La mesure de la radioactivité dans les filtres utilisés pour la surveillance de l’aérocontamination de l’air présente une difficulté métrologique majeure. En effet, l’absorption des rayonnements a dans le médium filtrant et la masse d’aérosols accumulés biaisent la réponse nucléaire. Ce travail de thèse porte sur la détermination de facteurs de correction de la dégradation de la radioactivité mesurée dans les filtres de surveillance. Dans un premier temps, des filtres radioactifs représentatifs des prélèvements atmosphériques ont été préparés à l’aide du banc d’essais nucléaire ICARE. L’étude expérimentale sur les filtres de référence a permis d’avoir une base de données pout la détermination des facteurs de correction dans diverses conditions de filtration. Dans un second temps, ce travail a conduit une nouvelle méthode numérique mise au point pour déterminer les facteurs de correction. Il s’agit de coupler des simulations de filtration des particules d’aérosol à l’aide de GeoDict, permettant de calculer des écoulements dans les milieux poreux et des simulations de parcours de particules a dans la matière à l’aide de MCNPX. Le bon accord obtenu, en comparant les réponses des spectres en énergie et des facteurs de correction numériques et expérimentaux, a permis de valider le modèle numérique / The measurement of radioactivity in the filters of airborne radioactive surveillance is a major difficulty metrology. Indeed, the absorption of a radiation in the filter media and the mass of aerosols accumulated distort the nuclear counters response. This thesis work focuses on the determination of correction factors for the radioactivity loss in the survey filters. In a first step, radioactive filters representing the atmospheric samples have been prepared using the nuclear test bench ICARE. The experimental study on reference filters provided a database to determine correction factors for various filtration conditions. The second step of the work proposed a new numerical method developed to determine the correction factors. It consists of coupling GeoDict for particles filtration simulations and MCNPX simulations for a transport in matter. The good agreement obtained by comparing the numerical and experimental correction factors has permitted to validate the numerical model

Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Nine 100x100x600 mm3 plastic scintillators, formerly built for the neutron time of ight measurements at iThemba LABS, were refurbished. The position resolution of these detectors was determined using muon cosmic rays and coincident measurement techniques. Average position resolution of 4.28 cm (FWHM) was found. In order to predict the time spectrum of the large-volume detector Monte Carlo simulations have been performed. These simulations aimed at anticipating the separation of statistical neutrons, prompt gamma rays and uncorrelated gamma rays from the fast neutrons emitted in the reaction of interest. One of the neutron detectors was tested using fast neutrons from the 232Th( ,xn) reaction at 42 MeV. Statistical neutrons from fusion evaporation reactions were produced in 152Sm(12C,xn) fusion evaporation reaction. Coincidences between neutrons and gamma rays were successfully identi ed. Prompt gamma rays and uncorrelated gamma rays were also identi ed. / AFRIKAANSE OPSOMMING: Nege 100x100x600 mm3 plastiese scintillators, wat aanvanklik gebou was vir neutron vlugtyds meetings by iThemba LABS, was hernu. Die posisie resolusie van die detektore was bepaal deurmiddel van muon kosmiese straling en koïnsidensie meet tegnieke. Posisie resolusie van 4.28 cm (FWHM) was verkry. Monte Carlo simulasies is gebruik om die posisie resolusie van'n groot volume detektor te voorspel. Hierdie simulasies is daarop gemik om onderskeid te maak tussen statistiese neutrone, gelyktydige gamma strale en ongekorreleerde gamma strale vanaf vinnige neutrone in die reaksie van belang uitgestraal word. Een neutron detektor was getoets deur gebruik te maak van vinnige neutrone wat uit die reaksie 232Th( ,xn) by 42 MeV ontstaan. Statistiese neutrone vanaf splitsings verdampingsreaksies, gelyktydige gamma strale en ongekorreleerde gamma strale was geidenti seer. Statistiese neutrone van samesmelting verdamping reaksies was geproduseer in die reaksie 152Sm(12C,xn). Toeval tussen neutrone en gamma strale was suksesvol geïdenti seer, gevra gamma strale en ongekorreleerd gamma strale was ook geïdenti seer.

