Browsing by Author "Oryema, Bosco"

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    A Comparative study of photon radiation-shielding properties of different glass types for use in health facilities
    (University of Warwick and Monash University, 2024-09-11) Nyangoma, Judith; Oryema, Bosco
    The usage of X-ray generating devices and gamma-ray sources such as 60Co and 137Cs for medical diagnostic and therapeutic applications has increased globally. However, exposure to radiation from these sources can cause detrimental effects on biological tissues. Thus, to optimise radiation safety, effective radiation shields are required. This study used the photon shielding and dosimetry (PSD) software to simulate and compare the photon shielding properties of phosphate, bismuthate, tellurite, silicate and borate glass for use in medical facilities. The parameters investigated included mass attenuation coefficient (MAC), linear attenuation coefficient (LAC), half-value layer (HVL), mean-free path (MFP), and effective atomic number (Zeff). The results showed that bismuthate glass had the highest MAC and LAC values followed by tellurite, silicate, phosphate and borate glass respectively. It was also found that bismuthate glass had the lowest HVL and MFP values followed by tellurite, silicate, phosphate and borate glass. Since materials with high MAC and LAC and low HVL and MFP are associated with higher photon stoppage powers, bismuthate glass are better photon shielding materials compared to the rest of the glass examined in this study. Conversely, borate glass presented the least shielding potential compared to phosphate, silicate and tellurite glass.
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    Atomistic simulation of primary radiation damage profiles in fluorine-doped tin oxide thin film target using SRIM code
    (University of South Africa (Unisa), 2024-11-12) Oryema, Bosco; Mtshali, Christopher B.; Madiba, Itani G.
    In this study, we investigated the discrepancy between the numbers of atomic displacements obtained from the Vac.txt method and those obtained from the Vac.dam method using SRIM-2013 operated in full cascade mode. The SRIM simulations also calculated energy partitioning, damage dose and distribution profiles of the implanted He, C and O ions at three different ion energies of 10 keV, 100 keV and 1 MeV. In all the simulations and at each ion energy value, the target thickness was increased until the entire ion beam was absorbed within the target. The simulated fluorine-doped tin oxide (FTO) thin film target stoichiometrically comprised 78.6% Sn, 16.4% O and 5.0% F, and a 6.013 g/cm3 bulk density. To achieve relatively good statistics with compromised computational time, each run followed 10 000 ion histories. The results indicated that, with increasing ion energies, the peaks of vacancy concentrations moved deeper into the material. For He ions, the vacancy profiles have peaks at ∼0.04, ~0.45 and ~2.9 µm at 10 keV, 100 keV and 1 MeV, respectively. Meanwhile, for C and O ions, the peaks were at ∼0.012, ~0.15 and ~1.23 µm for C ions and ∼0.01, 0.12 and 1.2 µm for O ions at 10 keV, 100 keV and 1 MeV, respectively. We also observed that for all the ions and at all ion energies considered, the Vac.txt method predicted more vacancies than the Vac.dam method, and the discrepancies generally increased with increasing Z by an average value of ∼1.21, ∼1.45 and 1.48 for He, C and O ions respectively. In addition, the electronic and nuclear partitioning profiles revealed that most of the energies of the ions were lost in collision with atomic electrons due to ionisation and excitations, and little to nuclear events. The simulations also revealed that nuclear stopping powers increase at low ion energies. This study also indicated that damage dose profiles strongly depend on the type of incident particle and its energy. A comparison of SRIM and iradina calculated vacancies and incident ion distribution profiles generally indicated perfect agreements between the two codes. FTO thin film remains a promising material for thermal control applications in future spacecraft. However, further analyses are still necessary to comprehensively understand its evolution under intense radiation environments comprising various ions and at different energies.
