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<p>This thesis describes the development of a method to measure <em>in vivo</em> gadolinium (Gd) content by prompt gamma neutron activation analysis (PGNAA). PGNAA is a quantitative measurement technique that is completely non-invasive. Gadolinium has the highest thermal neutron capture cross section of all the stable elements. Gadolinium-based contrast agents are widely used in magnetic resonance imaging (MRI). The primary intention of this work is to quantify <em>in vivo</em> Gd retention to investigate the potential toxicity of these agents. This study involves the optimization of the McMaster University ²³⁸Pu/Be PGNAA facility for Gd measurements. Monte Carlo simulations were performed in parallel with the experimental work using MCNP version 5. Excellent agreement has been demonstrated between the Monte Carlo model of the system and the experimental measurements (both sensitivity and dosimetry). The initial study on the sensitivity of Gd demonstrated the feasibility of the measurement system. The Monte Carlo dosimetry simulations and experimental survey measurements demonstrated consistently that the radiation exposures for a single measurement were quite low, with an effective dose rate of 1.1 µSv/hr for a leg muscle measurement, 74 µSv/hr for a kidney measurement, and 48 µSv/hr for a liver measurement. The initial studies confirmed the Gd measurement feasibility which ultimately led to an <em>in vivo</em> pilot study on 10 healthy volunteers. The pilot study was successful with 9 out of 10 volunteers having measureable Gd in muscle above the <em>in vivo</em> detection limit of 0.58 ppm within 1 hour of administration, and the remaining participant had detectable Gd 196 minutes post administration. The concentrations measured ranged from 6.9 to 56 uncertainties different from zero. The system has been validated in humans and can now be used in future studies of short or long-term retention of Gd after contrast administration in at risk populations, such as those with reduced kidney function, patients with multiple exposures over the treatment period, and patients who are prescribed higher dosages. In addition, experiments and simulations were extended to another high neutron absorbing element, samarium (Sm).</p> / Doctor of Philosophy (PhD)

Nuclear physics tells us a lot about astrophysics, particularly the energy generation in stars. The present work is a thesis in experimental nuclear physics, reporting the results of 30S radioactive beam development for a future experiment directly measuring data to extrapolate the 30S(α,p) stellar reaction rate in Type I X-ray bursts, a phenomena where nuclear explosions occur repeatedly on the surface of accreting neutron stars. On the astrophysics side, the work details basic stellar physics and stellar reaction formalism in Chapter 1, the behaviour of compact stars in Chapter 2, and a full literature review of Type I X-ray bursts in Chapter 3. Nuclear experiments are non-trivial, and the results reported here were not accomplished by the author alone. Stable-beam experiments are technically challenging and involved, but for the case at hand, the halflife of 30S is a mere 1.178 seconds, and in order to measure reaction cross-sections, we must make a beam of the radionuclide 30S in situ and use these rare nuclei immediately in our measurement. Particle accelerator technology and radioactive ion production are treated in Chapter 4, and the experimental facility and nuclear measurement techniques are discussed in some detail in Chapter 5. In order to perform a successful future experiment which allows us to calculate the stellar 30S(α, p) reaction rate, calculations indicate we require a 30S beam of ~ 10^5 particles per second at ~ 32 MeV. Based on our recent beam development experiments in 2006 and 2008, it is believed that such a beam may be fabricated in 2009 according to the results presented in Chapters 6 and 7. We plan to measure the 4He(30S,p) cross-section at astrophysical energies in 2009, and some remarks on the planned (α,p) technique are also elucidated in Chapters 5, 6 and 7. / Thesis / Master of Science (MSc)

