School of Physical Sciences (Phys-Sciences) Collections

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    Approximation of skin dose for selected setup parameters during external beam radiotherapy at Uganda Cancer Institute
    (Makerere University, 2025) Oyet, Moses
    Skin dose is unavoidable during radiation treatment. However, it should be within tolerance. Excessive cases can lead to radiation skin injuries. Investigation of radiation dose distributions to the skin surface and build-up region is vital for treatment planning against these effects. This study aimed at determining the skin dose and evaluating the accuracy of the Eclipse treatment planning system (TPS) within the build-up region under a range of clinical set-up parameters including field size, gantry angle, source-to-surface distance (SSD), multileaf collimator (MLC), and enhanced dynamic wedge angles. The study was conducted at the Uganda Cancer Institute, where no previous experimental assessment of skin dose and TPS accuracy had been reported. The EBT3 film was used for the skin dose measurements while CC13 ionisation chamber was used for verification of the TPS dose calculations at 1 cm depth within the build-up region. These measurements were done with a plastic phantom (SP34 slab phantom, IBA dosimetry, Germany) using two Varian TrueBeam linear accelerators; Linac 1 and Linac 3, each with three beam energies; 6 MV, 10 MV and 15 MV. Theresults show that the skin dose increased with field size, both for open fields and MLC fields but the MLC yielded more skin dose compared to open field, with the highest deviation being 5.1%. Skin doses for oblique beam incidences were more than for normal beams and the larger the gantry angle, the more the deviations. Skin dose reduced with increasing beam energy and SSDs. For the SSD, the effect was more significant for larger fields (difference was within 6.6% for field size more than 5 ×5 cm2)thanfor smaller fields (difference was within 3.5% for field size up to 5 × 5 cm2). The TPScalculations deviated from measured doses by up to ± 5.50% and ± 9.41% in Linac 1 and Linac 3, respectively, with the largest discrepancies observed for the 10 MV beam and the smallest for 6 MV. It is concluded that, field size, beam angle, energy, and SSD significantly influence skin dose in megavoltage photon therapy. Larger fields, lower beam energies and more oblique beam angles reduce the skin-sparing benefit of megavoltage beams. Their applications for treatments should be considered with precautions. Furthermore, TPS dose predictions in the build-up region, particularly at higher energies, are less reliable and should be supplemented with direct dosimetric verification for accurate skin dose assessment.
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    Optimizing potential drilling prospect using rock physics modelling: a case study of field X, Northern Lake Albert Basin, Uganda
    (Makerere University, 2025) Nibyagaba, Racheal
    Rock physics modelling (RPM) has been applied to the Northern Lake Albert Basin with the objective of accurately characterizing the reservoir, thereby optimizing the drilling prospects in the area. The Northern Lake Albert Basin comprises predominantly of syn-rift fluvial-deltaic and lacustrine sediments of Miocene-Pliocene age. The study comprised quantitative analysis of measured well logs from one (1) well and cross plotting of the logs to understand the main lithologies and the probable pore fluids and subsequently determine the main reservoir zone to be used in RPM. The interpretation of cross plots was guided by the known conventional trends of reservoir parameters (elastic and physical) that relate to diagenetic and depositional trends of sediments as well as guide in determining appropriate Rock Physics Models for the study. The unconsolidated sandstone model was used to model this particular geological area, by changing the reservoir parameters to those that fit this area. This was done through solid mixing of quartz, shale and clay minerals using averaging matrix method, fluid mixing to obtain fluid properties and fluid replacement modelling (FRM). Effective elastic properties (bulk modulus, shear modulus), density and porosity were obtained. FRM was also used to examine the effects of velocities with changes in gas saturation, to be able to obtain a saturated model. The Vp and Vs logs obtained from the FRM were used to construct a Rock Physics Template (RPT) of PImpedance against Vp/Vs ratio, which was in turn used to quantify the rock properties of the study area. The RPT showed fluid (hydrocarbon) saturation in the range of 0.45 to 0.65 in a very small portion of the reservoir, lithology as mainly comprised of sands (70-100%) but comprising of up to 30% shale in some locations of the area under study. The RPT also indicated a total porosity in a range of 15%-35%. Clay content and low effective pressure were also indicated RPT. Seismic inversion was done to help in validating the velocities from wells, and to compare the RPT from seismic inversion with that from RPM. However, since post stack data was used, shear velocities (Vs) were not obtained, and thus only the obtained compression velocities (Pwave) were compared with the P-wave velocities calculated from the log data, which correlated well. In conclusion, the reservoir under study did not show any commercial hydrocarbons and thus not recommended for drilling
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    Effect of palladium-doped magnetite nanoparticles in the hydrothermal liquefaction of mixed spentgrain to bio-oil
    (Makerere University, 2025) Tumwebaze, Adson
