Global ETD Search

21	Understanding the plasma and improving extraction of the ISIS Penning H⁻ ions source Lawrie, Scott January 2017 (has links) A Penning-type surface-plasma negative hydrogen (H<sup>-</sup>) ion source has been delivering beam at the ISIS pulsed spallation neutron and muon facility for over thirty years. It is one of the most powerful and well-renowned H<sup>-</sup> sources in the world. Although long-term experience has allowed the source to be operated reliably and set up in a repeatable way, it is treated as something of a 'black box': the detailed plasma physics of why it works has always been unclear. A vacuum Vessel for Extraction and Source Plasma Analyses (VESPA) has been developed to understand the ISIS ion source plasma and improve the beam extracted from it. The VESPA ion source is operated in a completely new regime whereby the analysing sector dipole magnet housed inside a refrigerated 'cold box', presently used on ISIS, is replaced by an on-axis extraction system. The new extraction system incorporates a novel einzel lens with an elliptical aperture. This is the first demonstration of an elliptical einzel being used to focus an asymmetric H<sup>-</sup> ion beam. With the dipole magnet removed, the ion source has been shown to produce 85 mA of H<sup>-</sup> beam current at normal settings; of which 80 mA is transported through the new einzel lens system, with a normalised RMS emittance of 0.2 π mm mrad. Optical emission spectroscopy measurements have shown a plasma density of 10<sup>19</sup> m<sup>â3</sup>, an H<sub>2</sub> dissociation rate of 70%, an almost constant electron temperature of 3.5 eV and an atomic temperature which linearly increases above the electron temperature. In support of these principal measurements, rigorous particle tracking, electrostatic and thermal simulations were performed. In addition, a suite of new equipment was manufactured by the author. This includes a fast pressure gauge, a temperature controller, a high voltage einzel lens circuit, a fast beam chopper and a caesium detection system.
22	Znalosti obyvatelstva vybraného regionu o následcích havárie na jaderné elektrárně v Černobylu / Knowledge of population in a selected region about the Chernobyl Nuclear Power Plant accident consequences PRAŽÁK, Marek January 2016 (has links) The Chernobyl nuclear disaster of April 26, 1986 is the worst nuclear accident in the history of mankind. An experiment conducted in the 4th reactor resulted in its explosion and a huge amount of radionuclides escaped into the environment in the course of the subsequent fire. The greater part of Europe was contaminated by radioactive fallout, including the former Czechoslovak Socialist Republic. From a health point of view, the most harmful radioactive substances causing radioactive contamination were caesium 137Cs and iodine 131I. The then government did not provide objective and true information to the citizens and the media depicted the disaster as an insignificant incident. I set the following goals of my thesis: a) to develop an overview of immediate and especially long-term consequences of the accident; b) to analyse the knowledge of the population of the South Bohemian Region of the consequences of the Chernobyl disaster depending on the age of respondents. For fulfilling the set goals, I set myself the following hypotheses: H1) the theoretical division of the population's knowledge will be normal; H2) the knowledge of persons over 45 years of age will statistically be significantly higher than that of younger people. I handled the given theme using available specialized literature, Internet sources and publications published by relevant institutions. In the introductory part I describe the construction of the power plant, basic technical parameters of the reactor used and the course and causes of the actual accident. The next section is focused on the consequences of the accident in individual time periods immediately, after 10 years and after 20 years. I devote myself both to influences on human lives and health and to environmental, social, economic and psychological consequences. Furthermore,I describe the situation in former Czechoslovakia and the way of informing the population by the then government. The last section of the theoretical part is dedicated to the present situation in the Chernobyl region and at the power plant itself. While compiling the research part of the thesis, I gathered data among the inhabitants of the South Bohemian Region through questionnaire investigation. I addressed a total of 280 respondents, of which 140 were under 45 years of age and 140 were over 45 years of age. The questionnaire contained 15 questions concerning basic, not professional knowledge in this area. For the purposes of my questionnaire investigation, I divided the South Bohemian Region into districts. The selection of individual towns within the framework of the questionnaire investigation was carried out at random, by drawing lots. 280 questionnaires were completed in all, of which 140 questionnaires were completed by respondents under 45 and 140 questionnaires were completed by respondents over 45. By drawing lots, I selected 100 questionnaires out of these completed questionnaires, each age group being included. The test of the set hypotheses and statistical evaluation are carried out using descriptive and mathematical statistics. I carried out statistical evaluation by testing normality, using X2-good agreement test. I mutually compared the knowledge of the groups monitored by testing using a two-sample t-test, based on the estimate of empirical parameters from each group. Based on statistical investigation I came to the conclusion that the division of the population's theoretical knowledge was normal, which confirms the first hypothesis. The results of the investigation also unambiguously confirmed the fact that the knowledge of the population over 45 years of age was statistically significantly higher than the knowledge of the younger group of respondents. As far as total evaluation is concerned, the average value of correct answers in case of the older group of respondents reached 71%, while the younger group showed just 44% of correct answers, which confirms the second se hypothesis.
