Thèses sur le sujet « Radioluminescenza »

In questo lavoro di tesi sono state studiate le proprietà di intrappolamento e luminescenza dei difetti di punto nel quarzo. Tali proprietà sono usate in dosimetria retrospettiva al fine di valutare età archeologiche di reperti ceramici, età geologiche di sedimenti e radiazioni assorbite in casi di incidenti nucleari. Lo studio vuole fare chiarezza sui meccanismi specifici che governano tali proprietà nel quarzo. Nonostante il materiale sia arcinoto e già esistano applicazioni di questo materiale nei campi citati, queste ultime si basano su metodi empirici ed una teoria che possa spiegare e prevedere nel dettaglio le emissioni del quarzo è ancora incompleta. Per fare ciò, sono state sfruttate sia tecniche di luminescenza indotte, direttamente o indirettamente, da radiazioni ionizzanti quali termoluminescenza (TL) e radioluminescenza (RL), sia una tecnica che studia i difetti paramagnetici, o in generale elettroni non accoppiati, ovvero la risonanza paramagnetica elettronica (EPR). TL e RL infatti non sono in grado da sole di poter identificare quali difetti siano responsabili delle emissioni del quarzo, ma è possibile cercare correlazioni usando tecniche che invece possono osservare direttamente tali difetti, come appunto la tecnica EPR. Correlando dati di TL ed EPR è stato possibile identificare impurezze di germanio con elettroni intrappolati, in particolare le trappole per elettroni [GeO4]- e [GeO4/Li+]0, come responsabili di emissioni di TL, i cosiddetti picchi a 110 °C e 375 °C. Nel corso dello studio è stato inoltre possibile individuare un'anomalia nella stabilità termica di uno di questi centri germanio, responsabile per il picco a 110 °C, confermando comunque la correlazione tra i due segnali ma sollevando nuove possibili criticità nelle applicazioni a fini di datazione e dosimetria. Tramite gli studi EPR è stato inoltre possibile individuare nuovi centri paramagnetici mai riportati in letteratura e ne è stata caratterizzata la stabilità termica. Uno di essi è stato assegnato a un centro compensato con idrogeno interstiziale, mentre gli altri ancora necessitano una precisa assegnazione. È stata inoltre studiata la stabilità termica di centri legati a impurezze di titanio e alluminio al fine di cercare possibili correlazioni con proprietà di luminescenza. Delle possibilità sono state proposte, ma sono necessari ulteriori studi riguardo questo specifico punto. Tramite RL e TL è stato mostrato inoltre come le lunghezze d'onda di emissione del quarzo siano molto dipendenti dal tipo di campione studiato e dalla sua storia termica. In particolare, tramite TL risolta in lunghezza d'onda è stato possibile mostrare come le proprietà dei campioni studiati non siano in accordo con alcuni modelli teorici pubblicati in letteratura. Lo studio ha consentito di proporre un'alternativa, seppur finora come modello qualitativo. Tale proposta sostiene che possano esistere correlazioni spaziali tra diversi difetti di punto nel quarzo, consentendo ricombinazioni specifiche senza l'ausilio delle bande di conduzione e valenza del materiale. Benché lo studio sia ben lontano dall'aver trovato una descrizione completa nei comportamenti del quarzo, nuovi importanti tasselli sono stati aggiunti ai decenni di studi pubblicati, avvicinando la comunità scientifica al traguardo finale della comprensione dei processi di luminescenza di questo materiale.
In this thesis work, the trapping and luminescence properties of point defects in quartz have been studied. Such properties are used in retrospective dosimetry in order to evaluate the age of archaeological artefacts, the age of geological sediments and the absorbed radiation in the event of nuclear accidents. The study aims at clarifying the specific mechanisms that rule such properties in quartz. Despite being quartz a well-known material and many applications in the aforementioned fields already existing, these are based on empirical methods and a theory that can explain and predict the emissions in quartz in a detailed way is still incomplete. To do so, two luminescence techniques are used, both induced, directly or indirectly, by ionizing radiation such as thermoluminescence (TL) and radioluminescence (RL), and a technique to study paramagnetic defects, or in general unpaired electrons, that is electron paramagnetic resonance (EPR). In fact, TL and RL alone are not enough to directly identify the defects that are responsible for such emissions, but it is possible to try to correlate their data with other techniques that can directly observe such defects, such as EPR. By correlating TL and EPR data, germanium related centres with trapped electrons, specifically [GeO4]- and [GeO4/Li+]0, have been identified as responsible for the TL emissions known as the peaks at 110 °C and 375 °C. At the same time, it was also possible to identify an anomaly in the thermal stability of one of these germanium centres, responsible for the 110 °C peak, confirming the correlation of the two signals, TL and EPR, but also raising new potential critical issues in the applications for dating and dosimetry. Through EPR studies, new unreported paramagnetic centres have been identified and their thermal stability has been characterized. One of them has been assigned to a centre compensated by interstitial hydrogen, while the others are still lacking a precise labelling. The thermal stability of titanium and aluminium related centres has also been studied, in search of possible correlations with luminescence properties. Some proposals have been advanced, but further studies are needed for this last specific point. Through RL and TL, it has been shown how the emission wavelengths in quartz are very sample dependent and how they are influenced by the thermal history of the studied sample. Specifically, through wavelength resolved TL it was possible to show how the properties of the studied samples do not agree with some published theoretical models. The study was able to propose an alternative, although so far just at a qualitative level. Such proposal claims that there may be spatial correlations between point defects in quartz, allowing specific direct recombination with no passage in the conduction and valence bands of the material. Despite this study is far from having found a complete description of quartz behaviour, new important steps have been added to the huge specific literature, contributing to a deeper comprehension of the luminescence properties of this material.