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Although widely recognized in the research community as one of the most accurate non-destructive methods for the determination of residual stress in polycrystalline structural materials, X-ray diffraction has not been widely adopted in the field. This is partly due to the fact that such measurements require, most often, a well-trained user with knowledge in both materials and mechanical sciences in addition to the specific know-how of the instrument. We believe that computer assistance could contribute to the promotion of this technique by increasing the productivity and accuracy of these measurements. We have developed a prototype of an expert system, using Nexpert Object's shell, to assist a non-trained operator in the validation and interpretation of X-ray diffraction residual stress data. The present work describes this prototype which has been designed to confirm the feasibility of the concept. Its knowledge base contains relevant examples of the rules necessary for data validation. The prototype has also validated most of the concepts required for the implementation of a full-scaled version by evaluating all of the major technical features such as graphics representation, external routine calls, and databases access. We have implemented significant rules to validate an experiment, link our expert system with a database management system, develop a superset of data able to receive output from any existing X-ray machine, and are working with a statistical pattern recognition software to discriminate between various d-vs-sin²Psi curves, to classify our data. / Master of Science

Soft materials are indispensable components of energy storage and conversion technologies necessary for the renewable energy transition. Two key examples are electrolytes used in solid-state batteries and ion-exchange membranes used in electrolysis and electrodialysis. The figures of merit for these applications are often summarized using upper-bound relationships, which define the best possible combination of performance metrics for a given material. A promising route to break the upper-bound and to improve upon the state-of-the-art is engineering materials at the nanoscale. Two commonly employed strategies are the use of block copolymers and polymer nanocomposites. In the former, the sequence of different monomers along the backbone of the polymer chain is varied; in the latter, ceramic nanoparticles are mixed with polymers and processed to achieve different dispersion states. In both of these classes of materials, the self-assembly of molecular and colloidal components controls the structure and function of the resulting material. This dissertation investigates these structure-property relationships in model soft nanomaterials, namely colloids, polymer nanocomposites, and ion-exchange membranes, using experiments, molecular dynamics simulations, and theory. The dissertation can be divided into three parts. The first, Chapters 2 and 3, investigates polymer and polymer nanocomposite electrolytes for applications in solid-state Li batteries. Chapter 2 investigates the coarse-graining and force field parameterization of polymer electrolytes for molecular dynamics simulations. Chapter 3 reports the experimental characterization of polymer nanocomposite electrolytes, with a key focus on understanding how the particle dispersion state affects the ionic conductivity and mechanical reinforcement of the composite. The second part, Chapters 4 and 5, studies fundamental structure-property relationships in two types of polymer nanocomposites. In Chapter 4, the surface chemistry of hydrophilic silica nanoparticles is altered to promote miscibility in organic solvents and in semicrystalline polymers. In these "bare" nanocomposites, the particles are stabilized against aggregation via the adsorption of a polymer bound layer, which is quantitatively studied via small angle X-ray scattering. In Chapter 5, the surface-modified particles are densely grafted with polymer chains via surface-initiated polymerization to obtain matrix-free polymer grafted nanoparticle films. The collective dynamics of the nanoparticle cores in these self-supporting films, where all of the polymer is grafted to the particle surface, is then measured using X-ray photocorrelation spectroscopy at a variety of temperatures. In Chapters 6 and 7, random copolymer chemistries are used to create cation- and anion-exchange membranes, respectively, with controlled ion-exchange capacity and swelling behavior. The key finding of Chapter 6 is that water-lean cation-exchange membranes selectively transport ions with low free energies of hydration, allowing the design of specific-ion selective electrodialysis stacks for Li+ recovery applications. The analogous properties of anion-exchange membranes are suggested as an avenue for future research.

