MST-Department of Physics
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Item Analysis of Energy Requirements for Grid-Tied Solar Energy Systems for Medium Industrial Application(Kenyatta University, 2023-04) Kasau Andrew MuthambiiAbstractItem Optical and Electrical Characterization Of CuS and CdS:B Thin Films For Solar Cells Application(Kenyatta University, 2019-05) Chumo, Kiprotich CosmasThin film Photovoltaic cells will have high cfficiency when a p-type material with a narrow band gap and a n-type material with wide band gap arc used. Their Efliciency is influenced byt deposition techniques, deposition conditions and the components in the reaction bath used in depositing the films. These factors influence the optical properties of the solar cell. Hetero-junction devices with Boron doped CdS (s-type) thin films used as window layers in solar cells show improved electrical conductivity. Despite CdS:B and CuS having good qualities for use as window and absorber layers respectively for a solar cell, there is no information on CdS:B / CuS p-n junction solar cell. In this rescarch, CdS:B thin films were prepared by CBD method on glass substrates and optimized for application as a window material. On the other hand. copper sulphide (Cu8) layer was prepared using same method on ordinary glass substrates and optimized as an absorber material. The [ilm’s clectrical resistivity was determined using the four point probe to determine their sheet resistance. Optical properties like Rellectance(%) and Transmittance(%) were measured by UV-VIS NIR 3700 spectrophotometer and used to calculate other optical constants like band gap (Ep)refractive index (n).extinction coefficient (k) and absorption coefficient (a). The results were analysed to determine how optical transmittance. absorbance and the electrical resistivity varied with the conditions of deposition using the Scout software. Conditions that gave Boron doped CdS and CuS optimum optical and clectrical properties were then chosen and used to prepare CdS:B-CuS photovoltaic cell. The CdS:B thin film deposited at 85°C using 20cm? of boric acid was selected as the best for fabricating the solar cell’s window layer. It had the highest clectrical conductivity 0f 83.71 (Qcm)™'. ransmittance of 82.2% and band gap of 2.4468eV. The CusS thin film deposited in a time of four hours was selected as the best for preparation of solar cell’s absorber layer. with low band gap of 1.77 eV. Solar cell simulator was used in characterizing the prepared CdS:B/CuS solar cell. The cell had the (ollowing parameters: Open circuit voltage (Vo) = 0.39V, Short circuit current (Isc) = 0.032A. maximum current (Tmas) = 0.028A, maximum voltage (V ma) = 0.26V, Maximum power =0.00728W cell area = 1.425x 10 °m?, Field factor (FF) =0.583 and efficiency (n) of 0.51%.Item Effect of Absorption and Polarization Potentials in the Distorted Wave Calculation of Position Impact Excitation of Autoionizing State of Positron Impact Excitation of Autoionizing State of Rubidium(Kenyatta University, 2024-01) Opungu, Zakayo KituiStudies have been done involving positron and electron impact on alkali atoms. However, for positron impact excitation of the autoionizing state of rubidium atom, there are only few results available. The positron impact excitation ofrubidium's lowest autoionrzing state has been investigated in this work with inclusion of absorption and polarization potentials as distortion potential. Differential cross sections, integral cross sections and angular parameters have been calculated using the distorted wave method and compared with available results. With all the potentials - static, absorption, polarization included, the current results for cross sections and angular parameters are qualitatively in good agreement with the results available in the literature. The absorption potential reduces the magnitude of both integral and differential cross sections, whereas the polarization potential increases the magnitude of both integral and differential cross sections at low impact energies. As the impact energy increases, the effect of these two potentials becomes insignificant because the projectile moves at a high speed and hence spends very little time in the interaction region. Inclusion of polarization potential also introduces resonance near the excitation threshold. The results of the alignment parameter indicate that there is a higher degree of scattering from the magnetic sub state m = 0 for impact energies below 400 eV. On the other hand, the lambda parameter results suggest that the scattering of particles alternates between the two magnetic sub states m = 0 and Nl = l . The present results demonstrate that the incorporation of polarization and absorption potentials greatly enhances cross sections and angular parameters.Item Geotechnical Characterization of Subsurface Using Seismic and Resistivity Geophysical Methods: A Case Study of Mikinduri, Meru County, Kenya(Kenyatta University, 2024-01) Wechuli, Moses MasindeThis study was undertaken at Mikinduri town the headquater of Tigania central sub county in M eru county which lies 23km from Meru town on the North. The town is rapidly growing due to its strategic location, increasing population and administrative functions. However, the Mikinduri area has been experiencing landslides during heavy downpours, accompanied by structural failure leading to loss of property and life. The study aimed at establishing the causes of landslides, thick alluvium deposits, subsurface