Lithium tetraborate (Li2B4O7) has aroused interest of scientists since 1960s by the courtesy of the thermoluminescence (TL) property it possesses. Over and above, it found widespread use in surface acoustic wave apparatuses, in sensor sector and in laser technology due to its non linear optical characteristics. For the uses in thermoluminescence dosimetry lithium tetraborate is activated by addition of a variety of metals as dopants. This study comprises the synthesis of lithium tetraborate by two methods (high temperature solid state synthesis and water/solution assisted synthesis) as well as doping and characterization of the material. Lithium tetraborate is readily commercially available in TL dosimetry / hence, the main aim is to specify practical production conditions to pioneer domestic production. In high temperature synthesis, the initial heating was performed at 400oC for 3 hours. Then the samples were heated at 750oC for two hours, intermittently mixed to enhance diffusion and exposed to the same temperature for another two hours. In water/solution assisted synthesis, stoichiometric quantities of reactants were mixed in water by heating and agitating in order to achieve homogenous mixing and good dispersion of the material. The remnant of water was removed from the system by 3 hours initial heating at 150oC. The synthesis stage is followed by doping step where the metals Cu, Ag and In in different proportions were doped in lithium tetraborate by solid state and solution assisted synthesis techniques. Powder X-ray diffraction method was employed for the characterization of the material. The thermal properties of doped and un-doped materials were studied by DTA (Differential Thermal Analyses). Besides, FT-IR (Fourier Transform Infra red) spectrometry analyses were performed in order to detect differences in the bond structure caused by doping The XRD patterns obtained showed that lithium tetraborate production was successful by both high temperature solid state synthesis and solution assisted synthesis Moreover, it was inferred from the XRD results that addition of dopants did not have a sound effect on the crystal structure. Furthermore, the DTA results displayed that addition of different dopants to the structure of lithium tetraborate did not cause any noticeable difference. The extensive TL measurements showed that the TL response of the material produced is affected by production and doping methods.

In this study, differences in glow curves of Mn doped LTB powder samples synthesized with solid and wet synthesis methods and doped by using solid and wet doping techniques were investigated. Firstly, LTB was synthesized by using wet synthesis method which mainly comprises dissolution of reactants in water as solvent. Second way to produce LTB which was used in this study was solid synthesis method. In solid synthesis method, reactants were mixed in powder form. In the second part of the study, LTB produced by two different methods were doped with Mn and additionally Ag, Mg or P by using two different doping techniques. In order to see structural differences between differently synthesized and differently doped LTB samples which contained different amount of dopant powder X-Ray Diffraction (XRD) method was employed. Besides, FTIR (Fourier Transform Infrared) spectroscopy analyses were performed in order to detect differences in the bond structure caused by doping. Additionally, Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) was used to determine the actual amount of dopant in LTB. Also morphological structures of samples were compared by using Scanning Electron Microscopy (SEM). Thermoluminescence measurements were performed with (TLD) Thermoluminescence Dosimeter equipment. XRD and FTIR analysis showed that syntheses of products were done in well success. Addition of dopants did not cause any changes in structural or bonding properties of LTB. It was possible to observe that, synthesis and doping methods and dopant concentration effect the thermoluminescence glow curves of doped LTB.

