Dissertations / Theses on the topic 'Bonner Sphere'

A novel broad spectrum neutron spectrometer has been created to extend the useful energy range of existing neutron Bonner Sphere Spectrometers (BSS). Both an active LiI(Eu) scintillator probe and passive gold foil detector were utilized to extend the energy response of the existing BSS. Above 20 MeV the energy structure for the standard polyethylene BSS are poor because the response functions are not unique. MCNPX was used to investigate several modifications to the BSS system which resulted in the Bonner Sphere Extension (BSE). This cost effective extension uses several concentric spheres of copper, lead, and tungsten heavy metal downscatter materials to extend the useful range of the current BSS from 20 MeV to above 1 GeV. Using both a 3" and 5" inner polyethylene spheres, aluminum shell sets were made with a 1" cavity and filled with the high Z materials for six total sets of spheres. a 12" and 8" polyethylene sphere were also milled to accept the heavy metal spheres. The system was validated at the Los Alamos Neutron Science Center (LANSCE) neutron beam. The system was calibrated at LANSCE for neutrons up to 800 MeV on target 4's 15 degree right flightpath (4FP15R) at 90 meters. Detailed models in MCNPX were made of the BSS, BSE and LANSCE facilities. Fine group responses were made and compared to the unfolded data from LANSCE. A vast improvement over the BSS system alone was seen with reasonable agreement with time of flight data measured at LANSCE and MCNPX calculated neutron spectra.

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Ces travaux de thèse sont le fruit d’une collaboration entre le Laboratoire de Métrologie et Dosimétrie des Neutrons de l’Institut de Radioprotection et de Sûreté Nucléaire et le Département d’Environnement Spatial de l’Office National d’Etudes et Recherches Aérospatiales. L’objectif était de caractériser et de mettre en service un système opérationnel de spectrométrie des neutrons, étendu au domaine des hautes énergies afin de mesurer de manière dynamique les variations de l’environnement radiatif naturel atmosphérique en altitude au sommet de l’Observatoire du Pic du Midi de Bigorre dans les Pyrénées. Pour ce faire, les réponses des différents détecteurs ont été calculées par simulations Monte Carlo avant d’être validées expérimentalement jusqu’au domaine des hautes énergies en champs neutroniques de référence. La méthode de reconstruction mathématique du spectre par déconvolution a été étudiée afin de quantifier les incertitudes systématiques. Ensuite, le système a été testé sous la roche au Laboratoire Souterrain à Bas Bruit de Rustrel avant d’effectuer les premières mesures en altitude à +500 m et +1000 m. A la suite de ces expériences, le spectromètre a été installé en mai 2011 au sommet du Pic du Midi à +2885 m. La méthodologie d’analyse en continu des données recueillies a été développée. Des oscillations saisonnières du spectre dont l’amplitude dépend du domaine énergétique ont été mises en évidence. Des décroissances Forbush,caractéristiques d’éruptions solaires, ont également été observées à l’approche du 24ème cycle solaire.Des simulations Monte Carlo ont permis d’analyser ces résultats. Les données ont été valorisées grâce à des applications en dosimétrie personnelle et en fiabilité des composants électroniques vis-à-vis des radiations
This PhD Thesis has been achieved thanks to the joint effort between two French organizations, the French Institute for Radiological Protection and Nuclear Safety (IRSN/LMDN, Cadarache) and the French Aerospace Lab (ONERA/ DESP, Toulouse). The aim was to develop an operational neutron spectrometer extended to high energies in order to measure the dynamics of the spectral variations of the natural radiative environment at the summit of the Pic du Midi Observatory in the French Pyrenees. Thereby, the fluence responses of each detector were calculated thanks to Monte Carlo simulations. Afterwards, they were validated by means of experimental campaigns up to high energies (>20 MeV) nearby reference neutron fields. The systematic uncertainties were deduced after detailed studies of the mathematic reconstruction of the spectra (i.e. unfolding procedure). Then, the system was tested under rocks at the LSBB of Rustrel before being installed at respectively+500 m and +1000 m above sea level for the first environmental campaigns. Finally, the spectrometer has been operating for two years after its deployment at the summit of the Pic du Midi (+2885 m). The continuous data were analysed thanks to an innovative method. Some seasonal and spectral variations were observed. Some Forbush decreases were also recorded after strong solar flares. These data were further analysed thanks to Monte Carlo simulations. The data were made more attractive thanks toseveral practical applications with personal dosimetry or reliability of submicron electronics components