90Y (T1/2 = 2,67 dias; Eβmáx = 2,28 MeV) é um radionuclídeo com eficácia estabelecida para diversas terapias de câncer, marcando biomoléculas e no tratamento da radiosinovectomia. Devido às suas propriedades nucleares, é obtido através do decaimento do 90Sr (T1/2 = 28 anos), na forma de um gerador. Vários tipos de geradores de 90Sr/90Y foram desenvolvidos, e os mais empregados são os que usam resinas de troca catiônica, onde Sr e Y são adsorvidos e 90Y é seletivamente eluído com acetato ou EDTA. A desvantagem deste tipo de gerador é a radiólise, que degrada o seu uso. O gerador eletroquímico é uma solução proposta devido ao fato de não haver efeitos significativos da radiação sobre o próprio gerador. Neste conceito, a diferença entre os potenciais eletroquímicos dos elementos Y e Sr é utilizada para se obter uma rápida separação do 90Y do 90Sr. A produção de 90Y via formação de colóides é o método mais simples para a separação, baseando-se na formação de colóides de Y em pH altamente alcalino, podendo ser filtrado e separado do Sr, sendo posteriormente dissolvido em HCl. O objetivo deste trabalho consistiu no desenvolvimento de tecnologias para o preparo de geradores de 90Sr/90Y, onde foram desenvolvidos três tecnologias, a saber: geradores do tipo coluna utilizando resinas catiônicas, geradores via formação de colóides e geradores eletroquímicos. Foram também avaliadas metodologias para o controle de qualidade radionuclídico do 90Y dos geradores desenvolvidos: cintilação líquida, identidade radionuclídica, cromatografia por extração em papel (EPC) utilizando complexantes para 90Y e técnica por Espectrometria de Emissão Ótica com Plasma Indutivamente Acoplado (ICPOES). Os resultados mostraram que os geradores utilizando resinas catiônicas obtiveram os melhores resultados em relação ao rendimento e eficiência (~ 83%) de eluição, reprodutibilidade e a pureza radionuclídica. O gerador eletroquímico mostrou um potencial para o desenvolvimento, tendo a vantagem de não sofrer os efeitos da radiólise do par 90Sr/90Y, como acontece com a resina. Das metodologias de controle qualidade radionuclídica estudadas, uma comparação e avaliação mostrou que a EPC é muito sensível e permite a avaliação praticamente instantânea da qualidade do 90Y eluído dos geradores. / 90Y (T1/2 = 2,67 d; Eβmáx = 2,28 MeV) is a radionuclide with efficacy established for various cancer therapies, labeling biomolecules and treating of radiosinovectomy. Due to its nuclear properties, is obtained through the decay of 90Sr T1/2 = 28 y in the form of a generator. Several types of 90Sr/90Y generators were developed, and the most employed are the cation exchange resins, where Sr and Y are adsorbed and 90Y is selectively eluted with acetate or EDTA. The disadvantage of this type of generator is the radiolysis, which degrades its use. The electrochemical generator is a proposed solution because there is no significant effect of radiation. In this concept, the difference between the electrochemical potentials of the elements Sr and Y is used to obtain a rapid separation of 90Y from 90Sr. The production of 90Y via colloid formation is the simplest method for the separation, based on the colloid formation of Y in high alkaline pH, which can be filtered and separated from Sr, and subsequently dissolved in HCl. The objective of this work was the development of technologies for the preparation of 90Sr/90Y generators, and three technologies were developed: generators using cation resins columns, generators through colloid formation and electrochemical generators. Radionuclidic quality control of 90Y was also evaluated by liquid scintillation, radionuclide identity, extraction paper chromatography (EPC) using complexing agents for 90Y and by Optical Emission Spectrometry with Inductively Coupled Plasma (ICP-OES). The results showed that generators using cation resins have the best results related to the elution efficiency (~83%), the reproducibility and radionuclidic purity. The electrochemical generator showed a potential for development, having the advantage of not suffering the effects of radiolysis of the pair 90Sr/90Y as the resin. A comparison and evaluation of the methods of the radionuclidic quality control showed that the EPC is very sensitive and allows for virtually instantaneous assessment of the quality of 90Y generator.