In this work, initially the radioluminescence (RL) and thermoluminescence (TL) techniques are presented. The radioluminescence is the prompt luminescence emitted by a material under ionizing radiation exposure. The thermoluminescence is the luminescence emitted by a material previously exposed to ionizing radiation when excited by heat. Enegy bands concepts, defects in crystals and the different processes of ionization that take place in matter when exposed to ionizing radiation are briefly discussed in order to present the mechanisms involved in RL and TL processes. The usage of the techniques in characterization of materials and dosimetry is reported, legitimating the importance of the instrument developed. Mechanical and structural parts as well as a description of each component of the instrument are fairly described. The implemented algorithm for controlling the instrument and acquiring data is also discussed. The development of the instrument enabled us to generate temperature ramps with a quite good performance, reaching temperatures up to 500 °C with deviations up to 2 °C, having used heating rates between 0.5 °C/s and 5 °C/s. Calibrations of optical spectrometer used in light collection and irradiation system were carried out. Lastly, TL and RL spectra tests were performed. The RL tests were carried out using several materials which emission spectra are well known by literature, namely, carbon-doped aluminium oxide Al2O3:C, terbium-doped gadolinium oxysulphide Gd2O2S:Tb, europium-doped yttrium oxide Y2O3:Eu and dysprosium-doped calcium borate CaB6O10:Dy. For the TL spectra test, the aluminium oxide doped with carbon Al2O3:C was used. The results of RL and TL spectra tests showed a good agreement with the literature, pointing out that the instrument developed in this work is comparable to others instruments in operation from others research groups, making our results reliable.
Nesse trabalho, inicialmente as técnicas de radioluminescência (RL) e termolumi- nescência (TL) são apresentadas. A radioluminescência é a luminescência imediata emitida por um material quando exposto à radiaçao ionizante. A termoluminescência é a luminescência emitida por um material previamente exposto à radiação quando este é aquecido. Conceitos de bandas de energia, defeitos em cristais e os diferentes processos de ionização que ocorrem na matéria quando exposta à radiação ionizante são brevemente discutidos a fim de apresentar os mecanismos envolvidos na RL e TL. A utilização das técnicas na caracterização de materiais e na dosimetria é reportada, justificando a importância do instrumento desenvolvido. As partes mecânicas/estruturais e uma descrição de cada componente do instrumento são descritos. O algoritmo implementado para controle do instrumento e aquisição de dados é também descrito. O desenvolvimento do instrumento possibilitou a geração de rampas de temperatura com uma boa performance, atingindo até 500 °C com variações de até 2 °C ao utilizar taxas de aquecimento entre 0.5 °C/s e 5 °C/s. Calibrações do espectrômetro óptico utilizado na aquisição da luminescência e do sistema de irradiação foram executadas. Por fim, testes de aquisição de espectros de RL e TL foram realizados. Os testes de RL foram realizados utilizando vários materiais cujos espectros de emissão são bem conhecidos pela literatura, a saber, óxido de alumínio dopado com carbono Al2O3:C , oxisulfeto de gadolínio dopado com térbio Gd2O2S:Tb , óxido de ítrio dopado com európio Y2O3:Eu e borato de cálcio dopado com disprósio CaB6O10:Dy. Para o teste dos espectros de TL, o Al2O3:C foi utilizado. Os resultados dos espectros de RL e TL mostraram concordância com a literatura, indicando que o instrumento desenvolvido é comparável a outros instrumentos em operação de outros grupos, tornando os nossos resultados confiáveis.

The aim of this thesis is to present a simple model for the radiation to light conversion processes in fluorescent layers as an aid in future developments and applications. Optimisation between sensitivity and spatial resolution for fluorescent layers in digital radiology is a delicate task where the extrinsic efficiency for various phosphors needs to be established for varying parameters. The extrinsic efficiency of a fluorescent layer can be expressed as the ratio of the light energy per unit area at the screen surface to the incident xray energy fluence. Particle size is a critical factor in determining the value of the extrinsic efficiency, but in most models it is not treated as an independent variable. Based on the definition of a light extinction factor (ξ), a model is proposed such that, knowing the intrinsic efficiency η, the particle size and the thickness of a certain make of screen, the extrinsic efficiency can be calculated for an extended range of particle sizes and / or screen thicknesses. The light extinction factor ξ is an optical parameter determined from experimental data on extrinsic efficiency. The proposed model is compared to established methods. Further experiments have confirmed the validity of the model. Monte-Carlo simulations have been utilised to refine the calculations of energy imparted to the phosphor by taking into account the escape of scattered and K-radiation generated in the screen and interface effects at the surfaces. The luminance was measured for a set of in-house manufactured screens of varying thicknesses and particle sizes. Utilising the proposed model, the corresponding calculated values deviated ± 14 %.within the studied range.

Ce travail porte sur l'étude de nanoparticules scintillatrices qui sont capables, par définition, de convertir un rayonnement ionisant en lumière visible ou proche UV. Si le processus de scintillation est actuellement bien connu dans le cas des matériaux macroscopiques, les perturbations susceptibles d'apparaître pour des nanomatériaux le sont moins. En effet, des modifications peuvent être induites par le confinement spatial et les spécificités de structure propres aux nanomatériaux. L'étude de ces perturbations constitue l'objet de cette thèse. Le manuscrit se divise en trois parties. La première vise à quantifier la fraction d'énergie qui se dépose dans une assemblée de nanoparticules après interaction avec un photon haute énergie (X ) ou en réalisant des simulations Monte Carlo basées sur le code de calcul Geant4. La deuxième partie présente un travail expérimental exploratoire qui consiste à comparer des mesures de spectroscopie résolue en temps pour des nanoparticules et un monocristal afin d'extraire des informations sur les étapes de thermalisation et de recombinaison radiative spécifiques aux nanoparticules. La dernière partie de ce manuscrit présente l'étude d'une application novatrice des nanoscintillateurs comme agents thérapeutiques. Ils sont alors utilisés pour activer sous excitation X l'effet photodynamique, base d'une thérapie anti-cancéreuse actuellement limitée au traitement de lésions superficielles
This work deals with scintillating nanoparticles, material able to convert ionizing radiations into visible or Ultra-Violet light. The scintillation process is currently well-known for bulk materials. However, for nanomaterials, several steps of the scintillation process are likely to be slightly modified mainly because of the spatial confinement of charges and the structure specificities in nanomaterials. The study of such perturbations is the aim of this thesis. The manuscript is divided into three parts. The first one aims to quantify the amount of deposited energy within a set of nanoparticles after the interaction with a high energy photon (X or –rays). We thus developed Monte Carlo simulations with the Geant4 toolkit to quantify this energy. The second part presents an exploratory experimental study that consists in comparing time resolved spectroscopy measurements for nanoparticles and a single crystal. The aim is to extract a few tendencies on the thermalization and on the radiative recombination processes specific to nanoscintillators. The last part of this thesis presents an application of nanoscintillators as therapeutic agents. In that case, they are used to activate the photodynamic effect under X-ray irradiation. This last effect is the basis of the photodynamic therapy, an anticancer treatment currently limited to superficial tumors

