Department of Physics

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Activity levels of gamma ray emitting radionuclides in food crop samples in selected tobacco farming areas in Aura and Maracha districts
(Kyambogo University (unpublished work), 2017-12) Anguani, Epiphany Mike
The farming activities, especially Tobacco production in Terego East and Terego West in Arua district and Maracha East County in Maracha district employ fertilizers such as NPK, DAP, CAN, TSP and UREA to enhance soil fertility property and to increase Tobacco production. Fertilizers are known to contain radionuclides such as uranium, radium, potassium etc., that originate from phosphate rocks; that could accumulate in the soil over the years and these may be absorbed by food crops grown on such soils. Humans who feed on these food crops may then absorb such radionuclides. As Human cells absorb radiation energy, molecules in them get damaged resulting into malfunction of cells through genetic mutation and this can then be a health risk. in this study the specific activity levels of gamma ray emitting radionuclides in selected food crop samples (maize, rice, sorghum, cassava, ground nuts, beans and simsim), grown in soils contaminated by fertilizers was determined using Gamma ray spectroscopy technique, that uses Nal(Tl) detector. The samples were obtained from the six Sub Counties of Omugo, Aii-vu, Odupi, Oriama, Katrini and Bileafe in Arua District and three Sub Counties of Tara, Yivu and Nyadri in Maracha District. The sampling technique used was purposive and simple random. In summary, the mean specific activity levels of radium, thorium, uranium and potassium were 64.0 Bqkg·1 , 6.0Bqkg·1, 3.5 Bqkg·1 and 185.1 Bqkg·1 respectively, in the crop samples considered. The mean specific activity levels for potassium was the highest, followed by radium, thorium ·and the least level shown by uranium. The mean absorbed dose rate was 40.9 nGy/h and the mean annual effective dose rate was 0.1 mSv/yr., for all the crop samples considered. The mean annual effective dose rate for all crop samples determined in this study were within the range recommended by the International Atomic Energy Agency as having no observable effects in the human body. Therefore it is recommended that consumption of the food crops investigated should continue as it poses no potential radiation hazard. It is further recommended that investigation should be performed on other crops which are not investigated in this study.
Assessing the radiological hazards due to radionuclides in sediments and tailings around Kilembe copper mines, Western Uganda
(International Journal of Environmental Analytical Chemistry, 2024-03-19) Evarist, Turyahabwa R. S.; Farooq, Kyeyune; Eric, Mucunguzi; Akisophel, Kisolo; Manny, Mathuthu
Copper mining in Kilembe Valley, Western Uganda, between 1956 and 1982 resulted in multiple tailing sites, raising concerns about potential increases in the natural background radiation. In this study, the radioactivity concentrations of 226Ra, 232Th, and 40K in 31 sediments and tailing samples from the Kilembe copper mines area were determined using HPGe-based gamma spectrometry. The mean activity concentrations of 226Ra, 232Th, and 40K in sediment samples were 38.6 ± 8.9, 37.4 ± 7.8, and 708.0 ± 147.3 Bq kg−1, respectively. While in tailing samples, the mean values were 171.3 ± 31.7, 34.8 ± 14.9, and 792.4 ± 208.2 Bq kg−1, respectively. These values exceeded global averages of 35, 30, and 400 Bq kg−1 for 226Ra, 232Th, and 40K, respectively. To assess the radiological hazards due to radionuclides in sediments and tailings, several parameters such as the radium equivalent activity (Raeq), external hazard index (Hex), internal hazard index (Hin), gamma representative index (Iγ), absorbed dose rate (D), total annual effective dose (Etot), and total excess lifetime cancer risk (ELCRtot) were determined. In sediments, most of these hazard parameters were above the world’s average values, except Raeq, Iγ, Hex, and Hin. While in tailings, all the hazard parameters surpassed the global average values except Raeq and Hex. Pearson correlation coefficient and hierarchical cluster analysis showed that 226Ra was the main contributor to the assessed radiological hazards. The study suggests potential radiological risks linked to natural radioactivity from sediments and mine tailings, especially when used as building materials.
Biomarker Raman bands of estradiol, follicle-stimulating, luteinizing, and progesterone hormones in blood
(Vibrational Spectroscopy, 2022-08) Annah, M. Ondieki; Zephania, Birech; Kenneth, A. Kaduki; Catherine, K. Kaingu; Anne, N. Ndeke; Loyce, Namanya
Variation of the levels of reproductive hormones outside the normal range indicates health problems that include cancer, infertility, and menstrual difficulties. This work reports on a potentially novel method of screening four (estradiol, follicle-stimulating hormone, FSH; luteinizing hormone, LH; and progesterone) hormones. The work involved first determining the characteristic Raman spectra of their standards. Thereafter, the Raman marker bands of the respective hormones in blood were determined experimentally. Simulate samples were prepared by mixing, at varying concentrations, the respective standard hormone samples with male mouse’s blood and concentration-sensitive Raman bands identified upon 785 nm laser excitation. The samples were applied, separately, onto prepared conductive silver paste smeared microscope glass slides. Spectral data analyses were done using both Principal Component Analysis (PCA) and Analysis of variance (ANOVA). The spectral profiles of respective standard hormones (with no blood) displayed common bands at 483, 1005, 1244, and 1455 cm−1 which were tentatively attributed to C-C stretching of glucose, lipid bands, and CH2/CH3 scissoring respectively. Other bands were observed at 542 cm−1 (for LH and progesterone), 859 cm−1 (for estradiol and FSH), 837 cm−1 (for FSH and LH) and at 1360 cm−1 (for progesterone). In blood, a large comparative Raman spectral intensity variation was observed at around 483 and 1450 cm−1 in LH; 902 and 1569 cm−1 in estradiol. These bands could be used as biomarker Raman bands for the respective hormones. The bands centered at 668 and 1219 cm−1 displayed almost identical intensity variation in the four hormones (estradiol, FSH, LH, and progesterone) and could be used as marker bands for level determination for the four combined. This work has shown the power of Raman spectroscopy in potential hormone concentration level determination when respective biomarker bands are employed.