fractures/faults and ground subsidence. Electrical resistivity and seismic refraction geophysical techniques were employed in this investigation. The subsurface was characterised in terms hosting/bearing capabilities. Geo-electric, acoustic layers, and subsurface structures were delineated and determined. Geological reports and borehole logs were used to constrain the models. Sounding curves, travel time curves, 2D geo electric sections, and 2D seismic models revealed 3-5 lithologic units to a depth of 30- 250 m. The study established thick loose alluvium deposits mixed with clay to a depth of 0.3- 15m on an impermeable sub-basement as the possible major trigger of the landslides witnessed during rainy seasons. Fractured and saturated zones ( aquifer) was established to far northwest with resistivity values of 10 -100 𝛺𝑚 to a depth of between 65-100 m. Resistivity values ≥ 1000 𝛺𝑚 represented hard zones or solid basaltic rock basement to a depth of between 2 m to 38 m in the southwest. Three acoustic layers were delineated with p-wave velocities of 250-450m/s, 500-650m/s, and 700-3300m/s for the first, second, and third layers respectively. Loose alluvium and clay soils have poor foundation bearing capabilities, while compacted gravel and hard basaltic rock basement have good foundation bearing capabilities. Piling among other engineering techniques are recommended for structures to rest on a direct competent basement also the northeast area of Mikinduri is recommended for underground water harvesting, construction of car parks, playfields, and shallow foundation structures. Landslide mitigation measures such as slope reinforcement,erosion control measures, revegetation and reforestation, slope monitoring and instrumentation among others should be implemented. Further research on slope inclination at mikinduri are recommended.Item Effects of Eight-Week Walking Programme on Health- Related Fitness and Perceived Body Image of Premenopausal Teachers in Mombasa County, Kenya(Kenyatta University, 2024-06) Odero, Violet AumaThe combined optimum health status attained from Health-Related Physical Fitness through participation in exercise and a positive mental picture a person has of one’s own physical body and one's attitude towards the physical self are all vital for the enhancement of overall health and contentment. This study sought to determine the relationship between health-related fitness (HRF) and perceived body image; and to assess the effects of an 8-week walk programme (with in-built conditioning sessions) on these two factors. The study used a quasi-experimental design. The target population was premenopausal female teachers aged between 30-45 years in Mvita Sub-county, Mombasa. Purposive sampling technique was used to select the sample of 50 premenopausal teachers. Health-Related Fitness tests and a Perceived Body Image questionnaire was used to capture data before and after the Eight-week walk programme. The Health-Related Fitness tests comprised (i) the 20 metre bleep test to estimate cardiovascular endurance, (ii) the one-minute sit-up test to determine abdominal muscle strength endurance, (iii) the sit-and-reach test to assess low back flexibility, (iv) the modified push-up test to establish upper body strength; and finally, (v) measured heights and weights to calculate Body Mass Index (BMI). The experimental group (n=23) received the intervention of a walking programme, while the control group (n=26) was excluded from the walking programme. Data collected was analysed using Statistical Package for the Social Sciences (SPSS) Version 22. One Way ANOVA was used for analysis. Hypotheses were tested at 5% significance level. The ANOVA results indicated significant mean differences (pre-test and post-test) between the experimental and control groups (p<0.05) indicating a positive effect of the 8-week walk programme to Abdominal muscular endurance (F(1, 48) = 56.72. P< 0.001), upper body strength-endurance (F (1, 48) = 55.86. P<0.001), cardiovascular endurance (F (1, 48) = 39.96. P< 0.001), low back flexibility (F (1, 48) = 37.75. P< 0.001) and Body Mass Index (F (1, 48) = 29.05. P< 0.001). Based on the statistically significant differences between pre-test and post-test means (t (48) = 2.07. P=.044), the perceived body image results suggest that participants consciously monitored their body weight. On whether participants wanted perfect bodies, the difference in pre-test and post-test means were statistically significant (t (48) = 3.15. P=.003) suggesting that they had preference for a perfect body. On whether the participants felt that their bodies did not represent them, the difference in pre-test and post-test means were statistically significant (t (48) = 3.26. P=.002) suggesting that the Eight-Week Walk Programme had a positive impact on perception of their body image. In addition, on whether the participants followed exercise regimes to the letter to maintain a good figure, the difference in means were statistically significant (t (48) = 4.28. P<.001) implying participants were more strict on exercise regime to maintain a good figure post the exercise. On whether the participants felt physically attractive, the difference in means were also statistically significant (t (48) = 2.72. P=.009) indicating that they felt more attractive after the exercise. On whether the participants were concerned about their body weight all the time, the difference in means were statistically significant (t (48) = 3.15. P=.003), an