6 research outputs found
Isospin fractionation in the nucleon emissions and fragment emissions in the intermediate energy heavy ion collisions
The degree of isospin fractionation is measured by /
, where and are the saturated
neutron-proton ratio of nucleon emissions (gas phase) and that of fragment
emissions (liquid phase) in heavy ion collision at intermediate energy . The
calculated results by using the isospin-dependent quantum molecular dynamics
model show that the degree of isospin fractionation is sensitive to the
neutron-proton ratio of colliding system but insensitive to the difference
between the neutron-proton ratio of target and that of projectile. In
particular, the degree of isospin fractionation sensitively depends on the
symmetry potential. However its dependences on the isospin dependent in-medium
nucleon-nucleon cross section and momentum dependent interaction are rather
weak.
The nucleon emission (gas phase) mainly determines the dynamical behavior of
the degree of isospin fractionation in the isospin fractionation process,
compared to the effect of fragment emission. In this case, we propose that
/ or can be directly compared with
the experimental data so that the information about symmetry potential can be
obtaine
Probing Mechanical and Chemical Instabilities in Neutron-Rich Matter
The isospin-dependence of mechanical and chemical instabilities is
investigated within a thermal and nuclear transport model using a Skyrme-type
phenomenological equation of state for neutron-rich matter. Respective roles of
the nuclear mean field and the 2-body stochastic scattering on the evolution of
density and isospin fluctuations in either mechanically or chemically unstable
regions of neutron-rich matter are investigated. It is found that the mean
field dominates overwhelmingly the fast growth of both fluctuations, while the
2-body scattering influences significantly the later growth of the isospin
fluctuation only. The magnitude of both fluctuations decreases with the
increasing isospin asymmetry because of the larger reduction of the attractive
isoscalar mean field by the stronger repuslive neutron symmetry potential in
the more neutron-rich matter. Moreover, it is shown that the isospin
fractionation happens later, but grows faster in the more neutron-rich matter.
Implications of these results to current experiments exploring properties of
neutron-rich matter are discussed.Comment: 18 pages & 15 figures, Nuclear Physics A (2001) in pres
Double neutron/proton ratio of nucleon emissions in isotopic reaction systems as a robust probe of nuclear symmetry energy
The double neutron/proton ratio of nucleon emissions taken from two reaction
systems using four isotopes of the same element, namely, the neutron/proton
ratio in the neutron-rich system over that in the more symmetric system, has
the advantage of reducing systematically the influence of the Coulomb force and
the normally poor efficiencies of detecting low energy neutrons. The double
ratio thus suffers less systematic errors. Within the IBUU04 transport model
the double neutron/proton ratio is shown to have about the same sensitivity to
the density dependence of nuclear symmetry energy as the single neutron/proton
ratio in the neutron-rich system involved. The double neutron/proton ratio is
therefore more useful for further constraining the symmetry energy of
neutron-rich matter
Isospin Physics in Heavy-Ion Collisions at Intermediate Energies
In nuclear collisions induced by stable or radioactive neutron-rich nuclei a
transient state of nuclear matter with an appreciable isospin asymmetry as well
as thermal and compressional excitation can be created. This offers the
possibility to study the properties of nuclear matter in the region between
symmetric nuclear matter and pure neutron matter. In this review, we discuss
recent theoretical studies of the equation of state of isospin-asymmetric
nuclear matter and its relations to the properties of neutron stars and
radioactive nuclei. Chemical and mechanical instabilities as well as the
liquid-gas phase transition in asymmetric nuclear matter are investigated. The
in-medium nucleon-nucleon cross sections at different isospin states are
reviewed as they affect significantly the dynamics of heavy ion collisions
induced by radioactive beams. We then discuss an isospin-dependent transport
model, which includes different mean-field potentials and cross sections for
the proton and neutron, and its application to these reactions. Furthermore, we
review the comparisons between theoretical predictions and available
experimental data. In particular, we discuss the study of nuclear stopping in
terms of isospin equilibration, the dependence of nuclear collective flow and
balance energy on the isospin-dependent nuclear equation of state and cross
sections, the isospin dependence of total nuclear reaction cross sections, and
the role of isospin in preequilibrium nucleon emissions and subthreshold pion
production.Comment: 101 pages with embedded epsf figures, review article for
"International Journal of Modern Physics E: Nuclear Physics". Send request
for a hard copy to 1/author