Thesis. 1979. Ph.D.--Massachusetts Institute of Technology. Alfred P. Sloan School of Management. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND DEWEY. / Includes bibliographies. / Ph.D.

No description available.

Natural enrichment of ²³⁴U with respect to ²³⁸U was investigated in perched water, vadose zone pore waters, and secondary minerals. The activity ratio (AR) for dissolved ²³⁴U increased from about 1.4 in runoff to >6 in perched water. The AR in the vadose zone increased sharply at a transition that correlated with increased magnetic susceptibility and decreasing hydraulic conductivity. This was evidently caused by auto—oxidative selective leaching controlled by matrix saturation. The direct recoil fractionation mechanism has been proposed for tuffs on the Nevada Test Site, and could imply enhanced retardation of U. Direct recoil was evaluated using a steady state isotopic mass balance formulated to represent matrix pore water, and including first order sorption and selective leaching. Matrix sorption parameters were estimated by selectively leaching intact core with hydroxylamine. Much U was recovered, fractionated similarly to pore water. Interpreting this as isotopic exchange limited by Fickian transport within a sorbent layer, the rate constant and distribution coefficient were estimated. Uranium—series analysis of fracture—lining MnO₂ indicated that isotopic exchange was operant. The isotopic mass balance showed that direct recoil is a minor contribution to fractionation, so the predominant mechanism is selective leaching. This result depends mainly on the sorption rate constant, and where direct recoil is likely such as in roll—front deposits, it implies that the rate constant is smaller than in typical oxidizing waters. Extrapolating matrix properties to formation scale transport, an upper bound on formation scale sorption was inferred from the isotopic mass balance. Formation scale sorption is greater where the perched water table lies in more porous, permeable tuff. The layer diffusion model predicts that the effective sorption rate constant decreases significantly for thicker sorbent layers. Thus although fracture lining MnO₂ minerals are common at Yucca Mountain, U retardation may be strongly rate limited. Elevated AR's (>5) generally signify conditions favorable to U retardation, based on hydraulic isolation from recharge. Elevated vadose zone AR's do not necessarily signify the former presence of perched water, but could be interpreted that way at Yucca Mountain if similar fractionation is not found where past perching is unlikely.

No description available.