A Bonner Sphere neutron spectrometer for low background environment was developed. The spectrometer consists of a 3He neutron detector, eight high density polyethylene spheres with size ranging from 5-inch to 12-inch and two Lead shells with thickness 1cm and 2 cm, which is used to increase the detect efficiency at high energy range. The dead time of the spectrometer is about 3.7 microseconds, which is mainly contributed by the extended TTL signal from the DAQ. The background of 3He detector is measured in CJPL which is the deepest underground laboratory in the world. The detector background is 15.50 × 10-4 ± 8.1 × 10-5 counts per second. The responses of Bonner Spheres were obtained by Geant4 Monte Carlo simulation. The responses were verified by a 241AmBe neutron source in HKU. A genetic algorithm unfolding program(GA) was developed and tested by unfolding the 241AmBe neutron source. The background neutron in HKU Observatory was measured by the spectrometer and unfolded by GA s. The unfolded neutron flux is (56.84 ± 6.01) × 10-4 s-1 cm-1 by NSUGA version 3 and (56.43 ± 2.53) × 10-4 s-1 cm-1from NSUGA_FORTRAN. Another unfolding program "Equalizer" with different algorithm, by scaling a initial guess spectrum, was also used to unfold the background spectrum in HKU Observatory. The unfolded neutron flux from "Equalizer" is (51.69 ± 2.79) × 10-4 s-1 cm-1. The neutron flux from three unfolding programs agree with each other. The measurement was repeated in Daya Bay EH1 and the results were used to unfold the background neutron spectrum. The unfolded spectrum flux was (34.50 ± 3.13) × 10-5 s-1cm-1from NSUGA version 3, (35.13 ± 1.45) × 10-5 s-1cm-1 from NSUGA_FORTRAN. The unfolded neutron fluxes from GA s agree with each other. However the shape of spectra shows a chaotic pattern in low energy region. The unfolded neutron flux from "Equalizer" is (30.85 ± 1.95) × 10-5 s-1c m-1. The unfolding programs show a dominant thermal neutron peak, a tiny (α, n) peak and a small cosmic-ray neutron peak. The Bonner Spheres Spectrometer has flaws due to the geometry and the nature of unfolding process. Some ideas are suggested to minimize the effect from the error sources.
published_or_final_version
Physics
Master
Master of Philosophy

La caractérisation par mesure spectrale de l'environnement neutronique atmosphérique ambiant s'avère être spécifiquement primordiale dans le contexte de la problématique actuelle liée à l'évaluation des effets de radiations naturelles dans les matériaux semi-conducteurs. Ces " effets singuliers " identifiés sont susceptibles d'altérer le bon fonctionnement des technologies sur silicium fortement intégrées jusqu'au niveau du sol terrestre. Les travaux menés au cours de cette thèse de doctorat ont ainsi porté sur le développement d'un spectromètre de neutron, basé sur le principe du système généralisé des sphères de Bonner, de sensibilité adaptée à la mesure en environnement radiatif atmosphérique naturel et d'efficacité étendue de surcroît jusqu'au domaine des hautes énergies. Le développement du spectromètre s'est alors grandement appuyé sur la simulation numérique de type Monte Carlo au moyen du code de transport MCNPX. Une fois le système multi-détecteurs défini sur le support d'une modélisation détaillée, la matrice de réponse en fluence a été déterminée sur un large spectre en énergie, depuis les énergies thermiques jusqu'à plusieurs GeV. Une phase d'extension puis d'optimisation de la réponse aux neutrons d'énergies supérieures à la dizaine de MeV ont été menées pour aboutir à la configuration et au dimensionnement finals du système de spectrométrie, jusqu'à sa propre réalisation. Une phase de caractérisation, par simulations Monte Carlo, du spectromètre s'est ensuite consacrée à l'évaluation des possibles déviations et incertitudes associées aux réponses en fluence calculées. Une analyse de la sensibilité du spectromètre aux composantes radiatives atmosphériques chargées complète et finalise cette étude exhaustive de caractérisation. Des tests de mesures réalisés au moyen du spectromètre auprès d'une source 241Am-Be de référence ont apporté des éléments de validation expérimentale préliminaire de la matrice de réponse calculée.

La caractérisation par mesure spectrale de l’environnement neutronique atmosphérique ambiant s’avère être spécifiquement primordiale dans le contexte de la problématique actuelle liée à l’évaluation des effets de radiations naturelles dans les matériaux semi-conducteurs. Ces « effets singuliers » identifiés sont susceptibles d’altérer le bon fonctionnement des technologies sur silicium fortement intégrées jusqu’au sol terrestre. Les travaux menés au cours de cette thèse de doctorat ont ainsi porté sur le développement d’un spectromètre de neutron, basé sur le principe du système généralisé des sphères de Bonner, de sensibilité adaptée à la mesure en environnement radiatif atmosphérique naturel et d’efficacité étendue de surcroît jusqu’au domaine des hautes énergies. Le développement du spectromètre s’est alors grandement appuyé sur la simulation numérique de type Monte Carlo au moyen du code de transport MCNPX. Une fois le système multi-détecteurs défini sur le support d’une modélisation détaillée, la matrice de réponse en fluence a été déterminée sur un large spectre en énergie, depuis les énergies thermiques jusqu’à plusieurs GeV. Une phase d’extension puis d’optimisation de la réponse aux neutrons d’énergies supérieures à la dizaine de MeV a été menée pour aboutir à la configuration et au dimensionnement finals du système de spectrométrie, jusqu’à sa propre réalisation. Une étude de caractérisation, par simulations Monte Carlo, du spectromètre s’est ensuite consacrée à l’évaluation des possibles déviations et incertitudes associées aux réponses en fluence calculées. Une étude de sensibilité du spectromètre aux composantes radiatives atmosphériques chargées complète cette étude de caractérisation. Des tests de mesures réalisés au moyen du spectromètre auprès d’une source 241AmBe de référence ont apportés des éléments de validation expérimentale préliminaire de la matrice de réponse calculée.

