Components of the response function of a high-purity germanium (HPGe) detector due to full or partial energy deposition by gamma- and X-rays were studied. Experimental response functions for 241Am, Ba and Tb were compared with those obtained from the Monte Carlo simulations. The role of physical mechanisms for each component was investigated by considering escape/absorption of photons, photoelectrons, Auger electrons, recoil electrons and X-rays of the detector material. A detailed comparison of the experimental Compton, photoelectron, detector X-ray escape components and full-energy peaks with those obtained from Monte Carlo program are presented.

Compton cameras localize γ-ray sources in 3D space by observing evidence of Compton scattering with detectors sensitive to ionizing radiation. This thesis proposes a software system for operating a novel Compton camera device comprised of Timepix3 detectors and Katherine readouts. To communicate with readouts using UDP-based protocol, a dedicated hardware library was developed. The presented software can successfully control the acquisition of multiple Timepix3 detectors and simultaneously process their measurements in a real-time setting. To recognize instances of Compton scattering among observed interactions, a chain of algorithms is applied with explicit consideration for a possibly high volume of measured information. Unlike alternate approaches, the presented work uses a recently published charge drift time model to improve its spatial resolution. In order to achieve localization of γ-ray sources, the software performs conical back projection into a discretized cuboid volume. Results of randomized evaluation with simulated data indicate that the presented implementation is correct and constitutes a viable method of γ-ray source localization in 3D space. Experimental verification with a prototype model is in progress.

Submitted by Edileide Reis (leyde-landy@hotmail.com) on 2014-09-11T12:48:31Z No. of bitstreams: 1 Indianara Lima Silva.pdf: 1509291 bytes, checksum: 2ed3dccb4ce7bfcceee6850f9e4ce690 (MD5) / Approved for entry into archive by Fatima Cleômenis Botelho Maria (botelho@ufba.br) on 2014-09-11T15:52:46Z (GMT) No. of bitstreams: 1 Indianara Lima Silva.pdf: 1509291 bytes, checksum: 2ed3dccb4ce7bfcceee6850f9e4ce690 (MD5) / Made available in DSpace on 2014-09-11T15:52:46Z (GMT). No. of bitstreams: 1 Indianara Lima Silva.pdf: 1509291 bytes, checksum: 2ed3dccb4ce7bfcceee6850f9e4ce690 (MD5) / A figura de Arthur Holly Compton geralmente é concebida como um dos pais fundadores da mecânica quântica devido à sua formulação quântica para explicar o processo de interação entre a radiação de alta frequência e a matéria. Todavia, a história de Compton evidencia-nos um personagem que destoa da imagem de um físico interessado no desenvolvimento da teoria quântica. De fato, o seu interesse e a sua motivação, de 1917 a 1922, estavam relacionados com o uso da física clássica para o estudo do espalhamento dos raios X e γ pela matéria. A descoberta do efeito Compton foi o resultado obtido por um físico clássico que relutava em aceitar o quantum de radiação. O objetivo desta investigação é, portanto, destacar a imagem de um físico clássico que estava inserido em um programa de pesquisa bem definido, a física dos raios X e γ, a partir do qual ele contribuiu tanto para o desenvolvimento dessa área de pesquisa quanto para a construção da mecânica quântica. Nós discutiremos, neste trabalho, desde a hipótese do grande elétron até a abordagem quântica construída por Compton para explicar o processo de espalhamento da radiação X e γ pela matéria.

