The development is described of a new ion source for atomic mass spectrometry which could lead to much wider applications of the technique. The source is based on an atmospheric pressure high temperature inductively coupled plasma. Samples are introduced to the plasma as aqueous solutions by a pneumatic nebulizer. Ion extraction from the plasma at temperatures up to 8000 K is based on sampling gas through an aperture placed in the tail flame. Initially apertures of 0.07 mm diameter were used which were protected from the full plasma temperature by the formation over them of a cooler boundary layer. High sensitivity and good resolution were obtained up to solute concentrations of 10 mug.ml-1, but matrix effects were severe. Conditions were then established in which ions could be sampled direct from the plasma core without passage through a boundary layer. Continuum flow through apertures up to 0.5 mm diameter enables plasma ion populations to be frozen rapidly in the supersonic expansion, before reactions can occur to disturb the composition. Much better matrix performance is obtained in this mode and sample concentrations up to 1000 mug.ml-1 can be introduced. Detection limits below 1 ng.ml-1 are obtained for a wide range of elements. Multi-element analysis is feasible at the rate of one sample per minute and isotope ratio determinations on solutions at about 30 mug.ml-1 are possible with precisions approaching 0.1% for integration times of 5 minutes. The performance of the system is discussed theoretically and reasonable agreement demonstrated with the experimental behaviour. The source already provides a viable analytical technique for samples introduced by any of the methods available for ICP-AES. These include solution nebulization, thermal evaporation, laser ablation and arc aerosol generation. Considerable scope exists for improving ion transport efficiency to provide sensitivity at least as high as any other routine analytical technique.

The main purpose of this work is to calculate the isotropic shielding of some nuclei, other than protons, of first- and second-row atoms in the periodic table and some transition metal elements in a wide variety of molecular environments, with a view to gaining an understanding of the various electronic factors which determine the observed nuclear shielding. Chapter One introduces some general concepts. Chapter Two presents a general servey of various Semi-empirical molecular orbital methods. Various MO calculations of nuclear shielding are briefly reviewed in Chapter Three with particular emphasis on Pople's GIAO-MO approach. This chapter also contains a description of the theory of medium effects on nuclear shieldings. Chapter Four is concerned with approximate MO theories and their application to the GIAO-MO method for Sum-Over-State (SOS) results of some shieldings of first-row elements. The medium effect models are used to explore the role of medium effects on nuclear shielding. This exploration is supplemented by performing some calculations on hydrogen-bonded models. Chapter Five records the SOS results for the nuclear shielding of some second-row elements in conjunction with the GIAO-MO method. The solvaton model is also used in an attempt to improve on our understanding of the relation between magnetic shielding and various features of molecular electronic structure. Chapter Six presents some shielding data for transition metal elements obtained by means of Pople's GIAO-MO method in conjunction with the INDO/5R parameterization scheme for SOS results of some inorganic molecules. A reasonable correlation between the calculated and experimental chemical shifts, compared by mean of a least-squares fit is obtained for some of the molecules considered.

Beta-induced fluorescence (BIF) is the luminescence excited from a compound as a result of the passage of beta-particle radiation through a compound or dilute solution of a compound. A liquid chromatographic detector, based on the principle of BIF, has been developed which allowed the detection and quantitation of fluorescent materials. A number of flow cells, incorporating ,a promethium-147 beta particle emitter, were designed and developed with the objective of attaining maximum sensitivity from the detection technique. The response of, the detector to eluted materials, the linearity of the detector response with sample loading and the sensitivity of the detector were examined in normal and reversed phase liquid chromatography. During the development of the BIF detector it became evident that the compounds detected need not be inherently fluorescent. The range of compounds detected could be increased to include those which quench the beta-induced fluorescent emission from the mobile phase. The technique of quenched beta-induced fluorescence was investigated as a detection technique and the response, linearity of response and sensitivity to eluted materials examined. Cerenkov photons are generated whenever a charged particle, travelling at a velocity greater than the velocity of light in the medium, passes through a transparent medium. Cerenkov photons are emitted from the medium as a continuum of wavelength range between 180 nm and 600 nm. The principle of absorption of Cerenkov photons was investigated as a detection technique in liquid chromatography. Strontium-90 was incorporated into a number of flow cells and the response, linearity of response and sensitivity of eluted materials, examined in normal and reversed phase liquid chromatography.

