184 research outputs found
Dynamical aspects of isotopic scaling
Investigation of the effect of the dynamical stage of heavy-ion collisions
indicates that the increasing width of the initial isospin distributions is
reflected by a significant modification of the isoscaling slope for the final
isotopic distributions after de-excitation. For narrow initial distributions,
the isoscaling slope assumes the limiting value of the two individual initial
nuclei while for wide initial isotopic distributions the slope for hot
fragments approaches the initial value. The isoscaling slopes for final cold
fragments increase due to secondary emissions. The experimentally observed
evolution of the isoscaling parameter in multifragmentation of hot
quasiprojectiles at E=50 AMeV, fragmentation of Kr projectiles
at E=25 AMeV and multifragmentation of target spectators at
relativistic energies was reproduced by a simulation with the dynamical stage
described using the appropriate model (deep inelastic transfer and incomplete
fusion at the Fermi energy domain and spectator-participant model at
relativistic energies) and the de-excitation stage described with the
statistical multifragmentation model. In all cases the isoscaling behavior was
reproduced by a proper description of the dynamical stage and no unambiguous
signals of the decrease of the symmetry energy coefficient were observed.Comment: LaTeX, 18 pages, 9 figures, to appear in Phys. Rev.
Production of cold fragments in nucleus-nucleus collisions in the Fermi-energy domain
The reaction mechanism of nucleus-nucleus collisions at projectile energies
around the Fermi energy is investigated with emphasis on the production of
fragmentation-like residues. The results of simulations are compared to
experimental mass distributions of elements with Z = 21 - 29 observed in the
reactions 86Kr+124,112Sn at 25 AMeV. The model of incomplete fusion is modified
and a component of excitation energy of the cold fragment dependent on isospin
asymmetry is introduced. The modifications in the model of incomplete fusion
appear consistent with both overall model framework and available experimental
data. A prediction is provided for the production of very neutron-rich nuclei
using a secondary beam of 132Sn where e.g. the reaction 132Sn+238U at 28 AMeV
appears as a possible alternative to the use of fragmentation reactions at
higher energies.Comment: LaTeX, 15 pages, 5 figures, minor modifications, accepted for
publication in Nuclear Physics
Isoscaling Studies of Fission - a Sensitive Probe into the Dynamics of Scission
The fragment yield ratios were investigated in the fission of 238,233U
targets induced by 14 MeV neutrons. The isoscaling behavior was typically
observed for the isotopic chains of fragments ranging from the proton-rich to
the most neutron-rich ones. The observed high sensitivity of neutron-rich heavy
fragments to the target neutron content suggests fission as a source of
neutron-rich heavy nuclei for present and future rare ion beam facilities,
allowing studies of nuclear properties towards the neutron drip-line and
investigations of the conditions for nucleosynthesis of heavy nuclei. The
breakdowns of the isoscaling behavior around N=62 and N=80 manifest the effect
of two shell closures on the dynamics of scission. The shell closure around
N=64 can be explained by the deformed shell. The investigation of isoscaling in
the spontaneous fission of 248,244Cm further supports such conclusion. The
Z-dependence of the isoscaling parameter exhibits a structure which can be
possibly related to details of scission dynamics. The fission isoscaling
studies can be a suitable tool for the investigation of possible new pathways
to synthesize still heavier nuclei.Comment: 7 pages, 3 figures, RevTex, final version, to appear in Phys. Rev. C
as a regular articl
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
Production mechanism of hot nuclei in violent collisions in the Fermi energy domain
A production mechanism of highly excited nuclei formed in violent collisions
in the Fermi energy domain is investigated. The collision of two nuclei is
decomposed into several stages which are treated separately. Simplified exciton
concept is used for the description of pre-equilibrium emission. A modified
spectator-participant scenario is used where motion along classical Coulomb
trajectories is assumed. The participant and one of the spectator zones undergo
incomplete fusion. Excitation energies of both cold and hot fragment are
determined. Results of the calculation are compared to recent experimental data
in the Fermi energy domain. Data on hot projectile-like, mid-velocity and
fusion-like sources are described consistently. Geometric aspects of
pre-equilibrium emission are revealed. Explanations to previously unexplained
experimental phenomena are given. Energy deposited into non-thermal degrees of
freedom is estimated.Comment: To appear in Nuclear Physics A, 27 pages, 19 figures, LaTe
Tracing the evolution of the symmetry energy of hot nuclear fragments from the compound nucleus towards multifragmentation
The evolution of the symmetry energy coefficient of the binding energy of hot
fragments with increasing excitation is explored in multifragmentation
processes following heavy-ion collisions below the Fermi energy. In this work,
high-resolution mass spectrometric data on isotopic distributions of
projectile-like fragments from collisions of 25 MeV/nucleon 86Kr and 64Ni beams
on heavy neutron-rich targets are systematically compared to calculations
involving the Statistical Multifragmentation Model. The study reveals a gradual
decrease of the symmetry energy coefficient from 25 MeV at the compound nucleus
regime (E*/A < 2 MeV) towards 15 MeV in the bulk multifragmentation regime
(E*/A > 4 MeV). The ensuing isotopic distributions of the hot fragments are
found to be very wide and extend towards the neutron drip-line. These findings
may have important implications to the composition and evolution of hot
astrophysical environments, such as core-collapse supernova.Comment: 5 pages, 4 figures, submitted to Phys. Rev.
Heavy Residue Isoscaling as a Probe of the Process of N/Z Equilibration
The isotopic and isobaric scaling behavior of the yield ratios of heavy
projectile residues from the collisions of 25 MeV/nucleon 86Kr projectiles on
124Sn and 112Sn targets is investigated and shown to provide information on the
process of N/Z equilibration occurring between the projectile and the target.
The logarithmic slopes and of the residue yield ratios
with respect to residue neutron number N and neutron excess N--Z are obtained
as a function of the atomic number Z and mass number A, respectively, whereas
excitation energies are deduced from velocities. The relation of the isoscaling
parameters and with the N/Z of the primary (excited)
projectile fragments is employed to gain access to the degree of N/Z
equilibration prior to fragmentation as a function of excitation energy. A
monotonic relation between the N/Z difference of fragmenting quasiprojectiles
and their excitation energy is obtained indicating that N/Z equilibrium is
approached at the highest observed excitation energies. Simulations with a
deep-inelastic transfer model are in overall agreement with the isoscaling
conclusions. The present residue isoscaling approach to N/Z equilibration
offers an attractive tool of isospin and reaction dynamics studies in
collisions involving beams of stable or rare isotopes.Comment: 15 pages, 4 figures, submitted to Phys. Lett.
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