
information we have extracted the critical exponents , and
from the data. Their values are also consistent with the values of the
universality class of the liquid gas phase transition. Taken together, this
body of evidence strongly suggests a phase change in an equilibrated mesoscopic
system at, or extremely close to, the critical point.Comment: Physical Review C, in press; some discussions about the validity of
excitation energy in peripheral collisions have been added; 24 pages and 32
figures; longer abstract in the preprin
Evidence of Critical Behavior in the Disassembly of Nuclei with A ~ 36
A wide variety of observables indicate that maximal fluctuations in the
disassembly of hot nuclei with A ~ 36 occur at an excitation energy of 5.6 +-
0.5 MeV/u and temperature of 8.3 +- 0.5 MeV. Associated with this point of
maximal fluctuations are a number of quantitative indicators of apparent
critical behavior. The associated caloric curve does not appear to show a
flattening such as that seen for heavier systems. This suggests that, in
contrast to similar signals seen for liquid-gas transitions in heavier nuclei,
the observed behavior in these very light nuclei is associated with a
transition much closer to the critical point.Comment: v2: Major changes, new model calculations, new figure
Towards the critical behavior for the light nuclei by NIMROD detector
The critical behavior for the light nuclei with A has been
investigated experimentally by the NIMROD multi-detectors. The wide variety of
observables indicate the critical point has been reached in the disassembly of
hot nuclei at an excitation energy of 5.60.5 MeV/u.Comment: 4 pages, 2 figures; Proceeding of 18th Nuclear Physics Division
Conference of the Euro. Phys. Society (NPDC18) "Phase transitions in strongly
interacting matter", Prague, 23.8.-29.8. 2004. To be published in Nuclear
Physics
Tracing the Evolution of Temperature in Near Fermi Energy Heavy Ion Collisions
The kinetic energy variation of emitted light clusters has been employed as a
clock to explore the time evolution of the temperature for thermalizing
composite systems produced in the reactions of 26A, 35A and 47A MeV Zn
with Ni, Mo and Au. For each system investigated, the
double isotope ratio temperature curve exhibits a high maximum apparent
temperature, in the range of 10-25 MeV, at high ejectile velocity. These
maximum values increase with increasing projectile energy and decrease with
increasing target mass. The time at which the maximum in the temperature curve
is reached ranges from 80 to 130 fm/c after contact. For each different target,
the subsequent cooling curves for all three projectile energies are quite
similar. Temperatures comparable to those of limiting temperature systematics
are reached 30 to 40 fm/c after the times corresponding to the maxima, at a
time when AMD-V transport model calculations predict entry into the final
evaporative or fragmentation stage of de-excitation of the hot composite
systems. Evidence for the establishment of thermal and chemical equilibrium is
discussed.Comment: 9 pages, 5 figure
A Ghoshal-like Test of Equilibration in Near-Fermi-Energy Heavy Ion Collisions
Calorimetric and coalescence techniques have been employed to probe
equilibration for hot nuclei produced in heavy ion collisions of 35 to 55 MeV/u
projectiles with medium mass targets. Entrance channel mass asymmetries and
energies were selected in order that very hot composite nuclei of similar mass
and excitation would remain after early stage pre-equilibrium particle
emission. Inter-comparison of the properties and de-excitation patterns for
these different systems provides evidence for the production of hot nuclei with
decay patterns relatively independent of the specific entrance channel.Comment: 7 pages, 2 figure
Properties of the Initial Participant Matter Interaction Zone in Near Fermi-Energy Heavy Ion Collisions
The sizes, temperatures and free neutron to proton ratios of the initial
interaction zones produced in the collisions of 40 MeV/nucleon Ar +
Sn and 55 MeV/nucleonAl + Sn are derived using total
detected neutron plus charged particle multiplicity as a measure of the impact
parameter range and number of participant nucleons. The size of the initial
interaction zone, determined from a coalescence model analysis, increases
significantly with decreasing impact parameter. The temperatures and free
neutron to proton ratios in the interaction zones are relatively similar for
different impact parameter ranges and evolve in a similar fashion.Comment: 7 pages, 8 figure
Thermal excitation of heavy nuclei with 5-15 GeV/c antiproton, proton and pion beams
Excitation-energy distributions have been derived from measurements of
5.0-14.6 GeV/c antiproton, proton and pion reactions with Au target
nuclei, using the ISiS 4 detector array. The maximum probability for
producing high excitation-energy events is found for the antiproton beam
relative to other hadrons, He and beams from LEAR. For protons
and pions, the excitation-energy distributions are nearly independent of hadron
type and beam momentum above about 8 GeV/c. The excitation energy enhancement
for beams and the saturation effect are qualitatively consistent with
intranuclear cascade code predictions. For all systems studied, maximum cluster
sizes are observed for residues with E*/A 6 MeV.Comment: 14 pages including 5 figures and 1 table. Accepted in Physics Letter
B. also available at http://nuchem.iucf.indiana.edu
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