PHD-Department of Physics
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Item Synthesis, Fabrication and Characterization of Solid Titanium Dioxide - Based Solar Cell Doped with Different Organic and Inorganic Luminescent Materials(Kenyatta University, 2024-01) Njoroge, David KimemiaEnergy is globally recognized as an important resource for social and economic development. Majority of the world population relies on fossil fuels, hydro and solar radiation as a source of energy. Fossil fuels immensely contribute to air pollution and global warming. Solar cells have been exploited and controlled to generate electrical energy from solar radiation. The available solar radiation is not constant at all times of the day and differs depending on the season of the year. Consequently, the solar cell output varies with the incident radiation. The study investigated use of photo luminescent materials as dopants in the photoactive layer of TiO2 –based solar cells with an aim to prolong the cell output in diminished radiation. Inorganic (Sb/Ca/Mn/Ag:) and organic (rhiodamine, allicin, gingerol, quinolone and neohesperidosyl: extracted from their fresh organic complexes) photo luminescent materials were used as dopants in TiO2 photoactive layer of the solar cell while a mixture of graphite, iodine and potassium iodate was used as the receptive layer. The effect of varying mass ratios and the thicknesses of both photo active and the receptive layers was investigated based on the solar cell output parameters. The synthesized inorganic (Sb/Ca/Mn/Ag) and the extracted organic luminescent materials were chemically characterized using the FTIR. Different masses of the photoactive TiO2 material, inorganic and organic luminescent materials were weighed separately and compressed to form the photoactive layer. Known masses of graphite powder mixed with a matrix of potassium iodate (KI3) were introduced into the molding dice over the photoactive layer and compressed to bind them sufficiently. Potential and short circuit generated by the cells were monitored and the data obtained used to determine their fill factor, and efficiency. The study concluded that the inorganic (Sb/Ca/Mn/Ag) and organic rhiodamine, flourene, allicin, gingerol, quinoline and neohesperidosyl particles absorbed radiation at different wavelengths. The absorption bands were evident at {(360 – 3750), (434.96-3950), (697.28-3750), (290.29-3850), (463.89-3850), (260.39-3750) and (273.90-3700)} cm-1 respectively. All the investigated photo luminescent materials showed promising properties for improving solar cell output in diminished solar radiation. The results obtained also showed different potential delay by the varied thicknesses with improved responsivity and efficiency. The fabricated solar cell employing rhiodamine doped -TiO2 photoactive layer (0.136) mm and 0.164 mm receptive thickness layer had the highest open circuit voltage (VOC =1.023V), and a residual potential of 0.586 V in diminished radiation after one hour. The corresponding fill factor and efficiency were determined as 0.416 and 2.32%, respectively. The study also concluded that optimized FSCs layers generated enhanced open circuit and residual potentials (VOC) observed after 60 minutes. The study recommends that dopant synthesis should be expanded to enhance further d-orbitals splitting for improved charged species d→d transitions and transpose IR spectrum into fluorescence, dopants molecular size with less energy instability should be extended to achieve uniform potential difference with less attenuation, wider dopants complexes ratios should be done to minimize recombination at the convergence within the solute and enhance quantum yield for higher charge carriers’ densities excitation, modified ratios relative dimensions should be investigated together with ambient conditions moderating pigments to balance FSCs interacting systems for uniform output parameters.Item Integrated Approach to Teaching and Learning English Language in Junior High Schools, Volta Region, Ghana(Kenyatta University, 2022-06) Adansi, Joana Emefa; Adelheid Marrie Bwire; Florence Abuyeka MiimaThe purpose of this study was to explore an Integrated Approach to teaching and learning English Language in Junior High Schools, Volta Region, Ghana. The underlying factor informing this study was the poor performance in students’ academics in English language. The integrated approach is crucial in teaching the English language and helps learners improve their language skills. The study was guided by four objectives which were: to establish the nature of integrated methods used by teachers of English in teaching English language in junior high schools in Hohoe Municipality, investigate the extent to which the integrated approach is used by teachers of English, establish the perceptions of teachers and students towards the integrated English and explore the challenges teachers face in using the integrated approach in teaching English language. The study was based on the guidelines of Basil Bernstein’s theory and supported by Theodore Frick’s Integrated Education Theory. The study employed descriptive and explanatory research designs. The target population for the study was 1382 (10 circuit supervisors, 52 heads of department, 93 teachers of English & 1227 form 3 students) in 55 Junior High Schools. The study used questionnaires, observation, and interview guide to collect data from teachers and students in the Junior High Schools in Hohoe Municipality. Stratified and simple random sampling techniques were used to sample size 422 teachers and students for the study. The study indicated that integrated approach to teaching English Language had a positive influence on learners' achievements and teachers were positive in teaching English Language. The study therefore proposed a model with the aim of making the integrated approach more appealing to students. This means to have an integrated approach in the teaching process, material availability and competence of teachers are two formidable pillars that must be emphasized. The study recommended that teachers needed to integrate language and literature into the teaching of English Language.Item Hydroxyapatite Nano-Fertilizers Effects on Adsorption and Uptake of Cadmium and Lead, Nutrient Release and Growth Performance of Selected Crops(Kenyatta University, 2023-09) Nyaenya, Ngorwe Evans; Hudson Nyambaka; Mildred P. Nawiri; Jane MurungiABSTRACT More than 9.1 million people globally are affected by famine. Spinach, kales and beans are among vegetables promoted for consumption as an intervention strategy. Until the development of nanofertilizers such as synthetic hydroxyapatite (Syn nHA), boosting vegetable production has been by employing commercial and organic fertilizers. Other than being micro-sized, nanofertilizers have reduced uptake of harmful heavy metals like Pb, Cd, and improved growth performance (height, dry weight, leaf diameter and number of leaves) of crops due to their numerous adsorption sites. Further advantages include, being stable, non-toxic and having enhanced surface area to volume ratio. Use of over 130 billion tones of bone being dumped per year to prepare nanofertilizers is likely to reduce its environmental menace. This study envisaged using bones to synthesize nanofertilizers (bone