Magister Scientiae - MSc (Physics)

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(p.n.) Reactions on 59co in the intermediate energy range
(University of the Western Cape, 1992) Bester, P.J; van Heerden, I.J.
Detailed theoretical investigations [Chi80,Mos82,Kle85] of (p,n) and (p,p') data indicate that the reaction mechanisms operative at intermediate energies and for energy losses up to several tens of MeV are predominantly single-step in nature. In these direct reactions, only a few nucleons take part in the reaction, with the remaining nucleons of the target serving as passive spectators. Many excited states of the product nucleus can be reached in these reactions.
Cross-sectional transmission electron microscopy of nickel silicide formation
(University of the Western Cape, 1993) Julies, Basil Allen; Knoesen, D; Pretorius, R
Silicides play a significant role in modern device technology. The operation of electronic devices heavily relies on the specific properties of metal-semiconductor interfaces. Although semiconductor technology has proven very successful in utilizing the properties of materials the knowledge on formation, structure and electrical behaviour of interfaces is still far from complete. In this study an investigation into the Ni-Si binary system was made. Several techniques namely Rutherford Backscattering Spectroscopy, Transmission Electron Microscopy, Scanning Electron Microscopy, Auger Emission Spectroscopy and X-ray Diffraction were employed in the characterization of nickel thin films on silicon and the respective silicides which were formed. Special attention was given to the phase transition from NiSi to NiSi2. First phase formation, namely Ni2Si, was investigated at a vacuum furnace temperature of 290°C. This phase was found to be polycrystalline and grew in layers of uniform thickness with sharp Si-silicide and Ni-silicide interfaces. Growth continued until all the Ni-metal was consumed. Second phase formation (NiSi) was observed at 330°C only after the Ni2Si has grown to its full thickness. This polycrystalline phase also grows in layers. These layers however, are not of uniform thickness, the interfaces between the silicide and silicon substrate therefore being less regular. It was found that NiSi grains could assume one of two crystal structures, orthorhombic or a FeSi cubic structure. Generally it seems as if NiSi initially crystallizes into an orthorhombic crystal structure, before undergoing an allotropic transformation to the FeSi cubic structure. Micro-diffraction was used to characterize individual grains. Final phase formation (NiSi2) was mainly examined at 750°C. A scanning electron microscopy investigation showed that after 5 minutes of annealing islands of NiSi2 was observed in a NiSi matrix. With longer annealing times these islands grew laterally and eventually joined up with others. Cross-sectional transmission electron microscopy very firmly confirms the presence of NiSi2 surrounded by NiSi. Rutherford backscattering, X-Ray diffraction and Auger electron spectroscopy complement these results. Scanning electron microscopy shows that after the coalescence of individual NiSi2 islands, holes appear on the grain boundaries. These holes probably result from an accumulation of vacancies on the grain boundaries during NiSi2 formation which occurs via Ni diffusion in NiSi into the underlying silicon. As the NiSi2 phase continues to grow these holes increase in size and later take on the same crystal structure as the surrounding cubic NiSi2 grains. Although the reaction: NiSi + Si => NiSi2 is thermodynamically favourable to occur at 750°C, it was found that even after 15 minutes of annealing at 750°C, some grains were still NiSi while many others had switched to NiSi2. Identification was once again done by micro diffraction. This means that there is more than just the thermodynamic aspect involved in deciding when NiSi should transform to NiSi2. A model has therefore been proposed in which the major factors in determining the time lapse for transformation to take place are presented. This model generally presents an atomistic approach which centres around the degree of Ni diffusion across the grain boundary of two individual grains. Observations also suggests that NiSi2 results from NiSi by a diffusion process although nucleation can take place at random. This model must not be seen as contradictory to models proposed in the literature which only allow for non-uniform growth at the Si-NiSi, interface, but must rather be seen as complementing it by allowing for diffusion processes as well.
Pre-equilibrium cross section calculations with a realistic effective nucleon-nucleon interaction
(University of the Western Cape, 1995) Karriem, Zainuddin; Lindsay, Robert
The principle aim of this work is to improve the way in which pre-equilibrium double differential cross-sections are currently calculated [1, 2, 3, 4]. The theoretical basis for these calculations is the Multistep Direct Theory by Feshbach, Kerman and Koonin (FKK theory) [5]. This theory leads to the simplification of multistep reactions as a folding of single-step reactions through the implementation of the Distorted Wave Born Approximation (DWBA). The pre-equilibrium cross-sections are subsequently calculated with a multistep direct code.
