No description available.

Die vorliegende Arbeit befasst sich mit der Synthese, Charakterisierung und Reaktivität von Nebengruppen-Metallkomplexen, die mindestens einen pi-koordinierenden Liganden tragen. Im ersten Abschnitt liegt der Fokus auf heteroleptischen Systemen mit carbocyclischen Liganden, zu deren Synthese die gängige Methodik der Salzeliminierung herangezogen wird. Das Metallierungsverhalten dieser Komplexe, sowie die Reaktivität von Komplexen mit reduktionsstabilen funktionellen Gruppen an den Ligandensystemen wird untersucht. Der zweite Abschnitt behandelt die Redox- und Koordinationseigenschaften des CAAC-stabilisierten 1,4 Diborabenzols, wobei Alkali-Metalle, Gruppe 10 Metalle, Lanthanoide, sowie die Actinoide Thorium und Uran untersucht werden. / The present work deals with the synthesis, characterization and reactivity studies of subgroup metal complexes bearing at least one sandwich-type carbo- or heterocyclic ligand. The first chapter covers studies on the synthesis of heteroleptic sandwich complexes employing the well-established salt-metathesis strategy. The metalation properties as well as the reactivity of the complexes is investigated. The second chapter of this work discusses further studies on the redox and coordination properties of neutral, CAAC-stabilized 1,4-diborabenze. To this end reactions with alkali and group 10 metals, elements of the lanthanides as well as the actinide metals Thorium and Uranium are reviewed.

<p> New complexes formed between U(VI), Th(IV) and Sc(III) and tropolone have been prepared. These include the solvates UO2T2⋅X and ThT4⋅X (T = the tropolone anion; X =H2O and CH3OH), and the unsolvated chelate Sc3⋅. Some U(VI), Th(IV) and Sc(III) tropolonates reported in the literature have been re-examined and found to be incorrectly formulated.</p> <p> The adduct chelates UO2T2⋅HT, ScT3⋅HT and the previously unreported ThT4⋅HT have been prepared. Evidence has been presented for hydrogen-bonding in the additional monodentate tropolone ligand.</p> <p> The thermal conversion of the above solvates and adducts to yield UO2T2, ThT4 and ScT3 has been described.</p> <p> The ability of tropolone and other bidentate ligands to displace the water molecule in UO2T2⋅H2O and ThT4⋅H2O, and the addition of such ligands to ScT3, has been studied.</p> / Thesis / Master of Science (MSc)

No description available.

The precipitation of thorium with certain organic reagents has been shown to afford a basis for polarographic methods for the determination of thorium. Appropriate conditions for the precipitation of thorium by certain reagents have been determined, and the advantages of a homogeneous precipitation of thorium 8-quitnolinate have been demonstrated. The precipitate that thorium forms with m-nitrobenzoic acid has been found to be the tetra-m-nitrobenzoate. The new polarographic methods tor thorium have been proven to be directly applicable to zirconium-free magnesium-base alloys . When zirconium is present, a simple anion exchange procedure will eliminate the interference of zirconium, and allow it's subsequent determination.The satisfactory nature of the precision and accuracy of the proposed methods, and their applicability to substances other than magnesium-base alloys, have been demonstrated. / Thesis / Master of Science (MS)

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1981. / Microfiche copy available in Archives and Science. / Vita. / Bibliography: leaves 262-273. / by Robert Frederick Anderson. / Ph.D.