Characterisation of copper indium gallium diselenide solar module in the Ugandan climate
(Kyambogo University [unpublished work], 2014-01) Kisitu, Zawedde Sarah
The photovoltaic solar energy from copper indium gallium diselenide (CIGS) solar module is one of the most promising sources of solar energy for large scale production of clean energy at competitive prices. The focus of the study was to determine the performance of CIGS solar module in terms of its performance parameters in the tropical region. The goal of this dissertation was hence to characterise the performance of CIGS solar modules in the Ugandan climate. The performance of the CIGS module was assessed when put out doors by measuring the current-voltage (1-V) characteristic of the device. A variable resistor was connected to the CIGS module and was varied from minimum (0 Ω) to maximum (l00 Ω) and the corresponding current and voltage were measured. The electrical performance parameters such as short circuit current, open circuit voltage, maximum power, fill factor and efficiency were then obtained from 1-V characteristic curves. The short circuit current obtained was l.03A that is 1.9% lower than the rated value. The open circuit voltage obtained was 19.25V that is 35.8% lower than the rated value. The maximum current obtained was 0.7 lA that is 12.3% lower than the rated value. The maximum voltage obtained was 13.4V that is 37.9% lower than the rated value. The maximum power obtained was 9.5W that is 36.7% lower than the rated value. There was no change in the fill factor. The efficiency obtained was 6.1 % that is 24.7% lower than the rated value. The study shows that out of the seven parameters it was only the fill factor which had the same value with the rated value. The short circuit current was close to the rated value while other parameters were significantly lower than the rated value varying between 12.3% and 37.9%. Basing on the findings of this study, it is recommended that a further study should be done over a longer period of time for example a year in both dry and wet seasons to cross check the reliability of the findings of this study. The results of this study will be useful to compare the performance of this type of module with others in the market to find out if they would give similar values. Current-voltage (1-V) characteristics measurements under the dark should also be considered to determine the performance of the CIGS solar modules. This would determine other electrical parameters such as series resistance, shunt resistance and diode parameters (ideality factor and reverse saturation current).
Co-sensitization effect of chlorophyll and anthocyanin on optical absorption properties and power conversion efficiency of dye-sensitized solar cells
(Springer, 2024-04) Mukhokosi, Emma Panzi; Mohammed, Tibenkana; Loyce, Namanya; Botha, Nandipha L.; Maaza, Maliki; Velauthapillai, Dhayalan
In this article, the chemical structure, optical absorption and photoluminescence properties of un/adsorbed dyes of hibiscus flower (H), pumpkin leaf (P), sweet potato leaf (S) and their composites (H: P & H: S) have been studied. The chemical structural properties revealed the O–H, C–C and C = O as the main anchoring functional groups. The optical absorption properties revealed two definite bands in between 450–500 nm and 600–680 nm wavelength for chlorophyll-based dyes and a peak at 526 nm for anthocyanin based dye extract. The composite dye extracts revealed optical absorption bands corresponding to chlorophyll and anthocyanin pigments with enhanced absorption of light. Five different solar cells based on H, P, S, H:P-3:1 and H:S-3:1 were developed and revealed an efficiency of ~ 0.08, 0.3, 0.5, 0.7 and ~ 1% respectively. The efficiency was reduced by half after 30 days. The composites had the highest power conversion efficiency due to more O–H, C–C and C = O binding sites on TiO2 nanoparticles, reduced rate of electron–hole pair recombination and a wide range of optical absorption. These studies suggest that co-pigmentation can be an alternative strategy to increasing the power conversion efficiency in DSSCs.
