2,935 research outputs found
Temperature effects on the nuclear symmetry energy and symmetry free energy with an isospin and momentum dependent interaction
Within a self-consistent thermal model using an isospin and momentum
dependent interaction (MDI) constrained by the isospin diffusion data in
heavy-ion collisions, we investigate the temperature dependence of the symmetry
energy and symmetry free energy for hot,
isospin asymmetric nuclear matter. It is shown that the symmetry energy
generally decreases with increasing temperature while the
symmetry free energy exhibits opposite temperature
dependence. The decrement of the symmetry energy with temperature is
essentially due to the decrement of the potential energy part of the symmetry
energy with temperature. The difference between the symmetry energy and
symmetry free energy is found to be quite small around the saturation density
of nuclear matter. While at very low densities, they differ significantly from
each other. In comparison with the experimental data of temperature dependent
symmetry energy extracted from the isotopic scaling analysis of intermediate
mass fragments (IMF's) in heavy-ion collisions, the resulting density and
temperature dependent symmetry energy is then used to
estimate the average freeze-out density of the IMF's.used to estimate the
average freeze-out density of the IMF's.Comment: 9 pages, 7 figures, 1 figure added to show the temperature dependence
of the potential and kinetic parts of the symmetry energy. Revised version to
appear in PR
Differential isospin-fractionation in dilute asymmetric nuclear matter
The differential isospin-fractionation (IsoF) during the liquid-gas phase
transition in dilute asymmetric nuclear matter is studied as a function of
nucleon momentum. Within a self-consistent thermal model it is shown that the
neutron/proton ratio of the gas phase becomes {\it smaller} than that of the
liquid phase for energetic nucleons, although the gas phase is overall more
neutron-rich. Clear indications of the differential IsoF consistent with the
thermal model predictions are demonstrated within a transport model for
heavy-ion reactions. Future comparisons with experimental data will allow us to
extract critical information about the momentum dependence of the isovector
strong interaction.Comment: Rapid Communication, Phys. Rev. C (2007) in pres
NUCLEAR CONSTRAINTS ON PROPERTIES OF NEUTRON STAR CRUSTS
The transition density and pressure at the inner edge
separating the liquid core from the solid crust of neutron stars are
systematically studied using a modified Gogny (MDI) and 47 popular Skyrme
interactions within well established dynamical and thermodynamical methods. It
is shown that the widely used parabolic approximation to the full Equation of
State (EOS) of isospin asymmetric nuclear matter may lead to huge errors in
estimating the \rho_{t} and P_{t}, especially for stiffer symmetry energy
functionals . The \rho_{t} and P_{t} decrease roughly linearly
with the increasing slope parameter of the using the full
EOS within both methods. It is also shown that the thickness, fractional mass
and moment of inertia of neutron star crust are all very sensitive to the
parameter through the . Moreover, it is shown that the
constrained in the same sub-saturation density range as the
neutron star crust by the isospin diffusion data in heavy-ion collisions at
intermediate energies limits the transition density and pressure to 0.040
fm^-3}< \rho_{t} < 0.065 fm^-3 and 0.01 MeV/fm^3 < P_{t} < 0.26\rho_tP_t\Delta I/I>0.014RM$ of neutron stars.Comment: 55 pages, 20 figures, 2 tables, new results and discussions added,
accepted version to appear in Ap
Nuclear symmetry potential in the relativistic impulse approximation
Using the relativistic impulse approximation with the Love-Franey \textsl{NN}
scattering amplitude developed by Murdock and Horowitz, we investigate the
low-energy (100 MeV MeV) behavior of the nucleon
Dirac optical potential, the Schr\"{o}dinger-equivalent potential, and the
nuclear symmetry potential in isospin asymmetric nuclear matter. We find that
the nuclear symmetry potential at fixed baryon density decreases with
increasing nucleon energy. In particular, the nuclear symmetry potential at
saturation density changes from positive to negative values at nucleon kinetic
energy of about 200 MeV. Furthermore,the obtained energy and density dependence
of the nuclear symmetry potential is consistent with those of the isospin- and
momentum-dependent MDI interaction with , which has been found to describe
reasonably both the isospin diffusion data from heavy-ion collisions and the
empirical neutron-skin thickness of Pb.Comment: 8 pages, 5 figures, revised version to appear in PR
Transition Density and Pressure at the Inner Edge of Neutron Star Crusts
Using the nuclear symmetry energy that has been recently constrained by the
isospin diffusion data in intermediate-energy heavy ion collisions, we have
studied the transition density and pressure at the inner edge of neutron star
crusts, and they are found to be 0.040 fm
fm and 0.01 MeV/fm MeV/fm,
respectively, in both the dynamical and thermodynamical approaches. We have
also found that the widely used parabolic approximation to the equation of
state of asymmetric nuclear matter gives significantly higher values of
core-crust transition density and pressure, especially for stiff symmetry
energies. With these newly determined transition density and pressure, we have
obtained an improved relation between the mass and radius of neutron stars.Comment: 7 pages, 3 figures, proceeding of "The International Workshop on
Nuclear Dynamics in Heavy-Ion Reactions and the Symmetry Energy (IWND2009)
Effects of isospin and momentum dependent interactions on thermal properties of asymmetric nuclear matter
Thermal properties of asymmetric nuclear matter are studied within a
self-consistent thermal model using an isospin and momentum dependent
interaction (MDI) constrained by the isospin diffusion data in heavy-ion
collisions, a momentum-independent interaction (MID), and an isoscalar
momentum-dependent interaction (eMDYI). In particular, we study the temperature
dependence of the isospin-dependent bulk and single-particle properties, the
mechanical and chemical instabilities, and liquid-gas phase transition in hot
asymmetric nuclear matter. Our results indicate that the temperature dependence
of the equation of state and the symmetry energy are not so sensitive to the
momentum dependence of the interaction. The symmetry energy at fixed density is
found to generally decrease with temperature and for the MDI interaction the
decrement is essentially due to the potential part. It is further shown that
only the low momentum part of the single-particle potential and the nucleon
effective mass increases significantly with temperature for the
momentum-dependent interactions. For the MDI interaction, the low momentum part
of the symmetry potential is significantly reduced with increasing temperature.
For the mechanical and chemical instabilities as well as the liquid-gas phase
transition in hot asymmetric nuclear matter, our results indicate that the
boundary of these instabilities and the phase-coexistence region generally
shrink with increasing temperature and is sensitive to the density dependence
of the symmetry energy and the isospin and momentum dependence of the nuclear
interaction, especially at higher temperatures.Comment: 21 pages, 29 figure
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