This research explores the synthesis of anthracene and stilbene-based metal-organic framework (MOF) structures as potential scintillating (radioluminescent) materials for use in the detection of gamma radiation. The organic molecules 9,10-anthracenedicarboxylic acid (ADCH2) and trans-4,4’-stilbenedicarboxylic acid (SDCH2), were each used as a linker, in combination with a range of lanthanide metal ions, to synthesize novel three dimensional MOF structures under hydrothermal conditions. With ADCH2, the early period lanthanides yield isostructures with the metal ion in higher coordination (nine) than for those with late period metals (seven). The ADC-MOFs show linker-based photoluminescence properties with well defined vibronic peaks in their emission profile and their emission (λmax~435 nm) blue shifting from that of the ADCH2 powder (~500 nm) and closer to the organic molecule in monomer arrangement (λmax ~ 420 nm). The structures also show photoluminescence lifetimes between 1 and 2 ns, which is similar to the reported value for monomeric anthracene units. The blue-shift and reduction in lifetime, compared to ADCH2, are indicative of minimal π-π interactions amongst the aromatic moieties, thereby limiting the non-radiative relaxation pathways. On exposure to ionizing radiation (protons and g- rays), the ADC-MOFs demonstrated scintillation properties, with a radioluminescence lifetime of ~ 6 ns which is similar to that of the ADCH2 powder. A combination of SDCH2 and lanthanide metal ions produced two isostructured MOFs containing Tm3+ and Er3+, under the hydrothermal synthesis conditions explored. The 3-D structure contained ultra large diamond-shaped pores with dimensions of 16 Å x 30 Å. A blue-shift of fluorescence spectra was observed for the SDC-MOF structures (λmax ~ 425 nm) compared to that of bulk SDCH2 powder (λmax ~475 nm), and closely resembling that of monomeric isolated SDC units (λmax~475 nm). Their photoluminescence lifetime is ~0.76 ns, about half of that observed for SDCH2 powder. The blue shift and reduction in lifetime (compared to SDCH2) is attributed to minimal π-π interactions between SDC units in the MOF structure, thus minimizing associated non-radiative relaxation pathways. The isolation of anthracene and stilbene in MOF structures therefore has the potential to improve their performance as scintillators.

This investigation studied the growth and characterisation of thin film phosphors to examine the feasibility of enhancing a solid-state neutron scintillation detector system for increased detection resolution and detection rate. Undertaken in collaboration with the neutron facility ISIS at the Rutherford Appleton Laboratory, it was to examine whether an improved radioluminescent detector could be designed, based on the application of thin film phosphors. Optimisation for the detector was in the areas of increased luminescent emission from each neutron captured, increasing the rate of capture for each measurement and improved spatial resolution. The current ZnS:Ag,Cl phosphor used at ISIS was characterised in terms of its luminescent emission properties and comparisons were made to thin films of potential phosphor materials and the source material used to create the thin films. The phosphors were characterised via photo and radio-luminescent excitation to examine the spectral emission and the luminescent decay properties. Thin films were grown onto a silicon substrate from a ZnS:Ag,Cl phosphor source using RF magnetron sputtering and were characterised in terms of morphology, crystallinity and luminescent properties. Thin films grown using this technique were found to not produce visible emission when excited with UV excitation nor alpha excitation. Following further literature research and using the analysis technique of Rutherford Backscattering it was concluded that the chlorine charge compensation dopant was lost during the growth process resulting in incomplete incorporation of the luminescent silver dopant into the lattice. A range of chlorine doping methods were examined in order to promote charge compensation within the thin films, with the most controlled method using ion implantation, carried out at the Ion Beam Facility at Surrey University. Three samples of ZnS were grown to 800nm, followed by implantation of 0.01at% of silver and either 0.01at%, 0.05at% or 0.20at% of chlorine. Following implantation the thin films were thermally annealed to activate the samples and characterised by their luminescent emission via photo- and radioluminescent excitation. The result of the study was that although a luminescent emission was created using laser excitation, the emission using a 241Am source was of such low intensity they were uncharacterisable using the detection setup. The emission spectrum created by ZnS:Ag,Cl using the PL setup was not the standard broadband emission peak centred around 450nm, but was distorted so that it preferentially enhanced the emission around 485nm, hence create a shoulder peak. This is not significant to the optimisation of the detector, but important to know for characterisation purposes. The emission and decay characteristics of the wafer used for neutron detection by ISIS and the ZnS:Ag,Cl powder purchased from Phosphor Technology are the same. Combining this with extensive experience within the research group of growing ZnS and ZnS:Mn thin films made this powder a suitable as a potential target material for thin film growth. Independent of the calibration problem, the PL emission spectrum from thin films grown using RF magnetron sputtering should have been the same as the PL emission spectrum of the target material used in this technique. However, once a thin film had been grown there was no resultant emission observed. Testing the thin films using Rutherford Back Scattering found that although there were relative proportions of zinc, sulphur and silver there was no chlorine detected. Alternative method of forming a thin film of ZnS:Ag,Cl were investigated, with the most significant method using ion implantation. This technique can accurately implant the small concentrations of dopant required into a thin film with good distribution, hence requiring minimal thermal processing for the dopants to be incorporated into the lattice to activate it. The result was a thin film that when annealed in a furnace in air it rapidly oxidised, where as when annealed under vacuum this did not occur. After a period of eight hours annealing at 600°C a PL emission was observed from the implanted thin films. When the emission spectrum was analysed there was a series of emission peaks. There was potential that one of these peaks related to the ZnS:Ag,Cl emission, however there was a prominent peak at 575nm which when further analysed with RBS and PIXE confirmed there had been contamination of manganese in the thin films.

Cette thèse a pour objectif de caractériser un système dosimétrique in vivo implantable pour la radiothérapie externe capable de réaliser, en temps réel, une mesure directe de la dose absorbée dans le volume cible. Ce système, nommé SECURIDOSE, met en œuvre une sonde implantable qui comporte à son extrémité distale un cristal de nitrure de gallium radioluminescent. La transduction par radioluminescence du nitrure de gallium a été étudiée et ses performances intrinsèques ont été comparées avec celles d'autres techniques de transduction mises en œuvre en dosimétrie in vivo. Ce mode de transduction offre un avantage en termes de un rendement de transduction qui est de 100000 photons/MeV. Le GaN a un temps de réponse très court (<1ns). Son émission bande à bande dans le UV est bien adaptée à une mesure en temps réel de la dose. Son spectre d'émission est étroit ce qui facilité la réjection spectrale des luminescences parasites. Le système proposé offre une réponse linéaire avec la dose d'irradiation qui ne dépend pas du débit de dose. Cette réponse reste linéaire même pour des doses d'irradiation très supérieures à celles délivrées au patient. De plus, les sondes SECURIDOSE restent opérationnelles après un cycle de stérilisation Gamma avec une irradiation par une source de 60Co à une dose de 29 kGy. Le GaN n'a pas une dépendance angulaire. Le seul désavantage du système, est la dépendance à l'énergie du faisceau du fait que le GaN n'est pas équivalent tissu. Une variation de 4.5% de la réponse du système a été observée entre deux énergies de faisceaux de photons 6MV et 18MV.