The determination of excitation functions for natRb+p up to 100 MeV with an emphasis on the production of 82Sr
(UWC, 2000) Buthelezi, E.Z; Green, A; Nortier, F.M
The radioisotope strontiuur-S2 (T172= 25.55 days) decays to short-lived t"Rb 1T,, = 76 seconds) by l00o/o electron caphue @C). The short-lived t'*Rb decays by g5.SYopositron-ernissiou p* and 4.5%oEC to stable'2Kr. Rubidiurn-82g is used in Positron Enr.ission Tonrography (PET) applications, including studies of myocardial infarction, kidney tissue, and brain blood florv. In the present study the excitation fi,rnctions for the production of 82Sr, other radio-strontiums, and radio-contaminants produced in the proton bonrbardrnenl of ""'Rb rvere measured by ureans of the stacked-foil teclutique
The influence of maternal nicotine exposure on neonatal rat trachea development and alveoli status
(University of the Western Cape, 2000) Vergotine, Zelda; Maritz, G. S.
The aim of this study was to determine the effect of maternal nicotine exposure on the status of the rat tracheal development as well as the rat lung of 7 to 42 day old offspring. Wistar dams were injected subcutaneously, using a dosage of 1 mg nicotine/kg body mass/day, and treatment commenced 7 days after conception. The morphological and morphometric data were used to evaluate any damage or change in the structure of the trachea and lungs due to maternal nicotine exposure. Three techniques were used namely, light microscopy, scanning electron microscopy and transmission electron microscopy. Both morphological status and morphometric data were obtained from the sample animals.
Antimicrobial activity of South African red algal secondary metabolites
(UWC, 2001) Cameron D; Keats, DW; Cyster, LF; Leng, H; Green, I
Infectious diseases, for example, measles, scarlet fever, malaria, tuberculosis, and cholera have claimed many lives. These infections are caused by pathogenic viruses, bacteria, or fungi that invade the body's tissues and multiply. According to the Online Medical Dictionary (2000), the multiplication may be clinically barely visible or result in local cellular injury because of competitive metabolism, toxins, intracellular replication, or antigen-antibody response. An infection may remain localized, sub-clinical, and temporary if the body's defensive mechanisms are effective or it could persist, spread, and become an acute, sub-acute, or chronic clinical infection or disease state.
Calibration of germanium detectors for applications of radiometric methods in South Africa.
(University of the Western Cape, 2001) Maleka, P.P; Lindsay, R.; de Meijer, R. I.
AII materials that are radioactive emit characteristic gamma-radiation. Natural radioactivity can be used in heavy minerals exploration and processing, as well as in understanding sediment transport. processes in coastal zones [Dem97][Dem98]. Differences in radionuclide concentrations between minerals, allows the mineral species to be identified and quantified by the activity concentrations of a011, 23216 and 238U using a technique called radiometric fingerprinting [Dem97]. A" important tool to determine sediment transport rates along the coastline is by the MEDUSA technology developed and tested at the Kernfysisch Versneller Instituut (KVI) [Dem98]. The data from the MEDUSA (Multi-Element Detector system for IJnderwater Sediment Activity) system needs to be calibrated first in the laboratory before field measurements can be converted to useful data. The National Accelerator Centre (NAC) is setting up a radiometric laboratory to do this by means of a high-resolution germanium detector used under low-background conditions and constant geometry.
Study of the use of Electret Ion chambers as radom dosimeters in South Africa
(University of the Western Cape, 2002) Vuza, Hurnphrey Monwabisi; Lindsay, R
Radon is a naturally occuring radioactive gas which has been shown to be a major contribution to background dose. The underground mines in South Africa present a major occupational hazard. A need for cheap personal monitoring has been identified. In this thesis, commercially available electret ion chambers (EICs) are studied, with a view to use them as personal monitors. These detectors were developed to measure radon activity concentrations in houses. Their use in the harsh underground mining environments has shown some complications such as water entering the detectors and their response time to a rapid change in radon concentration has been questioned. Several measurements are discussed in this thesis relevant to solve these problems. Firstly, the EIC's are checked for accuracy in the laboratory using a radon source, as well as the radon chamber at the CSIR in Pretoria. Comparisons with alpha track detectors are also carried out.
Modelling and measurement of radon diffusion through soil for application on mine tailings dam
(University of the Western Cape, 2004) Speelman, Wilcot John; Lindsay, R.; Dept. of Physics; Faculty of Science
Radon has been identified as an important factor that could result in a health hazard by studies all around the world. The health risks can be minimised by preventive measures where radon is highly concentrated as in some mines and homes. Measuring and modelling the radon concentrations in the mine dump soil, can help to deduce the radon flux to identify the problem areas for rehabilitation especially in the cases of gold and uranium mine tailings. Rehabilitation in those cases usually consists of a multilayer cover of solids like crushed rock or clay. A passive method incorporating electret technology was used in this study to determine the radon emanation coefficient of the soil. This investigation also describes the modelling of a depth profile with respect to the radon activity concentration to understand from how deep radon might be migrating, as well as the effect of different diffusion lengths.