Comparison of roki and sunflower oils as sensible heat storage materials for cooking applications
(Kyambogo University [unpublished work], 2022-07) Frank, Mndeme Sayuni
Sensible heat storage materials are cheaper than latent heat storage materials for small storage volumes. Static experiments to evaluate the thermal performances of two Ugandan locally available edible vegetable cooking oils for medium temperature thermal energy storage are presented. The two vegetable oils evaluated and compared are Sunflower oil and Roki oil (a blend of Palm oil and Sunflower oil). Temperature profiles are used to assess the thermal performances during heating cycles, cool-down cycles, energy, exergy, and heat utilization. The results show that Roki oil attains a higher maximum temperature (~ 170 ℃) compared to the Sunflower oil (~ 160 ℃) during low-temperature heating cycles. Roki oil shows higher temperatures during cooling compared to Sunflower oil, achieving a final temperature (~ 78 ℃) slightly higher than that of Sunflower oil (~ 76 ℃). Roki oil shows a maximum energy rate of 413 W compared to Sunflower oil showing a maximum energy rate of 387 W, this is possibly due to the low thermal mass (mc) of Roki oil compared to Sunflower oil. Roki oil also shows higher maximum exergy rate of ~ 129 W compared to that of Sunflower oil ~ 120 W. This occurs because of the lower thermal mass (mc) of the Roki oil which leads to a quick rise of temperature. The exergy factor of Roki oil (0.31 – 0.62) is slightly higher than Sunflower oil (0.27 – 0.59) within 1 hour and 40 minutes. This is possibly due to the higher difference in temperature of Roki oil compared to Sunflower oil. The heat utilization characteristics of the two heat storage materials are experimentally determined in water heating experiments using 1.0 kg to 3.0 kg water loads. Roki oil shows higher average heat utilization (151 – 350) kJ, and higher average heat utilization efficiency values (0.25 – 0.66) as compared to Sunflower oil (148 – 300) kJ and (0.25 – 0.60), respectively. The average heat utilization and average heat utilization efficiency values increase with the increase in the water load for both Sunflower oil and Roki oil. The best overall performance is shown by Roki oil compared to Sunflower oil. Preliminary results with parabolic dish solar cookers are also presented in this work. The results show that Roki oil performs better than Sunflower oil during heating, cooling/heat retention, and heat utilization.
Computational Insights for interactions between NsP2 and NsP3 of CHIKV and Hormones through DFT computations and Molecular Dynamics Simulations
(Chemistry & Biodiversity, 2024-08-13) Raman, Anirudh Pratap Singh; Kumar, Durgesh; Kumari, Kamlesh; Jain, Pallavi; Bahadur, Indra; Abedigamba, Oyirwoth P.; Preetam, Amreeta; Singh, Prashant
The non-structural protein (nsP2 & nsP3) of the CHIKV is responsible for the transmission of viral infection. The main role of nsp is involved in the transcription process at an early stage of the infection. In this work, authors have studied the impact of nsP2 and nsP3 of CHIKV on hormones present in the human body using a computational approach. The ten hormones of chemical properties such as 4-Androsterone-2,17-dione, aldosterone, androsterone, corticosterone, cortisol, cortisone, estradiol, estrone, progesterone and testosterone were taken as a potency. From the molecular docking, the binding energy of the complexes is estimated, and cortisone was found to be the highest negative binding energy (-6.57 kcal/mol) with the nsP2 protease and corticosterone with the nsP3 protease (-6.47 kcal/mol). This is based on the interactions between hormones and NsP2/NsP3, which are types of noncovalent intermolecular interactions categorized into three types: electrostatic interactions, van der Waals interactions, and hydrogen-bonding. To validate the docking results, molecular dynamics simulations and MM-GBSA methods were performed. The change in enthalpy, entropy, and free energy were calculated using MM-GBSA methods. The nsP2 and nsP3 protease of CHIKV interact strongly with the cortisone and corticosterone with free energy changes of -20.55 & -36.08 kcal/mol, respectively.
Determination of radiological hazard levels in soil, mine tailings and rock samples from selected gold mines in Busia district, Uganda
(Kyambogo University(unpublished), 2018-11-15) Eling, Jimmy
This study was designed to determine radiological hazard levels in soil, mine tailings and rock samples from Agata, Okame, Busia 90 and Greenstone Resource Limited Gold mines in Busia District. The specific activity of the radionuclides were determined using Nal (Ti) scintillation detector and the values were then used to determine the radiological hazard parameters due to radionuclides in the samples from the mines under study. The specific activity of 238U in soil, mine tailings and the rock samples from the four gold mines ranged from 18.7 Bqkg-1 to 27.9 Bqkg-1 , 7.4 Bqkg-1 to 13.2 Bqkg-1 and 1.7 Bqkg-1 to 27.8 Bqkg-1 respectively. The specific activity of 232Th in soil, mine tailings and rock samples from the mines ranged from 60.8 Bqkg-1 to 98.8 Bqkg-1 , 25.1 Bqkg-1 to 32.7 Bqkg-1 and 2.3 Bqkg-1 to 66.6 Bqkg-1 respectively while that of4°K in soil, mine tailings and rock samples ranged from 53.6 Bqkg-1 to 211.8 Bqkg-1 , 5.7 Bqkg-1 to 217.3 Bqkg-1 and 2.1 Bqkg-1 to 120.1 Bqkg-1 respectively. The Specific activity values of 232Th in soil sample from each of the four gold mines were above the worldwide average value of 30 Bqkg-1 . It is only Greenstone mine tailings and Okame rocks that had higher activity for 232Th than the world wide average value. The Absorbed Dose rates in soil, rock and mine tailings samples ranged from 41.7 nGyh-1 to 76.3 nGyh-1 , 13.3 nGyh-1 to 32.7 nGyh-1 and 2.3 nGyh-1 to 58.0 nGyh-1 respectively. Only Okame had a higher value for soil than the world wide average value of 60 nGyh-1 • The Annual Effective Dose rates in soil, mine tailings and rock samples ranged from 0.051 mSvy-1 to 0.093 mSvy-1 , 0.024 mSvf1 to 0.050 mSvf1 and 0.011 mSvy-1 to 0.047 mSvf1 respectively which were lower than the ICRP recommended value of 20 mSvf1 • The internal hazard indices in soil, mine tailings and rock samples ranged from 0.30 to 0.56, 0.15 to 0.27 and 0.02 to 0.43 respectively. External hazard indices of the radionuclides in the soil, mine tailings and rock samples ranged from 0.27 to 0.47, 0.10 to 0.23 and 0.01 to 0.36 respectively. They were found to be below unity as per ICRP, 2007 maximum permissible limit. The Excess Lifetime Cancer Risk (ELCR) ranged from 6.90x10-5 to 1.93x104 was lower than the ICRP maximum permissible excess lifetime cancer risk limit of 5.60x10-2 . Despite the low radiological health risk, miners need protective gears particularly at Okame and Greenstone mines and further research need to be done to validate these findings.
