This thesis deals with the diffusion of ions in compactedbentonite clay. Laboratory experiments were performed toexamine in detail different processes that affect thediffusion. To demonstrate that the results obtained from thelaboratory investigations are valid under in situ conditions,two different kinds of in situ experiments were performed. Laboratory experiments were performed to better understandthe impact of ionic strength on the diffusion of Sr2+ and Cs+ions, which sorb to mineral surfaces primarily by ion exchange.Furthermore, surface related diffusion was examined anddemonstrated to take place for Sr2+ and Cs+ but not for Co2+,which sorbs on mineral surfaces by complexation. The diffusion of anions in bentonite clay compacted todifferent dry densities was also investigated. The resultsindicate that anion diffusion in bentonite clay consists of twoprocesses, one fast and another slower. We ascribe the fastdiffusive process to intralayer diffusion and the slow processto diffusion in interparticle water, where anions are to someextent sorbed to edge sites of the montmorillonite. Two different types of in situ experiments were performed,CHEMLAB and LOT. CHEMLAB is a borehole laboratory, where cation(Cs+, Sr2+ and Co2+) and anion (I- and TcO4-) diffusionexperiments were performed using groundwater from a fracture inthe borehole. In the LOT experiments cylindrical bentoniteblocks surrounding a central copper rod were placed in a 4 mdeep vertical borehole. The borehole was then sealed and theblocks are left for 1, 5 or>>5 years. When the bentonitewas water saturated the central copper rod is heated tosimulate the temperature increase due to radioactive decay ofthe spent fuel. Bentonite doped with radioactive Cs and Co wasplaced in one of the lower blocks. Interestingly, the redox-sensitive pertechnetate ion (TcO4-)which thermodynamically should be reduced and precipitate asTcO2·nH2O, travelled unreduced through the bentonite.However, at some spots in the clay, the Tc activity wasconsiderably higher. We ascribe these activity peaks toiron-containing minerals in the bentonite, by which Tc(VII) hasbeen reduced to Tc(IV) and precipitated. The cations Sr2+, Cs+and Co2+, as well as the anion I-, behaved in the CHEMLABexperiments as expected from laboratory studies. Three experiments in the LOT series are completed. The firsttwo diffusion experiments in LOT were less successful, thefirst due to the fact that saturation of the bentonite was notobtained during the experimental period and the radionuclidesdid not move at all. In the second, the uptake of the bentoniteparcel was less successful. Water from the drilling flushedaway large pieces of the top part of the bentonite and thelower part of the test parcel was super-saturated with waterand expanded when released from the rock. The activity distribution in the second experiment wasanalysed. The Co2+ profile looked as we had expected, while Cs+had spread more than our calculations indicated. However, thethird experiment was successful from emplacement, watersaturation and heating to uptake. The activity distribution forboth cations was as expected from laboratory studies. Altogether the three different types of experiments give auniform picture of radionuclide diffusion in bentonite clay forthe ions investigated. / QC 20100621

Diss. (sammanfattning). Uppsala : Sveriges lantbruksuniv., 2003. / Härtill 5 uppsatser.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv. / Härtill 4 uppsatser.