nHA) and. investigated the effect of bone nHA and Syn nHA nano-fertilizers on Cd and Pb uptake and adsorption, growth performance, and nutrient release in beans, spinach and kale leaves grown for a 90 day period. Both bone-nHA and Syn nHA were encapsulated with commercial DAP and NPK fertilizers. The techniques SEM, XRD, and FTIR were employed to characterize the nanofertilizers, while AAS was used to determine levels of Cd and Pb, and UV measured NO3- and PO43-levels. The bone nHA was less coagulated with significantly smaller diameter compared to Syn nHA (P˂0.05). Further, bone-nHA significantly reduced Cd (range 58 – 89 %) and Pb (range 62 - 91 %) uptake and had higher adsorption of the metals (P˂0.05). Growth performance parameters for the crops grown with bone-nHA improved by over 56 %, being better than those grown with the Syn nHA and it is encapsulated nanofertilizers (P˂0.01). Results support presence of higher number of adsorption sites in the bone-nHA implying a better performance as a nanofertilizer. At 40 days bone nHA had significantly higher nitrate release rate of 28 % in comparison with syn nHA (P˂0.01). Adsorption equilibrium data fitted well with Langmuir for Cd while Pb fitted well with Freundlich isotherm. Bone nHA nanofertilizers are recommended to reducing Cd and Pb uptake and adsorption, improving growth performance and nutrient release on growing beans (P. Vulgaris L.), spinach (Spinacia oleracea) and kales (Brassica oleracea acephala).Item Risk Assessment Due to Naturally Occurring Radioactive Materials in Kilimambogo, Kenya(Kenyatta University, 2023-12) Nyambura, Catherine; Nadir Hashim; Margaret Chege; Shinji TokanamiABSTRACT Man is continually exposed to ionizing radiation whose main origin is either natural or artificial. The primordial radionuclides found in building materials are important sources of radon and thoron in the indoor air. The main objective of this research was to assess exposure due to radioactive elements in indoor air, crops and building materials (soil and rocks), and determine the level of the risks. The concentration levels of radon, thoron, and thoron progeny were measured in mud-walled, iron sheet walled, and stone walled modern houses in Kilimambogo region, Kenya. Radon and thoron concentration levels were determined using passive radon–thoron discriminative monitors (RADUET), while thoron progeny levels were measured using thoron progeny monitors. The activity concentration of 226Ra, 232Th and 40K present in the different environmental samples like rocks, soil, and cassava crop were determined using a Thallium- activated sodium-iodide scintillation (NaI (TI)) detector Model TS-2L. Elemental concentration in water samples was determined using an atomic absorption spectrophotometer (AAS). The mean external dose received indoors by the residents due to radionuclides present in rock and soil samples was measured to be 0.91 ± 0.26 mSv y-1 and 0.86 ± 0.19 mSv y-1 respectively. This is comparable to the total exposure dose limit of 1 mSv y-1 recommended by ICRP for members of the general public. This means that, soil and rocks in the region does not pose any radiological risk to the residents of Kilimambogo region. Consequently, they can be used for agriculture and construction of dwellings. The doses received due to intake of cassava tubers and leaves was 1.82 ± 0.60 mSv y-1 and 0.81± 0.30 mSv y-1 respectively, totaling to 2.63 ± 0.70 mSv y-1. The ingestion dose contributes to 42.1% of the total dose received by the resident from measured sources. Residents should therefore reduce the intake of cassava. The annual effective dose received by the residents of Kilimambogo and Gatuanyaga regions due to inhalation of radon and thoron was determined for the three types of dwellings, from their respective progenies and found to be 1.3 ± 0.2 mSv y-1, 1.1 ± 0.1 mSv y-1 and 1.4 ± 0.2 mSv y-1 for radon progeny and 2.4 ± 0.4 mSv y-1, 0.5 ± 0.1 mSv y-1 and 1.5 ± 0.2 mSv y-1 for thoron progeny in mud-walled, iron sheet-walled and stone-walled houses respectively. It was observed that, residents living in iron sheet - walled houses with cemented floors received the lowest doses from inhalation of the radon isotopes hence such houses are safer than other types of dwellings. Residents living in mud houses and uncemented houses should consider improving the ventilation of their houses to reduce radiation exposure. The lifetime cancer risks for the residents due to intake of metal carcinogens, Cd, Ni and Pb in borehole and surface water was also estimated. The cumulative cancer risk in the borehole samples was 0.12 ± 0.06 and 0.19 ± 0.09 in the dry and wet seasons respectively. Those from surface water sources were 0.10 ± 0.07 and 0.21 ± 0.06 in the dry and wet seasons respectively. In both seasons, the cancer risks were much greater than the acceptable risks of 10-6 to 10-4 by a factor of 1000 and above. This indicates that about 10% of the residents are likely to die of cancer related ailments. RESRAD computer simulation code was used to estimate the doses received by the resident farmer and the quarry worker scenarios at time, t = 0 years. The doses received by the resident farmer and quarry worker scenarios were 0.22 mSv y-1 and 0.16 mSv y-1 respectively only for the external radiation pathway. This risk is low and does not pose any significant health risk to the residents. The data measured in this research will be used by future researchers as baseline study.Item Development of a Photothermal Induced Optical Scattering Modulation Technique and Its Application in Malaria Diagnosis(Kenyatta University, 2023-08) Memeu, Daniel Maitethia; Abdallah M. Sarrone; Ciira wa MainaMalaria is one of the leading causes of mortality and mobility in Africa and the disease is endemic in many regions of the continent. Though curable, early diagnosis which is key to effective treatment is usually a challenge owing to lack of accurate, rapid and affordable diagnostic techniques in resource scarce settings. Therefore, there exists a need for development of an accurate, rapid, easy to operate and affordable technique for diagnosis of malaria. This work describes a novel optical based sensing and imaging technique termed as Photo-Thermal Induced Optical Scattering Modulation (PTIOSM) and its application in malaria diagnosis. The technique entails sample irradiation with two optical beams of different wavelength. One optical beam, referred to as pump beam is employed for exciting the sample chromophores to higher energy levels. What follows is chromophore transition from the excited states to lower states and subsequent photothermal processes such as photoacoustics and thermal lens effect. These processes are monitored using a second optical beam referred as probe beam. We hypothesized that application of the pump beam alters the sample optical properties and these changes can be monitored by tracking intensity modulation of the probe beam induced by the sample upon optical excitation and relaxation. The extent of the probe beam intensity modulation (referred to as PTIOSM signal) would be indicative of the molecular species present in the sample. We applied the technique for label-free detection of the presence of hemozoin (an endogenous malaria biomarker) in blood samples.Four PTIOSM setups; two for sensing and the other