De nos jours, les dosimètres existants sont insuffisants pour la surveillance et le contrôle des rayonnements ionisants dans toutes les configurations et surtout en environnement sévère. En dosimétrie optique, les systèmes fibrés permettent de répondre en temps réel à des débits de dose relativement faibles, de réaliser des mesures dans des endroits difficiles d’accès, avec une résolution spatiale intéressante. Ce travail a consisté en l’étude de verres de silice élaborés par voie sol-gel et dopés par du cuivre ou du cérium ionique, en vue de les utiliser dans un dispositif dosimétrique. Ces verres ont été caractérisés par différentes techniques spectroscopiques avant et après irradiations. Dans le cas des verres dopés Cu, après irradiation X ou γ (1 MGy), les défauts HC1, HC2 et E’ ont été identifiés. Quant aux verres dopés Ce, ils sont plus résistants et restent incolores, même après une dose de 8,8 MGy sous X. Des mesures de la réponse optique des échantillons sous rayons X ont été réalisées grâce à un dispositif fibré. Concernant les verres dopés Cu, la sensibilité en radioluminescence (RL) couvre la gamme de débits de doses allant de 0,25 à au moins 800 mGy/s et la linéarité de la luminescence optiquement stimulée (OSL) a été démontrée entre 40 mGy et 200 Gy. Les verres dopés Ce sont plus performants en termes de linéarité. En effet, les signaux de RL et d’OSL sont linéaires jusqu’à 1,2 Gy/s et 500 Gy respectivement pour ce dopant. Un fading de l’OSL à court-terme a été mis en évidence avant stabilisation du signal. Les résultats obtenus montrent que ces verres dopés présentent un grand intérêt pour la dosimétrie fibrée de radiations ionisantes
Nowadays, existing dosimeters are insufficient for monitoring and control of ionizing radiation in all configurations and especially in severe environments. In optical dosimetry, fiber systems allow to provide a real-time response to relatively low dose rates, making possible some measurements in hard-to-reach places with interesting spatial resolution. This work consisted in the study of sol-gel silica glasses doped with ionic copper or cerium, with the aim of using them in a dosimetry device. These glasses have been characterized by different spectroscopic techniques before and after irradiations. In the case of Cu-doped glasses, after X or γ irradiation (1 MGy), the defects HC1, HC2 and E' have been identified. As for Ce-doped glasses, they are more resistant and remain colorless, even after a dose of 8.8 MGy under X. Measurements of the optical response from the samples under X-rays were carried out using a fibered device. For Cu-doped glasses, radioluminescence (RL) sensitivity covers dose rates ranging from 0.25 to at least 800 mGy/s and the linearity of optically stimulated luminescence (OSL) has been demonstrated in the range 40 mGy-200 Gy. Ce-doped glasses are more efficient in terms of linearity. Indeed, for this dopant, RL and OSL signals are linear up to 1.2 Gy/s and 500 Gy, respectively. Short-term OSL fading was observed before stabilization of the signal. The obtained results show that these doped glasses are of great interest for fibered dosimetry of ionizing radiations

Les données chronologiques disponibles pour les gisements du Paléolithique moyen du Sud-Ouest de la France font état d’un manque de jalons chronologiques fiables. Pour ces périodes anciennes, l’établissement d’un cadre chronologique nécessite un investissement méthodologique important dans le domaine de la datation numérique. Les résultats obtenus dans cette étude reposent essentiellement sur la datation par luminescence optique de grains de feldspaths et de quartz contenus dans les sédiments. En particulier, l’étude des signaux de luminescence classiquement exploités (IRSL, pIR-IRSL), nous permet de mieux évaluer la fiabilité des datations à partir des feldspaths potassiques. Un protocole de datation fondé sur l’exploitation du signal de radioluminescence (IR-RF) de ces minéraux a aussi été développé. Ainsi, la luminescence optique a été appliquée à des échantillons provenant de six gisements de référence : Les Pradelles (Marillac, Charente), Combe Brune 2 (Creysse, Dordogne), Roc de Marsal (Campagne, Dordogne), Artenac (Saint-Mary, Charente), La Quina (Gardes-le-Pontaroux, Charente) et La Ferrassie (Savignac-de-Miremont, Dordogne). La combinaison des résultats obtenus nous a permis, au sein de chaque niveau archéologique, d’évaluer la pertinence des datations et de proposer pour chaque gisement un scénario chronologique qui nous semble fiable. À l’issue de cette étude, les occupations humaines, caractérisées selon leurs industries, ont pu être replacées sur une échelle des temps en regard des variations paléoclimatiques et paléoenvironnementales régionales. Plusieurs constats ont été dressés enrichissant le registre de nos connaissances sur les cultures néandertaliennes
Currently available chronological information for Middle Palaeolithic sites in southwestern France precludes the establishment of a robust chronological framework. For these early periods, developing such a framework relies upon important methodological advancements in numerical dating techniques. The results of this study are essentially based on the optical luminescence dating of sedimentary feldspars and quartz. Focusing on the most commonly employed luminescence signals (IRSL, pIR-IRSL), it was possible to more clearly evaluate the reliability of dates obtained on K-feldspars. A dating protocol for these materials based on their radioluminescence signal (IR-RF) was also developed. Optical luminescence dates were produced for six major archaeological sites: (Marillac, Charente), Combe Brune 2 (Creysse, Dordogne), Roc de Marsal (Campagne, Dordogne), Artenac (Saint-Mary, Charente), La Quina (Gardes-le-Pontaroux, Charente) et La Ferrassie (Savignac-de-Miremont, Dordogne). Collating the results for each archaeological level allowed the coherence of the dates to be tested and a reliable chronological sequence to be proposed for each site. The different human occupations, characterised by their industrial attribution, could be placed within a chronological framework that incorporates regional palaeoenvironmental and palaeoclimatic variations. Finally, several observations provide new insights for our understanding of Neandertal cultures

