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Optical properties of thin film scintillators
Onderišinová, Zuzana
In the present work we studied Pr, Sc co-doped and Eu-doped Lu3Al5O12 thin epitaxial garnet layers prepared by liquid phase epitaxy (LPE) on Y3Al5O12 (YAG) and Lu3Al5O12 (LuAG) single crystalline substrates. In the process of growth BaO - BaF2 - B203 (Pr, Sc co - doped layers) and PbO - B2O3 (Eu - doped layers) fluxes were used. These materials are considered perspective scintillators with high density, fast scintillation response, high quantum efficiency and good chemical and mechanical stability. They are used in a number of applications in which high spatial resolution is required. The absorption, emission and excitation spectra of experimental samples were measured and investigated. Our attention was focused especially on the study of influence of Sc3+ ions on the emission properties of Pr3+ ions in epitaxial layers which mutually contain various amounts of concentrations of dopants. The Sc3+ ions do not show any radiative transitions in visible and UV spectral regions, but they increase the scintillation response of Pr3+ ions. This phenomenon is caused by overlappig of the Sc-related emission around 275 nm with the 4f-5d absorption band of Pr3+ centers. By measurement of radioluminescence this energy transfer from Sc3+ to Pr3+ activator centres was confirmed.
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Optimization of scintillation detector for detection of low energy signal electrons in electron microscopy
Tihlaříková, Eva ; Kadlec, Jaromír (referee) ; Uruba, Václav (referee) ; Neděla, Vilém (advisor)
The dissertation thesis deals with optimization of the scintillation detector for efficient detection of low energy signal electrons in a specimen chamber of a scanning electron microscope. The solution was based on the study of signal electron energy loss mechanisms during their interaction with a conductive layer and a scintillator that can be studied using simulations based on the stochastics Monte Carlo methods. Based on test simulations and their comparison with experimental data, the ideal Monte Carlo software was chosen and used for the study of signal electron energy losses during their transport through the conductive layer as well as following interaction with scintillator, in dependency on the signal electron energy. Simulation results allowed to define criteria for the optimization of the conductive layer. According to these parameters, the optimized layers were deposited on the surface of different scintillators and experimentally tested in the scintillation detector of the scanning electron microscope. Experimental measurements allowed to verify accomplished simulations and provide new information about impact of materials and thicknesses of conductive layers in combination with materials of scintillators and light guides. The increase of the detection efficiency of the scintillation detector equipped with optimised conductive layers and its capability to detect low energy signal electrons were experimentally proved.
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Preparation and optical properties of scintillation oxide layers
Hanuš, Martin ; Kučera, Miroslav (advisor) ; Čuba, Václav (referee) ; Pejchal, Jan (referee)
In this work we studied properties of garnet scintillator layers (RxLu3-xAl5O12, RxY3-xAl5O12) doped by rare earth ions (Ce, Pr, Tb), orthosilicates (Y2SiO5; R = Ce, Tb) and influence of Sc codoping on Pr3+ and Tb3+ emissions. The Zr codoping on Ce3+ emission in orthosilicates was also studied. The samples were prepared by liquid phase epitaxy. The studied materials show high quantum efficiency and good chemical and mechanical stability. They represent ideal materials for 2D imaging devices. We studied optical absorption, excitation and emission spectra and scintillation properties (radiolunescence and photoelectron yield). The aim was to determine the properties of grown layers and their comparison to Czochralski grown single crystals. We looked for the impact of melt and growth conditions on measured layer properties. We also tried to determine optimal amount of dopants in layer. We used PbO - B2O3 and BaO - BaF2 - B2O3 fluxes. Using these fluxes, we succeeded in growing layers with less intrinsic defects in crystal lattice in comparison to single crystals. In grown layers of thickness from 1 to 30 µm higher dopant concentration was achieved than in single crystals.
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Oxide scintillator detectors
Lučeničová, Zuzana ; Kučera, Miroslav (advisor) ; Bryknar, Zdeněk (referee) ; Mihóková, Eva (referee)
The presented thesis focused on the study of a new material concept of Ce3+ doped multicom- ponent aluminum garnets (GdLu)3(GaAl)5O12. High purity single crystalline epitaxial films were grown by the method of liquid phase epitaxy from the BaO-B2O3-BaF2 flux with spe- cial emphasis on the elimination of the potential impurities coming from the flux. Combined experimental study of photoelectron yield (under alpha excitation), decay kinetics of fast and delayed recombination in the milisecond time range (under e-beam excitation) and photo-, cathodo- and radio-luminescence spectroscopies were used to characterize the studied mater- ial. The single-step nonradiative energy transfer from the donor Gd3+ to an acceptor Ce3+ was observed in the low Gd, Ce doped LuAG films and established as long-range dipole - dipole interaction. Special attention was devoted to the positive effect of combined Gd and Ga substitution on the extensive suppression of shallow traps, which are responsible for the slow component in the scintillation response. The best obtained scintillation characteristics of the studied epitaxial films were comparable with the top performance bulk crystals. 1
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Preparation and optical properties of scintillation oxide layers
Hanuš, Martin ; Kučera, Miroslav (advisor)
In this work we studied properties of garnet scintillator layers (RxLu3-xAl5O12, RxY3-xAl5O12) doped by rare earth ions (Ce, Pr, Tb), orthosilicates (Y2SiO5; R = Ce, Tb) and influence of Sc codoping on Pr3+ and Tb3+ emissions. The Zr codoping on Ce3+ emission in orthosilicates was also studied. The samples were prepared by liquid phase epitaxy. The studied materials show high quantum efficiency and good chemical and mechanical stability. They represent ideal materials for 2D imaging devices. We studied optical absorption, excitation and emission spectra and scintillation properties (radiolunescence and photoelectron yield). The aim was to determine the properties of grown layers and their comparison to Czochralski grown single crystals. We looked for the impact of melt and growth conditions on measured layer properties. We also tried to determine optimal amount of dopants in layer. We used PbO - B2O3 and BaO - BaF2 - B2O3 fluxes. Using these fluxes, we succeeded in growing layers with less intrinsic defects in crystal lattice in comparison to single crystals. In grown layers of thickness from 1 to 30 µm higher dopant concentration was achieved than in single crystals.