A determination of the resonance escape probability of thorium as thorium nitrate in aqueous solution has been made as a function of thorium concentration. The physical system used was an aluminum box surrounded by successive layers of cadmium, paraffin and borated paraffin to keep out neutrons scattered by objects in the laboratory. Neutrons were obtained from a Cockcroft-Walton type accelerator by the D(d,n)He³ reaction. The drive-in target was located at the center of one of the faces of the aluminum box. Neutron density was measured at nine spatial positions in the direction of the neutron beam with a bare boron trifluoride detector. The area under a curve of neutron density versus spatial position was obtained for various concentrations of absorber. The above process was carried out for the thorium solution and for a “mock solution," whose cross-section was similar to that of thorium except that it had no resonances in the thorium resonance region. By taking ratios of the neutron densities (area under curves of neutron density versus spatial position) in the thorium solution to the neutron density in the mock solution, it was possible to determine the resonance escape probability of neutrons in a homogeneous, aqueous solution of thorium nitrate. It is shown that, for the absorber concentrations used in the experiment, the resonance escape probability for an infinite geometry may be obtained by the above ratio method. The difference between a finite system and an infinite one is exhibited as leakage of neutrons from the system in the finite case. If one can compare neutron densities for systems which are large enough so that leakage is negligible or for systems with corresponding leakage rates, the effect of leakage can be overcome and the resonance escape probability for the infinite geometry obtained. Before taking the above ratios of neutron densities, it was necessary to compensate for the spectral shift of the thermal flux in the two solutions. After such a correction, the resonance escape probability so obtained shows good correlation with the results of the Monte Carlo prediction for this system. Over the range covered by the experiment (0 - 1 x 10²¹ atoms of thorium per cubic centimeter), experimental results agree with Monte Carlo predictions to within one percent. Counting statistics were good, with 10⁶ counts normally taken per spatial position. The curves from which the value of neutron density were determined were formed by nine points, each of which represented at least 10⁶ counts. Reproducibility of the neutron density at a point was of the order of one percent. Various changes made in the analysis of the data have caused corresponding changes in the values obtained for the resonance escape probability of less than one percent. These facts all indicate that the uncertainty in the experimental determination is of the order of one percent. Calculations of effective resonance integrals from the experimentally determined values of the resonance escape probability show good agreement with published measurements on other systems. / Ph. D.

Les travaux de recherche de ce mémoire portent sur l’utilisation de résines échangeuses d’ions afin de séparer les actinides (thorium et uranium) des lanthanides (éléments de terre rare). Puisque cette méthode est versatile,elle a été employée dans deux domaines distincts : le domaine minier ainsi que le domaine nucléaire.La problématique visée dans le contexte minier consiste en la séparation du thorium de lixiviats de minerais d’éléments de terre rare (ÉTR). En raison de leurs propriétés physiques similaires aux ÉTR, le thorium et l’uranium sont retrouvés à l’intérieur de la maille cristalline de divers minerais d’ÉTR. N’étant pas désiré dans la production d’ÉTR, ces métaux radioactifs doivent être retirés du lixiviat. De ce fait, la séparation du thorium parrésines échangeuses d’ions a été étudiée sur des lixiviats de minerais d’ÉTR. Un lixiviat en milieu sulfurique provenant de Search Minerals a été utilisé ainsi qu’un lixiviat en milieu nitrique issu d’essais en laboratoire. Deux procédés préliminaires ont émergé des résultats obtenus : l’un permettant la séparation successive des différents éléments et l’autre l’extraction sélective du thorium en mode continu.La problématique visée par le domaine nucléaire traite de la récupération de l’uranium hautement enrichi contenu dans divers déchets nucléaires. Ces déchets proviennent de la production d’isotopes médicaux des Laboratoires de Chalk River (LCR). Lors de la production, près de 90% de l’uranium n’est pas consommé.L’uranium se retrouve alors dans les déchets cimentés ou liquides. Afin de récupérer l’uranium contenu dans les déchets cimentés, l’échange ionique a été testé sur différents lixiviats sulfuriques de déchets solides synthétiques imitant les déchets cimentés réels. En ce qui a trait aux déchets liquides, les expériences d’échange ionique ont été faites sur une solution synthétique imitant la solution réelle. Deux procédés ont été développés pour chaque type de déchet. / This thesis investigates the use of ion exchange resins to separate actinides (thorium and uranium) from lanthanides (rare earth elements). This versatile method was used in two distinct areas : the mining sector and the nuclear field. The problem encountered in the mining sector consists in the separation of thorium from leachates of rare earth elements (REE) ores. Due to their physical properties similar to REE, thorium and uranium are found within themineral lattice of various REE ores. These radioactive metals are considered by the REE producers as impuritiesand must therefore be removed from the leachate. As a result, the separation of thorium by ion exchange resinshas been studied on REE leachates. A sulfuric acid leachate provided by Search Minerals and a nitric leachate produced from laboratory tests were used. Two preliminary processes emerged from the results : a process allowing the successive separation of thorium, heavy REE, and light REE in sulfuric leachate and a process allowing the selective and continuous extraction of thorium in nitric leachate.The problem encountered by the nuclear field deals with the recovery of highly enriched uranium contained indifferent nuclear waste. This waste comes from the production of medical isotopes from Chalk River Laboratories(LCR). During production, almost 90% of the uranium is not consumed. The unused uranium is then found in the cemented and liquid wastes. In order to recover the uranium contained in the cemented waste, the ionexchange methods has been tested on various sulfuric leachates of synthetic cemented waste simulating the radioactive cemented waste. For the liquid waste, the ion exchange experiments were done on a synthetic solution mimicking the nitric solution contained in the fissile solution storage tank. Two processes have been developed for each type of waste.

