No description available.

This thesis addresses one area of major interest in reaction kinetics, the theoretical description of recombination in nonhomogeneous systems. The reaction of the highly reactive particles formed by the passage of ionising radiation through a medium is an important example of this type of system. Stochastic effects are apparent in every stage of the development of a radiolysis system: in the interaction between the radiation and the medium and in the diffusion and reaction processes that follow. Conventional models for nonhomogeneous kinetics in radiation chemistry are based upon a deterministic analysis. These models are appraised together with an alternative stochastic approach. Three stochastic methods are discussed: a full Monte Carlo simulation of the diffusion and reaction and two approximate models based upon an independent pairs approximation. It is important that any kinetic model accurately describes the system it purports to represent and this can only be assured by extensive validation. The stochastic models are developed to encompass the diffusion-controlled reactions of ions and radicals and to include the effects of a bulk electrolyte upon the reactions between ions. To model a realistic radiation chemistry reaction scheme, it is necessary to consider reactions that are not fully diffusion-controlled. The radiation boundary condition is introduced and used to extend stochastic modelling to partially diffusion-controlled reactions. Recombination in an anisotropic environment is also considered. Although a complete analysis of the chemistry of a radiolysis system requires a complex reaction scheme, the scheme can be simplified, in acid and in alkali, by the use of an instantaneous scavenging approximation. In acid, this approximation produces a simple three reaction mechanism based upon five species: H, OH, H₂ , H₂0 and H₂0₂ . The acid system is used to demonstrate the stochastic treatment of realistic kinetics. The instantaneous scavenging approximation is examined in detail and techniques are developed for the explicit modelling of reactions with a homogeneously distributed scavenger. A stochastic treatment of nonhomogeneous reaction kinetics requires a description of the initial spatial distribution of the reacting particles. A rudimentary Monte Carlo simulation is used to determine a simple distribution of clusters of reactive particles similar to that found along the path of a high energy electron in water. This distribution provides a suitable basis for kinetic simulation. The kinetics of a more detailed idealised track structure are also considered and the stochastic and deterministic kinetics of extended particle distributions are discussed.

No description available.

To elucidate the structures of orgamc molecules in solution using pulse FT NMR, heteronuclear pulse sequence experiments to probe carbon-13 (13C) and proton (1H) spin systems are invaluable. The one-dimensional insensitive nucleus detected PENDANT experiment finds popular use for structure determination via one-bond 13C-1H scalar couplings. PENDANT facilitates the desired increase in 13C signal-to-noise ratio, and unlike many other pulse sequence experiments (e.g., refocused INEPT and DEPT), allows the simultaneous detection of 13C quaternary nuclei. The tlrst chapter herein details the characterisation of PENDANT and the successful rectification of spectral anomalies that occur when it is used without proton broadband decoupling. Multiple-bond (long-range) l3C-1H scalar coupling correlations can yield important bonding information. When the molecule under scrutiny is devoid of proton spectral crowding, and more sensitive 'inverse' pulse sequence experiments are not available, one may use insensitive nucleus detected long-range selective one-dimensional correlation methods, rather than more time consuming and insensitive multidimensional analogues. To this end a novel long-range selective one-dimensional correlation pulse sequence experiment has been invented. Based on PENDANT, the new experiment is shown to rival the popular selective INEPT technique because it can determine the same correlations while simultaneously detecting isolated 13C quaternary nuclei. INEPT cannot facilitate this, potentially leaving other important quaternary nuclei undetected. The novel sequence has been modified further to yield a second novel experiment that simultaneously yields selective 13C transient nOe data. Consequently, the need to perform the two experiments back-to-back is conveniently removed, and the experimental time reduced. Finally, the SNARE pulse sequence was further developed. SNARE facilitates the reduction of experimental time by accelerating the relaxation of protons upon which pulse sequences, to which SNARE is appended, relies. It is shown, contrary to the original publication, that reiaxation time savings can be derived from negative nOes.

