Philosophiae Doctor - PhD (Physics)

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Exploring poly (2, 5) benzimidazole enhanced with carbon nanotubes for space applications
(University of the Western Cape, 2023) Fourie, Lionel Fabian; Square, Lynndle
This work explores using polymeric materials for space radiation shielding in low-earth orbit. Shielding against radiation is essential on any space mission. Low atomic number materials, such as hydrogen, have shown to be effective in shielding ionising radiation. However, compared to metallic alloys, these materials suer from relatively low mechanical and thermal properties, which limit their application. Aluminium (Al) enjoyed wide use in space applications as a structural and radiation shielding material. However, weight and secondary radiation generation issues have made its use as a shielding material less viable on modern space missions where cost and safety play a crucial role in planning these missions. On modern space missions, conventional shielding materials include Al alloys, high-density polyethylene, and water. The disadvantages include low thermal properties, high atomic numbers, and complex maintenance systems. This lead to exploring other materials that can mitigate some of these drawbacks. A proposed approach to replacing high atomic number metals is deploying hydrogen-rich polymers enhanced with nanoﬁller materials to form polymer nanocomposites. Poly-mers enhanced with nanoﬁllers can achieve improved physical properties while pro-viding adequate radiation shielding functions at a lower weight with less secondary radiation generation.
Chemical pressure-induced transition of the magnetic ground state from ferromagnetic to antiferromagnetic order in CeCuGe and DyCuIn alloys
(University of the Western Cape, 2023) Altayeb, Anas Alamin Hassan; Tchoula Tchokont´e, Moise
Rare-earth intermetallic compounds continue to attract considerable attention, due to their fundamental importance in understanding physical properties and potential applications based on a variety of phenomena. The ternary intermetallic compounds of the RTX series (R = rare-earth element, T = 3d / 5d transition element, X = p-block element) in particular, were studied extensively for the past two decades. A number of interesting magnetic and electrical properties of practical and fundamental importance, were found in different compounds of the RTX series, including giant and large magnetocaloric effects and magnetoresistivity, antiferromagnetic (AFM) to ferromagnetic (FM) order transitions and rich magnetic transition phase diagrams. Most of these properties are related to the interaction between the R-4f (localized) electronic states and other (itinerant) electronic states in the electronic system. Several experiments have provided evidence for magnetic ground state switching between FM and AFM ordering, driven by pressure or chemical substitution in d and f electron compounds. The methods used to investigate the magnetic phase transitions could be divided into macroscopic and microscopic ones. The macroscopic method relied on the temperature dependences of magnetization, magnetic susceptibility and specific heat measurements while the microscopic method relied on neutron diffraction and Mössbauer effect.
Physics graduate preparedness for work and society
(University of the Western Cape, 2023) Audu, Bako Nyikun; Marshall, Delia
Both internationally and in South Africa, there have been renewed debates about the purposes of higher education and the attributes that should be developed in graduates. In the field of physics, many studies have reported that the preparation of physics graduates in the 21st century needs to be broader, to prepare graduates for a range of careers and roles in society. This case-study aims to understand the formation of graduate preparedness and the development of graduate attributes in a Physics Department at a South African university. A framework of physics graduate attributes was developed, drawing on skills and attributes benchmarked by several international physics bodies, as well as the South African Institute of Physics; the national SAQA critical cross-field outcomes and the UWC Charter of Graduate Attributes were also drawn on. The study adopted a range of research methods: document analysis of physics module descriptors was used to examine the embeddedness of graduate attributes in the physics curriculum; a questionnaire was developed to gauge students’ perceptions of their preparedness for work and society; focus group discussions with students, and interviews with graduates, were used to understand the structural and institutional arrangements that enabled or hindered the development of physics graduate attributes. The theoretical framework for this study is the capability approach, as developed by Amartya Sen and Martha Nussbaum. It offers an enlarged view of the purposes of higher education beyond the development of human capital; it also enabled an analysis of the structural challenges that students faced, while at the same time foregrounding student agency, and the strengths and resources that students bring to higher education. The findings revealed that the physics graduate attributes were unevenly and mostly scantily embedded as learning outcomes in the physics module descriptors; attributes least embedded in the curriculum were social and environmental awareness, ethical behaviour, and teamwork. Analysis of questionnaire and focus group discussion data showed that students felt that more could be done in the Physics programme to explicitly develop a wider set of physics graduate attributes to enhance their sense of graduate preparedness. In particular, the development of ICT skills, communication skills, practical skills and social awareness was found to be lacking. Concepts from the capability approach, including conversion factors, well-being and agency, were used to understand the ways in which the development of students’ graduate preparedness and their attainment of academic success and well-being were enabled or hindered by various structural and institutional factors.
