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The Z-pinches in a vacuum spark can be classified into slow, fast and superfast according to their pinch durations. Their emission characteristics are investigated in the visible, ultraviolet and the X-ray wavelengths. The plasma during a fast pinch was found to have an electron temperature between 100 and 600eV. The superfast pinch resulted in a minute cylindrical plasma approximately 40 μm in diameter, with an electron temperature of 1 to 4keV and a lifetime of less than 4ns. The slow and the fast pinch were found to be in agreement with the theoretical results predicted by a shock wave model. The formation of the superfast pinch and its associated high density and temperature were explained as the results of magnetohydrodynamic instability. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

M.Sc. (Chemistry) / The determination of 17 trace elements (As. Ba. Co. Cr. Cu. Mo. Nb. Ni. Pb. Rb. Sr. Th. U. V. Y. Zn and Zr) in uranium ores by X-ray fluorescence spectrometry was investigated in this study. The determination of major elements. however. was also necessary for the calculation of mass absorption coefficients. Major elements were determined on borate melts and trace elements on powder briquettes pressed at 7 t with a binder in liquid form. Initially a method was developed for the determination of the elements of interest in unmineralised rocks The rhodium tube was used for the Group 1 elements (As. Mo. Nb. Pb, Bb, Sr. Th, U. Y and Zr) and the gold tube for the Group 2 elements [Ba, Co. Cr. Cu. Ni. V and Zn). Background and peak overlap corrections were made by means of background and interference factors. Corrections for absorption of radiation by the sample were made by means of mass absorption coefficients. which were calculated from the major element composition or obtained from the relation between the inverse of the mass absorption coefficient and the intensity of the Compton scattering peak. Due to various problems. only the latter method was suitable for uranium ores. The high uranium content in uranium ores mainly affected the Group 1 elements. Because of the high intensity of various UL lines. large overlap corrections were necessary. while only a few completely interference-free background positions were available. Consequently. the Feather and Willis method was used for determining the background intensity at the peak positions as well as for mass absorption coefficients. As a result of the presence of the UL absorption edges both primarx and secondary mass absorption coefficients had to be used for matrix corrections. Furthermore. it was observed that the background intensity in the region of the uranium lines increases with increasing uranium content of the sample instead of the expected decrease due to the increasing mass absorption coefficient. This effect was greater for the LiF(11 0) crystal than for the LiF(100) and was attributed to the scattering of uranium lines in the spectrometer chamber. especially from the crystal. A method was developed to correct the measured intensities for this scattering effect. Calibration lines of the contribution from the scattering of uranium lines to the measured intensity at the different 28 positions versus the uranium peak intensity were plotted by using samples with various uranium concentrations (<2 %) and for which the mass absorption coefficients and concentrations of the various elements were known. The precision of the method was less than 2.5 % at concentrations greater than 50 ppm. With the exception of barium. detection limits varied between 1 and 5 ppm. Accurate results were obtained over large concentration ranges for various unmineralised samples and for uranium ores. The results of the analysis of a number of Karoo uranium ores are given.

No description available.

A mathematical model which is used to detect bone edges accurately is described in this thesis. This model is derived by assuming the X-ray source to be a square region. It is shown that for an ideal X-ray source (point source), the bone edge lies exactly at the location of maximum first derivative of the imaged object's transmission function. However, for the non-ideal case, it is shown that the bone edge does not lie at the maximum first derivative location. Also, it is shown that an offset can be calculated from the edge parameters. The Marr- Hildreth edge detector is used to detect the initial estimates for edge location. Precise estimates are obtained by using the facet model. The offset is then calculated and applied to these estimates. / Master of Science

