Made available in DSpace on 2014-10-09T12:26:51Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:14Z (GMT). No. of bitstreams: 0 / Os aplicadores clínicos de 90Sr+90Y são instrumentos utilizados em procedimentos de braquiterapia e devem ser calibrados periodicamente, de acordo com normas e recomendações internacionais. Neste trabalho, foram estudados quatro métodos de calibração de aplicadores dermatológicos e oftálmicos, comparando-se os resultados com os fornecidos pelos certificados de calibração dos fabricantes dos aplicadores. Os métodos envolveram o aplicador clínico padrão do Laboratório de Calibração de Instrumentos (LCI), calibrado pelo laboratório padrão primário americano do National Institute of Standards and Technology, como referência; um aplicador da Amersham, também pertencente ao LCI, como referência; uma mini-câmara de extrapolação desenvolvida no IPEN como padrão absoluto; e dosimetria termoluminescente. A mini-câmara de extrapolação e uma câmara de extrapolação comercial PTW foram estudadas com relação ao seu desempenho por meio de testes de controle de qualidade, como corrente de fuga, repetitividade e reprodutibilidade. A distribuição de dose em profundidade na água, estudo de grande importância na dosimetria de aplicadores clínicos, foi determinada utilizando-se a mini-câmara de extrapolação e dosímetros termoluminescentes. Os resultados obtidos foram considerados satisfatórios para os dois casos, quando comparados com os dados fornecidos pela norma IAEA (2002). Além disso, foi desenvolvido um sistema postal dosimétrico para a calibração de aplicadores clínicos por meio da técnica da termoluminescência, para ser enviado para clínicas e hospitais, sem a necessidade do transporte das fontes ao LCI do IPEN para calibração. / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:32:32Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:09Z (GMT). No. of bitstreams: 1 03259.pdf: 2834364 bytes, checksum: fcbdf9e370a39ffdb27be573e65f253c (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Le siècle dernier a vu le développement de la physique des particules, avec la fondation du célèbre modèle Standard de la physique des particules. Plus spécifiquement, durant les 70 dernières années de nombreuses particules ont été détecté et étudié. Parallèlement à ces découvertes, les moyens expérimentaux et les détecteurs ont grandement évolué. de la simple chambre à bulles de l'expérience Gargamel, qui a posé la première brique expérimentale du modèle standard, aux détecteurs complexes d'aujourd'hui tel que le LHC. Durant le développement de nouveaux détecteurs, nous pouvons distinguer deux grandes catégories: les détecteurs dits Solid State et les détecteurs gazeux. La première englobe les détecteurs tels que les Cherenkov ou les scintilateurs tandis que les derniers utilisent un gaz comme moyen de détection.Les détecteurs gazeux ont aussi grandement évolué durant le siècle dernier, des tubes Geiger-Muller au chambres à étincelles ou Pestov, qui peuvent faire face aux taux de détections toujours grandissant des accélérateurs de particules. The Parallel Plate Avalanche Chamber est un détecteur gazeux similaire mais fonctionne en mode avalanche, où les signaux électriques sont produits par une multiplication contrôlée des électrons dans le gaz. Les autres détecteurs susmentionnées fonctionnent eux en mode étincelle, où le signal détectée est produit par une décharge électrique dans le gaz.Le mode avalanche permets un taux de détection encore supérieur mais au prix de signaux électriques beaucoup plus faibles. Au début des années 80 un nouveau type de détecteur gazeux commence à se développer, les Resistive Plate Chambers. Ce détecteur présente la particularité de pouvoir fonctionner en mode étincelle ou avalanche, selon le design. Utilisé en mode avalanche, ils présentent un taux de détection particulièrement intéressant au prix de signaux électriques faibles, nécessitant un circuit d'amplification dédié. De nos jours les Resistive Plate Chambers sont très largement utilisés dans de nombreuses expériences de physique des particules, notamment pour leurs performances intéressantes et leur prix contenu. Malgré leur usage répandu, les Resistive Plate Chambers n'ont pas été beaucoup étudié d'un point de vue modélisation et simulation. La simulation d'un détecteur est un outil essentiel pour leur développement et leur fabrication, permettant de tester un design et calculer les performances que l'on est en droit d'attendre. Dans les travaux présentés dans ce document nous nous sommes intéressés à la description des différents phénomènes physiques se produisant durant une avalanche électronique au sein d'un Resistive Plate Chambers fonctionnant en mode avalanche, dans le but de les modéliser et simuler. Nous décrivons un modèle détaillé pour le processus d'ionisation, qui est l'évènement fondamental pour tout détecteur gazeux. Nous décrivons aussi un modèle mis au point par Riegler-Lippmann-Veenhof pour le développement d'avalanche électronique. Une simulation C++ a été produite dans le contexte de cette étude et quelques résultats sont présentés. / The 20th century saw the development of particle physics research field, with the fundationof the famous Standard Model of particle physics. More specifically during the past 70 years numerous particles have been detected and studied. Alongside those discoveries, the experimental means and detectors has greatly evolved. From the simple Gargamel bubble chamber, which lay the first brick to the Standard Model theory, to the nowadays complex detectors such as the LHC. In the development of newer particles detector, one can distinguish two big categories:the solid state detectors et the gaseous detectors. The former encompass detectors suchas Cherenkov and scintillator counters while the later make use of gases as detection medium. The gaseous detectors have also greatly evolved during the past century from theGeiger-Muller tube to the spark or Pestov chambers, which can cope with the increasing detection rate of particles accelerator. The Parallel Plate Avalanche Chamber is a similar gaseous detector but operates in avalanche mode, where the detected signal is producedby a controlled multiplication of electrons in the gas. The aforementioned detectors were operated in spark mode, where the detection is made through a spark discharge in the gas.The avalanche mode allows even greater detection rates at the expense of signal amplitude. In early 80s a new gaseous detector design began to emerge: the Resistive Plate Chambers.This detector has the particularity to operates in spark or avalanche mode depending on its design. Operated in avalanche mode, they present an impressing detection rates at the expense of very small electric signals, requiring dedicated amplification circuitries. Nowadays the Resistive Plate Chambers are widely used in numerous experiments worldwide,because of their interesting performances and relatively small price. Despite their widespread usage, the Resistive Plate Chambers have not been extensively studied from a simulation and modelisation point of view. Simulation of a detectoris an essential tool for its development and construction, as it allows to test a design and predict the performances one may get. In this work we focused on the description of the physics phenomenons occuring during an electronic avalanche inside a Resistive Plate Chambers operated in avalanche mode, in order to properly modelise and simulate them. We review a detailed model of the ionisation process, which is the fundamental event in any gaseous particle detector, alongside theRiegler-Lippmann-Veenhof model for the electronic avalanche. A C++ simulation has been produced in the context of this work and some results are presented.