A case study of university students' experiences of introductory physics drawn from their approaches to problem solving
(University of the Western Cape, 2001) Alant, Busisiwe Precious; Linder, Cendric; Marshall, Delia
This thesis explores the experience of leaming physics through a particular medium: problem-solving, which is seen by many educators as the primary medium in which physics is learnt at university. Situating itself within two theoretical perspectives: phenomenography and actor-network theory, the dissertation explores the variation in the ways of experiencing introductory physics leaming through problem-solving. phenomenography, which is the main theoretical framework, places emphasis on the variation of experience of phenomenon at a supra-individual level. Leaming is regarded as relational, which means that the act of leaming is apprehended (in terms of how the learning is done as well as what is leant) in the relation between the leamer and the phenomenon. Rather than regard the content of physics learning as the phenomenon, the study proposes the process of learning physics through problem, solving as the phenomenon under investigation. The thesis draws on insights from actor-network theory, particularly with regard to the spatiality of leaming. Learning is seen as a function of enrolment. Fifteen students were interviewed on introductory physics problems encountered in four end-of-module tests. The data were analyzed on the basis of strategy - conceived as "moments,' of problem-solving, as well as the factors (intentional and contextual) that could be seen to influence the strategy adopted. Two qualitatively distinct problem-solving strategies were identified, derived from the relative presence of reflective awareness. Further, factors influencing the strategies were identified and found to be indicative of two qualitatively distinct ways in which the students focused on the problems - either on problem content (the physics concepts) or on problem requirement (the formal requirements of the task within the test setting). These findings are seen to constitute the structural aspect of the students' experience of physics learning through problem solving. With regard to the referential aspect of the experience, the study derives two overall meanings that the students attached to their experience of physics learning through problem-solving, namely physics leaming as "reconstituting understanding', and physics learning as, confirming convention". It is argued that the variations identified in the strategies employed by the students, in the ways they focus on problems, in their perception of the problem-solving settings, in the meanings they attach to physics learning through problem-solving - call for a framework of learning that takes account of spatiotemporal intricacy. The notion of conceptual understanding in the learning of physics should be informed by the specific demands of the medium of problem-solving through which physics is learnt at undergraduate level
Synthesis of bimetallic immiscible alloy nanoparticles through green and gamma radiolysis approaches for environmental remediation applications
(University of the Western Cape, 2022) Noukelag, Sandrine Kamdoum; Arendse, Christopher
The synthesis of bimetallic immiscible alloy nanoparticles (NPs) using versatile routes, is a major concern since physio-chemical methods are not environmentally benign. Breaking down the immiscibility would generate NPs with remarkable properties and consequently more applications. As a result, it urges the development of one-step, eco-friendly, efficient, and reliable methods for getting more metastable bimetallic alloys from immiscible metals. To that aim, unconventional approaches such as green and gamma radiolysis were considered as the paths forward in this thesis. The wide immiscibility gaps of iron-silver (Fe-Ag), and iron-zinc (Fe-Zn) led to their selection.
HI intensity mapping: Impact of primary beam effects
(University of the Western Cape, 2023) Matshawule, Siyambonga Donald; Santos, Mario G.
Neutral hydrogen (HI) intensity mapping surveys with upcoming and future radio telescopes such as the MeerKAT, a precursor to the Square Kilometre Array Observatory (SKAO) MID telescope, have great potential for constraining cosmology, particularly in the post-reionization Universe provided that e ective cleaning methods are available to separate the strong foregrounds from the cosmological signal. The application of cleaning methods is usually conducted under the assumption of simplistic primary beam models. In this thesis, I simulate a single-dish wide-area survey with MeerKAT characteristics, and test foreground subtraction with a realistic model for the primary beam that contains a non-trivial frequency dependence. I also probe the impact of strong point sources on the cleaning. To conduct this evaluation, point source maps from a much more realistic full-sky point source catalogue are included as part of the foregrounds present in the sky model.
