Browsing by Author "Buffler, Andy"
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- ItemOpen AccessA compact high-energy particle detector for low-cost deep space missions(2015) Kemp, Dayne Hilton; Ginsberg, Samuel; Buffler, AndyOver the last few decades particle physics has led to many new discoveries, laying the foundation for modern science. However, there are still many unanswered questions which the next generation of particle detectors could address, potentially expanding our knowledge and understanding of the Universe. Owing to recent technological advancements, electronic sensors are now able to acquire measurements previously unobtainable, creating opportunities for new deep-space high-energy particle missions. Consequently, a new compact instrument was developed capable of detecting gamma rays, neutrons and charged particles. This instrument combines the latest in FPGA System-on-Chip technology as the central processor and a 3x3 array of silicon photomultipliers coupled with an organic plastic scintillator as the detector. Using modern digital pulse shape discrimination and signal processing techniques, the scintillator and photomultiplier combination has been shown to accurately discriminate between the di_erent particle types and provide information such as total energy and incident direction. The instrument demonstrated the ability to capture 30,000 particle events per second across 9 channels - around 15 times that of the U.S. based CLAS detector. Furthermore, the input signals are simultaneously sampled at a maximum rate of 5 GSPS across all channels with 14-bit resolution. Future developments will include FPGA-implemented digital signal processing as well as hardware design for small satellite based deep-space missions that can overcome radiation vulnerability.
- ItemOpen AccessDemOnline(2014-09-15) Buffler, Andy; Malahe, MichaelDemOnline is a collection of demonstrations and VPython scripts for use in an introductory physics course. The website catalogues both lecture demonstrations and VPython scripts. The lecture demos section contains descriptions of the setup and execution of various physics experiments, along with screenshots and a reference for finding the equipment in the UCT Physics labs. The VPython scripts section contains scripts that demonstrate various physics concepts.
- ItemOpen AccessDetermination of energy spectra of proton therapy beams(2002) Nchodu, M R; Brooks, F D; Buffler, Andy; Jones, Dan T LA technique has been developed for measuring the energy spectra of high-energy proton therapy beams in situ under conditions similar to those used for radiotherapy at the South African National Accelerator Centre. The method is based on proton elastic scattering, H(p,p)H, in a thin polyethylene radiator and uses two ΔE-E detector telescopes to detect coincident proton pairs. Measurements have been made to investigate the effect of standard beam modification elements on the energy spectra of proton therapy beams produced by a passive scattering system. Monte Carlo simulations of the spectra were computed with the MCNPX 2.1.5 Monte Carlo code to compare with experimental measurements.
- ItemOpen AccessDeveloping multi-representational problem solving skills in large, mixed-ability physics classes(2004) Leigh, Gregor; Buffler, AndyFirst time entering students at South African technikons (even those enrolling for science courses) are typically characterised by having poor numeracy and problem solving skills coupled with poor attitudes towards learning physics. Their secondary education experience of physics has left them with little fondness or appreciation for the subject, which they perceive as a purely formula-driven, mathematical discipline with little or no connection to either their everyday experiences or their future careers.Poor first year pass rates at technikons are but one consequence of such attitudes and under-preparedness. Inappropriate epistemologies hamper life-long learning by precluding students from developing conceptual mastery and from assimilating valuable generic skills such as problem solving. To address this situation, and the declining pass rates among Physics 1 students at the Cape Technikon, a new, research-based teaching strategy was introduced for the first year physics course in which multi-representational problem solving approaches were explicitly developed in order to provide an underlying foundation for the physics. It was found that more students were able to make appropriate use of the mathematical formulae needed to numerically solve a physics question after progressing through a series of non-mathematical representations of the particular problem situation. It was found that, as students’ confidence improved, so too did their attitudes towards the subject. Post course testing showed a shift towards a more positive view of learning physics which also manifested itself in a higher pass rate in the Physics 1 course.