indication that the participants were keen to maintain a healthy body. Given the positive significant effects of the Eight –Week Walk Programme the study recommends this Walk Programme for female pre-menopausal teachers to improve their Health-Related Physical Fitness Components as well as body image. It concludes that further research should determine the best ways of integrating walking into daily life routine to enhance HRF components and perceived body image.Item Measurement of Lateral Distribution of Cosmic Rays Muons Using Two-Fold Coincidence Technique(Kenyatta University, 2024-09) Kihagi, Veronicah NyamburaCharged primary cosmic ray particles constitute 85% protons, 12% helium, 3% iron, and heavier elements. These primary particles interact with the Earth's atmosphere, producing secondary particles known as Extensive Air Showers (EAS). Among the particles produced in EAS are pions and kaons, which subsequently decay into muons. Cosmic ray muons dominate the population of cosmic ray particles on the Earth's surface. Understanding the properties of EAS in the Earth's atmosphere is the aim of this investigation. The lateral distribution of cosmic ray muons was investigated using two-fold coincidences. Four detectors were positioned at two-fold coincidence separated from 0 to 35.5 meters at regular intervals. It was determined what the coincidence rate was between these detector stations. The data that was collected was fitted using the Nishimura-Kamata-Greisen (NKG) function in order to examine the lateral distribution The results showed that the muon flux decreased with increasing distance. Additionally, the study aimed to explore the hourly variation of cosmic ray muon flux. To achieve this, two detectors were used in coincidence to measure the variation over time. The highest muon flux was observed sometime after midmorning and lowest sometime after sunset. To support the understanding of EAS, Monte Carlo (MC) simulations of EAS were performed using the EPOS and GHEISHA models, which account for high and low-energy particle interactions, respectively. The simulations using EPOS LHC from this work with the measurements of the two-fold coincidence gave a primary composition cosmic ray as (protons (81±0.01) %, helium (10±0.04) %, and (9±5.88) % iron, and heavier elements). The EPOS LHC simulations were then compared to the experimental data and the muon count rate was found to align with the expected one. The knowledge gained from the lateral distribution of cosmic ray muons is essential for comprehending the development of extensive air showers. Furthermore, this information enhances our understanding of the chemical composition of primary cosmic ray particles. In addition, we also understand the interactions of cosmic ray particles in the atmosphere, particle production and formation of EASItem Positron Impact Elastic Scattering of Magnesium Using the Distorted Wave Method(Kenyatta University, 2024-08) Onyancha, Elvick Motanya MarsA profound grasp of cross sections, encompassing both differential and integral aspects, regarding positron interactions with atoms and molecules, proves highly valuable in eluci dating the dynamics of microscopic particles and shedding light on atomic structures and intermolecular forces. This understanding plays a crucial role in various fields, including astrophysics, plasma physics, and laser advancements. Over the last thirty years, exper imental and theoretical findings have been documented concerning positron-magnesium elastic scattering. This thesis presents an extensive computational study of positron-impact elastic scattering of atomic magnesium in the framework of Distorted Wave Born Approx imation (DWBA). Differential cross sections as well as integral elastic cross sections have been calculated at incident energies between 10 eV and 200 eV where . In order to per form the aforementioned calculation, a computer program called DWBA1, designed for e −-H scattering, was adapted to accommodate the specific process being investigated. The obtained results are then compared with the available theoretical and experimental results for analysis. The current findings regarding integral cross sections demonstrate a favorable qualitative alignment with experimental and the majority of theoretical results. At interme diate incident energies (30-100 eV), the DCS derived from the present study demonstrate satisfactory concurrence with both calculated and experimental results. However, at lower incident energies (10-20 eV), the obtained differential cross sections (DCS) do not exhibit satisfactory agreement with the available measured and calculated outcomes. Thus, it is evident that the current method is applicable for the elastic scattering of positrons and magnesium atoms at intermediate energiesItem Lateral Distribution of Cosmic Ray Muons(Kenyatta University, 2024-10) Mburu, Samuel ChegeCosmic rays are high-energy particles that travel through space at nearly the speed of light. Primary cosmic rays originate from sources such as the sun, supernovae, black holes, and active galactic nuclei. When these primary cosmic rays interact with the Earth's atmosphere, they produce secondary cosmic rays, including cosmic ray muons, which are a significant component that reaches the Earth's surface. The lateral distribution of cosmic ray muons is a key factor in understanding the elemental composition of primary cosmic rays and the development of extensive air showers in the atmosphere. The aim of this