280 research outputs found
Cross-sections for nuclide production in 56Fe target irradiated by 300, 500,750, 1000, 1500, and 2600 MeV protons compared with data on hydrogen target irradiation by 300, 500, 750, 1000, and 1500 MeV/nucleon 56Fe ions
Cross-sections for radioactive nuclide production in 56Fe(p,x) reactions at
300, 500, 750, 1000, 1500, and 2600 MeV were measured using the ITEP U-10
proton accelerator. In total, 221 independent and cumulative yields of products
of half-lives from 6.6 min to 312 days have been obtained via the
direct-spectrometry method. The measured data have been compared with the
experimental data obtained elsewhere by the direct and inverse kinematics
methods and with calculations by 15 codes, namely: MCNPX (INCL, CEM2k, BERTINI,
ISABEL), LAHET (BERTINI, ISABEL), CEM03 (.01, .G1, .S1), LAQGSM03 (.01, .G1,
>.S1), CASCADE-2004, LAHETO, and BRIEFF. Most of our data are in a good
agreement with the inverse kinematics results and disprove the results of some
earlier activation measurements that were quite different from the inverse
kinematics measurements. The most significant calculation-to-experiment
differences are observed in the yields of the A<30 light nuclei, indicating
that further improvements in nuclear reaction models are needed, and pointing
out as well to a necessity of more complete measurements of such reactions.Comment: 53 pages, 9 figures, 6 tables, only pdf file, submitted to Phys. Rev.
Anisotropic flow of charged and identified hadrons in the quark-gluon string model for Au+Au collisions at sqrt(s) = 200 GeV
The pseudorapidity behaviour of the azimuthal anisotropy parameters v_1 and
v_2 of inclusive charged hadrons and their dependence on the centrality has
been studied in Au+Au collisions at full RHIC energy of sqrt(s) = 200 GeV
within the microscopic quark-gluon string model. The QGSM simulation results
for the directed flow v_1 show antiflow alignment within the pseudorapidity
range |eta| < 2 in a fair agreement with the experimental v_1(eta) data, but
cannot reproduce the further development of the antiflow up to |eta| around
3.5. The eta dependence of the elliptic flow v_2 extracted from the simulations
agrees well with the experimental data in the whole pseudorapidity range for
different centrality classes. The centrality dependence of the integrated
elliptic flow of charged hadrons in the QGSM almost coincides with the PHOBOS
experimental distribution. The transverse momentum dependence of the elliptic
flow of identified and inclusive charged hadrons is studied also. The model
reproduces quantitatively the low p_T part of the distributions rather good,
but underestimates the measured elliptic flow for transverse momenta p_T > 1
GeV/c. Qualitatively, however, the model is able to reproduce the saturation of
the v_2(p_T) spectra with rising p_T as well as the crossing of the elliptic
flow for mesons and baryons.Comment: REVTeX, 10 pages, 10 figures, v2: extended discussion of the model
results, accepted for publication in Phys. Rev.
Production of spectator hypermatter in relativistic heavy-ion collisions
We study the formation of large hyper-fragments in relativistic heavy-ion
collisions within two transport models, DCM and UrQMD. Our goal is to explore a
new mechanism for the formation of strange nuclear systems via capture of
hyperons by relatively cold spectator matter produced in semi-peripheral
collisions. We investigate basic characteristics of the produced
hyper-spectators and evaluate the production probabilities of multi-strange
systems. Advantages of the proposed mechanisms over an alternative coalescence
mechanism are analysed. We also discuss how such systems can be detected taking
into account the background of free hyperons. This investigation is important
for the development of new experimental methods for producing hyper-nuclei in
peripheral relativistic nucleus-nucleus collisions, which are now underway at
GSI and are planned for the future FAIR and NICA facilities.Comment: 28 pages, including 10 figures. Submitted to Phys. Rev.