The upcoming Laser Interferometer Space Antenna (LISA) is expected to detect gravitational waves (GWs) from massive black hole binaries (MBHB). Finding the electromagnetic (EM) counterparts for these GW events will be crucial for understanding how and where MBHBs merge, measuring their redshifts, constraining the Hubble constant and the graviton mass, and for other novel science applications. However, due to poor GW sky localization, multi-wavelength, time-dependent electromagnetic (EM) models are needed to identify the right host galaxy. This dissertation investigates electromagnetic (EM) signatures to accompany compact black hole binaries, specifically those that occur prior to, during, and following the merger, as well as those originating via self-lensing flares (SLFs). Chapter 2 considers equal-mass merging massive black hole binaries (MBHBs) embedded in a circumbinary disk (CBD), using high-resolution two-dimensional simulations, with a 𝚪-law equation of state, incorporating viscous heating, shock heating, and radiative cooling. Beginning from before the decoupling limit and transitioning through into post-merger, distinct EM features are identified before, during, and after the merger. The main result is that the MBHB produces strong thermal X-ray emission until 1-2 days prior to the merger. However, as the binary decouples from the CBD, the X-ray-bright minidisks rapidly shrink in size, become disrupted, and the accretion rate drops precipitously. As a result, the thermal X-ray luminosity drops by orders of magnitude, and the source remains X-ray dark for several days, regardless of any post-merger effects such as gravitational wave (GW) recoil or mass loss. Looking for this abrupt spectral change where the thermal X-ray disappears is a tell-tale EM signature of LISA mergers that does not require extensive pre-merger monitoring. Chapter 3 follows up on and extends the results of Chapter~\ref{chap:ch2} by investigating the effects to the EM spectrum for unequal-mass MBHBs via comparable simulations. This work corroborates the findings of a several order of magnitude drop in the thermal X-ray luminosity near the time of merger, but with delayed timing than found in an equal-mass system, while the source still remains X-ray dark for hours post-merger. The main result, however, is a new signature, a sharp spike in the thermal X-ray emission just before the tell-tale steep drop occurs. This adds an additional EM signature that can be used to identify EM counterparts of LISA's unequal MBHBs before the merger and potentially measure the mass ratio of the system through EM means. Finally, Chapter 4 addresses the EM signature of self-lensing flares (SLFs). SLFs are expected to be produced once or twice per orbit by an accreting MBHB, if the eclipsing MBHBs are observed close to edge-on. Again, using high-resolution two-dimensional viscous hydrodynamical simulations of a CBD embedding a MBHB, a very high-cadence output of these hydrodynamical simulation is used as inputs for a general-relativistic ray-tracing code to produce synthetic spectra and phase-folded light curves. The main results show a significant periodic amplification of the flux with the characteristic shape of a sharp flare with a central dip, as the foreground black hole (BH) transits across the minidisk and shadow of the background BH, respectively. These corroborate previous conclusions based on the microlensing approximation and analytical toy models of the emission geometry. A realistic concern with incorporating a physical disk was that the CBD might obscure our view of the SLF, considering they only appreciably occur for a near edge-on line of sight. However, this work shows that the CBD is in fact more a friend than foe in the detection, because while the CBD does indeed block other sources of emission that constitute noise, the bent trajectories of the light from the lensed minidisks remain visible even for these edge-on configurations.

Dans le domaine des couches minces (épaisseur~Å) associant un métal magnétique (Fe, Co, Ni) et un élément non magnétique (essentiellement métallique ou isolant), de remarquables propriétés physiques (aimantation, transport) nécessitent des caractérisations structurales fines. En particulier, citons le cas de jonctions tunnel (métal/isolant/métal) à aimantation perpendiculaire qui sont en cours d'étude au laboratoire Spintec (UMR8191 (CEA/CNRS/UJF). Ces nanomatériaux sont déposés par voie physique (pulvérisation cathodique) au sein de ce laboratoire. Ces nanostructures sont également sondées par diffraction aux rayons X au sein de l'Institut Néel (UPR 2940) via une collaboration entre Spintec et une équipe de cet Institut (Surface, interfaces et nanostructures du Département MCMF, Matière Condensée, Matériaux, et Fonctions). Ces mesures de réflectivité X constituent la sonde privilégiée de choix dans la cadre de cette thèse. D'autres voies sont également exploitées: à l'aide des moyens de rayonnement synchrotron tels que la spectroscopie d'absorption de rayons X : EXAFS, XANES et XMCD. La thèse aura pour but d'étudier expérimentalement ces phénomènes en couches continues sur ces empilements à jonction tunnel avec aimantation perpendiculaire. Plus précisément, le travail de thèse permettra de comprendre les mesures magnétiques (effectuées à l'institut Néel notamment par magnétométrie SQUID et HALL à basse température) grâce à une batterie de mesures structurales (diffraction aux rayons X, rasant, figures de pôles, réflectivité, absorption X ...). Notamment, l'influence des paramètres de dépôt (types de couches, épaisseurs, recuits) du matériau sont étudiées via la collaboration entre les différents groupes de recherche précédemment cités. Cette thématique s'inscrit d'une part dans le cadre de travaux menés à Spintec et dédiés à la recherche de nouveaux matériaux à forte valeur ajoutée industrielle (sur le stockage d'information à ultrahaute densité sur media discrets par exemple). Elle s'inscrit d'autre part dans le renforcement de liens entre recherches fondamentales (laboratoire propre du CNRS comme l'institut Néel) et appliquées (CEA), avec un recours aux solides compétences en caractérisations structurales et magnétiques de l'Institut Néel.