Doctoral Degrees (Physics)

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Browsing Doctoral Degrees (Physics) by Author "De Bruyn, Andre"

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    Resonant ionization spectroscopy for laser isotope separation of zinc isotopes
    (Stellenbosch : Stellenbosch University, 2021-12) De Bruyn, Andre; Steenkamp, Christine M.; Rohwer, Erich G.; Du Plessis, Anton; Stellenbosch University. Faculty of Science. Dept. of Physics.
    ENGLISH ABSTRACT: The vast zinc (Zn) reserves in South Africa are currently being underutilized, as the Zn ore refinement and isotope enrichment occurs abroad. The enrichment process most commonly used thus relies only on mass separation techniques and is therefore limited when separating isotopes of similar masses like 68Zn and 67Zn. Pure 68Zn and 67Zn are important stable nuclides in the medical industry as these isotopes are used for production of gallium-based radiopharmaceuticals used in positron emission tomography (PET) and single-photon emission computerised tomography (SPECT) scans. Additionally, depleted 64Zn is used in the cooling water of nuclear reactors for the prevention of stress corrosion cracking as well as limiting the formation of cobalt radioisotopes. This study aimed to investigate, model and optimize resonant ionization spectroscopy (RIS) schemes for the Zn isotopes 68Zn and 67Zn that are suitable for laser-based enrichment of these isotopes from natural Zn. This study reports on the development and implementation of the first experimental RIS system combined with a time-of-flight mass spectrometer at Stellenbosch University. This system was used to investigate a resonance ionization scheme that has potential for laser-based enrichment of Zn isotopes from a natural Zn sample. The ionization scheme was chosen by considering transition wavelengths, the hyper fine splitting of 67Zn, and transition strengths of intermediate levels. The effect of physical conditions and laser parameters was experimentally investigated. The experimental results were complemented by a rate equation model of the RIS scheme developed in this study. The experimental measurements included laser induced fluorescence (LIF) from both the first and second intermediate levels in the RIS scheme. The experimental LIF results contributed to optimization of the experiment and refining the rate equation model by confirming the laser bandwidth and helping to estimate an unknown transition probability. The experimental RIS measurements confirmed the model results for the existing experimental conditions, including the effects of laser tuning, pulse timing and laser pulse energy. The limiting factor to the isotope selectivity of the RIS experiment was the bandwidth of the dye laser used for the first excitation step. The simulated results of the rate equation model that was developed in this study was tested against experimental results and was found to be in good agreement. The model was also applied to conditions which could be found in industrial scenarios. The results indicated that when using a commercially available narrow bandwidth Ti:sapphire laser ( 300 MHz) it is possible to achieve 85% enrichment of 67Zn if the Zn vapour is suffciently cooled ( 100 K).