    The mixed spent grain biomass, a mixture of maize and barley, has been used as a feedstock for bio-oil production through a hydrothermal liquefaction (HTL) process in the presence of iron oxide and palladium-doped magnetite nanoparticle catalysts. The study aimed at improving the quality of bio-oil produced through HTL in the presence of palladium-doped magnetite nanoparticles. The palladium-doped magnetite nanoparticles were synthesized by the co-precipitation method. The nanoparticles were characterized using Fourier transform infrared spectroscopy, Transmission electron microscopy, and X-ray diffraction techniques. The central composite design of response surface methodology was used to optimise three reaction parameters. Under the optimum conditions of temperature of 320 ℃, catalyst dosage of 1.5 g, and holding time of 60 min, the maximum bio-oil yield of 61.3% was obtained in the presence of palladium-doped magnetite particles, in comparison to 46.31% in the absence of the catalyst. The elemental analysis of bio-oil showed an increase of elemental carbon from 55.07 wt.% for uncatalyzed liquefaction to 76.47 wt.% for Pd-doped magnetite nanoparticle catalyzed liquefaction. Similarly, the elemental hydrogen increased from 5.32 wt.% for uncatalyzed to 7.63 wt.% for palladium-doped magnetic nanoparticle catalysed liquefaction. The elemental analysis further indicated improved bio-oil quality with the reduction of oxygen content from 36.52 wt.% to 14.33 wt.% and nitrogen from 2.51 wt.% to 1.32 wt.% for palladium-doped magnetite nanoparticle-catalysed liquefaction. The GC-MS showed an increase of hydrocarbons from 60.45% for uncatalyzed liquefaction to 88.03% for palladium-doped magnetite nanoparticle catalyzed liquefaction. The bio-oil produced in the presence of Pd-doped magnetite nanoparticles had a high heating value of 34.23 MJ/kg, the average kinematic viscosity of 4.7±0.11 mm2/s, the average flashpoint of 136 ℃, the iodine value of 122.64 ± 1.45 g I/100g, and the average acid number of 0.32 ± 0.36 mg KOH/g which were all in the permissible limits for crude bio-oils. The application of palladium-doped magnetite nanoparticles in the HTL of mixed spent grain biomass increases the yield of bio-oil and improves its quality by increasing the hydrocarbons and reducing the hetero atoms. This study offers a potential pathway for improving the yield and quality of bio-oils through the application of Pd-doped magnetite nanoparticles.
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    Hydrothermal liquefaction of polyethylene terephthalete and nitrile butadiene rubber plastic waste blend into fuels using Pd/Fe3O4/zeolite composite catalyst
    (Makerere University, 2025) Kalerembe, Daniel Bruce
    This study investigated the catalytic hydrothermal liquefaction (HTL) of mixed plastic waste feedstock into fuel using a Pd/Fe₃O₄/zeolite composite catalyst. The plastic waste feedstock was composed of polyethylene terephthalate (PET) and nitrile butadiene rubber (NBR) from nitrile gloves, both of which are widely used but pose significant environmental challenges due to their poor biodegradability. The work addressed the problem of high sulfur and oxygen heteroatom content in HTL-derived fuels, which lowers calorific value, increases viscosity, and contributes to engine wear and environmental pollution. The main objective was to develop and evaluate the Pd/Fe₃O₄/zeolite composite catalyst for producing high-quality fuels with reduced sulfur and oxygen content. The catalyst was synthesized from natural zeolite and magnetite via co-precipitation and palladium impregnation, then characterized using SEM-EDX, FTIR, XRD, and XRF. HTL experiments were conducted in a batch reactor with varying PET–NBR blend ratios, catalyst dosages, reaction times, and temperatures, optimized using response surface methodology (RSM). Results showed that the Pd/Fe₃O₄/zeolite catalyst achieved a maximum fuel yield of 55.4 wt.% under optimal conditions (350 °C, 180 min, PET–NBR ratio of 4:1, catalyst dose 0.2 g). Catalytic modification significantly reduced sulfur content from 9.41 wt.% to 1.85 wt.% and oxygen content from 9.10 wt.% to 3.00 wt.%. Improvements were also observed in fuel properties, including flash point (92.5 °C), kinematic viscosity at 40 °C (5.601 cSt), and higher heating value (40.806 MJ/kg). The study concludes that Pd/Fe₃O₄/zeolite is an effective multifunctional catalyst for HTL of PET–NBR waste, enabling simultaneous deoxygenation, desulfurization, and fuel quality enhancement. Interestingly, the catalyst can be recycled and reused a number of times without significant loss in activity. This catalytic approach offers a sustainable waste-to-energy pathway that mitigates plastic pollution while producing cleaner, high-energy liquid fuels.
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    A numerical solution to an optimal control of fractional order diffusion problem
    (Makerere University, 2025) Aliniitwe, Abel
    In this study, we present a practical numerical approach for solving a fractional-order diffusion problem, and extend it to address the optimality system of a fractional-order diffusion problem. The methodology involves numerical analysis of the solution to the optimal control problem within a fractional diffusion system. We utilize a finite difference method on a bounded domain, considering the fractional time derivative in a Riemann–Liouville sense. The discretisation of both state and adjoint equations forms the basis for developing numerical algorithms. The obtained results are then analysed, including an examination of convergence properties and stability under different conditions. To illustrate the applicability of our approach, we provide a numerical example. This example serves as a practical demonstration, showcasing the capabilities and insights offered by our numerical scheme.