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A continuous cloud chamber would be a valuable asset to laboratory work in nuclear and atomic physics. For this reason the construction and investigation of a continuously sensitive diffusion cloud chamber has been undertaken. It is the purpose of this paper to report the design and operating characteristics of such a chamber.

published_or_final_version / abstract / Physics / Master / Master of Philosophy

Made available in DSpace on 2014-10-09T12:49:35Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:02:13Z (GMT). No. of bitstreams: 1 09824.pdf: 13805608 bytes, checksum: bb156d35d4219c1080d090fad1bf255b (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP / FAPESP:99/06952-4

Made available in DSpace on 2014-10-09T12:49:35Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:02:13Z (GMT). No. of bitstreams: 1 09824.pdf: 13805608 bytes, checksum: bb156d35d4219c1080d090fad1bf255b (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP / FAPESP:99/06952-4

This thesis examines multiple different molecular networks adsorbed on several different substrates, namely, highly oriented pyrolytic graphite (HOPG), Au(111) and graphene. STM investigations into hydrogen-bonded structures formed by closely related tetracarboxylic acid molecules were performed. The molecule pterphenyl-3,5,3,5-tetracarboxylic acid (TPTC), which is known to form random tiling networks, was observed on a graphene on copper substrate. The network formed from deposition of TPTC from nonanoic acid was examined statistically. Aqueous solutions of TPTC were also examined on HOPG where a new structure, distinct from the random tiling, was observed. Aqueous solutions of related molecules biphenyl-3,3',5,5'-tetracarboxylic acid (BPTC) and quaterphenyl-3,3',5,5'-tetracarboxylic acid (QPTC), were also studied on HOPG. QPTC formed a similar structure to the aqueous solutions of TPTC, but BPTC formed two different phases, one of which was a kagome network. Addition of nonanoic acid to a dried network of TPTC deposited from aqueous solution resulted in solvent induced recrystallisation into a random tiling network comparable to that observed on graphene on copper, which was statistically analysed. Studies investigating the potential for covalent bonded molecular networks identified two distinct phases of the molecule 1,3,5-Tri(4-bromophenyl-benzene (TBPB)) adsorbed on Au(111). Concentration variation indicates an island based growth mechanism for these domains from solution. Dimerisation of TBPB was achieved by deposition onto heated substrates and a discussion of possible reasons for the reaction termination at dimers is provided. Attempts to repeat the TBPB experiments on graphene on copper failed due to excessive corrosion. Variations using larger molecules failed due to lack of solubility. Preliminary experiments on 10,10'-dibromo-9,9'-bianthryl (DBrBA) showed promise but were irreproducible, however micron scale dendritic structures were observed suggesting poor compatibility with the solvent. Finally, a discussion of the development of a nickel catalysis based graphene fabrication method is given and the limits of what is achievable with this method are discussed. The results from this thesis highlight the importance of solvent selection for the future understanding of molecular network fabrication. We also demonstrated the feasibility of covalently bonded networks prepared in ambient conditions.

