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Includes bibliographical references. / The origin of the experimentally observed density dependence of the effective muon alpha sticking fraction will in muon catalyzed deuterium- tritium fusion has been comprehensively reanalyzed with the particular emphasis put on the density dependence of the stopping power in dense hydrogen. The main technical details and improvements in this work are: The (aμ)+ 2s and 2p states are treated independently and are assigned individual reaction rates. The essential muonic excitation rates have been recalculated taking into account finite nuclear mass effects. The stopping power for a charged projectile in liquid heavy hydrogen is modified to account for dynamic screening effects and a density dependent effective ionization potential. It is shown that the medium dependent stopping power for the (aμ)+ ion is the crucial entity controlling the density dependance of the effective sticking fraction. It is also pointed out that the muonic helium Ka X-ray yield and the sticking fraction at high density can not be simultaneously brought into agreement with the experimental results without invoking novel mechanisms suppressing Stark mixing in the (Heμ) L-shell.

Includes bibliographical references. / A Monte Carlo code MUGLU has been, written for the simulation of experiments to measure alpha-muon sticking in muon catalysed deuterium-tritium fusion. The experiments simulated are those which measure the ratio of αμ to α from fusion in a low density gas target by detecting collinear alpha-neutron coincidences and relying on the differing stopping powers of the α and αμ ions. The Monte Carlo simulations provide estimates of geometrical and detection efficiency factors required for the calculation of the sticking coefficient from the experimental measurements. Simulations have been made of alternative experimental geometries in order to investigate the α-neutron coincidence signature and other characteristics of existing and proposed systems. The characteristics of a neutron detector used in, one of the current sticking experiments (Rutherford Appleton Laboratory) have been studied experimentally, as well as simulated, using the T(d,n)α reaction to emulate the fusion source. The results obtained show that the dependence of the neutron detection efficiency on the position and angle of neutron incidence on the detector is significant and should be taken into account when determining sticking coefficients from alpha-neutron coincidence measurements.

The radiological hazards from tritium are usually associated with exposure to tritium oxide either by inhalation, ingestion or permeation through skin. However, exposure from skin-contact with tritium gas contaminated surfaces represents a different radiological hazard in tritium removal facilities and future fusion power plants. Previous experiments on humans by Eakins et al. (8), and more recent experiments on hairless rats at Chalk River Laboratories have shown that when a tritium gas-contaminated surface is brought into contact with intact skin, high concentrations of organically-bound tritium in urine and skin are observed which were not seen from single tritiated water (liquid or vapour form) contamination. The results of the rat experiments, which involved measurements of tritium activity in urine and skin, after contact with contaminated stainless steel, are described. These results are also compared to previous data from human experiments. The effect of various exposure conditions and different contaminated surfaces such as brass, aluminum and glass are analysed and related to the results from contaminated stainless steel exposure. Dosimetric models are being developed in order to improve the basis for dose assessment for this mode of tritium uptake. The presently studied model is explained along with the assumptions and methods involved in its derivation. The features of 'STELLA', the software program used to implement the model, are discussed. The methods used to estimate skin and whole body dose from a model are demonstrated. Finally, some experiments for improving the accuracy of the model are proposed. Briefly, this study compares the results from animal and human experiments as well as different exposure conditions, and determine the range of whole body and skin dose that may be involved from skin-contact intake. This information is essential for regulatory purposes particularly in the derivation of doses for skin-contact contamination. / Thesis / Master of Science (MS)

Mono-energetic neutrons have been produced with the low-voltage Cockroft-Walton accelerator at North Texas State College using two different reactions. It is the purpose of this paper to report the angular distribution and total flux of the neutrons obtained from the T(D,n) reaction.

