197 research outputs found
Heavy-ion Collisions: Direct and indirect probes of the density and temperature dependence of Esym
Heavy-ion collisions provide a versatile terrestrial probe of the nuclear
equation of state through the formation of nuclear matter at a wide variety of
temperatures, densities, and pressures. Direct and indirect approaches for
constraining the density dependence of the symmetry energy using heavy-ion
collisions have been developed. The direct approach relies on scaling methods
which attempt to connect isotopic fragment distributions to the symmetry
energy. Using the indirect approach constraints on the equation of state are
extracted from comparison of experimental results and theoretical transport
calculations which utilize effective nucleon-nucleon interactions. Besides
exploring the density dependence of the equation of state, heavy-ion collisions
are simultaneously probing different temperature gradients of nuclear matter
allowing for the temperature dependence of the symmetry energy to be examined.
The current progress and open questions related to constraining the density and
temperature dependence of the symmetry energy with heavy-ion collisions are
discussed in the review.Comment: Review to appear in the upcoming EPJA special volume on nuclear
symmetry energ
Studies of reaction dynamics in the Fermi energy domain
An overview of recent results on reaction dynamics in the energy region 20 -
50 A.MeV is given. The results of the study of projectile multifragmentation
using the detector array FAUST are presented. Reaction mechanism is determined
and thermodynamical properties of the hot quasiprojectile are investigated.
Preliminary results on fragment isospin asymmetry obtained using the 4
detector array NIMROD are given. Procedure for selecting centrality in
two-dimensional multiplicity histograms is described. Possibility to extract
thermodynamical temperature from systematics of isotope ratios is investigated.
Reaction mechanism leading to production of hot sources is discussed.
Furthermore, the possibilities for production of rare isotopes are discussed
and recent experimental results obtained using recoil separator MARS are
presented.Comment: 18 pages, 11 figures, contribution to proceedings of the conference
DANF'2001, Casta-Papiernicka, Slovakia published by World Scientifi
Symmetry Energy in the Equation of State of Asymmetric Nuclear Matte
The symmetry energy is an important quantity in the equation of state of
isospin asymmetric nuclear matter. This currently unknown quantity is key to
understanding the structure of systems as diverse as the neutron-rich nuclei
and neutron stars. At TAMU, we have carried out studies, aimed at understanding
the symmetry energy, in a variety of reactions such as, the multifragmentation
of Ar, Ca + Fe, Ni and Ni, Fe +
Ni, Fe reactions at 25 - 53 AMeV, and deep-inelastic reactions of
Kr + Sn, Ni (25 AMeV), Ni + Ni,
Sn, Th, Pb (25 AMeV) and Xe + Ni,
Sn, Th, Au (20 AMeV). Here we present an overview
of some of the results obtained from these studies. The results are analyzed
within the framework of statistical and dynamical models, and have important
implications for future experiments using beams of neutron-rich nuclei.Comment: 10 pages, 4 figures, talk presented at VI Latin American Symposium on
Nuclear Physics and Application
Effective nucleon mass and the nuclear caloric curve
Assuming a schematic form of the nucleon effective mass as a function of
nuclear excitation energy and mass, we provide a simple explanation for
understanding the experimentally observed mass dependence of the nuclear
caloric curve. It is observed that the excitation energy at which the caloric
curve enters into a plateau region, could be sensitive to the nuclear mass
evolution of the effective nucleon mass.Comment: 5 pages, 5 figures, Accepted for publication in Phys. Rev. C. Minor
changes mad
Isoscaling in Peripheral Nuclear Collisions around the Fermi Energy and a Signal of Chemical Separation from its Excitation Energy Dependence
The isoscaling is investigated using the fragment yield data from fully
reconstructed quasi-projectiles observed in peripheral collisions of 28Si with
124,112Sn at projectile energies 30 and 50 MeV/nucleon. The excitation energy
dependence of the isoscaling parameter beta_prime is observed which is
independent of beam energy. For a given quasi-projectile produced in reactions
with different targets no isoscaling is observed. The isoscaling thus reflects
the level of N/Z-equilibration in reactions with different targets represented
by the initial quasi-projectile samples. The excitation energy dependence of
the isoscaling parameter beta_prime, corrected for the trivial 1/T temperature
dependence, does not follow the trend of the homogeneous system above 4
MeV/nucleon thus possibly signaling the onset of separation into isospin
asymmetric dilute and isospin symmetric dense phase.Comment: 4 pages, 4 figures, RevTeX, to appear in Physical Review
Symmetry energy and the isoscaling properties of the fragments produced in Ar, Ca + Fe, Ni reactions at 25 53 MeV/nucleon
The symmetry energy and the isoscaling properties of the fragments produced
in the multifragmentation of Ar, Ca + Fe, Ni
reactions at 25 - 53 MeV/nucleon were investigated within the framework of
statistical multifragmentation model. The isoscaling parameters , from
the primary (hot) and secondary (cold) fragment yield distributions, were
studied as a function of excitation energy, isospin (neutron-to-proton
asymmetry) and fragment symmetry energy. It is observed that the isoscaling
parameter decreases with increasing excitation energy and decreasing
symmetry energy. The parameter is also observed to increase with
increasing difference in the isospin of the fragmenting system. The sequential
decay of the primary fragments into secondary fragments, when studied as a
function of excitation energy and isospin of the fragmenting system, show very
little influence on the isoscaling parameter. The symmetry energy however, has
a strong influence on the isospin properties of the hot fragments. The
experimentally observed scaling parameters can be explained by symmetry energy
that is significantly lower than that for the ground state nuclei near
saturation density. The results indicate that the properties of hot nuclei at
excitation energies, densities and isospin away from the normal ground state
nuclei could be significantly different.Comment: 14 pages, 15 figure
Isospin non-equilibrium in heavy-ion collisions at intermediate energies
We study the equilibration of isospin degree of freedom in intermediate
energy heavy-ion collisions using an isospin-dependent BUU model. It is found
that there exists a transition from the isospin equilibration at low energies
to non-equilibration at high energies as the beam energy varies across the
Fermi energy in central, asymmetric heavy-ion collisions. At beam energies
around 55 MeV/nucleon, the composite system in thermal equilibrium but isospin
non-equilibrium breaks up into two primary hot residues with N/Z ratios closely
related to those of the target and projectile respectively. The decay of these
forward-backward moving residues results in the strong isospin asymmetry in
space and the dependence of the isotopic composition of fragments on the N/Z
ratios of the target and projectile. These features are in good agreement with
those found recently in experiments at NSCL/MSU and TAMU, implications of these
findings are discussed.Comment: 9 pages, latex, + 3 figures available upon reques
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