Thesis (PhD (Physics))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: Radioactivity is well known and well understood, but its usefulness in industrial applications to optimise processes or increase economic viability is not yet fully utilised by many industries. This study focuses on the measurement of natural radioactivity and its application in heavy mineral separation and vineyard soil classification. The gamma radiometry set-up consisted of a high purity germanium detector, a Marinelli beaker as sample container and associated electronics. It was calibrated for laboratorybased measurements by minimising the background radiation with the use of lead castle and energy and resolution calibrations. Furthermore, detection parameters were optimised; these included the counting time, the selection of gamma rays used for analysis of a sample, the peak area calculation for the detector dead time and the detector efficiency. Given that the samples had different densities and volumes, the detector efficiency had to be corrected for volume and density effects. After implementation of the corrections and optimisations the detection system was tested and found able to accurately measure radioactivity concentrations. The systematic measurement errors for 238U were 5.1 % in the case of the heavy mineral sands and 34.3 % for the vineyard soils, 4.5 % for the 232Th concentrations and 4.7 % for 40K concentrations. Statistical errors were kept below 2 %. The application of radiometry has not been done before at any South African heavy mineral separation plant. For this reason radiometry is suggested as an easier, faster and cheaper alternative to X-ray fluorescence (XRF) for effective implementation of grade control for zircon to improve the cost benefit of the heavy mineral separation process. Zircon is an example of a heavy mineral that is worldwide in demand with a consumption of more than a million tonnes per year. It is used in a wide range of industrial applications and products that include tiles, sanitary ware and plasma displays. South Africa is the second largest producer of zircon in the world and also has the second largest reserve of available zircon, making this mineral a viable source of income for several years to come. Radioactivity, in the form of uranium and thorium, and other impurities such as iron oxide and titanium oxide are found in the crystal lattice of zircon. For it to be a sellable product, the sum of the uranium and thorium concentrations must be less than 500 parts per million for prime or first grade zircon and less than 1000 parts per million for second grade zircon. At present the concentrations of uranium and thorium in zircon concentrates are measured on a whole rock basis by XRF during and at the end of the processing cycle before the final products are ready to be shipped. This is not an ideal situation as the grab samples are taken periodically and are not necessarily representative of the stream or final assignment and has resulted in significant losses by the producer. The solution is to accurately measure the uranium and thorium concentrations fast or immediately, preferably the measurements must be made online and in real time so that processing decisions can be implemented quickly to optimise the final product. Heavy mineral sand samples were obtained from the various separation processes in a Mineral Separation Plant and their 238U and 232Th concentrations determined. The results indicated that the samples’ uranium to thorium ratios together with their total concentrations can be used to differentiate between the samples (i.e. separation processes). The measurement results were compared with those obtained with XRF. The correlations with radiometry were excellent for the uranium (r2 = 0.992), thorium (r2 = 0.998) and total concentrations (r2 = 0.998). Radiometric measurements were also conducted by decreasing the counting time from 3600 s to 1 s to investigate its effect on the accuracy of the results. Correlations between the different times and 3600 s ranged from excellent to good. The obtained results are then used to recommend that radiometry is used in a Mineral Separation Plant to verify that the zircon and zirkwa meet the specifications, to optimise the entrance feed and the other separation processes and to monitor the tailings streams. Finally the practical aspects of the implementation of radiometry are discussed. As a second application was radiometry applied in an agricultural pilot study to demonstrate the applicability of radiometry as a possible useful tool in soil classification. The creation of a vineyard is a long term and expensive investment and its yield and quality will be influenced by many factors such as the type of soil, viticultural preparations and climate. Information on the different soil types in a vineyard is therefore indispensable for the optimisation of land use with respect to vine cultivar, wine quality and production. Soil samples were obtained from Kanonkop, Simonsig and Spier vineyards and their 238U, 232Th and 40K concentrations determined, assuming that fertilisers would have no effect on the results. The difference in 40K concentrations were related to the clay fraction of the soil and demonstrated that the Kanonkop and Simonsig soils are fine-grained and clay-rich compared to the sandy coarse-grained soils of Spier. The uranium and thorium concentrations were indicators of whether the mineralogy of the soil is the same as the underlying bedrock as well as soil maturity. The measurement results were compared with those obtained with XRF. The correlation with radiometry were poor for the uranium concentrations (r2 = 0.314), as many of the samples concentrations were below the XRF detection limit. The correlations were excellent for both thorium (r2 = 0.985) and potassium (r2 = 0.999). As a positive result from the findings of the study was an in-situ measurement performed by Newman et al. for the radiometric mapping of a Simonsig vineyard for soil classification. / AFRIKAANSE OPSOMMING: Radioaktiwiteit is wel bekend en word goed verstaan, tog is die gebruik daarvan in industriele toepassings om prosesses te optimiseer of winsgrense te verhoog nog nie deur baie industrië ten volle benut nie. Hierdie studie fokus op die meting van natuurlike radioaktiwiteit en die toepassing daarvan in swaar mineraal skeiding en wingerd grond klassifikasie. Die gamma radiometrie opstelling het bestaan uit ‘n hoë suiwerheid germanium detektor, 'n Marinelli beker as monster houer en verwante elektronika. Dit was gekalibreer vir laboratorium gebaseerde metings deur die vermindering van die agtergrondstraling met die gebruik