Determination of natural radioactivity concentrations in soil: a comparative study of Windows and Full Spectrum Analysis
(University of the Western Cape, 2004) Maphoto, Katse Piet; Lindsay, R.; Newman, R.T.; Dept. of Physics; Faculty of Science
In this study, two methods of analysing activity concentrations of natural radionuclides (U, Th and K) in soil are critically compared. These are the Window Analysis (WA) and Full Spectrum Analysis (FSA). In the usual WA method, the activity concentrations are determined from the net counts of the windows set around individual γ-ray peaks associated with the decay of U, Th and K. In the FSA method, the full energy spectrum is considered and the measured spectrum is described as the sum of the three standard spectra (associated with U, Th and K, respectively), each multiplied by an unknown concentration. The concentrations are determined from the FSA and correspond to the activity concentrations of U, Th and K in the soil. The standard spectra derived from separate calibration measurements using the HPGe detector, represents the response of the HPGe to a Marinelli sample beaker containing an activity concentration of 1 Bq/kg.
Modelling and measurement of radon diffusion through soil application on mine tailings dams.
(University of Western Cape, 2004) Speelman, Wilcot John; Lindsay, Robert
Radon (222Rn) has been identified as an important factor that could result in a health hazard by studies all around the world. The health risks can be minimised by preventive measures where radon is highly concentrated as in some mines and homes. A study in the diffusion of the inert gas, will give us a better understanding of its possible pathways through soil into the air surrounding mine dumps where the radon releases can become hazardous. Measuring and modelling the radon concentrations in the mine dump soil, can help to deduce the radon flux to identify the problem areas for rehabilitation especially in the cases of gold and uranium mine tailings.
Aluminium induced crystallization of hydrogenated amorphous silicon thin films
(University of the Western Cape, 2005) Kotsedi, Lebogang; Knoesen, Dirk; Madjoe, Reginalt
This study was carried out to crystallize hydrogenated amorphous silicon (a-Si:H) thin films using the aluminium induced crystallization (AIC) technique. This was done to investigate whether is there any lateral crystallization of the a-Si:H thin film away from the aluminium covered surface of the film. The hot wire chemical vapour deposition system (HWCVD) was used to deposit hydrogenated amorphous silicon thin films (a-Si:H) on Corning glass 7059 substrates. The substrate temperature was kept at 300oC while the filament temperature was l600oC during the deposition. The aluminium top layer was deposited at room temperature using the electron beam evaporator. The aluminium deposited, only partially covered the sample, this was done to investigate whether lateral crystallization of the uncovered part will take place. Samples were then annealed at 450oC for times ranging from 30 to 150 minutes in incremental steps of 30 minutes. A temperature series of annealings at l00oC, 150oC, 200oC,300"C and 350oC for 60 minutes were also performed. Energy Dispersive Spectroscopy (EDS) was used for elemental identification after annealing. Rutherford Backscattering Spectrometry was used for the depth profiling of the diffused species. X-ray diffraction (XRD) technique was used for crystallization studies on the aluminium covered side, transmission electron microscopy (TEM) was used to study lateral crystallization and diffraction patterns of crystallized part were taken using selected area diffraction (SAD).