Determination of radiological hazard levels of gammma rays from radionuclides in water from selected boreholes in Moroto district, Uganda
(Kyambogo University, 2021-03) Okello, Sam
This study was designed to identify gamma ray emitting radionuclides using the GDM 20 NaI(Tl) detector and to determine and compare the activity concentrations, absorbed dose rates, annual effective dose equivalent and the internal and external radiological hazard levels of gamma rays from radionuclides in water from boreholes in four sub counties of Rupa, Katikekile, Nadunget and Northern Division of Moroto District. The radionuclides of 226Ra and 232Th were found in water samples from all the boreholes of the four sub counties. The radionuclide of 40K was only found in two boreholes, three boreholes and five boreholes of Rupa, Katikekile and Nadunget respectively. None was found in the boreholes from Northern Division. The activity concentration of 226Ra exceeded the world average value of 35 Bql-1 in three boreholes of Rupa and Northern Division; in four boreholes of Katikekile and in all the seven boreholes of Nadunget. The activity concentration of 232Th was found to be less than the world average of 30 Bql-1 in all the water samples from all the regions. The activity concentration of 40K was found to exceed the world average of 400 Bql-1 in all the water samples from all the regions. The absorbed dose rates was found to be greater than the world average of 84 nGyh-1 for water samples from two boreholes of Rupa and Northern Division; in five boreholes of Katikekile and in six boreholes of Nadunget. The annual effective dose equivalent was found to be lower than the world internal exposure limit of 0.41 mSvy-1 in all the water samples analyzed. The internal radiological hazard level was found to exceed the permissible value of 1.00 (unity) only in one borehole and three boreholes in Katikekile and Nadunget respectively. The external radiological hazard level was found to exceeded the permissible limit in one borehole from Nadunget; and equal to 1.00 the permissible limit in one borehole from Katikekile. However activity concentration of 226Ra and 40K exceeded the world average value in seventeen boreholes and ten boreholes respectively. While 232Th activity concentrations in all boreholes were below the world average value. It is recommended that a similar study should be carried out to check the results of this study and to find the excess life time cancer risk on the populace that use the water especially those that show high activity and hazard levels. The scope of the study for later studies should be extended to more boreholes.
Determination of the characteristics of solid fuel developed from a mixture of thermoplastic wastes and clay materials
(Kyambogo University(Unpublished work), 2021-03) Oballim, Terence
This study was driven by the fact that plenty of plastics which have potentials to be used as source of fuel are left as wastes in the environment without proper utilization. The study was directed toward the use of a particular type of plastics for making a plastic based solid fuel and to find its viability for use as source of energy. Polyethylene – terephthalate (PET) material obtained from waste mineral water bottles and ball clay were mixed to form PET – Clay Solid Fuel (PETCSF) product. Clay was mixed with plastics to avoid melt flowing or dropping of the fuel in the stove during combustion. The parameters of the developed PETCSF those were determined to find its viability as source of energy were Mass of melt drops, mass combustion rate, mass of ash and the calorific value. The following Clay Plastic Ratio (CPR) 1:2.43, 1:2.33 and 1:1.20 were found to be sufficient in stopping melt dropping behavior of the developed solid fuel in the stove during combustion. The calorific values of the PETCSF were found to be 14,335 J g-1, 14,170 J g-1 and 11,182 J g-1 for CPR = 1:2.43, 1:2.33 & 1:1.20 respectively. Calorific values of an equal mass of charcoal, paper and Benzoic acid tablet (used as reference solid fuel materials) were 7,316 J g-1, 12,475 J g-1 and 24,239 J g-1 respectively. The mass combustion rates for CPR = 1:2.43, 1:2.33 & 1:1.20 were found to be 2.45 g minute-1, 2.43 g minute-1 and 1.98 g minute-1 respectively. The mass of ash left after combustion for the above respective CPR values were 36.64 g, 37.37 g and 50.73 g respectively. When compared, the calorific value of the developed PETCSF was found to be about two times higher than for charcoal of an equal mass. Benzoic acid tablet had the highest calorific value. Thus, PETCSF is a viable source of fuel compared to charcoal in terms of the calorific value and moreover its combustion rate can be controlled by using a specific CPR of 1:2.43 as shown by the result of the study. The population should be encouraged by the findings in this study and to begin thinking of using plastic based solid fuel as an alternative to charcoal and firewood which currently are the only predominant sources of fuel for majority of the population. The used plastic based solid fuel in an oxygen rich environment (or sufficient air circulation) is strongly recommended as complete combustion is guaranteed. Insufficient air supply may lead to incomplete combustion of the fuel and possibly release of particles (soot/smoke) which if inhaled may be harmful to the user.
