Os decaimentos dos nuclídeos 101mRh e 101fRh foram estudados por espectroscopia gama, tanto em medidas de espectros simples quanta de espectros em coincidência. As fontes foram produzidas na reação 103Rh(,2n) 101m,fRh, com fótons provenientes de Bremsstrahlung de elétrons no Acelerador linear do IFUSP. Diversas transições gama anteriormente atribuídas aos decaimentos desses nuclídeos não foram confirmadas, num total de 6 transições, e mais duas que foram observadas este trabalho foram atribuídas ao decaimento do 102mRh. As transições gama observadas seguindo o decaimento do 101mRh tem as seguintes energias em keV, e intensidades relativas, respectivamente: 127,226(9), 0,79(2); 157,41(4), 0,280(5); 179,636(15), 0,660(15); 184,11(5), 0,193(3); 233,74(4), 0,2198(15); 238,27(4), 0,2505(17); 306,857(5), 100; 311,367(19), 0,0175(9); 417,86(5), 0,005(2); 545,117(7), 5,3(3). As transições gama observadas seguindo o decaimento do 101fRh tem as seguintes energias e intensidades relativas: 110,94(12), 0,06(2); 127,226(9), 93,2(9); 184,22(13), 0,081(14); 198,01(13), 100; 295,01(3), 0,815(24); 352,23(3), 16,20(15); 422,19(8) ,0,272(15). A intensidade da captura eletrônica do 101fRh para o estado fundamental do 101Ru foi estimada em 51(17) % a partir do acompanhamento do crescimento da intensidade dos gamas de 198 keV decorrente da alimentação do estado fundamental pela transição isométrica de 157 keV, durante os primeiros 10 dias após o fim da irradiação. Os esquemas de decaimento dos 101m,fRh resultantes deste trabalho exigem apenas seis níveis excitados do 101Ru para acomodar todas as transições gama observadas, ao contrário do estudo anterior que concluía pela necessidade de 11 níveis. A estrutura nuclear do 101Ru para baixas energias de excitação pode, em razão da simplificação do esquema de níveis decorrente deste trabalho, ser bem descrita qualitativamente num modelo de quase-partícula-fonon com acoplamento fraco. Uma descrição quantitativa através desse modelo no esquema de acoplamento intermediário, tem sucesso limitado às probabilidades de transição de quadruplo elétrico e aos fatores espectroscópicos, conduzindo a um espectro de energia muito diferente do experimental, embora com a densidade de níveis correta. A mistura de estados de três quase-partículas foi introduzida através da teoria de perturbação. Verifica-se que a introdução desses estados permite uma melhor interpretação do espectro de energia. Os cálculos com o modelo de uma quase-partícula-fonon foram estendidos aos isótopos ímpares do Ru com 95 A 105. Os poucos dados ex perimentais disponíveis de probabilidades de transição de quadrupolo elétrico e de fatores espectroscópicos são razoavelmente reproduzidos. Já o espectro de energia calculado só concorda razoavelmente com o experimental para o 95Ru. Os resultados obtidos sugerem que os isótopos ímpares do Ru podem ser descritos utilizando-se quase-partículas e fonons como modos elementares de excitação , sendo necessário incluir no modelo estados intrínsecos de três quase-partículas. / The decays of 101mRh and 101fRh nuclides were studied by gamma-ray spectroscopy either or single or coincidence . spectra. The sources were obtained through the 103Rh(,2n) 101m,fRh reaction with the electron Bremsstrahlung beam of the Linear Accelerator of the IFUSP. Six transitions earlier attributed to the decays of these nuclides were not confirmed. Two other transitions that were observed in the present work were attributed to the 102mRh decay. The energies (keV) and the relative intensities for the observed gamma transitions following the 101mRh decay are respective1y: 127.226(9), 0.79(2); 157.41(4), 0.280(5); 179.636(15), 0.660(15); 184.11(5), 0.193(3); 233.74(4), 0.2198(15); 238.27(4), 0.2505(17); 306.857(5), 100; 311.367(19), 0.0175(9); 417.86(5) 0.005(2); 545.117(7), 5.3(3). The energies and the relative intensities of the gamma transitions observed for the 101fRh decay are the following: 110.94(12), 0.06(2); 127.226(9), 93.2(9); 184.22(13), 0.081(14); 198.01(3), 100; 295.01(3), 0.815(24); 325.23(3), 16.20(15); 422.19 (8), 0.272(15).The growth of the intensity of the 198 keV gammas due to the feeding of the ground state by the isomeric transition of 157 keV during the first ten days after the end of the irradiation allowed the measurement of the 101fRh electron capture intensity for the ground state of the 101Ru which was established as roughly 51(17)%. Previous work had shown that for the decay scheme of the 101m,fRh eleven excited levels of the 101Ru were needed to fit all observed