Browsing by Author "Peterson, Steve"
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- ItemOpen AccessDevelopment of an ion transport system for singly charged ion injection into an electron string ion source (ESIS) charge-breeder(2020) Segal, Matthew; Peterson, SteveA 1+ ion delivery system was designed and constructed for the purpose of ion injection into the Electron String Ion Source (ESIS) charge-breeder at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia. The transport system was initially developed at iThemba LABS in Cape Town. This system includes a Liquid Metal Ion Source (LMIS) and an ion extraction and focusing system. The ion delivery system is used to produce Ga+ and Au+ ions which are transported through a beam-line system consisting of charged particle optics such as focusing einzel-lenses, an electrical quadrupole switchyard for 90◦ beam bending, and subsequent correction and focusing lenses before the entry port into the ESIS. A replica of the full system was created and used to study injection and ion transport efficiency before implementation with the ESIS. A multi-wire harp beam profilometer was used to study ion beam profiles and to obtain geometric parameters of Ga+ beams. Ga+ injection into the KRION 6T ESIS was performed successfully using the ion injection system. The extraction of multiply charged gallium was successful after 1+ injection into the KRION 6T ESIS, with a maximum charge-state of 23+. Although 1+ to n+ injection has been performed with similar Electron Beam Ion Source (EBIS) devices, this work is the first case of 1+ to n+ injection using the ESIS. This research was conducted within the frame-work of the South Africa/JINR collaboration and has been funded by the National Research Foundation (NRF).
- ItemOpen AccessEnhancing PEPT: high fidelity analysis techniques with augmented detection systems(2024) Van Der Merwe, Robert; Leadbeater, Thomas; Peterson, StevePositron emission particle tracking (PEPT) is a non-invasive, tracer-based technique used in the study of dynamic systems, such as particulate and fluid flows. Relying on positron imaging principles, typical PEPT systems operate with millimetre precision at tracking speeds of up to 10 m/s, with applications in fields from engineering to medicine. Performance is constrained by the efficiency of conventional fixed geometry detector systems and achievable activity of tracer particles, creating challenges when addressing phenomena on the micro-scale. Previous work with a pair of pixelated cadmium zinc telluride (CZT) room temperature semiconductors (9680 pixels of 1.8 x 1.8 x 0.5 mm3) exhibited potential in micro-scale PEPT, but achievable location rates and field of view (FOV) were limiting. To address these issues, a modular bismuth germanate oxide (BGO) scintillator array, consisting of 1024 detector elements (512 pixels of 6.75 x 6.25 x 30 mm3 and 512 pixels of 4.1 x 4.0 x 30 mm3), has been developed and characterised for use in a hybrid system, combining semiconductor and scintillator de vices. Optimal detection system geometry was determined through numerical modelling of system sensitivity, with the BGO array covering a FOV of 120×174×102 mm3 and the high-resolution semiconductor FOV of 62 × 42 × 20 mm3 placed centrally. This design maximises absolute efficiency through the scintillators and spatial resolution through the semiconductors. A coincidence timing resolution of 5.37 ± 0.17 ns and an energy resolution of 30.51 ± 0.48% at 511 keV was measured for the BGO devices, enabling optimisation of coincidence gates and energy level discriminators respectively. Using a novel 3D positioning stage and a 20.11 ± 0.26 kBq Na-22 calibration source, measurements of system sensitivity, spatial resolution and accuracy were performed. Sensitivity profiles were found in agreement with simulation, with a maximal central sensitivity of 34.8 ± 0.6 cps/kBq. Sub-millimetre system accuracy was achieved in all axes except between the BGO detector faces, in which an expected warping effect was identified. Sub-millimetre spatial resolution, σ, was achieved for a maximum location rate per unit activity, L ′, of 0.45 Hz/kBq, with an identified σ = 1.5 √ L′ trade-off to be optimised for specific use cases. The results of this work demonstrate the applicability of PEPT to the study of micro-scale phenomena and outline the path towards hybrid implementation
- ItemOpen AccessEnhancing PEPT: high fidelity analysis techniques with augmented detection systems(2024) Van Der Merwe, Robert; Leadbeater, Thomas; Peterson, StevePositron emission particle tracking (PEPT) is a non-invasive, tracer-based technique used in the study of dynamic systems, such as particulate and fluid flows. Relying on positron imaging principles, typical PEPT systems operate with millimetre precision at tracking speeds of up to 10 m/s, with applications in fields from engineering to medicine. Performance is constrained by the efficiency of conventional fixed geometry detector systems and achievable activity of tracer particles, creating challenges when addressing phenomena on the micro-scale. Previous work with a pair of pixelated cadmium zinc telluride (CZT) room temperature semiconductors (9680 pixels of 1.8 x 1.8 x 0.5 mm3) exhibited potential in micro-scale PEPT, but achievable location rates and field of view (FOV) were limiting. To address these issues, a modular bismuth germanate oxide (BGO) scintillator array, consisting of 1024 detector elements (512 pixels of 6.75 x 6.25 x 30 mm3 and 512 pixels of 4.1 x 4.0 x 30 mm3), has been developed and characterised for use in a hybrid system, combining semiconductor and scintillator de vices. Optimal detection system geometry was determined through numerical modelling of system sensitivity, with the BGO array covering a FOV of 120×174×102 mm3 and the high-resolution semiconductor FOV of 62 × 42 × 20 mm3 placed centrally. This design maximises absolute efficiency through the scintillators and spatial resolution through the semiconductors. A coincidence timing resolution of 5.37 ± 0.17 ns and an energy resolution of 30.51 ± 0.48% at 511 keV was measured for the BGO devices, enabling optimisation of coincidence gates and energy level discriminators respectively. Using a novel 3D positioning stage and a 20.11 ± 0.26 kBq Na-22 calibration source, measurements of system sensitivity, spatial resolution and accuracy were performed. Sensitivity profiles were found in agreement with simulation, with a maximal central sensitivity of 34.8 ± 0.6 cps/kBq. Sub-millimetre system accuracy was achieved in all axes except between the BGO detector faces, in which an expected warping effect was identified. Sub-millimetre spatial resolution, σ, was achieved for a maximum location rate per unit activity, L ′, of 0.45 Hz/kBq, with an identified σ = 1.5 √ L′ trade-off to be optimised for specific use cases. The results of this work demonstrate the applicability of PEPT to the study of micro-scale phenomena and outline the path towards hybrid implementation