The rhodium speciation in nitric acid has been identified, primarily by the use of 103Rh Nuclear Magnetic Resonance Spectroscopy. The results have indicated that the rhodium species in stored high level waste (HLW) will range from the hexaaquo ion, {Rh(H20)6}3+-to complexes of the general formula {Rh(H20)6-n(NO2)nl(3-n)+, depending on the nitrite ion concentration. The solvent extraction of these complexes by dinonylnaphthalene sulphonic acid and various organo-phosphine sulphides has been investigated, and an integrated scheme for recovering rhodium from HLW is proposed.

14 MeV neutron activation analysis, based on the 82Se(n,2n) Se81m nuclear reaction, has been investigated for the measurement of selenium in environmental waters. The levels of the selenium present in environmental waters and the relatively high limit of detection achievable with fast neutron activation analysis resulted in the need to develop a concentration procedure for the extraction of selenium from large volumes of environmental water before neutron activation.

Lors d’un accident nucléaire grave, plusieurs produits de fission peuvent être libérés dans l'environnement. Parmi ces produits, l'iode radioactif (131I) est un des produits les plus dangereux en raison de ses conséquences radiologiques élevées durant les premières semaines suivant l'accident. Cet iode radioactif va principalement former des aérosols (CsI et AgI) dans le système de refroidissement du réacteur. Ils pourront ensuite réagir dans une atmosphère oxydante et humide pour former l’iode moléculaire gazeux I2. L'objectif de ce travail est d'étudier la réactivité des aérosols d'iodure afin d’identifier des voies chimiques possibles conduisant à la formation d'espèces d'iode volatiles. Nous avons mené une étude théorique basée sur la théorie fonctionnelle de la densité, comprenant les corrections de Van Der Waals, pour définir les mécanismes des réactions chimiques se produisant à la surface des aérosols. Les résultats montrent que l'adsorption de l'eau sur les particules CsI et AgI n'est possible qu’a basse des températures et pour des taux d’humidité élevées, non représentatives des conditions présentes dans l’enceinte de confinement mais pouvant être rencontrées à l’extérieur de cette même enceinte. Plusieurs voies de réaction conduisant à la formation d'espèces d'iode volatiles (I2, IOH et IH) ont été explorées. Ces travaux montrent que la formation de ces espèces nécessite une double oxydation de la surface. L’oxydant le plus réactif est OH°, résultant de la radiolyse à la vapeur. Dans ce cas, l'énergie d'activation pour formation d'I2 est respectivement de 1,2 eV et 1,0 eV pour CsI et du AgI. / If a nuclear severe accident happens to a nuclear power plant, fission products can be released in the environment by some leakages of the nuclear containment building. Among them radioactive iodine is one of the most dangerous species due to its high radiological consequences during the first weeks after the accident, mainly due to 131I isotope. Some iodide aerosols, formed in the reactor coolant system, are expected to reach the containment, typically CsI and AgI, and next can react in moist oxidizing atmosphere resulting from steam/oxygen radiolysis to form gaseous molecular iodine, I2. The aim of this work is to study the reactivity of iodide aerosols, it means understand/identify possible chemical pathways leading to the formation of volatile iodine species. Theoretical study based on density functional theory (DFT) including Van Der Waals corrections were performed to study at the molecular scale the chemical reactivity at the aerosol surfaces. Thermodynamic model was used also to determine the effect of temperature and pressure on the reactivity.The results show that adsorption of water on the CsI and AgI particles is only possible at low temperatures, not representative of severe accident conditions. Several reaction pathways leading to the formation of volatile iodine species (I2, IOH and IH) were explored. These works show that formation of these species requires the oxidation the surface twice. One type of oxidant were tested which is OH°, resulting from steam radiolysis and initially present in the containment after radiolysis of water. The activation energy of I2 formation using OH° oxidants is respectively 1.2 and 1.0 eV for CsI and AgI oxidation processes.