- ItemOpen AccessEffectiveness of a GUM-compliant course for teaching measurement in the introductory physics laboratory(European Physical Society, 2008) Pillay, Seshini; Buffler, Andy; Lubben, Fred; Allie, SaalihAn evaluation of a course aimed at developing university students' understanding of the nature of scientific measurement and uncertainty is described. The course materials follow the framework for metrology as recommended in the Guide to the Expression of Uncertainty in Measurement (GUM). The evaluation of the course is based on responses to written questionnaires administered to a cohort of 76 first year physics students both pre- and post-instruction, which were interpreted in terms of 'point' or 'set' reasoning. These findings are compared with responses from a control group of 70 students who completed a similar laboratory course apart from the use of traditional approaches to measurement and data analysis. The results suggest that the GUM framework, together with the specific teaching strategies described, provides opportunities for more effective learning of measurement and uncertainty in the introductory laboratory.
- ItemOpen AccessFast neutron scattering analysis(1998) Buffler, Andy; Brooks, F D; Aschman, David GThe scattering of a beam of fast monoenergetic neutrons is used to determine elemental compositions of small (0.2-1 kg) samples of materials. Particular emphasis is placed on the measurement of concentrations of the elements H, C, N and O, which are the principal constituents of contraband materials, such as explosives and narcotics. Scattered neutrons are detected by liquid scintillators located at forward and at backward angles, and different elements are identified by their characteristic scattering signatures derived either from a combination of time-of-flight and pulse height measurements or from pulse height measurements alone. Atom fractions for H, C, N, O and other elements are derived from unfolding analyses based on these scattering signatures and used to identify materials. Effects of neutron interactions in surrounding materials, either in the neutron beam or between the scatterer and the detectors, can be detected and allowed for in such a way as not to interfere significantly in the identification of the scatterer. The Fast Neutron Scattering Analysis technique provides a non- intrusive method for detecting and identifying sub-kilogram quantities of contraband materials. Methods for locating the positions of small contraband items in packages of volume up to about 0.5m³ are described and a two-stage screening system for detecting contraband hidden in small packages is proposed.
- ItemOpen AccessFirst year students' understanding of measurements in physics laboratory work(2005) Volkwyn, Trevor Stanton; Allie, Saalih; Buffler, AndyRecent collaborative work by the physics education research group at the University of Cape Town (South Africa) and the science education research group at the University of York (United Kingdom) has produced a suite of research instruments which may be used to probe the procedural understanding of first-year physics students. The work has led to the development of a model for classifying students' reasoning about measurement in terms of theoretical constructs which have been termed the point and set paradigms. The model accounts for the ways in which students make decisions in the areas of data collection, data processing and data comparison during experimental work. A set of questionnaires was modified and used in this study to investigate mainstream physics students' understanding of measurement both before and after completing a full year physics laboratory curriculum. It was found that although the mainstream students both entered and exited their course with high levels of proficiency in applying the more formalistic rules of data analysis, very few shifted in their fundamental understanding of the concepts that underlie experimentation. The results further suggest that the laboratory course may have indeed impeded these students from developing a deep understanding of the nature of measurement and uncertainty.
- ItemOpen AccessIdentification of platinum ores via trace element signatures(2011) Hassan, Maisson Mohamed Zeinelabieden; Buffler, AndyThis project studies the natural variation in the elemental composition of processed platinum ore from different extraction locations in South Africa in order to assess whether this provides sufficient information for the elemental fingerprinting" of the material.
- ItemOpen AccessImpact of a conventional introductory laboratory course on the understanding of measurement(American Physical Society, 2008) Volkwyn, Trevor S; Allie, Saalih; Buffler, Andy; Lubben, FredConventional physics laboratory courses generally include an emphasis on increasing students' ability to carry out data analysis according to scientific practice, in particular, those aspects that relate to measurement uncertainty. This study evaluates the efficacy of the conventional approach by analyzing the understanding of measurement of freshmen following the physics major sequence, i.e., top achievers, with regard to data collection, data processing, and data comparison, through pre and post-instruction tests by using an established instrument. The findings show that the laboratory course improved the performance of the majority of students insofar as the more mechanical aspects of data collection and data processing were concerned. However, only about 20% of the cohort of physics majors exhibited a deeper understanding of measurement uncertainty required for data comparison.