El presente trabajo versa sobre la dosimetría neutrónica en radioprotección alrededor de los aceleradores de electrones de alta energía desde el punto de vista de la espectrometría neutrónica experimental.
Concretamente, se ha caracterizado y calibrado un Espectrómetro por Esferas Bonner (BBS) comercial basado en un centelleador cilíndrico de 6LiI(Eu), 4 mm x 4 mm. Al conjunto de esferas de polietileno original, con diámetros de 2" a 12", se le ha añadido una esfera de 12" con una capa interna de 1 cm plomo, para ampliar el rango de energías de la respuesta del espectrómetro hasta la región de los 102 MeV. Se ha establecido la matriz de respuestas en función de la energía del espectrómetro y se ha procedido a su validación experimental con irradiaciones en campos neutrónicos de referencia. Se ha desarrollado un innovador código de deconvolución, FRUIT (FRascati Unfolding InTeractive code), para la obtención de la distribución energética de los neutrones a partir de las medidas experimentales. El código ha sido testado y validado en campos neutrónicos conocidos.
El sistema completo ha sido aplicado en la medida de los espectros neutrónicos alrededor del colisionador electrón/positron DA?NE de 510 MeV, en los Laboratorios Nacionales de Frascati del INFN (Istituto Nazionale di Fisica Nucleare). La información dosimétrica obtenida a partir de los espectros medidos ha sido implementada en los protocolos para la vigilancia radiológica alrededor del acelerador. Además, el conocimiento detallado de la dosis equivalente ambiental neutrónica en puntos seleccionados de la instalación ha permitido la determinación de factores de calibración específicos para los monitores de área usados en rutina en D??NE.
This work addresses the topic of the neutron dosimetry for radiation protection around high-energy electron accelerators through the approach of the experimental neutron spectrometry.
A commercial Bonner Sphere Spectrometer (BSS) based on a 4 mm x 4 mm cylindrical 6LiI(Eu) scintillator was characterized and calibrated. The original set of polyethylene spheres, with diameter from 2" to 12", was augmented with a lead loaded 12" sphere, in order to extend the energy range of the spectrometer response up to the 102 MeV region. The energy response matrix of the spectrometer was established and experimentally validated with irradiations in reference neutron fields. An innovative unfolding code, FRUIT (FRascati Unfolding InTeractive code) has been written in order to infer the neutron energy distribution from the experimental readings. The code has been tested and validated in known neutron fields.
The whole system has been used to measure the neutron spectra around the 510 MeV electron/positron DA?NE collider, at the Frascati National Laboratories on the INFN (Istituto Nazionale di Fisica Nucleare). The dosimetric information taken from the measured spectra was implemented in the procedures for the radiological surveillance around the accelerator. Moreover, the accurate knowledge of the neutron ambient dose equivalent in selected points of the installation allowed determining workplace specific calibration factors for the survey-meters routinely used at DA?NE.

L’Agence nationale pour la gestion des déchets radioactifs (l’Andra) en France propose un nouveau type de voussoirs de tunnel pour les ouvrages très profonds. Pour éviter des segments de tunnel trop épais, ils proposent d’intégrer une couche de matériau granulaire sur l’extrados d’un voussoir moins épais. Cette approche prétend utiliser la grande compressilibité de la couche granulaire constituée de particules broyables et les transferts de charge interne au matériau granulaire pour réduire l’épaisseur du voussoir tout en gardant des performances mécaniques importantes. Un segment de tunnel avec une telle conception est appelé un VMC monobloc compressible (brevet en instance de l’Andra & CMC). Il s’agit d’un nouveau type de revêtement de tunnel particulièrement innovant.Cette thèse est consacrée à la création d’un modèle numérique capable de reproduire le comportement mécanique d’un couche granulaire très compressible à l’aide de la méthode aux éléments discrets (DEM) en 3D. Le milieu granulaire est constitué de particules d’argile cylindriques creuses appelées textitcoques. Chaque coque est un tube de 2 cm de long avec un diamètre de 2 cm. La faible épaisseur de la coque cylindrique la rend essentiellement constituée de vide entourée d’une fine couche d’argile. Dans le modèle, un cluster sécable (la coque) est généré à l’aide de clumps sphéro-polyédriques allon- gées . Ces clumps, appelés secteurs, sont associés entre eux en utilisant deux lois de contact adhésives. Si la combinaison des forces de contact normales et tangentielles satisfait un critère de charge spécifique, la coque se casse au niveau de l’interface entre les deux secteurs. L’outil DEM Rockable mis au point pour cette recherche peut fonctionner sur ces particules fragiles. Les propriétés mécaniques des coques, composé de 12 à 24 secteurs, sont ajustées à l’aide d’essais de compression radiale uniaxiale (verticale). Les expériences à l’échelle du grain sur les coques en argile cuite ont servi de référence. Nous avons déterminé la plage réelle de rupture et sa distribution statistique (Weibull). Les paramètres numériques et mécanique ainsi obtenus ont été validés avec succès dans le cas de la compression radiale d’une coque contrainte latéralement.Dans un premier temps, l’étude des assemblages de coques porte sur la caractérisation expérimen- tale des échantillons avec un controle sur les variables d’état initiales telles que la densité et l’orienta- tions des coques. La reconstruction 3D à partir de tomographies à rayons X d’échantillons de coques carottés dans