Download or read book Origine et physique d annihilation des positrons dans la galaxie written by Anthony Alexis and published by . This book was released on 2015 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Une émission gamma à 511\kev\ est observée depuis le début des années 1970 dans la direction du centre Galactique. Cette émission est la signature de l'annihilation d'électrons avec des positrons qui sont les antiparticules des électrons. Malheureusement, l'origine de ces positrons galactiques reste à l'heure actuelle un mystère. De nombreuses sources de positrons ont été proposées mais elles présentent toutes des difficultés à expliquer cette émission d'annihilation galactique. Celle-ci possède une distribution spatiale particulière. Depuis 2002, le spectromètre SPI à bord de l'observatoire spatial INTEGRAL révèle une émission fortement concentrée dans le bulbe galactique et une faible émission en provenance du disque galactique. Cette distribution spatiale est totalement atypique car elle ne ressemble à aucune distribution galactique connue, que ce soit d'une population stellaire ou d'un gaz interstellaire. L'hypothèse selon laquelle les positrons s'annihilent à proximité de leur source (c.-à-d. que la distribution spatiale de l'émission d'annihilation est identique à la distribution spatiale des sources) a donc été remise en cause. Des études récentes semblent suggérer que les positrons pourraient se propager loin de leur source avant de s'annihiler. Ceci permettrait de résoudre éventuellement l'énigme sur l'origine des positrons galactiques. Cette thèse a été consacrée à modéliser la propagation puis l'annihilation des positrons dans la Galaxie, dans le but de comparer des modèles spatiaux de l'émission d'annihilation aux dernières données mesurées par SPI/INTEGRAL. Cette méthode nous permet en effet de poser des contraintes sur l'origine des positrons galactiques. Nous avons donc développé un code de simulation Monte Carlo de transport des positrons dans la Galaxie dans lequel nous avons implémenté toutes les connaissances théoriques et observationnelles de la physique des positrons (sources, modes de transport, pertes en énergie, modes d'annihilation) et du milieu interstellaire de la Galaxie (distributions du gaz interstellaire, champs magnétiques galactiques, structure des phases gazeuses). Dues aux incertitudes entourant de nombreux paramètres physiques (champs magnétique du halo galactique, structure des phases du milieu interstellaire, etc.), nous avons implémenté plusieurs modèles pouvant potentiellement rendre compte de ces paramètres. Ces paramétrages différents de la Galaxie nous ont ainsi permis d'estimer leur impact sur la propagation et l'émission d'annihilation des positrons. Nous avons appliqué ce code à l'étude des positrons émis par la décroissance \betaplus\ de l'\alu, du \titan\ et du \nickel\ qui sont continûment produits dans la Galaxie au coeur des étoiles massives et des explosions de supernovae. Nous avons étudié ces sources car l'idée que celles-ci pourraient expliquer l'émission d'annihilation galactique est largement répandue depuis des décennies. Nous avons montré que, peu importe le paramétrage de la Galaxie, ces positrons permettent d'expliquer l'émission du disque mais pas la totalité de l'émission du bulbe. La raison est simple : ces positrons ne se propagent pas très loin de leur source avant de s'annihiler. Dans ce cadre, une source supplémentaire de positrons dans le bulbe est nécessaire pour rendre compte de la totalité de l'émission. Nous avons montré qu'une source transitoire de positrons (d'énergie \simMeV) située au centre de la Galaxie pourrait expliquer l'émission du bulbe.

Download or read book Mod lisation de L mission D annihilation Des Positrons Galactiques written by William Gillard and published by . This book was released on 2008 with total page 226 pages. Available in PDF, EPUB and Kindle. Book excerpt: Positrons annihilate in the central region of our Galaxy. This has been known since the detection of a strong emission line centered on an energy of 511 keV in the direction of the Galactic center. This gamma-ray line is emitted during the annihilation of positrons with electrons from the interstellar medium. The spectrometer SPI, onboard the INTEGRAL observatory, performed spatial ans spectral analyses of the positron annihilation emission. This thesis presents a study of the Galactic positron annihilation emission based on models of the different interactions undergone by positrons in the interstellar medium. The models are relied on our present knowledge of the properties of the interstellar medium in the Galactic bulge, where most of the positrons annihilate, and of the physics of positrons (production, propagation and annihilation processes). To obtain constraints on the positrons sources and physical characteristics of the annihilation medium, we compared the results of the models to measurements provided by the SPI spectrometer.