two for imaging were developed. The PTIOSM sensing setup employed a photodiode as the optical detector while the PTIOSM imaging setup used an image sensor for spatial-temporal PTIOSM signal from the sample. Malaria infected and non-infected blood samples as well as whole blood mixed with synthetic hemozoin at different concentrations were interrogated using the PTIOSM setups. The synthetic hemozoin was mixed with whole blood in varying concentrations to simulate different Plasmodium parasite load (parasitemia) in blood. The acquired signals were transformed using principal of component analysis before features extracted and used for training and classification of different sample classes using machine learning models.The technique attained an overall malaria detection accuracy of 70.6% with a sensitivity of 68.4% and specificity of 72.9%. In addition, an accuracy of 100% was attained in the classification of synthetic hemozoin concentrations in whole blood samples. A total of 4200 feature vectors were used to train and test the classifiers. The training and testing set data was split in 80% to 20% respectively. Support vector machine attained the best classification accuracy. The technique was also able to yield images of sufficiently good quality to facilitate visual identification of Plasmodium parasites in unstained blood smear samples from malaria infected human subjects. The recorded performance points to the potential of PTIOSM technique potential for adoption as an optical biosensor for rapid screen of malaria and other diseases with known endogenous light absorbing molecular biomarkers.Item Exposure from Thoron, Radon and Modelling Indoor Gamma Radiation Dose in Homa Bay County, Kenya(Kenyatta University, 2023) Odongo, Willis Otieno Gor; Margaret W. Chege; Nadir Hashina; Shinji TekonamiHoma and Ruri hills in Homa Bay County, Kenya, are associated with high background radiation levels. Presently, they are experiencing high human settlement. Maize is the major food crop and Lake Victoria is the major water source. There is no sufficient data on radiation exposure from indoor gamma, air (222Rn and 220Rn) crops and water. The main objective of this research is to determine human exposure to ionizing radiation associated with natural radioactivity in dwellings, water and crops, besides assessing the risk of heavy metals from contamination of Lake Victoria waters and modeling indoor gamma absorbed dose due to non-secular equilibrium in 232Th decay series. Terrestrial radioactivity measurements were done using NaI (Tl) detector. Indoor 222Rn, 220Rn, and 220Rn progenies were measured using RADUET and EETC monitors while 222Rn in water was measured using big bottle system coupled with RAD7. For heavy metal analysis, AAS was used. A mathematical model on absorbed gamma dose was developed and validated. The modelled and measured absorbed doses in the dwellings registered a reasonable agreement. The modelled absorbed dose was 15% less than the experimental one, which considers secular equilibrium in the 232Th decay series. The total annual effective dose from indoor air in Ruri was 4.9±0.7 mSv/y1, nearly 1.5 times that of Homa. The average 222Rn concentration in Lake Victoria in Homa was 14.8 Bq/L, 10% higher than in Ruri. The average 222Rn ingested annual effective dose was 60% lower than the recommended WHO reference level of 100 μSv/y1 in both regions. Arguably, heavy-metal lead was the main contaminant in Lake Victoria around the study region as the average incremental lifetime cancer risk for heavy metals was above the WHO limit of 1 × 10-4 by a factor of 5 for adults in both Ruri and Homa, respectively. The total annual effective dose from indoor air, building materials, food stuff maize, and Lake Victoria in Homa was 45% lower than Ruri, which was 12.6±2.1 mSv/y, each contributing about 45%, 30%, 24%, and 1% of the dose respectively in both regions. These results indicate potential health risk of human exposure to ionizing radiations in these regions as the reported values in some of the considered dwellings and maize samples were above the ICRP and WHO safe limits. Indoor air was the major contributor to radiation exposure; thus, houses in the regions should be properly ventilated. Non-secular equilibrium in the 232Th decay series should be considered in determining absorbed gamma dose in earthen dwellings to avoid overestimation.Item Effects of Human Exposure and Associated Risks Due to Natural Radioactivity and Heavy Metals in Bureti, Kericho County, Kenya(Kenyatta University, 2022) Kipngeno, Rotich Charles; Margaret W. Chege; Nadir O. HashimThe knowledge of distribution of natural radiation sources as well as radiation levels in the environment is important for evaluating the risk associated with natural radiation exposure. The activity concentration of selected primordial radionuclides in soil, earthen building materials, maize and kales together with heavy metal concentration as well as 222Rn concentration in underground water samples from Butreti region was determined in this study. The choice of Bureti Sub County in this research was informed by the dominance of granitic rocks in the region which are known for high levels of radiation. The activity concentration of 226Ra, 232Th and 40K in soil, earthen building materials, maize and kales was determined using Thallium activated Sodium Iodide NaI (TL) detector. Soil samples recorded mean activity concentrations of 1164±70 Bqkg-1, 106±23 Bqkg-1 and 79±5 Bqkg-1 for 40K, 226Ra and 232Th respectively which are above the world average range. On the other hand, Bureti earthen building materials recorded mean activities of 1019±59 Bqkg-1, 98±7 Bqkg-1 and 79±5 Bqkg-1 for the same radionuclides respectively. The strong positive correlation due to 226Ra, 232Th and 40K for Bureti soil and earthen building materials implies that Bureti residents source their earthen building materials from the local soil. kales samples registered average activities of 651±33Bqkg-1, 68±4 Bqkg-1 and 77±5 Bqkg-1 while 827±45 Bqkg-1, 62±5 Bqkg-1 and 57±4 Bqkg-1are the activity concentrations in maize samples for the same radionuclides respectively. A mean outdoor absorbed dose rate in air at a height of 1m above the ground level was recorded as 145±10 nGyh-1 which is about 2.5 times the global mean value of 60 nGyh-1. Bureti earthen building materials recorded an indoor Annual Effective Dose of 0.6954 mSvy-1 which is below the International Commission on Radiological Protection (ICRP) limit of 1 mSvy-1. This value shows that the radiological risks associated with exposure from soil in Bureti is low hence the latter can be used for building houses. Maize and kales consumption contributed 3.68 mSvy-1 and 0.89 mSvy-1 respectively to the total absorbed dose rate. The activity concentration due to 222Rn in ground water was determined using Liquid Scintillating Counter detector and a mean concentration of 12.41 Bql-1 was reported. A Total Effective Dose (TED) of 33.23 𝜇Svy-1 due to inhalation and ingestion of waterborne radon was recorded and this is lower than the United States Environmental Protection Agency (USEPA) recommended limit of 100 𝜇Svy-1 for drinking water. Atomic Absorption Spectrophotometer was used to determine the concentration of selected heavy metals in ground water. Manganese, arsenic, copper, zinc