L'hadronthérapie est une technique innovante de radiothérapie par ions carbone ou protons visant à améliorer les traitements actuels. La précision balistique accrue renforce la nécessité d'un contrôle du dépôt de dose, si possible en temps réel. Une manière de réaliser ce contrôle est de détecter avec une caméra Compton le gamma prompt émis lors des fragmentations nucléaires pendant l'irradiation du patient. Dans un premier temps, la géométrie de deux types de caméra Compton (double diffusion puis simple diffusion) a été optimisée par simulation Monte Carlo. Cette optimisation a été réalisée en étudiant la réponse des caméras à une source ponctuelle de photons avec un spectre en énergie réaliste. La réponse de la caméra optimisée à l'irradiation d'un fantôme d'eau par un faisceau d'ions carbone ou de protons a ensuite été simulée. Ces simulations ont tout d'abord été confrontées à des mesures effectuées avec un prototype de taille réduite. Ces mesures ont ensuite été utilisées pour évaluer les taux de comptage dans les détecteurs attendus en conditions cliniques. Dans la configuration actuelle de la caméra, ces taux sont élevés et les phénomènes d'empilement risquent d'être problématiques. Enfin, il est démontré que le dispositif étudié est sensible à un déplacement du pic de Bragg de plus ou moins 5 mm malgré les problèmes de coïncidences fortuites et malgré le bruit introduit par l'algorithme de reconstruction utilisé. / Ion beam therapy is an innovative radiotherapy technique using mainly carbon ion and proton irradiations. Its aim is to improve the current treatment modalities. Because of the sharpness of the dose distributions, a control of the dose if possible in real time is highly desirable. A possibility is to detect the prompt gamma rays emitted subsequently to the nuclear fragmentations occurring during the treatment of the patient. In a first time two different Compton cameras (double and single scattering) have been optimised by means of Monte Carlo simulations. The response of the camera to a photon point source with a realistic energy spectrum was studied. Then, the response of the camera to the irradiation of a water phantom by a proton beam was simulated. It was first compared with measurement performed with small-size detectors. Then, using the previous measurements, we evaluated the counting rates expected in clinical conditions. In the current set-up of the camera, these counting rates are pretty high. Pile up and random coincidences will be problematic. Finally we demonstrate that the detection system is capable to detect a longitudinal shift in the Bragg peak of +or- 5 mm, even with the current reconstruction algorithm.

This thesis describes the analysis of Very High Energy (VHE) emission from the Active Galactic Nucleus PKS 0537-441. It also aims to put the results in a wider context by implementing previous work done on this source. The data chosen for the analysis is provided by the Fermi-LAT satellite and covers the energy range between 300 MeV and 300 GeV. Initially a lightcurve of the received flux from the source was generated, containing data from August 2008 to April 2017, with a mean flux of 4∗10−8 photons per second per squared centimeter. The lightcurve contained sections of different flux intensities giving periods of special interest, such as a flaring period at August 2008 to August 2011, an enormous flare at April 2010 and a less active period between April 2013 - January 2016 that could be identified for further investigations. The differences in observed flux over time was tested and PKS 0537-441 was found to be a significantly variable source. Spectral Energy Distribution (SED) analysis was performed over both the entire period as well as over the selected subperiods and fitted against models using the tools provided by the Fermi Science Support Center (FSSC). The models used in the fitting was PowerLaw2, LogParabola and PLSuperExpCutoff and the best fit for the data was obtained from the PLSuperExpCutoff, except for the less intense period where the LogParabola gave the best fit. The result from the SED analysis was integrated with results from previous work done on the source, ranging over multiple wavelengths in order to get a SED which spanned over the entire electromagnetic spectrum. Finally, modeling of this multi wavelength SED was performed in order to obtain parameters for the physical processes involved in the creation of the radiation received from PKS 0537-441.

No description available.

The “dialogue novel” is best understood as an ongoing novelistic experiment that replaces narration with dialogue, so that such basic narrative constituents as character, setting, chronology, and plot find expression not through the mediation of an external or character-bound narrative consciousness, but through the presented verbal exchange between characters. Despite sustained critical attention to the variety and “openness” of the novel form, dialogue novels have been largely ignored within English studies— treated as neither a sustained tradition within, nor a perverse manifestation of, the novel. This study seeks to address that absence and to situate the dialogue novel within narrative and novel studies. Drawing from analytic philosophy, narratology, literary theory, and the dialogue novels themselves, this study demonstrates how the unique formal texture of the dialogue novel opens onto valuable discussions about such topics as cooperative language communities, narrative desire, the power dynamics implicit in talk, and the relationship between time and narrative. Overriding these concerns is an attention to how the social nature of conversation determines how the dialogue novel represents institutional power and character agency, as well as how the dialogue novel establishes a dynamic between reader and text for the refiguration of meaning and the reconstruction of fictional worlds. Chapter One uses Paul Grice’s Cooperative Principle as a baseline for delineating how communities are formed and maintained through dialogue in Henry James’s The Awkward Age. Chapter Two considers Henry Green’s late dialogue novels alongside his novel theory and René Girard’s theory of mimetic desire to illustrate how both character and readerly desire function as imitative practices. Chapter Three considers the novels of Ivy Compton-Burnett through Aaron Fogel’s theory of “forced dialogue” to argue that dialogue’s constraints can offer liberative structure to the novel form and those who are subject to these strictures. And Chapter Four reads dialogue novels by William Gaddis and Nicholson Baker through Paul Ricoeur’s threefold mimesis and Lubomír Doležel’s possible-worlds theory to argue that the dialogue novel presents an ideal form for examining the complex intersection of formal texture and history, as well as the dialectic between narrative configuration and human time. / English