work was to estimate the elemental composition and interaction of primary cosmic rays in the atmosphere. Two NaI(Tl) detectors and associated electronics were used to carry out the measurements. The detectors were separated at regular intervals ranging from 0 to 30 meters. Cosmic ray muons were detected by the NaI(Tl) detectors. For each detector separation, the number of coincident muons and the total number of detected muons were recorded at two-hour intervals. The experiment was conducted at Kenyatta University during the months of March, April, and May 2019.The data collected were analyzed, and a decoherence curve was plotted, showing the number of counts per minute as a function of the separation distance between the detectors. The coincidence rate was fitted using the Nishimura-Kamata-Greisen (NKG) function and compared with Monte Carlo (MC) simulations of extensive air showers. The simulation were based on the DPMJET-III model, and the simulated results agree well with experimental data. The analysis of the experimental data revealed a primary cosmic ray composition of (86 ± 3)% protons, (10 ± 31)% helium, and (4 ± 3)% iron. These results for protons and iron are consistent with other reported values, while the helium component shows some deviation. This work contributes to our understanding of the mass composition of primary cosmic rays and their interaction with the Earth's atmosphere.Item Roof-Top Solar PV Performance Under Different Roofing Materials and Air Gaps in Tropical Climates.(Kenyatta University, 2024-05) Aigbedion, Nosakhare JeremiahHigh temperatures negatively impacts the performance of Photovoltaic (PV) modules. This is more pronounced on Roof-top installations where due to limited air spaces and the choice of materials influence the natural cooling of PV modules. Regions experiencing high temperature conditions such as the tropical African countries present a unique opportunity to study the interactions between the PV module and the base roofing materials. This study presents both simulation and experimental results of the thermal effects of roofing materials and air gaps on the performance of rooftop-installed PV modules. Clay and concrete tile roofs as well as various metal roofs commonly used in sub-Saharan Africa were studied. The base material properties of the roofs were studied and the effects of roof pigmentations were examined as well. Pigmentations of Iron (III) oxide (Fe2O3), Titanium dioxide (TiO2) and Basalt which are three commonly used roof pigmentations were studied and compared with PV heat interactions of unpigmented roofs. For the simulation study, the PV module and the various roofs under investigation are designed on Solid Works software and model designs are then exported to ANSYS workbench where modeling and simulations are implemented on ANSYS steady-state thermal. The roof pigmentation study was implemented in COMSOL Multiphysics software for transient thermal analysis. Surface radiosity is investigated to further differentiate the heat transfer influence of the various pigments and to underline the environmental impact of each of the models. The results obtained are validated with field-based experiments carried out at Kenyatta University in Nairobi, Kenya. Six different commonly used roofs namely; Decra roofs, Box Iron roofs, Clay tile roofs, Concrete tile roofs, Orientile roofs, and Galvanized Iron roofing sheets were specifically investigated. PV installation optimization was investigated for the various roof materials and optimal air gaps for specific roof materials were determined, to guide future installations. Results from the study provide relative PV performance on the six different roof materials. Results from the study also show the role of roof pigmentations in PV heat transfer. The clay tile roofing sheet revealed minimal deleterious effects on PV installations, closely followed by the concrete roof tiles. Among all the metal roofs investigated, the Orientile roofing sheet requires larger clearance for better performance, followed by the Galvanized Iron roofing sheet and Decra. The PV module on the Box Iron roof recorded lower temperatures when compared to those on the other metal roofs at specific air gaps, consequently leading to higher performance. PV maximum temperature across the different modules on the various roofs ranged from 64 °C – 50 °C, at instantaneous times at the 20 mm airgap. This range difference decreased as air gaps were raised to 100 mm. Open circuit voltage values ranged from 20.8 V – 21.1 V as airgap increased on the best-performing module on the Clay roof. The modules on the other roofs also revealed voltage gains at higher air gaps. Results also reveal the optimum airgap for PV installations of Concrete, Clay and Box-Iron roofing sheet at 100 mm. while Orientile, Decra, and Galvanized Ion roof materials have optimum airgaps at 150 mm, 140 mm, and 140 mm, respectively. Further, out of the three roof pigments investigated, the Fe2O3 pigmented roof gives the highest solar cell temperature. The unpigmented roof reveals solar cell temperatures that are notably higher than the cell temperatures of all pigmented models. From the three pigmentations, the Fe2O3 pigment gives the highest surface radiosity. The unpigmented model displays a surface radiosity that is significantly higher than that of the pigmented models. This study establishes that the type of roofing material will influence the minimum air clearance necessary for the natural convective