A beta spectrometer, consisting of a liquid scintillation counter, coupled to a programmable multichannel analyser was used to achieve the objective of detecting and measuring beta activity in low level aqueous environmental solution as well as identifying the radioisotopes present. Aqueous solutions of standard beta emitters, covering a range of energies between 18.6 KeV and 3550 KeV, were used to develop computer methods for analysis. The best proportions of the counting cocktail was found consist of 4.0 ml of aqueous sample, 3.0 ml of Triton X-100 and 3.0 ml of toluene containing 4.0 g per litre PRO and 0.4 g per litre POPOP. The effects of pH, acids, bases, buffers, and salts on the stability of the mixture and on the detection efficiency of the radioisotopes, were investigated and found not to be severe. Pretreatment of the sample was not required. It was found that temperature changes, beyond the operating temperature range, could result severe errors. 1024 channels of aquisition area, for the collection of the spectra, give good conditions for computer analysis. End channel and channel number of maximum count calibration gave a linear relationship to the Em, of standard beta emitters. It was found that the theoretical fitting of the spectra is possible and the normalisation ratio V of the theoretical to the experimental fitting procedure has alinear relationship to the activity of emitter. Kurie plot was applied for checking the Emav value of the emitters used. Application of the Cerenkov counting technique for beta emitters, gives extra data to support the main results. For the analysis of environmental solutions, which may contain a variety of radioisotopes, the system was used to obtain spectra of alpha emitters, beta emitters with internal conversion and Cerenkov radiation. Synthetic mixtures of tritium and carbon-14 of activity ratios between 8:1 and 1:8 were used to investigate the problems of multielement spectral analysis.

Glassy methanolic and ethanolic solutions of molecular oxygen were exposed to X-rays at 4.2 K. A marked inhibition of the formation of e-t centres together with formation of O2- was observed. The results suggest that the environment of O2 in methanol is such that initial hydrogen-bond transfer to O2- is facile even at 4.2 K. In ethanol, O2- is too far from hydrogen bonded OH groups for this mechanism to operate. Dilute aqueous glassy solutions of the enzyme superoxide dismutase (SOD) were exposed to ?-radiation. Reduction of the native Cu(II) centre to Cu(I) was observed. A reaction was established between this reduced form and O2-. Potassium hexacyanoferrate II was shown to be a suitable chemical reducing agent for SOD after purification, whereas sodium dithionite was shown to modify the copper centre. Study of the disulphide bridge of reduced SCD revealed RSSR- radicals and, in sane cases, species 'X', depending on the nature of the reducing agent. The pH dependence of S(X) and the effect of some anions has been illustrated and serves to confirm documented results. Dilute aqueous glassy solutions of powered haemoglobin and diluted sarrples of whole blood were exposed to ?-radiation. ? and ? subunit haem Fe-O2 centres were identified at 77 K and several spectral changes recorded during warming. Tentative identification of these species has been made.

Afin de miser sur un nucléaire durable les recherches sur les cycles du futur doivent évoluer vers une co-gestion de l’ensemble des actinides et mieux, leur co-conversion. La préparation de solides mixtes intégrant l’uranium et le plutonium est actuellement privilégiée par voie oxalique. Cependant, l’utilisation de peroxydes mixtes comme précurseurs d’oxydes mixtes parait une voie alternative. En effet, la découverte récente de nombreux nano-clusters de peroxydes ou peroxo-oxalates d’uranyle, stabilisés par des cations mono- ou di- ou tri-valents permet d’envisager l’obtention de peroxydes mixtes. Ce travail a pour objectif de former des peroxydes mixtes d’uranium (VI) et de lanthanide (III), utilisé comme analogue des actinides (III), afin d’obtenir, in fine, des oxydes mixtes uranium-lanthanide par traitement thermique. L’examen du système UO22+/NH4+/O22-/C2O42- a permis, non seulement, d’affiner le diagramme d’existence des peroxydes et peroxo-oxalates d’uranyle et d’ammonium en fonction des concentrations des réactifs et du pH mais également d’obtenir douze nouvelles phases cristallines. A partir de pH 9 des phases amorphes précipitent et conduisent, après échange avec le néodyme (III) et calcination, à la formation d’oxydes mixtes homogènes qui intègrent 20 à 30% de néodyme au sein de l’oxyde final. Finalement l’utilisation de cations non labiles thermiquement a permis l’obtention de nouvelles phases U-Ca ou U-Rb. / In order to improve nuclear energy industry sustainability, future research needs to focus on the use of co-management of actinides and their co-conversion. The synthesis of uranium/plutonium mixed oxide by oxalic approach is currently the preferred method. Nevertheless the use of mixed peroxides, like precursors of mixed oxides, is considered as an alternative pathway.In fact, the recent advances on several uranyl peroxides or pero-oxalates nano-clusters stabilized by mono-, di- or tri-valent cations has permitted to investigate the formation of mixed peroxides. This study aims to investigate the formation of mixed uranium (VI) and lanthanide (III) peroxides leading to the formation of uranium-lanthanide mixed oxides, by heat treatment. Lanthanide (III) are used as actinides (III) analogs. The study of the UO22+/NH4+/O22-/C2O42- system allowed us to (i) refine the domains of existence of uranyl and ammonium peroxide and peroxo-oxalates as a function of reactive concentrations or pH (ii) obtain twelve news crystalline phases. At pH 9 and above, amorphous phases precipitated and after neodymium (III) exchange and calcination, led to the formation of mixed oxides. Mixed oxides can thus incorporate from 20 to 30% of neodymium. Finally the use of non thermically labile cations permits the formation of new U-Ca or U-Rb phases.

