Made available in DSpace on 2014-10-09T12:29:11Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:02:41Z (GMT). No. of bitstreams: 1 00973.pdf: 3680396 bytes, checksum: 62f3f85a25ae91726723f130884f9345 (MD5) / Dissertacao (Mestrado) / IEA/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Le présent travail a pour but le développement d’une caméra gamma à masque codé permettant d’estimer la position tridimensionnelle (3D) des sources radioactives. Cela est d’un intérêt considérable dans le cadre d’un grand nombre d'applications, de la reconstruction de la forme 3D des objets radioactifs aux systèmes de réalité augmentée appliqués à la radioprotection. Les caméras gamma portables actuelles ne fournissent que la position angulaire relative des sources gamma à localiser, c'est-à-dire qu'aucune information métrique concernant les sources n’est disponible, comme par exemple leur distance par rapport à la caméra. Dans cette thèse, nous proposons principalement deux approches permettant d’estimer la position 3D des sources. La première approche consiste à étalonner la caméra gamma avec un capteur de profondeur à lumière structurée. La seconde approche permet d'estimer la distance source-détecteur par une méthode d’imagerie gamma stéréoscopique. Pour aligner géométriquement les images obtenues par la caméra gamma, le capteur de profondeur, et la caméra optique, une procédure d'étalonnage n’utilisant qu’une seule source ponctuelle radioactive a été conçue et mise en œuvre. Les résultats expérimentaux démontrent que les approches proposées permettent d'obtenir une précision inférieure au pixel, tant pour l’erreur de reprojection que pour la superposition des images gamma et optiques. Ces travaux présentent également une analyse quantitative de la précision et de la résolution relatives à l’estimation de la distance source-détecteur. De plus, les résultats obtenus ont validé le choix de la géométrie du modèle sténopé pour les caméras gamma à masque codé. / A coded aperture gamma camera for retrieving the three-dimensional (3-D) position of radioactive sources is presented. This is of considerable interest for a wide number of applications, ranging from the reconstruction of the 3-D shape of radioactive objects to augmented reality systems. Current portable γ-cameras only provide the relative angular position of the hotspots within their field of view. That is, they do not provide any metric information concerning the located sources. In this study, we propose two approaches to estimate the distance of the surrounding hotspots, and to autonomously determine if they are occluded by an object. The first consists in combining and accurately calibrating the gamma camera with a structured-light depth sensor. The second approach allows the estimation of the source-detector distance by means of stereo gamma imaging. To geometrically align the images obtained by the gamma, depth, and optical cameras used, a versatile calibration procedure has been designed and carried out. Such procedure uses a calibration phantom intentionally easy to build and inexpensive, allowing the procedure to be performed with only one radioactive point source. Experimental results showed that our calibration procedure yields to sub-pixel accuracy both in the re-projection error and the overlay of radiation and optical images. A quantitative analysis concerning the accuracy and resolution of the retrieved source-detector distance is also provided, along with an insight into the respective most influential factors. Moreover, the results obtained validated the choice of the geometry of the pinhole model for a coded aperture gamma camera.

A study has been made of the external conversion spectrum of gamma-rays of less than 200 kev. A set of semi-empirical curves relating the photoelectric peak height to the gamma-ray intensity has been established using antimony radiators. These results will be discussed. A method of preparing thin beta sources will also be described. / Thesis / Master of Science (MSc)

Lignes spectrales de rayons gammas provenants de la matière noire. <p>Approches indépendantes de modèles/ Gamma-Ray Lines from the Dark Side of Matter: Model-Independent Approaches<p><p> Cette thèse a pour thématique centrale la matière noire, et plus particulièrement un type de signal qu’elle pourrait émettre, à savoir des lignes spectrales de rayons gammas. La nature de la matière noire demeure mystérieuse, et ce que l’on sait de ses propriétés est exposé dans le premier chapitre. En particulier, la pertinence des lignes spectrales de rayons gammas dans l’étude de la matière noire est soulignée. Cette thèse est consacrée à l’étude des connexions possibles entre la phénoménologie de ce type de signal et d’autres manifestations, qu’il s’agisse de détection directe ou indirecte, ou bien de détection dans des collisionneurs tels que le LHC. Le but est d’établir la possibilité de discriminer différents modèles et/ou d’obtenir des contraintes indépendantes.<p>\ / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

