6 research outputs found
Searching for the statistically equilibrated systems formed in heavy ion collisions
Further improvements and refinements are brought to the microcanonical
multifragmentation model [Al. H. Raduta and Ad. R. Raduta, Phys. Rev. C {\bf
55}, 1344 (1997); {\it ibid.} {\bf 61}, 034611 (2000)]. The new version of the
model is tested on the recently published experimental data concerning the
Xe+Sn at 32 MeV/u and Gd+U at 36 MeV/u reactions. A remarkable good
simultaneous reproduction of fragment size observables and kinematic
observables is to be noticed. It is shown that the equilibrated source can be
unambiguously identified.Comment: Physical Review C, in pres
Effects of the secondary decays on the isotopic thermometers
The sharp microcanonical multifragmentation model from [Al. H. Raduta and Ad.
R. Raduta, Phys. Rev. C 55, 1344 (1997); Phys. Rev. C, in press] is employed
for evaluating the nuclear caloric curve predictions of nine isotopic
thermometers for three representative nuclei. Evaluations are performed for
both primary decay and asymptotic stages. Effects of the secondary decays on
the primary decay caloric curves are evidenced and discussed. In both cases a
dispersive character of the isotopic caloric curves with increasing the source
excitation energy is observed. A procedure of calibrating the isotopic
thermometers on the microcanonical predictions for both primary decay and
asymptotic stages is proposed. The resulting set of calibrating parameters for
each thermometer is independent on the source size, on its excitation energy
and, in the case of the primary decay, on the freeze-out radius assumption.Comment: 13 pages, 5 figures, Nuclear Physics A, in pres
Homogeneity and Size Effects on the Liquid-Gas Coexistence Curve
The effects of (in)homogeneity and size on the phase diagram of Lennard-Jones
fluids are investigated. It is shown that standard multifragmentation scenarios
(finite equilibrated systems with conserved center of mass position and
momentum) are implying a strong radial inhomogeneity of the system strongly
affecting the phase diagram. The homogeneity constraint is therefore necessary
for finite systems in order to align to the ``meaning'' of infinite systems
phase diagrams. In this respect, a method which deduces the equation of state
of homogeneous finite systems from the one corresponding to bulk matter is
designed. The resultant phase diagrams show a strong dependence on the system's
size.Comment: 4 pages, 4 figure
On the free volume in nuclear multifragmentation
In many statistical multifragmentation models the volume available to the
nonoverlapping fragments forming a given partition is a basic ingredient
serving to the simplification of the density of states formula. One therefore
needs accurate techniques for calculating this quantity. While the direct
Monte-Carlo procedure consisting of randomly generating the fragments into the
freeze-out volume and counting the events with no overlapped fragments is
numerically affordable only for partitions with small , the present paper
proposes a Metropolis - type simulation which allows accurate evaluations of
the free volume even for cases with large . This procedure is used for
calculating the available volume for various situations. Though globally this
quantity has an exponential dependence on , variations of orders of
magnitude for partitions with the same may be identified. A parametrization
based on the virial approximation adjusted with a calibration function,
describing very well the variations of the free volume for different partitions
having the same is proposed. This parametrization was successfully tested
within the microcanonical multifragmentation model from [Al. H. Raduta and Ad.
R. Raduta, Phys. Rev. C {\bf 55}, 1344 (1997); {\it ibid.}, {\bf 56}, 2059
(1997)]. Finally, it is proven that parametrizations of the free volume solely
dependent on are rather inadequate for multifragmentation studies producing
important deviations from the exact results.Comment: 20 pages, 9 figures, Nucl. Phys. A (in press
Comparisons of Statistical Multifragmentation and Evaporation Models for Heavy Ion Collisions
The results from ten statistical multifragmentation models have been compared
with each other using selected experimental observables. Even though details in
any single observable may differ, the general trends among models are similar.
Thus these models and similar ones are very good in providing important physics
insights especially for general properties of the primary fragments and the
multifragmentation process. Mean values and ratios of observables are also less
sensitive to individual differences in the models. In addition to
multifragmentation models, we have compared results from five commonly used
evaporation codes. The fluctuations in isotope yield ratios are found to be a
good indicator to evaluate the sequential decay implementation in the code. The
systems and the observables studied here can be used as benchmarks for the
development of statistical multifragmentation models and evaporation codes.Comment: To appear on Euorpean Physics Journal A as part of the Topical Volume
"Dynamics and Thermodynamics with Nuclear Degrees of Freedo