cooling of PV cells.Item Fabrication and Characterization of Zinc Oxide Nanostructured Natural Dye Sensitized Solar Cell(Kenyatta University, 2023-05) Nthiga, Njiru James Lincon; Migwi Charles; Wawire IsaacAbstractItem Electron Impact Elastic Scattering by Calcium Atom Using First Order Distorted Wave Method with a Complex Potential(Kenyatta University, 2023-06) Egesa, Waswa Vincent; P. K. Kariuki; E. O. JobungaAbstractItem Design of a Microcontroller Based Home Access System Using the Global System for Mobile Communication(Kenyatta University, 2023-04) Nyaga, Janeleah Wanja; M.K. Munji; R.L NyengeAbstractItem Natural Radionuclide concentration in Phosphate fertilisers found in Kenyan market(Kenyatta University, 2023-11) Mutwiri, Mbaka E; Nadir hashim and Naftally KimaniABSTRACT Human exposure to radiations from natural radionuclides is an inevitable aspect of life on earth. Cosmic sand radioactive materials are the two main sources of ionizing radiation on the earth's surface. Phosphate bearing rock, a material used to manufacture phosphate fertilizers, is known to contain relatively high content of uranium, thorium and potassium radionuclides. Continuous application of these phosphate fertilizers in our agricultural soils lead to contamination of our farming land with these radionuclides. Radiations from these radionuclides pose health risks such as cancer to the exposed individuals. Apart from the radionuclides, phosphate rock also contains traces of heavy metals such as cadmium (Cd) which is considered a big threat to human health. This research has analyzed the activity concentration of 238U, 232Th and 40K in various fertilizer types from three different brands sourced from Kenyan market. NaI(TI) detector and AAS were used for spectrometric analysis. The different types of fertilizers analyzed were; DAP, SSP, TSP, CAN and NPK (17:17:17). The radiological parameters; Radium equivalent, absorbed dose rate, external radiation hazard index, annual effective dose and excess lifetime cancer risk have been evaluated. The mean radium equivalent (Bq/kg) were 133±9 for DAP, 74±8 for CAN, 118±12 for SSP, 128±9 for TSP and 104±9 for NPK. The mean dose rate (nGy/h) were 69±5 for DAP, 37±4 for CAN 58±6 for SSP, 62±5 for TSP and 52±4 for NPK. The mean external radiation hazard index were in the range 0.20±0.03 to 0.36±0.04. The mean outdoor annual effective dose (mSvy1) were in the range 0.045±0.007 to 0.081±0.009. The mean excess life time cancer risk ranged from 0.157±0.010 to 0.283±0.020. DAP had the highest mean values while CAN had the lowest mean values for all the radiological parameters evaluated. The mean concentration of Cd ranged from 1.42±0.20 mg/kg to 11.13±0.48 mg/kg. The obtained results show that fertilizer samples are safe for use as cadmium levels and the radiological parameters assessed are below the maximum permissible limits of 60mg/kg for Cd concentration, 370 Bq/kg for radium equivalent, 60 nGy/h for dose rate,1 mSvy1 for annual effective dose and 0.29 x 10-3 for outdoor ELCRItem Design and Implementation of High Frequency Signal Generator Based on Phase Locked Loop(Kenyatta University, 2023) Mutinda, Boniface Musyoka; Mathew Munji; Raphael NyengeA signal generator is an electronic test instrument that has a wide range of applications.Some of these applications include testing systems in cellular communications, radar,microstrip antennas and testing components in electronics labs. For a signal generator to be used in these applications, it should generate high frequencies, have a low level of phase noise, and also have a fast locking time. The purpose of this research was to design and build a signal generator that operates on the principle of a phase-locked loop, has the capacity to generate frequencies ranging from 35 MHz to 3 GHz, and has a low degree of phase noise. The simulation of the phase-locked loop synthesizer was done using the ADIsimPLL design tool. The phase locked loop chip used in simulation was the ADF4351 from Analog Devices. In the design, we implemented a loop filter of the third order and chose a reference frequency of 10 MHz. The layout of the phase locked loop was simulated, and the results showed that the optimal values for loop bandwidth and phase margin were 10 kHz and 45°, respectively. Following the simulation, the optimal values for each of the loop filter’s components were analyzed and calculated. The signal generator was built by integrating the phase locked loop synthesizer and a keypad shield with an Arduino UNO microcontroller. The ADF4351 was programmed via Serial Peripheral Interface (SPI) to enable the changing of frequencies using the keypad shield. The nature of the generator’s signal was investigated using a cathode ray oscilloscope in the 35-100 MHz frequency range. The testing was also done for 101-3000 MHz using a spectrum analyser. The level of phase noise was calculated at 35 megahertz, 387 megahertz, 1 gigahertz, 2 gigahertz, and 2.9 gigahertz at 1, 10, 100, and 1000 kilohertz. The amount of phase noise that was acquired after experimental work was higher than the level obtained after simulation. For example, at the output frequency of 387 MHz, the experimental phase noise was -104.2 dBc/Hz while the simulated was -126 dBc/Hz at 100 kHz offset frequency. The reason for this is that the phase noise contribution in the simulation was only from the phase locked loop components while in the experimental, in addition to the phase noise from the PLL components, there were other