La présente thèse porte sur quatre aspects différents de l’astronomie des hautes énergies.La première partie de ma thèse est dédiée à un développement instrumental pour les télescopes Cherenkov imageurs, le système de déclenchement de niveau 2 du télescope de 28 mètres du réseau H.E.S.S. (High Energy Stereoscopic System). Mon travail s’est focalisé sur l’invention d’algorithmes et les simulations Monte-Carlo du système de déclenchement, ainsi que la comparaison de la reconstruction au niveau de la carte de déclenchement à la reconstruction ”hors-ligne” (Moudden,Barnacka, Glicenstein et al. 2011a; Moudden, Venault, Barnacka et al. 2011b). Je décris le système et j’évalue ses performances.Le réseau H.E.S.S. a observé le blazar PKS1510-089. La deuxième partie de ma thèse traite de l’analyse des données et la modélisation de l’émission large bande de ce blazar. C’est un exemple de quasar radio à spectre plat (FSRQ), pour lequel il n’est attendu aucune émission aux très hautes énergiesJ’ai modélisé les données observées pendant un "flare” de PKS1510-089. Ce modèle est basé sur un scénario de choc interne à une zone.Le troisième chapitre de ma thèse est une étude d’un autre phénomène affectant potentiellement les blazars observés par FERMI-LAT: l’effet de lentille gravitationnelle fort. Cette partie de ma thèse montre le premier indice de présence d’un effet de lentille gravitationnelle dans le domaine des photons de haute énergie. Cet indice provient de l’observation d’un écho dans la courbe de lumière du blazar distant PKS1830-211, qui est une lentille gravitationnelle connue. Les méthodes d’estimation des retards temporels dans les systèmes de lentille gravitationnelles reposent sur la corrélation croisée des courbes de lumière individuelles. Dans l’analyse présentée dans cette thèse, j’ai utilisé des photons de 300 MeV à 30 GeV détectés par l’instrument FERMI-LAT. L’instrument FERMI-LAT ne peut pas séparer spatialement les images des lentilles gravitationnelles fortes connues. La courbe de lumière observée est donc la superposition des courbes de lumière des images individuelles. Les données du FERMI-LAT ont l’avantage d’être des séries temporelles régulièrement espacées,avec un bruit de photons très bas. Cela permet d’utiliser directement les méthodes de transformées de Fourier. Un retard temporel entre les images compactes de PKS1830-211 a été recherché par deux méthodes : une méthode d’auto-corrélation et la méthode du ”double spectre”. La méthode du double spectre fournit un signal de 27 ± 0.6jours (statistique) avec une significativité de 4.2 σ. Ce résultat est compatible avec ceux de Lovell et al (1998) et Wiklind et Combes (2001).La dernière partie de ma thèse est consacrée à un effet de lentille différent, le ”femtolensing”. La recherche d’effets de femtolensing a été utlisée pour obtenir des limites sur l’abondance de trous noirs primordiaux. Celle-ci a été contrainte de manière significative dans un large domaine de masses. Les limites les moins contraignantes ont été établies pour les objets de faible masse, pour lesquels la détection représente un défi expérimental. J’ai utilisé les sursauts gamma de redshift connus d´etectés par le Fermi Gamma Ray Burst Monitor (GBM) pour rechercher d’éventuels effets de femtolensing produits par des objets compacts sur la ligne de visée. L’absence de ces effets de femtolensing montre que des trous noirs primordiaux de masse comprises entre 5×10^17 et 10^20 g ne constituent pas une fraction importante de la matière noire. J’ai effectué mes études de thèse en co-tutelle entre le Centre Astronomique Nicolaus Copernicus de l’académie des sciences polonaise, à Varsovie et l’Institut de Recherches sur les Lois fondamentales de l’Univers du CNRS à Saclay, en France. / This thesis presents the study of four aspects of high energy astronomy.The first part of my thesis is dedicated to an aspect of instrument development for imaging atmospheric Cherenkov telescopes, namely the Level 2 trigger system of the High Energy Stereoscopic System (H.E.S.S.). My work on the project focused on the algorithm development and the Monte Carlo simulations of the trigger system and overall instrument (Moudden, Barnacka, Glicenstein et al. 2011a; Moudden, Venault, Barnacka et al. 2011b). The hardware implementation of the system is described andits expected performances are then evaluated. The H.E.S.S. array has been used to observe the blazar PKS 1510-089.The second part of my thesis deals with the data analysis and modeling of broad-band emission of this particular blazar. In part II of my thesis, I am presenting the analysis of the H.E.S.S. data: the light curve and spectrum of PKS 1510-089, together with the FERMI data and a collection of multi-wavelength data obtained with various instruments. I am presenting the model of PKS 1510-089 observations carried out during a flare recorded by H.E.S.S.. The model is based on a single zone internal shock scenario.The third part of my thesis deals with blazars observed by the FERMI-LAT, but from the point of view of other phenomena: a strong gravitational lensing. This part of my thesis shows the first evidence for gravitational lensing phenomena in high energy gamma-rays. This evidence comes from the observation of a gravitational lens system induced echo in the light curve of the distant blazar PKS 1830-211. Traditionalmethods for the estimation of time delays in gravitational lensing systems rely on the cross-correlation of the light curves from individual images. In my thesis, I used 300 MeV-30 GeV photons detected by the Fermi-LAT instrument. The FERMI-LAT instrument cannot separate the images of known lenses. The observed light curve is thus the superposition of individual image light curves. The FERMI-LAT instrument has the advantage of providing long, evenly spaced, time series with very low photonnoise. This allows to use directly Fourier transform methods. A time delay between the two compact images of PKS 1830-211 has been searchedfor both by the autocorrelation method and a new method: the “double power spectrum”. The double power spectrum shows a 4.2 σ evidence for a time delay of 27.1±0.6 days (Barnacka et al. 2011), consistent with the results from Lovell et al. (1998) and Wiklind & Combes (2001).The last part of my thesis concentrates on another lensing phenomena called ”femtolensing”. The search for femtolensing effects has been used to derive limits on the primordial black holes abundance. The abundance of primordial black holes is currently significantly constrained in a wide range of masses. The weakest limits are established for the small mass objects, where the small intensity of the associated physical phenomenon provides a challenge for current experiments. I have usedgamma-ray bursts with known redshifts detected by the FERMI Gamma-ray Burst Monitor (GBM) to search for the femtolensing effects caused by compact objects. The lack of femtolensing detection in the GBM data provides new evidence that primordial black holes in the mass range 5 × 10^17 – 10^20 g do not constitute a major fraction of dark matter (Barnacka et al. 2012). My Ph.D. studies have been carried out jointly between the Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences, in Warsaw in Poland and the IRFU institute of the Commissariat à l’énergie atomique et aux énergies alternatives(CEA) Saclay in France.