gamma transitions. This work shows that only six excited levels are necessary. Due to the simplification of the level scheme obtained in this work, the nuclear structure of the 101Ru for low excitation energy can be described as a quasi-particle-phonon with weak coupling. Using this model in the intermediate coupling scheme, a quantitative description is successful in the calculation of electric quadrupole transition probabilities and spectroscopic factors. The calculated energy spectrum is very different from the experimental one although the level densities coincide. Through the perturbation theory, mixture with three quasi-particle states was introduced. The introduction of these states allows a better interpretation of the energy spectrum. For the other Ru isotopes the calculations using the one quasi-particle-phonon model were performed with 95 A I05. The small amount of experimental data available for electric quadrupole transition probabilities and spectroscopic factors agreed fairly well with the theoretical calculations. Nevertheless, the calculated energy spectrum agrees reasonably with the experimental one only for 95Ru. The theoretical results suggest that the odd-A Ru isotopes can be described using quasi-particle and phonons as elementary excitation modes, provided that the three quasi-particle intrinsic states are taken into account.

Des calculs théoriques utilisant la méthode de champ moyen ont suggérée l'existence des formes du noyau avec la symétrie tétraédrique et/ou octraédrique dans la région des terres rares au voisinage des noyaux 156Gd et 160Yb. Dans les noyaux avec une symétrie tétraédrique pure, des transitions intra-bande E2 à bas spin dans des bandes de parité négative disparaissent ou sont très faibles. Ce travail est dédié à une recherche expérimentale de la symétrie tétraédrique dans le noyau 156Gd. Une expérience a été faite à Jyväskylä avec le multi-détecteur JUROGAM, sur la réaction de fusion - évaporation 154Sm(, 2n)156Gd. L'analyse des données, a établi les rapports d'embranchement de deux bandes de parité négative et a permis, par distribution angulaire, de connaître la nature d'une nouvelle transition. Les rapports d'embranchement obtenus sont comparables avec ceux des expériences précédentes et quelques limites supérieures ont été déterminées. L'absence de transitions à bas spin (I$^{pi}<9$) dans la bande de parité négative à spin impair a été confirmée. Ces résultats ont renforcé l'hypothèse d'une symétrie tétraédrique dans le noyau 156Gd. La spectroscopie gamma est l'outil majeure utilisé dans ce travail. Les principes ainsi qu'une étude de simulation réaliste sont détaillés dans ce manuscrit. La simulation avec des événements réalistes a été faite pour comparer la fonction de réponse de deux types de multidétecteurs EUROBALL et AGATA. Les résultats montrent que sous certain conditions la phase démonstrateur d'AGATA peut être utilisée pour la recherche d'événements rares. / Theoretical calculations using realistic mean-eld method suggest the existence of nuclear shapes with tetrahedral and/or octahedral symmetries in some rare earth nuclei around 156Gd and 160Yb. In nuclei with exact tetrahedral symmetry, the E2 intra-band transitions are predicted to vanish completely or to be very weak. This work is devoted to an experimental research of the tetrahedral symmetry in the nucleus 156Gd. An experiment has been carried out with the JUROGAM - rays detector at Jyväskylä by using the fusion - evaporation reaction 154Sm(, 2n)156Gd. In analysis, the branching ratios of two parity negative bands were determined, the angular distribution has been analyzed to determine the nature of one inter-band transition between these two bands. The transitions strength ratios determined are of the same order of magnitude as previous experiments, and some upper limits have been established for the lowest spin. The missing of the E2 transitions below the (I$^{pi}<9$)states in the odd spin parity negative band were conrmed. The results of this work reinforced the hypothesis of the tetrahedral symmetry in the nucleus 156Gd. -ray spectroscopy is the major tool used for this work. Detection principles and -ray simulations are detailed in the document. The simulation, based on realistic events, has been realised to compare the response function of two multidetectors EUROBALL and AGATA. The results show that under certain conditions the rst phase of AGATA (demonstrator) is also a tool to search for rare events

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.

