272 research outputs found
Simulation study of a highly efficient, high resolution X-ry sensor based on self-organizing aluminum oxide
State of the art X-ray imaging sensors comprise a trade-off between the
achievable efficiency and the spatial resolution. To overcome such limitations,
the use of structured and scintillator filled aluminum oxide (AlOx) matrices
has been investigated. We used Monte-Carlo (MC) X-ray simulations to determine
the X-ray imaging quality of these AlOx matrices. Important factors which
influence the behavior of the matrices are: filling factor (surface ratio
between channels and 'closed' AlOx), channel diameter, aspect ratio, filling
material etc. Therefore we modeled the porous AlOx matrix in several different
ways with the MC X-ray simulation tool ROSI [1] and evaluated its properties to
investigate the achievable performance at different X-ray spectra, with
different filling materials (i.e. scintillators) and varying channel height and
pixel readout. In this paper we focus on the quantum efficiency, the spatial
resolution and image homogeneity
Influence of Annealing on the Optical and Scintillation Properties of CaWO Single Crystals
We investigate the influence of oxygen annealing on the room temperature
optical and scintillation properties of CaWO single crystals that are being
produced for direct Dark Matter search experiments. The applied annealing
procedure reduces the absorption coefficient at the peak position of the
scintillation spectrum ( nm) by a factor of and leads to an
even larger reduction of the scattering coefficient. Furthermore, the annealing
has no significant influence on the \emph{intrinsic} light yield. An additional
absorption occurring at nm suggests the formation of O hole
centers. Light-yield measurements at room temperature where one crystal surface
was mechanically roughened showed an increase of the \emph{measured} light
yield by and an improvement of the energy resolution at 59.5 keV by
for the annealed crystal. We ascribe this result to the reduction of
the absorption coefficient while the surface roughening is needed to compensate
for the also observed reduction of the scattering coefficient after annealing
Large-scale ultrasound simulations using the hybrid OpenMP/MPI decomposition
The simulation of ultrasound wave propagation through biological tissue has a wide range of practical applications including planning therapeutic ultrasound treatments of various brain disorders such as brain tumours, essential tremor, and Parkinson's disease. The major challenge is to ensure the ultrasound focus is accurately placed at the desired target within the brain because the skull can significantly distort it. Performing accurate ultrasound simulations, however, requires the simulation code to be able to exploit several thousands of processor cores and work with datasets on the order of tens of TB.We have recently developed an efficient full-wave ultrasound model based on the pseudospectral method using pure-MPI with 1D slab domain decomposition that allows simulations to be performed using up to 1024 compute cores. However, the slab decomposition limits the number of compute cores to be less or equal to the size of the longest dimension, which is usually below 1024.
This paper presents an improved implementation that exploits 2D hybrid OpenMP/MPI decomposition. The 3D grid is first decomposed by MPI processes into slabs. The slabs are further partitioned into pencils assigned to threads on demand. This allows 8 to 16 times more compute cores to be employed compared to the pure-MPI code, while also reducing the amount of communication among processes due to the efficient use of shared memory within compute nodes.
The hybrid code was tested on the Anselm Supercomputer (IT4-Innovations, Czech Republic) with up to 2048 compute cores and the SuperMUC supercomputer (LRZ, Germany) with up to 8192 compute cores. The simulation domain sizes ranged from 2563 to 10243 grid points. The experimental results show that the hybrid decomposition can significantly outperform the pure-MPI one for large simulation domains and high core counts, where the efficiency remains slightly below 50%. For a domain size of 10243, the hybrid code using 8192 cores enables the simulations to be accelerated by a factor of 4 compared to the pure-MPI code. Deployment of the hybrid code has the potential to eventually bring the simulation times within clinically meaningful timespans, and allow detailed patient specific treatment plans to be created
Design of plasma shutters for improved heavy ion acceleration by ultra-intense laser pulses
In this work, we investigate the application of the plasma shutters for heavy
ion acceleration driven by a high-intensity laser pulse. We use
particle-in-cell (PIC) and hydrodynamic simulations. The laser pulse,
transmitted through the opaque shutter, gains a steep-rising front and its peak
intensity is locally increased at the cost of losing part of its energy. These
effects have a direct influence on subsequent ion acceleration from the
ultrathin target behind the shutter. In our 3D simulations of silicon nitride
plasma shutter and a silver target, the maximal energy of high-Z ions increases
significantly when the shutter is included for both linearly and circularly
polarized laser pulses. Moreover, application of the plasma shutter for
linearly polarized pulse results in focusing of ions towards the laser axis in
the plane perpendicular to the laser polarization. The generated high energy
ion beam has significantly lower divergence compared to the broad ion cloud,
generated without the shutter. The effects of prepulses are also investigated
assuming a double plasma shutter. The first shutter can withstand the assumed
sub-ns prepulse (treatment of ns and ps prepulses by other techniques is
assumed) and the pulse shaping occursvia interaction with the second shutter.
On the basis of our theoretical findings, we formulated an approach towards
designing a double plasma shutter for high-intensity and high-power laser
pulses and built a prototype.Comment: 30 pages 13 figure
Crystal growth and scintillation properties of Ce-doped PrAlO 3
Abstract Using the micro-pulling-down method, the undoped and Ce 3+ -doped PrAlO 3 single crystals were grown. Absorption spectra and luminescence characteristics under UV and X-ray excitations were measured at room temperature. Weak 5d-4f emission of Pr 3+ was found at 265 nm in the undoped sample. Energy transfer from the Pr 3+ sublattice to Ce 3+ ions seems plausible, but absence of efficient Ce 3+ emission was found and explained as due to the positioning 5 d 1 relaxed excited state of Ce 3+ within the host conduction band
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