Thesis (M.S.)--University of Michigan, 1983.

Thesis (M. Sc.)--University of Hong Kong, 2003. / Also available in print.

First published in the Bulletin of the American Mathematical Society in Vol.69, 1963, published by the American Mathematical Society

First published in the Bulletin of the American Mathematical Society in Vol.70, 1964, published by the American Mathematical Society

Orientador: André Virmond Lima Bittencourt / Co-orientadores: Luiz Eduardo Mantovani, João Jachic / Tese (doutorado) - Universidade Federal do Paraná / Resumo: A principal contribuição desta pesquisa é a apresentação do conhecimento que possibilita a seleção de áreas com diferentes intensidades de fluxos de radônio (222Rn e 220Rn) em paisagens tropicais úmidas com espessas coberturas residuais. Objetivando determinar os controles dos processos radioativos de geração, emanação, migração e exalação de Rn, e estabelecer uma metodologia de estudo que permita elaborar modelos previsionais de Rn adaptados ao contexto enfocado, são demonstradas e analisadas as principais relações entre os processos radioativos mencionados e os elementos morfológicos e dinâmicos das paisagens, verificando-se como tais inter-relações afetam a exalação de Rn. Para tanto avaliou-se o papel dos processos supergênicos, atuantes sobre rochas graníticas com teores normais e homogeneamente distribuídos de U e Th (Ra), durante os tempos geológico e pedológico, na evolução das vertentes de uma unidade de drenagem e conseqüente redistribuição dos radionuclídeos, numa visão multidisciplinar, tridimensional e sistêmica. Foram utilizados inúmeros dados, informações e conceitos, com destaque para os conceitos de sistema pedológico de transformação e de geoquímica de paisagens, consubstanciados por outros da física e geologia nucleares, e pela aplicação das razões Th/U e Us/Ut, além de elementos hidrogeológicos e climatológicos do macroambiente. Os processos supergênicos configuram as vertentes nas paisagens eluvial, transeluvial, supraqual e aqual, caracterizadas por diferentes geoformas, tipos e espessuras de solos residuais e permoporosidades. A cada paisagem se associam diferentes concentrações e fases hospedeiras dos radionuclídeos U e Th (Ra), bem como regimes hídricos específicos do aqüífero freático por porosidade secundária. No contexto investigado, o sistema de transformação Latossolo-Solo Podzólico encerra uma segunda geração pedogenética de radioanomalias, decorrente da podzolização dos Latossolos, mais intensas e com maior proporção de U adsorvido, além de alterar a distribuição das permoporosidades dos solos existentes, conformando um subsistema aqüífero freático suspenso na paisagem transeluvial. Na paisagem eluvial, as principais anomalias de U e Th (Ra) estão situadas no topo do horizonte B latossólico, e são devidas à acumulação relativa de minerais resistatos, U e compostos insolúveis de Th fixados por oxihidróxidos de Fe e Al e argilas. Na paisagem transeluvial, no topo do horizonte B textural dos Solos Podzólicos, as radioanomalias são em parte relativas e em parte absolutas. Na paisagem supraqual são essencialmente absolutas e uraníferas, com U adsorvido às fases argilo-orgânicas dos horizontes AO e A1 dos Solos Hidromórficos em duas etapas principais. A primeira, de maior duração e mais antiga que 1 Ma, ocorreu durante a latolização. A segunda, mais jovem e afetando espaços geográficos mais limitados, durante a podzolização dos Latossolos, entre 100.000 e 500.000 anos. Assim, com base nas intensidades das radioanomalias e forma de hospedagem do U e Th (Ra), nas permoporosidades dos solos, e suas relações espaciais com o sistema freático e respectivos regimes de umidade, as possibilidades de maiores taxas de exalação de Rn, principalmente Rn, são nas paisagens supraqual e transeluvial. Exceções podem ocorrer em áreas adjacentes à atual rede de drenagem, na paisagem supraqual, onde o 238U mais jovem que 1 Ma condiciona desequilíbrio radioativo significativo, com impacto negativo na geração de Rn. Na paisagem eluvial, a despeito da existência de intensas anomalias gama, devido ao acúmulo de resistatos com U e Th e compostos de Th, os fluxos de Rn são menos significativos, caracterizados pelo 220Rn. Finalmente, a abordagem utilizada possibilitou uma avaliação das condicionantes da exalação de Rn nas paisagens. Com base no estudo da distribuição espacial da cobertura residual, enfatizando os sistemas pedológicos de transformação e a cronologia relativa dos diferentes processos que atuaram nas vertentes, a geoquímica de paisagens e outros conceitos importantes, foi possível estabelecer modelos previsionais de Rn em escalas compatíveis com as dimensões de pequenos núcleos habitacionais ou mesmo de residências unitárias. Isto é particularmente válido para paisagens sobre granitos com relevo moderado, em regiões quentes e úmidas com florestas, em que se verifica a associação entre Latossolos, Solos Podzólicos e Solos Hidromórficos. Por isso, sugere-se estudos em contextos climáticos de transição e embasados por diferentes