Thorium(IV) and uranium(IV) coordination complexes have been studied for the last 60 years. They have shown interesting reactivity that is often divergent from that of transition metal complexes, and that also provides an insight into some unanticipated differences between thorium(IV) and uranium(IV). An introduction to thorium(IV) and uranium(IV) organometallic chemistry supported by carbocyclic and N-donor ligands is given in Chapter One. The reactivity of actinide alkyl, amide and alkynyl complexes towards small molecules is discussed and select examples provided. The redox chemistry of thorium and uranium is also introduced. Chapter Two describes the alkylation and amination chemistry of uranium(IV) and thorium(IV) trans-calix[2]benzene[2]pyrrolide ((L)2-) complexes, [(L)AnCl2], yielding new actinide(IV) complexes of the type [M(L-2H)An(R)] (M = Li or K, R = Me, CH2SiMe3, CH2Ph, N(SiMe3)2), where (L)2- undergoes further deprotonation to (L-2H)4-. Additionally, the lability of the [M(L-2H)An(R)] “ate”-complexes towards M+ ion exchange is addressed. Further, the selective ligand reprotonation of (L-2H)4- to (L)2- using HSiR'3 (R' = Me, iPr) and [Et3NH][BPh4] yielding [(L)An(C≡CSiR'3)2] and [(L)An(R)][BPh4] respectively, is explained. The reactivity of these complexes towards amines, silanes, alkenes, tin hydrides, silicone grease, tBuNC, H2, CO, CO2 or CS2 is described. Crystallographic characterisation shows that [(L)Th(N(SiMe3)2)][BPh4] contains an unusual example of a thorium(IV) bis-arene coordination mode. The reactivity of [(L)Th(C≡CSiMe3)2] towards a number of substrates including alkenes, [Ni(COD)2], [Pt(norbornene)3], P4, CO2 or H2 is also discussed. Activation of CO2 by [(L)Th(C≡CSiMe3)2] at 80 °C results in (L)2- functionalisation and abstraction to yield a new tricyclic organic molecule with the general formula LCO. The addition of [Ni(COD)2] to [(L)Th(C≡CSiMe3)2] and PR''3 (R'' = phenyl, cyclohexyl) yields heterobimetallic complexes [(L)Th(C≡CSiMe3)2·Ni(PR''3)]; these products display both dipyrrolic and bis-arene coordination. The changes in ligand coordination mode are discussed alongside DFT computational analyses that have been carried out by collaborators. The substitution reactions of [(L)AnCl2] with NaBH4 to form actinide(IV) borohydride complexes [(L)An(BH4)2] and subsequent attempted abstractions of BH3 from [(L)Th(BH4)2] are presented. Conclusions are provided at the end of the chapter. Chapter Three focusses on the oxidation chemistry of uranium(IV) within the (L)2- and (L-2H)4- ligand framework, prompted by the isolation of a uranium(V) complex [Li[(L)UO2]·LiI] from the oxidation of the uranium(IV) complex [Li(L-2H)U(Me)]. Conclusions are provided at the end of the chapter. Experimental methods and characterising data are given in Chapter Four.

Caesium-137 is one of the major artificial radioactive elements, whose sources are atmospheric nuclear tests carried out in the 20th century and nuclear power plant incidents such as Chernobyl. Because of uneven precipitation, there were significant differences in radioactive fallout levels in different areas of the Czech Republic during the passage of the radioactive cloud from Chernobyl. Due to the high solubility of Caesium-137 in water and easy distribution in the environment, there is contamination of the lower soil levels where the plant root systems are located. The aim of this work is to collect soil samples from selected localities, where in 1986 significant contamination was detected as originating from Chernobyl, determination of their Caesium-137 content by gamma semiconductor spectrometry and comparison depending on the type of soil. The research question was set as: Does Caesium-137 content differ in different soil types? As part of this study, samples of uncultivated agricultural land and forest land were collected from layers 0-5, 5-10 and 10-15 cm in Kvilda, Zadov and Churanov. For comparison, results were also collected from a locality where the radioactive fallout was not so significant. This locality is around the village Straz nad Nezarkou, which is found on the protected nature reserves of Trebon. From the results of measuring the soil it was found that even after thirty years since the Chernobyl disaster occurred, Caesium-137 is still found in the upper layers of soils, specifically to depths of 5 cm. The highest specific activity of Caesium-137 was measured in the forest soils in Zadov at depths of 0-5 cm (364 Bq.kg-1) from the total range of all samples, 2,24 Bq.kg-1 to 364 Bq.kg-1. The highest specific activity of potassium K-40 was measured in uncultivated agricultural land in the locality of Kvilda at depths of 0-5 cm (883 Bq.kg-1).