l’extrados d’un voussoir nous a permis de caractériser l’anisotropie de l’orientation des particules. Il s’agit là d’une information précieuse pour la génération d’échantillons numériques ayant les caractéristiques initiales pertinentes. Deuxièmement, des simulations DEM de compressions oedo- métriques sur des échantillons de ⟨2 000⟩ coques sont réalisées. Une étude paramétrique permet de mettre en évidence le rôle des variables d’état initiales. Un ensemble bien choisi de variables initiales et des paramètres DEM correctement adaptés permettent d’obtenir des simulations prédictives pertinentes pour une comparaison avec les expériences de laboratoire. Une analyse micro-mécanique de l’effet de la proportion des grains cassés sur les contraintes locales exercées sur les coques (et les fragments) est effectuée. Il est observé que la rupture des coques entraîné une compressibilité élevée du matériau. Par conséquent, la réponse mécanique en déformation est considérée comme une conséquence directe de l’évolution de la rupture des particules. Pour finir, un modèle analytique de prédiction de la re- lation Contrainte↔Déformation est proposé dans le cas de la compression oedométrique. Ce modèle prédictif tient compte des variables internes du milieu granulaire comme la résistance mécanique en compression des coques
The National Agency for Radioactive Waste Management (FR Andra) in France suggested a new way to design a tunnel lining, especially, beneficial in the case of very deep tunnels. To avoid very thick tunnel segments, they propose to integrate a layer of granular material on the extrados of the thinner lining. This approach takes the advantages of the compressible capacity of the crushable particles and the load transfer in the granular material. A tunnel segment with such design is called a Mono-block Compressible Arch-segment VMC (Andra’s & CMC’s pending patent) and is an innovative new type of tunnel linings.This PhD dissertation is dedicated to the creation of a numerical model capable of reproducing the mechanical behaviour of this compressible granular layer using 3D Discrete Element Method (DEM). The granular packing is made of the brittle hollow coarse-size cylindrical particles, called shells. Each shell is a 2 cm long tube with a diameter of 2 cm. Its small thickness makes the cylindrical shell mainly made of void surrounded by a thin layer of clay. In the model, a breakable cluster (shell) is generated using sphero-polyhedral elongated clumps. These clumps, called sectors, are glued together using two adhesive contact force laws. If the combination of the normal and tangential contact forces exceeds a suitable failure criterion, a de-clustering of the shell (breakage) occurs. The DEM tool Rockable devel- oped for this research can operate on such crushable particles. The mechanical properties of the shell model, composed of 12 to 24 sectors, are adjusted in the case of a uniaxial (vertical) radial compres- sion of shells. The preceding grain-scale experiments on the true shells made of baked clay serve as a reference. We determine the true range of the failure tensile load and its statistical Weibull distribu- tion. The user-specified parameters is then successfully validated in the case of radial compression of a horizontally constrained shell.Firstly, the macroscopic study of shell assemblies focuses on the experimental characterisation of the samples with a control of the initial state variables like a number density and a spatial arrangement of shells (shells orientations). 3D reconstruction from X-ray tomographies of the original coated shells samples extracted from the extrados of a tunnel segment help us to characterise the anisotropy of the shells orientation. This is a piece of valuable information to the generation the numerical samples of shells with relevant initial features. Secondly, a series of DEM oedometric tests on ⟨1 000 : 2 000⟩ shells is simulated. A parametric study successfully leads to the understanding of each internal state variable role. A well-chosen set of initial variables with properly adapted DEM parameters give the relevant predictive simulations for a final comparison with the experimental oedometer tests. Thanks to a discrete insight into the micromechanics, the evolutions of the breakage level, the orientation anisotropy and the local stresses exerted on the shells (and/or the fragments) are quantified during the compression. The breakage of the shells result in high compressibility of the material. Therefore, the mechanical response is seen as a consequence of the breakage evolution. Finally, an analytical model is suggested in order to predict the Stress↔Void ratio relationship knowing the initial state of the sample and the tensile strength of the constituents: the shells

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Diversos biomateriais tem sido desenvolvidos para preencher ou reconstruir defeitos ósseos, dentre esses destaca-se a quitosana por seu potencial osteoindutor. Outras substâncias que tem despertado o interesse da comunidade científica são os fitoterápicos, nesse grupo encontra-se o mastruz (Dysphania ambrosioides (L.) Mosyakin & Clemants), por apresentar capacidade de estimular e acelerar o reparo ósseo. Sendo assim, este trabalho objetivou desenvolver e avaliar esferas de quitosana/ Dysphania ambrosioides (L.) Mosyakin & Clemants para aplicação como biomaterial para regeneração óssea. Para tanto foi feita a coleta e identificação botânica da espécie vegetal, em seguida foi produzido o extrato alcoólico bruto (EAB) do qual foi realizada a caracterização fitoquímica. Feito isso, foram confeccionadas esferas, pela técnica de geleificação ionotrópica, utilizando o Tripolifosfato de sódio (TPP) como