Objetivou-se avaliar a taxa de emissão de metano (CH4) pela técnica do gás traçador hexafluoreto de enxofre (SF6) e fermentação ruminal dos animais alimentados com feno de Brachiaria brizantha em diferentes estágios de crescimento. Os três tratamentos foram: I-Feno de Brachiaria brizantha com 15 dias de crescimento, II- Feno de Brachiaria brizantha com 45 dias de crescimento e III- Feno de Brachiaria brizantha com 90 dias de crescimento. Seis bovinos da raça nelore, machos, castrados, canulados no rúmen e com peso médio inicial de 402 ± 51,62 kg foram utilizados em delineamento em quadrado latino 3x3 duplicado. O experimento teve duração total de 60 dias. A adaptação às dietas durou 7 dias. No oitavo dia foram feitas coletas de fezes (5 dias) e mensuração do consumo voluntário para determinação da digestibilidade in vivo dos alimentos. No 13° dia iniciaram-se as coletas de metano (7 dias) através da técnica do gás traçador hexafluoreto de enxofre (SF6). No 20° dia foram tomadas amostras do líquido ruminal às 0, 2, 4, 6, 8 e 10 horas após a primeira alimentação para determinação do potencial hidrogeniônico (pH), N-amoniacal e ácidos graxos voláteis do líquido ruminal. A idade de corte não afetou substancialmente a concentração total ou a proporção molar dos AGV, bem como o pH, embora a concentração de N-NH3 ruminal tivesse diminuído com o avanço da idade de corte. Para os dados de digestão, apenas a digestibilidade da PB aumentou e os dados dos CNF diminuíram com o avanço da idade. A produção de metano por animal/dia não foi afetada pela idade de corte do capim. Os animais alimentados com o feno produzido com 45 dias de crescimento do capim apresentaram diminuição de consumo de MS, o que resultou em maior produção de metano por unidade de MS ingerida. / The objective was to evaluate methane (CH4) emission rate by sulfur hexafluoride (SF6) tracer technique in bovines of the Nelore breed fed with Brachiaria brizantha hay in different maturation stages. The three treatments wore: I- Hay of Brachiaria brizantha with 15 days of maturation, II- Hay of Brachiaria brizantha with 45 days of maturation and III- Hay of Brachiaria brizantha with 90 days of maturation. Six bovines of the Nelore breed, males, castrated, rumen-cannulated, and 402 ± 51,62 kg of initial average weight had been used in a duplicated 3X3 latin square design. Trial lasted 54 days. The adaptation to the diets lasted 7 days. In the eighth day excrement collections (5 days) and feed sampling were done. In 13th day the methane collections were initiated using the sulfur hexafluoride SF6) tracer technique. The 20th day was used for ruminal fluid sampling at 0, 2, 4, 6, 8, and 10 hours after 1st meal for determination of pH, amoniacal-N, and volatile fatty acids in ruminal fluid. The ammoniacal nitrogen (NH3-N) concentration in treatment I was higher than II, 7,21; 2,22 mg/dl, respectively. Methane emission (g/kg DM) in treatment II was higher than I and II 23,41, 17,38, 20,02, respectively.