Made available in DSpace on 2014-06-11T19:32:18Z (GMT). No. of bitstreams: 0 Previous issue date: 2005-06-23Bitstream added on 2014-06-13T19:02:50Z : No. of bitstreams: 1 silva_ml_dr_rcla.pdf: 21027584 bytes, checksum: 7cb732b23cad6eb774812ecce2087b54 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Este trabalho tem por objetivo investigar a hidroquímica elementar, assim como o comportamento geoquímico dos isótopos de 238U e 234U nas águas de subsuperfície em quinze cidades do estado do Amazonas, de maneira a proceder a caracterização de contaminantes ou poluentes que possam estar afetando a qualidade dos recursos hídricos subterrâneos, bem como avaliar a potencialidade do uso dos isótopos naturais de urânio como traçadores hidrológicos nas águas estudadas. Os resultados obtidos para os parâmetros analisados mostram que as águas estudadas são excelentes para o consumo humano, por se situarem dentro dos limites de potabilidade estabelecidos pela legislação vigente. No que diz respeito aos isótopos de urânio, verifica-se que foram determinados valores de razão de atividade 234U/238U entre 1 e 3,5 e de concentração de urânio 238U entre 0,01 ægL-1 e 1,4 ægL-1. Esses resultados e os determinados para outros parâmetros analisados, permitiram classificar os ambientes hidrológicos como redutores, com circulação das águas por estratos contendo minerais com baixas concentrações de urânio. Na cidade de Manaus foi observado acréscimo de razão de atividade 234U/238U na fase líquida no sentido do fluxo subterrâneo. Foram identificadas quatro regiões com tendência de aumento de razão de atividade, no sentido de Uarini a Tefé, Manacapuru a Manaus, Presidente Figueiredo a São Sebastião do Uatumã e Boa Vista do Ramos a Barreirinha, relacionadas a possíveis feições estruturais, à declividade da área de estudo, ao estreitamento da Bacia Sedimentar do Amazonas a partir do seu curso médio, e drenagem orientada pela tectônica. / The purpose of this investigation is to evaluate the hydrochemistry and the geochemical behavior of uranium isotopes (234U e 238U) in groundwaters from cities of the Amazonas State. It intends to verify whether concentrations of one or more dissolved constituents are in such high levels to be considered harmful for consumption. It also aims to evaluate the possible use of the uranium isotopes as natural tracers on the studied aquifers. The obtained data show that the groundwater is appropriate for drinking and industrial purposes, in accordance with the maximum limits established by the legislation. Concerning the uranium isotopes data, the 234U/238U activity ratio ranges between 1 and 3.5, whereas the total 238U uranium concentration from 0.01 ægL-1 up to 1.4 ægL-1. These and other results allowed classify the hydrological environment as reducing, with water circulating through strata containing minerals with low uranium concentration. The 234U/238U activity ratio in the liquid phase increased in the direction of the underground flow in Manaus city. In the direction from Uarini to Tefé, from Manacapuru to Manaus, from Presidente Figueiredo to São Sebastião do Uatumã and from Boa Vista do Ramos to Barreirinha it was verified a 234U/238U activity ratio increase possibly related to geologic structures, declivity of the areas, narrowing of the Amazonic sedimentary basin from its middle course, and drainage guided by tectonics.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 1977 / Vita. / Includes bibliographical references. / Ph. D. / Ph. D. Massachusetts Institute of Technology, Department of Physics

Includes bibliographical references. / Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1980. / by Richard Keith Lester. / Ph.D.

Orientador: Daniel Marcos Bonotto / Banca: Uriel Duarte / Banca: Francisco Yukio Hiodo / Banca: Flavio Juarez Távora / Banca: Elisabete Maria Pascholati / Resumo: Este trabalho tem por objetivo investigar a hidroquímica elementar, assim como o comportamento geoquímico dos isótopos de 238U e 234U nas águas de subsuperfície em quinze cidades do estado do Amazonas, de maneira a proceder a caracterização de contaminantes ou poluentes que possam estar afetando a qualidade dos recursos hídricos subterrâneos, bem como avaliar a potencialidade do uso dos isótopos naturais de urânio como traçadores hidrológicos nas águas estudadas. Os resultados obtidos para os parâmetros analisados mostram que as águas estudadas são excelentes para o consumo humano, por se situarem dentro dos limites de potabilidade estabelecidos pela legislação vigente. No que diz respeito aos isótopos de urânio, verifica-se que foram determinados valores de razão de atividade 234U/238U entre 1 e 3,5 e de concentração de urânio 238U entre 0,01 ægL-1 e 1,4 ægL-1. Esses resultados e os determinados para outros parâmetros analisados, permitiram classificar os ambientes hidrológicos como redutores, com circulação das águas por estratos contendo minerais com baixas concentrações de urânio. Na cidade de Manaus foi observado acréscimo de razão de atividade 234U/238U na fase líquida no sentido do fluxo subterrâneo. Foram identificadas quatro regiões com tendência de aumento de razão de atividade, no sentido de Uarini a Tefé, Manacapuru a Manaus, Presidente Figueiredo a São Sebastião do Uatumã e Boa Vista do Ramos a Barreirinha, relacionadas a possíveis feições estruturais, à declividade da área de estudo, ao estreitamento da Bacia Sedimentar do Amazonas a partir do seu curso médio, e drenagem orientada pela tectônica. / Abstract: The purpose of this investigation is to evaluate the hydrochemistry and the geochemical behavior of uranium isotopes (234U e 238U) in groundwaters from cities of the Amazonas State. It intends to verify whether concentrations of one or more dissolved constituents are in such high levels to be considered harmful for consumption. It also aims to evaluate the possible use of the uranium isotopes as natural tracers on the studied aquifers. The obtained data show that the groundwater is appropriate for drinking and industrial purposes, in accordance with the maximum limits established by the legislation. Concerning the uranium isotopes data, the 234U/238U activity ratio ranges between 1 and 3.5, whereas the total 238U uranium concentration from 0.01 ægL-1 up to 1.4 ægL-1. These and other results allowed classify the hydrological environment as reducing, with water circulating through strata containing minerals with low uranium concentration. The 234U/238U activity ratio in the liquid phase increased in the direction of the underground flow in Manaus city. In the direction from Uarini to Tefé, from Manacapuru to Manaus, from Presidente Figueiredo to São Sebastião do Uatumã and from Boa Vista do Ramos to Barreirinha it was verified a 234U/238U activity ratio increase possibly related to geologic structures, declivity of the areas, narrowing of the Amazonic sedimentary basin from its middle course, and drainage guided by tectonics. / Doutor

