1,846 research outputs found
Simultaneous Heavy Ion Dissociation at Ultrarelativistic Energies
We study the simultaneous dissociation of heavy ultrarelativistic nuclei
followed by the forward-backward neutron emission in peripheral collisions at
colliders. The main contribution to this particular heavy-ion dissociation
process, which can be used as a beam luminosity monitor, is expected to be due
to the electromagnetic interaction. The Weizsacker-Williams method is extended
to the case of simultaneous excitation of collision partners which is simulated
by the RELDIS code. A contribution to the dissociation cross section due to
grazing nuclear interactions is estimated within the abrasion model and found
to be relatively small.Comment: Talk given at Bologna 2000 Conference - Structure of the Nucleus at
the Dawn of the Century, May 29 - June 3, 2000, 4 pages, 2 figure
Nuclear multifragmentation induced by electromagnetic fields of ultrarelativistic heavy ions
We study the disintegration of nuclei by strong electromagnetic fields
induced by ultrarelativistic heavy ions. The proposed multi-step model includes
1) the absorption of a virtual photon by a nucleus, 2) intranuclear cascades of
produced hadrons and 3) statistical decay of the excited residual nucleus. The
combined model describes well existing data on projectile fragmentation at
energy 200 GeV per nucleon. Electromagnetic multifragmentation of nuclei is
predicted to be an important reaction mechanism at RHIC and LHC energies.Comment: 18 LaTeX pages including 4 figures, uses epsf.sty. Submitted to
Phys.Rev.
Ion-induced electron production in tissue-like media and DNA damage mechanisms
We propose an inclusive approach for calculating characteristics of secondary
electrons produced by ions/protons in tissue-like media. This approach is based
on an analysis of the projectile's interaction with the medium on the
microscopic level. It allows us to obtain the energy spectrum and abundance of
secondary electrons as functions of the projectile kinetic energy. The physical
information obtained in this analysis is related to biological processes
responsible for the irrepearable DNA damage induced by the projectile. In
particular, we consider double strand breaks of DNA caused by secondary
electrons and free radicals, and local heating in the ion's track. The heating
may enhance the biological effectiveness of electron/free radical interactions
with the DNA and may even be considered as an independent mechanism of DNA
damage. Numerical estimates are performed for the case of carbon-ion beams. The
obtained dose-depth curves are compared with results of the MCHIT model based
on the GEANT4 toolkit.Comment: 9 pages, 7 figures, submitted to EPJD, included class files
svepj.clo, svjour.cl
Antiproton-nucleus collisions simulation within a kinetic approach with relativistic mean fields
The Giessen Boltzmann-Uehling-Uhlenbeck transport model with relativistic
mean fields is used to simulate -nucleus collisions. Antiproton
absorption cross sections and momentum distributions of annihilation products
are calculated by varying the coupling strength to the mean meson
fields. Parameters of the antiproton-nucleus optical potential are extracted
from the comparison of the model calculations with experimental data.Comment: 11 pages, 4 figures, modified discussion, version accepted to PRC
including two additional figure
Proton and carbon-ion minibeam therapy: from modeling to treatment
Arrays of minibeams of protons and C in tissue-like media were modeled
with Geant4 toolkit. A set of beam energies was used in simulations to provide
a Spead-out Bragg peak (SOBP) extended by 6 cm in depth for protons as well as
for C. In both cases, beams of 0.3 mm or 0.5 mm FWHM were arranged at
the entrance to a water phantom either on a rectangular or an hexagonal grid to
compare two kinds of projectiles and different minibeam patterns. Differential
and cumulative dose-volume histograms (DVH) were calculated and compared for
protons and C as dose uniformity metrics. A uniform dose distribution
was easily achieved with protons due to an enhanced lateral scattering of these
projectiles in comparison to C. The cumulative DVHs calculated for 0.3
mm or 0.5 mm minibeams almost coincide in the target volume, but diverge for
different grid patterns. In contrast, cumulative entry DVHs were found similar
for both grid patterns, but different for 0.3 mm and 0.5 mm minibeams.Comment: 8 pages, 5 figures, talk given at the XXV International Baldin
Seminar on High Energy Physics Problems "Relativistic Nuclear Physics and
Quantum Chromodynamics", September 18-23, 2023, Dubna, Russi
Evaluation of the total photoabsorption cross sections for actinides from photofission data and model calculations
We have calculated the fission probabilities for 237-Np, 233,235,238-U,
232-Th, and nat-Pb following the absorption of photons with energies from 68
MeV to 3.77 GeV using the RELDIS Monte-Carlo code. This code implements the
cascade-evaporation-fission model of intermediate-energy photonuclear
reactions. It includes multiparticle production in photoreactions on
intranuclear nucleons, pre-equilibrium emission, and the statistical decay of
excited residual nuclei via competition of evaporation, fission, and
multifragmentation processes. The calculations show that in the GeV energy
region the fission process is not solely responsible for the entire total
photoabsorption cross section, even for the actinides: ~55-70% for 232-Th,
\~70-80% for 238-U, and ~80-95% for 233-U, 235-U, and 237-Np. This is because
certain residual nuclei that are created by deep photospallation at GeV photon
energies have relatively low fission probabilities. Using the recent
experimental data on photofission cross sections for 237-Np and 233,235,238-U
from the Saskatchewan and Jefferson Laboratories and our calculated fission
probabilities, we infer the total photoabsorption cross sections for these four
nuclei. The resulting cross sections per nucleon agree in shape and in
magnitude with each other. However, disagreement in magnitude with
total-photoabsorption cross-section data from previous measurements for nuclei
from C to Pb calls into question the concept of a ``Universal Curve'' for the
photoabsorption cross section per nucleon for all nuclei.Comment: 39 pages including 11 figure
Inclusive meson production in peripheral collisions of ultrarelativistic heavy ions
There exist several proposals to use Weizs\"{a}cker-Williams photons
generated by ultrarelativistic heavy ions to produce exotic particles in
fusion reactions. To estimate the background conditions for such
reactions we analyze various mechanisms of meson production in very peripheral
collisions of ultrarelativistic heavy ions at RHIC and LHC energies. Besides
fusion they include also electromagnetic interactions
and strong nucleon-nucleon interactions in grazing collisions. All these
processes are characterised by low multiplicities of produced particles.
and events are simulated by corresponding Monte Carlo codes,
RELDIS and FRITIOF. In each of these processes a certain fraction of pions is
produced close to the mid-rapidity region that gives a background for the
events. The possibility of selecting mesons produced in
fusion events via different cut procedures is
demonstrated.Comment: 27 pages with 4 eps-figures included, uses axodraw.sty Tab.2 and 3
correcte
Gene pool similarities and differences between Ukrainians and Russians of slobozhanshchina based on Y-chromosome data
Results from studying Y chromosomal polymorphisms of Russian and Ukrainian populations are presented for Slobozhanshina, which is a contemporary border region, inhabited in the 17th–18th centuries at the “Wild Field” boundary due to migrations of both the Russians from the north and Ukrainians from the west. In general, the Ukrainian and Russian populations of Slobozhanshchina are very close genetically; their set and frequency range of Y chromosome haplogroups are typical for Eastern Europe. However, a detailed analysis of highly informative Y chromosome markers showed that both nations retain the ethnic specificity of their gene pools after 3.5 centuries of coexistence in the same historical territory: the Ukrainian popula tions are similar to the rest of Ukraine, and Russian populations gravitate towards the south of European Rus sia. The persistent genetic differences may be due to the spatial characteristics of marriage migration and the predominant ethnic environmentyesBelgorod State National Research Universit
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