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    Effects of 7 MeV proton irradiation on microstructural, morphological, optical, and electrical properties of fluorine-doped tin oxide thin films
    (Elsevier, 2021-12-18) Oryema, Bosco; Jurua, Edward; Madiba, Itani G.; Ahmad, Ishaq; Aisida, Samson O.; Ezema, Fabian I.; Maaza, Malik
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    Effects of low-dose γ-irradiation on the structural, morphological, and optical properties of fluorine-doped tin oxide thin films
    (Radiation Physics and Chemistry, 2020-07-1) Oryema, Bosco; Jurua, Edward; Madiba, Itani G.; Nkosi, Mlungisi; Sackey, Juliet; Maaza, Malik
    This paper presents the effects of low-dose γ-irradiation on the structural, morphological, and optical properties of Fluorine-doped tin oxide (FTO) thin films for application as a passive thermal control coating in future miniaturized lightweight spacecraft. Commercial-grade FTO films on glass substrate (Pilkington Ltd, UK) with a bulk density of 2.5 g/cm3, sheet resistance of 12 Ω.sq-1, coating thickness of 450 nm, optical band-gap of 3.80 eV, a carrier concentration of 1.50×1020 cm−3 and a mobility of 15 cm2/Vs were irradiated at room temperature and atmospheric pressure using a 60Co gamma source (with gamma energies of 1.17 MeV and 1.33 MeV) at iThemba Laboratory for Accelerator Based Sciences, Cape Town, South Africa. Each sample was exposed to γ-rays for a different span of time to achieve a series of different integrated absorbed doses of 20, 30, and 50 Gy, at a dose rate of 0.207 Gy/min. Evolution in structural properties of the films was characterized using a Bruker AXS D8 Advance XRD with Cu-Kα (λ = 1.54056 Å) scanned in the 2θ degree range of 20 – 80 degrees. Surface properties were analyzed using a VEECO Dimension 1100 AFM machine. Meanwhile, variations in optical transmittance of the films was investigated using a Cary 5000 UV-vis-NIR spectrophotometer of Varian, Inc. model internal DRA- 2500 in the wavelength range of 200 – 2500 nm. XRD results indicate an enhancement of crystallization after irradiation, slight peak shifts, and variations in crystallite sizes with increasing dose. Surface roughness decreased with increasing dose and the grain structures also seen to vary with dose. No significant variations in optical transmittance of the FTO films.
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    Evaluation of radionuclide concentrations and average annual committed effective dose due to medicinal plants and soils commonly consumed by pregnant women in Osukuru, Tororo (Uganda).
    (Journal of Environmental Radioactivity, 2020-11-17) Biira, Saphina; Ochom, Peter; Oryema, Bosco
    The intention of the study was to establish the activity concentrations and the annual committed effective dose due to ingestion of medicinal plants and soils by pregnant women and their probable effects to infants. The samples of medicinal plants and soils were collected from Osukuru, Tororo District (Uganda). The naturally occurring radionuclides investigated were 226Ra, 232Th and 40K and their activity concentrations were determined using NaI gamma detector. In the medicinal plants, the average activity concentrations of 226Ra, 232Th and 40K were found to be 6.04 Bq/kg, 9.65 Bq/kg and 359.59 Bq/kg respectively. African Basil registered the highest activity concentration of 226Ra of 10.02 Bq/kg, spider plant had the highest activity concentration of 232Th of 18.60 Bq/kg whereas the pumpkin registered the highest activity concentrations of 40K of 437.92 Bq/kg. The average activity concentrations of 226Ra, 232Th and 40K in ‘medicinal soils’ were 68.87 Bq/kg, 78.20 Bq/kg and 477.44 Bq/kg respectively. The soils from the anthills registered the highest activity concentration of 226Ra and 40K while the one from bricks registered the highest activity concentration of 232Th. The annual committed effective dose due to the ingestion of medicinal plants varied from 0.096 to 0.297 mSv/y with an average of 0.194 mSv/y in infants, 0.016–0.040 mSv/y with an average of 0.029 mSv/y for individuals of age range 12–17 years and 0.007–0.018 mSv/y with an average of 0.013 mSv/y for individuals older than 17 years. Whereas the annual committed effective dose due to the ingestion of ‘medicinal soils’ varied from 1.28 to 1.65 mSv/y with an average of 1.46 mSv/y in infants, 0.23–0.30 mSv/y with an average of 0.26 mSv/y (12–17 years) and 0.07–0.09 mSv/y with an average of 0.08 mSv/y for individuals older than 17 years. In medicinal plants, the annual committed effective dose for the all age groups examined were below 0.3 mSv/y (maximum world permissible as reported UNSCEAR, 2000) while that due to the ingestion of ‘medicinal soils’ had values higher 0.3 mSv/y in infants. The results of this study show that there is inherent danger to the infants in consuming soils during pregnancy and this should be discouraged.