A demanda por combustível nuclear para reatores de pesquisa está aumentando em nível mundial, enquanto várias de suas fábricas têm pequeno volume de produção. Este trabalho estabeleceu um modelo conceitual com duas estratégias para o aumento da capacidade produtiva dessas fábricas. Foram abordadas as fábricas que produzem elementos combustíveis tipo placa carregados com LEU U3Si2-Al, tipicamente usados em reatores nucleares de pesquisa. A primeira estratégia baseia-se na literatura da área de administração da produção e é uma prática frequente nas fábricas em geral. A segunda estratégia aproveita a possibilidade de desmembrar setores produtivos, comum em instalações de produção de combustível nuclear. Ambas as estratégias geraram diferentes cenários de produção, os quais devem ser seguros em relação à criticalidade. Foram coletados dados de uma fábrica real de combustível nuclear para reatores de pesquisa. As duas estratégias foram aplicadas a esses dados com a finalidade de testar o modelo proposto, o que configurou um estudo de caso. A aplicação das estratégias aos dados coletados deu-se por meio de simulação de eventos discretos em computador. Foram criados diversos modelos de simulação para abranger todos os cenários gerados, de forma que o teste indicou um aumento da capacidade produtiva de até 207% sem necessidade de aquisição de novos equipamentos. Os resultados comprovam que o modelo atingiu plenamente o objetivo proposto. Como principal conclusão pode-se apontar a eficácia do modelo proposto, fato que foi validado pelos dados da fábrica. / Although many nuclear fuel factories have small production volumes, the demand for nuclear fuel for research reactors is increasing worldwide. This work established a conceptual model with two strategies to increase the production capacity of these factories. We addressed factories that produce plate-type fuel elements loaded with LEU U3Si2-Al, which are typically used in nuclear research reactors. The first strategy is based on production management literature and is a regular practice in general manufacturing plants. The second strategy takes advantage of the fact that productive sectors can be separated in nuclear fuel production facilities. Both strategies have generated different production scenarios that are assumed to be safe in relation to nuclear criticality. We collected data from a real plant that produces nuclear fuel for research reactors and applied the model to that data, aiming to test the proposed model by setting up a case study. Through the use of computer software, we applied the two strategies to this data by means of discrete events simulation and created several simulation models in order to cover all generated scenarios. Our tests indicated an increase of up to 207% in productive capacity without the need of acquiring new equipment, thus showing that the model has fully achieved its proposed objective. One of the main conclusions that we point out is the models effectiveness, which was validated by the factory data.

L’hexafluorure d’uranium (UF6), est le seul composé utilisé à l’état gazeux dans les procédés d’enrichissement pour la production du combustible nucléaire. Pour le bon déroulement de l’étape d’enrichissement, la qualité de UF6  est primordiale. Cette étude s’est intéressée principalement aux impuretés volatiles sous forme de fluorures et oxyfluorures et leur réactivité avec des matériaux en présence ou non de l’UF6. La nature des produits adsorbés et de réactions a été identifiée. Les mécanismes physico-chimiques mis en jeux lors de la sorption ont été investigués. Les performances (capacité de sorption, sélectivité et régénération) de ces matériaux absorbants et adsorbants ont été évaluées en vue de leur utilisation comme filtre UF6 dans les usines de conversion. / Uranium hexafluoride (UF6), is the only compound used in the gaseous state in the process of enrichment to produce nuclear fuel. For the success of the enrichment step, the UF6 quality is paramount. This study is mainly concerned with volatile impurities in form of fluorides and oxyfluorides and their reactivity with the materials in presence or not of UF6. The nature of the adsorbed compounds and reactions products was identified. The physico-chemical mechanisms of sorption were investigated. The performances (sorption capacity, selectivity and regeneration) of the absorbent and adsorbent materials have been evaluated to be used as UF6 filters in conversion plants.