Dans ce travail de thèse, nous avons étudié l'effet des rayonnements ionisants (rayons X et γ) jusqu'à une dose maximale de 1 Grad sur différents types de fibres multimodes (dopées -P, -P-Ce, -Ge, -Ge-F, -Ge-Ce et -N). Les caractérisations ont été réalisées principalement avec trois techniques expérimentales : online Atténuation Induite par Radiation en temps réel (RIA), Résonance Paramagnétique Electronique (EPR), Micro-Luminescence (ML). Dans la première partie du travail de cette thèse, nous avons étudié la réponse aux radiations de différents types de fibres optiques. L'absorption liée aux défauts du phosphore induits par irradiation a été étudiée par des mesures RIA dans le domaine spectral UV-Visible. Les mesures EPR nous permis de détecter les défauts POHC, P1 et P2. En particulier, pour la détection de P1 et P2, nous avons utilisé le mode de détection de la seconde harmonique pour déterminer la cinétique de croissance des P1 et P2 en fonction de la dose. Nous avons également étudié les effets dus au changement des conditions de fibrage et ceux liés à la variation de la température d'irradiation (25-280 ° C). Nous avons aussi étudié l’effet du codopage du coeur de la fibre avec du Cérium. Dans ce cas, nous avons observé une production moins importante de centres POHC et P2 sous irradiation. De plus, les mesures EPR ont montré que la génération des défauts P1 n’est pas sensiblement influencée par le codopage avec le Cérium. En ce qui concerne les fibres optiques dopées Ge, on a étudié trois types de dopage : Ge seul, co-dopage Ge-F et Ge-Ce. Pour chaque type, nous avons examiné trois conditions de fibrage. La réponse à l’irradiation de ces fibres a été étudiée par les trois techniques utilisées. Plus particulièrement la ML, nous a permis d'obtenir une vision plus complète du rôle du codopant et des précurseurs dans la formation des défauts induits par l'irradiation. Nous avons également étudié la réponse au rayonnement de la fibre dopée N avec trois différentes conditions de fibrage. Les réponses à l’irradiation dans les régions spectrales UV-visible ont été obtenues par des mesures RIA. Par EPR, nous avons pu détecter deux défauts liés à l'azote pour les doses élevées de radiation. Enfin, les mesures ML sur les fibres irradiées ont montré trois bandes d'émission dans le visible qui ont été attribuées clairement à des centres émetteurs liés à l'azote. Dans la deuxième partie de la thèse, nous avons étudié les effets liés au chargement en oxygène des fibres étudiées. Par des mesures en microspectroscopie Raman, nous démontrons qu'un traitement à haute température et haute pression peut favoriser l’introduction d’une grande quantité de O2 dans les fibres optiques à cœur de silice pure (PSC) ou dopées F, Ge ou P. Les réponses à l’irradiation de certaines des fibres optiques chargées en O2 ont été étudiés (et en particulier PSC et celle dopée F. Sur la base des données de la littérature, nous avons effectué les décompositions des spectres RIA en fonction de la dose. De plus, l'étude EPR des fibres optiques dopées P et chargées en O2 a montré une forte réduction des défauts P1 et P2 comparées aux fibres non traitées. Dans cette partie de la thèse, j’ai également présenté les résultats concernant la radioluminescence infrarouge (1272 nm) des molécules O2 dans la fibre optique. La faisabilité d'un capteur de radiation pour des environnements sous fortes doses et forts débits de dose a été discutée
In this Thesis work we have investigated the effect of ionizing irradiation (X and γ rays) up to 1 Grad on different types of multimode optical fibers (P-doped, P-Ce-doped , Ge-doped, Ge-F-doped, Ge-Ce-doped, and N-doped). The experiments were carried out by three main experimental techniques: online Radiation Induced Attenuation (RIA), Electron Paramagnetic Resonance (EPR) and Confocal Micro-Luminescence (CML). In the first part of the Thesis work we report on the radiation response of several types of optical fibers. The absorption due to radiation induced P-related defects was studied by RIA in the UV-Visible domain. Moreover, by EPR measurements we were able to detect POHC, P1 and P2 defects. In particular, for the detection of P1 and P2 defects we have validated the use of EPR second-harmonic detection mode which allowed us to obtain the growth kinetics of P1 and P2 with the dose. The effects due to the variation of the drawing conditions of the fibers were investigated as well as the ones due to the change of the temperature of irradiation (from 25 to 280 °C). Finally, concerning the P-doped OFs, we report on the effects due to the Cerium codoping of the core of the optical fiber. We observed a reduced generation of POHC and P2 centers under irradiation. However, EPR investigation has shown that the generation of P1 defects is essentially unaffected by the Ce-codoping. Regarding Ge-doped optical fibers we report on three basic typologies: Ge-doped, Ge-F-doped and Ge-Ce-doped. For each fiber typology we investigated three drawing conditions. The radiation responses of these fibers were characterized by RIA and EPR measurements. Furthermore, performing CML measurements we were able to obtain further insight on the role of the co-dopants and of the defect precursors in determining the radiation induced defects. We have also investigated the radiation response of N-doped OFs (three drawing conditions). The radiation responses in the UV-Visible domains were obtained by RIA, and by EPR measurements we were able to detect the signals of two N-related defects at high radiation doses. Finally, CML measurements on irradiated samples have shown three emission bands in the visible domain which are tentatively assigned to N-related centers. In the second part of the Thesis we report on the effects of an O2 loading treatment produces on some of the investigated samples. By micro-Raman measurements we demonstrate that a high pressure high temperature treatment can incorporate high quantity of O2 into Pure-Silica-Core (PSC), F, Ge and P doped optical fibers. The radiation responses of some of the O2-loaded optical fibers were investigated with particular regard to the fluorine doped and pure-silica-core optical fibers. On the basis of literature data we performed band decompositions of the RIA spectra as a function of the dose. Moreover, the EPR study of the O2 loaded P-doped optical fiber have shown a strong reduction of the signals associated to the P1 and P2 defects as compared to the untreated fibers. In this part of the thesis we also report on the characterization of the near infrared radioluminescence (1272 nm) of O2 molecules embedded in the optical fiber matrix and the feasibility of a radiation sensor based on this phenomenon for environments characterized by high radiation doses and high dose-rates