agente de reticulação e em seguida as mesmas foram lavadas com água destilada e colocadas para secagem na estufa. Após esse processo, as esferas de quitosana e quitosana com diferentes concentrações do EAB foram caracterizadas utilizando Microscopia Ótica (MO); Microscopia Eletrônica de Varredura (MEV); Espectroscopia na região do infravermelho com transformada de Fourier (FTIR); Medida do diâmetro das mesmas; ensaios de Citotoxicidade in vitro, Biodegradação enzimática in vitro e Compressão. O resultado da caracterização fitoquímica, demonstrou a presença de esteróides, saponinas e principalmente flavonóides no extrato alcóolico bruto (EAB). A MO evidenciou a formação de esferas bem delimitadas e com tendência a ficarem mais escuras a medida em que se aumentava a concentração do EAB; a MEV revelou a presença de uma superfície externa enrugada e uma superfície interna com aspecto denso devido ao processo de secagem na estufa. O estudo químico realizado através do FTIR identificou todas as bandas características típicas de cada material estudado nesta pesquisa; e nas esferas produzidas, verificou-se a interação do TPP com a quitosana. A medida do diâmetro das esferas de quitosana sem incorporação EAB (Q0) foi menor em comparação aos demais grupos: quitosana+5% de EAB (Q5), quitosana+10% de EAB (Q10) e quitosana+20% de EAB (Q20). Todas as amostras foram consideradas não citotóxicas; com relação à biodegradação, na presença de lisozima, as esferas de todos os grupos apresentaram perda de massa em todos os tempos estudados, já na solução Phosphate Buffered Saline (PBS) foi observado um ganho de massa em todos os grupos nos diversos tempos estudados. O grupo Q0 suportou maior carga compressiva e também deformou mais, antes de fraturar, quando comparado aos grupos Q5, Q10 e Q20. Desta forma pode-se concluir que a metodologia para produção de esferas foi de fácil execução, sendo por tanto reprodutível e que por meio das caracterizações realizadas observou-se que o EAB, tornou as esferas maiores, atuou como agente reticulante da quitosana, aumentando o tempo de degradação e também a carga compressiva suportada e deformação sofrida até a fratura. Dessa forma a incorporação do EAB foi favorável para utilização das esferas como possível agente osteoindutor, visto que os produtos da sua degradação podem atuar com esse propósito, sendo as esferas do grupo Q20 as mais indicadas para áreas com dimensões anatômicas reduzidas
Several biomaterials have been developed to fill in or reconstruct bone defects, among these the chitosan stands out due to its osteoinductive potential. Other substances have aroused the interest of the scientific community are the phytotherapics, in this group can be found the ‘mastruz’ (Dysphania ambrosioides (L.) Mosyakin & Clemants), for presenting the capacity of stimulating and accelerate bone repair. Thereby, this work aimed to develop and assess chitosan Dysphania ambrosioides (L.) Mosyakin & Clemants spheres for application as a biomaterial for bone regeneration. For this purpose the collection and botanical identification was carried out, and after the crude ethanolic extract (CEE) was produced, and its phytochemical characterization was performed. Having done this, spheres were made, by the ionotropic gelation method, using the Sodium tripolyphosphate (TPP) as a cross-linking agent and after, they were washed with distilled water and placed to dry in the oven. After this process, the chitosan spheres and chitosan with different concentrations of the EAB were characterized using Optical Microscopy (OM); Scanning Electron Microscopy (SEM); Fourier transformed infrared spectroscopy (FTIR); measurement of the diameter; in vitro Cytotoxicity, in vitro Enzymatic biodegradation and Compression tests. The result of the phytochemical characterization, demonstrated the presence of steroids, saponins and mainly flavonoids, in the crude ethanolic extract (CEE). The OM revealed the formation of well delimited spheres with a tendency of becoming darker as the EAB concentration increased; the SEM revealed the presence of a wrinkled external surface and an internal surface with a dense aspect due to the drying in the oven process. The chemical study performed by the FTIR identified all the bands typical characteristics of each material studied in this research; and in the produced spheres, the interaction of the TTP with the chitosan was found. The measures of the chitosan sphere’s diameters without the incorporation of the CEE (Q0) were smaller in comparison to the other groups: chitosan+5% of CEE (Q5), chitosan+10% of CEE (Q10) and chitosan+20% of CEE (Q20). All the samples were considered not cytotoxic; in relation to the biodegradation, in the presence of lysozyme, the spheres of all the groups presented mass loss at all the studied times, as for in the solution Phosphate Buffered Saline (PBS) a mass gain was observed in all the groups at the various studied moments. The Q0 group bared a greater compressive load and also deformed more, before fracturing, when compared to the Q5, Q10 and Q20 groups. This way it can be concluded that the methodology for the production of spheres was easy to carry out, therefore being reproducible and by means of the characterizations performed it was observed that CEE, made the spheres bigger, acted as a crosslinking agent of the chitosan, increasing the degradation time and also the supported compressive load and deformation suffered until the fracture. This way the incorporation of the CEE was favorable for the use of the spheres as a possible osteoinductor agent, seen as the products of their degradation may act with this purpose, being the spheres of the Q20 group the most indicated for areas with reduced anatomic dimensions.