- ItemOpen AccessImproving the selectivity of the radio-labelling of ion exchange resin tracers for positron emission particle tracking(2015) Van Heerden, Michael Rudi; Franzidis, Jean-Paul; Buffler, AndyPositron emission particle tracking (PEPT) is a technique which non-invasively tracks tracer particles labelled with a positron emitting radionuclide in a system of flow. The tracers are tracked through the detection in a PET scanner, of the two nearly collinear 511 keV gamma rays resulting from the annihilations of the positrons. For this technique to be effective, the tracer must be representative of the media in the system under study, and labelled with a sufficient activity of radionuclides. Organic ion exchange resins are suitable tracer materials for PEPT experiments, and are usually labelled with ⁶⁸Ga at the laboratories of PEPT Cape Town. The labelling performance relies on the chemical and physical properties of organic strongly acidic cation exchange resins and the nuclear chemistry of ⁶⁸Ga. The objective of this study is to obtain consistent tracer labelling throughout, or even beyond, the lifespan of the SnO₂ ⁶⁸Ge/⁶⁸Ga generator which degrades over time. The objective 1s achieved by integrating a purification technique into a "standard" radiolabelling method used at iThemba LABS. A small 0.5 ml Amberchrom CG-71 column is loaded with the ⁶⁸Ga generator eluent in 7 M HCl, then rinsed of most the contaminants before eluting the product with distilled water and used in the radiolabelling method. Using a 1-year-old 30 mCi SnO₂ ⁶⁸Ge/⁶⁸Ga generator eluent that has been purified by this method improved the radiolabelling performance by an average of at least 10% when compared to the performance of the un-purified product. Purifying the generator eluent will enable PEPT experiments of longer duration, and in highly shielded systems where tracers with high activity are required, such as granular and fluid flow in engineering applications.
- ItemOpen AccessInvestigations into a positron emission imaging algorithm(2012) Bickell, Matthew; Buffler, Andy; Govender, IndresanA positron emission imaging algorithm which makes use of the entire set of lines-of-response in list-mode form is presented. The algorithm parameterises the lines-of-response by a Cartesian mesh over the field-of-view of a Positron Emission Tomography (PET) scanner to find their density distribution throughout the mesh. The algorithm is applied to PET image reconstruction and Positron Emission Particle Tracking (PEPT). For the PET image reconstruction, a redistribution of the lines-of-response is employed to remove the discrete nature of the data caused by the finite size of the detector cells, and once the density distribution has been determined, it is filtered and corrected for attenuation. The algorithm is applied to static and dynamic systems of hard phantoms, biological specimens and fluid flow through a column. In the dynamic systems, timesteps as low as 1 second are achieved. The results from the algorithm are compared to the standard Radon transform reconstruction algorithm, and the presented algorithm is observed to produce images with superior edge contrast, smoothness and representation of the physical system.
- ItemOpen AccessMeasurement of fluence at the D-line fast neutron facility at iThemba LABS(2011) Musonza, Emmanuel Tapiwa; Buffler, AndyMeasurements of fluence were made for the neutron beams produced at the fast neutron beam facility of iThemba LABS, using an NE213 organic liquid scintillator detector and a 238U fission ionisation chamber. Neutron beams were produced by irradiating a 6 mm natural lithium target with pulsed proton beams obtained from the k = 200 separated sector cyclotron. Three incident proton beam energies were used in this work, namely 65.99 MeV, 99.44 MeV and 203.33 MeV. From time-of-flight measurements with the NE213 scintillator, the spectral fluence of the neutron beams was obtained. Pulse shape discrimination was used to correct for gamma ray induced signals in the NE213 detector. Simultaneous measurements of the neutron beam flux were performed at 0° and 16°. The 238U detector was used to obtain peak fluence measurements relative to the 238U(n,f) cross section.
- ItemOpen AccessMeasurement of neutron fluence at En=20-100 MeV using a stacked scintillator spectrometer(2003) Makupula, Siphiwo Aquinas; Buffler, AndyThe present work demonstrates a new application of a stacked spectrometer which has been developed in the Physics Department of the University of Cape Town. The spectrometer used in the present work consists of two identical segments of NE213 liquid scintillator, of dimensions 13.0 x 13.0 x 7.0 cm³ The present work demonstrates a new application of a stacked spectrometer which has been developed in the Physics Department of the University of Cape Town. The spectrometer used in the present work consists of two identical segments of NE213 liquid scintillator, of dimensions 13.0 x 13.0 x 7.0 cm³, stacked behind one-another, and allows response functions to be measured for neutrons of energy up to 100 MeV, which are minimally affected by charged particle escape.
