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Analysis of pressure distribution in the variant detector with three aperture by CAE system
Tomášek, Martin ; Vyroubal, Petr (referee) ; Maxa, Jiří (advisor)
This master`s thesis analyzes the pressure distribution on the premises of scintillation detector secondary electron in the variant with three aperture. The aim of this study is analyzing the fluid flow depending on the application of the third aperture in the entrance of the detector, thus creating more self-pumped chamber, which is responsible for ensuring a better distribution of pressure in the premises of the detector. The result of the analysis would be determining how to change parameters within the detector. If it is found that application of the third aperture has a positive effect on water flow in the premises of the detector, this arrangement may be used for improvement of the detector. Master`s thesis is divided into several chapters. First describes the basic principles of electron microscopy, including sample preparation, conditions for the proper functioning of microscopes and sharing different types of electron microscopes. The next chapters describe briefly the physical descriptions of gases flow in low pressures and small apertures, the mathematical models and simulation software used in this analysis. The analysis is done in SolidWorks with the module called Cosmos FloSimulation. The conclusion summarizes the results of the analysis, including graphical representations of simulation.
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Comparison of organic scintillators
Nikl, Martin
Optical, luminescence and scintillation characteristics of several organic scintillator samples were compared. Quality of starting materials was found to play a role in the efficiency, while timing characteristics were not changed that much. Energy transfer processes were studied as well.
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Performance of YAG:Ce Scintillators for Low-Energy Electron Detectors in S(T)EM
Lalinský, Ondřej ; Bok, Jan ; Schauer, Petr ; Frank, Luděk
Cerium activated single crystals of yttrium aluminium garnet (YAG:Ce) Y3-xCexAl5O12 are widely used as scintillators in electron detectors for S(T)EM. Nowadays, it is sometimes necessary to detect low-energy electrons without post-acceleration. In such cases, extremely sensitive detectors are required that are able to detect even electrons with energies of only hundreds of eV while avoiding charging of the scintillator surface. However, commonly used scintillators strongly lose their light yield with the decrease of the incident electron energy. Moreover, a thinner conductive layer on the scintillator surface has to be used to allow low-energy electrons to pass through. Possible charging of the surface negatively affects its cathodoluminescence (CL) light yield. The low-energy electron excitation takes place closer to the scintillator surface where damage can be expected owing to its preparation, which also reduces the CL light yield. The aim was to study the influence of the scintillator and its conductive layer on the low-energy electron detection efficiency.
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Innovation possibilities of scintillation electron detector for SEM
Schauer, Petr ; Bok, Jan
To evaluate performance of a scintillation detection system for SEM, it is necessary to consider many scintillator parameters. Various attributes of the scintillator for the SEM electron detector are listed in. The very important parameters are those affecting the detective quantum efficiency (DQE) which is primarily a measure of image noise. Not a less important indicator of image quality is the modulation transfer function (MTF) which describes the ability to show fine image details. Therefore, using a scanning imaging system, the detector bandwidth, which is given especially by the scintillator decay time, is the key to the good MTF. Currently, the YAG:Ce single crystal scintillator (introduced already in 1978 having somewhat limiting decay characteristic is the most frequently used scintillator in the SEM. The aim of this paper is to outline possibilities of scintillator innovation to get the improved MTF and DQE.
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Highly luminescent nanophosphors - new physics, technologies and applications
Nikl, Martin ; Čuba, V. ; Bárta, J. ; Jarý, Vítězslav
The application of radiation synthesis in the manufacturing nanopowders of binary and ternary oxide nanophosphors is reviewed. Technological routes are described: irradiation of specific solutions containing soluble metal salts and OH radical scavenger by UV or ionizing radiation results in the formation of finely dispersed solid phase which is separated from the solution and subsequently converted by further thermal treatment into crystalline nanopowders with typical dimension of grains of several tens of nanometers. Doped ZnO, Y2O3, Y3Al5O12, Lu3Al5O12 and Gd3(Ga,Al)5O12 nanophosphors were prepared and their luminescence and scintillation characteristics were measured. In the photoluminescence decay of doped garnets the distinct effect of nanosized grains was found consisting in the slowing-down of the decay due to the change of effective refractive index.
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Energy loss in the conductive layer on single crystal scintillator surface
Flodrová, E. ; Neděla, Vilém
This work deals with study of mechanisms of loosing signal electron energy in the single crystal scintillator which depend on the type and thickness of the conductive layer on the surface. The types and amount of loss processes will he described. Monte Carlo simulations were performed for quantification of energy loss for individual processes and materials which are commonly used in scintillations detection systems.
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Optická část mnohakanálového energiového analyzátoru elektronů
Čižmár, Petr
Our version of the multichannel energy analyzer consists of two main parts. At first it is an electron optical part, which separates the entering electrons by their energy. Then the electrons land onto a scintillating screen. Secondly there is the optical part, which should project the light signal on the scintillator onto a detecting CCD. There are several ways how to do this
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Optimalizace podmínek hydratace v ESEM
Autrata, Rudolf ; Neděla, Vilém
Study of biological specimens of soft tissues with fine and very fine hydrated structure still remains a big problem because this structure can be easily damaged by dehydration during the initiating phase of vacuum pumping of a microscope. The attention is thus focused on setting up the conditions for complete dehydration of samples, ensuring the nature state of a sample during the critical phase of pumping of a microscope
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