23	On the synthesis, measurement and applications of octanuclear heterometallic rings Faust, Thomas Benjamin January 2012 (has links) Inorganic macrocycles have stimulated interest in recent years for their magnetic properties, their associated host-guest chemistry and their aesthetically appealing structures. These characteristics have led to suggestions that they could be exploited for the purposes of ion recognition, catalysis, as single molecule magnets, MRI agents, antibacterial agents and as part of larger architectures in a molecular machine. This thesis explores the properties of a group of chromium(III) macrocycles, with functionality tailored towards different pursuits. Firstly the magnetic properties of a newly synthesised family of ring dimers are investigated. The nature of magnetic exchange within each ring leads to a net electronic spin which, it has been proposed, could represent a quantum binary digit within a quantum information processing system. By linking together pairs of rings, the degree of inter ring communication can be determined. Such interactions are important for the correlation of spin as initiation of quantum entanglement, a pre-requisite for quantum computing. The rings can also act as fluoro-metallocrowns, hosting the molecule which templated their formation. A range of rings with different guests are synthesised and their solid and solution state structures are explored. On templating about bulky dialkyl amines hybrid organic-inorganic rotaxanes are formed where the guest is fixed. In contrast when using small amines and alkali metals, exchange of guests is possible. The dynamics of all of these systems are investigated with proton NMR, quite remarkable for such highly paramagnetic complexes. 547.5
24	Electron Transfer and Other Reactions Using Atomic Metal Anions Butson, Jeffery M. 04 February 2014 (has links) The atomic metal anions Rb-, Cs-, Cu-, Ag- and Fe- have been generated in the gas phase and reacted with various neutral reactants in a triple quadrupole mass spectrometer. The metal anions were formed via electrospray ionization of the metal-oxalate solutions and form in gas phase between the capillary and the first quadrupole. Neutral gas phase reactants investigated include NO, NO2, SO2, C6F5OH, C6F5NH2, C6F6, E-octafluoro-butene and 1,2,3/1,2,4/1,3,5 trifluoro-benzene. When possible, CBS-4M methods were used to suggest the lowest energy products based on relative energy. Observed reactions of atomic metal anions with the aforementioned neutral species include electron transfer and dissociative electron transfer to the neutral gas phase reactants. In addition, hydrogen abstraction and fluorine abstraction forming a neutral metal hydride or fluoride as well as the formation of multiply substituted metal-oxide/fluoride anions was also observed. Metal-complex anions observed from the gas phase reactions include CuF-,CuF2-,CuO-,CuO2-, FeO-, FeO2-, FeO3-, FeF-, FeF2-, FeF3-, CsF- and CsF2-. Metal Anion Metal Anion Atomic Atomic Metal Anion Atomic Metals Atomic Metal Anions Anions Metals Mass Spectrometer Triple Quadrupole Rb Cs Fe Cu Ag Cs- Rb- Fe- Cu- Ag- pentafluoroaniline pentafluorophenol nitrogen dioxide sulfur dioxide nitrogen oxide nitrogen monoxide oxygen oxalic oxalic acid gas phase electrospray ionization electrospray ionization electro-spray ionization electro-spray hexafluorobenzene 1,2,3-trifluorobenzene 1,2,4-trifluorobenzene 1,3,5-trifluorobenzene fluorine E-octafluoro-butene octafluoro-butene octafluoro butene CBS-4M abstraction hydrogen abstraction fluorine abstraction hydride fluoride metal hydride metal fluoride caesium fluoride rubidium fluoride iron fluride copper fluoride rubidium caesium iron copper silver iron anion copper anion rubidium anion caesium anion silver anion cesium cesium anion atomic caesium anion atomic cesium anion atomic rubidium anion atomic iron anion atomic copper anion atomic silver anion 1,2,3 trifluorobenzene 1,2,4 trifluorobenzene 1,3,5 trifluorobenzene copper fluoride anion iron fluoride anion copper difluoride copper difluoride anion iron difluoride iron difluoride anion iron trifluoride iron trifluoride anion cesium fluoride cesium fluoride anion caesium difluoride anion caesium difluoride cesium difluoride cesium difluoride anion caesium fluoride anion nitrogen monoxide anion sulfur dioxide anion nitrogen dioxide anion copper oxide copper oxide anion copper dioxide copper dioxide anion iron oxide iron oxide anion iron dioxide iron dioxide anion iron trioxide iron trioxide anion electron transfer