Electron density irregularities influence Global Navigation Satellite System (GNSS) signals, manifesting as ionospheric scintillation. Scintillation poses a service risk to safety-critical GNSS applications at high latitudes. It is difficult to predict, as ionospheric instability processes are not yet fully characterised. This research combines the fields of ionospheric imaging and scintillation monitoring, to investigate the causes of scintillation in the Antarctic and Arctic. Results revealed a plasma patch structure above Antarctica, in response to the impact of a solar wind shock front. Measurements from a network of Global Positioning System scintillation receivers across the continent revealed moderate levels of phase scintillation associated with Total Electron Content (TEC) gradients at the patch break-off point. Scintillation was also driven by solar particle precipitation at E and F region altitudes, verified with in situ spectrometers on polar-orbiting satellites. The current receiver coverage in the region provided the Multi-Instrument Data Analysis Software (MIDAS) tomography tool with sufficient data to track the lifetime of the plasma patch without a convection model. A second experiment was performed at the South Pole, using a collocated GPS scintillation receiver and auroral imager. This allowed simultaneous line-of-sight tracking of GPS signals through the optical auroral emissions. Results showed the first statistical evidence that auroral emissions can be used a proxy for ionospheric irregularities causing GPS scintillation. The relationship was strongest during the presence of discrete auroral arcs. Correlation levels of up to 74% were found over periods of 2-3 hours. The use of multiple emission wavelengths provided basic altitude discrimination. Current capability of ionospheric TEC mapping in the Arctic was tested, where GPS receiver distribution is extensive compared to present Antarctic coverage. Analysis of the ionosphere’s response to a storm event revealed a sequential picture of polar cap patch activity, without the aid of plasma convection modelling. The electron density enhancements of the auroral oval were imaged in completeness for the first time using GPS tomography. Reconstructions were verified using ultraviolet auroral imagery from polar-orbit satellites, and vertical profiles from an incoherent scatter radar.

90Y (T1/2 = 2,67 dias; Eβmáx = 2,28 MeV) é um radionuclídeo com eficácia estabelecida para diversas terapias de câncer, marcando biomoléculas e no tratamento da radiosinovectomia. Devido às suas propriedades nucleares, é obtido através do decaimento do 90Sr (T1/2 = 28 anos), na forma de um gerador. Vários tipos de geradores de 90Sr/90Y foram desenvolvidos, e os mais empregados são os que usam resinas de troca catiônica, onde Sr e Y são adsorvidos e 90Y é seletivamente eluído com acetato ou EDTA. A desvantagem deste tipo de gerador é a radiólise, que degrada o seu uso. O gerador eletroquímico é uma solução proposta devido ao fato de não haver efeitos significativos da radiação sobre o próprio gerador. Neste conceito, a diferença entre os potenciais eletroquímicos dos elementos Y e Sr é utilizada para se obter uma rápida separação do 90Y do 90Sr. A produção de 90Y via formação de colóides é o método mais simples para a separação, baseando-se na formação de colóides de Y em pH altamente alcalino, podendo ser filtrado e separado do Sr, sendo posteriormente dissolvido em HCl. O objetivo deste trabalho consistiu no desenvolvimento de tecnologias para o preparo de geradores de 90Sr/90Y, onde foram desenvolvidos três tecnologias, a saber: geradores do tipo coluna utilizando resinas catiônicas, geradores via formação de colóides e geradores eletroquímicos. Foram também avaliadas metodologias para o controle de qualidade radionuclídico do 90Y dos geradores desenvolvidos: cintilação líquida, identidade radionuclídica, cromatografia por extração em papel (EPC) utilizando complexantes para 90Y e técnica por Espectrometria de Emissão Ótica com Plasma Indutivamente Acoplado (ICPOES). Os resultados mostraram que os geradores utilizando resinas catiônicas obtiveram os melhores resultados em relação ao rendimento e eficiência (~ 83%) de eluição, reprodutibilidade e a pureza radionuclídica. O gerador eletroquímico mostrou um potencial para o desenvolvimento, tendo a vantagem de não sofrer os efeitos da radiólise do par 