No description available.

The Red Scare of the late 1940s and 1950s was fueled by claims of governmental espionage from former members of the communist underground. Harry Dexter White, Assistant Secretary of the Treasury was accused of being a Soviet agent of influence. This paper will analyze the current issues in the discussion of Soviet espionage and focus on White's activities in this regard. The evidence on White is clear enough to show that he did pass sensitive information to the Soviets. He also succeeded in subverting American policy to favor Soviet interests over U.S. interests. White's activities in government service suggest that American government officials passed on vital government information to the Soviet Union and subversive activity went on in the U.S. in the 1930s and 1940s.

The combustion process of a fuel is a challenging subject when it comes to analyze its performance and resultant emissions. The main task of this study is to optimize the selection of a hydrogen-rich fuel based on its performance and emissions. Computational Fluid Dynamics analysis is performed to test the combustion performance and emissions from the vortex trapped combustor when natural gas fuel (methane) is replaced with renewable and alternative fuels such as hydrogen and synthesis gas. Correlation graphs for the trapped vortex combustor performance and NOx, CO, and CO2 emissions for various types of fuels with different compositions and heat of combustion values were established. Methane, Hydrogen and 10 different syngas fuels were analyzed in this study using computational fluid dynamics numerical method. The trapped vortex combustor that represents an efficient and compact combustor for flame stability was investigated. The TVC consists of a fore body and two after body disks . These components are all encircled with a Pyrex tube. The purpose of the after body disks is to create the vortex wakes that will enhance the combustion process and minimize the NOx emissions. The TVC CFD model was validated by comparing the CFD model results using propane fuel with existing experimental results that were established in Rome, Italy. The static temperature distribution and NOx, CO emissions, combustor efficiency and total pressure drop results of the three dimensional CFD model were similar to the experimental data. Effects of H2/CO and H2/CH4 ratios and the mass fraction of each constituent of syngas fuels and Hydrogen-Methane fuel mixture on the TVC performance and emissions were investigated. / Moreover, the fuel injector Reynolds number and Lower heating values for Methane, Hydrogen and 10 syngas fuels on the TVC performance and emissions were also investigated. Correlation plots for the NOx, CO and CO2 emissions versus the fuel injector Reynolds number and low heating value were established. These correlation curves can be used as a fair design diagram to optimize the fuel selection process for aerospace and electrical power plant applications. / by Khaled Zbeeb. / Thesis (Ph.D.)--Florida Atlantic University, 2011. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2011. Mode of access: World Wide Web.