Measurements and applications of radon in South African aquifer and river waters
(University of the Western Cape, 2009) Abdalla, Siddig Abdalla Talha; Lindsay, Robbie; de Meijer, Rob J.; Newman, Richard T
In the natural decay series of 238Uan inert radioactive gas, 222Rn(radon) is formed in the decay of 226Ra.Because radon is relatively soluble in water, it migrates from places of its generation in rocks and soils to other places either by soil air, or travels with underground water. Therefore, there is a growing interest among hydrogeologists in using radon as a natural tracer for investigating and managing fresh water reservoirs. This work is aimed at investigating and developing radon-in-water measuring techniques applicable to aquifers and rivers. A gamma-ray spectrometry method using a hyper-pure germanium (HPGe) detector, based at iThemba LABS, Cape Town and Marinelli beakers, has been optimized to measure radon in borehole water via the y-rays associated with the decay of radon daughters 214Pband 214Bi(in secular equilibrium with their parent). An accuracy better than 5% was achieved. Moreover, long-term measurements of radon in water from an iThemba LABS borehole have been carried out to investigate the role of radon for characterizing aquifers. These investigations led to the development of a simplified physical model that reproduces the time-evolution of radon concentration with borehole pumping and may be used to estimate the time for representative sampling of the aquifer. A novel method is also proposed in this thesis to measure radon-in-water in the field after grab sampling - a so-called quasi in-situ method. The quasi in-situ method involves inserting a y-ray detector in a container of large volume filled with water of interest. The y-ray spectra are analyzed using an approach involving energy intervals on the high-energy part of the spectrum (1.3 - 3.0 MeV). Each energy interval corresponds to contributions from one of the major y-ray sources: 40K and the decay series of 238Uand 23~h, and cosmic rays. It is assumed that the U interval will be dominated by y-rays emitted from the radon daughters e14Pband 214Bi).Minor contributions to an interval with major radionuclide are corrected using an MCNPX simulated standard spectra. The two methods in this thesis make a significant contribution to measuring and modelling of radon in aquifers and surface waters. It forms a basis for further development in an interactive mode with hydrological applications.
New Collective structures in the Z=76 stable odd neutron nucleus, 187Os
(University of the Western Cape, 2021) Sithole, Makuhane Abel; Lawrie, E A
Low- and medium-spin bands of 187Os have been studied using the AFRODITE array, following the 186W(4He,3n)187Os reaction at a beam energy of 37 MeV. The measurements of γ − γ coincidences, angular distribution ratios (RAD), polarization and γ-intensities were performed using eleven High Purity Germanium (HPGe) clover detectors. In the current work, all the previously known bands have been significantly extended and five new bands have been added to the level scheme. The observed bands are interpreted within the cranked shell model (CSM), cranked Nilsson-StrutinskyBogoliubov (CNSB) formalism and Quasiparticle-plus-Triaxial-Rotor (QTR) model. Systematic comparison of bands with the neighbouring isotopes has also been made. Comparison of the models with experimental data shows good agreement. The configurations of some of the previously observed bands have been modified. Most importantly, the coupling of 2+ γ band to the 11/2+[615] neutron configuration is observed for the first time.
New collective structures in the Z=76 stable odd neutron nucleus, 187Os
(University of Western Cape, 2021) Sithole, Makuhane Abel; Lawrie Elena
Low- and medium-spin bands of 187Os have been studied using the AFRODITE array, following the 186W(4He,3n)187Os reaction at a beam energy of 37 MeV. The measurements of 􀀀 coincidences, angular distribution ratios (RAD), polarization and -intensities were performed using eleven High Purity Germanium (HPGe) clover detectors. In the current work, all the previously known bands have been signi cantly extended and ve new bands have been added to the level scheme. The observed bands are interpreted within the cranked shell model (CSM), cranked Nilsson-Strutinsky- Bogoliubov (CNSB) formalism and Quasiparticle-plus-Triaxial-Rotor (QTR) model. Systematic comparison of bands with the neighbouring isotopes has also been made. Comparison of the models with experimental data shows good agreement.