This dissertation surveys the history of tritium beginning in Ernest Rutherford's lab in 1934 with its discovery and ending at the Fukushima Daiichi disaster site in 2023 when TEPCO began releasing tritiated wastewater into the Pacific ocean. In this time, expert conceptions of tritium have experienced interdependent and overlapping phases. Each phase is characterized by a dominant "nuclearity" and situated in context of "nuclear exceptionalism" (Hecht 2014) that directly and indirectly affects material conditions, elite decision-making, and radiological impacts on the environment and human health. Because it is pervasive, diffuse, and laborious to measure, a great deal of uncertainty surrounds tritium's contribution to radiological risks. Beyond various commercial and scientific uses, it is also integral to both nuclear energy as a waste and nuclear weapons as a mechanism for dramatically increasing explosive yields. This versatile and powerful material operates at the technological nexus of two existential risks for humanity: climate change and nuclear weapons. I divide the history of tritium into three distinct phases. First, super nuclearity characterizes early designs for the "superbomb" by Manhattan project scientists who believed vast amounts of tritium would be required. This phase extends to the late 1950s when thermonuclear warheads based on more feasible designs requiring significantly less tritium were beginning to be incorporated into the U.S. nuclear weapon stockpile. Second, special nuclearity describes the status of tritium throughout the Cold War as a critical nuclear weapons material that was referred to and treated as a special nuclear material (SNM) in practice even though it was never legally defined as such. Third, byproduct nuclearity is the current post-Cold War paradigm defining tritium as a form of incidental waste or as an innocuous "other accountable material" intentionally produced by the nuclear fission process. While tritium's super nuclearity proved to be an animating fiction with political and material impacts on the early U.S. post war nuclear weapons program, tritium's special and byproduct nuclearities have since been fully embodied in technological artifacts—primarily nuclear weapons and nuclear power plants—and remain in dynamic tension. Tritium does not fit neatly into existing nuclearity narratives. It is accurately referred to as both "highly" and "weakly" radioactive. Having a half-life of ~12 years and being the lightest radioisotope, it has high activity by weight, but when it decays into stable helium-3 it emits only a relatively weak beta particle which poses a potential risk as internal dose. I argue that the nuclearity processes constituting various conceptualizations of tritium provide insight into navigating the complex sociotechnical relationships between humans and nuclear technology. Additionally, I anticipate tritium's next nuclearity transformation as reactor fuel for a still nascent fusion power industry. I argue that rather than allowing fusion energy proponents to dictate the next phase of tritium's nuclearity, efforts should be made to assess and synthesize salient aspects of this unique material to provide a more holistic accounting of its risks, benefits, and tradeoffs. / Doctor of Philosophy / Hydrogen is the most abundant element in the universe. It fuels the stars and forms compounds like water that are essential to life. Most atoms of hydrogen contain one proton and one electron, but hydrogen also has two less common, naturally occurring "heavy" forms that additionally contain neutrons. One is deuterium, which contains one neutron and can be concentrated to make heavy water. The other type of hydrogen is tritium, which contains two neutrons. This dissertation is about tritium, an extremely rare and valuable material that can be used to produce a faint green light source without electricity, to increase the explosive power of nuclear weapons, or to fuel fusion power reactors. Tritium is also a radioactive waste material produced by both military and civilian nuclear activities. I divide the history of tritium into three phases: super, special, and byproduct. When tritium was first discovered in 1934, it was an exotic scientific curiosity. During the 1940s, scientists with the Manhattan Project began working out how tritium could be weaponized into a "superbomb" that would be vastly more powerful than the atomic bombs the U.S. dropped on Japan in WWII. While the "superbomb" designs proved to be unviable, powerful hydrogen weapons were developed in the 1950s that relied on tritium alongside specially prepared masses of uranium and plutonium. To limit the spread of nuclear weapons, these special forms of uranium and plutonium have been tightly regulated as special nuclear material (SNM). Tritium, on the other hand, never met the legal definition of SNM but was nonetheless treated as a "special" material throughout the Cold War until the 1990s. Tritium has remained a critical material for all modern nuclear weapons, but in the last thirty years it has been primarily thought of and regulated as a byproduct material. Because the radiological risks posed by tritium are ambiguous and technically challenging to measure at low concentrations, many proponents of nuclear technologies suggest that they are negligible and, at the same time, anti-nuclear activists claim that more research is needed to show tritium's dangers clearly. I argue that it is important to prioritize a more thorough assessment of tritium's radiological risks and role in nuclear weapons before the implementation of large-scale fusion technologies that will require the production of many thousands more times the amount of tritium currently available in the world.