This work aims the production of luminescent materials based on MgB4O7 (MBO) and Li2B4O7 (LBO), doped and undoped, by alternative routes, verifying the influence of the route on the optical properties and grain size. Sol-gel protein (SGP) and Pechini (MP) methods were chosen for the production of the samples. Structural characterization of the materials was performed through thermal measurements and X-ray diffraction (XRD). Thermal analyses indicate that the crystallization process of the samples at intervals of 700 to 1000 C for MBO and 500 to 700 C for LBO by both production methods. XRD measurements confirm the formation of single crystalline phase under synthesis conditions 900 C/2h (SGP) and 800 C/2h (MP) for MBO crystal and 650 C/2h (SGP) and 600 C/2h (MP) for MBO. These conditions also were used to doped samples but single phases for doped LBO cannot be obtained. All samples present a coloration that could disrupt the luminescent signal during thermoluminescence (TL) and optically stimulated luminescence (OSL) readings. Samples were washed with hydrogen peroxide aiming to test the influence of coloration in optical properties. Optical measurements showed that the samples no washed with hydrogen peroxide have more efficient TL signal than washed samples. As a rule, the unwashed samples of MBO:Ce,Li produced by both methods showed the best TL signal. The MBO:Dy,Li – SGP – washed samples showed only 10% of the batch discharge units 20 tablets with homogeneity tests. On the other hand, for both MBO:Dy,Li (SGP,MP) were verified that the TL signal decays with the decrease of the grain size and occurs a displacement of the position of the TL peaks. The minimum detectable dose calculated for the washed samples of the MBO:Ce,Li and MBO:Dy,Li were 0.02 Gy and approximately 0.3 Gy respectively for both production methods. The OSL measurements showed MBO:Dy,Li – SGP have the best signal and that grain size have no influence in OSL signal. Phototransferred thermoluminescence effect (PTTE) occurred to MBO:Dy,Li – washed samples. Photoluminescent (PL) measurements indicate high symmetry in the dopant region for the MBO:Ce,Li – MP - washed sample. The LBO samples produced by both methods presented high sensitivity to the production method, precursor reagents used and dopants. / Esse trabalho propõe a produção de materiais luminescentes baseados em MgB4O7 (MBO) e Li2B4O7 (LBO), puros e dopados, por rotas alternativas, verificando a influência da rota sobre as propriedades ópticas e o tamanho do grão. Os métodos sol-gel proteico (SGP) e Pechini (MP) foram escolhidos para a produção das amostras. A caracterização estrutural dos materiais foi realizada através de medições térmicas e difração de raios X (XRD). As análises térmicas indicam que o processo de cristalização das amostras ocorre em intervalos de 700 a 1000 C para MBO e 500 a 700 C para LBO por ambos os métodos de produção. As medidas de XRD confirmam a formação de fase monocristalina em condições de síntese 900 C/2h (SGP) e 800 C/2h (MP) para o MBO; e 650 C/2h (SGP) e 600 C/2h (MP) para o LBO. Essas condições também foram usadas para a preparação de amostras dopadas, porém não foram obtidas fases únicas das amostras de LBO dopadas. Todas as amostras apresentaram uma coloração que poderiam atrapalhar o sinal luminescente durante a termoluminescência (TL) e as leituras de luminescência opticamente estimulada (OSL). Os procedimentos de lavagem com peróxido de hidrogênio foram realizados nas amostras com o objetivo de testar a influência da coloração nas propriedades ópticas. As medições ópticas mostraram que as amostras sem lavagem com peróxido de hidrogênio apresentaram sinais TL com maior intensidade que as amostras lavadas com peróxido de hidrogênio. Em regra, as amostras não lavadas com peróxido de hidrogênio de MBO:Ce,Li produzidas por ambos os métodos mostraram o melhor sinal TL. As amostras lavadas MBO:Dy,Li - SGP mostraram apenas 10% das unidades em lote 20 comprimidos em testes de homogeneidade foram descartadas. Por outro lado, tanto para MBO:Dy,Li (SGP, MP) foram verificados que o sinal TL decai com a diminuição do tamanho do grão e ocorre ao deslocamento da posição dos picos TL. A dose mínima detectável calculada para as amostras lavadas do MBO:Ce,Li e MBO:Dy,Li foram 0,02 Gy e aproximadamente 0,3 Gy, respectivamente, para ambos os métodos de produção. As medidas OSL mostraram MBO:Dy,Li - SGP têm o melhor sinal e que o tamanho do grão não tem influência no sinal OSL. O efeito de termoluminescência fototransferido (PTTE) ocorreu em amostras lavadas com MBO:Dy,Li. As medidas fotoluminescentes (PL) indicam uma simetria elevada na região dopante para a amostra lavada com MBO:Ce,Li - MP. As amostras LBO produzidas por ambos os métodos apresentaram alta sensibilidade ao método de produção, reagentes precursores utilizados e dopantes. / São Cristóvão, SE

Axial offset anomaly (AOA) in pressurized water reactors (PWR) refers to deviation of the measured neutron flux in the top half of the core from the predicted values. Among other difficulties, AOA reduces the shutdown margin, and may force the plant to reduce power output. AOA is believed to be caused by three related phenomena occurring in the core while operating at full power: sub-cooled nucleate boiling concentrated mainly in the upper half of the core, corrosion product deposition on the cladding surface (crud), and the deposition of boron within the porous crud layer in regions of vigorous sub-cooled boiling. This study replicates the conditions within the PWR primary coolant; specifically, the temperature, pressure, peak surface heat flux, coolant velocity and water chemistry are simulated in order to produce prototypical crud on an electrically heated Zircaloy-4 test element. At the conclusion of each test run, the heated Zircaloy-4 test element is rapidly isolated from the coolant in order to trap any soluble boron species that may be present in the crud layer. The results of this investigation indicate that prototypical crud with significant boron deposition can be produced. The deposited boron compound has been determined to be lithium tetraborate (Li2B4O7). Comparative experiments have been run to determine the effect of coolant pH, concentration and type of additives, and duration of exposure on the thickness of the crud deposit. The data obtained in this investigation can be used to validate mechanistic models for crud deposition and AOA in pressurized water reactors.