Vitamin E exhibits anti-tumor activity by regulating pathways in cancer cells, potentially the lipoxygenase (LOX) pathway. We studied the effects of alpha tocopherol (AT), gamma tocopherol (GT), gamma tocotrienol (GT3), and an alpha-gamma tocopherol mixture (ATGT) on the production of the LOX metabolites 13-hydroxyoctadecaenoic acid (HODE), 15-hydroxyeicosatetraenoic acid (HETE), 12-HETE, and 5-HETE in colorectal cancer. These metabolites were examined in the HCT-116 cell line after 24 h treatment with select vitamin E isoforms and quantified by LC/MS/MS. Under physiological conditions, we find that treatment with varying vitamin E isoforms have different effects on the production of 13-HODE, 15-HETE, 12-HETE, and 5-HETE. GT increases 13-HODE and decreases 12-HETE. AT reverses the effects of GT regulation on the LOX pathway, while GT3 has no significant effect on the metabolites tested. GT shows superiority in regulating the LOX pathway as it increases 13-HODE and decreases 12-HETE for possible prevention of colorectal cancer.

<p>En metod för detektering och kvantifiering av <em>gamma</em>-hydroxysmörsyra (GHB) i urin med gaskromatografi (GC) är framtagen på Sahlgrenska universitetssjukhuset. Metoden är relativt unik då den inte kräver upparbetning i form av derivatisering, indunstning eller extraktion. Urinen surgörs med koncentrerad saltsyra och internstandard, <em>gamma</em>-valerolakton, tillsätts. GHB övergår då till laktonformen, <em>gamma</em>-butyrolakton (GBL). Därefter injiceras provet direkt på en GC-FID med en kapillärkolonn för glykoler och alkoholer. Detektion ner till 100 μmol/L är möjligt med en variationskoefficient mellan 6 och 12 %. Provsvar erhålls efter 6,5 minuter. Metoden är dock inte fullständig då en del frågetecken kvarstår. Bland annat bör det undersökas om andra föreningar, som kan förekomma i urin, kan eluera samtidigt som GHB. Om ja så bör vidare analyser genomföras för att separera GHB och den andra föreningen. Metoden kan däremot användas i nuläget som en screeninganalys för att snabbt få ett svar på om GHB finns närvarande eller inte. Verifiering kan sedan ske med GC-MS.</p> / <p>A method for determination and quantification of <em>gamma</em>-hydroxyburyric acid (GHB) in urine samples is developed at Sahlgrenska universitetssjukhus. No time consuming procedures as derivatization and exctration is required, which makes the method fairly unique. Hydrochloric acid and internal standard, <em>gamma</em>-valerolakton, is added to the urine sample before the sample is injected to a gas chromatograph with a flame ionization detector and a column for glycols and alcohols. The hydrochloric acid makes the GHB convert into <em>gamma</em>-butyrolactone (GBL) which is easier to separate in the gas chromatograph. Limit of detection was found to be 100 μmol/L and test result is received after 6,5 minutes. There are still some question marks around the method, for example, there is a possibility that another substance elute at the same time as GHB. More tests are required to determine whether or not it is so. For now the method can be used as a screening analysis to hastily detect GHB presence. Verification can be done with GC-MS.</p>