Metabolically active microbial communities are present in a wide range of subsurface environments. Techniques like enumeration of microbial cells, activity measurements with radiotracer assays and the analysis of porewater constituents are currently being used to explore the subsurface biosphere, alongside with molecular biological analyses. However, many of these techniques reach their detection limits due to low microbial activity and abundance. Direct measurements of microbial turnover not just face issues of insufficient sensitivity, they only provide information about a single specific process but in sediments many different process can occur simultaneously. Therefore, the development of a new technique to measure total microbial activity would be a major improvement. A new tritium-based hydrogenase-enzyme assay appeared to be a promising tool to quantify total living biomass, even in low activity subsurface environments. In this PhD project total microbial biomass and microbial activity was quantified in different subsurface sediments using established techniques (cell enumeration and pore water geochemistry) as well as a new tritium-based hydrogenase enzyme assay. By using a large database of our own cell enumeration data from equatorial Pacific and north Pacific sediments and published data it was shown that the global geographic distribution of subseafloor sedimentary microbes varies between sites by 5 to 6 orders of magnitude and correlates with the sedimentation rate and distance from land. Based on these correlations, global subseafloor biomass was estimated to be 4.1 petagram-C and ~0.6 % of Earth's total living biomass, which is significantly lower than previous estimates. Despite the massive reduction in biomass the subseafloor biosphere is still an important player in global biogeochemical cycles. To understand the relationship between microbial activity, abundance and organic matter flux into the sediment an expedition to the equatorial Pacific upwelling area and the north Pacific Gyre was carried out. Oxygen respiration rates in subseafloor sediments from the north Pacific Gyre, which are deposited at sedimentation rates of 1 mm per 1000 years, showed that microbial communities could survive for millions of years without fresh supply of organic carbon. Contrary to the north Pacific Gyre oxygen was completely depleted within the upper few millimeters to centimeters in sediments of the equatorial upwelling region due to a higher supply of organic matter and higher metabolic activity. So occurrence and variability of electron acceptors over depth and sites make the subsurface a complex environment for the quantification of total microbial activity. Recent studies showed that electron acceptor processes, which were previously thought to thermodynamically exclude each other can occur simultaneously. So in many cases a simple measure of the total microbial activity would be a better and more robust solution than assays for several specific processes, for example sulfate reduction rates or methanogenesis. Enzyme or molecular assays provide a more general approach as they target key metabolic compounds. Since hydrogenase enzymes are ubiquitous in microbes, the recently developed tritium-based hydrogenase radiotracer assay is applied to quantify hydrogenase enzyme activity as a parameter of total living cell activity. Hydrogenase enzyme activity was measured in sediments from different locations (Lake Van, Barents Sea, Equatorial Pacific and Gulf of Mexico). In sediment samples that contained nitrate, we found the lowest cell specific enzyme activity around 10^(-5) nmol H_(2) cell^(-1) d^(-1). With decreasing energy yield of the electron acceptor used, cell-specific hydrogenase activity increased and maximum values of up to 1 nmol H_(2) cell^(-1) d^(-1) were found in samples with methane concentrations of >10 ppm. Although hydrogenase activity cannot be converted directly into a turnover rate of a specific process, cell-specific activity factors can be used to identify specific metabolism and to quantify the metabolically active microbial population. In another study on sediments from the Nankai Trough microbial abundance and hydrogenase