Download or read book L annihilation des positrons galactiques written by Vincent Lonjou and published by . This book was released on 2005 with total page 179 pages. Available in PDF, EPUB and Kindle. Book excerpt: L'origine des positrons galactiques reste un des sujets les plus controversés de l'Astrophysique des hautes énergies depuis la découverte de la raie d'annihilation électron-positron en provenance du centre galactique à la fin des années 1970. L'étude de la raie d'annihilation à 511 keV est actuellement un des objectifs majeurs de SPI : le spectromètre d'INTEGRAL. Cette thèse s'ouvre sur l'étude de la partie centrale de SPI: son plan de détection. La procédure de calibration en énergie ainsi que l'étude de la dégradation des détecteurs sont reportées. Par la suite, une étude approfondie du bruit de fond instrumental permet d'utiliser SPI dans les meilleures conditions. Le traitement des données aboutit alors à des cartes du ciel et des spectres avec une précision inégalée. Pour finir, les contributions des diverses sources potentielles de positrons galactiques sont confrontées aux résultats obtenus.

Download or read book L ANNIHILATION DES POSITRONS ET LE CENTRE GALACTIQUE written by PIERRE.. WALLYN and published by . This book was released on 1912 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: LE CENTRE GALACTIQUE EST L'OBJET D'ETUDES INTENSIVES DE LA PART DES ASTROPHYSICIENS QUI ETUDIENT LE RAYONNEMENT GAMMA DEPUIS LE DEBUT DES ANNEES 70, DATE A LAQUELLE LES CHERCHEURS DE L'UNIVERSITE DE RICE (USA) DETECTENT POUR LA PREMIERE FOIS, LA RAIE D'ANNIHILATION ELECTRON-POSITRON EN PROVENANCE DE CETTE REGION. CETTE RAIE D'ENERGIE 511 KEV EST LE RESULTAT DE DEUX PROCESSUS DISTINCTS: (1) L'ANNIHILATION DE POSITRONS EMIS PAR DES OBJETS ASTROPHYSIQUES COMME LES SUPERNOVAE, LES NOVAE, ETC... ET QUI S'ANNIHILENT DANS LE MILIEU INTERSTELLAIRE POUR PRODUIRE UNE COMPOSANTE DIFFUSE ET STATIONNAIRE; (2) L'ANNIHILATION DE BOUFFEES DE POSITRONS EMIS SPORADIQUEMENT, SUR DE COURTES PERIODES, PAR UN OU PLUSIEURS CANDIDATS TROUS NOIRS SITUES DANS LA DIRECTION DU CENTRE GALACTIQUE ET PRODUISANT UNE COMPOSANTE A 511 KEV, VARIABLE DANS LE TEMPS. LE PROFIL DE LA RAIE D'ANNIHILATION OBSERVE PAR DES EXPERIENCES A HAUTE RESOLUTION EN ENERGIE (DETECTEURS AU GERMANIUM) INDIQUE QUE LE MILIEU D'ANNIHILATION DES POSITRONS DE LA COMPOSANTE DIFFUSE EST UN GAZ CHAUD, EVENTUELLEMENT IONISE, A 8000 K ENVIRON. LA COMPOSANTE A 511 KEV, VARIABLE DANS LE TEMPS, SEMBLE CORRESPONDRE A L'ANNIHILATION DE POSITRONS DANS UN NUAGE FROID, AUTOUR DE 80 K COMME LE NUAGE G-0.86-0.08, SITUE A PROXIMITE DE LA SOURCE 1E1740.7-2942. L'EXPERIENCE BALLON HEXAGONE (MAI 1989) A MIS EN EVIDENCE UNE RAIE AUTOUR DE 170 KEV DANS LA DIRECTION DU CENTRE GALACTIQUE. NOUS PROPOSONS UN MODELE EXPLICATIF DU PHENOMENE EN TERME DE RETRODIFFUSION DE PHOTONS D'ANNIHILATION A LA SURFACE D'UNE BULLE DE MATIERE EJECTEE PAR LE DISQUE D'ACCRETION AUTOUR D'UN TROU NOIR, LORS D'UN ETAT SUPER-CRITIQUE DU SYSTEME. CE MODELE EST EGALEMENT UTILISE POUR EXPLIQUER LA SEQUENCE TEMPORELLE DES STRUCTURES AUTOUR DE 170 ET 102 KEV OBSERVEE PAR SIGMA SUR NOVA MUSCAE. L'ANNIHILATION DES POSITRONS DANS LA PHASE FROIDE DU MILIEU INTERSTELLAIRE (80 K) EST ETUDIEE EN SE BASANT SUR DES MESURES RECENTES DE SECTIONS EFFICACES D'INTERACTION DES POSITRONS AVEC L'HYDROGENE ATOMIQUE ET MOLECULAIRE. NOUS CALCULONS LA VALEUR DE LA FRACTION DE POSITRONIUM AVANT THERMALISATION POUR H ET H#2 ET PRECISONS LE TEMPS DE THERMALISATION DES POSITRONS EN FONCTION DE LA DENSITE DU MILIEU ET DE L'ENERGIE INITIALE DE LA PARTICULE. LA DUREE DU PHENOMENE D'ANNIHILATION EN VOL PAR ECHANGE DE CHARGE EST EGALEMENT CALCULEE. CECI NOUS PERMET DE DEFINIR DE NOUVELLES CONTRAINTES SUR L'OBSERVATION EVENTUELLE DES RAIES DE RECOMBINAISON DU POSITRONIUM