litologias. Também, sugere-se testes comparativos com modelos baseados em dados gamaespectrométricos, em que não seja considerada a redistribuição dos radionuclídeos gama-emissores durante a alteração supergênica. Palavras-chave: Distribuição de Radônio; Paisagens; Processos Supergênicos; Sistema de Transformação Latossolo - Solo Podzólico / Abstract: The main contribution of this research is the knowledge acquired which allows for the selection of areas with different intensities of Rn fluxes in humid tropical landscapes covered by thick residual soil profiles. Studies were carried out to determine the Controls of the radioactive processes of Rn generation, emanation, migration and exhalation and to come out with an approach that permits the elaboration of predictable models of Rn adapted to the context in focus. The main relationships concerning the radioactive processes and the morpho-dynamic landscape elements and their effect on the exhalation of Rn were analyzed. The weathering processes have a major role on granitic rocks with U and Th ( Ra ) normal concentration and distribution during geological and pedological times, on a drainage unit slope evolution and consequent redistribution of radionuclides. This role was examined considering a multidisciplinary, tridimensional and systemic viewpoint. Several data and concepts were used, mainly the pedological systems of transformation and landscape geochemistry, supported by others pertaining to nuclear physics, Th/U and Us/Ut ratios, besides hydrogeological and climatic elements of the macroambient. The weathering processes on slopes promote differentiation into the eluvial, transeluvial and superaqual and aqual landscapes, characterized by different geoforms, residual soil types and thicknesses, permeabilíties and water regimes of phreatic aquifer, and by different U and Th ( Ra ) concentrations and host phases. In the focused context, the Latosol-Podzolic transformation system includes a secondary pedogenetic generation of radioanomalies, more intenses and with a higher proportion of adsorbed U, due to the Latosol podzolization, and with the characteristic of altering the water regime of phreatic aquifer by changing the permeability of soils and increasing versant slope, resulting in a perched phreatic aquifer subsystem in the transeluvial landscape. In the eluvial landscape, the main anomalies of U and Th ( Ra ) are located on the top of latosolic B horizon, and are caused by the relative accumulation of resistate minerais, U and Th insoluble compounds, fixed by Fe and Al oxyhydroxides and clays. In the transeluvial landscape, on the top of the textural B horizon of Podzolic Soils, the radioanomalies are partially relative and partially absolute. In the superaqual landscape, the anomalies are mainly absolute and uraniferous, with U fixed by the adsorption on argillaceous and organic phases of AO and A1 horizons of Hydromorphic Soils, during two principal stages. The first one, longer and older than 1 My happened during the latolization. The second, younger and acting over more limited geographic areas, happened during the Latosol podzolization, approximately between 100,000 and 500,000 years. Consequently, the possibilities of encountering the highest rates of Rn exhalation, mainly 222Rn, are in superaqual and transeluvial landscapes. This conclusion was reached by considering the intensity of radioanomalies and the type of host phases of U and Th ( Ra ), the soil permeability and its spatial relationships with the phreatic system and water regimes. Exceptions may occur in areas adjacent to the present drainage system, in the superaqual landscape, where the 238U younger than 1 My presents a significant radioactive disequilibrium, with a negative impact on Rn generation. In the eluvial landscape, despite the existence of intense gamma anomalies, caused by the accumulation of resistates with U and Th and Th compounds, the fluxes of Rn are less significant, characterized by 220Rn. Finally, the approach chosen allowed to evaluate the circumstances in which Rn exhalation takes place in the landscapes. Based on the studies about the spatial distribution of residual cover, with emphasis on pedologic transformation systems and the relative chronology of different processes that acted on slopes, the geochemistry of landscapes and other important concepts, it was possible to establish Rn previsional models in scales compatible with small dwelling centers or even single houses. This is specially valid about landscapes over granitic rocks with moderate relief, in hot and humid regions covered by forests, where the association between Latosol - Podzolic and Hydromorphic soils takes place. For this reason, studies in transitory climatic contexts with different rocks are suggested. Moreover, comparative tests with models based on gammaspectrometric data, disregarding the redistribution of gammaemitters radionuclides during supergenic alterations are suggested. Key-words: Radon Distribution; Landscapes; Supergenic Processes; Latosol - Podzolic Transformation System