Tendo em vista a importância da calibração de instrumentos medidores de radiação e do conhecimento das principais características destes instrumentos, diversos tipos de câmaras de ionização foram intercomparados em termos de seus coeficientes de calibração e dependência energética, em feixes padrões de raios X, níveis radioterapia, radiodiagnóstico e radioproteção. Foi realizada uma intercomparação de activímetros utilizados em medicina nuclear, com três radionuclídeos: 67Ga, 201Tl e 99mTc. Todos os activímetros que participaram da intercomparação apresentaram resultados dentro dos limites recomendados pela norma CNEN-NE-3.05. Para completar o conjunto de qualidades de radiação do Laboratório de Calibração de Instrumentos do IPEN, foram estabelecidos feixes de radiação-X, nível radioproteção e radioterapia de energias baixas, seguindo recomendações internacionais. Três metodologias para a obtenção de coeficientes de calibração de câmaras de ionização não seladas em feixes de radiação-X foram estudadas e comparadas. Um conjunto de câmaras de ionização Victoreen, especialmente projetado para uso em intercomparações laboratoriais, foi submetido a testes de caracterização. O desempenho destas câmaras mostrou que elas podem ser utilizadas em feixes de radiação-X nível radioproteção de maneira segura, visto que nestes feixes estas câmaras apresentaram resultados em conformidade com recomendações internacionais. No entanto, seu uso em feixes de radioterapia e de radiodiagnóstico deve ser feito com algumas considerações, pois especialmente nos testes de dependência energética e de tempo de estabilização, estas câmaras não atenderam às respectivas recomendações internacionais. Este trabalho apresenta dados sobre o desempenho de diversos modelos de câmaras de ionização em diferentes feixes de radiação-X, fornecendo uma ferramenta para a escolha do instrumento mais adequado para a realização de medições em feixes de radiação ionizante / Since the calibration of radiation measurement instruments and the knowledge of their major characteristics are very important subjects, several different types of ionization chambers were intercompared in terms of their calibration coefficients and their energy dependence, in radiotherapy, diagnostic radiology and radioprotection standard beams. An intercomparison of radionuclide calibrators for nuclear medicine was performed, using three radionuclides: 67Ga, 201Tl and 99mTc; the results obtained were all within the requirements of the national standard CNEN-NE-3.05. In order to complete the range of radiation qualities of the Calibration Laboratory of IPEN, standard radiation beam qualities, radiation protection and low energy radiation therapy levels, were established, according international recommendations. Three methodologies for the calibration of unsealed ionization chambers in X-ray beams were studied and compared. A set of Victoreen ionization chambers, specially designed for use in laboratorial intercomparisons, was submitted to characterization tests. The performance of these Victoreen ionization chambers showed that they are suitable for use in radioprotection beams, because the results obtained agree with international recommendations. However, these Victoreen ionization chambers can be used in radiotherapy and diagnostic radiology beams only with some considerations, since their performance in these beams, especially in relation to the energy dependence and stabilization time tests, did not agree with the international recommendations for dosimeters used in radiotherapy and diagnostic radiology beams. This work presents data on the performance of several types of ionization chambers in different X-ray beams, that may be useful for choosing the appropriate instrument for measurements in ionizing radiation beams.

A mamografia é um exame realizado no mamógrafo, que utiliza raios X para obter imagens da anatomia interna da mama. Para que esta imagem seja capaz de fornecer um diagnóstico correto, é necessário que os equipamentos passem constantemente por programas de controle de qualidade para que se possa garantir que as pacientes submetidas a este exame não estejam recebendo dose além da necessária, evitando-se assim possíveis efeitos biológicos indesejados. As câmaras de ionização são detectores muito utilizados para se realizar o controle de qualidade de equipamentos que utilizam radiação, como os mamógrafos. No presente trabalho foram utilizadas quatro câmaras de ionização desenvolvidas no Laboratório de Calibração de Instrumentos do IPEN LCI/IPEN, que foram submetidas a testes de caracterização em feixes padrões de radiação X do LCI. Elas apresentaram resultados satisfatórios, dentro dos limites estabelecidos pelas normas nacionais e internacionais. Como aplicação, estas câmaras de ionização foram utilizadas para testes de controle de qualidade em quatro mamógrafos clínicos de diferentes instituições quanto à repetibilidade e linearidade da taxa de kerma no ar. Os resultados obtidos nestes testes encontram-se dentro dos limites recomendados pelas normas nacionais e internacionais. / Mammography is an examination in mammography, which uses X-rays to obtain images of the internal anatomy of the breast. To provide a correct diagnosis, it is necessary that the equipment constantly undergo quality control programs to ensure that patients submitted to this examination do not receive more than the necessary dose, thus avoiding unwanted possible biological effects. The ionization chambers are widely used detectors to perform the quality control program of equipment with radiation, as mammographers. In the present study, four different special ionization chambers, developed at the Calibration Laboratory of Instruments of IPEN - LCI / IPEN, were submitted to the characterization tests in standard X radiation beams at the LCI. The results were satisfactory, within the limits estabilished by national and international standards. As an application, the ionization chambers were used for quality control tests in four mammography clinics from different institutions, as the repeatability and linearity of the air kerma rate. The results obtained in these tests were within the limits recommended by national and international standards.