Download or read book The Origin of the Galactic 511 KeV Positron Annihilation Emission Morphology written by and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The origin of the Galactic 511 keV positron annihilation emission morphology.

Download or read book Positron Annihilation written by Wayne State University and published by . This book was released on 1967 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Positron Annihilation written by National Symposium on Positron Annihilation (1979 ; Delhi) and published by . This book was released on 1980 with total page 359 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Etude de l annihilation lectron positon dans la r gion du centre galactique avec le spectrom tre INTEGRAL SPI written by Patrick Sizun and published by . This book was released on 2007 with total page 222 pages. Available in PDF, EPUB and Kindle. Book excerpt: The imaging and spectral capabilities of the SPI spectrometer onboard the INTEGRAL satellite enabled us to further study the source of the 511 keV line from electron-positron annihilation detected in the Galactic centre region. A better determination of the spatial extent of the source, the intrinsic width of the line and the fraction of positrons annihilating in-flight, directly or via the formation of ortho-Positronium atoms would improve our knowledge of both the annihilation medium and the initial source of positrons. The first part of this thesis deals with a key ingredient of the extraction of the annihilation spectrum: the optimization of the instrumental background model. New data screening and tracer selection procedures are presented. Classical multi-linear models are compared to neural and bayesian networks. Finally, three years of observation are used to constrain the width of the source and derive its spectrum. The second part of the thesis focuses on one of the possible scenarios explaining the high positron injection rate deduced from the flux of the 511 keV line: the annihilation of light dark matter particles into electron-positron pairs. The various radiation mechanisms involved are modeled and confronted to observations in order to set an upper limit on the mass of the light dark matter particle.

Download or read book Astroparticle Particle and Space Physics Detectors and Medical Physics Applications written by Michele Barone and published by World Scientific. This book was released on 2006 with total page 1162 pages. Available in PDF, EPUB and Kindle. Book excerpt: The exploration of the subnuclear world is done through increasingly complex experiments covering a wide range of energies and in a large variety of environments ? from particle accelerators, underground detectors to satellites and space laboratories. For these research programs to succeed, novel techniques, new materials and new instrumentation need to be used in detectors, often on a large scale. Hence, particle physics is at the forefront of technological advancement and leads to numerous applications. Among these, medical applications have a particular importance due to the health and social benefits they bring. This volume reviews the advances made in all technological aspects of current experiments in the field.

Download or read book Lasers and Nuclei written by Heinrich Schwoerer and published by Springer Science & Business Media. This book was released on 2006-05-22 with total page 258 pages. Available in PDF, EPUB and Kindle. Book excerpt: Lasers and Nuclei describes the generation of high-energy-particle radiation with high-intensity lasers and its application to nuclear science. A basic introduction to laser--matter interaction at high fields is complemented by detailed presentations of state of the art laser particle acceleration and elementary laser nuclear experiments. The text also discusses future applications of lasers in nuclear science, for example in nuclear astrophysics, isotope generation, nuclear fuel physics and proton and neutron imaging.