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Optical properties of thin film scintillators
Onderišinová, Zuzana
In the present work we studied Pr, Sc co-doped and Eu-doped Lu3Al5O12 thin epitaxial garnet layers prepared by liquid phase epitaxy (LPE) on Y3Al5O12 (YAG) and Lu3Al5O12 (LuAG) single crystalline substrates. In the process of growth BaO - BaF2 - B203 (Pr, Sc co - doped layers) and PbO - B2O3 (Eu - doped layers) fluxes were used. These materials are considered perspective scintillators with high density, fast scintillation response, high quantum efficiency and good chemical and mechanical stability. They are used in a number of applications in which high spatial resolution is required. The absorption, emission and excitation spectra of experimental samples were measured and investigated. Our attention was focused especially on the study of influence of Sc3+ ions on the emission properties of Pr3+ ions in epitaxial layers which mutually contain various amounts of concentrations of dopants. The Sc3+ ions do not show any radiative transitions in visible and UV spectral regions, but they increase the scintillation response of Pr3+ ions. This phenomenon is caused by overlappig of the Sc-related emission around 275 nm with the 4f-5d absorption band of Pr3+ centers. By measurement of radioluminescence this energy transfer from Sc3+ to Pr3+ activator centres was confirmed.
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An assessment of interferences influence on tritium volume activities measurement in liquid discharges of Temelin NPP
ŘEHÁČEK, Martin
The aim of this bachelor thesis is to evaluate the importance of selected disturbance effects on the accuracy of tritium determination in wastewater by means of liquid scintillation spectrometry. The thesis studies three disturbance effects: the pH of the sample, the UV radiation illumination of the sample and increased background in sample measurement caused by samples containing beta and gamma radiation emitting radionuclides placed inside the analyzer. The TriCarb 2910TR measuring analyzer and Ultima Gold XR scintillation cocktail were used for the study. Four samples with the following tritium volume activity were prepared for the study: < 3,7 Bq/l, 199,1 +- 4.1 Bq/l, 20 298,2 +- 73,5 Bq/l and 2 659 078,8 +- 6555,2 Bq/l. Each sample was influenced by disturbance effects of increasing intensity. For the experiment with the pH effect, a set of 12 samples with a pH ranging from 1 to 12 was prepared. For the illumination of samples, a room illuminated with fluorescent lamps, which are also a source of UV radiation besides visible radiation, was used. To examine the effect of increased background, three samples containing isotopes of caesium 134Cs and 137Cs emitting beta and gamma rays were prepared. Each sample was gradually affected by these disturbance factors and measured ten times. The measured data were statistically processed and evaluated. The conducted experiment and the statistical processing of the results, taking into account the accuracy of the instrument, revealed that the disturbance effects of the increased background of beta and gamma radiation and UV light exposure only have a significant effect on samples with very low tritium activity. In samples with high tritium activity, this effect is insignificant. The examination of the effect of the pH confirmed that the scintillation cocktail used showed satisfactory stability of the efficiency of the conversion of beta radiation to photons in the pH range of 2-12.
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New detectors for low-energy BSE
Lalinský, Ondřej ; Schauer, Petr ; Kučera, M. ; Hanuš, M. ; Lučeničová, Z.
Backscattered electrons (BSE) are mostly used to study the specimen’s topography. Nowadays, low energy (units of keV) electron beam imaging is often necessary for example for the research of nanomaterials, biomaterials or semiconductors. Because BSE detectors are mostly non-accelerating or low-accelerating, electrons with approximately the same energy as primary beam (PB) have to be detected. Therefore, BSE detectors need to become optimized for such low-energy electrons. For the scintillation detectors, the biggest problem probably lies in the scintillator. Semiconductor detectors aren’t studied in this work. Cerium activated bulk single crystals of yttrium aluminium garnet (YAG:Ce)Ce(X):Y(3-X)Al(5)O(12) are widely used as scintillators for the detection of high-energy backscattered electrons (BSE). However, commonly used YAG:Ce single crystal strongly loses its light yield (LY) with the decrease of the PB energy. As possible available alternatives for this application, bulk single crystals of yttrium aluminium perovskite (YAP:Ce) Ce(x)Y(1-X)AlO(3) and CRY018 can be predicted. However, similar LY drop can be expected also with these scintillators.
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