Os objetivos deste trabalho foram a implantação e a otimização da técnica de sinterização a laser de corpos cerâmicos, o estudo da cinética do processo e a avaliação de propriedades físicas dos compostos Bi4Ti3O12 e Bi4Ge3O12 sinterizadas a laser, em comparação com as cerâmicas processadas em forno convencional. A escolha dos materiais baseou-se em seu potencial de aplicação: o Bi4Ge3O12 como dispositivo cintilador e o Bi4Ti3O12 como cerâmica eletrônica. A sinterização a laser mostrou-se eficiente para estes materiais, produzindo cerâmicas com densidade superior a 98 % e pequeno tamanho de grão. A combinação de pré-aquecimento e subida gradual da potência do laser evitou gradientes de temperatura e taxas de aquecimento excessivos, e reduziu consideravelmente a incidência de trincas e a porosidade nas cerâmicas. No estudo cinético da sinterização a laser, registraram-se energias de ativação inferiores às observadas no processamento convencional, exceto para o BIT no estágio final de sinterização, e os resultados sugerem um adiantamento no processo de sinterização, provocado por efeito da irradiação a laser. A caracterização física do BIT foi feita por espectroscopia de impedância e medidas de histerese ferroelétrica. Comparado à cerâmica convencional, o corpo cerâmico sinterizado a laser apresentou condutividade elétrica 3 vezes menor na região de bulk, maior permissividade dielétrica acima de 300 °C, com igual perda dielétrica, mesmo campo coercitivo e polarização remanescente 35 % superior. A caracterização física do BGO foi feita por medidas de absorção óptica, radioluminescência e termoluminescência. Os resultados mostraram que a cerâmica de BGO sinterizada a laser possui grau de transparência 50 % maior, densidade de defeitos estruturais 2 vezes menor, eficiência levemente superior e mesmo dano por radiação, se comparada à cerâmica sinterizada em forno elétrico. Os resultados obtidos foram interpretados com base na escala de tempo característica da sinterização a laser, que afeta a formação e distribuição dos defeitos durante o processo, e resulta em cerâmicas com microestrutura diferenciada.
The goals of this work were the implantation and optimization of the laser sintering technique for ceramic bodies, the kinetic study of the process and the evaluation of the physical properties of the laser sintered compounds Bi4Ti3O12 and Bi4Ge3O12, compared to ceramics sintered in conventional furnace. The choice of the materials was based on their potential applications: Bi4Ge3O12 as scintillator device and Bi4Ti3O12 as an electronic ceramic. Laser sintering showed to be efficient for these materials, producing ceramics with density higher than 98 % and small grain sizes. The combination of pre-heating with a gradual rising of the laser power prevented excessive temperature gradient and heating rate, and reduced considerably the incidence of cracks and pores in the ceramics. The kinetic study of the laser sintering revealed lower activation energies than that observed in the conventional processing, except for BIT ceramics during the final stage of sintering. The results suggest that the laser irradiation anticipates the stages of the sintering process. The physical characterization of BIT was done through impedance spectroscopy and ferroelectric hysteresis measurements. Compared to the conventional sample, this material presented bulk electrical conductivity 3 times smaller, higher dielectric permittivity above 300 °C, comparable dielectric loss, the same coercive field and 35 % higher remanent polarization. The physical characterization of BGO was done through optical absorption, radioluminescence and thermoluminescence measurements. The results showed that the transparency of the laser sintered BGO ceramic was 50 % higher than the transparency of the conventional BGO ceramic, the density of structural defects is 2 times lower, the radiation damage levels are comparable and the overall scintillating efficiency is slightly higher. The obtained results were interpreted on the basis of the time scale of the laser sintering, which affects the formation and distribution of defects during the process, and results in a particular microstructure.

Depuis quelques dizaines d’années, la surveillance des rayonnements ionisants est particulièrement importante dans des endroits difficiles d’accès, voire dangereux, surtout en environnement sévère. La fibre optique constitue une solution de choix lorsqu’une mesure à distance est obligatoire. De plus, les fibres optiques assurent la séparation spatiale de la sonde, sensible aux rayonnements, et du système de traitement électronique, ce qui permet des mesures à distance dans des géométries complexes. Lors de ce travail, des verres à base de silice élaborée par voie sol-gel et codopée par des ions actifs Ce/Tb ou Ce/Cu ont été soudés à une ou deux fibres de transport pour réaliser des mesures de débits de dose et de dose à distance. De plus, la présence au sein de la matrice de deux types de centres luminescents émettant à des longueurs d’ondes différentes permet d’étendre la gamme spectrale de luminescence. Ces échantillons ont été caractérisés, avant et après irradiations 1MGy, par plusieurs techniques spectroscopiques. Dans le cas des verres dopés Cu ou Tb seul, des défauts (NBOHC, HC1...) ont été créés après irradiation. Grace à la présence des ions cérium dans la silice codopé Ce/Cu ou Ce/Tb qui a joué un rôle très important où il a protégé la matrice et atténue la création de certains défauts sous irradiation. Des mesures dosimétriques réalisées sous rayons X ont permis d’évaluer la linéarité du signal RL et OSL pour les verres de silice codopés Ce/Tb et Ce/Cu. Concernant les verres codopés Ce/Cu, le signal de RL présente une réponse linéaire dans la gamme 0,0011 - 34 Gy/s à Saint-Etienne et entre 13,3 µGy/s et 7,3 Gy(SiO2)/s à Nice et la linéarité d’OSL a été démontrée jusqu’à 50 Gy à Saint-Etienne et 33 Gy à Nice. Les verres codopés Ce/Tb ont montré une sensibilité en RL dans la gamme de débits de dose comprise entre 13,3 µGy/s et 7,3 Gy/s avec une excellente reproductibilité des mesures. Il a été démontré que ce matériau a une réponse OSL qui reste proportionnelle à la dose jusqu’à 66 Gy(SiO2). Grâce à ces résultats, on en déduit que ces échantillons codopés constituent une solution pour les mesures dosimétries à distance en environnement sévère
For several decades now, monitoring ionizing radiation has been particularly important in places that are difficult to access or even dangerous, especially in harsh environments. Optical fiber is the solution of choice when remote measurement is mandatory. In addition, the optical fibers ensure the spatial separation of the probe, sensitive to radiation, and the electronic processing system, which allows remote measurements in complex geometries. During this work, silica-based glasses developed by the sol-gel route and codoped with active Ce / Tb or Ce / Cu ions were welded to one or two transport fibers to make measurements of dose rates and remote dose. In addition, the presence within the matrix of two types of luminescent centers emitting at different wavelengths makes it possible to extend the spectral range of luminescence. These samples were characterized, before and after 1MGy irradiation, by several spectroscopic techniques. In the case of Cu or Tb doped glasses alone, defects (NBOHC, HC1 ...) have been created after irradiation. Thanks to the presence of the cerium ions in the codoped silica Ce / Cu or Ce / Tb which played a very important role where it protected the matrix and attenuates the creation of certain defects under irradiation. Dosimetric measurements carried out under X-rays made it possible to evaluate the linearity of the RL and OSL signal for the codoped silica glasses Ce / Tb and Ce / Cu. For Ce / Cu codoped glasses, the RL signal has a linear response in the range 0.0011 - 34 Gy / s in Saint-Etienne and between 13.3 µGy / s and 7.3 Gy (SiO2) at Nice and the linearity of OSL has been demonstrated up to 50 Gy in Saint-Etienne and 33 Gy in Nice. Co-coded Ce / Tb glasses showed sensitivity in RL in the dose rate range of between 13.3 µGy / s and 7.3 Gy / s with excellent reproducibility of the measurements. This material has been shown to have an OSL response which remains dose proportional up to 66 Gy (SiO2). Thanks to these results, we deduce that these codoped samples constitute a solution for remote dosimetry measurements in severe environment