A demanda por combustível nuclear para reatores de pesquisa está aumentando em nível mundial, enquanto várias de suas fábricas têm pequeno volume de produção. Este trabalho estabeleceu um modelo conceitual com duas estratégias para o aumento da capacidade produtiva dessas fábricas. Foram abordadas as fábricas que produzem elementos combustíveis tipo placa carregados com LEU U3Si2-Al, tipicamente usados em reatores nucleares de pesquisa. A primeira estratégia baseia-se na literatura da área de administração da produção e é uma prática frequente nas fábricas em geral. A segunda estratégia aproveita a possibilidade de desmembrar setores produtivos, comum em instalações de produção de combustível nuclear. Ambas as estratégias geraram diferentes cenários de produção, os quais devem ser seguros em relação à criticalidade. Foram coletados dados de uma fábrica real de combustível nuclear para reatores de pesquisa. As duas estratégias foram aplicadas a esses dados com a finalidade de testar o modelo proposto, o que configurou um estudo de caso. A aplicação das estratégias aos dados coletados deu-se por meio de simulação de eventos discretos em computador. Foram criados diversos modelos de simulação para abranger todos os cenários gerados, de forma que o teste indicou um aumento da capacidade produtiva de até 207% sem necessidade de aquisição de novos equipamentos. Os resultados comprovam que o modelo atingiu plenamente o objetivo proposto. Como principal conclusão pode-se apontar a eficácia do modelo proposto, fato que foi validado pelos dados da fábrica. / Although many nuclear fuel factories have small production volumes, the demand for nuclear fuel for research reactors is increasing worldwide. This work established a conceptual model with two strategies to increase the production capacity of these factories. We addressed factories that produce plate-type fuel elements loaded with LEU U3Si2-Al, which are typically used in nuclear research reactors. The first strategy is based on production management literature and is a regular practice in general manufacturing plants. The second strategy takes advantage of the fact that productive sectors can be separated in nuclear fuel production facilities. Both strategies have generated different production scenarios that are assumed to be safe in relation to nuclear criticality. We collected data from a real plant that produces nuclear fuel for research reactors and applied the model to that data, aiming to test the proposed model by setting up a case study. Through the use of computer software, we applied the two strategies to this data by means of discrete events simulation and created several simulation models in order to cover all generated scenarios. Our tests indicated an increase of up to 207% in productive capacity without the need of acquiring new equipment, thus showing that the model has fully achieved its proposed objective. One of the main conclusions that we point out is the models effectiveness, which was validated by the factory data.

This thesis project aims to develop an innovative technique for the production of high-purity uranium nitride (UN) through the ammonolysis of fluorides. The desired objective is to perform a controlled gas/gas reaction between uranium hexafluoride (UF6) and ammonia (NH3) at 800°C. The intermediate product thereby obtained (uranium dinitride, UN2) is subjected to further heating up to 1100°C under argon atmosphere, to ultimately produce UN. An inherent challenge faced in previous experiments was related to the dissociation of ammonia, which is alimiting factor for upscaling. Therefore, in this project a new setup is invented to address this challenge and it is proved experimentally: the idea is to achieve a coaxial laminar flow of UF6 and a carrier gas, where a central stream of the former is shielded by the latter so that the tworeacting gasses mix only in the hot point of the furnace, where the desired reaction can happen. To implement this approach, the ammonia dissociation has been studied, an apparatus for the controlled evaporation of UF6 has been designed and built, and two different injection nozzleshave been tested in different setup configurations. Eventually, the complete prototype has been tested altogether in a synthesis experiment at 800°C, and the products thus obtained have been converted into UN at 1100°C. Numerous auxiliary experiments have been performed using UF4as a reactant, as it is easier to handle and the results thus obtained can be largely extended to UF6. Lastly, a UF4 synthesis experiment has been performed, as educationally helpful to further dig into some chemistry features of this material, and a UN pellet has been sintered with Spark Plasma Sintering (SPS). / Detta examensarbete syftar till att utveckla en innovativ teknik för framställning av urannitrid (UN) med hög renhet genom ammonolys av fluorider. Målsättningen med arbetet är att utföra en kontrollerad gas/gasreaktion mellan uranhexafluorid (UF6) och ammoniak (NH3) vid 800°C. Den därigenom erhållna mellanprodukten (urandinitrid, UN2) värms därefter upp till 1100°C i en argonatmosfär, för att slutligen producera UN. En utmaning i tidigare experiment var relaterat till dissociationen av ammoniak, vilket är en begränsande faktor för uppskalning av processen. För att möta denna utmaning utvecklas därför en ny process i detta projekt och den bevisas experimentellt. Tanken är att skapa ett koaxiellt laminärt flöde bestående av UF6 och en bärgas, där en central ström av den första är avskärmad av det senare så att de två reagerande gaserna enbart blandas i ugnens heta zon, där den önskade reaktionen sker. För att implementera denna metod så har ammoniakdissociationen studerats, en apparat för kontrollerad avdunstning av UF6 har designats och byggts, och två olika insprutningsmunstycken har testats i olika konfigurationer. Den kompletta prototypen har testats i sin helhet med ett syntesexperiment vid 800°C, och produkterna som erhållits har konverterats till UN vid 1100°C. Ett flertal hjälpexperiment har utförts med UF4 som reaktant, eftersom den är enklare att hantera, och de erhållna resultaten kan till stor del utvidgas till UF6. Slutligen har ett UF4-syntesexperiment genomförts för att som ett pedagogiskt hjälpmedel ytterligare studera vissa kemiska egenskaper hos detta material. En UN-pellet har sintrats med starkströmsassisterad varmpressning (eng. Spark Plasma Sintering, SPS).