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Detriments caused by ionizing radiation are the reason of many studies in medical physics. Both in experimental and computational fields, many studies seek to limit the risks involved in the practice with ionizing radiation. Accordingly, the field of computational simulation seeks to create scenarios in the most realistic way in order to measure with the greatest precision the radiation doses deposited in organs and tissues of patients, workers and the public. In this study, we generated scenarios that simulate exams involving mobile radiography equipment in beds of clinics and hospital. Through a pair of computational phantons, these scenarios allow the calculation of effective dose values and the conversion coefficients for individuals from the public and pacient based on the physical quantity absorbed dose. One of the simulators were irradiated with the direct beam (patient) simulating examinations of thorax and abdomen, each one with two fields of irradiation. For each of these situations, the X rays spectra were varied from 60 to 80 keV. The other simulator was positioned by the side of the patient simulator (individual from the public) from different distances for the assessment of the effective dose generated by the scattered beam and the subsequent calculation of the conversion coefficients. Regarding the effective dose measured in the patient, we obtained the maximum increase between the irradiation fields of 53,1% for thorax examination with 80 kVp. For abdomen examination, we obtained a maximum increase between the fields of irradiation of 6,4% to the beam of 80 kVp. For the radiation doses in the individual from the public, coming from the scattered beam, the maximum percentage difference between the ideal field and the extrapolated field was 76,1% when the beam was positioned at 50 cm away from the patient in a abdomen exam with 60 kVp. For the pacient, the greatest risk of cancer was 43,46.10-6 mGy-1 for extrapolated field with 80 kVp for abdomen examinations. For the individuals from the public, positioned at 200 cm, the risk of cancer decreases 83,0%, when it was positioned at 50 cm. Finally, radiation doses evaluated for a typical scenario in a hospital or clinic that provides services through mobile X ray equipment allows the measurement of possible damages related to this practice, both for the patient as for the individual from the public. / Os detrimentos causados pela radiação ionizante são a razão de diversos estudos na área da física médica. Tanto na área experimental quanto no campo computacional, diversos estudos buscam limitar os riscos que envolvem a prática com radiação ionizante. Nesse sentido, a área da simulação computacional busca criar cenários da forma mais real possível para mensurar com maior precisão as doses de radiação depositadas em cada órgão e tecido dos pacientes, trabalhadores e do público. Neste trabalho foram gerados cenários que simularam exames envolvendo equipamento de radiografia móvel em leitos de clínicas e hospitais. Através de uma dupla de simuladores computacionais, estes cenários permitem calcular os valores de dose efetiva bem como os coeficientes de conversão para indivíduos do público e pacientes baseados na grandeza física dose absorvida. Um dos simuladores foi irradiado com o feixe direto (paciente) simulando exames de tórax e abdômen, cada um com dois campos de irradiação. Para cada uma destas situações os espectros do feixe foram variados de 60 a 80 keV. O outro simulador foi posicionado ao lado (indivíduo do público) em diferentes distâncias para a avaliação da dose efetiva gerada pelo feixe espalhado e posterior cálculo dos coeficientes de conversão. Em relação à dose efetiva medida no paciente, foi obtido um aumento máximo entre os campos de irradiação de 53,1% para o exame de tórax com 80 kVp. Para o exame de abdômen foi obtido um aumento máximo entre os campos de irradiação de 6,4% para o feixe de 80 kVp. Para as doses de radiação, no indivíduo do público, proveniente do feixe espalhado, a diferença percentual máxima entre o campo ideal e o campo extrapolado foi de 76,1% quando o mesmo foi posicionado a 50 cm em um exame de abdômen com 60 kVp. Para o paciente, o maior risco de câncer foi de 43,46.10-6 mGy-1. para campo extrapolado a 80 kVp para exames de abdômen. Para um indivíduo do público posicionado a 200 cm, o risco de câncer diminui 83,0% quando o mesmo estava posicionado a 50 cm. Por fim, as doses de radiação avaliadas para um cenário típico em clínica e hospitais que prestam serviço com equipamento móvel de raios X permitem mensurar os possíveis danos relacionados a esta prática, tanto para o paciente quanto para o indivíduo do público.