activity data show that both the habitat and the activity of subseafloor sedimentary microbial communities have been impacted by seismic activities. An increase in hydrogenase activity near the fault zone revealed that the microbial community was supplied with hydrogen as an energy source and that the microbes were specialized to hydrogen metabolism. / Mikrobielle Gesellschaften und ihre aktiven Stoffwechselprozesse treten in einer Vielzahl von Sedimenten unterschiedlichster Herkunft auf. In der Erforschung dieser tiefen Biosphäre werden derzeit Techniken wie Zellzählungen, Aktivitätsmessungen mit Radiotracer-Versuchen und Analysen der Porenwasserzusammensetzung angewendet, darüber hinaus auch molekularbiologische Analysen. Viele dieser Methoden stoßen an ihre Nachweisgrenze, wenn Sedimente mit geringer Zelldichte und mikrobieller Aktivität untersucht werden. Bei der Untersuchung von Stoffwechselprozessen mit herkömmlichen Techniken kommt dazu, dass von mehreren Prozessen, die zeitgleich ablaufen können, jeweils nur einer erfasst wird. Deswegen wäre die Entwicklung einer neuartigen Messtechnik für die gesamte mikrobielle Aktivität ein wesentlicher Fortschritt für die Erforschung der tiefen Biosphäre. Ein vielversprechender Ansatz, um die gesamte lebende Biomasse auch in Proben mit geringer Aktivität zu bestimmen, ist eine Hydrogenase-Enzym-Versuchsanordnung mit Tritium als quantifizierbarer Messgröße. In dieser Doktorarbeit wurde die gesamte mikrobielle Biomasse und Aktivität von unterschiedlichen Sedimentproben einerseits mit herkömmlichen Methoden (Zellzählungen, Analyse der Porenwasserzusammensetzung) als auch mit einer neu entwickelten Hydrogenase-Enzym-Versuchsanordnung quantifiziert. Mit einer großen Anzahl eigener Zellzählungsdaten von Sedimenten aus dem Äquatorialpazifik und dem Nordpazifik und ergänzenden publizierten Daten konnte gezeigt werden, dass Zellzahlen sich in ihrer globalen geographischen Verteilung je nach Bohrlokation um 5 bis 6 Größenordnungen unterscheiden. Dabei bestehen Korrelationen zur Sedimentationsrate und zur Entfernung zum Land, mit deren Hilfe sich die Gesamtbiomasse in Tiefseesedimenten zu 4,1 Petagramm-C abschätzen lässt. Das entspricht ~0,6 % der Gesamtbiomasse der Erde und ist damit erheblich weniger als in früheren Schätzungen angegeben. Trotz der Korrektur auf diesen Wert spielt die Biomasse der tiefen Biosphäre weiterhin eine erhebliche Rolle in biogeochemischen Kreisläufen. Um die Zusammenhänge zwischen Aktivität der Mikroben, der Häufigkeit ihres Auftretens und Zustrom von organischem Material zu verstehen, wurde eine Expedition ins Auftriebsgebiet des Äquatorialpazifiks und zum nordpazifischen Wirbel durchgeführt. Daten der Sauerstoffaufnahme in Sedimenten des nordpazifischen Wirbels, die mit Sedimentationsraten von 1 mm pro 1000 Jahren abgelagert werden, zeigen, dass mikrobielle Gesellschaften über Millionen von Jahren ohne Zufuhr von frischem organischen Kohlenstoff überleben konnten. Im Gegensatz zum nordpazifischen Wirbel wird in Sedimenten des äquatorialpazifischen Auftriebsgebiets Sauerstoff bei höherer mikrobieller Aktivität und Verfügbarkeit organischer Verbindungen oberflächennah in den ersten Milli- bis Zentimetern komplett umgesetzt. Auftreten und Variabilität von Elektronenakzeptoren nach Tiefe und Bohrlokation machen die tiefe Biosphäre zu einer komplexen Umgebung für die Quantifizierung der gesamten mikrobiellen Aktivität. Aktuelle Studien zeigen das verschiedene Elektronenakzeptorprozesse gleichzeitig ablaufen können, obwohl man bisher davon ausgegangen war, dass diese sich thermodynamisch ausschließen. In vielen Fällen wäre also eine einfache Methode zur Messung der gesamten mikrobiellen Aktivität eine bessere und verlässlichere Lösung aktueller Analyseaufgaben als Messungen mehrerer Einzelprozesse wie beispielsweise Sulfatreduktion und Methanogenese. Enzym-oder Molekular-Versuchsanordnungen sind ein prozessumfassender Ansatz, weil hier Schlüsselkomponenten der Stoffwechselprozesse untersucht werden. Das Hydrogenase-Enzym ist eine solche Schlüsselkomponente und in Mikroben allgegenwärtig. Deshalb kann die Quantifizierung seiner Aktivität mit der neu entwickelten Hydrogenase-Enzym-Versuchsanordnung