Cette thèse décrit le travail expérimental sur différentes techniques visant l'obtention du contrôle de l'état quantique d'atomes et de molécules, pour application dans l'informatique quantique, la métrologie et l'astrophysique. Le contrôle cohérent exige des conditions précises de fonctionnement d'un système où la décohérence est minimisée. La construction d'une machine à jet atomique de calcium est présentée comme l'élément de base d'expériences où des schémas d'excitation laser choisis permettront de préparer de façon robuste un état quantique au moyen d'impulsions composites. La deuxième section décrit ma contribution pour améliorer la stabilité de fréquence relative de l'horloge à fontaine de cesium CSF2, à l'institut allemand de métrologie. Un piège magnéto-optique modifié produit un faisceau d'atomes de césium lents. Ils sont préparés dans un état noir spécifique puis sont efficacement transférés à la mélasse optique de la fontaine. L'augmentation du nombre d'atomes participant ainsi au cycle d'horloge améliore sa stabilité d'un facteur 6. La troisième section concerne les spectres de molécules NiH et FeH. Plusieurs sources pour leur production en laboratoire ont été développées et testées. Une expérience d'absorption laser différentielle et une technique de spectroscopie intra-cavité sont appliquées aux molécules faiblement absorbantes NiH, afin d'obtenir leurs coefficients d'absorption dans le rouge. La réponse Zeeman de la molécule FeH (une sonde du champ magnétique des étoiles froides) dans le proche infrarouge est étudiée par spectroscopie laser de précision afin d'établir des facteurs Landé pour 33 niveaux rovibrationnelles de l'état électronique F 4? / This thesis describes experimental work on different techniques aiming to achieve control of the quantum state of atoms and molecules, envisaging applications in quantum computing, metrology and astrophysics.Successful coherent control requires careful design of operating conditions for a system where decoherence is minimized. The construction of a calcium atomic beam is presented as a necessary element in experiments with laser excitation schemes chosen to provide high-fidelity preparation of a quantum satate by means of composite pulses. The second section describes my contribution to the improvement of the relative frequency stability of the Cs fountain clock CSF2 at the German institute of metrology. A modified magneto-optical trap is employed to form a beam of slow cesium atoms. They are prepared in a specific dark state and subsequently are efficiently transferred to the optical molasses of the fountain. Increasing number of atoms participating in the clock cycle in this way improves the stability of the clock by a factor of 6.The third section is concerned with spectra of metal hydride molecules NiH and FeH. Several sources for production of these molecules in laboratories were developed and tested. A differential laser absorption experiment and a cavity-enhanced spectroscopy technique are applied on the w??kly absorbing NiH molecules, to obtain absorption coefficients for the red bands of NiH. The Zeeman response of the FeH molecule (a probe for magnetic fields in cool stars) in the near-IR is investigated by precision laser spectroscopy establishing Landé factors for 33 rovibrational levels of the F 4? electronic state

Potassium is essential macroelement and large amount of potassium is taken up by plants, because it's the major osmotic of plant cell. Due to various potassium availability in different kinds of soil, plants have evolved transport system that can maintain sufficient K+ uptake between several orders of magnitude of potassium concentration. In Arabidopsis thaliana mechanism of K+ acquisition is well understood and it's known that AtHAK5 is mainly involved in K+ uptake in its very low concentrations. AtHAK5 belongs to KT/HAK/KUP family that consist 13 members in A. thaliana. There's known function for some members for example in auxin transport in root tip (TRH1) or in K+ efflux in stomatal closure (KUP6). In this thesis possible involvement of yet unstudied transporters KUP5, KUP7, KUP9 and KUP10 in K+ acquisition and homeostasis in A. thaliana was investigated. In vitro cultivation showed that kup9 mutant has very short lateral roots in K+ deficiency. On the other hand kup5 mutant showed significantly higher dry weight in K+ deficiency than Col-0. Kup9 phenotype was successfully replicated in subsequent cultivations and anatomy of lateral root apical meristems was investigated. Root tips of kup9 were differently organized in K+ deficiency and they showed signs of early termination of meristems. To...