Magister Scientiae - MSc / Radon has been identified as an important factor that could result in a health hazard by studies all around the world. The health risks can be minimised by preventive measures where radon is highly concentrated as in some mines and homes. Measuring and modelling the radon concentrations in the mine dump soil, can help to deduce the radon flux to identify the problem areas for rehabilitation especially in the cases of gold and uranium mine tailings. Rehabilitation in those cases usually consists of a multilayer cover of solids like crushed rock or clay. A passive method incorporating electret technology was used in this study to determine the radon emanation coefficient of the soil. This investigation also describes the modelling of a depth profile with respect to the radon activity concentration to understand from how deep radon might be migrating, as well as the effect of different diffusion lengths. / South Africa

This thesis presents an algorithm for image reconstruction from projections intended for use in a new class of volume imaging PET scanners. The algorithm is based on the inversion of the three dimensional Radon Transform as it applies to the truncated cylindrical detector geometry and is derived from the X-ray Transform inversion given by the Orlov recovery operator. The algorithm is tested using Monte Carlo simulations of several phantom geometries and employs a single iterative step to include all detected events in the reconstruction. The reconstructed images are good representations of the original objects, however the iterative step is a source of some significant artefacts in the images. Also discussed is the extension of the Radon Transform technique to a non-iterative method for three dimensional image reconstruction using all detected events. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

No description available.

The EPA recently completed a major study to evaluate exposure and risk associated with a primary contaminant, radon and its progeny in drinking water (EPA, 1995). This work resulted in the development of a Monte Carlo Simulation model written in the programming language C. The model developed by the EPA has been used to estimate the cancer fatality risk from radon in water for exposed populations served by community ground water supplies, and to provide a quantitative analysis of the uncertainty associated with the calculations (EPA, 1995). This research is a continuation of the study conducted by the EPA. In this project, a Monte Carlo computer model will be developed to evaluate the risk associated with exposure to volatile compounds in drinking water. The model will be based on a computer program (developed previously by the EPA) for estimating the risks associated with exposure to radon in drinking water. The model will be re-implemented in the form of a computer program written in C. The analysis for radon will be extended to include the entire range of contaminants found in drinking water supplies. The initial focus of the project has been on extending the analysis to cover the ingestion exposure pathway for volatile compounds, but ultimately the risk via ingestion and dermal sorption will also be evaluated. The integrated model can estimate the risks associated with various levels of contaminants in drinking water and should prove valuable in establishing Maximum Contaminant Levels (MCLs) for the entire range of contaminants found in water supplies and generated in water treatment and distribution systems. / Master of Science

Orientador: Marcos Fernando de Souza Teixeira / Resumo: Os principais objetivos desse trabalho, que envolve importantes áreas da ciência como química, física nuclear e geologia, são quantificar as atividades de gás radônio e concentração de chumbo total em regiões específicas do Brasil e Portugal, além de elaborar mapas indicativos do teor geogênico desses elementos em regiões de falhas geológicas. As zonas de falha geológica são regiões onde ocorreram fraturamentos e esmagamentos intensos de rocha e possuem a característica intrínseca de liberarem maior quantidade de gás Rn. As regiões de falhas também podem ser alvo de estudos voltados à quantificação de metais, principalmente de chumbo (Pb) por estar inserido na série natural de decaimento radioativo do urânio. As amostras de solo e rocha foram coletadas de acordo com estudos prévios em dois cenários, o primeiro abrange regiões específicas de Portugal (Sangemil e Oliveira do Hospital) e o segundo cenário refere-se ao município de Presidente Prudente, estado de São Paulo, Brasil. As amostras foram analisadas utilizando-se de algumas técnicas como: espectrometria com detector de germânio de alta resolução, onde quantificou-se as atividades de 235U, 228Ac, 226Ra, 210Pb, 212Pb, 214Pb, 212Bi, 214Bi, 234Pa, 208Tl e 40K; medidor Alpha Guard instalado em contentores metálicos onde determinou-se o coeficiente de emanação por meio das concentrações de Rn e Ra; medidor Alpha Guard e câmara de ionização que possibilitou quantificar Rn e U in situ, análise eletroquímica via técnica de volta... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The main objectives of this work, that involve important areas of science such as chemistry, nuclear physics and geology, are to quantify uranium, radon gas and total lead concentration in specific areas from Brazil and Portugal, and to prepare geogenic maps indicating the content of these elements in geological faults regions. The geologic fault zones are regions where fractures and intense crushing of the rock occurred, with varying thickness in centimeters until kilometers. Due to the intrinsic characteristic of releasing a larger amount of Rn gas, geological fault regions can also be the target of studies aimed at the quantification of metals, mainly lead (Pb), as it is included in the natural decay series of uranium. Soil and rock samples were collected according to previous studies in two scenarios, the first covering specific regions of Portugal (Sangemil and Oliveira do Hospital) and the second scenario refers to Presidente Prudente municipality, state of São Paulo, Brazil. The samples were analyzed using some techniques such as HPGe detector, where the activities of 235U, 228Ac, 226Ra, 210Pb, 212Pb, 214Pb, 212Bi, 214Bi, 234Pa, 208Tl and 40K were quantified; Alpha Guard installed in metal containers where the emanation coefficient was determined by the Rn and Ra concentrations ; Alpha Guard and ionization chamber that possibilited to quantify Rn and U in situ and Anodic Stripping Voltammetry that the total Pb content of the samples was measured. The radionuclides acti... (Complete abstract click electronic access below) / Doutor