als Parameter für die gesamte mikrobielle Aktivität der lebenden Zellen verwendet werden. Hydrogenase-Aktivitäten wurden in Sedimenten unterschiedlicher Lokationen (Vansee, Barentssee, Äquatorialpazifik, und Golf von Mexico) gemessen. In Sedimentproben, die Nitrat enthielten, haben wir mit ca. 10^(-5) nmol H_(2) cell^(-1) d^(-1) die geringste zellspezifische Hydrogenase-Aktivität gefunden. Mit geringerem Energiegewinn des genutzten Elektronenakzeptors steigt die zellspezifische Hydrogenase-Aktivität. Maximalwerte von bis zu 1 nmol H_(2) cell^(-1) d^(-1) wurden in Sedimentproben mit >10 ppm Methankonzentration gefunden. Auch wenn die Hydrogenase-Aktivität nicht direkt in die Umsatzrate eines spezifischen Prozesses konvertierbar ist, können zellspezifische Aktivitätsfaktoren verwendet werden, um die metabolisch aktive Mikrobenpopulation zu quantifizieren. In einer weiteren Studie mit Sedimenten des Nankai-Grabens zeigen Daten der Zelldichte und der Hydrogenase-Aktivität einen Einfluss von seismischen Ereignissen auf Lebensraum und Aktivität der mikrobiellen Gesellschaften. Ein Anstieg der Hydrogenase-Aktivität nahe der Verwerfungszone machte deutlich, dass die mikrobiellen Gesellschaften mit Wasserstoff als Energiequelle versorgt wurden und dass die Mikroben auf einen Wasserstoff-Stoffwechsel spezialisiert waren.

Lors du fonctionnement d'un réacteur de fusion nucléaire par confinement magnétique comme ITER, une fraction de tritium est piégée par les composants face au plasma et doit être mesurée pour des raisons de sureté nucléaire. La spectroscopie de plasma induit par laser est proposée pour effectuer cette mesure. Le plasma laser produit sur des tuiles de Tore Supra en composite à fibre de carbone est analysé à l'aide d'une étude paramétrique : il doit avoir une température supérieure à 10000 K et une densité électronique supérieure à 10^17 cm^-3 pour optimiser l'application. Une méthode "autocalibrée" prenant en compte l'auto-absorption des raies est utilisée pour déterminer la concentration relative d'hydrogène à partir des spectres expérimentaux. La caractérisation spatio-temporelle du panache d'ablation révèle la présence d'un gradient de température dirigé du centre vers la périphérie du plasma. La prise en compte de ce gradient permet de déduire le rapport des concentrations H/C. L'incertitude de la mesure est évaluée et discutée. La mesure du rapport isotopique D/H sous pression réduite d'argon met en évidence un effet de ségrégation qui doit être pris en compte afin d'éviter des erreurs de mesure de l'ordre de 50%. Les matériaux à base de tungstène sont analysés et les difficultés associées aux données spectroscopiques sont abordées. Enfin, la faisabilité de l'analyse LIBS résolue en profondeur est validée pour des échantillons métalliques multicouches préalablement étalonnés. / During the operation of a nuclear fusion device like the future reactor ITER, a fraction of tritium is trapped in the plasma facing components and has to be measured in order to fulfill nuclear safety requirements. Laser-induced breakdown spectroscopy is proposed to achieve this measurement. The laser plasma produced on carbon fibre composite tiles from the Tore Supra reactor is analyzed via a parametric study : it has to have a temperature over 10000 K and an electron density over 10^17 cm^-3 to optimize the application. A calibration-free procedure that takes into account self-absorption is proposed to determine the relative concentration of hydrogen from the experimental spectra. The time- and space-resolved spectral emission of the plasma plume is investigated and reveals the presence of a temperature gradient from the core towards the periphery. This gradient is taken into account and the H/C concentration ratio is deduced. The accuracy of the results is evaluated and discussed. The study of the D/H isotopic ratio under low pressure argon reveals the presence of plume segregation that leads to an error of about 50%, error that can partially be reduced. Tungsten materials are investigated and difficulties related to spectroscopic databases are discussed. Finally, the feasibility of LIBS analysis with depth resolution is validated for multilayered metallic samples.

