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 2014 with total page 193 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 Positron Annihilation written by A.T. Steward and published by Elsevier. This book was released on 2012-12-02 with total page 455 pages. Available in PDF, EPUB and Kindle. Book excerpt: Positron Annihilation focuses on the process of positron annihilation in different environments. Partitioned into two parts with 42 chapters, the book contains the contributions of authors who have done research on the annihilation of positrons, which brought about valuable information on the properties of matter. The first part of the book deals with lengthy review articles, including a survey of the physics of positron annihilation; positron annihilation in metals and the theory involved in the process; and positron annihilation in alkali halides and ionic crystals. Positronium formation and interaction in gases, molecular substances, and ionic crystals are also given attention. Gaseous positronics and positron annihilation in condensed gases and liquids are also discussed. The second part of the book focuses on developments on positron annihilation and the direction of research on this field. The studies concentrate on positron annihilation in various crystals, metals, mercury, liquefied gases, helium, and metal oxides. Numerical representations and analyses are presented to support the processes involved. The book can best serve the interest of those who want to explore further the annihilation of positrons.
Download or read book Positron Annihilation in Chemistry written by Ole E. Mogensen and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 279 pages. Available in PDF, EPUB and Kindle. Book excerpt: The only critical discussion available on the chemistry of the two "strange" light particles, the positron and positronium, with much space devoted to the excess electron. Positron annihilation allows the investigation of many unusual phenomena in the reaction kinetics of the positron, positronium, and excess electron, and in radiation chemistry and physics, while also providing important information on defects in solids.
Download or read book Progress in Positron Annihilation written by Rados?aw Zaleski and published by Trans Tech Publications Ltd. This book was released on 2010-12-30 with total page 172 pages. Available in PDF, EPUB and Kindle. Book excerpt: Volume is indexed by Thomson Reuters CPCI-S (WoS). The aim of this special collection is to present recent progress made, and reflect current ideas, in research fields where positron and positronium are involved. The contents cover a wide range of positron-related research topics; including both fundamental (theoretical calculations, radiation chemistry, hyperfine interactions, positronium physics and chemistry) and applied (metal, polymer, thin film and other materials, development of experimental techniques) aspects.
Download or read book Electron Positron Annihilation Physics written by Brian Foster and published by CRC Press. This book was released on 1990 with total page 256 pages. Available in PDF, EPUB and Kindle. Book excerpt: A detailed introduction to the main topics in e +e - annihilation, with particular emphasis on experimental work. Invaluable to both graduate students studying high-energy physics & scientists entering the field.
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 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 Positrons in Solids written by Pekka Hautojärvi and published by Springer. This book was released on 1979 with total page 280 pages. Available in PDF, EPUB and Kindle. Book excerpt: In condensed matter initially fast positrons annihilate after having reached equi librium with the surroundings. The interaction of positrons with matter is governed by the laws of ordinary quantum mechanics. Field theory and antiparticle properties enter only in the annihilation process leading to the emergence of energetic photons. The monitoring of annihilation radiation by nuclear spectroscopic methods provides valuable information on the electron-positron system which can directly be related to the electronic structure of the medium. Since the positron is a positive electron its behavior in matter is especially interesting to solid-state and atomic physi cists. The small mass quarantees that the positron is really a quantum mechanical particle and completely different from any other particles and atoms. Positron physics started about 25 years ago but discoveries of new features in its interac tion with matter have maintained continuous interest and increasing activity in the field. Nowadays it is becoming part of the "stock-in-trade" of experimental physics.
Download or read book Positron Annihilation written by L. Dorikens-Vanpraet and published by . This book was released on 1989 with total page 1038 pages. Available in PDF, EPUB and Kindle. Book excerpt:
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 Positrons from Supernova and the Origin of the Galactic center Positron annihilation Radiation written by and published by . This book was released on 1983 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The emission of positrons from supernova ejecta is dicussed in terms of the galactic-center annihilation radiation. The positrons from the radioactive sequences 56Ni.-->.56Co.-->.56Fe are the most numerous source from supernova. Only type I supernova will allow a significant fraction to escape the expanding ejecta. For a neutron star model of a type I SN a fraction 4 x 10−3 of the escaped positron is enough to create the observed several year fluctuation of the annihilation radiation. The likelihood of this model is discussed in terms of other astrophysical evidence as well as the type I SN light curve.
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 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 Single photon Annihilation of Positrons with Electrons written by James Arthur Whalen and published by . This book was released on 1957 with total page 170 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Positron Annihilation written by 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 Annihilation in Gases and Galaxies written by Richard J. Drachman and published by . This book was released on 1990 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
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.