sources of phase noise while carrying out the experiment. The rise in output frequency was also accompanied by an increase in phase noise. The reason for this is that the signal generator was built with the concept of a phase locked loop which implements the idea of frequency multiplication by dividing along the feedback loop with the use of a counter. This concept raised the phase noise by 20 multiplied by the logarithm of the number of counter. The maximum spur appeared at the third harmonic and was found to be -18.6 dBc, while the minimum spur appeared at the fourth harmonic and was found to be -44.5 dBc.Item Natural Radionuclide Concentrations in Phosphate Fertilizers Found in the Kenyan Market(Kenyatta University, 2023) Mbaka, Eric Mutwiri; Nadir Hashim; Naftali KimaniHuman exposure to radiations from natural radionuclides is an inevitable aspect of life on earth. Cosmic rays and radioactive materials are the two main sources of ionizing radiation on the earth’s surface. Phosphate bearing rock, a material used to manufacture phosphate fertilizers, is known to contain relatively high content of uranium, thorium and potassium radionuclides. Continuous application of these phosphate fertilizers in our agricultural soils lead to contamination of our farming land with these radionuclides. Radiations from these radionuclides pose health risks such as cancer to the exposed individuals. Apart from the radionuclides, phosphate rock also contains traces of heavy metals such as cadmium (Cd) which is considered a big threat to human health. This research has analyzed the activity concentration of 238U, 232Th and 40K in various fertilizer types from three different brands sourced from Kenyan market. NaI(Tl) detector and AAS were used for spectrometric analysis. The different types of fertilizers analyzed were; DAP, SSP, TSP, CAN and NPK (17:17:17). The radiological parameters; Radium equivalent, absorbed dose rate, external radiation hazard index, annual effective dose and excess lifetime cancer risk have been evaluated. The mean radium equivalent (Bq/kg) were 133±9 for DAP, 74±8 for CAN, 118±12 for SSP, 128±9 for TSP and 104±9 for NPK. The mean dose rate (nGy/h) were 69±5 for DAP, 37±4 for CAN 58±6 for SSP, 62±5 for TSP and 52±4 for NPK. The mean external radiation hazard index were in the range 0.20±0.03 to 0.36±0.04. The mean outdoor annual effective dose (mSvy-1) were in the range 0.045±0.007 to 0.081±0.009. The mean excess life time cancer risk ranged from 0.157±0.010 to 0.283±0.020. DAP had the highest mean values while CAN had the lowest mean values for all the radiological parameters evaluated. The mean concentration of Cd ranged from 1.42±0.20 mg/kg to 11.13±0.48 mg/kg. The obtained results show that fertilizer samples are safe for use as cadmium levels and the radiological parameters assessed are below the maximum permissible limits of 60mg/kg for Cd concentration, 370 Bq/kg for radium equivalent, 60 nGy/h for dose rate,1 mSvy-1 for annual effective dose and 0.29 x 10-3 for outdoor ELCR.Item Design and implementation of high frequency signal generator based on phase locked loop(Kenyatta university, 2023-11) Musyoka, Mutinda Boniface; Mathew MunjiA signal generator is an electronic test instrument that has a wide range of applications. Some of these applications include testing systems in cellular communications, radar, microstrip antennas and testing components in electronics labs. For a signal generator to be used in these applications, it should generate high frequencies, have a low level of phase noise, and also have a fast locking time. The purpose of this research was to designandbuildasignalgeneratorthatoperatesontheprincipleofaphase-lockedloop, has the capacity to generate frequencies ranging from 35 MHz to 3 GHz, and has a low degree of phase noise. The simulation of the phase-locked loop synthesizer was done using the ADIsimPLL design tool. The phase locked loop chip used in simulation was the ADF4351 from Analog Devices. In the design, we implemented a loop filter of the third order and chose a reference frequency of 10 MHz. The layout of the phase locked loop was simulated, and the results showed that the optimal values for loop bandwidth and phase margin were 10 kHz and 45°, respectively. Following the simulation, the optimal values for each of the loop filter’s components were analyzed and calculated. The signal generator was built by integrating the phase locked loop synthesizer and a keypad shield with an Arduino UNO microcontroller. The ADF4351 was programmed via Serial Peripheral Interface (SPI) to enable the changing of frequencies using the keypad shield. The nature of the generator’s signal was investigated using a cathode ray oscilloscope in the 35-100 MHz frequency range. The testing was also done for 101-3000MHzusingaspectrumanalyser. Thelevelofphasenoisewascalculatedat35 megahertz, 387 megahertz, 1 gigahertz, 2 gigahertz, and 2.9 gigahertz at 1, 10, 100, and 1000 kilohertz. The amount of phase noise that was acquired after experimental work washigherthanthelevelobtainedaftersimulation. Forexample,attheoutputfrequency of 387 MHz, the experimental phase noise was -104.2 dBc/Hz while the simulated was -126 dBc/Hz at 100 kHz offset frequency. The reason for this is that the phase noise contribution in the simulation was only from the phase locked loop components while in the experimental, in addition to the phase noise from the PLL components, there were other sources of phase noise while carrying out the