Identifying what makes up the Dark Matter is a long-standing problem to which the abundance of gravitational and cosmological evidence fails to answer. Indirect detection techniques have the aim to unveil the nature of Dark Matter by catching and identifying the products of potential decays and/or annihilations. The work exposed in this thesis is in line with this strategy and has for common thread the quest for line(-like) features in the extraterrestrial fluxes of gamma-rays and neutrinos. The motivation behind this specific interest is that, due to the absence of astrophysical counterparts beyond the GeV scale, these features constitute the ultimate probes (also called “smoking guns”) of the existence of Dark Matter.The thesis is organized in three Parts, the first of which is an introduction to the different facets of the Dark Matter conundrum and why it is not a trivial issue. The works involving gamma-ray line considerations are gathered in Part II, and those exclusively focusing on neutrino lines in Part III.Part II focuses on the effective field theory of Dark Matter decay, first in the context of millicharged particles decaying to gamma-ray lines, and then in the context of (neutral and millicharged) Dark Matter decays involving the simultaneous emission of gamma-ray and neutrino lines. In both cases, the simultaneous emission of cosmic rays is unavoidable and the decays are constrained in a multi-messenger fashion. The complementarity of the results obtained is used to derive model-independent constraints on the Dark Matter lifetime, and shows the possibility to exclude or distinguishsome specific scenarios on the basis of an explicit experimental conjecture.After an introduction to the neutrino detection principles and to the operation of the IceCube detector, Part III focuses on two careful searches for spectral features in the neutrino spectrum. The main goal behind these analyses, conducted in two different regions of the energy spectrum but using the same likelihood ratio procedure, is to popularize dedicated energy distribution studies by showing their ability to reach sensitivity levels comparable to—sometimes even going beyond—those obtained with angular distribution studies or even in the context of gamma-ray line searches. / Option Physique du Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Les Sursauts de Rayonnement Gamma (GRBs) sont des flashs émanant du cosmos qui sont classés en deux groupes : les longs/doux et les courts/durs. Le lancement du satellite Swift a ouvert une nouvelle ère dans la recherche sur les GRBs. Cette thèse présente une étude détaillée du GRB 141221A qui montre une forte et inhabituelle hausse des valeurs des courbes de lumière dans le domaine optique lors de l'émission rémanente alors que dans le domaine des rayons X ces valeurs sont plus normales. GRB 141221A est un des GRBs qui mettent à l'épreuve les modèles car il exclut tout vent stellaire du progéniteur. Un regroupement des courbes de lumière dans le domaine X lors de l'émission rémanente GRBs a été observé avant le lancement de Swift. Cette classification a été débattue après le lancement de Swift. Nous avons construit un échantillon de 254 GRBs qui montre un éparpillement des distributions du flux à un jour. Cette distribution a été normalisée avec un décalage vers le rouge de 1. Nous avons investigué ce problème selon trois directions: un problème instrumental, un problème de calibration des données ou l'absence de regroupement. Coté instrument, le problème pourrait être observationnel, nous avons en effet observé des effets saisonniers durant les solstices et les équinoxes. Coté calibration des données, un tel problème pourrait avoir une influence sur les résultats de l'étude. La comparaison entre analyse manuelle et automatique des données telle que disponible sur le dépôt Swift-XRT montre de sérieux aléas sur les résultats. Les cas où l'analyse manuelle est judicieuse sont exposés. La dernière possibilité de l'absence de regroupement pourrait être un effet de sélection. / GRBs are ashes of gamma-rays coming from cosmos. They are one of the most mysteriousevents we have been able to observe since their discovery. GRBs are classified into two groups: long/soft GRBs and short/hard GRBs. Their emission mechanism consists of two phases: prompt emission and afterglow emission. The launch of the Swift satellite opened a New Era in the GRBs research. Swift is able to provide accurate position for more GRBs than previous missions, thanks to its fast capabilities of slewing. Furthermore, the Swift shows that GRBs have a canonical behaviour for the X-ray afterglow light curves. The data analysis process remains the key point of GRBs studies. I present a detailed study of the peculiar GRB 141221A at different wavelengths. GRB 141221A shows an unusual steep rise in the optical light curve of the afterglow. The broad band spectral energy distribution, taken near the maximum of the optical emission, presents either a thermal component or a behaviourbreak. This burst displays unusual feature in the optical band, whereas the X-ray data is more common. GRB 141221A is one of the challenging bursts that excludes a stellar wind from the progenitor of the GRBs. A clustering in the X-ray afterglow light curves was observed before the launch of the Swift satellite. This feature has been debated after the launch of the Swift. We have built a sample which consists of 254 GRBs that shows a scattering of the data for the flux distribution at one day. This distribution was investigated with a normalization of light curves at redshift one. We have investigated the problem into three different directions