This thesis describes an experimental study of superelastic electron scattering from the 6^2P_3/2 state of caesium. The present status of electron-atom collision studies is initially reviewed and the motivation behind the current work is then presented. A description of the theoretical framework is subsequently provided in the context of the present experimental study, followed by an overview of the several theoretical approaches for describing electron-atom interactions which are currently available. The apparatus and experimental setup used throughout the project are also described in detail. Technical specifications and data are provided, including diagrams (where appropriate) for a laser frequency locking system, electron gun and spectrometer, atomic beam source and data acquisition system. The experimental procedures are explained and discussed, including a detailed analysis of the optical pumping process required to excite the atomic target. A substantial component of this project was to address several potential sources of systematic error and to reduce these wherever possible. All of the errors and uncertainties relevant to the experiment are discussed in chapter 5. In chapter 6 the results of the present superelastic electron scattering experiments are reported for incident electron energies of 5.5eV, 8.5eV and 13.5eV, corresponding to superelastic electron energies of 7eV, 10eV and 15eV. These results are presented as three reduced Stokes parameters, P1, P2, P3 and a coherence parameter, P+ . For comparison, predictions from a number of currently available theories are presented alongside the experimental results. Finally, conclusions are drawn on this work in the context of the current status of electron-atom scattering from alkali-metals.

Ce travail vise à développer un modèle générique capable de mieux rendre compte et de prédire les transferts de radionucléides dans le système sol/solution du sol/plante. La première partie de ce travail a été consacrée à l’analyse critique des modèles disponibles dans la littérature pour décrire l’adsorption du césium par les minéraux argileux (principal processus contrôlant sa disponibilité dans les sols). Cette analyse a débouché sur la formulation d’un nouveau modèle mécaniste combinant deux approches: la complexation de surface et l’échange d’ions. Cette approche, a été testée afin de modéliser l’adsorption du Cs sur plusieurs substrats argileux naturels. Ce travail a permis de valider le modèle proposé et de démontrer qu’il constitue un avantage majeur par rapport aux différents modèles existants. La deuxième partie a été consacrée, à la réalisation d’une série d’expérimentations, conduite en milieux contrôlés sur des systèmes dynamiques, et la modélisation de la (bio)disponibilité du Cs dans ces systèmes. A la suite de ces essais, les interactions entre solide et solution observées ont pu être correctement reproduites à partir du modèle proposé en prenant en compte la fraction argileuse du sol uniquement. Ces simulations ont également été comparées aux simulations obtenues à partir des modèles empirique (Kd) et cinétique (EK). Enfin, le développement d’un outil numérique permettant de coupler la description des interactions géochimiques au transfert vers la plante (approche cinétique) a permis de reproduire correctement les essais réalisés en Rhizotests couplant sol, solution et plante et de mieux caractériser la fraction du Cs disponible pour les plantes. / The overall objective of this work is to develop a generic model able to better account and predict the transfer of radionuclides in the soil / soil solution / plant. The first part of the work was devoted to the critical analysis of the models available in the literature to describe the cesium adsorption on clay minerals (the process that mainly controls its availability in the soils). This analysis enabled us to propose a new mechanistic model combining two approaches: surface complexation and cation exchange. Our approach has been tested in order to model the adsorption of Cs on several natural clay substrates, in a wide range of Cs concentrations and physicochemical conditions. This work allowed to validate the proposed mechanistic model and to demonstrate that it constitutes a major advantage over the various existing models. The second part was devoted, to the performing of a series of experiments, carried out in controlled environments on dynamic systems and modeling the (bio)availability of Cs in these systems. Following these tests, the observed interactions between solid and solution could be correctly reproduced with the proposed model taking into account only the clay fraction of the soil. These simulations were also compared with simulations obtained using a empiric (Kd) kinetic models (E-K approach). Finally, the development of a numerical tool for coupling the description of geochemical interactions with transfer to the plant (Michaelis-Menten approach) allowed to reproduce adequately the trials carried out in Rhizotests coupling soil, solution and plant, and to better characterize of the Cs fraction available for plants.

Diss. (sammanfattning) Umeå : Sveriges lantbruksuniv. / Härtill 4 uppsatser.