Probing large-scale structure with the SKAO and other cosmological surveys
(University of the Western Cape, 2022) Viljoen, Jan-Albert; Maartens, Roy
In recent history there have been several advances in cosmology, which has significantly shaped our understanding of the Universe. The current leading theory is called ΛCDM, which can successfully model the expansion of the Universe from a primordial state and describe the dynamics of its contents, thereby resulting in the large-scale structure present today. The model is based on general relativity, that describes gravitational interaction as the curvature of a four-dimensional manifold called space-time. However, despite the many successes of ΛCDM, there are a number of things that need further investigation. The Cosmic Microwave Background (CMB) is the oldest observable radiation in the Universe, and this cosmological relic contains a detectable structure. The process leading up to the CMB determines the initial conditions of ΛCDM, but is still poorly understood. It is widely accepted that inflation was responsible for the rapid expansion after the Big Bang, although this is yet to be verified experimentally. The distribution of the primordial potential is imprinted on ultra-large scales of the matter distribution, which offers an important insight into uncovering this mystery. In addition to the primordial Universe, there are other concepts that still puzzle us in ΛCDM itself. The fact that we have been unable to directly detect and explain these dark components (that make up around 96% of the Universe) has prompted several theorists to consider alternative cosmological models. Therefore, testing general relativity and ΛCDM is still an essential part of cosmological research. A key observational discriminant between general relativity and modified theories of gravity is the rate at which the large-scale structure grows from small perturbations. The relativistic effects (or light-cone effects) expected in general relativity also offer an independent test of the gravitational model.
A multi-wavelength study of powerful high redshift radio galaxies
(2021) Marubini, Takalani; Jarvis, J
We present a new sample of distant powerful radio galaxies, in order to study their host-galaxy properties and provide targets for future observations of Hi absorption with new radio telescopes. We cross-match the Sydney University Molonglo Sky Survey radio catalogue at 843 MHz with the VISTA Hemisphere Survey near-infrared catalogue using the Likelihood Ratio technique, producing contour plots as a way to inspect by eye a subset of bright sources to validate the automated technique. We then use the Dark Energy Survey optical and near-infrared wavelength data to obtain photometric redshifts of the radio sources. We find a total of 249 radio sources with photometric redshifts over a 148 square degree region. By fitting the optical and near-infrared photometry with spectral synthesis models, we determine the stellar masses and star-formation rates of the radio sources. We find typical stellar masses of 1011−1012 M for the powerful high-redshift radio galaxies. We also find a population of low-mass blue galaxies. We then report results from the first search for associated Hi 21 cm line absorption with the new MeerKAT radio telescope (shared-risk early science programme). We used a 16-antenna sub-array of MeerKAT to carry out a survey for Hi absorption in the host galaxies of nine powerful (L1.4 GHz > 1026 W Hz−1 ) radio galaxies at cosmological distances (z = 0.29 to 0.54). We found no evidence of absorption with 5σ optical depth detection limits. We only obtain a tentative absorption towards a radio source 3C 262 at z = 0.44 with significant ongoing star formation at a rate of 10.5 M yr−1 . The source consists of two radio lobes separated by 28.5 kpc with no evidence of a compact core. If the absorption arises from neutral gas from an extended disc, the line is redshifted by 79(21) km s−1 with respect to the nucleus and has an average Hi column density across the source of NHI ∼ 7 × 1019−20 cm−2 , which is consistent with the rate of star formation. But after further tests, we find that the Hi detection towards 3C 262 is likely to be an artefact. We conclude that the new correlator with 32 k channel resolution will be needed before searching for its associated absorption in MIGHTEE data.
Nial and steel as matrices and tic and oxynitrides as reinforcements in metal-matrix composite fabrication
(University of Western Cape, 2021) Camagu, Sigqibo Templeton; Bolokang, A. S.
Metal matrix composites harness the superior attributes of their individual constituents to form high performance materials that would rather be impossible from monolithic substances. Owing to many possible combinations, a myriad of metal matrix composite systems can be fabricated with a metal (or a metal alloy) as a matrix (continuous) phase and a ceramic as a reinforcement (discontinuous) phase. The current study focuses on two matrices, namely Nickel Aluminide and Austenitic Steel as well as two reinforcements namely, Titanium Carbide and Oxynitrides. NiAl alloys are candidates for high temperature structural materials due to their high melting temperature, low density, good thermal conductivity, and excellent oxidation resistance.
Inleiding tot die eksperimentele Sielkunde
(University of the Western Cape, 1948) Schlebusch, B. J.; Van Rensburg, J. A. J.