90Sr/90Y, como acontece com a resina. Das metodologias de controle qualidade radionuclídica estudadas, uma comparação e avaliação mostrou que a EPC é muito sensível e permite a avaliação praticamente instantânea da qualidade do 90Y eluído dos geradores. / 90Y (T1/2 = 2,67 d; Eβmáx = 2,28 MeV) is a radionuclide with efficacy established for various cancer therapies, labeling biomolecules and treating of radiosinovectomy. Due to its nuclear properties, is obtained through the decay of 90Sr T1/2 = 28 y in the form of a generator. Several types of 90Sr/90Y generators were developed, and the most employed are the cation exchange resins, where Sr and Y are adsorbed and 90Y is selectively eluted with acetate or EDTA. The disadvantage of this type of generator is the radiolysis, which degrades its use. The electrochemical generator is a proposed solution because there is no significant effect of radiation. In this concept, the difference between the electrochemical potentials of the elements Sr and Y is used to obtain a rapid separation of 90Y from 90Sr. The production of 90Y via colloid formation is the simplest method for the separation, based on the colloid formation of Y in high alkaline pH, which can be filtered and separated from Sr, and subsequently dissolved in HCl. The objective of this work was the development of technologies for the preparation of 90Sr/90Y generators, and three technologies were developed: generators using cation resins columns, generators through colloid formation and electrochemical generators. Radionuclidic quality control of 90Y was also evaluated by liquid scintillation, radionuclide identity, extraction paper chromatography (EPC) using complexing agents for 90Y and by Optical Emission Spectrometry with Inductively Coupled Plasma (ICP-OES). The results showed that generators using cation resins have the best results related to the elution efficiency (~83%), the reproducibility and radionuclidic purity. The electrochemical generator showed a potential for development, having the advantage of not suffering the effects of radiolysis of the pair 90Sr/90Y as the resin. A comparison and evaluation of the methods of the radionuclidic quality control showed that the EPC is very sensitive and allows for virtually instantaneous assessment of the quality of 90Y generator.

Improving the functionality and reducing revision rates are important driving forces in the development of orthopaedic implants. FibMat is a fibrinogen based matrix developed towards commercialisation by the company Optovent AB. This matrix can be coated on implants and act as a local drug delivery system for bisphosphonates (BPs). BPs are drugs inhibiting bone resorption, and applied with FibMat to improve stability of implants in bone, e.g. when fixing bone fractures. In this thesis, FibMat loaded with BP (FibMat/BP) was coated on stainless-steel screws and titanium screws in order to investigate some technology properties relevant to its clinical applicability. Bone-mimicking materials were used to study scrape-off effect upon insertion. The coagulation properties of fibrinogen as well as the structural properties of BPs were studied after exposure to gamma radiation. The screws were coated with FibMat and BP (alendronate and 14C-alendronate) using standard coupling techniques. The total amount and distribution of BP after insertion was measured by liquid scintillation and autoradiography. Coagulation assays were performed in order to determine the coagulation properties of fibrinogen, exposed to doses up to 35 kGy, mixed with thrombin. The structural properties of four different BPs (alendronate, pamidronate, zoledronate and ibandronate), exposed to doses up to 35 kGy were analysed by transmission infrared spectroscopy. The results show that FibMat/BP coating on porous stainless-steel screws is virtually unaffected by insertion into bone materials. The anodised, planar titanium screws are more affected by the insertion process, but an even BP distribution in the cancellous material is indicated. The coagulation assays show that gamma-irradiated fibrinogen has a slower coagulation process compared to non-irradiated fibrinogen and form interrupted network unable to clot. The chemical structures of the BPs seem unaffected by exposure to gamma irradiation. In conclusion, the FibMat/BP is a promising technology for local distribution of BP in conjunction with bone implants.