Determination of thermal diffusivity of fired clay bricks produced from cow pie mixed with selected Ugandan clays
(Kyambogo University [unpublished work], 2023-05) Kansiime, Evalyne Mary
This study was designed to determine the thermal diffusivity of fired clay samples produced by mixing cow pie with clays from selected districts in Uganda. The focus of the study was to find out the effect of clay particle sizes and the ratio of kaolin clay, ball clay and cow pie on thermal diffusivity. The clay particle sizes considered were 0-74, 75-89, 90-149, 150-299 and 300-349 μm, the cow pie particle sizes considered were 75-149 and 150-299 μm and the clay-cow pie ratios considered were 9:7:4, 9:6:5 and 9:7:0. The samples used in the study were compacted by using a compression machine International, England at a pressure of 50 MPa and were fired in a heating chamber (CARBOLITE, GERO, HTF 1700) up to a temperature of 950 0C at different firing rates of 1.2 0C/s, 1.3 0C/s, 1.5 0C/s and 0.5 0C/s. Thermal conductivity was measured by using a QTM-machine, density was obtained from mass per unit volume and specific heat capacity was obtained by using a simple calorimeter and applying the method of mixtures. The average values obtained for the thermal properties in the order of increasing particle sizes were as follows; for the kaolin: ball clay: cow pie ratio 9:7:4, thermal conductivity values were 0.2254, 0.2210, 0.2214, 0.2204 and 0.2195 Wm-1K-1, density values were 1.1800, 1.1535, 1.1537, 1.1433 and 1.1490 gcm-3, specific heat capacity values were 1.0670, 1.0510, 0.9810, 1.0490 and 1.0100 Jg-10C-1, the average calculated thermal diffusivity values were 0.1924 e -6, 0.2021 e-6, 0.1883 e-6, 0.2441 e-6, and 0.2039 e-6 m2s-1, for the kaolin: ball clay: cow pie ratio 9:6:5 thermal conductivity values were 0.2237, 0.2221, 0.2188, 0.2200 and 0.2178 Wm-1K-1, density values were 1.1866, 1.1661, 1.1945, 1.1789 and 1.2002 gcm-3, specific heat capacity values were 1.0490, 1.0810, 1.0630, 1.0450 and 1.0020 Jg-10C-1, the average calculated thermal diffusivity values were 0.1919 e-6, 0.2005e-6, 0.2046 e-6, 0.2080e-6, and 0.2031 e-6 m2s-1 and for the kaolin: ball clay: cow pie ratio 9:7:0, thermal conductivity values were 0.2871, 0.2781, 0.2771, 0.2654 and 0.2654 Wm-1K-1, density values were 1.1685, 1.1578, 1.1379, 1.1450 and 1.1280 gcm-3, specific heat capacity values were 1.0690, 1.0490, 1.0460, 1.0200 and 1.0510 Jg-10C-1, the average calculated thermal diffusivity values were 0.2546 e-6, 0.2439 e-6, 0.2427 e-6, 0.2466 e-6, and 0.2254 e-6 m2s-1. From the results, thermal diffusivity increased with the decrease in particle sizes of kaolin and ball clay; however, it was lower for the ratio 9:6:5. Thermal diffusivity values for the control experiment were very high and this implies that cow dung was a good pore former and should be incorporated into clay bricks to improve on their thermal insulation.
Effects of microstructure on mechanical strength of selected clays from Uganda
(Makerere University (unpublished work), 2004-04) Obwoya, Kinyera Sam
This thesis presents results of a study of the dependence of modulus of rupture (MOR), Young's modulus, {.E), and flexural rigidity,{ DJ, of sintered clay specimens on microstructure, average particle size and production variables. The production variables considered were sintering time, sintering temperature, and compaction pressure. The study shows that the MOR, Young's modulus and flexural rigidity of the clay product increase as compaction pressure, sintering temperature and sintering time are increased, but decrease as the particle size increases for all the processing conditions. The microstructure of clay specimens of higher strength are such that, the pores are well rounded and fewer in number. The grain boundaries are also thin and well defined with glassy phase being dominant as compared to liquid and pore phases. Higher strength of the clay specimens is also associated with formation of mullite which forms needle-shaped crystals with an interlocking network that gives high stability at elevated temperatures. The variation between MOR and sintering time, t, can be described by a relation of the form MOR = ot2 + /3t + 9 where a, /3 and 9 are constants with some of their mean values for samples compacted at 49.584MPa and sintered at 12oooc are: a = -0 .37±0.16MPas2, /3 =4.93x0.87MPas·1 and 9 = 21.05±7.26MPa
Enhancing infrared solar absorption efficiency through plasmonic solar absorber using machine learning-assisted design
(Springer Link- Plasmonics, 2024-10-18) Muheki, Jonas; Patel, Shobhit K.; Ainembabazi, Fortunate; Al-Zahrani, Fahad Ahmed
This research introduces the architecture of an infrared solar energy absorber coupled with absorption prognosis employing machine learning techniques. Our approach involves creating an efficient absorber tailored for infrared wavelengths complemented by a machine learning model for accurately predicting absorption levels. The absorber's design focuses on maximizing absorption within the 0.7 µm to 4.0 µm range. We optimized the absorber's parameters, including resonator thickness, substrate thickness, and angle of incidence. Simulation results demonstrate excellent absorption performance, capturing over 90% of light within the specified range. At angles between 0° and 40°, the average absorptance exceeds 80%, peaking at 97.16%. However, at an 80° angle of incidence, absorptance drops to 23.3%. The study employs a 1D-CNN regression model to estimate absorption at various wavelengths, which greatly decreases the time required for simulations and experiments. The findings demonstrate the promise of combining metamaterial structures with machine learning approaches to boost the efficiency of solar energy harvesting and conversion processes.
