3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Neutron activation analysis for the determination of gold and the platinum group elements in large samples(1994) Lycoudi, MariaThe method of activation analysis is extended to the analysis of very large samples (up to 1kg) of ores and minerals. The use of such large samples has two advantages: first, the sensitivity of the method is greatly increased, and secondly, inhomogeneity of distribution and hence sampling problems are greatly reduced. Samples are used without any kind of treatment and the method is non - destructive. There are also disadvantages associated with the use of large samples. Absorption effects (both of neutron and y - rays) become important and as a result the calibration curves are influenced by the bulk density and composition of the samples. In certain cases, the calibration curves may also be non - linear. These effects have been studied in detail for the determination of gold, through the reaction 198Au(n,y)l98Au. After irradiating various samples of known concentrations of gold, calibration curves for gold in gold ore and carbon samples have been established. The effect of y -ray and neutron absorption has been studied in carbon samples using either thermal or epithermal neutrons and the optimum sample thickness has been established. In addition, the curve for the optimum decay time has been obtained for gold in ore samples. Based on the experimental results, a theoretical model has been applied to study the variation of the statistical error with the various factors involv~d, i.e. irradiation, decay, counting times, source strength and sample size. It has been also used to analyse theoretically the results for the optimum thickness and the variation of the background under the 411. 8 keV peak of Au-198. Further work has been undertaken to investigate whether the method can be used to determine elements from the platinum group which are much less active than the gold. Gamma ray peaks from Ir - 192, Au - 199, Pt - 199 Rh - 104m and Os-193 could be identified and possibly from Pd-109. Further work is necessary to study each element separately. In the case of gold, very satisfactory results were obtained. It is too early to state that it provides a replacement for the fire - essay method for gold, but the potential definitely exists.Item A content analysis of presentations of electrostatics in South African upper secondary school textbooks(2017) Lycoudi, MariaThe reality of South African education leaves little doubt that the school science textbook is the primary means by which the „what is taught and learnt‟ in science classrooms is determined. Reports from different countries suggest the same trait. The possibility that not all learners‟ „naïve ideas‟ originate in everyday life has also emerged in the literature along with allusions to the quality of textbooks. If school textbooks are to be blamed, even partially, for learners‟ naïve ideas, a systematic analysis of their subject content becomes requisite. The present study is a systematic content analysis of presentations of foundational aspects of Electrostatics, in approved South African physical sciences textbooks in use after the first democratic elections of 1994, thus representing and addressing three curricula school education has gone through since. The study was perceived as a first step to an anticipated analysis of the entire topic Electromagnetism to which Electrostatics is part of, given its difficulty as has been widely reported in the literature and its status in school curricula. Using the conceptual framework of the Classical Electromagnetic Theory, six foundational aspects of Electrostatics were demarcated for the analysis, targeting the concept charge, its origins, transfer and conservation, the distinction between conductors and insulators, the attraction between charged and uncharged objects, as well as global perceptions of Electrostatics and its place within Electromagnetism. Categorisation tables with theoretically grounded indicators were developed as the primary constructs against which texts were analysed, but inductive categorisation tables emerged from the texts as well. An additional construct was necessitated and developed, the “Organisation of the science educator‟s thought”, based on the notion of a scientific explanation and the nature of scientific models, for analysing links between macro and micro. The analysis revealed that the subject matter content of Electrostatics in South African textbooks is of major concern, giving learners no reason to make sense or develop an appreciation for science, physics in particular. In fact it is not science. The analysis suggests that the long lists of problems revealed, have their origin in two main drawbacks: Firstly, inadequate author understanding of the concept charge, disregarded or misused in the texts, and secondly, author unawareness of the inferred nature of science models, affecting purpose of accounts, explanations and reasoning. Furthermore, certain unprofessional author practices are suggested, such as lack of familiarity with curricula and the content of other topics (not a single link was found), lack of research, and general disregard for learners‟ difficulties, while misconceptions identified in the literature are all communicated in the texts, most explicitly so. The findings suggest that science textbook authors are in need of training.