Mass spectrometers are analytical instruments that convert neutral atoms and molecules into gaseous ions and separate those ions according to the ratio of their mass to charge, m/z. The measurement is reported as a mass spectrum: a plot of relative intensity vs. m/z that can be used to deduce the chemical structure and composition of materials and compounds. Initially, the use of mass spectrometers was restricted to the analysis of volatile compounds. Recent advances in the development of ionisation techniques to produce intact molecules directly from samples in the liquid or solid phase, has extended the powerful use of mass spectrometry to compounds of increasingly higher molecular mass. The aim of this study was twofold: develop diagnostic techniques for the in-situ measurement of isotope ratios in laser isotope separation experiments; and to correlate it with the measured isotope ratios on the collected product. The outcome is a thesis that can be divided into two distinct fields of application: Firstly; the Atomic Vapour Laser Isotope Separation (AVLIS) of lithium, and secondly the Molecular Laser Isotope Separation (MLIS) of uranium, In both AVLIS and MLIS pulsed laser systems were used to ionise and/or dissociate atomic or molecular beams. The pulsed nature of the lasers is ideally suited to in-situ time-of-flight detection of the produced ions. Different types of inter-changeable ion sources are common to the same TOF mass spectrometer. Each of these sources is selected according to its application. For instance, applications vary from photo- and multiphoton ionisation (laser ionisation) to surface analysis (laser desorption or particle bombardment) to chromatography (electron impact ionisation). Four different source configurations were considered in this study: (i) Atomic Laser Isotope Separation (AVLIS) of lithium; (ii) Multiphoton Ionisation (MPl) of UF6 gas; (iii) Non-resonant ionisation during Laser Desorption (LDI) of solids; and (iv) Matrix-Assisted Laser Desorption (MALD) of biopolymers. The design of each of these sources will be discussed in detail in chapters to follow. Bulk analysis of harvested laser-produced products needs to be in correlation with in-situ analysis. Three different characterisation methods were used in this study: (i) Laser Desorption Time-of-Flight Mass Spectrometry (LD-TOF-MS) (ii) Quadrupole-based Secondary Ion Mass Spectrometry (SIMS); and (iii) TOF-MS-based Secondary Ion Mass Spectrometry (TOF-SIMS). Chapter I describes the principles of time-of-flight mass spectrometry, design parameters, as well as the instrumentation that were designed and constructed for the purposes of this study. Chapter II describes the principles of Secondary Ion Mass Spectrometry (SIMS). In particular, research done on the establishment of tools to the non-expert user of SIMS to select analyses conditions, is described. Chapter III reports on the application of TOF-MS and SIMS during the AVLIS of lithium. Chapter IV reports on the application of the different combinations of TOF-MS, LD-TOF-MS, SIMS, and TOF-SIMS during the MLIS of uranium. / Thesis (Ph.D.)-University of Natal, Durban, 1999.

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