Gamma radiation exposure levels due to radionuclides in soils from selected gold mines in Karamoja
(Kyambogo University(unpublished work), 2016-01) Chelangat, Kadafi
The aim of this study was to determine radiation exposure levels due to gamma ray emitting radionuclides in soils from selected gold mines in Karamoja and the associated hazard indices. The people of Karamoja use poor methods of mining gold, therefore they are exposed to ionizing radiation of unknown concentrations. In this study, 60 samples from Rupa, Nakabaat, Morulem, Acerer, Nabulatuk and Morita were analysed using a Nal (TI) gamma-ray detector. The activity concentrations of natural radionuclides 226 Ra, 232 Th, 238 U and 4° K in soils were measured by gamma spectroscopy using sodium iodide detector. In addition, radiological assessment due to these radionuclides was also carried out. To ensure quality control, the samples collected from the sites were transferred to polythene bags, labeled and double-bagged. They were transported in boxes whose background radiation emissions were measured with an identifier. The average activity concentrations of 226 Ra, 232 Th, 238 U and 4° K were 49.26 ± 1.58, 44.29 ± 0.74, 16.57 ± 0.40 and 599.64 ± 7.33 Bqkg-1 respectively. The mean absorbed dose rate was 50.44 ± 1.48 nGhr-1 which is below the world average dose rate of 60 nGhr-1 • Radium equivalent values for the area studied ranged from 83 .83 ± 2.33 to 186.12 ± 3.52 Bqkg-1 with mean of 117.22 ± 2.30 Bqkg-1 which is below the world average of 370 Bqkg-1 • The mean external and internal hazard indices were both below unity. Therefore, though the results in the study indicated higher levels of natural radionuclides in soils of Karamoja region than the world average values, the mining activities pose no significant radiological hazard to the population and the soils from these areas can be safely used for construction purposes. The observed unprofessional practices such as lack of use of gas masks while working in the dust-filled mine caves could expose workers to possible risks from inhalation of respirable crystalline silica and radon gas; therefore miners must be educated and sensitized on the effects of exposure to radiation by the Atomic Energy Council of Uganda. These can be done by introducing Safety and Health awareness days. People of Nabulatuk and Acerer in Nakapiripirit district where concentrations of radionuclides are twice the world average levels must be advised to reduce on the time they spend in mines.
Gamma ray activity levels and radiological hazard indices of Radionuclides in mine tailings from selected mines in Southwestern Uganda.
(Kyambogo University [unpublished work], 2016-01) Turyahabwa, Evarist Rutahweire Silver
This study was designed to determine and compare the specific activity levels and the radiological hazard indices of gamma ray emitting radionuclides in mine tailings from three selected mines in Southwestern Uganda. This was achieved by analyzing 72 soil and rock mine tailing samples using the GDM 20 Nal(TI) detector. The specific activities of the principal primordial radionucides of 238U, 232Th and 4°K in the samples were measured. The values obtained were used to determine the absorbed dose rates, the annual effective dose rates, the radium equivalent activity, external and internal hazard index and the excess lifetime cancer risk. The mean specific activities of 238U, 232Th and 4°K in mine tailings at 90% confidence level ranged from 23±14 Bqkg-1 to 59±16 Bqkg-1 for 238U, 49±39 Bqkg-1 to 244±19 Bqkg-1 for 232Th, and 226±232 Bqkg-1 to 893±167 Bqkg-1 for 4°K. The mean outdoor and indoor absorbed dose rates in air for Mashonga, Kikagati and B utare were (181±36 nGyh-1 and 338±67 nGyh-1 ), (167±23 nGyh-1 and 310±47 nGyh-1 ) and (192±16 nGyh-1 and 355±32 nGyh-1 ) respectively for waste soil samples and (67±50 nGyh-1and 127±102 nGyh-1 ), (85±37 nGyh-1 and 159±80 nGyh-1 ) and (115±33 nGyh-1 and 215±66 nGyh-1 ) respectively for waste rock samples. The ratio of the mean indoor to outdoor absorbed dose rates in all the samples was 1.9 but this was 36% higher than the world average. The total annual effective dose rates, radium equivalent activities, external and internal hazard indices for waste soil samples were above the maximum permissible limits recommended for members of the public. Potential radiological hazards on miners and the people living in the neighborhood of the sites due to external irradiation are significant. There is need to improve waste management practices in the mining sites in order to prevent health hazards associated with the radionuclides in the mine tailings.