and lead recorded mean metal concentrations of 97±11 𝜇gl-1, 7.11±0.11 𝜇gl-1, 31±5 𝜇gl-1, 373±15 𝜇gl-1 and 24±5 𝜇gl-1 respectively which are lower than the WHO permissible limits for drinking water. Incremental Life Time Cancer Risk (LTCRMP) due to heavy metal pollution in ground water and (LTCRRC) due to radionuclides concentration in soil was found to be 5.61×10-5 and 1.23×10-3 respectively and are within the recommended safe limits. In terms of dose contribution by waterborne radon and heavy metal concentration levels, Bureti ground water is considered safe for human consumption. Residual Radiations (RESRAD) code was adapted for a 100 - year extrapolation period to simulate annual effective dose due to concentration of 40K, 238U and 232Th in Bureti soil for inhalation, ingestion and external radiation exposure pathways. The results revealed that ingestion (food i.e., plants, meat and milk) pathways contributed the highest percentage of about 64.61 % to the Total Effective Dose Equivalent (TEDE) compared to 35.06 %, 0.06 % and 0.25 % contribution from ground, inhalation (excludes radon) and soil/rocks respectively. The simulated values of TEDE throughout a 100 - year extrapolation period is lower than ICRP 2007 recommended dose limit of 2.4 mSvy-1.Item Relativistic Distorted Wave Approach to Electron Impact Excitation of Heavy Rare Gases Using a Complex Potential(Kenyatta University, 2022) Marucha, Alex Magembe; Chandra S. Singh; Peter K. Kariuki; John OkumuData on excitation of rare gases is important in the study of plasma displays, lighting and lasers. From literature, both relativistic and non-relativistic computations performed on electron impact excitation of low-lying states of rare gases often fail to give satisfactory agreement with available experimental data mostly at low impact energies and at intermediate scattering angles. With this in view, in the present study, we have applied relativistic effects in a fully-relativistic distorted-wave approach to excitation of the lowest lying resonance states of argon, krypton and xenon gases, by modifying the electron-atom interaction distortion potential in such a way that the complex part, the absorption potential, and the real part, which includes an energy dependent polarization potential, exchange and electrostatic potentials, form the complex distortion potential used in calculating radial wavefunctions. The atomic wavefunctions are constructed in the multi-configuration Dirac-Fock approach by modifying the general-purpose relativistic atomic structure code GRASP for numerical procedures. In this study, the WKB approximation is used to compute the free continuum electron wavefunctions which are then used in computing scattering cross sections and angular parameters using our program RDWBA1. Present results from this study predict that use of a complex distortion potential in the relativistic approach to excitation of argon, krypton and xenon generally lowers integral cross sections as impact energies of the incident electron increases, compared to those obtained using real distortion potentials only. For argon, the effect of the absorption potential, which accounts for loss of flux into other open scattering channels is more visible at electron impact energies above 50 eV, while for krypton, absorption becomes more dominant above 100 eV. For xenon, which is the heaviest of the three, absorption in the distortion potential generally has minimal effect on cross sections at impact energies below 50 eV then significantly improves these results when compared with experiments as kinetic energy of the electron increases. Furthermore, for all the rare gases under investigation, it is the energy dependent polarization potential adopted, that plays a major role in improving shapes of cross-sections at low and near threshold impact energies, where available distorted-wave methods fail to give satisfactory results when compared to experiments. We have also obtained angular correlation parameters lambda to predict the magnetic sublevel responsible for most excitations, and Stokes parameters to predict the polarization of the emitted photon during atomic decay. Cross section results obtained from this study are in good agreement with experiments at all impact energies under investigation, therefore it will be interesting to see how these cross sections vary when this present approach is used to investigate excitation of the metastable states of rare gases with both electron and positron impact.Item Crystallization Kinetics, Structural and Optical Properties of In-Se-Bi Bulk and Thin Films for Reversible Phase Change Memory Applications(Kenyatta University, 2021) Wanjiku, Muchira Irene; Walter K. Njoroge; Mathew K. Munji; Simon D. MakhotjwaA detailed study of crystallization kinetics and structural properties of In-Se-Bi alloys has been carried out in this research. Kissinger’s analysis method was employed to investigate crystallization kinetics of the material sample. Electrical, morphological and optical characteristics have also been studied. Bulk samples of In2Se3 doped with Bi were synthesized using melt quenching technique. The elemental composition of the bulk samples was realized using Field Emissions Scanning Electron Microscope (FE-SEM) attached with Energy Dispersive Spectroscopy (EDS). To investigate thermal properties of the samples, Differential Scanning Calorimetry (DSC) technique was employed. DSC runs were done at 5, 10, 15 and 20K/min heating rates in dry nitrogen ambient at 200 ml per minute flow rate in isothermal conditions. X-ray diffractometer (XRD) technique was used to determine the structural properties of the samples. Copper target was used as the X-ray source of wavelength 1.54 (CuKα1). The 2θ spectrum scan ranged from 5 to 90o at a speed of 2oper minute. The XRD results showed the as-deposited samples were amorphous which upon annealing changed to polycrystalline. To deposit In-Se-Bi thin films, Pulsed laser deposition (PLD) technique was used. Electrical characteristics tests were carried by four point probe using Keithly 237 source meter interfaced with a computer. Electrical resistivity was found to decrease from 85.19 MΩcm to 22.96 MΩcm with increase in percentage bismuth. Elemental mapping carried out on the thin film samples using FE-SEM equipped with EDS revealed irregular distribution of spherical particles. Bulk samples showed agglomeration of particles without a definite shape. To determine optical band-gap, Kubelka-Munk function was applied on Ultraviolet Visible Spectroscopy (UV-VIS) reflectance spectrum. The optical band gap values were higher for the doped samples as compared with the un-doped. The values ranged from 1.36 eV to 1.30 eV for as-synthesized powder samples. There was decrease in optical band gap with increase in bismuth concentration. Similar findings were made for annealed powder samples where band gap values decreased from 1.85 eV to 1.79 eV as percentage bismuth increased. Photoluminescence (PL) properties were studied by use of He-Cd laser of wavelength 325 nm. Emission increased with increase in bismuth concentration for both as prepared and annealed powder samples. X-ray photoelectron spectroscopy (XPS) output showed that bismuth was present in all doped samples. Activation energy of the samples was determined using