The goal in medical x-ray imaging is to obtain the image quality requiredfor a given detection task, while ensuring that the patient dose is kept as lowas reasonably achievable. The two most common strategies for dose reductionare: optimizing incident x-ray beams and utilizing energy informationof transmitted beams with new detector techniques (spectral imaging). Inthis thesis, dose optimization schemes were investigated in two x-ray imagingsystems: digital mammography and computed tomography (CT). In digital mammography, the usefulness of anti-scatter grids was investigatedas a function of breast thickness with varying geometries and experimentalconditions. The general conclusion is that keeping the grid is optimalfor breasts thicker than 5 cm, whereas the dose can be reduced without a gridfor thinner breasts. A photon-counting silicon-strip detector developed for spectral mammographywas characterized using synchrotron radiation. Energy resolution, ΔE/Ein, was measured to vary between 0.11-0.23 in the energy range 15-40 keV, which is better than the energy resolution of 0.12-0.35 measured inthe state-of-the-art photon-counting mammography system. Pulse pileup hasshown little effect on energy resolution. In CT, the performance of a segmented silicon-strip detector developedfor spectral CT was evaluated and a theoretical comparison was made withthe state-of-the-art CT detector for some clinically relevant imaging tasks.The results indicate that the proposed photon-counting silicon CT detector issuperior to the state-of-the-art CT detector, especially for high-contrast andhigh-resolution imaging tasks. The beam quality was optimized for the proposed photon-counting spectralCT detector in two head imaging cases: non-enhanced imaging and Kedgeimaging. For non-enhanced imaging, a 120-kVp spectrum filtered by 2half value layer (HVL) copper (Z = 29) provides the best performance. Wheniodine is used in K-edge imaging, the optimal filter is 2 HVL iodine (Z = 53)and the optimal kVps are 60-75 kVp. In the case of gadolinium imaging, theradiation dose can be minimized at 120 kVp filtered by 2 HVL thulium (Z =69). / <p>QC 20160401</p>

Ion beam therapy is an innovative radiotherapy technique using mainly carbon ion and proton irradiations. Its aim is to improve the current treatment modalities. Because of the sharpness of the dose distributions, a control of the dose if possible in real time is highly desirable. A possibility is to detect the prompt gamma rays emitted subsequently to the nuclear fragmentations occurring during the treatment of the patient. In a first time two different Compton cameras (double and single scattering) have been optimised by means of Monte Carlo simulations. The response of the camera to a photon point source with a realistic energy spectrum was studied. Then, the response of the camera to the irradiation of a water phantom by a proton beam was simulated. It was first compared with measurement performed with small-size detectors. Then, using the previous measurements, we evaluated the counting rates expected in clinical conditions. In the current set-up of the camera, these counting rates are pretty high. Pile up and random coincidences will be problematic. Finally we demonstrate that the detection system is capable to detect a longitudinal shift in the Bragg peak of +or- 5 mm, even with the current reconstruction algorithm.

Spectroscopic measurements are detailed within this thesis, utilising incoherent neutron scattering to examine the dynamics of various condensed-matter systems, from nanosecond to sub-femtosecond timescales. The body of this work is divided into two distinct areas of research. I. Nuclear Momentum Measurements of Multiple Masses Deep inelastic neutron scattering (DINS) is used to probe the nuclear momentum distributions and kinetic energies of individual atomic species in sodium hydride (both in bulk and as nanoparticulates within a silica matrix), enriched lithium-7 fluoride and lithium tetra-ammoniate. Extension of DINS to examine heavier (M>4amu) nuclei is detailed, accomplished by the application of a simple stoichiometric fixing technique within the standard DINS theory and analysis protocols. The validity and accuracy of such simultaneous measurements are discussed. II. The Dynamics of Coordinated Ammonia in Zeolite A Inelastic neutron scattering (INS) and quasielastic neutron scattering (QENS) are utilised in the examination of vibrational and stochastic dynamics of the ammonia molecule, as coordinated to the internal surface of a zeolite host. Both sodium and copper-exchanged forms of zeolite-A are studied, with proton-weighted, low energy phonon-modes and rotational processes being observed and assigned.