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Capes
A policaprolactona (PCL), utilizada como matriz biodegradável em combinação à nanohidroxiapatita (nHA), intrinsecamente bioativa, é uma alternativa promissora para a produção de matrizes tridimensionais (3D) porosas, visando a regeneração do tecido ósseo. No entanto, rotas de processamento visando otimizar a interação entre esses materiais devem ser investigadas. O objetivo deste trabalho foi desenvolver matrizes 3D de PCL/nHA estruturadas por esferas, via agregação por aquecimento a baixas temperaturas. Para isto, foram produzidas nHA por precipitação química via úmida, utilizando o Ca(NO3)2.4H2O e o (NH4)2HPO4 como precursores, conduzido à 80 °C (pH>10). Estas foram caracterizadas por difração de Raios X (DRX), espectroscopia na região no infravermelho com transformada de Fourier (FTIR) e microscopia eletrônica de transmissão (MET). A superfície das nHA foi modificada com ácido esteárico (AE), verificada pelos resultados de FTIR, MET e monitoramento de estabilidade. Esferas de PCL e PCL/nHA foram produzidas pelo método de emulsão simples com evaporação do solvente, o diclorometano, em 02 etapas, para obtenção de diâmetros entre 10-150 µm e maiores que 800 µm. Foram investigadas as influências da concentração de PCL, da adição de nHA com e sem AE, da concentração de álcool polivinílico e da velocidade de emulsificação. O material foi caracterizado por DRX, FTIR, microscopia eletrônica de varredura (MEV), calorimetria exploratória diferencial (DSC) e análise termogravimétrica (ATG), sendo calculado também o rendimento. Matrizes 3D porosas de PCL e de PCL/nHA foram produzidas e analisadas por microscopia ótica (MO), MEV e ensaios in vitro de bioatividade e de adesão celular. nHA deficientes em cálcio, em formato de haste (~47 nm x ~8 nm) e com superfície específica de 90,1 m2/g, foram obtidas. Esferas de PCL e PCL/nHA foram produzidas com diâmetros entre 2-3000 µm, densas ou porosas, contendo nHA distribuídas interna e externamente. Matrizes 3D foram obtidas a partir da agregação das esferas produzidas, estruturadas entre si a partir da formação de pescoços entre esferas adjacentes, com hierarquia de poros medindo até 1500 µm. As matrizes apresentaram capacidade bioativa e satisfatória adesão e desenvolvimento celular. Os resultados sugerem a aplicação vantajosa desses dispositivos para a regeneração de tecidos ósseos.
Polycaprolactone (PCL) have been largely used as a biodegradable matrix. This polymer in a combination with bioactive calcium deficient nanohydroxyapatite (CD-nHA) represent promising materials to be applied for bone tissue engineering. Nevertheless, processing routes to optimize the interaction between these materials should be investigated. Thus, the aim of this work was to develop PCL/nHA spherebased scaffolds structured by sinterization at low temperatures. For this, nHA were produced by wet chemical precipitation method, using the precursors Ca(NO3)2.4H2O and (NH4)2HPO4, conducted at 80 °C (pH>10). The powder was characterized by Xray diffraction (XRD), fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). nHA surface was modified with stearic acid (SA), verified with FTIR and TEM analysis and stability control in dichloromethane (DCM). PCL and PCL/nHA spheres were produced by oil-in-water and solid-in-oil-in-water emulsion solvent evaporation method. This production occurred in 02 steps, to obtain diameters ranging 10-150 µm and higher than 800 µm. The follow parameters were investigated: PCL concentration, nHA content with and without AE, polyvinyl alcohol concentration (stabilizing agent) and emulsification stirring. The material was characterized by DRX, FTIR, scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetric analysis (ATG), and the percent yield was calculated. PCL and PCL/nHA porous scaffolds were produced and characterized by SEM, optical microscopy (MO), and in vitro bioactivity and cell adhesion assays. Calcium deficient nHA, shaped as rods (~47 nm x ~8 nm), with a specific surface of 90,1 m2/g was obtained. PCL and PCL/nHA spheres were produced with diameters ranging 2-3000 µm, dense or porous, containing nHA effectively distributed internally and at the surface. Scaffolds were successfully obtained by sintering the spheres at low temperatures. It was observed connections shaped as necks in adjacent spheres, and a hierarchical porous architecture with pores measuring up to 1500 µm. It was demonstrated satisfactory bioactivities capacity, cellular adhesion, and cellular development. Our results suggested the advantageous applicability of these scaffolds to bone tissue regeneration.