Recently the laser sintering process has attracted the attention of researchers due to advantages such as: possibility of using very high heating and cooling rates, possibility of sintering materials with high melting point, among others. It has been observed that each material responds differently to the incident laser radiation, i.e., the same power density can generate different temperatures and temperature gradients that depend of the physics characteristics of the material. The correlation between these properties and the laser sintering process has been scarcely discussed in the literature, thus become it an important study subject for laser sintering process optimization. In this doctoral study, the main objective was the study of the laser sintering kinetics of common oxides, making a comparative study between experimental results and simulations of Fourier´s Law for heat conduction in solids. Ceramic bodies of TiO2, ZnO, CaTiO3 and Y2O3 pure and doped were produced starting from powders synthesized by the polymeric precursors method. For the production and characterization of the samples were used the Differential Thermal Analysis, Thermogravimetry, X-Ray Diffraction, Dilatometry, Scanning Electron Microscopy, radioluminescence, X-ray Fluorescence Spectroscopy and Impedance Spectroscopy. The four studied compositions obtained presented single crystalline phase. The numeric solution of the heat flow equation for Gaussian e Linear profiles allowed the analyses of specific situations of the temperature in function of the thermal conductivity, spot size, sample thickness and optical absorption coefficient. Significant correlations between the experimental observations and simulated data were obtained, mainly in the analyzes of the thermal properties. The results presented in the present work strengthen the understanding of the laser sintering technique for oxide systems and allow a considerable advance for the study of new systems.
Recentemente o processo de sinterização a laser tem atraído a atenção de pesquisadores devido a vantagens como: possibilidade de utilização de altíssimas taxas de aquecimento e resfriamento, possibilidade de sinterização de materiais com alto ponto de fusão, entre outras. É observado que cada material responde de maneira diferente à radiação laser incidente, ou seja, uma mesma densidade de potência pode gerar diferentes temperaturas e gradientes de temperatura a depender das características físico-químicas do material. A correlação entre estas propriedades e o processo de sinterização a laser tem sido pouco abordada na literatura científica, tornando-se desta forma um importante objeto de estudo para otimização do processo de sinterização a laser. Este trabalho de doutoramento teve como objetivo principal o estudo da cinética de sinterização laser de óxidos comuns pelo estudo comparativo entre resultados experimentais e simulações da lei de Fourier para condução de calor em sólidos. Foram produzidos corpos cerâmicos de TiO2, ZnO:Bi, CaTiO3 e Y2O3 puros e dopados com íons divalentes partindo de pós sintetizados pelo método dos precursores poliméricos. Para a produção e caracterização das amostras foram utilizadas as técnicas de Análise Térmica Diferencial, Termogravimetria, Difração de raios X, Dilatometria, Microscopia Eletrônica de Varredura, Radioluminescência, Fluorescência de raios X e Espectroscopia de Impedância. As quatro composições estudadas apresentaram fase cristalina única. A resolução numérica da equação do fluxo de calor para perfis de feixe gaussiano e linear permitiu a análise de situações específicas de temperatura em função da condutividade térmica para diversos óxidos, largura do feixe, espessura da amostra e coeficiente de absorção óptica. Correlações importantes entre as observações experimentais e os dados simulados foram obtidos, principalmente na análise das propriedades térmicas. Os resultados apresentados no presente trabalho fortalecem o entendimento da técnica de sinterização a laser para sistemas óxidos e permitirá um avanço considerável para o estudo de novos sistemas.