Kissinger equation. It was found to decrease from 0.231 eV to 0.172 eV with increase in percentage bismuth for values with 0% Bi to 6% Bi concentration. However, activation energy increased with bismuth concentration for higher bismuth concentration of 8% Bi and 10% Bi. XPS studies confirmed elemental composition of the samples where for indium 3d5/2 peak was at 445.0 eV and 3d3/2 peak was at 452.5 eV binding energies. The two peaks are due to spin-orbit splitting of the d orbitals. XPS spectrum for selenium showed a peak for 3d orbitals at 54.3 eV binding energy. Bismuth exhibited two asymmetrical peaks at 4f5/2 and 4f 7/2 respectively. In conclusion, addition of Bismuth to the binary alloy of indium and selenium enhanced its qualities for use in phase change memory applications in terms of low power consumption and less switching time due to decrease in resistivity and activation energy.Item Human Exposure and Associated Risks Due to Natural Radioactivity and Heavy Metals In Ortum, West Pokot County, Kenya(Kenyatta University, 2021) Felix Omonya, Wanjala; Nadir Hashim; Otwoma DavidThe background radiation in air, the activity concentration of selected radionuclides in soil and rock samples, the radon and thoron concentration in selected mud houses and elemental concentration of heavy metals in soil and water samples from Ortum, West Pokot County in Kenya was determined in this study. Ortum was chosen due to the presence of granitic and silicon rocks which are associated with high levels of background radiation. The activity concentration of 238U, 232Th and 40K in soil was determined using the High Purity Germanium detector (HPGe) and the average values were 40 ± 3 Bq/kg, 56 ± 4 Bq/kg and 425 ± 19 Bq/kg respectively which is within the world average range. The activity concentration of 238U and 232Th in soil samples reduced with increasing depth while that of 40K increased slightly with increase in depth. The average activity concentration of 238U, 232Th, and 40K in soil samples was higher than in the rock samples implying that the soils originate from other regions. The average outdoor absorbed dose rate in air at 1 m above the ground was found to be 112 ± 30 nGy/h which is almost double the world average value of 60 nGy/h. The average Raeq was 153 ± 49 Bq/kg which is less than the limit of 300 Bq/kg and the external hazard indices (Hex) and the internal hazard index (Hin) were 0.41 ± 0.13 and 0.52 ± 0.16 respectively which is below the limit values of unity (>1). This implies that soil and rocks in Ortum poses low radiological risk and they can therefore, be used for construction of houses, industrial and agricultural purposes. The average radon and thoron concentration in mud houses was determined using RADUET detector and found to be 40 ± 19 Bq/m3 and 54 ± 30 Bq/m3 respectively which is below the ICRP recommended lower and upper limit of 100 Bq/m3 and 300 Bq/m3 respectively. The elemental concentration of Ni, Cu, Zn, Pb, K, Ca, Fe, Ti, Mn, Rb, Sr, Zr and Nb in soil was determined using the Energy dispersive X-Ray Fluorescence Spectrometer (EDXRF) and found to be below the WHO recommended limits. The mean concentration of trace elements Pb, Zn and Cu in soil samples reduced with increasing depth while that of Ni increased with increasing depth. The Geoaccumulation Index (Igeo), Potential Ecological Risk Index (Ei) and synthesized potential ecological risk index (Er) were evaluated and found to be -0.40, 4.92 and 19.69 respectively. The results show that soil from Ortum is moderately polluted and the risk associated with exposure to heavy metals in soil is low. The concentration of Ni, Cu, Pb, Zn, Ag, Al, As, Ba, Ca, Cd, Co, Cr, Fe, K, Mg, Mn, Mo, Na and Se in water samples was determine using Agilent-5100 Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES). The elemental concentrations in water samples from the two rivers was found to be lower than the WHO permissible limits, except for calcium (Ca) which was higher than the permissible levels in borehole water. Hence, water from rivers in Ortum is unpolluted and fit for use except for borehole water which has high calcium levels. The lifetime cancer risk due to background radiation (LTCRBR) and elemental pollution in water (LTCREP) was found to be 1.47 x 10-3 and 1.92 x 10-6 respectively which is within the recommended safe limits. The lifetime cancer risk due to exposure to background radiation evaluated using RESRAD programme for a resident farmer in Ortum was found to be 0.011 or 1.1%. This implies that cancer risk due to exposure to background radiation in Ortum is low.Item First Principles Study of Structural, Electronic and Mechanical Properties of Lanthanum Fluoride and Lanthanum Doped Barium Fluoride(Kenyatta University, 2020) Wabululu, Elicah NafulaLanthanum Fluoride (LaF3) has several applications for instance, in electrodes manufacture, fluorescent lamps and fiber optic devices due to its high heat capacity. Barium fluoride (BaF2) is an alkaline-earth element with a wide band gap with many optical applications, such as lithography. BaF2 has been established as an excellent candidate that is useful for hosting optically active centers (OAC).Lanthanide elements have been used as dopants in BaF2 lattice to achieve the desired optical properties, which has not been fully explored .With these vast applications of these compounds, it is necessary to carry out complementary theoretical investigations on their properties to explore full applications. The structural, electronic, mechanical and optical properties for LaF3, BaF2 and BaF2:La have been investigated in this current work using theoretical computational modeling. These properties have been studied using the generalized gradient approximation (GGA) employing pseudopotentials and plane wave basis sets as implemented in Density functional theory. Lattice constants and bulk modulus for LaF3 were calculated and the values obtained were found to be in good agreement with experimental and other theoretical values. Density of states and energy band structure for LaF3, BaF2 and BaF2:La have been obtained along high symmetry points in k-space, respectively. A band gap of 7.79eV was obtained for LaF3 which is an underestimation in comparison to the 9.0eV of experiment. Values of elastic constants calculated for LaF3 are comparable with those from other experimental and theoretical calculations.LaF3 exhibits mechanical stability from the obtained elastic constants. Doping BaF2 with La reduced the band gap and introduced new energy bands within the band gap from the charge compensating fluorine. The elastic constants calculated for BaF2:La show a decrease in the first two elastic constants with no change in the third component of the elastic constants compared to the pure BaF2.This has been attributed to the lattice distortion introduced by the La atom. From the defect formation energy calculated, nearest neighbor (NN) formation energy was found to be -26.48eV compared to the next nearest neighbor (NNN) of -27.58e.Itwas observed that the next nearest neighbor is most favorable in BaF2 lattice. For optical properties, there was a shift in the absorption coefficient from 5.32 m-1 to 6.25 m-1 of BaF2 when doped with La. The refractive index of BaF2 is obtained as 1.52 compared to experimental value of 1.45. The obtained refractive