Ce travail porte sur la synthèse et la caractérisation de fluorures à base d’alcalins, d’alcalinoterreuxet de terres rares et sur la réactivité de ces composés vis-à-vis de ReF6 pour lapurification de UF6. L’étude traite dans un premier temps de la synthèse de fluorures tels queKMgF3, MgF2 et CaF2 en couplant une voie solvothermale assistée par micro-ondes et uneétape de fluoration à partir de fluor élémentaire (F2). Les techniques de caractérisationutilisées mettent notamment en avant le caractère basique au sens de Lewis de ces composéset la possibilité de contrôler leur surface spécifique et leur taux d’oxygène, à l’origine dessites basiques, via la température de fluoration (F2) en phase gaz. Dans un second temps, lasolution solide Ce1-xZrxF4 à base de Ce4+ et Zr4+ a été obtenue par fluoration directe d’oxydesmixtes à partir de fluor élémentaire dilué. L’étude par DRX et RMN du 19F montre laprésence d’une solution solide pour des compositions voisines de x=0,5. Enfin, la réactivité deReF6 et UF6 sur KMgF3, MgF2 et CaF2 montre que KMgF3 est un très bon candidat pour lapurification de UF6 vis-à-vis de ReF6, qui dépend à la fois de paramètres intrinsèques auxfluorures divisés (surface spécifique, taux d’oxygène, basicité, cations mis en jeu…) maisaussi du procédé de purification (température, temps de contact). / This work deals with the synthesis and characterization of alkali, alkali-earth and rare earthbased fluorides and the reactivity of the latter with ReF6 for UF6 purification. In a first part,we focused our attention on the synthesis of KMgF3, MgF2 and CaF2 high surface area metalfluorides coupling both microwave assisted solvothermal process and a fluorination step withelemental fluorine (F2). The higher the surface area, the higher the oxygen rate. Thesenanofluorides exhibit Lewis basic character. In a second part, several compositions of theCe1-xZrxF4 solid solution were synthesized by direct fluorination of mixed oxides usingelemental fluorine (F2). XRD an 19F NMR characterizations show the occurence of a newsolid solution for compositions close to x=0.5. Finally, the reactivity between ReF6/UF6 andKMgF3, MgF2 and CaF2 leads to conclude that KMgF3 is the best candidate for thepurification of UF6. This study indicates that the purification depends on several parameters :intrinsic parameters of the divided fluorides (surface area, oxygen rate, basicity, cations…)and parameters directly related to the process (temperature, contact time).