- ItemOpen AccessMeasurement of neutron production from an ¹⁸O target for the production of radioactive-ion beams at iThemba LABS(2018) Ngcobo, Phumlani Zipho; Buffler, Andy; Bark, R AiThemba LABS, in the South African Isotope Facility (SAIF) project, proposes to produce radioactive ion beams by the fission of uranium. A natural way to fission uranium is to use high-intensity proton beams from a cyclotron. However, neutron-induced fission gives enhanced production of neutron-rich fission fragments compared to proton-induced fission, thus there is a need to find efficient ways of producing neutrons from protons. Beryllium targets have been suggested, but increasing the proton beam current to achieve higher fission rates could lead to cooling problems. Cooling might be achieved in a natural way by using enriched water as a converter, but ¹⁶O is a poor neutron converter compared with ⁹Be. An alternative would be to use water enriched in ¹⁸O. With no data available for ¹⁸O above 25 MeV, this necessitated the measurement of neutron yields from the ¹⁸O(p,xn) reactions between 30 and 66 MeV. Quasi-monoenergetic neutron spectra were therefore measured at proton energies of 66; 54; 42 and 30 MeV on a 2.03 mm thick H₂¹⁸O water target using the time of flight (ToF) technique at 0˚ and 16˚. Neutron energy spectra from a ⁷Li (2.5 ± 0.5 mm thick) target were also measured at the same energies to validate the H₂¹⁸O measurements. The spectra deduced at these energies were used to simulate the neutron fluence spectra from a stopping-length H₂¹⁸O target and were compared with the measured neutron fluence spectra from a thick target of 40.0 ± 0.1 mm at 0˚ and 16˚, using a proton beam of 62 MeV. The neutron differential cross sections, dσ(E)/dΩ for the ¹⁸O(p,n) reactions at 66; 54; 42 and 30 MeV were derived and compared to those of ⁷Li(p,n) and ⁹Be(p,n). The cross sections of ⁷Li and ⁹Be are higher than those of ¹⁸O between 20 MeV and 50 MeV at 0°. At above 60 MeV, the ⁷Li target produces double the amount of neutrons produced by ¹⁸O and ⁹Be targets, but importantly ¹⁸O produce neutrons more than ⁹Be. The ¹⁸O(p,xn) neutron cross sections (d²σ(E)/dΩdE in mb/MeV/sr) from the thick stopping-length target (40 mm) were compared to the corresponding cross sections of ⁹Be thick stopping-length target (24.1mm). Conclusively, on average, the ¹⁸O neutrons cross sections are half those of ⁹Be.
- ItemOpen AccessModel-based teaching and learning of kinematics in an introductory physics course for underprepared students(2009) Ibrahim, Bibi Bashirah; Buffler, AndyThis study concerns the application of a model-based approach for problem solving and conceptual understanding, in the context of kinematics, relating to the "foundation" component of an introductory physics course designed for students who are academically and scientifically underprepared. A new method for portraying objects in motion, "freeze frame" representation, was introduced. The particular visual conceptual model was employed as a representational bridge for translating physics information between different modes of representations as well as for eliciting qualitative information.
- ItemOpen AccessNeutron activation analysis of plantinum converter and furnace mattes using a D-T sealed tube neutron generator(2013) Majawa, Louis John; Buffler, AndyNeutron activation analysis (NAA) has been applied to furnace matte and converter matte samples with the objective of studying the natural variation in the elemental composition of the samples, with a view to characterize the samples for their source of origin. The experimental work was carried out at iThemba LABS national laboratory near Cape Town, South Africa. A new NAA facility was designed and built for this purpose, and fully characterized, featuring a 14 MeV neutron generator. Gamma-ray spectra were measured using an HPGe detector. A number of isotopes were identified in the measured spectra and the elemental concentrations calculated. Radiometric spectral measurements were also made of the samples, without prior irradiation, and the spectra analysed for isotopic variation. Consequences for sample identification via these techniques are discussed.