Download or read book Quantum Mechanics Volume 3 written by Claude Cohen-Tannoudji and published by John Wiley & Sons. This book was released on 2019-12-16 with total page 790 pages. Available in PDF, EPUB and Kindle. Book excerpt: This new, third volume of Cohen-Tannoudji's groundbreaking textbook covers advanced topics of quantum mechanics such as uncorrelated and correlated identical particles, the quantum theory of the electromagnetic field, absorption, emission and scattering of photons by atoms, and quantum entanglement. Written in a didactically unrivalled manner, the textbook explains the fundamental concepts in seven chapters which are elaborated in accompanying complements that provide more detailed discussions, examples and applications. * Completing the success story: the third and final volume of the quantum mechanics textbook written by 1997 Nobel laureate Claude Cohen-Tannoudji and his colleagues Bernard Diu and Franck Laloë * As easily comprehensible as possible: all steps of the physical background and its mathematical representation are spelled out explicitly * Comprehensive: in addition to the fundamentals themselves, the books comes with a wealth of elaborately explained examples and applications Claude Cohen-Tannoudji was a researcher at the Kastler-Brossel laboratory of the Ecole Normale Supérieure in Paris where he also studied and received his PhD in 1962. In 1973 he became Professor of atomic and molecular physics at the Collège des France. His main research interests were optical pumping, quantum optics and atom-photon interactions. In 1997, Claude Cohen-Tannoudji, together with Steven Chu and William D. Phillips, was awarded the Nobel Prize in Physics for his research on laser cooling and trapping of neutral atoms. Bernard Diu was Professor at the Denis Diderot University (Paris VII). He was engaged in research at the Laboratory of Theoretical Physics and High Energy where his focus was on strong interactions physics and statistical mechanics. Franck Laloë was a researcher at the Kastler-Brossel laboratory of the Ecole Normale Supérieure in Paris. His first assignment was with the University of Paris VI before he was appointed to the CNRS, the French National Research Center. His research was focused on optical pumping, statistical mechanics of quantum gases, musical acoustics and the foundations of quantum mechanics.

Download or read book Protection of Materials and Structures from Space Environment written by J. Kleiman and published by Springer Science & Business Media. This book was released on 2006-03-09 with total page 553 pages. Available in PDF, EPUB and Kindle. Book excerpt: This publication presents the proceedings of ICPMSE-6, the sixth international conference on Protection of Materials and Structures from Space Environment, held in Toronto May 1-3, 2002. The ICPMSE series of meetings became an important part of the LEO space community since it was started in 1991. Since then, the meeting has grown steadily, attracting a large number of engineers, researchers, managers, and scientists from industrial companies, scientific institutions and government agencies in Canada, U. S. A. , Asia, and Europe, thus becoming a true international event. This year’s meeting is gaining even stronger importance with the resumption of the ISS and other space projects in LEO, GEO and Deep Space. To reflect on these activities, the topics in the program have been extended to include protection of materials in GEO and Deep Space. The combination of a broad selection of technical and scientific topics addressed by internationally known speakers with the charm of Toronto and the hospitality of the organizers brings participants back year after year. The conference was hosted and organized by Integrity Testing Laboratory Inc. (ITL), and held at the University of Toronto’s Institute for Aerospace Studies (UTIAS). The meeting was sponsored by the Materials and Manufacturing Ontario (MMO) and the CRESTech, two Ontario Centres of Excellence; Air Force Office of Scientific Research (AFOSR/NL); MD Robotics; EMS Technologies; The Integrity Testing Laboratory (ITL); and the UTIAS.

Download or read book Brilliant Light in Life and Material Sciences written by Vasili Tsakanov and published by Springer Science & Business Media. This book was released on 2007-03-31 with total page 484 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book contains an excellent overview of the status and highlights of brilliant light facilities and their applications in biology, chemistry, medicine, materials and environmental sciences. Overview papers on diverse fields of research by leading experts are accompanied by the highlights in the near and long-term perspectives of brilliant X-Ray photon beam usage for fundamental and applied research.

Download or read book Nuclear Science Abstracts written by and published by . This book was released on 1973 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Physics Briefs written by and published by . This book was released on 1986 with total page 838 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Government Reports Annual Index written by and published by . This book was released on 1992 with total page 1128 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Astroparticle Physics written by Claus Grupen and published by Springer Nature. This book was released on 2020-01-27 with total page 616 pages. Available in PDF, EPUB and Kindle. Book excerpt: Describes the branch of astronomy in which processes in the universe are investigated with experimental methods employed in particle-physics experiments. After a historical introduction the basics of elementary particles, Explains particle interactions and the relevant detection techniques, while modern aspects of astroparticle physics are described in a chapter on cosmology. Provides an orientation in the field of astroparticle physics that many beginners might seek and appreciate because the underlying physics fundamentals are presented with little mathematics, and the results are illustrated by many diagrams. Readers have a chance to enter this field of astronomy with a book that closes the gap between expert and popular level.