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

Obiektem zainteresowania niniejszej pracy są procesy rekombinacji promienistej zachodzące w krysztale fluorku baru aktywowanym trójwartościowymi jonami ceru, prazeodymu, terbu i erbu. Pod pojęciem rekombinacji rozumiemy połączenie dwóch uprzednio rozdzielonych, różnoimiennych nośników ładunku elektrycznego (w badanych materiałach są nimi elektrony i dziury). Jeżeli skutkiem rekombinacji jest emisja promieniowania, mówimy o rekombinacji promienistej. Szczególną uwagę zwracamy na rekombinację promienistą następującą w wyniku absorpcji kwantu lub cząstki jonizującej. Ma to ścisły związek z programami badawczymi, w ramach których wyhodowano kryształy, zakupiono aparaturę i sfinansowano wyjazdy zagraniczne. Nadzieją owych programów było znalezienie nowoczesnego, uniwersalnego scyntylatora, czyli materiału reagującego na promieniowanie jonizujące szybką i wydajną luminescencją w nadfiolecie lub świetle widzialnym. Należy podkreślić, że kandydatami były tu kryształy dość szczególne, stanowiące połączenie dobrze znanej w świecie scyntylatorów sieci fluorkowej z optymistycznie zapowiadającymi się w roli aktywatorów jonami ziem rzadkich. Podstawową techniką eksperymentalną umożliwiającą ocenę słuszności wyboru aktywatora z punktu widzenia zastosowań scyntylacyjnych jest pomiar radioluminescencji. Polega on na rejestracji widma emisji próbki naświetlanej w sposób ciągły promieniowaniem jonizującym (np. rentgenowskim). Liczba i pochodzenie pasm emisyjnych obecnych w takim widmie pozwala na dokonanie selekcji negatywnej, tzn. jesteśmy w stanie od razu odrzucić kryształy nieprzydatne, zaś pozostałe powinniśmy poddać dalszym badaniom spektroskopowym. Mimo iż na podstawie selekcji negatywnej moglibyśmy ograniczyć te badania do dwóch, a co najwyżej trzech materiałów, zrezygnowaliśmy z takiego ułatwienia. I chociaż jedynym motywem była wówczas „pasja kolekcjonerska”, zaobserwowane ciekawe zjawiska fizyczne w pełni wynagrodziły poświęcony czas. Praca składa się z ośmiu rozdziałów. Trzy pierwsze porządkują dotychczasowy stan wiedzy na temat właściwości kryształów fluorków ziem alkalicznych, ich aktywacji jonami ziem rzadkich oraz oddziaływania z promieniowaniem jonizującym. I tak kolejno: • w rozdziale 1 przedstawiamy strukturę krystaliczną fluorków, określamy energię spójności, szacujemy położenia pasm energetycznych i charakteryzujemy dwie emisje własne; • w rozdziale 2 omawiamy strukturę elektronową lantanowców, poruszamy problem kompensacji ładunku, a następnie w szerokim zakresie prezentujemy podstawy teoretyczne spektroskopii jonów ziem rzadkich ze szczególnym uwzględnieniem rozkładów poziomów energetycznych i przejść emisyjnych pomiędzy nimi; • w rozdziale 3 analizujemy poszczególne etapy zjawiska radioluminescencji, zapoznajemy się z własnościami scyntylatorów i stawianymi im wymaganiami, rozważamy mechanizmy transferu energii od sieci BaF2do jonów ziem rzadkich, przeglądamy defekty radiacyjne, po czym wprowadzamy istotny dla analizy wyników model pułapkowy scyntylatora. Następny rozdział(4) zawiera krótką charakterystykę wykorzystanych próbek oraz opis układów, przy użyciu których przeprowadzono badania. Wyniki eksperymentalne wraz z interpretacjami są przedstawione w czterech ostatnich rozdziałach, poświęconych odpowiednio kryształom BaF2:Ce (5), BaF2:Pr (6), BaF2:Tb (7) i BaF2:Er (8). Dla przejrzystości, struktura tych rozdziałów jest zawsze zbliżona, a mianowicie istnieje podział na część stanowiącą rodzaj raportu z pomiarów (n.1; n = 5, 6, 7, 8) i część przeznaczoną na dyskusję uzyskanych wyników (n.2). Ewentualne różnice wynikają z właściwości poszczególnych materiałów i związanej z nimi liczby zastosowanych technik badawczych. Liderem jest pod tym względem kryształ BaF2:Ce, który jako jedyny został poddany pomiarowi termoluminescencji powyżej temperatury pokojowej. Przyznajemy, że jest to nie tyle efekt zapotrzebowania na taki pomiar, co „pasja kolekcjonerska” wsparta przypadkowym dopasowaniem zakresu widmowego emisji jonów Ce3+ do transmisji filtru interferencyjnego zamontowanego na stałe w czytniku termoluminescencyjnym. Standardem dla wszystkich kryształów były natomiast pomiary radioluminescencji (n.1.1) i fotoluminescencji (n.1.2), które w przypadku obecności szybkiej emisji jonów aktywatora uzupełniano o profile czasowe fotoluminescencji w funkcji temperatury (n.1.3) i termoluminescencję poniżej temperatury pokojowej (n.1.4). W częściach dyskusyjnych pierwszy z rozdziałów (n.2.1) jest zawsze poświęcony mechanizmowi rekombinacji promienistej (ze szczególnym nastawieniem na transfer energii sieć-jon), kolejny (n.2.2) szybkości emisji jonów aktywatora (o ile szybka emisja występuje), a ostatni (n.2.3 lub n.2.2) ocenie danego materiału pod kątem zastosowań scyntylacyjnych. Dodatkowo zestawienie porównawcze własności badanych kryształów jest zamieszczone w zakończeniu.
This Thesis summarizes a systematic research on spectroscopic and scintillation properties of barium fluoride (BaF2) crystals activated with trivalent rare earth (RE) ions. The experimental data are interpreted with attention focused on the mechanisms of radiative recombination. The speed and efficiency of the activator’s emission are also analyzed, in order to evaluate the studied materials as modern scintillators. In the theoretical part the present state of knowledge on the basic properties of alkaline earth fluorides, activation of such crystals with rare earths and interaction with ionizing radiation is reviewed. In particular, in chapter 1 the crystal structure of the fluorides is presented, the components of the cohesive energy are characterized, the band structure is predicted, and two host emissions are described. Chapter 2 is devoted to the RE ions: their electronic structure, site symmetries (in crystals), energy levels, absorption and emission spectra. In chapter 3 the consecutive stages of radioluminescence are characterized, requirements and properties of scintillators are discussed, possible mechanisms of the host to ion energy transfer are considered, a variety of radiation induced defect centers is shown, and the trap model of a scintillator is introduced. The experimental part begins with a description of the samples and facilities employed during the studies (chapter 4). Experimental techniques such as measurements of radioluminescence spectra, photoluminescence (emission and excitation) spectra, photoluminescence time profiles at various temperatures, and thermoluminescence below and above room temperature have been utilized. The next chapters (5-8) present and discuss the results obtained for the BaF2:Ce, BaF2:Pr, BaF2:Tb, and BaF2:Er crystals, respectively. Under X ray excitation only cerium and praseodymium activated barium fluoride samples exhibit a fast and efficient luminescence, due to interconfigurational 4fn-15d -> 4fn transitions. In case of terbium and erbium slow intraconfigurational 4fn -> 4fn emission ascribed to a nonradiative energy transfer from the 4fn-15d levels to some high lying 4fn levels is observed. Therefore the first two materials are potentially interesting from the scintillator point of view. The radiative lifetimes of Ce3+ and Pr3+ ions are found to be almost the same, about 20-22 ns (in BaF2:Ce a thermal prolongation caused by the effect of radiation trapping appears). It is suggested that the fast and efficient (particularly in BaF2:Ce) activator emission is preceded by a consecutive capture of charge carriers (free band electrons and holes) at RE3+ sites, being a competitive process to formation of self trapped excitons. On the other hand, rare earth absorption reduces the intensity of the extremely fast core to valence emission. The most interesting observation derives from the photoluminescence time profiles. At VUV excitation (75-90 nm) distinct temperature dependent variations of the rise and decay times of the cerium and praseodymium emission occur. In accordance with the trap model of a scintillator these variations are associated with radiation defect centers playing a role of traps and thus participating in the host to ion energy transfer. Although the glow curves of BaF2:Ce and BaF2:Pr consist of many glow peaks, indicating a variety of traps, there is an evidence that only the self trapped holes in the form of so called VK centers are responsible for modifying the time profiles. The two remaining materials, BaF2:Tb and BaF2:Er, are much less promising for scintillator applications. Nevertheless, it is worth to note that their slow (although quite efficient, particularly in Tb activated samples) activator emission is also preceded by a consecutive capture of charge carriers at RE3+ sites. Summarizing, the pioneering achievements of this work are as follows: • the consecutive capture of charge carriers is suggested as the dominant mechanism of host to ion energy transfer in RE activated barium fluoride; • the temperature dependent variations of rise and decay times of the cerium and praseodymium emission are successfully explained in the frame of the trap model of a scintillator; • the radiative lifetime of the Ce3+ ions in BaF2:Ce is evaluated as about 20 ns.

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.