Submitted by Pedro Silva Filho (pfsilva@ipen.br) on 2017-11-22T17:00:26Z No. of bitstreams: 0 / Made available in DSpace on 2017-11-22T17:00:26Z (GMT). No. of bitstreams: 0 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / A demanda por combustível nuclear para reatores de pesquisa está aumentando em nível mundial, enquanto várias de suas fábricas têm pequeno volume de produção. Este trabalho estabeleceu um modelo conceitual com duas estratégias para o aumento da capacidade produtiva dessas fábricas. Foram abordadas as fábricas que produzem elementos combustíveis tipo placa carregados com LEU U3Si2-Al, tipicamente usados em reatores nucleares de pesquisa. A primeira estratégia baseia-se na literatura da área de administração da produção e é uma prática frequente nas fábricas em geral. A segunda estratégia aproveita a possibilidade de desmembrar setores produtivos, comum em instalações de produção de combustível nuclear. Ambas as estratégias geraram diferentes cenários de produção, os quais devem ser seguros em relação à criticalidade. Foram coletados dados de uma fábrica real de combustível nuclear para reatores de pesquisa. As duas estratégias foram aplicadas a esses dados com a finalidade de testar o modelo proposto, o que configurou um estudo de caso. A aplicação das estratégias aos dados coletados deu-se por meio de simulação de eventos discretos em computador. Foram criados diversos modelos de simulação para abranger todos os cenários gerados, de forma que o teste indicou um aumento da capacidade produtiva de até 207% sem necessidade de aquisição de novos equipamentos. Os resultados comprovam que o modelo atingiu plenamente o objetivo proposto. Como principal conclusão pode-se apontar a eficácia do modelo proposto, fato que foi validado pelos dados da fábrica. / Tese (Doutorado em Tecnologia Nuclear) / IPEN/T / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP / CNPq:310274/2012-5

Gasisolierte Systeme im Gleichspannungsbetrieb vereinen für Anwendungen moderner Energieübertragung die Forderungen nach kleinräumigen Anlagen und verlustarmem Energietransport über große Entfernungen. Für einen zuverlässigen und sicheren Betrieb muss das Verhalten der eingesetzten Gas-Feststoff-Isolierung im technologischen System bis an die Grenzen des Isolationsvermögens bekannt sein. Gegenstand der vorliegenden Arbeit ist deshalb das Überschlagsverhalten von Gas-Feststoff-Isoliersystemen unter Gleichspannungsbelastung. Dabei stehen zwei wesentliche Einflussfaktoren im Vordergrund: die Temperatur, motiviert durch reale Stromwärmeverluste, und eine feste Störstelle auf der Gas-Feststoff-Grenzfläche, motiviert durch in der Praxis nicht völlig auszuschließende, metallische Partikel. Die Effekte dieser beiden Parameter auf die Feldverteilung, die Oberflächen- und Raumladungsbildung sowie das Isolationsvermögen bei Gleichspannung werden zunächst in zwei Versuchsanordnungen separat experimentell untersucht. Anschließend wird deren Zusammenwirken und gegenseitige Beeinflussung im Gesamtsystem analysiert. Die betriebsbedingte Erwärmung der Leiter gasisolierter Systeme führt zu einer inhomogenen Temperaturverteilung, die sich auf die Eigenschaften der Isolierstoffe Gas und Epoxidharz auswirkt. Die von der Temperatur abhängige Leitfähigkeit der Feststoffisolatoren führt zu einer temperaturabhängigen Feldverteilung, bei der sich der Ort der Höchstfeldstärke verschiebt. Dabei kann sich der Absolutwert der Höchstfeldstärke erhöhen und somit das Isolationsvermögen verringern. Gleichzeitig weist das Isoliergas nahe des erwärmten Leiters lokal eine geringere Dichte und damit eine geringere dielektrische Festigkeit auf. Die thermisch bedingte Minderung des Isolationsvermögens bei Gleichspannung beträgt in der untersuchten Anordnung (25 ... 35) %. In den schwach inhomogenen Feldern gasisolierter Anlagen erweisen sich metallische Partikel auf Isolatoren ab drei Millimetern Länge als besonders kritisch. Bei einem Gasdruck unterhalb von 0,3 MPa setzen an den Partikelspitzen zum Teil bereits ab 50 % der Durchschlagsspannung ohne Partikel Teilentladungen ein, sodass die Koronastabilisierung zu einer vergleichsweise hohen Überschlagsspannung führt. Durch diese stabilen Glimmentladungen kann die Störstelle bei Gleichspannung durch die üblichen Detektionsverfahren jedoch nicht zweifelsfrei nachgewiesen werden. Oberhalb von 0,3 MPa treten vor dem Überschlag keine Teilentladungen auf. Aufgrund der fehlenden Koronastabilisierung kann die Isolationsfestigkeit durch einen erhöhten Gasdruck nicht oder nur stark unterproportional gesteigert werden. Die mit der Modellanordnung