Elke skolier wat rue tevrede is om dit op skool slegs met lepels in te kry nie, het seker al gewonder hoe kennis oorspronklik verkry word. In daardie stadium is ons gewoonlik nog tevrede om die feite wat die onderwyser aan ons voorlê, of wat ons in die boeke gelees het, op gesag aan te neem. Maar selfs dan toets ons dikwels daardie gesag deur gewone en terloopse waarnemings. Byvoorbeeld: in die fisika leer ons dat as ons 'n groot en 'n klein klippie gelyktydig van enige hoogte laat val, hulle ook gelyktydig op die aarde sal beland as daar nie met die een klip intussen iets gebeur het wat nie met die ander klip gebeur het nie: met ander woorde as aIle faktore gelyk gebly het. Toe ons van hierdie gelyk-vallende klippies gehoor het, het party van ons op 'n dubbelverdieping gebou, of selfs op die dak van die buitegebou, opgeklim en die twee klippies self laat val om na te gaan of dit werklik so was. En hiermee het ons 'n eenvoudige eksperiment uitgevoer om te toefs of die hennis wat ons geleer het wel reg was. Dit was 'n eenvoudige eksperiment omdat die invloed van die lugdruk, en van die wind wat waai en 'n groter uitwerking op die groot klip het as op die klein klippie, buite rekening gehou is by die waarneming. Ons het ook net van ons oë gebruik gemaak om te kyk of die twee klippe gelyktydig op die aarde beland. Maar as ons middels kon aangewend het om die invloed van die genoemde twee faktore te bepaal, sou dit 'n meer presiese eksperiment gewees het en nie 'n terloopse waarneming nie. Sulke presiese eksperimente word in die laboratorium uitgevoer met die doelom betroubare kennis te kry. Die soort wetenskaplike kennis wat ons op skool leer, is reeds in die verlede deur navorsers vasgestel, en hulle bevindings is nou beskikbaar vir ons in teksboeke. Hulle eksperimente was bedoel om op nuwe kennis uit te kom. Maar die student wat sy verstand gebruik is nie noodwendig tevrede met gesag nie; hy wil self graag eksperimente maak om te sien of wat die gesag beweer werklik so is. Sy eksperimente is bedoel om eerstens te toets of die ander navorsers se resultate reg is, en tweedens 0111 hom oefening te gee met die uitvoering van eksperimente. Navorsers werk op wetenskaplike manier om nuwe kennis te verkry. Dit word vertel dat Newton S)' idee van die aantrekkingskrag van die aarde gekry het toe hy 'n appel sien val het, en dat Archimedes die idee van sy wet: dat voorwerpe in water van hulle gewig verloor, en dat die gewig wat daardie voorwerpe verloor gelykstaan aan die gewig van die volume water wat deur die voorwerpe verplaas word, gekry het terwyl hy besig was om te bad. Waarheid is dat albei allank besig was om oor hulle probleme na te dink en na te soek, en dat toe Newton die appel sien val het en Archimedes die gedagte in die. bad gekry het, dit feite was wat by vorige kennis aangesluit het. Hulle was egter nie daarmee alleen tevrede nie; daarna het albei die gedagte gaan toets .met wetenskaplike proefnemings om op kennis uit te kom. Die proefnemings en wetenskaplike navorsing kan jare en jare se harde werk vereis het. Om die eerste atoombom te laat ontplof het tientalle wetenskaplikes en duisende geskoolde assistente en werksmense jare se werk gekos. So het dit ook baie jare geverg om vas te stel dat mense wat siek word nie getoor is nie maar dat, byvoorbeeld, kieme 'n groot rol kan speel byeen of ander siekteverskynsel; en dit weer het ons aan die wetenskaplike navorsingsmetodes van 'n Pasteur te danke. Die verslag valt wetenshaplilu: navorsers se werk is nou ons wetenskaplike literatuur. Hierdie mense wat 'n eksperiment vir die eerste keer gemaak het, het dit nie gedoen om te toets of ander mense se feite korrek is nie, maar om uit te kom op oorspronklike feite van hul eie. In die Sielkunde is die basis vir die metodes van ondersoek dieselfde as vir ander wetenskappe. Daar is die noodsaaklikheid om deur middel van wetenskaplike proefneming op nuwe kennis uit te kom. Om dit te kan doen moet 'n mens eers leer hoe om 'n proefneming in te rig en moet jy voldoende oefening kry met proefnemings. As studente is dit vir ons 'n vereiste om die verskillende verskynsels self te kan ondersoek en later miskien self op nuwe kennis uit te kom en, wie weet, self een of ander oorspronklike bydrae te maak. Maar dan moet ons weet hoe om 'n eksperiment of ondersoek uit te voer. Om dit geleerd te stel: Ons moet die objektiewe metodes van 'n wetenskaplike eksperiment beheer; ons moet weet hoe om 'n proefneming in te rig.