Ce travail de thèse décrit la synthèse, l’étude cristallochimique et le comportement thermique de polymères de coordination à base de cations uranyle, ou mixtes uranyle-lanthanide complexés par des ligands carboxylates aromatiques (acide phthalique et dérivés). L’emploi de 7 molécules polycarboxylates a conduit à la formation de plus de 25 nouveaux composés type Uranyl-Organic Framework (UOF) ou hybrides uranyle-organique, ou encore mixtes uranyle-lanthanide-organique. Certains de ces ligands on montré une grande diversité d’arrangements atomiques, avec par exemple, l’isophthalate qui conduit à la formation de 10 complexes de coordination, alors que d’autres (par exemple terephthalate) ont permis d’isoler un seul type d’assemblage. Certaines de ces phases contiennent classiquement des briques de construction inorganiques monomériques ou tétramériques alors que d’autres mettent en évidence des blocs trimériques linéaires ou octamériques originals, ou encore des systèmes de chaînes inorganiques générant des structures à tunnels inédits. Une configuration rare d’interaction cation-cation (CCI ou U=O-U) a été également identifiée dans l’isophthalate à base d’unité octamérique. La synthèse de toutes ces phases a permis une meilleure compréhension des réactions hydrothermales et de l’influence de différents paramètres influant la formation du produit final. Pour les phases obtenues sous formes pures, les comportements thermiques et leur stabilité ont été étudiés. Ces expériences ont permis d’établir des relations entre le précurseur initial, la dégradation thermique et les conditions de formation de l’oxyde final. Les spectres de fluorescence ont été collectés et indiquent des informations sur l’influence de la nature du ligand organique ou du type du motif de construction inorganique. / This thesis work concerns the synthesis, crystal structural study and thermal behavior of coordination polymers type uranyl and mixed uranyl-lanthanide aromatic carboxylates. Using a series of 7 aromatic carboxylate ligands, more than 25 new uranyl (so-called Uranyl-Organic Framework or UOF) and mixed uranyl-lanthanide coordination polymers have been synthesized and described in this manuscript. Some of the ligands have proven to be very prolific such as the isophthalic acid, which is present in 10 coordination polymers and with others (such as terephthalic acid) only one complex could be isolated. Some of the obtained phases contain typical monomeric or tetrameric SBUs and others possess unique features such as octanuclear SBU with an edge sharing CCI (U=O-U), linear trinuclear SBU or polymeric SBU delimiting large tunnel systems. The synthesis of all these phases conducted to a better understanding of the hydrothermal reactions and the influence of different parameters over the final reaction product. For each of the phases obtained pure the thermal behavior and thermal stability have been studied. These experiments offer a better understanding of the relation between the structure of the initial complex, the thermal degradation conditions and the nature of final oxide. Also for these phases the fluorescence emission spectra were recorded, offering information about the influence of different ligands or different type of SBUs over the typical uranyl spectrum.

No description available.

L’analyse de sûreté des réacteurs à neutrons rapides refroidis au sodium de Génération IV nécessite l'étude des conséquences d'un accident grave en cas de rejet dans l'environnement du sodium et des radionucléides qu'il transporte (terme source chimique et radiologique). Le terme source global dépend donc à la fois de la spéciation chimique des aérosols de sodium, issus de la combustion du sodium dans l'enceinte, et de leurs interactions avec les radionucléides. Au cours de cette thèse, les interactions entre le carbonate de sodium et les produits de fission gazeux iodés (I2 et HI) ont été étudiées aux échelles atomique et macroscopique, via une double approche théorique et expérimentale. Une expression analytique de l'isotherme d'adsorption a été développée. La stabilité relative des surfaces du carbonate de sodium a été déterminée par des calculs ab initio utilisant la théorie de la densité fonctionnelle. La réactivité de l'iode a été étudiée pour les surfaces les plus stables et les isothermes d'adsorption évaluées. En parallèle, la cinétique de capture de l'iode moléculaire par le carbonate de sodium a été déterminée expérimentalement pour différentes conditions. L'ensemble des résultats montrent une capture efficace de l'iode moléculaire par le carbonate de sodium à 373 K, variant selon la pression partielle d'iode et la surface du carbonate. Pour les conditions représentatives d'un accident grave, les sites d'adsorption de la surface de carbonate de sodium la plus favorable seront majoritairement vides ou doublement occupés selon la pression partielle d'iode moléculaire, conduisant à une pression d'équilibre inférieure à 2x10-4 bar à 373 K. / The safety analysis of Generation IV sodium-cooled fast neutron reactors requires the study of the consequences of a severe accident in case of release into the environment of sodium and the radionuclides it carries (term chemical and radiological source). The global source term therefore depends on both the chemical speciation of sodium aerosols, resulting from the combustion of sodium in the containment, and their interactions with radionuclides. During this thesis, the interactions between sodium carbonate and iodinated gaseous fission products (I2 and HI) were studied at the atomic and macroscopic scales, via a combined theoretical and experimental approach. An analytical expression of the adsorption isotherm has been developed. The relative stability of the sodium carbonate surfaces was determined by ab initio calculations using density functional theory. The reactivity of iodine has been studied for the most stable surfaces and the adsorption isotherms evaluated. In parallel, the kinetics of capture of molecular iodine by sodium carbonate has been determined experimentally for different boundary conditions.The results show an effective capture of the molecular iodine by sodium carbonate at 373 K, varying according to the partial pressure of iodine and the surface of the carbonate sorbent. For the representative conditions of a severe accident, the adsorption sites of the most favorable sodium carbonate surfaces will be mostly bare or doubly occupied depending on the partial pressure of molecular iodine; leading to an equilibrium pressure of less than 2x10-4 bar at 373 K.

