We have performed a blind search for a gamma-ray transient of arbitrary duration and energy spectrum around the time of the LIGO gravitational-wave event GW150914 with the six-spacecraft interplanetary network (IPN). Four gamma-ray bursts were detected between 30 hr prior to the event and 6.1 hr after it, but none could convincingly be associated with GW150914. No other transients were detected down to limiting 15-150 keV fluences of roughly 5 x10-(8) -5 x 10(-7) erg cm(-2). We discuss the search strategies and temporal coverage of the IPN on the day of the event and compare the spatial coverage to the region where GW150914 originated. We also report the negative result of a targeted search for the Fermi-GBM event reported in conjunction with GW150914.

The purpose of this paper is to study the possible excited states in the nucleus of Cs133. At North Texas State College a 100-Kev Cockcroft-Walton accelerator has been constructed for use as a neutron source for exciting various nuclei and for studying the gamma spectra obtained to determine their energy levels.

This paper is concerned with the design, testing and performance of a coincidence system, the proposed North Texas State College accelerator.

La volonté d'améliorer l'efficacité énergétique des réacteurs nucléaires a motivé de nouvelles solutions dans leur conception. L'une d'elles est l’utilisation d’un réflecteur lourd dans les réacteurs de génération III+ et les futurs réacteurs de génération IV. Lorsque la matière est traversée par des rayons γ, les excitations induites entraînent une élévation de sa température. Ce processus, appelé échauffement γ, est responsable de plus de 90% de la production de chaleur dans la région hors combustible d'un réacteur nucléaire. C’est également le cas dans le réflecteur. Pour simuler l'effet de l’échauffement γ en fonction de la composition du combustible, il faut disposer de données précises sur les γ prompts émis par les différents fragments produits dans le processus de fission. En 2012, une campagne d’expériences inédite, EXILL, a été menée au réacteur de recherche de l'ILL. Un grand nombre de détecteurs HPGe a été placé autour d’une cible fissile et a mesuré les rayons γ émis par la cible alors qu’elle était irradiée par un faisceau intense de neutrons froids. Dans ce travail, nous avons analysé les données obtenues avec des cibles ²³⁵U. Elles nous ont permis d’étudier la désexcitation de plusieurs fragments de fission et plus globalement le processus de fission induite par des neutrons. Dans un premier temps, nous avons utilisé la méthode standard d'analyse par coïncidence γ-γ-γ. Nous avons pu filtrer les données expérimentales, identifier les transitions γ dans des fragments bien produits et calculer leur intensité relative. Les problèmes que nous avons rencontrés concernent le bruit de fond. Les résultats obtenus dépendent de ce choix et présentent donc des problèmes de reproductibilité. Nous avons développé et testé une nouvelle méthodologie d'analyse. Son principe est un balayage des portes de coïncidence selon trois directions, ce qui permet de trouver le bruit de fond le mieux adapté. L'idée principale était finalement de passer d'une méthode "spectroscopique", dont le but est de trouver de nouvelles transitions et des états excités dans un noyau, à une méthode "spectrométrique", qui nous permet d'obtenir plus précisément l’intensité de transitions γ connues, avec une meilleure estimation de leur incertitude. Cela nous a amené à développer un logiciel d'analyse semi-automatique d'ajustement des pics. Divers schémas de calcul de l'intensité des transitions γ ont été également élaborés pour tenir compte des contaminations possibles, selon leur emplacement dans la matrice de coïncidence et leur intensité. La méthode standard et la nouvelle méthode d'analyse ont été comparées pour l'analyse du ¹⁴²Ba. Dans ce travail, nous avons également comparé nos résultats sur quelques noyaux, tel que le ¹⁰⁰Zr, avec des simulations réalisées avec le code FIFRELIN. Ce dernier est un code Monte-Carlo qui simule le processus de fission et la désexcitation des fragments de fission. FIFRELIN utilise plusieurs modèles différents pour décrire ces processus. Nous avons testé le comportement des différents modèles, trouvé les valeurs optimales des paramètres de