Durant cette thèse nous avons, dans un premier temps, mis au point un protocole robuste pour quantifier l’échange de ligands à la surface de nano-objets, en prenant les quantum dots comme particules d’étude. Cette méthode se base sur la sensibilité de détection d’un élément radioactif, le tritium. Pour étudier l’échange de ligands, nous avons synthétisé de l’acide oléique tritié, dont l’équivalent non-marqué est un composé très couramment utilisé dans la chimie des QD. Nous avons élaboré un protocole permettant de déterminer la densité de ligands à la surface de quantum dots de type CdSe zinc blende par une méthode innovante. Par ailleurs, nous avons réalisé une étude permettant de déterminer la capacité qu’a un ligand à remplacer l’acide oléique présent à la surface des QD. On a ainsi obtenu une échelle des forces relatives de liaison de diverses fonctions chimiques suivant leur aptitude à déplacer l’acide oléique. Cette étude devrait permettre d’améliorer la compréhension et la mise au point des protocoles utilisés pour la préparation des QD. Dans un second temps, nous avons développé deux stratégies d’encapsulation de QD afin de les solubiliser dans l’eau avec comme objectif des applications en imagerie in vivo. Ces deux approches tentent de répondre aux nombreuses exigences liées à l’utilisation de QD en milieux biologiques. Dans cette optique, nous avons synthétisé des amphiphiles polymérisés d’une part et des amphiphiles perfluorés d’autre part. Des lots de QD, de type CdSe/CdS/ZnS émettant dans le visible, solubilisés selon ces deux stratégies ont été préparés et leur stabilité éprouvée dans plusieurs conditions. Nous avons ensuite appliqué l’encapsulation à des QD de type CuInS2/ZnS émettant dans le proche infrarouge. Des études préliminaire sont pu être réalisées par d’imagerie de fluorescence chez la souris afin d’évaluer in vivo ces nouvelles formulations de QD. / In this thesis we have, at first, developed a robust protocol to quantify the exchange of ligands on the surface of nano-objects, using quantum dots in this study. This method is based on the detection sensitivity of a radioactive element, tritium. To study the exchange of ligands, we synthesized tritiated oleic acid, whose unmarked equivalent is commonly used for the synthesis of QD. Thanks to an innovative method, we have developed a protocol to determine the density of ligands on the surface of zinc blende CdSe quantum dots. In addition, we conducted a study to determine the ability of a ligand to replace oleic acid on the surface of the QD. A scale of relative bond strengths of various chemical functions according to their ability to displace oleic acid has been obtained. This study is expected to improve the understanding and the development of protocols for the preparation of QD.In a second step, we developed two encapsulation strategies of QD in order to obtain colloidal stability in water with in vivo imaging applications as final aim. Both approaches attempt to answer the requirements for the use of QD in biological media. In this context, we have synthesized photopolymerisable amphiphilic compounds on the one hand and perfluorinated amphiphilic compounds on the other. Batches of CdSe/CdS/ZnS QD emitting in the visible, solubilized by these two strategies have been prepared and their stability tested in several conditions. We then applied the encapsulation strategy developed to CuInS2/ZnS QD emitting in the near infrared. Some preliminary studies have been carried out by in vivo fluorescence imaging in mice to assess these new QD formulations.