147 research outputs found
Constraints on the density dependence of the symmetry energy
Collisions involving 112Sn and 124Sn nuclei have been simulated with the
improved Quantum Molecular Dynamics transport model. The results of the
calculations reproduce isospin diffusion data from two different observables
and the ratios of neutron and proton spectra. By comparing these data to
calculations performed over a range of symmetry energies at saturation density
and different representations of the density dependence of the symmetry energy,
constraints on the density dependence of the symmetry energy at sub-normal
density are obtained. Results from present work are compared to constraints put
forward in other recent analysis.Comment: 8 pages, 4 figures,accepted for publication in Phy. Rev. Let
Probing the density dependence of symmetry energy at subsaturation density with HICs
The reaction mechanism of the central collisions and peripheral collisions
for at is investigated within the
framework of the Improved Quantum Molecular Dynamics model. The results show
that multifragmentation process is an important mechanism at this energy
region, and the influence of the cluster emission on the double n/p ratios and
the isospin transport ratio are important. Furthermore, three observables,
double n/p ratios, isospin diffusion and the rapidity distribution of the ratio
for at E/A=50MeV are analyzed with the
Improved Quantum Molecular Dynamics model. The results show that these three
observables are sensitive to the density dependence of the symmetry energy. By
comparing the calculation results to the data, the consistent constraint on the
density dependence of the symmetry energy from these three observables is
obtained.Comment: IWND2009 proceedin
Neutron and Proton Transverse Emission Ratio Measurements and the Density Dependence of the Asymmetry Term of the Nuclear Equation of State
Recent measurements of pre-equilibrium neutron and proton transverse emission
from (112,124)Sn+(112,124)Sn reactions at 50 MeV/A have been completed at the
National Superconducting Cyclotron Laboratory. Free nucleon transverse emission
ratios are compared to those of A=3 mirror nuclei. Comparisons are made to BUU
transport calculations and conclusions concerning the density dependence of the
asymmetry term of the nuclear equation-of-state at sub-nuclear densities are
made. The double-ratio of neutron-proton ratios between two reactions is
employed as a means of reducing first-order Coulomb effects and detector
efficiency effects. Comparison to BUU model predictions indicate a density
dependence of the asymmetry energy that is closer to a form in which the
asymmety energy increases as the square root of the density for the density
region studied. A coalescent-invariant analysis is introduced as a means of
reducing suggested difficulties with cluster emission in total nucleon
emission. Future experimentation is presented
Extrapolation of neutron-rich isotope cross-sections from projectile fragmentation
Using the measured fragmentation cross sections produced from the 48Ca and
64Ni beams at 140 MeV per nucleon on 9Be and 181Ta targets, we find that the
cross sections of unmeasured neutron rich nuclei can be extrapolated using a
systematic trend involving the average binding energy. The extrapolated
cross-sections will be very useful in planning experiments with neutron rich
isotopes produced from projectile fragmentation. The proposed method is general
and could be applied to other fragmentation systems including those used in
other radioactive ion beam facilities.Comment: accepted for publication in Europhysics Letter
Comparison of statistical treatments for the equation of state for core-collapse supernovae
Neutrinos emitted during the collapse, bounce and subsequent explosion
provide information about supernova dynamics. The neutrino spectra are
determined by weak interactions with nuclei and nucleons in the inner regions
of the star, and thus the neutrino spectra are determined by the composition of
matter. The composition of stellar matter at temperature ranging from
MeV and densities ranging from to 0.1 times the saturation density is
explored. We examine the single-nucleus approximation commonly used in
describing dense matter in supernova simulations and show that, while the
approximation is accurate for predicting the energy and pressure at most
densities, it fails to predict the composition accurately. We find that as the
temperature and density increase, the single nucleus approximation
systematically overpredicts the mass number of nuclei that are actually present
and underestimates the contribution from lighter nuclei which are present in
significant amounts.Comment: 12 pages, 11 figure
Probing the Symmetry Energy with Heavy Ions
Constraints on the EoS for symmetric matter (equal neutron and proton
numbers) at supra-saturation densities have been extracted from energetic
collisions of heavy ions. Collisions of neutron-deficient and neutron-rich
heavy ions now provide initial constraints on the EoS of neutron-rich matter at
sub-saturation densities. Comparisons are made to other available constraints.Comment: 7 pages, 4 figures, Erice 2008 proceedin
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