experiment. The rise in output frequency was also accompanied by an increase in phase noise. The reason for this is that the signal generator was built with the concept of a phase locked loop which implements the idea of frequency multiplication by dividing along the feedback loop with the use of a counter. This concept raised the phase noise by 20 multiplied by the logarithm of the number of counter. The maximum spur appeared at the third harmonic and was found to be -18.6 dBc, while the minimum spur appeared at the fourth harmonic and was found to be -44.5 dBc.Item Levels of Natural Radionuclides in Khat (Catha Edulis) Leaves and Soils in Selected Areas in Embu County, Kenya(Kenyatta University, 2022) Ngari, Vindesio Njagi; Nadir Hashim; Abdallah MerengaEnvironmental data and information on levels of accumulation of radionuclides is crucial towards putting in place mitigation measures to ensure a safe environment. Over the past years, khat (Catha edulis) has been the major cash crop grown in some parts of the Eastern side of Kenya especially in Embu and Meru areas. The khat grown in Embu which is the study area is mainly the Muguka variety while the variety grown in Meru is the Miraa. The leaves from this plant are chewed for their stimulating effect. However, some studies have reported detrimental effects on the users of khat. In spite of its extensive use which extends to the Arabian Peninsula and the European markets, research on radionuclide concentrations in khat and in soils where it is grown has not been done. This therefore necessitated this research in order to provide public awareness on natural radiation levels. This research established the level of human exposure due to radiation by natural sources in the khat growing areas of Embu County by measuring the specific activities of 238U, 232Th and 40K, estimate the dose rate absorbed and obtain the hazard indices due to these radionuclides. Thirty samples were collected from different areas distributed throughout Embu County. The samples were then prepared and analyzed using the NaI(Tl) detector. The mean activities for khat leaves were obtained as 875.8±11, 10.1±1 and 51.1±4 Bq/kg for 40K, 238U and 232Th respectively. The activities of soil in the same region were however lower than the world average at 344±12, 22±11 and 33±5 Bq/kg for 40K, 238U and 232Th respectively. The mean absorbed dose rates obtained for soil was 44±0 nGyh-1 which is lower than the admissible dose standard of 1500 nGy/h. The AED for ingested radionuclides for khat had an average of 0.45±0.19 mSv/y. The average values of hazard indices for soil were 0.26, 0.32, 0.70 and 0.76 for external index, internal index, gamma index and ELCR respectively. All the indices in this work were within the safe. Results from this study therefore reveal that the khat grown in the Embu County poses no significant risk to the consumers and the general populace. The soils from the area are also safe for humans.Item Enhancement of Morphological and Opto-Electronic Properties of Perovskite (Ch3nh3pbi3) Thin Films for Solar Cell Applications.(Kenyatta University, 2022) Moracha, Daniel Juma; Walter Kamande Njoroge; FanuelMugwanga KehezeThe functionality of the photovoltaic devices greatly depends on the film morphology, which is determined by the deposition methods and annealing techniques. Organometal halide perovskite based solar cells represents an upcoming photovoltaic technology. Perovskites have been widely and extensively studied for some years now, but comprehending their properties has slowed down their advancement. Finding a link between their morphology and the resulting properties is important in dealing with some of the basic issues like high band gap and sheet resistivity that hinder further development of this solar cell. Herein the perovskite thin films were prepared by single and double step deposition methods. Concentrations of solutions, annealing temperatures and dipping time were used as parameters to form different morphologies during self-assembly processes. The optical band gaps for the films prepared by single step were observed to decrease from 2.10eV to 1.96eV when the annealing temperature was increased from 80oC to 160oC. An increase of annealing temperature beyond 160oC led to the formation of yellowish substance on the substrate, this indicated the presence of lead iodide. Further these results implied the decomposition of methyl ammonium which resulted to an increase of the optical band gap to 2.16eV. Films that were deposited by double step displayed similar trend where the optical band gap was observed to decrease significantly from 2.14eV to 1.95eV when the dipping time was varied from 2 hours to 8 hours. The optical band gap was observed to increase to 2.15eV when the dipping time was prolonged to 10 hours and beyond. This indicated that the nucleation and film growth of perovskite is a reversible process and 8 hours was found to be ideal for the two process to that is nucleation and film growth to perfectly take place. The transmittance data was simulated using multi-peak fitting SCOUT software from which other optical constants like refractive index was obtained as n = 2.3803, extinction coefficient k= 0.2215 and absorption coefficient α= 69855.23 for single step film samples. For the double step deposition method the refractive index of n=2.4011, extinction coefficient k= 0.2998 and absorption coefficient α= 71450.42 were revealed. The sheet resistivity of the films was evaluated using