Hybrid lead halide perovskite thin films and solar cells by chemical vapour deposition
(University of the Western Cape, 2021) Ngqoloda, Siphelo; Arendse, C.J
The organic-inorganic hybrid perovskites such as methyl ammonium lead iodide (MAPbI3) or mixed halide MAPbI3-xClx (x is usually very small) have emerged as an interesting class of semiconductor materials for their application in photovoltaic (PV) and other semiconducting devices. A fast rise in PCE of this material observed in just under a decade from 3.8% in 2009 to over 25.2% recently is highly unique compared to other established PV technologies such as c-Si, GaAs, and CdTe. The high efficiency of perovskites solar cells has been attributed to its excellent optical and electronic properties. Perovskites thin film solar cells are usually deposited via spin coating, vacuum thermal evaporation, and chemical vapour deposition (CVD).
Silicon nanowires by metal-assisted chemical etching and its incorporation into hybrid solar cells
(University of Western Cape, 2021) Khanyile, Sfiso Zwelisha; Arendse, C. J.
The rapid increase in global energy demand in recent decades coupled with the adverse environmental impact of conventional fuels has led to a high demand for alternative energy sources that are sustainable and efficient. Renewable solar energy technologies have received huge attention in recent decades with the aim of producing highly efficient, safe, flexible and robust solar cells to withstand harsh weather conditions. c-Si has been the material of choice in the development of conventional inorganic solar cells owing to it superior properties, abundance and higher efficiencies. However, the associated high costs of Si processing for solar cells have led to a gravitation towards alternative organic solar cells which are cheaper and easy to process even though they suffer from stability and durability challenges. In this work, combination of both inorganic and organic materials to form hybrid solar cells is one of the approaches adopted in order to address the challenges faced by solar cell development.
Disentangling star formation and AGN activity in the GAMA (G23) region
(University of the Western Cape, 2021) Cluver, Michelle; Marc, Harris Yao Fortune
Observations of galaxies at di↵erent wavelengths have shaped our understanding of their formation and evolution through time. The commonly derived parameters, such as stellar mass and star formation rate (SFR), rely on the assumption that the radiation received is exclusively generated by the stars within the galaxy. This assumption is true for pure star-forming (SF) galaxies, but not in the presence of an active galactic nucleus (AGN). AGNs are structures that also radiate in the full electromagnetic spectrum, inducing additional flux to that emitted by stars. Their small sizes in comparison to the host galaxy (⌧1 %) generally make them invisible in galaxy images. AGNs come in many variations making the most powerful (e.g., quasi-stellar objects) easily identifiable, whereas others with much weaker signatures can be hidden in the total emission from the host. Therefore it is imperative to find accurate methods to separate and study the properties of AGNs versus pure SF galaxies.
Coulomb excitation of 66ge
(University of Western Cape, 2021) Abrahams, Kenzo; Orce, Nico
The Coulomb excitation of 66Ge has been performed for the rst time using \safe" bombarding energies at the HIE-ISOLDE facility at CERN in July 2017. A particle- coincidence experiment using the MINIBALL array and double-sided silicon detectors has allowed the determination of transitional and diagonal matrix elements in 66Ge, yielding new measurements of the reduced transition probability connecting the ground state, 0+1 , and the rst excited state, 2+1 , or B(E2; 2+1 ! 0+1 ) value, and the spectroscopic quadrupole moment of the 2+1 state, QS (2+1 ). A relatively large B(E2) = 29:4(30) W.u. has been extracted using beam-gated data at forward angles { less sensitive to secondorder e ects { as compared with the adopted value of 16:9(7) W.u., but in closer agreement with modern large-scale shell-model calculations using a variety of e ective interactions and beyond-mean eld calculations presented in the current work.