index is in good agreement with experimental values. The introduction of La atom together with the interstitial fluorine affects electronic, mechanical and optical properties of BaF2.Item Effect of Spatial Dielectric Function on the Total Energy of Cubic Quantum Dots and Frequency Dependent Dielectric Functions in Binary Semi-Conductors(Kenyatta University, 2020) Kahuthu, Stanley WambuguSpatial and frequency dependent response functions of medium-direct band gap binary semiconductors were studied at both nanoscale and in bulk form using ab initio method. To understand why the total energy and the band gap energy of semiconducting materials at nanoscale, such as quantum dots, vary with the particle sizes, this study has invoked dielectric function of binary semiconductors from spatial dependent point of view. Moreover, this study has addressed the discrepancy between theoretical results and experimental data when studying bulk semiconductors which was attributed to failure of full implementation of dielectric funtion which is frequency dependent. Yester years, failure to implement frequency dependent dielectric functions has been attributed to computational demand which has, in this study, been made possible through the use of High Performing Computation (HPC). At nanoscale, Hermanson0s spatial dependent dielectric function was applied in the Hamiltonian when determining total energy of on-center donor impurity in gallium arsenide Quantum-Dot (QD), where the QD was embedded in a matrix of gallium aluminium arsenide. This was necessitated by the fact that behaviour of semiconductors at nanoscale completely deviate from those of their bulk systems. This was studied using both Bloch functions and atomic-like basis functions; the latter from perturbative point of view. The effect of both room temperature and hydrostatic pressure of one atmosphere, on the total energy, were also studied and implemented using Bloch functions. MatLab computation mathematical tool, version 2015, was used for solving relevant Schrodinger equations and for simulation purposes. In bulk systems, frequency dependent dielectric functions of gallium arsenide (GaAs), indium phosphide (InP) and cadmium telluride (CdTe) were studied under the influence of electromagnetic radiations with wavelengths in the range between infrared and visible light. These materials are candidates for heterojunctions such as those that are used to fabricate solar cells and in laser technology. Quantum en-source package for research in electronic structure, simulation and optimization (ESPRESSO) computer code version 5.2.1 with plane waves self consistent field (PWSCF) computer package was used to determine their ground state electronic properties while Yambo computer code version 4.1.4 and BerkeleyGW version 1.2.0 were used to determine their excitation energies and optical properties. From this study, spatial dependent dielectric function was found to give total energy of quantum dots that is higher than that of commonly used dielectric constant. Atomic-like basis functions resulted to higher energies compared to those obtained using Bloch functions. The combined effects of room temperature and atmospheric pressure were found to increase the total energy. This was more pronounced from dots whose size were more than 2:5nm and 3:5nm for spatial independent and spatial depenedent dielectric functions, respectively. Also, electronic structures and optical absorption got from the solution to Bethe-Salpeter Equation was compared with that based on Random Phase Approximation in the presence of the local field (RPA+LF) using Yambo. From frequency dependent dielectric functions, it was observed that different binary semiconductors are excited differently by electromagnetic radiations at different frequencies. From this observation, frequency dependent dielectric functions invoke full interactions in real systems and when considered, optical absorption spectra was found to predict well the order in which heterojunctions should be arranged in optoelectronic devices for optimal output. This study recommends theoretical study of semiconducting materials from full frequency dependent dielectric functions so that the obtained electrical, electronics and optical properties can compare well with those from experimental data.Item Numerical Simulation of Fluid Flow in a Dual Porosity Geothermal System with a Thin Zone of High Horizontal Permeability(Kenyatta University, 2007) Ambusso, Willis J.A numerical simulator capable of mode ling fluid flow in layered dual porosity geothermal systems with high horizontal permeability has been developed. The simulator can match multiple-peaked tracer profiles from injection tests and reliably predict temperature and pressure changes caused by injection of brine in these systems. The simulator was tested and validated using data from Svartsengi geothermal field in Iceland, a non-layered geothermal field, and Olkaria geothermal field in Kenya, a layered geothermal reservoir. Simulated results show significant improvement over regular geothermal simulators and indicate that fluid flow within the horizontal layers with high permeability are best represented by fracture flow theory where fluid flow between the matrix-fracture network occurs in both directions rather than what is normally assumed that fluid flow is governed purely by dual porosity model where fluid flow occurs only from the matrix to the fracture. The study shows that fluid movement in horizontal fractures will dominate main fluid flow features in the reservoir and shall uniquely modify tracer profiles. These horizontal fractures will also lead to high returns of injected fluid at relatively low speeds in reservoirs with moderate permeability as has been noted in Olkaria. This simulator makes it possible to extract quantitative values of the hydrologic parameters of the respective layers. This should lead to better planned and managed brine injection programs.Item Comparison of the optical potential method and the distorted wave born approximation method in electron – atom elastic scattering.(Kenyatta University, 2015-11) Kariuki, Peter KinuthiaThe optical potential (OP) method has been widely used in electron-atom elastic scattering since for a given distorting potential, a solution valid to all orders of perturbation series can be obtained. The first-order distorted-wave Born approximation (DWBA) is only valid to first order. However by use of a distorting potential that accurately models the electron-atom interaction, the DWBA method can yield quite reliable results for elastic scattering and possibly for inelastic scattering as well. In this study, elastic differential cross sections (DCS) and integral cross sections (ICS) have been calculated using the OP method and the DWBA method for the alkali atoms sodium and potassium at intermediate electron-impact energies E 7 200eV . In both methods, and for both atoms, distorting potentials in the form of the sum of the static potential, the local Furness-McCarthy exchange potential, a non-local polarization potential involving discrete excited states of the atoms, and a local absorption potential, have been used. For the sodium atom the 3p, 3d, 4s, and 4p, excited states were used in the polarization potential, while for the potassium atom 4p, 5p, 3d, and 