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Made available in DSpace on 2014-10-09T12:34:35Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:07Z (GMT). No. of bitstreams: 0 / Neste trabalho, cristais de TlBr foram crescidos e purificados pelo método de Bridgman Repetido a partir de sais comerciais de TlBr e caracterizados para serem usados como detectores de radiação à temperatura ambiente. Para avaliar a eficiência de purificação, estudos da diminuição da concentração de impurezas foram feitos após cada crescimento, analisando as impurezas traços por Espectrometria de Massas com Plasma (ICP-MS). Um decréscimo significativo da concentração de impurezas em função do número de purificações foi observado. Os cristais crescidos apresentaram boa qualidade cristalina de acordo com os resultados de análise por Difração de Raios X (DRX). Para avaliar os cristais a serem usados como detectores de radiação, medidas de suas resistividades e resposta à incidência de radiação gama da fonte de 241Am (59,5 keV) foram realizadas. Essa resposta foi dependente da pureza do cristal. Um modelo compartimental foi proposto para avaliar as concentrações de impurezas no cristal de TlBr e suas segregações em função do número de crescimentos pelo método de Bridgman. Este modelo compartimental definido por equações diferenciais pode ser usado para calcular o coeficiente de migração das impurezas e mostrou ser útil para prever o número necessário de repetições de crescimento Bridgman para atingir nível de pureza adequado para assegurar a qualidade do cristal como detector de radiação. A diferença dos valores dos coeficientes de migração das impurezas nos cristais entre os sais, de duas procedências diferentes, utilizados foi significativa. Portanto, a escolha do sal de partida deve ser realizada experimentalmente, independente da declaração nominal da sua pureza. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Thermodynamic equilibrium constants for silver(I) bromide complexes were determined by ion-selective membrane electrode potential measurements in water and in mixtures of water and acetone of approximately 5, 10 and 15 percent acetone by weight. Values of the solubility product constant were determined in each solvent system by calibration of a silver bromide membrane electrode with silver nitrate solutions and with sodium bromide solutions. Stability constants of silver(I) bromide complexes were determined using a silver ion-selective, silver sulfide membrane electrode in unsaturated solutions in which the formal concentrations of silver(I) and of bromide ranged from approximately I x 10-8 to 7 x 10-7 and 10-3 to 10-1 molal, respectively. Non-Nernstian electrode response was observed in these solutions. The magnitude of the corrections made for the non-linearity was found to be a function of formal silver concentration. Comparison of the values of the stability constants obtained with those reported in the literature substantiated the validity of the corrections. The data were interpreted by assuming the presence of AgBr, AgBr-2, and AgBr32-.

Physisorption and reaction at silicon surfaces of a series of brominated organic molecules: bromoethane, 1,2-dibromoethane, 1-bromopropane, 1-bromobutane and 1-bromopentane were examined by Scanning Tunneling Microscopy (STM). On Si(111)-7×7, a widely-spaced “one-per-corner-hole” pattern was observed, formed by the physisorption and reaction of several alkyl bromides. This “one-per-corner-hole” pattern suggested long-range repulsion between the adsorbates. Density Functional Theory (DFT) calculations, performed by others in parallel with these experiments, showed that this long-range repulsion was due to lateral charge transfer in the Si(111)-7×7 surface consequent on the physisorption of an alkyl bromide or chemisorption of a Br atom. The reaction rate of bromine ‘abstraction’ (transfer of a Br-atom from the adsorbate to the silicon) was examined for two physisorbed states of 1 bromopentane on Si(111)-7×7, one vertical and one horizontal, each distinguishable by STM. The energy barrier was found to be significantly lower for abstraction of Br-atom from the vertical than for the horizontal 1 bromopentane, both for thermal and electron-induced reaction. This finding accords with previous DFT calculations for methyl bromide, for which theory exhibited a clear preference for a vertical transition state in the bromination of Si(111)-7×7. The effect of alkyl chain-length on the rate of thermally-induced dissociative attachment reactions was investigated for a series of primary bromo-alkanes (bromoethane, 1-bromopropane and 1-bromobutane) on a different face of silicon; Si(100)-c(4×2). These three bromo-alkanes all physisorbed exclusively ‘inter-row’, bridging the gap between Si dimer-rows of Si(100)-c(4×2). Thermal reaction was highly ‘localized’, i.e. the chemisorbed Br-atom was formed directly below the parent bromo-alkane. The thermal barrier heights were found experimentally to increase systematically with chain length. This trend was interpreted, on the basis of DFT calculations performed by the author, as being due to the extra energy required to lift the alkyl group in going from the initial physisorbed state to the more-nearly vertical transition state.

Physisorption and reaction at silicon surfaces of a series of brominated organic molecules: bromoethane, 1,2-dibromoethane, 1-bromopropane, 1-bromobutane and 1-bromopentane were examined by Scanning Tunneling Microscopy (STM). On Si(111)-7×7, a widely-spaced “one-per-corner-hole” pattern was observed, formed by the physisorption and reaction of several alkyl bromides. This “one-per-corner-hole” pattern suggested long-range repulsion between the adsorbates. Density Functional Theory (DFT) calculations, performed by others in parallel with these experiments, showed that this long-range repulsion was due to lateral charge transfer in the Si(111)-7×7 surface consequent on the physisorption of an alkyl bromide or chemisorption of a Br atom. The reaction rate of bromine ‘abstraction’ (transfer of a Br-atom from the adsorbate to the silicon) was examined for two physisorbed states of 1 bromopentane on Si(111)-7×7, one vertical and one horizontal, each distinguishable by STM. The energy barrier was found to be significantly lower for abstraction of Br-atom from the vertical than for the horizontal 1 bromopentane, both for thermal and electron-induced reaction. This finding accords with previous DFT calculations for methyl bromide, for which theory exhibited a clear preference for a vertical transition state in the bromination of Si(111)-7×7. The effect of alkyl chain-length on the rate of thermally-induced dissociative attachment reactions was investigated for a series of primary bromo-alkanes (bromoethane, 1-bromopropane and 1-bromobutane) on a different face of silicon; Si(100)-c(4×2). These three bromo-alkanes all physisorbed exclusively ‘inter-row’, bridging the gap between Si dimer-rows of Si(100)-c(4×2). Thermal reaction was highly ‘localized’, i.e. the chemisorbed Br-atom was formed directly below the parent bromo-alkane. The thermal barrier heights were found experimentally to increase systematically with chain length. This trend was interpreted, on the basis of DFT calculations performed by the author, as being due to the extra energy required to lift the alkyl group in going from the initial physisorbed state to the more-nearly vertical transition state.

Thesis (Ph. D.)--Institute of Paper Chemistry, 1961. / Includes bibliographical references (p. 85-86).

Thesis (M.S. - Hydrology)--University of Arizona, 1984. / Includes bibliographical references (leaves 68-72).

Thesis (Ph. D.)--University of Washington, 1999. / Vita. Includes bibliographical references (p. [151]-156).