gewonnenen Erkenntnisse sind nachweislich auf Isolatoren kommerzieller Anlagen übertragbar. Das in der vorliegenden Arbeit untersuchte Überschlagsverhalten von Gas-Feststoff-Isoliersystemen unter Gleichspannungsbelastung wird maßgeblich durch die Temperaturverteilung und durch feste Störstellen auf der Grenzfläche beeinflusst. Oberflächen- und Raumladungen verändern das üblicherweise ohmsch-kapazitiv beschriebene Verhalten des Isolierstoffsystems bei Gleich- und Mischspannungsbelastung. Der Einfluss zusätzlicher Ladungsträger auf die stark temperaturabhängige Feldumbildung demonstriert, dass das Isoliergas in diesem Fall mit teilchendichte- und feldstärkeabhängigen Drift- und Diffusionsprozessen zur Modellierung des transienten Verhaltens von Gleichspannungssystemen berücksichtigt werden muss. Die Untersuchung des Systemverhaltens an den Grenzen des Isolationsvermögens ist wichtiger Bestandteil bei der Entwicklung innovativer Technologien der modernen Energieübertragung bei steigender Übertragungsleistung. / DC operated gas-insulated systems combine the demand for space saving installations and lowloss energy transport over long distances for applications of recent energy transmission. In order to ensure a reliable and safe operation, the behaviour of the gas-solid insulation, which is used in the technological system, has to be known up to the limits of the insulation properties. Hence, this thesis deals with the flashover behaviour of gas-solid insulation systems under DC voltage stress. Thereby, it focuses on two main influence factors: the temperature, due to real current heat losses, and an adhesive defect on the gas-solid interface, due to metallic particles that cannot be fully excluded in practice. Firstly, it is investigated experimentally in two test arrangements, how each parameter separately affects the electrical field distribution, the surface and volume charge accumulation and the insulation performance under DC voltage stress. Following that, their interaction and mutual influence is analysed in the whole system. Due to operating currents, the heating of the conductors in gas-insulated systems causes an inhomogeneous temperature distribution, that affects the properties of the insulating materials gas and epoxy resin. The temperature-dependent conductivity of the solid insulators leads to a temperature-dependent field distribution. Thereby, the location of the highest field strength is shifted. Since the absolute value of the highest field strength can increase, the insulation performance can decrease. Simultaneously, the insulating gas close to the heated conductor locally has a lower gas density and therefore a lower dielectric strength. The thermal related reduction of the insulation performance under DC voltage stress amounts to (25 ... 35) % in the investigated arrangement. Metallic particles, with a length of more than three millimetres and adhering on spacers, turn out to be particularly critical in the weakly inhomogeneous field of gas-insulated systems. At pressures below 0,3 MPa, partial discharges at the particle tips partly ignite already at 50 %of the breakdown voltage without a particle. The corona stabilisation leads to a relatively high flashover voltage. However, due to these stable glow discharges under DC voltage stress, the defect can not be unequivocally proven by usual detection methods. Above 0,3 MPa, no partial discharges occur before the flashover. Due to the missing corona stabilisation, with a higher gas pressure, the insulation strength is not or only disproportionately low increasing. The findings gained with the model arrangement are evidently applicable to spacers of commercial installations. The flashover behaviour of gas-solid insulation systems under DC voltage stress, examined in this thesis, is influenced significantly by the temperature distribution and adhesive particles on the interface. Surface and volume charges change the generally resistive-capacitive described behaviour of the insulation system under DC and superimposed voltage stress. The influence of additional charge carriers on the strongly temperature-dependent field transition demonstrates, that in this case, the insulating gas with its drift and diffusion processes, depending on the particle density and the field strength, has to be considered, when modelling the transient behaviour of DC operated systems. Investigating the system behaviour to the limits of the insulation properties is a crucial element of developing innovative technologies of the modern energy transmission at increasing transmissions powers.