simulation et testé comment ces configurations reproduisaient les résultats expérimentaux. FIFRELIN n'a pas été en mesure de reproduire simultanément les intensités des transitions γ émises par les fragments de ¹⁰⁰Zr et la multiplicité de neutrons prompts moyennée sur tous les fragments de fission. Cependant, avec des paramètres modifiés, FIFRELIN a fourni localement une multiplicité de neutrons prompts correcte pour les fragments de masse atomique A=100 et des intensités de transition γ bien reproduites pour le noyau de ¹⁰⁰Zr. Nous avons également comparé nos résultats expérimentaux sur les fragments de ¹⁰⁰Zr provenant du processus ²³⁵U(n,f) avec les autres données expérimentales disponibles provenant des expériences sur ²⁴⁸Cm(sf) et ²⁵²Cf(sf), et une autre expérience sur ²³⁵U(n,f). / The desire to improve the fuel efficiency of nuclear reactors has motivated new solutions in their design. One of them is the heavy reflector used in the generation III+ and in the future generation IV reactors. γ-rays passing through matter cause its excitation and temperature rise. It is a process called γ-heating, and it is responsible for more than 90% of the heat production in the non-fuel region of the nuclear reactor. This is also the case of the heavy reflector. To simulate the γ-heating effect in every state of the nuclear reactor it is necessary to have precise data on the prompt γ-rays emitted by different fission fragments produced in the course of the nuclear chain reaction. In 2012, at the research reactor of the ILL, an innovative experiment, called EXILL, was conducted. It produced a large amount of useful data on the de-excitation of the fission fragments. A large number of HPGe detectors were used to study the neutron induced fission process by measuring the emitted γ-rays. Fissile targets were irradiated by an intense cold neutron beam. In this work we analyzed the ²³⁵U targets. We studied several fission fragments and more generally the fission process by using high-resolution γ-ray spectroscopy. At the beginning, we used the standard γ-γ-γ coincidence analysis method. We were able to filter experimental data, identify the well produced γ-rays, and calculate their relative intensities. The problems we have encountered are related to the background. The results obtained with this method were background dependent and thus presented some problems with reproducibility. We therefore developed and tested a new analysis methodology. Its crucial feature is a coincidence gates scanning in three directions which helps to find the most suitable background. The idea was to move from a “spectroscopic” method, which main purpose is finding new transitions and excited states in a nucleus, to a “spectrometric” method, which allows us to obtain more precise γ-ray intensities. We developed a semi-automatic analysis software which facilitates fitting of the chosen γ-ray peak, the contamination and the background. Various γ-ray intensity calculation schemes were derived to take into account different contamination strengths and placements. The results of the analysis with the new technique are reproducible and more reliable. The standard and the new analysis method were compared in the ¹⁴²Ba analysis. In this work, we also compared our experimental results on some nuclei, such as ¹⁰⁰Zr, with the simulation results performed with the FIFRELIN code. It is a Monte-Carlo code which simulates the fission process and the de-excitation of the fission fragments. It uses various models to describe these processes. We were able to test the behavior of different models implemented in FIFRELIN to find the optimal simulation parameter values and to test how well these setups reproduce the experimental results. FIFRELIN was unable to simultaneously reproduce the γ-ray intensities of ¹⁰⁰Zr and the prompt-neutron multiplicity averaged over all fission fragments. However, with modified simulation parameters, FIFRELIN locally provided correct prompt-neutron multiplicity for the fission fragment with the atomic mass A=100 and well reproduced γ-ray intensities of ¹⁰⁰Zr. We also compared our experimental results on ¹⁰⁰Zr coming from the ²³⁵U(n,f) process with the other available experimental data coming from the experiments on ²⁴⁸Cm(sf) and ²⁵²Cf(sf), and another experiment on ²³⁵U(n,f).