Je présente ma thèse sur l'analyse des ondes gravitationnelles dans les deux domaines suivants. Pour le premier il s'agit de vérifier que les collaborations LIGO et Virgo sont prêtes pour la détection d'un fond gravitationnel stochastique astrophysique pendant l'ère des détecteurs avancés qui va démarrer à l'été 2015. Pour le deuxième il s'agit de poursuivre l'étude du potentiel scientifique, notamment pour l'astrophysique et la cosmologie, d'un détecteur de troisième génération, le Einstein Telescope. Dans les deux cas, j'utilise des "mock data and science challenges" qui consistent à simuler Les données des détecteurs gravitationnels contenant un grand nombre de sources distribuées de façon réalistes dans l'espace des paramètres. / Here I present my thesis investigating gravitational-wave data analysis in the following two areas. The first is to test the readiness of the LIGO-Virgo collaborations to the advanced detector era, which will begin in the summer of 2015, to make a detection of an astrophysical stochastic gravitational-wave background. The second is to continue an investigation into the science potential of a conceived, third generation gravitational-wave detector, the Einstein Telescope, in terms of astrophysics and cosmology. Both of these are conducted with the use of mock data and science challenges which consists of the production of expected gravitational-wave detector data, containing a large number of sources, that are simulated using realists distributions.

Magister Scientiae - MSc / Natural radioactivity studies have been carried out to study the textural characteristics, heavy mineral composition, provenance, sediment transport, and depositional environment of beach placer deposits. The naturally occurring radionuclides such as 232Th, 238U and 40K are used as the tracers of the mineralogical properties of beach sands, which reflect the geological characteristics such as transport and sorting processes and the depositional environment. The present work focuses on the radiometric characteristics of beach sand deposits along the west coast of South Africa. Beach sands samples were collected at the Melkbosstrand (MBS) and Ouskip (OSK) beach. The activity concentrations of these radionuclides were determined by high-resolution gamma-ray spectrometry using a high-purity germanium (HPGe) detector in a low-background configuration.

Depuis leur découverte en 1912, l'origine des rayons cosmiques, composés à 90% de protons, n'est toujourspas connue. Les vestiges de supernovae sont de bons candidats à la production des rayons cosmiquesgalactiques.Pour étudier les sites de production des protons, sensibles aux champ magnétiques, nous nousappuyons sur les rayons gamma (neutres et stables).L'onde de choc créée par l'explosion de la supernova se propage dans un milieu interstellairedense, les nuages moléculaires, pouvant être concidéré comme une cible pour les protons accélérés.L'objectif de ce travail est de rechercher des sites d'émission gamma en coïncidence avec des vestiges etdes nuages moléculaires.Nous avons utilisé pour cela les données du télescope spatial Fermi-LAT et du télescopes au solH.E.S.S.L'analyse conjointe des données a permis de tirer profit des points forts de chaque intrument.La production d'images de la région du ciel étudié est primordiale en astronomie.Nous avons tenté d'améliorer la production des images obtenues avec l'imageur H.E.S.S. en proposant uneméthode de lissage différente de celle employée actuellement. / Since their discovery in 1912, the cosmic rays origin is still unknown.Supernovae remnants (SNR) are good candidates to product Galactic cosmic rays.Because protons are sensitive to magnetic field, we lean on gamma rays, neutrals and stables particles.The shock wave of the SNR go through the interstellar medium which can be dense: the molecular clouds.They can be seen as target for accelerated protons.The objective of this work is to search for gamma-ray emission in coincidence with remnants and molecularclouds.We analysed data from Fermi-LAT space telescope and H.E.S.S., a Tcherenkov ground based telescope.The data joined analysis allow us to get the strong point out of each instrument.The sky view produced from the data is very important in astronomy.We tryied to improve the smoothing method of the images performed in H.E.S.S. analysis.