Un accident nucléaire grave peut entrainer un rejet de composés radiotoxique dans l’environnement. La nocivité de ces rejets est fonction de leurs périodes radioactives, de leurs évolutions chimiques et de leurs absorptions par l’organisme. Parmi les produits les plus importants, on peut citer 131I, 103Ru et 106Ru. La formation de produits gazeux doit être évitée pour limiter les contaminations à grandes distances. Les aérosols radioactifs qui sont formés à haute température vont se condenser sur les parois du circuit primaire. Dans ce travail, nous avons étudié théoriquement (par DFT) l’adsorption d’iodures métalliques et d’oxydes de ruthénium sur la surface du circuit primaire qui est constitué en majorité d’oxyde Fe et Cr ainsi que les mécanismes conduisant à la revolatilisation de ces dépôts. Nos résultats montrent que la formation de l’I2 (g), RuO3 (g) et RuO4 (g) est possible à partir des surfaces adsorbées avec ou sans un oxydant (OH● ou O2). / A severe nuclear accident leads to releases of radio toxic compounds. Due to their radioactive half-lifetimes, chemical evolution and absorption in the human’s body, 131I, 103Ru and 106Ru are particularly dangerous. The formation of gaseous products should be avoided in order to limit the contamination. Radioactive aerosols, formed at high temperature, will condense on primary circuit wall. We studied theoretically (by DFT) the adsorption of control rod metal iodides and ruthenium oxides on the surface of circuit that is composed mainly by Fe and Cr oxide. The mechanism leading to the revolatilization of these deposits is investigated. Our results showed that formations of I2 (g), RuO3 (g) and RuO4 (g) are possible from surfaces with or without an oxidant (OH● or O2).

The presence of the a- and S- emitters, uranium and thorium, in industrial waste streams poses a serious threat to the environment. This is due to both the potentially damaging nature of the radioactive emissions when incorporated into biological systems and to the general toxicity of these heavy metals. A programme of work to remove these heavy metals especially thorium, from a particular raffinate was undertaken. It was desirable to use zeolites specifically to remove thorium and some uranium. A survey of the uptake of thorium onto a ndide range of zeolites, both natural and synthetic is included. It was necessary to find a zeolite which could take up the radioactive cations, resist acid attack and which was suitable for use in a large scale, industrial removal plant. Due to the nature of the radiochemical components in conjunction with zeolite behaviour, several radiochemical techniques had to be modified to provide analytical methods for this project. Effects of competing cations on the uptake of thorium onto zeolites were also studied. The best all-round candidate was found to be an Eastgate zeolite, although clinoptilolite showed a reasonable uptake of thorium. The work carried out attempted to elucidate the mechanisms of thorium removal from solution.

Monoclonal antibodies which recognise tumour-associated antigens provide a means of targeting radionuclides selectively to tumour cells. (^99m)Tc and (^64)Cu are potentially useful isotopes for radioimmunoimaging;(^ 90)Y and (^67)Cu may be suitable for radioimmunotherapy. The synthesis of functionalised macrocycles for binding these four radioisotopes to antibodies is described. In each case, a macrocycle has been selected to provide a complex which is kinetically inert, thereby preventing dissociation of the radiolabel in vivo. A novel strategy for conjugating a C-alkylated cyclam derivative (for binding Tc and Cu) to an antibody is described. This method facilitates the selective acylation of an exocyclic primary amino group in the presence of the secondary ring nitrogens. Unfortunately, the labelling of antibody-bound cyclam with (^99m)Tc required conditions (pH 11) which produced extensive binding of the radiolabel to the protein backbone. "Non-specific" (^99m) Tc was subsequently found to dissociate in vivo. Pre-labelling the macrocycle with (^99m)Tc solved the "non-specifics" problem but required a pH which meant that the conjugation step was too slow for sufficient specific activity to be bound. A phenol-pendent derivative of cyclam was found to incorporate (^99m)Tc at a lower pH than cyclam itself. The "non-specific" binding of copper to the protein was minimised using a low pH labelling strategy in conjunction with a chelate wash. Macrocycle antibody conjugates labelled manner provide very promising biodistribution profiles in normal mice. A labelling buffer was selected to enhance the rate of uptake of copper by the macrocycle at low pH. Macrocycle-antibody conjugates containing 13N(_4), which was found to provide faster association kinetics than cyclam, have been prepared and await radiolabelling studies. A derivative of I3N(_4), containing 4 carboxylic acid donor sites, has been functionalised for conjugation to an antibody to act as a (^90)Y binder.