Thesis (Ph. D.)--University of Wisconsin--Madison, 1989. / Cover title. Includes bibliographical references (p. 245-251).

The efficiency of NaI(T1) scintillation counters for the detection of gamma rays is discussed and experimentally determined. Experimental efficiencies, based upon the number of counts above a bias equal to one-half the gamma ray energy and a solid angle defined to the crystal effective centre, for a three-inch-diameter by three-inch long (3 x 3) crystal are given for gamma ray energies of 0.51, 1.275 and 6.14 MeV. Gamma ray spectra at 1.275 and 6.14 MeV are extrapolated to zero energy in order to compare theoretical efficiencies, based upon the integrated primary absorption, with the experimental results. These results show that, with experience, one can expect accuracy to better than 5% at these energies. Tables are given of the theoretical efficiency for 3x3, 2¾ x 4½ and 5x4 crystals for several gamma ray energies and source-to-counter distances of from 0.1 cm to 1 m. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

No description available.

Ce travail est consacré à l'étude des processus de relaxation de l'énergie et des canaux de perte d'énergie dans les cristaux scintillateurs CsI:A (A = Tl, In). Dans le chapitre 1 les principaux processus d'interaction des rayonnements ionisants avec les solides luminescents sont discutés. Les méthodes expérimentales et techniques utilisées dans cette étude ainsi que les méthodes de synthèse, de caractérisation cristal, de pureté, etc sont présentées dans le chapitre 2. La deuxième section traite de la description des méthodes spectroscopiques d'analyse utilisées. Il comprend des techniques spécifiques d'investigation, telles que la spectroscopie en temps résolue, la méthode de thermoluminescence, la spectroscopie de photoluminescence excitée dans l'ultraviolet lointain, obtenues à l'aide des synchrotrons. L'étude des propriétés de luminescence des centres luminescents dans CsI:Tl et CsI:In est présentée dans le Chapitre 3 et permet de caractériser le paramètre Q. La spectroscopie d'excitation et d'émission de la luminescence (surface 3D) le type, la structure électronique et le rendement des centres luminescents liés aux ions dopants sont déterminés. Dans le chapitre 4, les propriétés de scintillation de CsI:Tl et CsI:In sont présentés. Le rendement de scintillation et la résolution énergétique sont meilleurs dans les cristaux CsI:Tl. L'étude des chaines de transfert d'énergie vers les centres luminescents et des pertes d'énergie sont décrits dans le chapitre 5. Cette approche de modélisation appliquée comprend une solution numérique des équations de population. Elle est suffisamment générale pour être utilisée dans le cas d'une grande variété de matériaux scintillateurs / This work is devoted to study of energy relaxation processes and energy loss channels in CsI :A scintillation crystals (A=Tl, In). Study of energy loss mechanisms in activated CsI scintillation crystals aims to answer the question, if the fundamental limit of scintillation yield in classical alkali halide scintillators has been reached. Concentration series of CsI:Tl and CsI:In single crystalline samples were grown by the Bridgman technique. Investigation of electron excited states in this system is done using luminescence spectroscopy methods. Analysis of the experimental results allows to come up with a general model of energy relaxation in CsI:A. The model includes the activator-induced and the intrinsic (STE) energy relaxation channels, and three possible charge states of the activators. A system of kinetic rate equations (compiled based on the energy relaxation model) allows simulating many scintillation properties of CsI:A system as a function of temperature and the activator concentration

This thesis aims to answer the question, “What physical process dominates the formation of plasma irregularities, capable of directly or indirectly causing GPS L1 band scintillation, in polar cap plasma patches during magnetic storm conditions?.” A novel modelling technique utilising an ionospheric imaging algorithm is developed and used to elucidate the relative importance of the two most commonly discussed processes. These are the Gradient Drift Instability (GDI) and turbulence induced by electric field mapping to the ionosphere from the magnetosphere. The results show that in magnetic storm conditions, at times the GDI process is dominant, but that at other times turbulence may be as significant as the GDI in determining how the plasma within a polar cap patch behaves, possibly more so. This in turn suggests that further study of the turbulence process is necessary in order to fully understand how big a role it plays in causing GPS L1 band scintillation in the polar cap. The success of the modelling technique developed here shows the utility of ionospheric imaging as a tool for understanding physical problems of the ionosphere; efforts to improve it and to apply it in other contexts would be worthwhile.

Bibliography: leaves 191-202. 1. Introduction -- 2. Instrumentation and calibration -- 3. A radio monitoring program for southern blazars -- 4. Analysis of long-term blazar radio variability -- 5. Probing microarcsecond-scale structure using interstellar scintillation -- 6. The rapid scintillator, PKS 1257-326 -- 7. Conclusions and scope for further work.

No description available.

No description available.

A detector with a target mass of 7 kg of liquid argon was designed, constructed and operated at Queen’s University. This detector is a scaled model for the DEAP project toward a tonne-scale argon detector to search for the WIMP candidate of the so far undetected, dark matter of the universe. The primary intent of the scaled detector was to measure the achievable level to reject background events by use of pulse shape discrimination, being based upon the scintillation timing properties of liquid argon. After refining the apparatus and components, the detector was in operation from the 20th of August until the 16th of October 2007 before being moved to its current location in SNOLAB. During this time, a population of 31 million well-tagged gamma events were collected, of which 15.8 million were in the energy range of interest for calibration. This population was sufficient to demonstrate the discrimination of background events by pulse shape discrimination at the level of 6.3 × 10-8. An analytical model was constructed, based on the scintillation processes and detector response, and has been sufficiently investigated to make predictions of further achievable discrimination. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2008-04-25 01:39:39.121

Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 53-54). Also available on the World Wide Web.