four-point probe. It was observed that an increase in annealing temperature from 80oC to 160oC led to decrease in sheet resistivity of films from 0.7982 Ω cm-1 to 0.4231Ω cm-1.The sheet resistivity of films deposited by double step decreased from 0.5675Ω cm-1 to 0.2290Ω cm-1. From the results herein it was deduced that the morphology of the perovskite thin films can be enhanced by not only the deposition methods but also annealing temperatures and dipping times.Item Design and fabrication of an energy efficient smart air conditioning system(Kenyatta University, 2022) Kavita, Dennis Mwania; Raphael Nyenge; Mathew MunjiResidential and commercial space cooling demands are increasing steadily throughout the world. This has led to high growth in demand for air conditioning (AC) systems. Technology is playing a key role in digitization of these systems with sensors and microcontrollers being used extensively. Energy conservation remains the main focus of scientists and engineers. In line with working towards developing energy efficient systems, we carried out research to optimize the control of air conditioners for energy conservation purposes. This research was geared towards having an energy efficient system. In this research, temperature, proximity and a passive infrared sensor (PIR) were used as smart sensors. The system was designed such that when room occupants’ approach a room, the system is activated and rapid cool down or warm up achieved within a predetermined time depending on the size of the room. As long as there is occupant in the room, the system settles quickly into the set conditions. When there is no one in the room, the system need not to be working and therefore it switches off. This ensures that the system only works when needed hence helps in energy conservation thus reducing bills paid by home owners and companies. The designed prototype is able to detect room occupancy, responds perfectly to temperature changes as well as human presence in the field of view of the PIR with an overall performance efficiency of 55.95% which is a good start towards actual implementation of an energy efficient A.C. system. We also recommend that utilization of more sensors like radiation detectors can be explored to diversify the working of this system.Item Positron Impact Elastic Scattering by Calcium Atom Using First Order Distorted Wave Born Approximation with a Complex Potential(Kenyatta University, 2022) Wakhu, Wechuli Benard; Peter K. Kariuki; Linturi J. MugambiThe concept of elastic scattering of projectiles by atomic targets has the fundamental importance in understanding the complex projectile-target interaction and the dynamics of the collision process. Compared to electrons, positron scattering is considered as the alternative way to acquire knowledge about atomic structures and to examine phenomena such as the Fermi surface of metal and nano-precipitates in solids. Further, positron scattering cross section data is essential for the development of various technological fields; for example astrophysics, plasma sciences, material sciences and bio-medicine. Additionally, positron cross sections are used as input data in some modeling software. Accurate cross section data is required in these applications. Thus, lack of complete agreement among the available theoretical data, unavailability of experimental data and the DWBA method with a complex potential at impact energy range 10-200 eV not having been utilized in such a study; are the reasons that informed this investigation. Consequently, this research sought to establish whether the second term of the DWBA T-matrix element significantly affect the cross sections and how the cross sections obtained herein compare with other calculations when the distorting potential is varied. After formulating the complex potential with positronium formation channel proficiently incorporated, the radial Schrödinger equation was solved numerically for low values of orbital angular momentum quantum number using the Numerov’s method. The associated integral equation was solved iteratively for high values of orbital angular momentum quantum number. The extracted phase shifts were used to compute the T-matrix which was then used to determine DCS while the optical theorem was applied to calculate TCS. With only static potential, the DWBA and OP methods yield same DCSs. The polarization potential increases the DCS at small scattering angles and further introduces a local minimum whose position shifts toward forward scattering angles with increasing projectile-target impact energy. With a real potential that incorporates static-polarization potentials, the structure of the present TECS for OP and DWBA is consistent with those of the available data. With a complex potential, the agreement between the present OP and DWBA DCS results is excellent. In conclusion, with a complex potential that incorporates positronium formation effect, the exact agreement between the DWBA and OP results implies insignificant effect of the second term of the direct T-matrix element on DCS as well as TCS while the effect of positronium on the cross sections does not extend beyond 150 eV. From these findings, it is recommended that at intermediate energies, a complex potential inclusive of positronium formation channel should be applied and the procedure of accounting for inelastic cross section suggested herein this study be comprehensively tested on positron-alkaline earth atoms to clearly establish its suitability.