Browsing by Author "De Bruyn, Andre"

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    Fluorescence and self-absorption free excitation spectroscopy of carbon monoxide isotopomers in the vacuum ultraviolet
    (Stellenbosch : Stellenbosch University, 2017-03) De Bruyn, Andre; Steenkamp, Christine M.; Stellenbosch University. Faculty of Science. Dept. of Physics
    ENGLISH ABSTRACT : Carbon Monoxide (CO) is the most abundant heteronuclear diatomic molecule in the universe and has been of great interest in the fields of astrophysics and astronomy. CO is additionally, a prototype molecule for theoretical models. By using a supersonic free-jet expansion it is possible to conduct spectroscopy of this molecule under collision-free and low temperature conditions similar to that found in space. The radiation used in this study to conduct spectroscopy is tuneable coherent vacuum ultraviolet (VUV) light which is generated by four-wave sum frequency mixing in a magnesium vapour medium. For the first time in our laboratory, the fluorescence of CO upon rovibronic excitation has been investigated using a scanning monochromator. Vibrationally resolved fluorescence spectra resulting from population of single rovibronic levels in the A1Π(v 0 = 3, 4) bands for 12C 16O and the A1Π(v 0 = 3) bands for 13C 16O, 12C 18O were recorded. The theoretical models of Morse and Dunham were applied to calculate vibrational constants of the X1Σ +(v 00 = 0) state, Franck-Condon factors, r-centroid values and the r-centroid dependence of the electronic transition moments for the A1Π(v 0 = 3, 4) − X1Σ +(v 00 = 0) bands for the different isotopomers. Using the tuneable coherent VUV light it was possible to record the rotationally resolved excitation spectra for X1Σ +(v 00 = 0) − A1Π(v 0 = 3) and X1Σ +(v 00 = 0) − A1Π(v 0 = 4) bands of 12C 16O. In the high-resolution excitation spectra, several forbidden singlet-triplet rovibronic transitions of the X1Σ +(v 00 = 0) − a 03Σ +(v 0 = 14) band were recorded. Two new measuring techniques were developed in this study. The first measuring technique allows for an accurate measurement of the amount of VUV light generated during excitation measurements. The second measuring technique allows for recording of self-absorption free rotationally resolved excitation measurements. These two techniques additionally resulted in a significant improvement in spectral resolution. Using the new measuring techniques it was possible to accurately determine the rotational temperature of the supersonic gas jet. Using the temperature, limiting values for the Mach number, gas flow speed and effective density in the supersonic gas were calculated.
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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).