A mamografia é um exame realizado no mamógrafo, que utiliza raios X para obter imagens da anatomia interna da mama. Para que esta imagem seja capaz de fornecer um diagnóstico correto, é necessário que os equipamentos passem constantemente por programas de controle de qualidade para que se possa garantir que as pacientes submetidas a este exame não estejam recebendo dose além da necessária, evitando-se assim possíveis efeitos biológicos indesejados. As câmaras de ionização são detectores muito utilizados para se realizar o controle de qualidade de equipamentos que utilizam radiação, como os mamógrafos. No presente trabalho foram utilizadas quatro câmaras de ionização desenvolvidas no Laboratório de Calibração de Instrumentos do IPEN LCI/IPEN, que foram submetidas a testes de caracterização em feixes padrões de radiação X do LCI. Elas apresentaram resultados satisfatórios, dentro dos limites estabelecidos pelas normas nacionais e internacionais. Como aplicação, estas câmaras de ionização foram utilizadas para testes de controle de qualidade em quatro mamógrafos clínicos de diferentes instituições quanto à repetibilidade e linearidade da taxa de kerma no ar. Os resultados obtidos nestes testes encontram-se dentro dos limites recomendados pelas normas nacionais e internacionais. / Mammography is an examination in mammography, which uses X-rays to obtain images of the internal anatomy of the breast. To provide a correct diagnosis, it is necessary that the equipment constantly undergo quality control programs to ensure that patients submitted to this examination do not receive more than the necessary dose, thus avoiding unwanted possible biological effects. The ionization chambers are widely used detectors to perform the quality control program of equipment with radiation, as mammographers. In the present study, four different special ionization chambers, developed at the Calibration Laboratory of Instruments of IPEN - LCI / IPEN, were submitted to the characterization tests in standard X radiation beams at the LCI. The results were satisfactory, within the limits estabilished by national and international standards. As an application, the ionization chambers were used for quality control tests in four mammography clinics from different institutions, as the repeatability and linearity of the air kerma rate. The results obtained in these tests were within the limits recommended by national and international standards.

Solidified igneous intrusions from originally liquid magma chambers display a large number of different sedimentary features. These features include the gravitational collapse of sidewalls producing slumps and the layering produced by gravitational settling of crystals. In the chamber fluid-dynamic processes such as convection are expected to occur due to cooling at the roof producing dense gravitationally unstable liquid, and the crystallisation of interstitial liquid changing the composition of the remaining liquid possibly reducing the density causing the liquid to rise up. The crystals which form in basaltic magma chambers have a high propensity to be mobilised due to convection and other fluid-dynamic processes including replenishment by a secondary intrusion. Convective mobilisation of plagioclase grains in vertical, tabular intrusions is seen from flat profiles of apparent aspect ratio as a function of dyke width. These flat profiles were formed due to scouring of gravitationally unstable sidewall mushes, and these crystals then become entrained in the convecting liquid. Convection only ceases once the volume of crystals in suspension reaches a critical volume fraction leading to an increase in viscosity, which dampens the vigour of convection. The majority of this study is performing and analysing a number of different experiments to look at the behaviour of different styles of analogue particle piles. Particle piles that are formed of inert, plastic particles are subjected to convection in the particle layer and in the bulk overlying fluid, and different styles of mobilisation depending on the heat flux driving convection and the density profile of the pile are observed. The mobilisation style goes from rolling of particles on the surface, to puffs of particles from the surface being lofted into the interior, followed by large particle fountains and then the entire particle pile being completely disaggregated and lofted into the interior of the chamber as the force driving convection is increased. The initiation of mobilisation can be explained by the fluidisation of a particle pile, whilst the high degrees of mobilisation seen in some high Rayleigh number regimes can be explaining by resuspending particles. In experiments where particle piles have a positive density profile (dense particles overlying low density particles) the underlying low density particles can break through the overlying layer in particle fountains and can be explained by a modified fluidisation parameter. These experiments lack the reactivity and cohesion that realistic crystal piles would have. To try and quantify this, I have also performed a series of experiments looking at the rheology of an ice-sucrose suspension, where ice crystals can sinter and aggregate together. Under sheared conditions the forces required to disaggregate ice aggregates can be calculated, with the viscosity of an ice-sucrose suspension being described by a power-law relationship of shear rate and crystal radius. The particle pile experiments show that mobilisation of equivalent crystal piles in magma chambers should be readily observed. As it is not observed, except in replenished magmatic systems, this suggests that the additional forces coming from cohesion and aggregation in crystal piles prevent mobilisation of magmatic crystals. The replenishment by secondary intrusions can lead to forces which overcome the strength of the pile.