van lood kasteel en energie en resolusie kalibrasies. Verder was deteksie parameters geoptimaliseer, dit sluit in die teltyd, die keuse van gammastrale wat gebruik word vir die ontleding van 'n monster, die piek area berekening, die korreksie vir die detektor se dooie tyd en die detektor doeltreffendheid. Gegee dat die monsters van mekaar verskil het in terme van dighteid en volume was dit nodig om die detektor doeltreffendheid te korrigeer vir volume en digtheid effekte. Na die implementering van die korreksies en optimalisasie was die detektor stelsel getoets en was gevind dat radioaktiwiteit konsentrasies akkuraat gelewer kan lewer. Die sistematiese meet foute vir 238U was 5.1 % vir die mineraal sand en 34.3 % vir wingerd grond, 4.5 % vir 232Th konsentrasies en 4.7 % vir 40K konsentrasies. Statistiese foute was onder 2 % gehou. Die toepassing van radiometrie was nog nie voorheen by enige Suid-Afrikaanse swaar mineraal skeidings aanleg gedoen nie. Vir die rede is radiometrie voorgestel as ‘n makliker, vinniger en goedkoper alternatief teenoor XSF vir effektiewe implementering van graad beheer vir zirkon om die koste voordeel van die swaar mineral skeiding proses te verbeter. Zirkon is ‘n voorbeeld van ‘n swaar mineraal wat wêreldwyd in aanvraag is met ‘n verbruik van meer as ‘n miljoen ton per jaar. Dit word in ‘n wye reeks van industriele toepassings en produkte gebruik onder andere teëls, sanitêre ware en plasma skerms. Suid Afrika is die tweede grootste vervaardiger van zirkon in die wêreld en het ook die tweede grootste reserwe van besikbare zirkon. Dit veroorsaak dat die mineraal ‘n lewensvatbare brom van inkomste is vir nog etlike jare. Radioaktiwiteit, in die vorm van uraan en thorium, word tesame met ander onsuiwerhede soos ysteroksied en titaanoksied in zirkon se kristal rooster gevind. Om ‘n verkoopbare produk te wees moet die som van die uraan en thorium konsentrasies minder wees as 500 dele per miljoen vir prima en eerste graad zirkon en minder wees as 1000 dele per miljoen vir tweede graadse zirkon. Huidiglik word die uraan en thorium konsentrasies in die zirkon konsentraat gemeet op ‘n heel gesteente basis met X-straal fluoroskopie (XSF) gedurende en op die einde van die prosesering siklus net voor die finale produk reg is om versend te word. Dit is nie die ideale situasie nie, want die monsters word periodies geneem en is nie noodwendig verteenwoordigend van die stroom of die finale produk nie en het al tot beduidende verliese deur die vervaardiger gelei. Die oplossing is om die uraan en thorium konsentrasies vinnig of onmiddelik te meet, verkieslik moet die metings inlyn en intyds gedoen word om verwerkings besluite vinnig geimplementeer kan word om die finale produk te optimaliseer. Swaar mineraal sand monsters was verkry van die verskeie skeidingsprosesse in ‘n Mineraal Skeidings Aanleg en hul 238U en 232Th konsentrasies bepaal. Die resultate het aangetoon dat die monsters se uraan en thorium verhoudings saam met hul totale konsentrasies gebruik kan word om te onderskei tussen die monsters (oftewel die skeiding prosesse). Die meting resultate was vergelyk met dié verkry met XSF. Die korrelasies met radiometrie was uitstekend vir die uraan (r2 = 0.992), thorium (r2 = 0.998) en totale konsentrasies (r2 = 0.998). Radiometriese metings was ook uigevoer deur die teltyd te verminder van 3600 s tot 1 s om die uitwerking daarvan op die akkuraatheid van die resultate te ondersoek. Korrelasies tussen die verskillende tye en 3600 s het gewissel van uitstekend tot goed. Die bevindinge was dan gebruik om aan te beveel dat radiometrie in a Mineraal Skeidings Aanleg gebruik kan word om te verifeer dat daar aan die zirkon en zirkwa spesifikasies voldoen word, om die begin voer en ander skeidings prosesse te optimaliseer en ook die uitskot strome te monitor. Laastens is die praktiese aspekte van die implementering van radiometrie bespreek. Vir die tweede toepassing was radiometrie toepgepas in ‘n loods studie in die landbou om die toepaslikheid van radiometrie as ‘n moontlike nuttige instrument in grond klassifikasie te demonstreer. Die skepping van ‘n wingerd is ‘n lang termyn en duur belegging waarvan die opbrengs en kwaliteit beinvloed sal word deur vele faktore, onder andere die tipe grond, wynbou voorbereidings en die klimaat. Inligiting oor die verskillende grond tipes in ‘n wingerd is daarom onmisbaar vir die optimalisering van land gebruik in betrekking tot die wingerdstok kultivar, wyn kwaliteit en produksie. Radiometrie is toegepas om te demonstreer die toepaslikheid daaran as ‘n moontlike nuttige instrument in grond klassifikasie. Grondmonsters was verkry vanaf Kanonkop, Simonsig en Spier wingerde en hul 238U, 232Th en 40K konsentrasies bepaal met die aanname dat kunsmis nie ‘n uitwerking op die resultate sou hê nie. Die verskil in 40K konsentrasies was verwant aan die kleifraksie van die grond en het getoon dat die Kanonkop en Simonsig gronde is fyn korrelrig en kleiryk is in vergelyking met die sanderige growwe korrel grond van Spier. Die uraan en thorium konsentrasies het gedui op die samestelling van die grond en ook aangedui watter grond dieselfde is as die onderliggende rots. Die meting resultate was vergelyk met dié verkry met XSF. Die korrelasie met die radiometrie was sleg vir die uraan konsentrasies (r2 = 0.314) aangesien baie van die monster konsentrasies laer was as die XSF deteksie limiet. Die korrelasies was uitstekend vir beide thorium (r2 = 0.985) en kalium (r2 = 0.999). As ‘n positiewe resultaat van die studie se bevindinge was ‘n in-situ meting gedoen deur Newman et al. om ‘n Simonsig wingerd radiomeries te karteer vir grond klassifasie.

No description available.

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This is a mathematical study of certain aspects of the interacting electron system in very high perpendicular magnetic field. We analyse restrictions imposed upon the density correlation functions of this system and propose a set of sum rules which they must obey. We study the possibility of building a bosonisation scheme for the projected density operators in the lowest Landau level. We suggest a second order bosonisation, along with an approximation scheme, which may be useful for carrying out calculations in the lowest Landau level. We analyse the possible ground states of the system. We suggest a set of variational wavefunctions which can have lower energy than the Laughlin state for sufficiently soft interaction potentials. We study the collective excitations of the system, paying particular attention to its symmetries. We suggest a set of variational excited states and discuss their applicability to finite as well as infinite systems.