This thesis explores the use of U-Th series isotopes as tracers to study ocean mixing and chemical inputs to the open ocean from atmospheric dust, rivers, continental shelves and ocean sediments. The use of Th isotopes as an improved tracer of dust input has been tested by measuring ²³²Th and ²³⁰Th concentrations of upper-ocean seawater at six stations along a meridional Atlantic section that spans the Saharan dust plume. The results of ²³²Th-derived dust fluxes show good agreements with dust model depositions, and suggest that thorium may be a more accurate tracer of dust input than Aluminium, which is frequently used for this purpose. A new technique has been developed for the precise measurement of ²²⁸Ra/²²⁶Ra ratios and ²²⁸Ra and ²²⁶Ra concentrations in seawater by multi-collector ICP mass spectrometry (MC-ICP-MS). This methods offers improved analytical precision and detection limits relative to previous decay-counting approaches, though is more labour intensive. The accuracy of this method has been proved in the GEOTRACES Ra intercalibration, and shows consistent results with decay counting measurements from other labs. This technique has been applied to water samples in Loch Etive, a Scottish fjord, and in the Cape Basin during the UK-GEOTRACES cruise (GA10E) to investigate ocean mixing and trace-metal fluxes in the oceans. In Loch Etive, Ra data provide an estimation of sedimentary ²²⁸Ra flux of 5.5 ± 0.3 (× 10⁹ atoms m^-2 yr^-1) in the inner loch deep basin. Short-lived Ra isotope (²²³Raex) has also been used to estimate surface water transport rate, which is ~ 2.4 ±0.2 cm s^-1 from the mouth to the head of the loch. In the Cape Basin, seawater ²²⁸Ra and ²²⁶Ra activities have been used to estimate vertical and horizontal mixing in the surface ocean. The horizontal mixing (K_x) from the continental shelf to the open ocean is 3.8 ± 0.8 (× 10⁷ cm² s^-1) and the vertical mixing (K_z) in the upper 400 m layer is 0.9 – 2.1 cm² s^-1. These mixing rates enable the calculation of nutrient flux in the surface ocean. The calculated vertical nitrate fluxes in the Cape Basin are 0.4 – 0.5 mmol N m^-2 d^-1. This finding shed light on the nutrient inputs to the South Atlantic Subtropical Gyre.

Thesis: Ph. D., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 321-351). / Many chemical constituents are removed from the ocean by attachment to settling particles, a process referred to as "scavenging." Radioisotopes of thorium, a highly particle-reactive element, have been used extensively to study scavenging in the ocean. However, this process is complicated by the highly variable chemical composition and concentration of particles in oceanic waters. This thesis focuses on understanding the cycling of thorium as affected by particle concentration and particle composition in the North Atlantic. This objective is addressed using (i) the distributions 228,230,234 Th, their radioactive parents, particle composition, and bulk particle concentration, as measured or estimated along the GEOTRACES North Atlantic Transect (GA03) and (ii) a model for the reversible exchange of thorium with particles. Model parameters are either estimated by inversion (chapter 2-4), or prescribed in order to simulate 230Th in a circulation model (chapter 5). The major findings of this thesis follow. In chapters 2 and 3, I find that the rate parameters of the reversible exchange model show systematic variations along GA03. In particular, k1 , the apparent first-order rate "constant" of Th adsorption onto particles, generally presents maxima in the mesopelagic zone and minima below. A positive correlation between k, and bulk particle concentration is found, consistent with the notion that the specific rate at which a metal in solution attaches to particles increases with the number of surface sites available for adsorption. In chapter 4, I show that Mn (oxyhydr)oxides and biogenic particles most strongly influence k1 west of the Mauritanian upwelling, but that biogenic particles dominate ki in this region. In chapter 5, I find that dissolved 230Th data are best represented by a model that assumes enhanced values of k, near the seafloor. Collectively, my findings suggest that spatial variations in Th radioisotope activities observed in the North Atlantic reflect at least partly variations in the rate at which Th is removed from the water column. / by Paul Lerner. / Ph. D.