1,351 research outputs found
The Influence of in-medium NN cross-sections, symmetry potential and impact parameter on the isospin observables
We explore the influence of in-medium nucleon-nucleon cross section, symmetry
potential and impact parameter on isospin sensitive observables in
intermediate-energy heavy-ion collisions with the ImQMD05 code, a modified
version of Quantum Molecular Dynamics model. At incident velocities above the
Fermi velocity, we find that the density dependence of symmetry potential plays
a more important role on the double neutron to proton ratio and the
isospin transport ratio than the in-medium nucleon-nucleon cross
sections, provided that the latter are constrained to a fixed total NN
collision rate. We also explore both and as a function of the
impact parameter. Since the copious production of intermediate mass fragments
is a distinguishing feature of intermediate-energy heavy-ion collisions, we
examine the isospin transport ratios constructed from different groups of
fragments. We find that the values of the isospin transport ratios for
projectile rapidity fragments with are greater than those constructed
from the entire projectile rapidity source. We believe experimental
investigations of this phenomenon can be performed. These may provide
significant tests of fragmentation time scales predicted by ImQMD calculations.Comment: 24 pages, 9 figures, to be published in Phys. Rev.
Influence of Transport Variables on Isospin Transport Ratios
The symmetry energy in the nuclear equation of state affects many aspects of
nuclear astrophysics, nuclear structure, and nuclear reactions. Recent
constraints from heavy ion collisions, including isospin diffusion observables,
have started to put constraints on the symmetry energy below nuclear saturation
density, but these constraints depend on the employed transport model and input
physics other than the symmetry energy. To understand these dependencies, we
study the influence of the symmetry energy, isoscaler mean field
compressibility and momentum dependence, in-medium nucleon-nucleon cross
sections, and light cluster production on isospin diffusion within the pBUU
transport code. In addition to the symmetry energy, several uncertain issues
strongly affect isospin diffusion, most notably the cross sections and cluster
production. In addition, there is a difference in the calculated isospin
transport ratios, depending upon whether they are computed using the isospin
asymmetry of either the residue or of all forward moving fragments.
Measurements that compare the isospin transport ratios of these two quantities
would help place constraints on the input physics, such as the density
dependence of the symmetry energy.Comment: 31 pages, 15 figures, submitted to PR
Angular Dependence in Proton-Proton Correlation Functions in Central and Reactions
The angular dependence of proton-proton correlation functions is studied in
central and nuclear reactions at E=80
MeV/A. Measurements were performed with the HiRA detector complemented by the
4 Array at NSCL. A striking angular dependence in the laboratory frame is
found within p-p correlation functions for both systems that greatly exceeds
the measured and expected isospin dependent difference between the neutron-rich
and neutron-deficient systems. Sources measured at backward angles reflect the
participant zone of the reaction, while much larger sources observed at forward
angles reflect the expanding, fragmenting and evaporating projectile remnants.
The decrease of the size of the source with increasing momentum is observed at
backward angles while a weaker trend in the opposite direction is observed at
forward angles. The results are compared to the theoretical calculations using
the BUU transport model.Comment: 8 pages, 3 figures, submitted to PR
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