<p>Clusters are finite ensembles of atoms or molecules with sizes in the nanometer regime (<i>i.e.</i> nanoparticles). This thesis present results on the geometric and electronic structure of homogeneous and heterogeneous combinations of atoms and molecules. The systems have been studied with synchrotron radiation and valence, core and Auger electron spectroscopic techniques.</p><p>The first theme of the thesis is that of mixed clusters. It is shown that by varying the cluster production technique both structures that are close to that predicted by equilibrium considerations can be attained as well as far from equilibrium structures.</p><p>Electronic processes following ionization constitute the second theme. The post-collision interaction phenomenon, energy exchange between the photo- and the Auger electrons, is shown to be different in clusters of argon, krypton and xenon. A model is proposed that takes polarization screening in the final state into account. This result is of general character and should be applicable to the analysis of core level photoelectron and Auger electron spectra of insulating and semi-conducting bulk materials as well.</p><p>Interatomic Coloumbic Decay is a process that can occur in the condensed phases of weakly bonded systems. Results on the time-scale of the process in Ne clusters and mixed Ar/Ne clusters are herein discussed, as well observations of resonant contributions to the process. In analogy to Auger <i>vis-à-vis</i> Resonant Auger it is found that to the ICD process there is a corresponding Resonant ICD process possible. This has later been observed in other systems and by theoretical calculations as well in subsequent works by other groups.</p><p>Delocalization of dicationic valence final states in the hydrogen bonded ammonia clusters and aqueous ammonia has also been investigated by Auger electron spectroscopy. With those results it was possible to assign a previously observed feature in the Auger electron spectrum of solid ammonia.</p>

Clusters are finite ensembles of atoms or molecules with sizes in the nanometer regime (i.e. nanoparticles). This thesis present results on the geometric and electronic structure of homogeneous and heterogeneous combinations of atoms and molecules. The systems have been studied with synchrotron radiation and valence, core and Auger electron spectroscopic techniques. The first theme of the thesis is that of mixed clusters. It is shown that by varying the cluster production technique both structures that are close to that predicted by equilibrium considerations can be attained as well as far from equilibrium structures. Electronic processes following ionization constitute the second theme. The post-collision interaction phenomenon, energy exchange between the photo- and the Auger electrons, is shown to be different in clusters of argon, krypton and xenon. A model is proposed that takes polarization screening in the final state into account. This result is of general character and should be applicable to the analysis of core level photoelectron and Auger electron spectra of insulating and semi-conducting bulk materials as well. Interatomic Coloumbic Decay is a process that can occur in the condensed phases of weakly bonded systems. Results on the time-scale of the process in Ne clusters and mixed Ar/Ne clusters are herein discussed, as well observations of resonant contributions to the process. In analogy to Auger vis-à-vis Resonant Auger it is found that to the ICD process there is a corresponding Resonant ICD process possible. This has later been observed in other systems and by theoretical calculations as well in subsequent works by other groups. Delocalization of dicationic valence final states in the hydrogen bonded ammonia clusters and aqueous ammonia has also been investigated by Auger electron spectroscopy. With those results it was possible to assign a previously observed feature in the Auger electron spectrum of solid ammonia.