Beam profile monitors provide position and ux distribution information to facilitate the configuration of an experimental apparatus and are an important component of any accelerator facilities beam diagnostic system. Nuclear physics experiments typically involve the incidence of high energy particles or gamma-rays on some target material and the detection of the products of the ensuing interactions. Therefore, knowing the profile of the incident radiation beam is desirable. To address the need for a profile monitor for the High-Intensity Gamma-Ray Source, development of a CCD-based gamma-ray beam profiler was undertaken. The profiler consisted of plastic scintillator, a lens system and a Starlight Express MX5 CCD camera, all contained within a light tight box. The scintillation pattern, created by the interaction between the incident gamma-rays and the scintillator, could be focused onto the CCD. Simulations were used to determine the amount of power that would be absorbed for different beam energies and scintillator thicknesses. The use of a converter material, placed directly against the scintillator to improve power deposition, was also investigated. The system was tested in order to and the camera noise characteristics, the optical resolution and magnification and the systems responsivity to power absorption in the scintillator. Using a 137Cs source, preliminary beam proles were obtained. By combining the results of the testing and simulation, predictions of the required length of exposure were made. It was determined that a beam with a flux of 10^6/s and a diameter of 2.5 cm could be profiled, using 6.0 mm of plastic scintillator and 0.6 mm of iron converter, to within 5% error per 0.64 mm x 0.91 mm resolving unit, in less than 1 minute.

Beam profile monitors provide position and ux distribution information to facilitate the configuration of an experimental apparatus and are an important component of any accelerator facilities beam diagnostic system. Nuclear physics experiments typically involve the incidence of high energy particles or gamma-rays on some target material and the detection of the products of the ensuing interactions. Therefore, knowing the profile of the incident radiation beam is desirable. To address the need for a profile monitor for the High-Intensity Gamma-Ray Source, development of a CCD-based gamma-ray beam profiler was undertaken. The profiler consisted of plastic scintillator, a lens system and a Starlight Express MX5 CCD camera, all contained within a light tight box. The scintillation pattern, created by the interaction between the incident gamma-rays and the scintillator, could be focused onto the CCD. Simulations were used to determine the amount of power that would be absorbed for different beam energies and scintillator thicknesses. The use of a converter material, placed directly against the scintillator to improve power deposition, was also investigated. The system was tested in order to and the camera noise characteristics, the optical resolution and magnification and the systems responsivity to power absorption in the scintillator. Using a 137Cs source, preliminary beam proles were obtained. By combining the results of the testing and simulation, predictions of the required length of exposure were made. It was determined that a beam with a flux of 10^6/s and a diameter of 2.5 cm could be profiled, using 6.0 mm of plastic scintillator and 0.6 mm of iron converter, to within 5% error per 0.64 mm x 0.91 mm resolving unit, in less than 1 minute.

A high-efficiency gamma-ray counting system has been built at Los Alamos National Laboratory for use in analyzing nuclear forensics samples. This system consists of two clover high-purity germanium detectors and is surrounded by a thallium-doped sodium iodide annulus. Special precautions have been taken to ensure the system has a low background. The system is connected to XIA Pixie-4 fast digitizers and collects data in list-mode. This work is split into two main parts. The first part describes the proper steps and techniques to initialize the settings of a detector system connected to fast digitizers in order to optimize the system for resolution and throughput. The various counting modes for this particular system are described in detail, including the benefits and drawbacks of each mode. Steps are then shown to characterize the system by obtaining efficiency curves for various counting modes and sample geometries. Because of the close counting geometry involved with this system, true-coincidence summing factors must be calculated, and are done so in part by measuring the peak-to-total ratios of the system in its various counting modes across a wide energy range. The dead-time for the system can be complicated due to the multiple inputs of the system. Techniques for calculating the dead-time of multiple-detector systems are discussed. The second part of this work shows the system's usefulness in analyzing nuclear forensics samples, specifically irradiated enriched uranium. Three fission product parent-daughter pairs of different lifetimes are analyzed over a course of six months. The activities of each nuclide are calculated at each time step. Age dating techniques using the parent-daughter pairs are discussed, as well as the detection limits of each nuclide for a range of sample ages. Finally, avenues for further research are presented, as well as potential sources of error or uncertainty for this work. / text