3,671 research outputs found
Cascade-Exciton Model Analysis of Nucleon-Induced Fission Cross Sections of Lead and Bismuth at Energies from 45 to 500 MeV
An extended version of the Cascade-Exciton Model (CEM) of nuclear reactions
is applied to analyze nucleon-induced fission cross sections for Bi-209 and
Pb-208 nuclei in the 45-500 MeV energy range. The available data on linear
momentum transfer are analyzed as well. The results are compared with
analytical approximations resulting from a comparative critical analysis of all
available experimental data. Systematic discrepancies between calculations and
experimental data are revealed. A modification of the CEM is proposed, which
significantly improves the model predictions for projectile energies above 100
MeV.Comment: 38 pages, 16 figures, 7 tables, LaTeX, submitted to Nucl. Sci. En
Detailed Geant4 simulations of the ANITA and ANITA-CUP neutron facilities
Simulations of the ANITA spallation neutron source at The Svedberg Laboratory (TSL) are described. Neutron radiation calculations show close agreement with measurements at both standard and close user positions. Gamma radiation characteristics are also predicted
Magnetic Properties of the low dimensional spin system (VO)PO: ESR and susceptibility
Experimental results on magnetic resonance (ESR) and magnetic susceptibility
are given for single crystalline (VO)PO. The crystal growth
procedure is briefly discussed. The susceptibility is interpreted numerically
using a model with alternating spin chains. We determine =51 K and
=0.2. Furthermore we find a spin gap of meV from our ESR
measurements. Using elastic constants no indication of a phase transition
forcing the dimerization is seen below 300 K.Comment: 7 pages, REVTEX, 7 figure
Anisotropic Exchange in LiCuVO probed by ESR
We investigated the paramagnetic resonance in single crystals of LiCuVO
with special attention to the angular variation of the absorption spectrum. To
explain the large resonance linewidth of the order of 1 kOe, we analyzed the
anisotropic exchange interaction in the chains of edge-sharing CuO
octahedra, taking into account the ring-exchange geometry of the
nearest-neighbor coupling via two symmetric rectangular Cu-O bonds. The
exchange parameters, which can be estimated from theoretical considerations,
nicely agree with the parameters obtained from the angular dependence of the
linewidth. The anisotropy of this magnetic ring exchange is found to be much
larger than it is usually expected from conventional estimations which neglect
the bonding geometry. Hence, the data yield the evidence that in copper oxides
with edge-sharing structures the role of the orbital degrees of freedom is
strongly enhanced. These findings establish LiCuVO as one-dimensional
compound at high temperatures.
PACS: 76.30.-v, 76.30.Fc, 75.30.EtComment: 18 pages, 6 figure
On Dissipation Rate of Ocean Waves due to White Capping
We calculate the rate of ocean waves energy dissipation due to whitecapping
by numerical simulation of deterministic phase resolving model for dynamics of
ocean surface. Two independent numerical experiments are performed. First, we
solve the Hamiltonian equation that includes three- and four-wave
interactions. This model is valid for moderate values of surface steepness
only, . Then we solve the exact Euler equation for non-stationary
potential flow of an ideal fluid with a free surface in geometry. We use
the conformal mapping of domain filled with fluid onto the lower half-plane.
This model is applicable for arbitrary high levels of steepness. The results of
both experiments are close. The whitecapping is the threshold process that
takes place if the average steepness . The rate of
energy dissipation grows dramatically with increasing of steepness. Comparison
of our results with dissipation functions used in the operational models of
wave forecasting shows that these models overestimate the rate of wave
dissipation by order of magnitude for typical values of steepness.Comment: 6 pages, 2 figure
Ion counting efficiencies at the IGISOL facility
At the IGISOL-JYFLTRAP facility, fission mass yields can be studied at high
precision. Fission fragments from a U target are passing through a Ni foil and
entering a gas filled chamber. The collected fragments are guided through a
mass separator to a Penning trap where their masses are identified. This
simulation work focuses on how different fission fragment properties (mass,
charge and energy) affect the stopping efficiency in the gas cell. In addition,
different experimental parameters are varied (e. g. U and Ni thickness and He
gas pressure) to study their impact on the stopping efficiency. The simulations
were performed using the Geant4 package and the SRIM code. The main results
suggest a small variation in the stopping efficiency as a function of mass,
charge and kinetic energy. It is predicted that heavy fragments are stopped
about 9% less efficiently than the light fragments. However it was found that
the properties of the U, Ni and the He gas influences this behavior. Hence it
could be possible to optimize the efficiency.Comment: 52 pages, 44 figure
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