Ce travail de thèse consistait en premier lieu à accélérer un modèle de Monte Carlo Cinétique Atomique visant à simuler l’évolution de la microstructure d’alliages modèles du type FeCuMnNiSiP représentatifs de l’acier de cuve sous irradiation neutronique. Cette accélération était nécessaire pour atteindre des doses ainsi que des flux comparables à l’expérience en des temps raisonnables. Pour cela, une accélération algorithmique du code de calcul LAKIMOCA a d’abord été réalisée. Les diverses optimisations apportées ont permis d’accélérer le code d’un facteur 7. Cette accélération ne s’avérant pas suffisante, l’approche retenue a été le développement d’une approche hybride entre une approche Monte Carlo atomique et Monte Carlo d’objets. La paramétrisation du modèle objet a permis de mieux comprendre les macro évènements en jeux dans les simulations, mais s’est révélée être d’une grande difficulté lorsque la complexité chimique des objets devient trop importante. Néanmoins, l’approche hybride a apporté une accélération des temps de calcul d’environ deux ordres de grandeur permettant de simuler des doses correspondant à 40 ans d’irradiation en production. De ces résultats, différentes limitations du modèle ainsi que de sa paramétrisation ont été mises en évidence. La difficulté du modèle à reproduire des effets de flux a été comblée par l’ajout d’un absorbeur visant à réduire la force de puits des joints de grains ainsi que par l’ajout de pièges pour rendre compte de la présence d’impureté dans le fer pur. Les simulations à hautes doses dans les alliages du type FeCuMnNiSiP ont aussi mis en évidence des différences entre les microstructures simulées et celles observées expérimentalement. Ainsi, dans un second temps, un nouveau modèle de cohésion basée sur des interactions de paires dépendantes de la concentration locale a été développé et paramétré. Bien que le nouveau modèle de cohésion soit numériquement plus lourd, il a été possible d’atteindre la dose ciblée en le couplant à l’approche hybride. Les résultats obtenus sont en meilleur en accord avec les calculs DFT récents ainsi qu’avec les microstructures expérimentales. / This PhD thesis work consisted, in the first place, in accelerating an atomic kinetic Monte Carlo model aiming at simulating the microstructure evolution of the FeCuMnNiP model alloys, representative of the reactor pressure vessel steels, under irradiation. This acceleration was required to reach, in a reasonable amount of time, doses and flux conditions comparable to the experimental ones. To do so, an algorithmic optimization has first been performed. The different optimizations introduced lead to an acceleration of the code of a 7 factor. Since this acceleration was not sufficient, the retained approach was to develop an hybrid between an AKMC and an OKMC. The parameterization of the object model provided a better understanding of the macro events involved in the simulations. It turns out that parameterize the model became too complex when increasing the chemical complexity of the objects. However, the hybrid approach brings an acceleration of two orders of magnitude allowing reaching doses corresponding to 40 years of irradiation in service condition. From these results, different limitations of the model as well as the parameterization were highlighted. The difficulty of the model to reproduce flux effect has been solved by adding an absorber that reduced the grain boundary sink strength. Traps have also been introduced to simulate the presence of impurities in pure iron. The high doses simulations in FeCuMnNiSiP model alloys also highlighted differences between the microstructures simulated and those observed experimentally. Thus, in a second time, a new cohesive model based on concentration dependent pair interactions has been developed and parameterized. While the new cohesive model is numerically heavier than the previous one, it has been possible to reach the target dose by coupling it with the hybrid model. The results obtained are in better agreement with recent DFT calculations and experimental microstructures.