4,194 research outputs found
Study of non-equilibrium effects and thermal properties of heavy ion collisions using a covariant approach
Non-equilibrium effects are studied using a full Lorentz-invariant formalism.
Our analysis shows that in reactions considered here, no global or local
equilibrium is reached. The heavier masses are found to be equilibrated more
than the lighter systems. The local temperature is extracted using hot Thomas
Fermi formalism generalized for the case of two interpenetrating pieces of
nuclear matter. The temperature is found to vary linearly with bombarding
energy and impact parameter whereas it is nearly independent of the mass of the
colliding nuclei. This indicates that the study of temperature with medium size
nuclei is also reliable. The maximum temperatures obtained in our approach are
in a nice agreement with earlier calculations of other approaches. A simple
parametrization of maximal temperature as a function of the bombarding energy
is also given.Comment: LaTex-file, 17 pages, 8 figures (available upon request), Journal of
Physics G20 (1994) 181
Nuclear Dynamics at the Balance Energy
We study the mass dependence of various quantities (like the average and
maximum density, collision rate, participant-spectator matter, temperature as
well as time zones for higher density) by simulating the reactions at the
energy of vanishing flow. This study is carried out within the framework of
Quantum Molecular Dynamics model. Our findings clearly indicate an existence of
a power law in all the above quantities calculated at the balance energy. The
only significant mass dependence was obtained for the temperature reached in
the central sphere. All other quantities are rather either insensitive or
depend weakly on the system size at balance energy. The time zone for higher
density as well as the time of maximal density and collision rate follow a
power law inverse to the energy of vanishing flow.Comment: 9 figures, Submitted to Phys. Rev.
Microscopic approach to the spectator matter fragmentation from 400 to 1000 AMeV
A study of multifragmentation of gold nuclei is reported at incident energies
of 400, 600 and 1000 MeV/nucleon using microscopic theory. The present
calculations are done within the framework of quantum molecular dynamics (QMD)
model. The clusterization is performed with advanced sophisticated algorithm
namely \emph{simulated annealing clusterization algorithm} (SACA) along with
conventional spatial correlation method. A quantitative comparison of mean
multiplicity of intermediate mass fragments with experimental findings of
ALADiN group gives excellent agreement showing the ability of SACA method to
reproduce the fragment yields. It also emphasizes the importance of clustering
criterion in describing the fragmentation process within semi-classical model
Mass independence and asymmetry of the reaction: Multi-fragmentation as an example
We present our recent results on the fragmentation by varying the mass
asymmetry of the reaction between 0.2 and 0.7 at an incident energy of 250
MeV/nucleon. For the present study, the total mass of the system is kept
constant (ATOT = 152) and mass asymmetry of the reaction is defined by the
asymmetry parameter (? = | (AT - AP)/(AT + AP) |). The measured distributions
are shown as a function of the total charge of all projectile fragments,
Zbound. We see an interesting outcome for rise and fall in the production of
intermediate mass fragments (IMFs) for large asymmetric colliding nuclei. This
trend, however, is completely missing for large asymmetric nuclei. Therefore,
experiments are needed to verify this prediction
Isospin effects on the mass dependence of balance energy
We study the effect of isospin degree of freedom on balance energy throughout
the mass range between 50 and 350 for two sets of isotopic systems with N/Z =
1.16 and 1.33 as well as isobaric systems with N/Z = 1.0 and 1.4. Our findings
indicate that different values of balance energy for two isobaric systems may
be mainly due to the Coulomb repulsion. We also demonstrate clearly the
dominance of Coulomb repulsion over symmetry energy.Comment: 5 pages, 3 figures In this version the discussion is in terms of N/Z
whereas in the journal the whole discussion is in terms of N/A. The
conclusions remain unaffecte
Domain Growth in Random Magnets
We study the kinetics of domain growth in ferromagnets with random exchange
interactions. We present detailed Monte Carlo results for the nonconserved
random-bond Ising model, which are consistent with power-law growth with a
variable exponent. These results are interpreted in the context of disorder
barriers with a logarithmic dependence on the domain size. Further, we clarify
the implications of logarithmic barriers for both nonconserved and conserved
domain growth.Comment: 7 pages, 4 figure
The study of multifragmentation around transition energy in intermediate energy heavy-ion collisions
Fragmentation of light charged particles is studied for various systems at
different incident energies between 50 and 1000 MeV/nucleon. We analyze
fragment production at incident energies above, below and at transition
energies using the isospin dependent quantum molecular dynamics(IQMD) model.
The trends observed for the fragment production and rapidity distributions
depend upon the incident energy, size of the fragments, composite mass of the
reacting system as well as on the impact parameter of the reaction. The free
nucleons and light charged particles show continous homogeneous changes
irrespective of the transition energies indicating that there is no relation
between the transition energy and production of the free as well as light
charged particles
Analytical parametrization of fusion barriers using proximity potentials
Using the three versions of proximity potentials, namely proximity 1977,
proximity 1988, and proximity 2000, we present a pocket formula for fusion
barrier heights and positions. This was achieved by analyzing as many as 400
reactions with mass between 15 and 296. Our parametrized formula can reproduced
the exact barrier heights and positions within an accuracy of . A
comparison with the experimental data is also in good agreement.Comment: 12 pages, 5 figure
Simulated Annealing Clusterization Algorithm for Studying the Multifragmentation
We present the details of the numerical realization of the recently advanced algorithm developed to identify the fragmentation in heavy ion reactions. This new algorithm is based on the Simulated Annealing method and is dubbed as Simulated Annealing Clusterization Algorithm [SACA]. We discuss the different parameters used in the Simulated Annealing method and present an economical set of the parameters which is based on the extensive analysis carried out for the central and peripheral collisions of Au-Au, Nb-Nb and Pb-Pb. These parameters are crucial for the success of the algorithm. Our set of optimized parameters gives the same results as the most conservative choice, but is very fast. We also discuss the nucleon and fragment exchange processes which are very important for the energy minimization and finally present the analysis of the reaction dynamics using the new algorithm. This algorithm is can be applied whenever one wants to identify which of a given number of constituents form bound objects
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