Submitted by Irene Nascimento (irene.kessia@ufpe.br) on 2016-04-15T15:07:33Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação CONTROLE DA INJEÇÃO DE CATALISADOR EM UMA UNIDADE PILOTO TIPO FCC A FRIO.pdf: 3413557 bytes, checksum: 5abbf7dd3a8cab8c21085e585d6282f6 (MD5) / Made available in DSpace on 2016-04-15T15:07:33Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação CONTROLE DA INJEÇÃO DE CATALISADOR EM UMA UNIDADE PILOTO TIPO FCC A FRIO.pdf: 3413557 bytes, checksum: 5abbf7dd3a8cab8c21085e585d6282f6 (MD5) Previous issue date: 2015-08-31 / CNPQ / O Craqueamento Catalítico Fluidizado (FCC) é largamente utilizado no processo de refino do petróleo para transformar hidrocarbonetos de baixo valor comercial em produtos de elevado valor agregado, como gasolina, diesel e GLP. A crescente demanda de combustíveis fósseis, que são recursos não renováveis, requer melhor compreensão do processo e da operação, desafios que tem atraído o interesse da indústria e da academia pelo FCC. Esse processo é bastante competitivo e está em continuo desenvolvimento tecnológico, cujas pesquisas estão divididas em duas grandes linhas: modelos fluidodinâmicos frios e modelos cinéticos. A combinação das informações obtidas nas linhas de pesquisas deve retornar ao processo industrial e garantir a competitividade. Com essa perspectiva, foi construída uma Unidade Piloto a Frio (UPF), no Departamento de Energia Nuclear da UFPE, para a investigação de parâmetros fluidodinâmicos no riser da unidade com auxílio das medidas de transmissão gama. A transmissão gama é requerida como método não intrusivo para medir a distribuição da concentração do catalisador no reator do FCC o riser. Com a operação da UPF realizam-se medidas em tempo real de pressão, vazão, intensidade da radiação, com a condição de que a automação garante que as variáveis do sistema estão sob controle. Este controle é necessário para realização das medidas porque as hipóteses dos modelos matemáticos para simular o escoamento bifásico ar–catalisador de FCC, assumem que o sistema é um leito fluidizado circulando em regime estacionário. Numa unidade piloto como no processo industrial, o controle da injeção de catalisador é um processo de extrema importância, pois a eficiência da reação de craqueamento dos hidrocarbonetos depende da concentração e da distribuição do catalisador no riser. No presente trabalho foi desenvolvido um novo tipo de injetor de sólidos, com desempenho avaliado em função da pressão, intensidade gama e da estabilidade do sistema sob controle automatizado. Os resultados apresentados demonstram que as variáveis do processo, medidas em tempo real, apresentaram a precisão requerida para a operação do sistema em regime estacionário. / The Fluid Catalyst Cracking FCC is a worldwide used process in petroleum refinery aiming to break fossils long carbohydrates chains into more commercial interesting products as gasoline, diesel, GLP. Increasing demand for renewable energy due to time limiting of the fossils sources and also for environmental reasons requires a continuous development and innovation of the FCC process. Such a demand brings technologic and academic efforts in order to keep FCC as a competitive commercial process. Therefore, the research follows two big lines: fluid dynamics and kinetic which for physical models are developed to simulate industrial plants for studying and return the obtained innovation. Looking for such a research perspective a cold model UPF was installed at Nuclear Energy Department of UFPE for fluid dynamic parameters investigation by means of gamma ray transmission measurements. The nuclear nonintrusive technique is required in the riser for the solid concentration distribution measurements. Online measurements of pressure, flow and gamma intensity are carried out during UPF automated operation that is keeping by control a stead state regime. Such operational conditions are assumed in the hypotheses of mathematical models that air-FCC catalyst flow can be simulated as a circulating fluidized bed in a stead state regime. As for a pilot unit in industrial plants the solid injection in riser is very important as the catalyst concentration distribution maps the cracking reactions, therefore, determining process efficiency. In this work a new solid injector was developed, its capability in keeping stable operational conditions was demonstrated by pressure and gamma intensity measurements under automation control.