Microscopic study of freeze-out in relativistic heavy ion collisions at SPS energies
The freeze-out conditions in the light (S+S) and heavy (Pb+Pb) colliding
systems of heavy nuclei at 160 AGeV/ are analyzed within the microscopic
Quark Gluon String Model (QGSM). We found that even for the most heavy systems
particle emission takes place from the whole space-time domain available for
the system evolution, but not from the thin ''freeze-out hypersurface", adopted
in fluid dynamical models. Pions are continuously emitted from the whole volume
of the reaction and reflect the main trends of the system evolution. Nucleons
in Pb+Pb collisions initially come from the surface region. For both systems
there is a separation of the elastic and inelastic freeze-out. The mesons with
large transverse momenta, , are predominantly produced at the early stages
of the reaction. The low -component is populated by mesons coming mainly
from the decay of resonances. This explains naturally the decreasing source
sizes with increasing , observed in HBT interferometry. Comparison with
S+S and Au+Au systems at 11.6 AGeV/ is also presented.Comment: REVTEX, 26 pages incl. 9 figures and 2 tables, to be published in the
Physical Review
Cosmogenic activation of Germanium and its reduction for low background experiments
Production of Co and Ge from stable isotopes of Germanium by
nuclear active component of cosmic rays is a principal background source for a
new generation of Ge double beta decay experiments like GERDA and
Majorana. The biggest amount of cosmogenic activity is expected to be produced
during transportation of either enriched material or already grown crystal.
In this letter properties and feasibility of a movable iron shield are
discussed. Activation reduction factor of about 10 is predicted by simulations
with SHIELD code for a simple cylindrical configuration. It is sufficient for
GERDA Phase II background requirements. Possibility of further increase of
reduction factor and physical limitations are considered. Importance of
activation reduction during Germanium purification and detector manufacturing
is emphasized.Comment: 10 pages, 3 tables, 6 figure
Probing the deuteron structure at small N-N distances by cumulative pion production
The fragmentation of deuterons into pions emitted forward in the kinematic
region forbidden for free nucleon-nucleon collisions is analyzed. It is shown
that the inclusion of the non-nucleonic degrees of freedom in a deuteron
results in a satisfactory description of the data for the inclusive pion
spectrum and improves the description of the data about . According to
the data, has very small positive values, less than 0.2, which
contradicts the theoretical calculations ignoring these degrees of freedom.Comment: 3 pages, 2 postscript figures; to appear in the proceedings of
Conference on Quarks and Nuclear Physics (QNP 2002), Julich, Germany, 9-14
Jun 200
Study of correlations at LHC and RHIC energies in collisions within the quark-gluon string model
The Quark Gluon String Model (QGSM) reproduces well the global
characteristics of the collisions at RHIC and LHC, e.g., the
pseudorapidity and transverse momenta distributions at different centralities.
The main goal of this work is to employ the Monte Carlo QGSM for description of
femtoscopic characteristics in collisions at RHIC and LHC. The study is
concentrated on the low multiplicity and multiplicity averaged events, where no
collective effects are expected. The different procedures for fitting the
one-dimensional correlation functions of pions are studied and compared with
the space-time distributions extracted directly from the model. Particularly,
it is shown that the double Gaussian fit reveals the contributions coming
separately from resonances and from directly produced particles. The comparison
of model results with the experimental data favors decrease of particle
formation time with rising collision energy.Comment: 9 pages, 14 figures, 2 table
A Fast Hadron Freeze-out Generator
We have developed a fast Monte Carlo procedure of hadron generation allowing
one to study and analyze various observables for stable hadrons and hadron
resonances produced in ultra-relativistic heavy ion collisions. Particle
multiplicities are determined based on the concept of chemical freeze-out.
Particles can be generated on the chemical or thermal freeze-out hypersurface
represented by a parameterization or a numerical solution of relativistic
hydrodynamics with given initial conditions and equation of state. Besides
standard space-like sectors associated with the volume decay, the hypersurface
may also include non-space-like sectors related to the emission from the
surface of expanding system. For comparison with other models and experimental
data we demonstrate the results based on the standard parameterizations of the
hadron freeze-out hypersurface and flow velocity profile under the assumption
of a common chemical and thermal freeze-out. The C++ generator code is written
under the ROOT framework and is available for public use at
http://uhkm.jinr.ru/.Comment: 28 pages,7 figure
Fast hadron freeze-out generator, part II: noncentral collisions
The fast Monte Carlo procedure of hadron generation developed in our previous
work is extended to describe noncentral collisions of nuclei. We consider
different possibilities to introduce appropriate asymmetry of the freeze-out
hyper-surface and flow velocity profile. For comparison with other models and
experimental data we demonstrate the results based on the standard
parametrizations of the hadron freeze-out hyper-surface and flow velocity
profile assuming either a common chemical and thermal freeze-out or the
chemically frozen evolution from chemical to thermal freeze-out. The C++
generator code is written under the ROOT framework and is available for public
use at http://uhkm.jinr.ru/Comment: 27 pages including 7 figures as EPS-files; prepared using LaTeX
package for publication in Physical Review
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