25	Electron Transfer and Other Reactions Using Atomic Metal Anions Butson, Jeffery M. January 2014 (has links) The atomic metal anions Rb-, Cs-, Cu-, Ag- and Fe- have been generated in the gas phase and reacted with various neutral reactants in a triple quadrupole mass spectrometer. The metal anions were formed via electrospray ionization of the metal-oxalate solutions and form in gas phase between the capillary and the first quadrupole. Neutral gas phase reactants investigated include NO, NO2, SO2, C6F5OH, C6F5NH2, C6F6, E-octafluoro-butene and 1,2,3/1,2,4/1,3,5 trifluoro-benzene. When possible, CBS-4M methods were used to suggest the lowest energy products based on relative energy. Observed reactions of atomic metal anions with the aforementioned neutral species include electron transfer and dissociative electron transfer to the neutral gas phase reactants. In addition, hydrogen abstraction and fluorine abstraction forming a neutral metal hydride or fluoride as well as the formation of multiply substituted metal-oxide/fluoride anions was also observed. Metal-complex anions observed from the gas phase reactions include CuF-,CuF2-,CuO-,CuO2-, FeO-, FeO2-, FeO3-, FeF-, FeF2-, FeF3-, CsF- and CsF2-. Metal Anion Metal Anion Atomic Atomic Metal Anion Atomic Metals Atomic Metal Anions Anions Metals Mass Spectrometer Triple Quadrupole Rb Cs Fe Cu Ag Cs- Rb- Fe- Cu- Ag- pentafluoroaniline pentafluorophenol nitrogen dioxide sulfur dioxide nitrogen oxide nitrogen monoxide oxygen oxalic oxalic acid gas phase electrospray ionization electrospray ionization electro-spray ionization electro-spray hexafluorobenzene 1,2,3-trifluorobenzene 1,2,4-trifluorobenzene 1,3,5-trifluorobenzene fluorine E-octafluoro-butene octafluoro-butene octafluoro butene CBS-4M abstraction hydrogen abstraction fluorine abstraction hydride fluoride metal hydride metal fluoride caesium fluoride rubidium fluoride iron fluride copper fluoride rubidium caesium iron copper silver iron anion copper anion rubidium anion caesium anion silver anion cesium cesium anion atomic caesium anion atomic cesium anion atomic rubidium anion atomic iron anion atomic copper anion atomic silver anion 1,2,3 trifluorobenzene 1,2,4 trifluorobenzene 1,3,5 trifluorobenzene copper fluoride anion iron fluoride anion copper difluoride copper difluoride anion iron difluoride iron difluoride anion iron trifluoride iron trifluoride anion cesium fluoride cesium fluoride anion caesium difluoride anion caesium difluoride cesium difluoride cesium difluoride anion caesium fluoride anion nitrogen monoxide anion sulfur dioxide anion nitrogen dioxide anion copper oxide copper oxide anion copper dioxide copper dioxide anion iron oxide iron oxide anion iron dioxide iron dioxide anion iron trioxide iron trioxide anion electron transfer
26	Room temperature caesium quantum memory for quantum information applications Michelberger, Patrick Steffen January 2015 (has links) Quantum memories are key components in photonics-based quantum information processing networks. Their ability to store and retrieve information on demand makes repeat-until-success strategies scalable. Warm alkali-metal vapours are interesting candidates for the implementation of such memories, thanks to their very long storage times as well as their experimental simplicity and versatility. Operation with the Raman memory protocol enables high time-bandwidth products, which denote the number of possible storage trials within the memory lifetime. Since large time-bandwidth products enable multiple synchronisation trials of probabilistically operating quantum gates via memory-based temporal multiplexing, the Raman memory is a promising tool for such tasks. Particularly, the broad spectral bandwidth allows for direct and technologically simple interfacing with other photonic primitives, such as heralded single photon sources. Here, this kind of light-matter interface is implemented using a warm caesium vapour Raman memory. Firstly, we study the storage of polarisation-encoded quantum information, a common standard in quantum information processing. High quality polarisation preservation for bright coherent state input signals can be achieved, when operating the Raman memory in a dual-rail configuration inside a polarisation interferometer. Secondly, heralded single photons are stored in the memory. To this end, the memory is operated on-demand by feed-forward of source heralding events, which constitutes a key technological capability for applications in temporal multiplexing. Prior to storage, single photons are produced in a waveguide-based spontaneous parametric down conversion source, whose bespoke design spectrally tailors the heralded photons to the memory acceptance bandwidth. The faithful retrieval of stored single photons is found to be currently limited by noise in the memory, with a signal-to-noise ratio of approximately 0.3 in the memory output. Nevertheless, a clear influence of the quantum nature of an input photon is observed in the retrieved light by measuring the read-out signal's photon statistics via the g<sup>(2)</sup>-autocorrelation function. Here, we find a drop in g<sup>(2)</sup> by more than three standard deviations, from g<sup>(2)</sup> ~ 1.69 to g<sup>(2)</sup> ~ 1.59 upon changing the input signal from coherent states to heralded single photons. Finally, the memory noise processes and their scalings with the experimental parameters are examined in detail. Four-wave-mixing noise is determined as the sole important noise source for the Raman memory. These experimental results and their theoretical description point towards practical solutions for noise-free operation.

Page generated in 0.0358 seconds