5s, excited states were used. Exchange effects have also been incorporated in the distorted-wave Born approximation method through the exchange T-Matrix element. In doing so, the frozen-core approximation has been applied which allows for exchange between the incident electron and the valence atomic electron, as well as the core electrons. For both sodium and potassium the present differential cross sections in the OP and DWBA calculations are in very good agreement with various experimental DCS at small scattering angles at all electron-impact energies considered. This indicates that the optical potential used describes adequately polarization effects which influence small-angle scattering. It is found that the difference between the DWBA and OP methods increases with decrease in electron-impact energy. This difference is as a result of the exchange T-matrix element in the DWBA calculations. The difference between the two methods decreases as the distorting potential becomes more accurate (complete) as the DWBA calculations converge to the OP results. Comparison with available experimental and theoretical results shows the need to use a complex distorting potential to account for loss of flux into inelastic channels.Item Influence of silver nanoparticles on the optical properties of methylene blue and curcumine dyes(Kenyatta University, 2014) Ochoo, Lawrence Otieno; Migwi, C. M.; Okumu, J.It is emerging that dyes and nanoparticles (NP) of Ag, Au and Cu have optical properties with the potential for transforming and enhancing applications of light energy in opto-electronics, solar cells and even radiotherapy on cancer. Investigations are opening up on their modes of influence, conflict of theories on their mechanisms of influence and the important parameters of influence in various systems, In this study, the influence of Ag nanoparticles (below 50nm) on the optical properties of curcumine and methylene blue dyes was investigated experimentally and theoretically. The nanoparticles of Ag were prepared by the method of photo-reduction of AgNO3 in ethanol solution and characterized by spectroscopic analysis in the UV-IR spectral range (300-900nm) using Spectro 320 analyzer, transmission electron microscopy and EDX spectroscopy. Samples of the individual dyes and mixtures of dye- silver nanoparticles were also prepared in ethanol solutions and deposited on glass substrates by spin-coating method, for the spectroscopic analysis. The influence of Ag nanoparticle size and morphology on their own optical properties and that of the dyes were investigated. The results have shown that the optical absorption of Ag nanoparticles and their influence on the dyes depend non-linearly on the nanoparticle size and shape. The results have shown enhancement on dye absorption, with the maximum enhancement factor of ~4.3, realized with Ag nanoparticle size average of 22.4 ± 3nm. A comparative analysis with the results of other studies on Au and Ag has revealed an interesting correlation about the nanoparticle sizes for optimum enhancement effect towards dyes, solar cell materials, and radiotherapy on cancer. That the most effective are the nanoparicle sizes of minimum absorption bandwidth, a size range of 15-30 nm for both metals. As a result, a new theoretical model has been proposed for the purpose of understanding the mechanisms and parameters behind the influence of metal nanoparticle size on their own absorption and in other systems. The model has shown very good qualitative and quantitative agreement with both the experimental results of this study and those of other studies, for Ag, Au and Cu. The model predicts an optimum absorption by Ag nanoparticles of the size ~30 nm and a minimum absorption bandwidth at the Ag size of ~24 nm and ~21 nm for Au. With regard to the theoretical analysis of Ag, Au and Cu the model finds weak interaction between the conduction band and interband transition absorption in silver but strong interaction in Au and Cu, which influence their optical spectra, how they interact with their environment and difference in their potential optical applications. On the Ag nanoparticles size with the highest enhancement in dye absorbance (22.4 nm), the Ag-Methylene blue dye interaction has revealed an evolving selective binding for Ag particles in the range 10-25 nm. A similar physical interaction has been reported in Ag-HIV-I and Au-cancer cell interaction and attributed to sulphur in their structures, an element also contained in Methylene blue dye. The correlation between nanoparticle sizes (10-30nm) with optimum effect in different systems is proposed to be a consequence of the electric field and dependent on the wavelength of light and the absorption bandwidth.Item Modelling Radon and Thoron Exhalation and Measurement of Total Natural Radiation Exposure in Mrima Hill, Kenya(Kenyatta University, 2015-01-22) Chege, Margaret WairimuMrima hill in Kwale County is one of the regions in Kenya with the highest levels of background radiation. Rich deposits of mineral ores such as niobium and manganese are also known to exist. Small-scale farming is the mainstay of the economy with cassava as the main cash as well as food crop; raw soil constitutes the primary building material while hand-dug wells serve as the source of water for the residents. The main objective of this research was to determine the exposure associated with radioactivity in indoor air, crops and well water in the region. This involved the determination of 222Rn and 220Rn concentration in dwellings and measurement of 226Ra, 232Th, and 40K concentrations in building materials, soil, cassava and well water. A model on radon and thoron exhalation rates was developed and validated through exhalation measurements. In addition, physico-chemical parameters of water that included heavy metals, pH and conductivity were investigated. CR-39 SSNTD were used for simultaneous measurements of 222Rn and 220Rn; accumulation chamber coupled with RAD7 monitor for exhalation measurements; HPGe detectors for radioactivity measurements in crops and water samples; and the AAS for heavy metal determination in water samples. Conductivity and pH were measured on site using standard digital meters. A total annual effective dose of 24.1 mSv/y was obtained with indoor air, crops and water, and building materials contributing 56 %, 36 % and 8 % of the dose respectively. All radon concentration values were below 200 Bq m-3 while 65 % of thoron measurements were above 300 Bq m-3. A mean thoron concentration of 652.8±397.0 Bq m-3 was obtained against that of radon of 35.2±13.9 Bq m-3. Building materials registered average radon and thoron exhalation rates of 0.0043 Bq m-2 s-1 and 19.6 Bq m-2 s-1 respectively and average concentrations of 226Ra and 232Th of 134 Bq kg-1 and 431 Bq kg-1 respectively. Modelled and measured isotopes exhalation values showed good agreement which meant that exhalation rate was dependent on the content of mother radionuclide in the building material. A correlation coefficient of near unity was observed between 226Ra and 232Th content in building materials and in soil. Over 70 % of cassava tubers and leaves had detectable amounts 226Ra with average concentrations of 60±5 Bq kg-1 and 141±11 Bq kg-1 respectively. 