910 research outputs found
Isotopic and velocity distributions of Bi produced in charge-pickup reactions of 208Pb at 1 A GeV
Isotopically resolved cross sections and velocity distributions have been
measured in charge-pickup reactions of 1 A GeV 208Pb with proton, deuterium and
titanium target. The total and partial charge-pickup cross sections in the
reactions 208Pb + 1H and 208Pb + 2H are measured to be the same in the limits
of the error bars. A weak increase in the total charge-pickup cross section is
seen in the reaction of 208Pb with the titanium target. The measured velocity
distributions show different contributions - quasi-elastic scattering and
Delta-resonance excitation - to the charge-pickup production. Data on total and
partial charge-pickup cross sections from these three reactions are compared
with other existing data and also with model calculations based on the coupling
of different intra-nuclear cascade codes and an evaporation code.Comment: 20 pages, 12 figures, background information on
http://www-w2k.gsi.de/kschmidt
Measurement of nuclide cross-sections of spallation residues in 1 A GeV 238U + proton collisions
The production of heavy nuclides from the spallation-evaporation reaction of
238U induced by 1 GeV protons was studied in inverse kinematics. The
evaporation residues from tungsten to uranium were identified in-flight in mass
and atomic number. Their production cross-sections and their momentum
distributions were determined. The data are compared with empirical
systematics. A comparison with previous results from the spallation of 208Pb
and 197Au reveals the strong influence of fission in the spallation of 238U.Comment: 20 pages, 10 figures, background information at
http://www-wnt.gsi.de/kschmidt
Cross-sections of spallation residues produced in 1.A GeV 208Pb on proton reactions
Spallation residues produced in 1 GeV per nucleon Pb on proton
reactions have been studied using the FRagment Separator facility at GSI.
Isotopic produc- tion cross-sections of elements from Pm to Pb
have been measured down to 0.1 mb with a high accuracy. The recoil kinetic
energies of the produced fragments were also determined. The obtained
cross-sections agree with most of the few existing gamma-spectroscopy data.
Data are compared with different intra nuclear-cascade and evaporation-fission
models. Drastic deviations were found for a standard code used in technical
applications.Comment: 4 pages, 3 figures, accepted for publication in Phys. Rev. Lett.
Revised version May 12, 200
A quadtree-polygon-based scaled boundary finite element method for image-based mesoscale fracture modelling in concrete
A quadtree-polygon scaled boundary finite element-based approach for image-based modelling of concrete fracture at the mesoscale is developed. Digital images representing the two-phase mesostructure of concrete, which comprises of coarse aggregates and mortar are either generated using a take-and-place algorithm with a user-defined aggregate volume ratio or obtained from X-ray computed tomography as an input. The digital images are automatically discretised for analysis by applying a balanced quadtree decomposition in combination with a smoothing operation. The scaled boundary finite element method is applied to model the constituents in the concrete mesostructure. A quadtree formulation within the framework of the scaled boundary finite element method is advantageous in that the displacement compatibility between the cells are automatically preserved even in the presence of hanging nodes. Moreover, the geometric flexibility of the scaled boundary finite element method facilitates the use of arbitrary sided polygons, allowing better representation of the aggregate boundaries. The computational burden is significantly reduced as there are only finite number of cell types in a balanced quadtree mesh. The cells in the mesh are connected to each other using cohesive interface elements with appropriate softening laws to model the fracture of the mesostructure. Parametric studies are carried out on concrete specimens subjected to uniaxial tension to investigate the effects of various parameters e.g. aggregate size distribution, porosity and aggregate volume ratio on the fracture of concrete at the meso-scale. Mesoscale fracture of concrete specimens obtained from X-ray computed tomography scans are carried out to demonstrate its feasibility
Fission-Residues Produced in the Spallation Reaction 238U+p at 1 A GeV
Fission fragments from 1 A GeV 238U projectiles irradiating a hydrogen target
were investigated by using the fragment separator FRS for magnetic selection of
reaction products including ray-tracing and DE-ToF techniques. The momentum
spectra of 733 identified fragments were analysed to provide isotopic
production cross sections, fission-fragment velocities and recoil momenta of
the fissioning parent nuclei. Besides their general relevance, these quantities
are also demanded for applications. Calculations and simulations with codes
commonly used and recently developed or improved are compared to the data.Comment: 60 pages, 21 figures, 4 tables, 2 appendices (15 pages
Evaporation residues produced in spallation of 208Pb by protons at 500A MeV
The production cross sections of fragmentation-evaporation residues in the
reaction Pb+p at 500A MeV have been measured using the inverse-kinematics
method and the FRS spectrometer (GSI). Fragments were identified in nuclear
charge using ionisation chambers. The mass identification was performed
event-by-event using the B-rho - TOF - Delta-E technique. Although
partially-unresolved ionic charge states induced an ambiguity on the mass of
some heavy fragments, production rates could be obtained with a high accuracy
by systematically accounting for the polluting ionic charge states. The
contribution of multiple reactions in the target was subtracted using a new,
partly self-consistent code. The isobaric distributions are found to have a
shape very close to the one observed in experiments at higher energy. Kinematic
properties of the fragments were also measured. The total and the isotopic
cross sections, including charge-pickup cross sections, are in good agreement
with previous measurements. The data are discussed in the light of previous
spallation measurements, especially on lead at 1 GeV
Pion radii in nonlocal chiral quark model
The electromagnetic radius of the charged pion and the transition radius of
the neutral pion are calculated in the framework of the nonlocal chiral quark
model. It is shown in this model that the contributions of vector mesons to the
pion radii are noticeably suppressed in comparison with a similar contribution
in the local Nambu--Jona-Lasinio model. The form-factor for the process
gamma*pi+pi- is calculated for the -1 GeV^2<q^2<1.6 GeV^2. Our results are in
satisfactory agreement with experimental data.Comment: 7 pages, 7 figure
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