La spectrométrie des neutrons rapides est une technique essentielle dans plusieurs domaines notamment pour les expériences de détection d'évènements rares, telles que celles de détection directe de la matière noire, et pour les centres de recherches nucléaires. La détection des neutrons rapides se fait habituellement de manière indirecte. Les neutrons sont d'abord ralentis par des matériaux modérateurs pour être détectés ensuite dans une gamme d'énergie plus basse. Ces techniques de détection sont cependant complexes à mettre en place et sont limitées en résolution en énergie. Un nouveau type de spectrométrie de neutrons rapides a été développée à l'Institut d'Astrophysique Spatiale (IAS) dans le but d'avoir une meilleure connaissance des fonds de neutrons : il associe la technique bolométrique à des cristaux à base de lithium sensibles aux neutrons. Le lithium-6 est en effet un élément ayant une des plus grandes sections efficaces de capture neutronique avec la réaction 6Li(n,)3H. La réaction libère 4.78 MeV signant ainsi énergétiquement chaque capture de neutron et lors de l'interaction avec un neutron rapide, l'énergie totale mesurée par le bolomètre devrait être la somme de cette énergie de réaction et de l'énergie cinétique du neutron rapide incident. Afin de valider ce principe, un prototype de spectromètre à neutrons rapides, compact et semi portable, a été construit à l'IAS. Ce détecteur cryogénique, fonctionnant entre 300 et 400 mK, consiste en un cristal de 0.5 g de 6LiF enrichi à 95%, associé un thermomètre en Ge-NTD. Cette thèse a porté sur l'étude des caractéristiques de ce spectromètre, des premières mesures à l'IAS, aux mesures dans le centre de recherche de l'Institut Paul Scherrer (PSI), jusqu'au calibrage final sur l'installation Amande de l'Institut de Radioprotection et de Sûreté Nucléaire (IRSN).

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Made available in DSpace on 2018-06-15T19:48:16Z (GMT). No. of bitstreams: 1 MARIA JUCÉLIA LIMA DANTAS – DISSERTAÇÃO (PPG-CEMat) 2016.pdf: 3511044 bytes, checksum: c308b22312ce9f189d694fc843ba74af (MD5) Previous issue date: 2016-02-29
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Estruturas tridimensionais são ferramentas bastante atrativas para a engenharia de tecidos, mimetizado fisicamente a matrix extracelular natural que atuam como suportes para o desenvolvimento celular. O objetivo do trabalho foi produzir estruturas tridimensionais biodegradáveis de quitosana-hidroxiapatitagelatina (CS/HA/G) com diferentes quantidades de HA e avaliar suas propriedades e comportamento in vitro. As estruturas tridimensionais foram produzidas em duas etapas. Numa primeira etapa foram obtidas esferas de CS contendo diferentes quantidades de HA de baixa cristalinidade (20, 50 e 70 % m/m). A HA de baixa cristalinidade foi gerada in situ no interior das esferas de CS. Para isso foi precipitado CaHPO4 em uma dissolução de CS e a suspensão resultante foi conformada na forma de esferas mediante gotejamento em dissolução de Na5P3O10 (TPP) com pH 8-9. As esferas precipitadas foram mantidas sob agitação nesta solução para conseguir a reticulação da CS e a transformação do CaHPO4 em HA, e finalmente liofilizadas. Para a obtenção das estruturas tridimensionais, as esferas de CS HA foram aglutinadas mediante impregnação com dissolução aquecida (40°C) de 5 % de G, arrefecimento até -18°C e liofilização. As esferas foram caracterizadas mediante microscopia ótica (MO), microscopia eletrônica de varredura (MEV), difração de raios X (DRX), análises termogravimétricas (TG) e espectroscopia de infravermelho (IV). E as estruturas tridimensionais por Porosidade, Grau de Intumescimento (GI), propriedade mecânica de resistência à comrpressão via seco e úmido. O diâmetro médio das esferas segundo os resultados de MO foi de 2,6 ± 0,22mm e 2,8± 0,28mm para CS-HA 20% e CS-HA50%,respectivamente. Já as partículas de CS-HA70% apresentaram diâmetro médio de 3,9± 0,37mm tendo sua morfologia e porosidade superficial variou com o conteúdo de HA. A presença de HA de baixa cristalinidade no interior das esferas foi confirmada pelos resultados DRX e IV. Nas imagens de MEV foi possível observar que os cristais de HA estão homogeneamente dispersos no interior das esferas. Os resultados de TG revelaram boa concordância entre as quantidades de HA projetadas e as realmente obtidas nas esferas. Os resultados das estruturas tridimensionais indicam influência pelas diferentes concentrações de hidroxiapatita. Com o aumento na fração cerâmica observa-se a densificação da superfície, uma pequena diminuição da porosidade e no grau de intumescimento, como também um aumento no modulo de elasticidade via seca e uma pequena diminuição nas propriedades mecânicas via úmido, causado pelo intumescimento da estrutura. O compósito que apresentou resultados mais satisfatórios foi CS-HA20%, exibindo um melhor perfil à porosidade, grau de intumescimento e prorpriedades mecânicas. O estudo sugere que as estruturas tridimensionais necessitam de reajustes para serem aplicadas em regeneração óssea, entretanto podem ser indicadas para aplicações em engenharia de tecidos, em situações preferencialmente ex-vivo, como suportes temporários de células.