232Th, with an average concentration of 35.3±61.5 Bq kg-1 was detected in 28 % of the tubers; it was not detected in the leaves. 37 % and 7 % of water samples detected for 226Ra and 232Th with average concentrations of 4.3±0.3 Bq kg-1 and 2.0±0.1 Bq kg-1 respectively. 40K was present in all samples in averages of 842±539 Bq kg-1, 1708±552 Bq kg-1 and 91.4 Bq kg-1 in cassava tubers, leaves and water respectively. In terms of heavy metals, over 90% of the water samples were enriched with at least one metal with Mn and Cd as the main contaminants. The average electrical conductivity was 862±949 μSv/cm; 17 % of the samples had pH values lower than 6.5. From the results obtained, the main source of exposure in Mrima hill region is indoor air with thoron as the main source of the radiation dose. Exposure through ingestion is mainly due to 226Ra and 40K. Groundwater in the region is generally of poor quality mainly due to heavy metal enrichment.Item ''A study of a system equation of thin elastic quadric shells''(2012-05-07) Sengottaiyan, DevannaA problem connected with the study of doubly curved thin elastic shallow shells in the theory of nonlinear elasticity is considered. The equations of equilibrium are derived in the form, 1(x,y) +Eh42(x,y) = 0 D42 (x,y) -41 (x,y)=P (x,y). in the domain of m, the shape of the shell. Here 4(...)=22(...)=(4 + 24 + 4) (...) (x4 x2y2 y4) 4 is the pucher's operator, 4(...) = (22f 2 +2f 2)(...) (x2 y2 xdy xdy y2 x2) E: Young's modulus of elasticity of the material of h : The uniform thickness of the shell D= Eh3 (1-2)-1 is the flexural ligidity of the material 12 :poisson's ratio The entire boundary of the shell, in the form is assumed clamped so that the deflections and slopes are zero on these boundaries. xyis the stress function and 2 (x,y) is the deflection function P(x,y) is the external force on the projection of the shell on xy plane. The entire domain of the shell is bounded in R3 having its middle surface F(x,y,z) =0, which is the most general noncentral quadric with surface F(x,y,z) =0, which is the most general quadric with respect to an orthogonal cartesian coordinate system x,y,z and the equation to this middle surface is reduced to the explicit form z=f=f(x,y). Galerkin's orthogonality conditions are applied to solve the equilibrium equations. The appropriate form of orthonormal Fourier's double series are formulated for the functions 1 (x,y) and 2(x,y) to satisfy the boundary conditions. Galerkin's equations for generalised orthonormal series are established,. such that the mean square errors in the calculation of Fourier's constants are minimum when finite number of terms are considered. the function 1 (x,y) and 2(x,y) and f(x,y) are substituted inthe equations and solved. The expressions for the normal stresses, shearing stresses, bending moments, displacements in the direction of x,y and z axes rotations about x and y axes are determined. The magnititude of the maximum values of these quantities and the points where they occur are also determined. The existence and uniqueness of the solutions are established. Some applications for particular type of shells, whose middle surfaces are anticlastic, synclastic, developable or surfaces of revolution, under specific loading on the surface of the shell are considered.Item Pozzolanicity of selected kaolinites with special focus on pyroprocessing parameters(2011-12-20) Gathua, Joseph KimiriIn this study, the pozzolanic reactivity of selected clay minerals (kaolin) with lime was investigated mainly to establish their suitability in low cost housing. Clay minerals from eleven different regions in Kenya were characterized using x-ray diffraction, x-ray fluorescence and the differential thermal analysis coupled with thermogravimetry. The X-ray diffraction tracings for all the samples showed features of disorder that made the exact quantification of the clay minerals difficult, but estimates showed that kaolinite ranged between 30-74%. The results also showed that the clay minerals were mixed- layered or interstratified. The results of chemical analysis showed predominance of Si02 and A1203 with Fe203 being the next major constituent. All the samples met the Standards IS-1344-1981 on chemical composition of pozzolanas. The thermal behaviour was monitored using differential thermal analysis coupled with thermogravimetry. Adsorbed water was released in the range 50-90°C. The dehydroxylation reaction occurred in the range 525-600°C and was accompanied by phase transformation from the crystalline kaolinite to the amorphous or quasi- amorphous metakaolin phase. Another change of phase in some samples was observed in the range 900-980°C, which signified recrystallization (fusion) of the collapsed structure into spinel. Three samples with the highest content of kaolinite namely, Mwingi Kaolin (sample A-2), Kisii kaolin (sample A-3) and Nyeri kaolin (sample G) were selected for pozzolanic reactivity tests with lime alongside kaolin Caminau, Kaolin Guttau and diatomaceous earth. Kaolin Caminau and Guttau were sourced as packaged industrial products from Freiberg, Federal Republic of Germany, while diatomaceous earth was sourced as an industrial product from the African Diatomite Company, Gilgil- KenyaThe optimum activation temperature and thermal activation time were established by thermally activating the samples at varied temperatures and time using soak method in a muffle furnace. The two parameters were then determined on the basis of compressive strength of the pozzolanallime mortars cured for 7 days and dissolution method. The latter method entailed dissolution of thermally activated pozzolana in dilute hydrofluoric acid and subsequent measurement of electrical conductivity. The optimum activation temperature and thermal activation time ranged between 650-800°C and 3-4 hours respectively. The results showed that dissolution can be an effective and quick method of establishing the pyroprocessing parameters. The optimum pozzooanal Lime ratio for the six pozzolanas was in the range 2.3-3.0 and the results were in agreement with pozzolanic investigations done elsewhere.. Kaolin Caminau and diatomaceous earth registered high compressive strengths during the first 7 days of curing and limited strength development thereafter indicating a very fast rate of hydration. Kisii, Mwingi and Nyeri kaolin recorded very low strength during the first 7 days but the strength developed progressively upon curing up to 28 days signifying slow rate of hydration. The pozzolanicity of soak calcined Kisii kaolin using the Thattle model of vertical shaft kiln (VSK) was compared with that of electric muffle furnace (EMF). The results indicated that kaolin calcined in EMF was more reactive with lime than the V SK calcined one. Investigations were extended to comparison of the soak and flash calcinations methods. The flash method produced more reactive metakaolin than the soak method. Thermal decomposition under isothermal conditions was also implicitly monitored on the basis of electrical conductivity measurements. The results indicated that this method is a good indicator of the structural changes taking place within a pozzolana upon thermal activation. All the samples attained compressive strength of 4MP after 28 days of curing as per the IS-1344-1981 standards, an indication that they can be used as pozzolanas for ordinary masonry purpose.