Structural and physical properties of ReN i03 (Re=Sm, N d) nanostructured films prepared by Pulsed Laser Deposition
(University of the Western Cape, 2010) Diop, Ngom, Balla; Maaza, M .
Very few systems allow the study of the relationship between structural changes and physical properties in such a clear way as rare earth nickelate ReNi03 perovskites (Re (rare earth) = Pr, Nd, Sm and Gd). Synthesized for the first time by Demazeau et al [1] in 1971 and completely forgotten for almost twenty years, these compounds have regained interest since the discovery of high-temperature superconductivity and giant magnetoresistive effects in other perovskite-related systems. Due to its Metal-Insulator Transition (MIT) and thermochromic properties, the rare earth nickelate perovskite ReNi03 has received a great deal of attention for the past ten years in their thin films form [12]. Such unusual electronic and optical features are all the more interesting since the metal-insulator transition temperature (TMn) can be tuned by changing the Re cation: LaNi03 is metallic. No minimum of the metallic conductivity of Sm0 . ssNd 0.45Ni03, as observed by Gire et al [12] (entropic effect), was reported by Ambrosini and Hamet [11]. It has been suggested by Obradors et al. [13] that changing the rare earth cation in the ReNi03 system, acts as internal chemical pressure (increasing internal pressure by substituting the rare earth cation with another one of larger ionic radius) which can lead, as for the isostatic pressure experiment, to a tunability of the metal-insulator transition temperature [14, 15]. Obradors et al [13] reported on a decrease of T MIT upon increasing isostatic pressure but with remaining metallic properties of PrNi03 and NdNi03 (same magnitude and thermal dependence of the electrical resistivity)
Development and study of a Thoron (Rn-220) standard source
(University of Western Cape, 2019) Elhag, Elmughera Hussein Salim; Lindsay, R.
Thoron Rn-220 is a radioactive gas with a half-life of 55.6 s. It has been identified as a possible health concern in specific places such as monazite processing plants and (rare-earth) mines. The short half-life of Rn-220 makes Rn-220 calibration sources and chambers less common than for the isotope Rn-222. There are many Rn-220 standard sources and chambers that are widely described in the literature and used for different applications and calibration. However, some of these chambers and sources are not easy to set up in typical nuclear environmental laboratories. In this project, we developed a Rn-220 standard source using a thorium nitrate solution (Th(NO3)4.6H2O). The solution was split into a large volume which was used in a Marinelli beaker to characterize its strength using a Hyper Pure Germanium (HPGe) detector, and a smaller volume of around 30 ml which was poured into a small bottle. The Rn-220 is extracted by bubbling air through the solution in the small bottle using an aerator. Gamma rays from the solution were measured simultaneously using a 76.2 mm × 76.2 mm NaI(Tl) detector. The gamma rays were measured for 66 hours. The accumulated spectra were thereafter analysed using an Excel spreadsheet where the counts in the Tl-208(2614 keV) peak were extracted and used to obtain the percentage of Rn-220 pumped out of the solution in the small bottle.
Probing galaxy evolution below the noise threshold with radio observations
(University of the Western Cape, 2020) Malefahlo, Eliab D; Santos, Mario
The faint radio population consisting of star forming galaxies (SFG) and radio-quiet active galactic nuclei (AGN) is important in the study of galaxy evolution. However, the bulk of the faint population is below the detection threshold of the current radio surveys. I study this population through a Bayesian-stacking technique that I have adapted to probe the radio luminosity function (RLF) below the typical 5σ detection threshold. The technique works by fitting RLF models to radio flux densities extracted at the position of galaxies selected from an auxiliary catalogue. I test the technique by adding Gaussian noise (σ) to simulated data and the RLF models are in agreement with the simulated data for up to three orders of magnitude (3 dex) below the detection threshold (5σ). The source of radio emission from radio quiet quasars (subset of AGN) is widely debated. I apply the technique to 1.4-GHz flux densities from the Faint Images of the Radio Sky at Twenty-cm survey (FIRST) at the positions of the optical quasars from the Sloan Digital Sky Survey (SDSS). The RLF models are constrained to 2 dex below the FIRST detection threshold. I found that the radio luminosity where radio-quiet quasars emerge coincides with the luminosity where SFGs are expected to start to dominate the RLF. This Implies that the radio emission of radio-quiet quasars and radio-quiet AGN, in general, could have a significant contribution from star formation in the host galaxies.

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