Three-dimensional structures are very attractive tools for tissue engineering, physically mimicked the natural extracellular matrix, these structures act as supports for cell development. The goal was to produce biodegradable threedimensional structures of chitosan-hydroxyapatite-gelatin (CS / HA / L) with different HA contents and evaluate their properties and behavior in vitro. The three-dimensional structures were produced in two steps. In a first step CS were obtained spheres containing different amounts of HA low crystallinity (20, 50 and 70% w / w). The poorly crystalline HA was generated in situ within the CS spheres. To this precipitate was dissolved in CS CaHPO4 and the resulting suspension was shaped in the form of spheres by dripping in dissolution Na5P3O10 (TPP) at pH 8-9. The precipitated spheres were kept in this solution under stirring to obtain the halftone processing and the CS HA CaHPO4 , and finally lyophilized. To obtain the three-dimensional structures, CS-HA spheres were bonded by impregnation with warm solution (40 ° C) 5% C, cooling to -18 °C and lyophilization. The spheres were characterized by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TG) and infrared spectroscopy (IR). And the three dimensional structures by porosity, Degree of Swelling (GI), mechanical property of resistance comrpressão via dry and wet. The average diameter of the spheres according to the results of MO was 2.6 ± 0.22 mm and 2.8 ± 0,28mm CS-20% CSHA50% respectively. Already the particles of CS-HA70% had a mean diameter of 3.9 ± 0,37mm having their morphology and surface porosity varied with the HA content. The presence of low crystallinity with in the HA spheres was confirmed by the XRD results and IV. In the SEM images was observed that HA crystals are homogeneously dispersed within the sphere. The TG data showed good agreement between the HA and the amounts actually projected on the spheres obtained. The results indicate influences of threedimensional structures for various concentrations of hydroxyapatite. With the increase in the ceramic fraction is observed densification of the surface, a slight reduction of the porosity and the degree of swelling, as well as an increase in the modulus of elasticity via a small decrease in the mechanical properties wet route, caused by swelling of the structure. The composite that presented better results was CS-HA20%, showing a better profile to the porosity, degree of swelling and mechanical prorpriedades. The study suggests that threedimensional structures require adjustments to be applied in bone regeneration, but can be suitable for applications in tissue engineering, in situations preferably ex vivo, as temporary supports cells.

The use of Bonner Sphere Spectrometer (BSS) is a well-established method of measuring the energy distribution of neutron emission sources. The purpose of this research is to apply the Generalized Regression Neural Network (GRNN), a kind of Artificial Neural Network (ANN), to predict the neutron spectrum using the count rate data from a BSS. The BSS system was simulated with the MCNP5 Monte-Carlo code to calculate the response to neutrons of different energies for each combination of thermal neutron detector and polyethylene sphere. One hundred and sixty-three different types of neutron spectra were then investigated. GRNN Training and testing was carried out in the MATLAB environment. In the GRNN testing, eight-one predicted spectra were obtained as outputs of the GRNN. Comparison with standard spectra shows that 97.5% of the prediction errors were controlled below 1%, indicating ANN could be used as an alternative with high accuracy in neutron spectrum unfolding methodologies. Advantages and further improvements of this technique are also discussed.

This thesis investigates the differences in Bonner Sphere detector response for anisotropic neutron fields as a function of borehole orientation. Monte Carlo simulations using MCNPX were used to calculate the difference for a borehole oriented directly behind a unidirectional neutron field and one in which the borehole is normal to the neutron flux. The differences in detector response depend on the size of the Bonner Sphere and the energy of the incident flux, which could introduce significant error in the determination of the neutron field’s energy spectrum.

碩士
國立清華大學
生醫工程與環境科學系
104
Nowadays, high-energy radiation particles are used in radiation therapy gradually. High-energy radiation particles always accompany with high-energy neutrons. To evaluate the distributions of neutron energies and fluences, the Bonner Sphere Spectrometer (BSS) is most commonly used to assess the neutron spectrum in international, but it is not good when particle energy exceed 10 MeV. High atomic number materials like lead, or copper is added to traditional BSS to increase (n, xn) cross-section, and then enhance the magnitude of the response functions in high energies. This new detection system is called Extended-Range Bonner Sphere Spectrometer (ERBSS). In this research, 7 different sizes BSS and self-made ERBSS including 2 lead sphere-shells and 2 polyethylene sphere-shells with gold foil were used to measure neutron spectra of standard neutron source Cf-252 and Tsing-Hua Open-pool Reactor (THOR). The neutron spectra of Cf-252 and THOR measured by means of traditional BSS and ERBSS were compared. The results showed that the neutron spectra of ERBSS and traditional BSS are similar in measuring standard Cf-252 source and THOR, and the ability of self-made ERBSS measuring neutron spectra was verified and proved. The results also showed that traditional BSS accompany with PbPE sphere-shell is more fit to real neutron spectrum. It can increase the calculation accuracy of program UMG 3.3, which calculate the neutron spectrum, when the sphere set is increased. The high-energy neutron facilities are going to be constructed and operated in the future, in Taiwan. By experimental verification of this study, the feasibility of using self-made ERBSS system to evaluate and analysis high-energy neutron spectrum is approved.