- ItemOpen AccessExperimental investigation of the characteristics of prompt gammas produced in tissue during proton therapy treatment(2014) Jeyasugiththan, Jeyasingam; Peterson, SteveProtons entering matter have a finite range while photons have a gradual, exponential attenuation as they travel through material. Proton radiation therapy takes advantage of this difference, by aligning the cancerous tissue with the end of the proton range where it deposits the maximum amount of energy, resulting in significant tissue sparing compared to traditional photon therapy. These properties of protons also require a more precise delivery of the radiation since a small uncertainty in the positioning of the proton beam could result in the over- or under-dosing of critical structures. This highlights the importance of an in-vivo dose measurement technique. Due to the nature of protons, there are no primary particles exiting the patient to be used for verification purposes. One option is to use secondary radiation for dose verification purposes, like prompt gammas produced by proton-nuclei inelastic collisions. The primary aim of this work was to report on the detection of prompt gammas and their specific characteristics when produced by the important elements of tissue, like oxygen, carbon, hydrogen and nitrogen. A number of different targets containing these elements such as water, Perspex, graphite and liquid nitrogen were irradiated in a passive-scatter proton therapy treatment facility and the gammas were detected by a high resolution 2' x 2" LaBr3 detector. The measurements were carried out at iThernba LABS in Somerset West, South Africa using the proton therapy beamline. In order to determine the shielding required to sufficiently block the secondary neutrons and scattered gamma-rays emitted from the beam line elements, a significant problem in a passive-scatter proton beam, preliminary Monte Carlo simulations were performed. The energy spectra of the prompt gammas produced in the various targets was measured, looking specifically at the discrete elemental prompt gamma peaks at 4.44 MeV from ¹²C and 6.13 MeV from ¹⁶0. Measurements were also performed to investigate prompt gamma emission as a function of depth along the beam path. The depth measurements were carried out for water and Perspex phantoms at several detector positions surrounding the depth location of the Bragg peak in each material. The discrete prompt gamma-ray measurements reveal that in-vivo range verification is feasible for clinical passive-scatter proton irradiations. The secondary aspect of this work was to develop a Monte Carlo model of the entire experimental measurement set-up including the entire iThemba LABS passive-scatter proton beam line. In recent years, the Geant4 Monte Carlo toolkit has played an important role in the development of a device for real time dose range verification purposes using prompt gamma radiation. Unfortunately, in Geant4, the default physics models were not suitable for replicating measured prompt gamma emission. Determining a suitable physics model for low energy proton inelastic interactions will boost the accuracy of prompt gamma simulations.
- ItemOpen AccessMeasuring cross-section data for prompt gammas emitted during proton-nucleus collisions(2017) Ramanathan, Vijitha; Peterson, SteveIn Radiation Oncology, proton therapy has become an increasingly popular treatment modality due to the superior dose distribution of the proton beam while sparing more surrounding normal healthy tissues and critical organs. This advantage can quickly turn into a disadvantage if there is any uncertainty in the delivery of the proton beam. To fully utilize the benefits of proton therapy, it is important to monitor the in-vivo dose deposition. Due to the fact that the treatment protons stop within the patient as they deliver the dose, secondary radiation is the potential method to obtain a dose verification measurement. The detection of secondary prompt gamma rays have been proposed as an in-situ method to determine the proton range since the location of the prompt gamma emission is strongly correlated with the proton depth dose profile. This correlation has been confirmed in both experimental measurements and in Monte Carlo simulations, but absolute prompt gamma productions have been unsuccessful, due to discrepancies the Monte Carlo prompt gamma production data particularly for the prominent elements found in tissue within the therapeutic range (50-200 MeV). The goal of this work was to evaluate the prompt gamma production for both carbon and oxygen at energies relevant for proton therapy. The first part of this study was to experimentally measure the interaction cross section for proton-nucleus collisions in both carbon and oxygen. In order to determine these cross-sections, measurements using thin targets of natural Carbon and Mylar over the energy range of 66-125 MeV were performed using the AFRODITE detector system at iThemba LABS in Cape Town, South Africa. Energy and efficiency calibrations of the detection system were performed using three standard gamma emitting sources (137Cs, 60Co, and 152Eu). The second part of this work was to model the AFRODITE detector system using the Geant4 Monte-Carlo radiation transport code in order to compare the simulated to the measured results and to evaluate the previously observed discrepancies for prompt gamma production in the Geant4 code.
- ItemOpen AccessPHY1025F(2013) Peterson, SteveA series of lectures for first-year physics students covering sound, heat, light, thermodynamics, optics, and fluids. These lecture notes are designed for introductory physics courses at a university level and contain notes, diagrams and graphs helping convey core physics concepts. These materials can be used by lecturers looking to supplement their notes or students interested in self-study.