123 research outputs found
Expectations of fragment decay from highly excited nuclei
The statistical model is used to illustrate the consequences of a successive binary decay mechanism as the initial nuclear excitation is pushed towards the limits of stability. The partition of the excitation energy between light and heavy fragments is explicitly calculated, as are the consequences of the decay of the primary light fragments to particle-bound residual nuclei which would be observed experimentally. The test nucleus 100 44 Ru is considered at initial excitations of 100, 200, 400, and 800 MeV. Exit channels of n, p, and α; and 100 clusters of 3 ≤ Z ≤ 20 ≤ 4, 6 ≤ A ≤ 48 are considered from all nuclides in the deexcitation cascade. The total primary and final cluster yields are shown versus Z and initial excitation. The primary versus final yields are also shown individually for 12C, 26Mg, and 48Ca. We show how multifragmentation yields will change with the excitation energy due to a successive binary decay mechanism. Measurements that may be prone to misinterpretation are discussed, as are those that should be representative of initial nucleus excitation
Dynamical treatment of Fermi motion in a microscopic description of heavy ion collisions
A quasiclassical Pauli potential is used to simulate the Fermi motion of nucleons in a molecular dynamical simulation of heavy ion collisions. The thermostatic properties of a Fermi gas with and without interactions are presented. The inclusion of this Pauli potential into the quantum molecular dynamics (QMD) approach yields a model with well defined fermionic ground states, which is therefore also able to give the excitation energies of the emitted fragments. The deexcitation mechanisms (particle evaporation and multifragmentation) of the new model are investigated. The dynamics of the QMD with Pauli potential is tested by a wide range of comparisons of calculated and experimental double-differential cross sections for inclusive p-induced reactions at incident energies of 80 to 160 MeV. Results at 256 and 800 MeV incident proton energy are presented as predictions for completed experiments which are as yet unpublished
The Multifragmentation Freeze--Out Volume in Heavy Ion Collisions
The reduced velocity correlation function for fragments from the reaction Fe
+ Au at 100 A~MeV bombarding energy is investigated using the
dynamical--statistical approach QMD+SMM and compared to experimental data to
extract the Freeze--Out volume assuming simultaneous multifragmentation.Comment: 8 pages; 3 uuencoded figures available with figures command, LateX,
UCRL-J-1157
Quantum Molecular Dynamics Approach to the Nuclear Matter Below the Saturation Density
Quantum molecular dynamics is applied to study the ground state properties of
nuclear matter at subsaturation densities. Clustering effects are observed as
to soften the equation of state at these densities. The structure of nuclear
matter at subsaturation density shows some exotic shapes with variation of the
density.Comment: 21 pages of Latex (revtex), 9 Postscript figure
Deuteron formation in nuclear matter
We investigate deuteron formation in nuclear matter at finite temperatures
within a systematic quantum statistical approach. We consider formation through
three-body collisions relevant already at rather moderate densities because of
the strong correlations. The three-body in-medium reaction rates driven by the
break-up cross section are calculated using exact three-body equations
(Alt-Grassberger-Sandhas type) that have been suitably modified to consistently
include the energy shift and the Pauli blocking. Important quantities are the
lifetime of deuteron fluctuations and the chemical relaxation time. We find
that the respective times differ substantially while using in-medium or
isolated cross sections. We expect implications for the description of heavy
ion collisions in particular for the formation of light charged particles at
low to intermediate energies.Comment: 19 pages, 5 figure
Au+Au central collisions at 150, 250 and 400 AMeV energies in QMD with relativistic forces
An extensive comparison of the recent experimental data published by the FOPI
collaboration at GSI with the results of a relativistically covariant
formulation of a QMD code is presented. For most of the quantities we find
agreement with the experimental results showing that the derived force has a
reasonable momentum dependence.Comment: 33 pages with 18 EPSF figures included. Final version to appear in
Nucl. Phys.
Medium corrections in the formation of light charged particles in heavy ion reactions
Within a microscopic statistical description of heavy ion collisions, we
investigate the effect of the medium on the formation of light clusters. The
dominant medium effects are self-energy corrections and Pauli blocking that
produce the Mott effect for composite particles and enhanced reaction rates in
the collision integrals. Microscopic description of composites in the medium
follows the Dyson equation approach combined with the cluster mean-field
expansion. The resulting effective few-body problem is solved within a properly
modified Alt-Grassberger-Sandhas formalism. The results are incorporated in a
Boltzmann-Uehling-Uhlenbeck simulation for heavy ion collisions. The number and
spectra of light charged particles emerging from a heavy ion collision changes
in a significant manner in effect of the medium modification of production and
absorption processes.Comment: 16 pages, 6 figure
Nuclear Stopping as A Probe to In-medium Nucleon-nucleon Cross Section in Intermediate Energy Heavy Ion Collisions
Using an isospin-dependent quantum molecular dynamics, nuclear stopping in
intermediate heavy ion collisions has been studied. The calculation has been
done for colliding systems with different neutron-proton ratios in beam energy
ranging from 15MeV/u to 150MeV/u. It is found that, in the energy region from
above Fermi energy to 150MeV/u, nuclear stopping is very sensitive to the
isospin dependence of in-medium nucleon-nucleon cross section, but insensitive
to symmetry potential. From this investigation, we propose that nuclear
stopping can be used as a new probe to extract the information on the isospin
dependence of in-medium nucleon-nucleon cross section in intermediate energy
heavy ion collisions
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