Determination of the photopeak detection efficiency of a HPGe detector, for volume sources, via Monte Carlo simulations
(University of the Western Cape, 2005) Damon, Raphael Wesley; Lindsay, R.; Newman, R.T.; Dept. of Physics; Faculty of Science
The Environmental Radioactivity Laboratory (ERL) at iThemba LABS undertakes experimental work using a high purity germanium (HPGe) detector for laboratory measurements. In this study the Monte Carlo transport code, MCNPX, which is a general-purpose Monte Carlo N − Particle code that extends the capabilities of the MCNP code, developed at the Los Alamos National Laboratory in New Mexico, was used. The study considers how various parameters such as (1) coincidence summing, (2) volume, (3) atomic number (Z) and (4) density, affects the absolute photopeak efficiency of the ERL’s HPGe detector in a close geometry (Marinelli beaker) for soil, sand, KCl and liquid samples. The results from these simulations are presented here, together with an intercomparison exercise of two MC codes (MCNPX and a C++ program developed for this study) that determine the energy deposition of a point source in germanium spheres of radii 1 cm and 5 cm. A sensitivity analysis on the effect of the detector dimensions (dead layer and core of detector crystal) on the photopeak detection efficiency in a liquid sample and the effect of moisture content on the photopeak detection efficiency in sand and soil samples, was also carried out. This study has shown evidence that the dead layer of the ERL HPGe detector may be larger than stated by the manufacturer, possibly due to warming up of the detector crystal. This would result in a decrease in the photopeak efficiency of up to 8 % if the dead layer of the crystal were doubled from its original size of 0.05 cm. This study shows the need for coincidence summing correction factors for the gamma lines (911.1 keV and 968.1 keV) in the 232Th series for determining accurate activity concentrations in environmental samples. For the liquid source the gamma lines, 121.8 keV, 244.7 keV, 444.1 keV and 1085.5 keV of the 152Eu series, together with the 1173.2 keV and 1332.5 keV gamma lines of the 60Co, are particularly prone to coincidence summing. In the investigation into the effects of density and volume on the photopeak efficiency for the KCl samples, it has been found that the simulated results are in good agreement with experimental data. For the range of sample densities that are dealt with by the ERL it has been found that the drop in photopeak efficiency is less than 5 %. This study shows that the uncertainty of the KCl sample activity measurement due to the effect of different filling volumes in a Marinelli beaker is estimated in the range of 0.6 % per mm and is not expected to vary appreciably with photon energy. In the case of the effect of filling height on the efficiency for the soil sample, it was found that there is a large discrepancy in the trends of the simulated and experimental curves. This discrepancy could be a result of the use of only one sand sample in this study and therefore the homogeneity of the sample has to be investigated. The effect of atomic number has been found to be negligible for the soil and sand compositions for energies above 400 keV, however if the composition of the heavy elements is not properly considered when simulating soil and sand samples, the effect of atomic number on the absolute photopeak efficiency in the low energy (< 400 keV) region can make a 14 % difference.
Emission of ³He ⁴He and ⁶He particles produce from the interaction of ¹²C with ⁹³Nb at 400 MeV incident energy
(University of the Western Cape, 2005) Mudau, Lufuno Julia; Lindsay, R; Dept. of Physics; Faculty of Science
The inclusive double di®erential cross sections of 3He, 4He, and 6He par- ticles produced from the interaction of 12C with 93Nb at 400 MeV incident energy were extracted from the prescaled singles spectra which were mea- sured in conjunction with the correlation between 8Be fragments and ® par- ticles. A further aim of this project was to test the detector e±ciencies and energy calibrations by comparing the alpha and 8Be prescaled singles data with existing inclusive cross sections of the same reaction. The absolute cross sections of 3He and 6He fragments have been extracted based on the absolute normalization of the alpha particle spectra. A study of the inclusive spectra of 3He and 6He suggest similar features to those seen in the alpha particle spectra. These features are described by the projectile break-up and nucleon coalescence mechanisms. A theoretical model which takes both these mech- anisms into account was applied to describe 3He and 6He fragments. The model is able to reproduce reasonably well the inclusive energy spectra of the 3He and 6He fragments. These results are found to be consistent with previous studies of the emission of intermediate mass fragments.
Radon in the Cango Caves
(University of the Western Cape, 2005) Nemangwele, Fhulufhelo; Lindsay, R; Dept. of Physics; Faculty of Science
Radon is a naturally occurring radioactive element in the 238U decay series that is found in high concentrations in certain geological formations such as Caves. Exposure to high concentrations of radon has been positively linked to the incidence of lung cancer. This study used Electret ion chambers and the RAD7 continuous radon monitor to measure radon concentrations in the Cango Caves in the Western Cape Province, South Africa. Measurements were taken during summer i.e. February 2004 and March 2005. The results for the radon activity concentrations range from the minimum of about 800 Bq.m-3 to a maximum of 2600 Bq.m-3. The two techniques give very similar results, though the Electret ion chamber results appear to be consistently higher by a few percent where measurements were taken at the same locations. A mathematical model has been developed to investigate the radon concentrations in the Cave. Diffusion and ventilation have been considered as mechanisms for explaining the distribution of radon concentrations. The ventilation rate in the Cave has been estimated under certain assumptions, and it is found to be about 7 ×10−6 s−1 for the Van Zyl hall which is the first large chamber in the Cave. The radon concentration increases as one goes deeper into the Cave, but then becomes fairly constant for the deeper parts. The annual effective dose that the guides are exposed to in the Cave as a result of the radon concentrations, depends strongly on the time that they spend in the Cave and in which, halls they spend most of their time in the Cave. The initial results indicate an annual effective dose of 4-10 mSv, but this needs to be further investigated.