<p>Improving the functionality and reducing revision rates are important driving forces in the development of orthopaedic implants. FibMat is a fibrinogen based matrix developed towards commercialisation by the company Optovent AB. This matrix can be coated on implants and act as a local drug delivery system for bisphosphonates (BPs). BPs are drugs inhibiting bone resorption, and applied with FibMat to improve stability of implants in bone, e.g. when fixing bone fractures. In this thesis, FibMat loaded with BP (FibMat/BP) was coated on stainless-steel screws and titanium screws in order to investigate some technology properties relevant to its clinical applicability. Bone-mimicking materials were used to study scrape-off effect upon insertion. The coagulation properties of fibrinogen as well as the structural properties of BPs were studied after exposure to gamma radiation.</p><p>The screws were coated with FibMat and BP (alendronate and 14C-alendronate) using standard coupling techniques. The total amount and distribution of BP after insertion was measured by liquid scintillation and autoradiography. Coagulation assays were performed in order to determine the coagulation properties of fibrinogen, exposed to doses up to 35 kGy, mixed with thrombin. The structural properties of four different BPs (alendronate, pamidronate, zoledronate and ibandronate), exposed to doses up to 35 kGy were analysed by transmission infrared spectroscopy.</p><p>The results show that FibMat/BP coating on porous stainless-steel screws is virtually unaffected by insertion into bone materials. The anodised, planar titanium screws are more affected by the insertion process, but an even BP distribution in the cancellous material is indicated. The coagulation assays show that gamma-irradiated fibrinogen has a slower coagulation process compared to non-irradiated fibrinogen and form interrupted network unable to clot. The chemical structures of the BPs seem unaffected by exposure to gamma irradiation. In conclusion, the FibMat/BP is a promising technology for local distribution of BP in conjunction with bone implants.</p>

In preparation for the large backgrounds expected to be present in the Belle II detector from the SuperKEKB e+e- collider, the radiation hardness of several large (5 x 5 x 30 cm3) thallium doped cesium iodide (CsI(Tl)) scintillation crystals are studied. The crystal samples studied consist of 2 spare crystals from the Belle experiment using PIN diode readout and 7 spare crystals from the BaBar experiment using photomultiplier tube readout. The radiation hardness of the scintillation properties of the CsI(Tl) crystals was studied at accumulated 1 MeV photon doses of 2, 10 and 35 Gy. At each dose, the longitudinal uniformity of the crystals light yield, scintillation decay times, time resolution and energy resolution was measured. As the Belle II collaboration is considering an upgrade to pure CsI crystals if CsI(Tl) does not satisfy radiation hardness requirements, the scintillation properties of a pure CsI scintillation crystal were also measured and compared to the CsI(Tl) crystal measurements. In addition to experimental work, Monte Carlo simulations using GEANT4 were written to compare ideal pure CsI and CsI(Tl) crystals and to study the effects of radiation damage on the performance of the Belle II electromagnetic calorimeter. / Graduate

Thesis (M.S.)--Mississippi State University. Department of Physics and Astronomy. / Title from title screen. Includes bibliographical references.

La nanotechnologie est devenue un domaine clé de la technologie du XXIe siècle. L’important développement des approches pour la synthèse des nanoparticules (NPs) avec une composition, une taille et une forme désirées rend compte du potentiel de leur utilisation comme « blocs de construction » pour des structures de plus grande échelle. Cela permet d’envisager à la fois la fabrication de matériaux fonctionnels et de dispositifs directement à partir de colloïdes par approche ascendante et la conception de matériaux sur plusieurs échelles de grandeur. Le procédé utilise l'assemblage ou l'auto-assemblage de NPs et conduit à des matériaux avec des architectures différentes notamment 1D (bâtonnets), 2D (films) ou 3D (super-réseaux ou gels). Cependant, la plupart des assemblages 3D sont limités à l'échelle micrométrique et sont difficiles à contrôler. Pratiquement, la seule voie permettant la préparation de structures 3D macroscopiques à partir de NPs est la gélification et la préparation d'aérogels. Une voie alternative consiste à disperser les NPs dans une matrice, conduisant ainsi à un matériau composite massif, avec des NPs non agrégées distribuées de manière homogène.Le présent travail est