- ItemOpen AccessNew technique for radiolabelling tracer with 64CU for positron emission particles tracking (PEPT) experiments(2015) Liu, Cong; Franzidis, Jean-Paul; Buffler, Andy; Cole, KatiePositron emission particle tracking (PEPT) is a non-invasive technique for studying the flow of particulate systems within industrial equipment. The technique tracks a tracer particle labelled with a positron emitting radionuclide moving within the field-of-view of a positron emission tomography (PET) scanner. Two important components of the technique are a PET camera and PEPT tracers, which are particle tracers labelled with a positron emitting radionuclide. Currently, the majority of PEPT tracers are made with 68Ga or 18F. However, the relatively short half-life of these two radionuclides limits the application of PEPT to a maximum of 3 hours of experimental time. 64Cu is a potential candidate for PEPT tracer fabrication due to its relatively long half-life (12.7 h) which could extend the experimental running time of PEPT experiments to two uninterrupted days. The objective of the research described in this thesis was to develop a technique for radiolabelling tracers with 64Cu, and to test their efficacy in PEPT experiment. The work was conducted at Radionuclide Production Department, iThemba LABS near Cape Town, where high purity 64Cu was obtained by a two stages separation method using ion exchange chromatography.
- ItemOpen AccessA one-way coupled DEM-CFD scheme to mode free-surface flows in tumbling mills(2012) Malahe, Michael; Buffler, Andy; Govender, IndresanThere is a great need in the minerals processing industry for accurate prediction of slurry flows in tumbling mills. This flow is currently best understood through empirical, mechanistic and computational models. In the case of computational models, a realistic description of the system requires two fluid phases (for slurry and air) and one solid phase (for the charge). Existing 3-phase work makes use of a purely particle-based description, coupling the discrete element method (DEM) for the solids with smoothed particle hydrodynamics (SPH) for the fluids. This work is the first presentation of a 3-phase approach for tumbling mills that combines a particle description for the solids, DEM, and a continuum description for the fluids, computational fluid dynamics (CFD). In this approach, the phase coupling is only one-way, in the sense that forces are applied from the solids to the fluids, but not the other way around. In the course of developing the approach, some computational geometry algorithms are presented for efficiently converting the particle description of DEM into an appropriate continuum description for CFD.
- ItemOpen AccessPHY1004W - Matter & Interactions(2014-09-18) Buffler, Andy; Fearick, Roger; Govender, Indresan; Peshier, AndrePHY1004W is a first-year, calculus-based introductory Physics course for Science students intending to continue with second-year Physics. MODERN MECHANICS: Matter and interactions, conservation laws, the momentum principle, atomic nature of matter, conservation of energy, energy in macroscopic systems, energy quantization, multiparticle systems, exploring the nucleus, angular momentum, entropy, kinetic theory of gases, efficiency of engines. ELECTRIC AND MAGNETIC INTERACTIONS: Electric fields, electric potential, magnetic fields, electric circuits, capacitance, resistance, magnetic force, Gauss' law, Ampere's law, Faraday's law, induction, electromagnetic radiation, waves and particles, semiconductor devices.
- ItemOpen AccessPHY1023H - Principles of Physics A(2014-09-18) Buffler, Andy; Morrison, AngusPHY1023H is a a first-year, calculus-based introductory course primarily for students on the General Entry for Programmes in Science (GEPS). The first half of this course provides students with the essential tools and skills that are required for dealing successfully with physics at first-year university level. The three broad areas that are covered are (a) mathematical techniques and their relationship with physical phenomena, (b) experimental procedures and (c) communication skills, in particular report writing. The second half of the course covers material similar to that of the first half of PHY1004W. Second semester: Mechanics: vectors, kinematics, dynamics, work, energy power, conservative and non-conservative forces, friction, impulse, momentum, collisions, rotation, rotational dynamics, torque, rotational inertia, rotational energy, angular momentum, static equilibrium, gravitation. Properties of matter: elasticity, elastic moduli, hydrostatics, hydrodynamics. Thermodynamics: temperature, heat, kinetic theory of gases, thermodynamic laws, entropy.