The purpose of this study is to investigate the pricing of variable annuity embedded derivatives in a Lévy process setting. This is one of the practical issues that continues to face life insurers in the management of derivatives embedded within these products. It also addresses how such providers can protect themselves against adverse scenarios through a hedging framework built from the pricing framework. The aim is to comparatively consider the price differentials of a life insurer that prices its variable annuity guarantees under the more actuarially accepted regime-switching framework versus the use of a Lévy framework. The framework should address the inadequacies of conventional deterministic pricing approaches used by life insurers given the increasing complexity of the option-like products sold. The study applies finance models in the insurance context given the similarities in payoff structure of the products offered while taking into account the differences that may exist. The underlying Lévy process used in this study is the Variance-Gamma (VG) process. This process is useful in option pricing given its ability to model higher moments, skewness and kurtosis, and also incorporate stochastic volatility. The research results compare well with the regime-switching framework besides the added merit in the use of a more refined model for the underlying that captures most of the observed market dynamics. / Dissertation (MSc)--University of Pretoria, 2014. / tm2015 / Mathematics and Applied Mathematics / MSc / Unrestricted

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<p> The polymerization of styrene to polystyrene was studied using gamma radiation from a Co^60 source as the free radical initiator. Conversions up to 50% were obtained and the molecular weight distribution, intrinsic viscosity, bulk viscosity, and osmotic pressure of several samples were measured. A theoretical kinetic model was developed using a slightly modified conventional kinetic scheme and employing a viscosity correction for the termination rate constant. The model predicts conversion over the range studied and molecular weight distributions are in agreement within the limitations of the experimental equipment to measure this parameter.</p> / Thesis / Master of Engineering (MEngr)

<p> This thesis is divided into two parts, the first part being devoted to the application of Neutron Capture Gamma Ray Analysis in determining S/Si and Fe/Si ratios in Allende meteorite and lunar samples and the second part, to evidence for a possible iron isotopic anomaly in the Allende meteorite obtained by the same method. The samples were irradiated in an in-core irradiation system in the McMaster swimming-pool nuclear reactor and the collimated beam of gamma rays was detected by a pair-spectrometer consisting of a Ge(Li) detector and NaI annulus. In the first part, besides the mainstream of the work, the basic principles of Neutron Capture Gamma Ray Analysis and Neutron Activation Analysis and the supremacy of the former over the latter for this particular problem has been discussed. In the second part, along with the implications and evidence of isotopic variations of other elements in the Allende meteorite, a brief description of the classification, structure and mineralogy of the Allende meteorite is given. The success and advantage of the method along with its limitations and further directions along these lines are also discussed.</p> / Thesis / Master of Science (MSc)

<p> The reaction 165Ho (3He,d) 166Er was studied using the University of Rochester Tandem Van de Graaff accelerator and an Enge-type split-pole magnetic spectrograph. The observed cross sections for the ground state rotational band and the gamma vibrational band were consistent with predictions based on the unified nuclear model. The population of the 1574 keV level was consistent with that expected for the K^π=4^-, 7/2-[523] + 1/2+[411] assignment obtained from decay scheme studies. The K^π=2^- octupole vibrational band based on the 1460 keV state was not populated as strongly as expected, indicating that the admixture of the 7/2-[523] - 3/2+[411] two proton state into this vibration is only about one-fifth as large as predicted by Soloviev et al.</p> / Thesis / Master of Science (MSc)

<p> The use of gamma radiation to initiate the iodination of methane in liquid phase was studied using a semi-batch technique whereby the methane was bubbling through a column of iodine solution in a reactor. Yields of CH3I and CH2I2 lower than 10% and G < 500 were obtained as contrasted with the 60% yield and G=7xl0^7 reported in the gas-phase reaction. In view of the propensity of the iodine as a radical scavenger and the endothermic nature of the reaction, various attempts to improve the low yields were carried out. Results are eiven that indicate the chances of achieving a laree G value for liquid-phase reaction are very low even if the operating conditions are optimized. </p> / Thesis / Master of Engineering (MEngr)