In Medizin und Technik besteht ein Bedarf an flexiblen, miniaturisierten Dosisleistungs-messgeräten mit hoher Ortsauflösung für den Einsatz in Strahlungsfeldern hoher Dosisleistung und Dosisleistungsgradienten. Lichtwellenleiterbasierte Dosisleistungsmess-systeme können diese Anforderungen erfüllen. Sie bestehen aus einem strahlungssensitiven Leuchtstoff, welcher über einen flexiblen Lichtleiter an einen Lichtdetektor gekoppelt ist. Die Eliminierung des dominierenden Störeinflusses, des bei Bestrahlung des Lichtleiters generierten Stem-Effekts, ist eine inhärente Herausforderung aller lichtwellenleiter¬basierten Dosisleistungsmesssysteme. In der vorliegenden Arbeit wird ein solches System unter Verwendung der Lumineszenz der gewebeäquivalenten Detektormaterialien Berylliumoxid und Lithiumtetraborat realisiert. Der Schwerpunkt liegt dabei auf der Untersuchung von Methoden der Stem-Eliminierung unter Nutzung der zeitlichen Charakteristik der Lumineszenzmaterialien sowie der zeitlichen Struktur des Strahlungsfeldes oder einer modulierten optischen Stimulation. Eine performante Ausleseelektronik auf FPGA-Basis ermöglicht Echtzeit-Messungen mit einer Abtastung von 10 ns. Verschiedene Auswertemethoden generieren aus den Rohdaten in Zeitstempelform eine stem-unabhängige, dosisleistungsproportionale Detektorantwort. / In medicine and technology there is a demand for flexible, miniaturized dose rate measurement systems with high spatial resolution for the application in radiation fields of high dose rates and dose rate gradients. Fiber optic coupled dosimeters can meet these requirements. They consist of a radiation sensitive luminescent material which is connected to a light detector with a flexible light guide. The elimination of the dominant perturbation, which is the stem effect generated by irradiation of the light guide, is one inherent challenge of all fiber optic dosimeters. In the present work such a system is realized, using the luminescence of the two tissue equivalent detector materials beryllium oxide and lithium tetraborate. The main focus is on the investigation of methods of stem elimination, exploiting the temporal characteristics of the luminescent materials, as well as the time structure of the irradiation or a modulated optical stimulation. For this purpose, capable FPGA-based read out electronics are employed, which enable real time measurements with 10 ns sampling. Different methods of analysis process the time stamp raw data and generate a stem-free, dose rate proportional detector response.

In Medizin und Technik besteht ein Bedarf an flexiblen, miniaturisierten Dosisleistungs-messgeräten mit hoher Ortsauflösung für den Einsatz in Strahlungsfeldern hoher Dosisleistung und Dosisleistungsgradienten. Lichtwellenleiterbasierte Dosisleistungsmess-systeme können diese Anforderungen erfüllen. Sie bestehen aus einem strahlungssensitiven Leuchtstoff, welcher über einen flexiblen Lichtleiter an einen Lichtdetektor gekoppelt ist. Die Eliminierung des dominierenden Störeinflusses, des bei Bestrahlung des Lichtleiters generierten Stem-Effekts, ist eine inhärente Herausforderung aller lichtwellenleiter¬basierten Dosisleistungsmesssysteme. In der vorliegenden Arbeit wird ein solches System unter Verwendung der Lumineszenz der gewebeäquivalenten Detektormaterialien Berylliumoxid und Lithiumtetraborat realisiert. Der Schwerpunkt liegt dabei auf der Untersuchung von Methoden der Stem-Eliminierung unter Nutzung der zeitlichen Charakteristik der Lumineszenzmaterialien sowie der zeitlichen Struktur des Strahlungsfeldes oder einer modulierten optischen Stimulation. Eine performante Ausleseelektronik auf FPGA-Basis ermöglicht Echtzeit-Messungen mit einer Abtastung von 10 ns. Verschiedene Auswertemethoden generieren aus den Rohdaten in Zeitstempelform eine stem-unabhängige, dosisleistungsproportionale Detektorantwort. / In medicine and technology there is a demand for flexible, miniaturized dose rate measurement systems with high spatial resolution for the application in radiation fields of high dose rates and dose rate gradients. Fiber optic coupled dosimeters can meet these requirements. They consist of a radiation sensitive luminescent material which is connected to a light detector with a flexible light guide. The elimination of the dominant perturbation, which is the stem effect generated by irradiation of the light guide, is one inherent challenge of all fiber optic dosimeters. In the present work such a system is realized, using the luminescence of the two tissue equivalent detector materials beryllium oxide and lithium tetraborate. The main focus is on the investigation of methods of stem elimination, exploiting the temporal characteristics of the luminescent materials, as well as the time structure of the irradiation or a modulated optical stimulation. For this purpose, capable FPGA-based read out electronics are employed, which enable real time measurements with 10 ns sampling. Different methods of analysis process the time stamp raw data and generate a stem-free, dose rate proportional detector response.