Influence of device architectures and mobility on response/recovery time of metal halide perovskites: A review
(Journal of Materials Science, 2022-01) Emma, Panzi Mukhokosi; Maliki, Maaza
Organic–Inorganic perovskite materials have attracted great interest in the research community for photo-detector and solar energy applications. For various photo-detector applications, the response time is a very important parameter. In telecommunication, a high response speed is required and for this special class of materials, a fast response time in the order of ns has been realized by some authors. The main challenge is their stability. It is established that the response time is primarily controlled by the electron/hole mobility, electrode spacing and the depletion width. In this review, we discuss the recent developments of photo-detector devices composed of mixed halide perovskites and their performance with the main emphasis on the role played by mobility and internally generated electric field to the response/recovery speed. We discuss how the response speed clear relates to charge carrier mobility and depletion width. We further suggest ways on how to improve the response speed to match those of the conventional commercial photo-detectors like Si and InGaAs. We hope this article will find a suitable audience who will utilize this knowledge in the design and construction of ultra-fast photo-detectors.
Infra-red reflectance and transmittance by thin film coatings of some selected metals on glass substrate
(Kyambogo University(unpublished), 2018-11-14) Kamwasir Hellene
Reflection and transmission of light serve as key parameters in thin films coatings meant for temperature regulation in warm climates. In this study, the infrared reflectance and transmittance for three different thicknesses of thin films of palladium and platinum were determined. The thin films were made by thermally evaporating various masses of the platinum and palladium on glass substrates. A Shimadzu UV-VIS-NIR Spectrophotometer was used to determine the reflectance and transmittance of the samples from which the spectra were determined. Ex situ measurements, using Point wise Unconstrained Minimization Approach (PUMA) were made to determine the exact thicknesses of the films. Reflectance was found to vary with film thickness. The results showed that the 60 nm film of palladium had a maximum reflectance of 33%, 140 nm film, a maximum reflectance of 39% and 230 nm film, a maximum reflectance of 72%. For platinum, the 140 nm film had a maximum reflectance of 28%, 146 nm film a maximum of 35% and 395 nm film a maximum reflectance of 42%. In all the cases, the reflectance in the infrared part of the spectra (800-2500 nm) was higher than in the visible region which suggests that palladium and platinum thin films may be used as heat mirrors. The transmittances of palladium and platinum thin films were high (over 80%) an indication that the thin films probably had voids. The study also showed that for the same thickness of palladium and platinum films (Palladium film of 140 nm and platinum film of 140 nm), palladium has greater reflectance than platinum showing dependence of reflectance of thin film on material used for its fabrication.
Intensity of secondary scattered x-rays during x-ray diagnostic procedures in selected diagnostic centres in Uganda
(Kyambogo University[unpublished work], 2014-01) Byaruhanga, Bonaventure
The purpose of the study was to investigate the intensity of secondary scattered X-rays when different body regions; the chest, the abdomen and the lower limbs were exposed to X-rays during radiography. The study used experimental design where the secondary scattered X-ray dose from three diagnostic centres in South Western Uganda were measured us.ing TLDs that were worn at the back of the radiographer. The cards were then read monthly and the process repeated for a period of six months. The number of patients exposed to X-rays for each procedure for the same period was also noted. From the study, it was found that the limb exposures constituted the highest proportion of the patients X-rayed (42%), followed by the chest· (35%) and finally the abdomen (23%). In addition, it was found that the chest exposures generally lead to the highest intensity of secondary scattered X-rays to the radiographers which was 2,670 mSv, 2,756 mSv and 2,505 mSv for Mutolere Hospital, Goodwill Imaging Centre and Mbarara Diagnostic Centre respectively. The limbs contributed the second highest intensity of secondary scattered X-rays (2,442 mSv) at Mutolere Hospital, though generally the abdomen contributed the second highest secondary scattered X-rays (1,712 and 1,294 mSv for Goodwill and Mbarara Diagnostic Centre respectively). The limbs contributed the lowest intensity of secondary scattered X-rays in Goodwill and Mbarara Diagnostic Centre i.e 1,578 and 1,236 mSv respectively. In relation to the safety standards set by the International Atomic Energy Agency ( IAEA, 2002), the predicted cumulative annual dose to radiographers from Mutolere Hospital, Goodwill Imaging Centre and Mbarara Diagnostic Centre are 13,704, 11,964 and 10,692 mSv respectively. These values are below the annual dose limit of 20 mSv for radiation worker as recommended by IAEA (IAEA, 2002). This means that the radiographers from the three diagnostic centres are at a low risk of developing stochastic health effects. However, the annual dose from the diagnostic centres could be dangerous if radiographers are exposed over many years in a lifetime.