Gamma spectroscopy of the doubly– ODD 194Tl Nucleus
(University of the Western Cape, 2006) Ramashidzha, Tshifhiwa Marius; Gueorguieva, E. A.; Lindsay, R.; Dept. of Physics; Faculty of Science
The odd – odd Tl nuclei with A ≥ 190 have moderate oblate nuclear deformation and show rotational bands built on different quasiparticle excitations. Several phenomena, not yet fully understood, were observed in these nuclei, such as large signature splitting in the yrast band (built on a πh9/2⊗νi13/2 configuration), possible non – axiality of the nuclear shape, etc. In this work the high – spin states in 194Tl were studied. The 194Tl nuclei were produced in the 181Ta (18O, 5n) 194Tl reaction at a beam energy of 93 MeV and the γ - rays were detected using the AFRODITE array. The obtained extended level scheme of 194Tl is presented and discussed in this work. CSM (Cranking shell model) and TRS (Total Routhians Surface) models were both applied to interpret the results for band 1. The results were compared with the neighboring isotone 193Hg.
Investigation of stains existing on fossil samples from the sterkfonfein archeaologica sites
(University of the Western Cape, 2006) Hlatshwayo, Sicebiso Richman; Venter, A.M
It is known that fossilized bone samples excavated from the Sterkfontein archaeological sites have prominent brown stains on their surfaces. Their existence has been postulated by researchers from Transvaal museum to be reminiscent of Mn deposits from lichen growth in the Mn rich geological environment of the area [Tha2005]. To investigate the chemical nature of the stains, we report results from experimental studies on fossilized antelope bone samples as well as rocks from the archaeological sites. The fossil samples cover the age period 1 to 2.5 million years ago. A chert rock sample is of specific interest to this study as it contains both live lichen growth (green residue) and brown stains (believed to be the residue of dead lichen).
Intense pulsed neutron generation based on the principle of Plasma Immersion Ion Implantation (PI3) technique
(University of the Western Cape, 2006) Motloung, Setumo Victor; Franklyn, Chris B.; Dept. of Physics; Faculty of Science
The development of a deuterium-deuterium/ tritium-deuterium (D-D/ D-T) pulsed neutron generator based on the principle of the Plasma Immersion Ion Implantation (PI3) technique is presented, in terms of investigating development of a compact system to generate an ultra short burst of mono-energetic neutrons (of order 1010 per second) during a short period of time (< 20μs) at repetition rates up to 1 kHz. The system will facilitate neutron detection techniques, such as neutron back-scattering, neutron radiography and time-of-flight activation analysis. Aspects addressed in developing the system includes (a) characterizing the neutron spectra generated as a function of the target configuration/ design to ensure a sustained intense neutron flux for long periods of time, (b) the system was also characterised as a function of power supply operating conditions such as voltage, current, gas pressure and plasma density.
Hot-wire chemical vapour deposition of carbon Nanotubes
(University of the Western Cape, 2006) Cummings, Franscious Riccardo; Arendse, C.J; Knoesen, D.; Dept. of Physics; Faculty of Science
In this study we report on the effect of the deposition parameters on the morphology and structural properties of CNTs, synthesized by means of the hot-wire chemical vapour deposition technique. SEM, Raman and XRD results show that the optimum deposition conditions for the HWCVD synthesis of aligned MWCNTs, with diameters between 50 and 150 nm and lengths in the micrometer range are: Furnace temperature of 500 ºC, deposition pressure between 150 and 200 Torr, methane/hydrogen dilution of 0.67 and a substrateto- filament distance of 10 cm.
Intense pulsed neutron generation based on the principle of plasma immersion ion implantation technique (PIp3s) technique
(University of the Western Cape, 2006) Victor, Motloung, Setumo; Franklyn, Chris. B.; Lindsay, R
The development of a deuterium deuterium/ tritium-deuterium (D-D/ D-T) pulsed neutron generator based on the principle of the Plasma Immersion Ion Implantation 1Pl) technique is presented, in terms of investigating development of a compact system to generate an ultra short burst of mono-energetic neutrons (of order 1910 per second) during a short period of time (.20ps) at repetition rates up to 1 kHz. The system will facilitate neutron detection techniques, such as neutron back-scattering, neutron radiography and time-of-flight activation analysis. Aspects addressed in developing the system includes (a) characterizing the neutron spectra generated as a function of the target configuration/ design to ensure a sustained intense neutron flux for long periods of time, (b) the system was also characterised as a function of power supply operating conditions such as voltage, current, gas pressure and plasma density.

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