Call number: LD2668 .T4 1985 G73 / Master of Science

Ternary indium aluminum nitride (InXAl1-XN) semiconductor is an attractive material with a wide-range bandgap energy varied from ultraviolet (Eg(AlN): 6.2 eV) to near infrared (Eg(InN): 0.7 eV). With tuning composition, it can be widely used to many optoelectronic device applications. In this thesis, I have studied InXAl1-XN film deposited on Si (111) substrate using natural and isotopically enriched nitrogen as reactive gas by reactive magnetron sputter epitaxy (MSE). Four series of experiments were performed, which are I. InAlN presputtering, II. InAlN sputter deposition, III. InAlN direct deposition, and IV. InAlN direct deposition using isotopically enriched nitrogen. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX). The θ-2θ XRD scan confirms that the designed composition x = 0.17 of InXAl1-XN film was obtained. TEM images shows that an amorphous interlayer with a thickness ranging from 1.2 nm to 1.5 nm was formed between Si substrate and InXAl1-XN film. However, high-resolution TEM shows that the interlayer actually contains partial crystalline structures. EDX line profile indicates that the chemical composition of the amorphous interlayer is silicon nitride (SiNX). By comparing d-spacing measurement of partial crystalline structures with EDX line profile, it reveals that partial SiNX crystal is formed in the interlayer. Nonetheless, the samples (IAD01, IAD02, IAD03, IAD04), grown without presputtering procedure, contain both crystalline SiNX and InXAl1-XN embedded in the amorphous interlayer. It means that SiNX and InXAl1-XN film can be directly grown on the substrate in the beginning of deposition. Moreover, the samples (IAD01, IAD03), quenched directly after deposition, have less crystalline structures in the interlayer then the samples (IAD02, IAD04), maintained at 800℃ for 20 min.

Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Non-destructive portable X-ray Fluorescence (pXRF) and Particle Induced X-ray Emission (PIXE) were used to measure the elemental concentration of rock art fragment paintings. For pXRF the Amptek Silicon Drift Detector (SDD) and Niton XL3t spectrometers were used to perform the measurements. These two spectrometers use different spectrum analysis methods. The Peak Deconvolution (PD) analysis method is used for the Amptek SDD and an Inverse Overlap Matrix (IOM) method is used for the Niton XL3t spectrometer. The pXRF methods were validated by using alloys, coins and rock standards. The validation is important to establish if the pXRF technique is properly understood and used and to advance the investigation to more complex rock art paintings, with heterogeneous and layered properties. The elemental concentrations obtained for the Standard Reference Materials (SRMs), which were used for the validation, were in good agreement with that of the known concentration of the SRMs. The two rock art fragments which were analysed from the Mount Ayliff and Ha Khotso caves were part of larger rock art painting prior to it being naturally exfoliated from the rock. For the Mount Ayliff rock art, seven paint points, two unpainted rock (varnish) point adjacent to the paint and the back of the rock were analysed. The colour of the paint ranged from black, shades of brown and shades of red. The black paint is due to manganese or charcoal. The red colour is due to iron oxide and the red-brown colour is due to Hematite (a type of ferrous oxide) [1]. For the Ha Khotso fragment the paint on the front of the rock and the rock substrate (back of the rock) were analysed. For the Mount Ayliff rock art fragment the results for both pXRF spectrometers indicated that the elemental concentration was uniform across the fragment. This is due to the formation of a uniform layer of minerals such as silica and calcium introduced by the seepage of water through the cracks of the cave. Therefore no correlation could be established between the colour of the rock art paint and the elements detected, as was found with the work done by Peisach, Pineda and Jacobson [1]. For the Ha Khosto rock fragment a relation between the Ca composition and the cream colour of the rock art paint was established. Both the PIXE and pXRF techniques were used to identify the compound concentrations of the Ha Khotso rock art fragment. The comparison between the two techniques highlights the complexity of rock art paint analysis. The results from the PIXE elemental mapping indicated the non-uniform distribution of the elements in the analysed region. From the rock art fragment measuring the analysed points 5 times and obtaining the same results, indicated that the particle size and inhomogeneities did not have much effect on the compound compositions. In order to obtain high accuracy results with pXRF, sound scientific methodology with specific knowledge and expertise, not only about the XRF technique, but also about the sample under investigation is required. For alloy analysis pXRF is well suited, the analysis of geological material however more complex, since they are composed predominately of low atomic elements e.g. silicon, aluminium, magnesium, sodium, oxygen and carbon – all of which are excited with very low efficiencies. / AFRIKAANSE OPSOMMING: Nie-beskadigended X-straal Fluoresensie (pXRF) en Deeltjie Geinduseerde X-straal emmissie (PIXE) was gebruik om die elementêre konsentrasie van die rotstekeninge in hierdie studie te bepaal. Vir die pXRF-tegniek is die “Amptek Silicon Drift Detector (SDD)” en die “Thermo Scientific Niton XL3t” spektrometers gebruik gemaak om die metings uit te voer. Die twee spektrometers maak gebruik van verskillende spektrum analiseringsmetodes.Die “Peak Deconvolution (PD)” analiseringsmetode is gebruik vir die “Amptek SDD” en die “Inverse Overlap Matrix (IOM)” analiseringsmetode is gebruik vir die “Thermo Scientific Niton XL3t” spektrometer. Vir die validasie van die pXRF-metode is van allooie, muntstukke en rots standaarded gebruik gemaak. Die validasie is belangrik om vas te stel of die pXRF tegniek behoorlik verstaan en gebruik word en om die ondersoek te bevorder na meer komplekse rotstekeninge, met heterogene en lae eienskappe. Die element konsentrasies wat vir die “Standard Reference Material (SRM)” wat gebruik is vir die validasie, was in 'n goeie ooreenkoms met die van die konsentrasie van die SRM, wat bekend is. Die twee rotstekeninge wat ontleed is van die Mount Ayliff en Ha Khotso grotte en was deel van 'n groter rots kuns skildery voordat hul natuurlik afgebreek het. Vir die Mount Ayliff rotskuns, is sewe verf punte, twee ongeverfde rots (vernis) punte aangrensend aan die verf en die agterkant van die rots ontleed. Die kleur van die verf het gewissel van swart, skakerings van bruin en skakerings van rooi. Die swart verf kan toegeskryf word aan mangaan of houtskool. Die rooi kleur is as gevolg van ysteroksied en die rooi-bruin kleur is as gevolg van Hematiet ('n tipe van yster oksied) [1]. Vir die Ha Khotso rotskuns is die verf aan die voorkant van die rots en die rots substraat (agterkant van die rots) ontleed. Vir die Mount Ayliff rotstekening het die resultate vir beide pXRF spektrometers aangedui dat die elementele konsentrasie uniform oor die rotstekening is. Dit is as gevolg van die vorming van 'n uniforme lagie van silica en kalsium, wat deur die sypeling van water deur die krake van die grot na die oppervlak van die rotstekening beweeg het. Daarom kon geen korrelasie tussen die kleur van die rotstekening en die elemente wat gemeet is bepaal word nie, soos gevind deur die werk van Peisach, Pineda en Jacobson [1]. Vir die Ha Khotso rotstekening is ‘n verband tussen die room kleur van die rotstekening verf en Ca konsentrasie gevind. Beide die PIXE en pXRF tegnieke is gebruik om die konsentrasies van die Ha Khotso rotstekening te identifiseer. Die vergelyking tussen die twee tegnieke beklemtoon die kompleksiteit van rotstekening verf analise. Die resultate van die PIXE elementele karakterisering het aangedui die nie-eenvormige verspreiding van die elemente in die ontlede area. Deur die meting van die ontlede punte 5 keer te herhaal, en dieselfde resultate verkry, is ‘n aanduiding dat die deeltjie grootte en inhomogeniteite nie veel invloed op die elementele konsentrasies het nie. Ten einde 'n hoë akkuraatheid resultate te kry met pXRF, moet goeie wetenskaplike metode toegepas word met spesifieke kennis en kundigheid, nie net oor die XRF tegniek, maar ook oor die rotstekening wat ondersoek word vereis. pXRF is wel geskik vir die ontleding van allooie, die ontleding van geologiese materiaal is egter meer kompleks, aangesien die materiaal hoofsaaklik bestaan uit lae atoomgetal elemente bv silikon, aluminium, magnesium, natrium, suurstof en koolstof - wat almal met lae doeltreffentheid opgewek en baie afgerem word in die materiaal.

No description available.