consacré au développement de matériaux à partir de NPs d'oxydes métalliques (principalement Y3Al5O12: Ce et Li4Ti5O12) de différentes dimensions et pour diverses applications. La première partie de ce travail décrit la synthèse de NPs de YAG: Ce et de LTO par approche glycothermale. Dans le cas du YAG: Ce, les conditions de réaction ont été ajustées de façon appropriée pour obtenir des nanocristaux (NCs) non agrégés de quelques nanomètres. Des solutions colloïdales de différentes concentrations contenant de tels NCs ont été utilisées, pour la fabrication par la technique de « spin-coating », de films minces avec une épaisseur contrôlable. A l’inverse, la synthèse de LTO conduit à des NPs agrégées dans une structure hiérarchique très bénéfique pour les batteries au lithium. La grande surface spécifique et la porosité du matériau obtenu assurent en effet un échange efficace des ions lithium entre l'électrolyte et le matériau d'anode.Par ailleurs, les NCs de YAG: Ce ont été utilisés pour la préparation de matériaux monolithiques de grande taille avec une porosité et une transparence élevées. Pour cela, la solution colloïdale de NCs a été gélifiée par le changement brusque de la constante diélectrique du solvant de dispersion des NCs. Les gels ainsi obtenus ont été par la suite séchés de manière supercritique, donnant ainsi des aérogels à base de NPs de YAG:Ce, avec une porosité et une transparence élevées. La même approche s'est avérée appropriée pour d'autres systèmes à base de NPs de GdF3 ou de mélanges de NPS de YAG: Ce et de GdF3.Alternativement, les NPs de YAG: Ce ont été incorporées dans des aérogels de silice formant ainsi des aérogels macroscopiques robustes et hautement transparents présentant les propriétés des NPs incorporées. Ces aérogels composites ont été utilisés en tant que nouveaux types de capteurs pour les rayonnements ionisants de basse énergie dans les liquides ou les gaz. Leur porosité élevée permet un contact optimal entre l'émetteur radioactif et le scintillateur assurant ainsi une bonne récupération de l'énergie radioactive. / Nanotechnology has become a key domain of technology in XXI century. The great development of the synthetic approaches toward nanoparticles (NPs) with desired composition, size and shape expose the potential of their use as building blocks for larger scale structures. It allows fabrication of functional materials and devices directly from colloids by bottom-up approach, thus involving possibility of material design over several length scales. The process is referred to NPs assembly or self-assembly and leads to materials with varying architectures as for instance 1D (rods), 2D (films) or 3D (superlattices or gels). However most of 3D assemblies are limited to the micrometric scale and are difficult to control. Practically the only route allowing preparation of macroscopic 3D structures from NPs is their gelation and preparation of aerogels. As an alternative, NPs can be embedded in some matrix creating bulk composite material, with homogenously distributed non-aggregated NPs.Therefore, this work is devoted to development of materials with different dimensionalities for various applications from metal oxides NPs (mainly Y3Al5O12:Ce and Li4Ti5O12). The first part describes the syntheses of YAG:Ce and LTO NPs by glycothermal approach. In the case of YAG:Ce, the reactions conditions were appropriately adjusted in order to obtain non-aggregated nanocrystals (NCs) of few nanometers. The colloidal solution containing such NCs with different concentration was used for fabrication of thin films with controllable thickness by spin-coating method. Contrary, the synthesis of LTO led to aggregated NPs with hierarchical structuration which was highly beneficial for Li-ion batteries. The large surface area and porosity ensured efficient exchange of Li ions between electrolyte and anode material. Furthermore, the YAG:Ce NCs were used for preparation of macroscopic monoliths with high porosity and transparency. For that reason, colloidal solution of NCs was gelled by the abrupt change of solvent dielectric constant. The gels were further supercritically dried yielding YAG:Ce NPs-based aerogels with high porosity and transparency. The same approach turned o be appropriate for other systems like GdF3 or hybrid aerogels of YAG:Ce and GdF3.Alternatively, YAG:Ce NPs were incorporated into silica aerogels forming robust macroscopic and highly transparent aerogels exhibiting properties of incorporated NPs. They served for novel type of sensors for low-energy ionizing radiation in liquids and gases. Their high porosity assured well-developed contact between radioactive emitter and the scintillator ensuring good harvesting of radioactive energy.