SVOM est une mission spatiale franco-chinoise qui sera lancée à la fin de l’année 2021. Son objectif est d’étudier les sursauts gamma et autres sources transitoires du ciel X et gamma. Les sursauts gamma sont des explosions cosmiques brèves et très énergétiques permettant leurs détections à des distances extrêmes. Ils apparaissent de manière aléatoire sur tout le ciel et émettent de la radiation dans une large gamme de longueurs d’ondes, allant de l’émission en infrarouge jusqu’aux rayons gamma. SVOM, qui évoluera en orbite basse autour de la Terre, sera composé de quatre instruments, sensibles du domaine visible aux rayons gamma, et sera couplé à des télescopes situés sur Terre qui effectueront des observations complémentaires dans les longueurs d’ondes allant du visible à de l’infrarouge. Le travail que je présente dans cette thèse est basé sur l’étude des performances du télescope MXT, dont l’optique est inspirée du principe de fonctionnement des “yeux des langoustes”. Elle sera mise en place pour la première fois dans le cadre de télescopes X, nécessitant donc de comprendre la réponse de cette optique. MXT est chargé d’observer, la contrepartie qui suit les sursauts gamma, dite émission rémanente, dans la gamme des rayons X entre 0,2 et 10 keV. Il joue un rôle clé dans la localisation précise de ces sources astrophysiques afin de transmettre, en temps réel, leurs positions aux télescopes situés au sol, qui observeront à leur tour, rapidement et précisément, le phénomène. Au cours de mon travail de thèse, j’ai mis en place un simulateur d’observation de MXT qui m’a permis d’estimer et d’étudier les performances attendues de l’instrument au cours de la mission. J’ai également développé des algorithmes de localisation qui seront implémentés à bord du satellite. Ceux-ci m’ont ensuite permis de tester les capacités de localisation de MXT à partir d’une base de données des rémanences de sursauts gamma et de montrer que 50% de ces rémanences seront localisées plus précisément que la minute d’arc. J’ai enfin appliqué une partie de mes modélisations numériques dans le cas de sources d’ondes gravitationnelles afin d’évaluer la détection des contreparties X d’étoiles à neutrons binaires. / SVOM is a Sino-French space mission to be launched at the end of 2021. Its objective is the study of gamma-ray bursts (GRBs) and other transient high energy sources. These GRBs are very powerful cosmic explosions that can be detected at extreme distances. They appear randomly on all the sky and emit radiation in a wide wavelength range, from the infrared emission to gamma rays. SVOM space mission will shed new light on the physical phenomena associated to GRBs by detecting and observing them in real time over a wide energy range. The satellite, which will be injected on a low Earth orbit, will carry four instruments sensitive from the visible to the gamma-ray domain. Ground based telescopes will complement the space borne ones and will allow for follow-up observations from the visible to the infrared band. The MXT instrument, whose optics are based on the “lobster eyes” principle, will observe GRBs soft X-rays counterparts (afterglows) between 0.2 and 10 keV. This optics will be used for the first time for an X-ray telescope which means to characterize this optics. MXT will play a key role in the localization of these astrophysical sources that will be transmitted, in real time, to ground based instruments allowing for fast and precise observations. During my thesis, I developed an MXT observation simulator in order to predict the performances of the instrument during the mission. I also developed localization algorithms to be implemented on board the SVOM satellite and made use of the state of the art knowledge about X-ray afterglows in order to predict the localization capabilities of MXT. I demonstrated thaht 50% of these afterglows will be localized with a better precision than the arc-minute. I finally applied my simulation tools in the case of gravitational wave sources and, in particular, to assess the capabilities of MXT to observe bright X-ray counterparts of binary neutron star mergers.