Investigation of mechanical properties of ceramic tiles developed from selected clay deposits in Uganda
(Kyambogo University [unpublished work], 2023-10) Mukwaya, George William
In this study the characteristics of Buwambo kaolin, Lunya feldspar, Ntawo ball clay and Liddo beach sand were determined. The Modulus of Rapture (MOR) and Compressive Strength (CS) of the tiles produced using kaolin:feldspar of different composition ratios were determined. The composition ratios of kaolin:feldspar used were 4:3, 3:4, 5:9 and 2:5 by mass. On the other hand, a fixed composition ratio was used for ball clay:sand of 5:1 by mass (Ochen et.al 2012). The samples were fired at 1100 0C for 8 hours. Using the scanning electron microscope (SEM), the Buwambo kaolin had a porous cellular structure of irregular-shaped particles of average size of 0.202 ± 0.131 μm. Liddo beach sand had porous particles with average particle size of 0.168 ± 0.198 μm, the Lunya feldspar had irregular confined particles with average particle size of 0.153 ± 0.105 μm and the Ntawo ball clay had fine grained uniform rounded particles of average size of 0.095 ± 0.055 μm. X-ray fluorescence (XRF) and Energy dispersive x-ray (EDX) spectroscopy were used to determine the elemental composition. The XRF on Liddo beach sand showed that it is mainly composed of 99.5 % SiO2 with trace amounts of Al2O3 and Fe2O3 each 0.2 %. The EDX revealed that Buwambo kaolin mainly had 11.15 % Aluminium and 10.83 % Silicon. The Lunya feldspar mainly had 19.53 % Silicon and 5.46 % Sodium. The Ntawo ball clay mainly had 12.91 % silicon and 4.52 % aluminium. X-ray diffraction (XRD) on Liddo beach sand showed a broad reflection peak at 2θ = 22.86 o indicating its amorphous nature. The Lunya feldspar showed major peaks at 20.69, 26.40 and 29.52 o which are within the acceptable range of sodium feldspar. The Ntawo ball clay showed major peaks at 2θ = 20.82, 26.53 and 27.35 o. For Buwambo kaolin, the major peaks were located at 2θ = 12.29 and 27.40 o. The MOR and CS were significantly dependent on composition ratios at significant levels α = 0.01 and α = 0.05 and therefore the null hypotheses that the CS and MOR of the tiles produced are not affected by the composition ratios of the clay mixture rejected at the two levels of significance. The sample with the highest kaolin-feldspar ratio of 4:3 had the highest MOR of 30.84 ± 2.67 MPa at α = 0.01 and 30.84 ± 1.60 MPa at α = 0.05. It also had the highest CS of 1.36 ± 0.06 MPa at α = 0.01 and 1.36 ± 0.04 MPa at α = 0.05. Similarly, the sample with the lowest kaolin-feldspar ratio of 2:5 had the least MOR of 18.58 ± 0.51 MPa at α = 0.01 and 18.58 ± 0.31 MPa at α = 0.05. It also had the least CS of 0.82 ± 0.03 MPa at α = 0.01 and 0.82 ± 0.02 at α = 0.05. Further investigation should be carried out using other clay deposits to find out how the variation in the amount of kaolin and feldspar in them would affect the CS and MOR of tile samples developed using these clays.
Investigation of the compressive strength of ntawo ball clay fired to different temperatures at different rates of temperature rise
(Kyambogo University (un published work), 2017-12) Byekwaso, Ronald
This study was to investigate the compressive strength of fired Ntawo Ball Clay found in Mukono District in Central Uganda. The clay sample was first analyzed using X-ray Diffraction Spectrometer Model RIX3000 to determine the relative abundance of the chemical components and then compressive strengths were determined. Ball clay of particle size 45.0 μm was used to produce 150 rectangular clay slabs fired in an electric furnace, model P59 l 0. They were then subjected to compressive strength test by first determining the breaking force for each sample using a compressive test machine, compact 500Sn-12994917 on samples fired at different rates of temperature rise, ranging between 2°C min- 1 and 6°C min-1 in intervals of 1°C min-1 for set firing temperatures. The compressive strength tests were then carried out on another set of samples fired at set rates of temperature rise to different firing temperatures ranging between 500°C and I 000°C in intervals of I 00°C. The compressive strength of fired tawo ball clay was found to decrease with increase in rates of temperature rise between 2°Cmin-1 and 6°Cmin-1 for the six firing temperatures. For temperatures of 500°C to I 000°C in intervals of I 00°C, the percentage decrease in compressive strength ' ere 11 %, 3%. 3%. 8%, 2.9%, and 11 % respectively. At a level of significance a = 0.05 and a = 0.0 I, it was established that compressive strength was related to the rate of temperature rise. The study further revealed that compressive strength increased with increase in firing temperature. The percentage increase was 279%, 273%, 247%, 257% and 279% for the rates of temperature rise between 2°Cmin-1 and 6°Cmin-1 respectively, overall average percentage increase being 267%. At a level of significance a= 0.05 and a = 0.0 I, compressive strength depended on firing temperature ntawo clay was found to be composed of mainly silica (67.20%), alumina ( 18.20%), ferrous oxides (2 .83%) and other fluxing oxides such as CaO (0.31 %). K20 (0.98%), and a20 (0. 19%), among other compounds. The compressive strength of fired samples decreased with increase in rates of temperature rise during firing between 500°C and I 000°C. Other investigations should be made to find out the effect of firing beyond I 000°C and firing at a rate above 6°C min1 on the compressive strength, and the effect of changing the mineralogical composition of clay on the compressive strength.

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