MST-Department of Physics

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Analysis of Microstrip Antenna using Arbitrlily Shaped Patches Having Similar Surface Area
(2013-12-17) Kariuki, J. W.; Konditi, D. B. O.; Munji, M. K.
Microstrip patch antenna has become very vital in communication system due to its attractive features such as its light weight, small size, low cost, low profile, ease of installation and its conformability to planar and non planar surfaces. When a particular mode and shape is selected MSA are also versatile in terms of resonant frequency, impedance, polarization and electromagnetic wave pattern. However MSA suffer from relatively narrow bandwidth .The consumers of these devices can enjoy diversity of shapes aesthetically pleasing to them without compromising the efficiency of the device. The antenna will be analysed using HFSS software to determine the characteristic of the designed MSA antenna, The results will be compared with the simulated data as well as data in the open literature. The prototype will be fabricated on PCB and tested in the laboratory. The aspect of bandwidth will be considered in this work.
Analysis of Natural Radioactivity Levels and Radiation Hazards due to Murram Quarried in Kakamega County, Kenya
(Kenyatta University, 2021) Luke, Songa Kamwani; Nadir O. Hashim; Margaret W. Chege
Exposure to ionizing radiation from 40K and those in the decay chains of 238U and 232Th for a prolonged time poses danger to human population. While 238U, 232Th and 40K are universally present in rock and soil, their concentration levels are not uniformly distributed. Rock and soil serve as building materials in many parts of the world and therefore can act as important sources of radiation exposure. Murram results from weathering of rocks and d espite its mining and use in construction, research on its radionuclide concentration was previously absent absent. 25 samples of murram were collected through random sampling in Malava sub county of Kakamega for measurements of radioactivity of 226Ra, 232Th and 40K. Activity concentration of 226Ra, 232Th and 40K was measured using NaI(TI) gamma ray spectrometer. The concentration obtained was used to calculate; absorbed dose, annual effective dose rate, radium equivalent activity, external and internal gamma hazard indices. The mean activity concentration for 226Ra, 232Th and 40K obtained were; 200±10 Bqkg-1 within the range of 19±1-318±16 Bqkg-1, 80±4 Bqkg-1 within the range of 11±1-194±10 Bqkg-1 and 968±48 Bqkg-1 within the range of 79±4-1965±98 Bqkg-1 respectively. The mean values of activity concentration for 226Ra, 232Th and 40K exceeded the world average of 33 Bqkg-1, 45 Bqkg-1 and 420 Bqkg-1 respectively. The average dose rate was found to be 180±9 nGyh-1 within the range 66±3-263±13 nGyh-1 which is below the hazard limit of 1500 nGyh-1but above world’s average of 55 nGyh-1. The indoor and outdoor annual effective dose rate was found to be 0.88±0.04 mSvy-1 within the range of 0.32±0.2-1.29±0.06 mSvy-1 and 0.22±0.011 mSvy-1 within the range of 0.08±0.04-0.32±0.02 mSvy-1 respectively. These health hazard parameters were below the safe limit of 1.0 mSvy-1 but above world’s average of 0.07 mSvy-1(UNSCEAR, 2016). The mean values for radium equivalent activity, external and internal gamma hazard indices were; 390±19 Bqkg-1 within the range of 144±7-596±30 Bqkg-1, 1.05±0.05 within the range of 0.39±0.02-1.61±0.08 and 1.60±0.08 within the range of 0.44±0.02-2.36±0.12 respectively. The average for radium equivalent activity exceeded the world’s average of 89 Bqkg-1 and acceptable limit of 370 Bqkg-1 and for external and internal gamma hazard indices slightly exceeds the world’s average and safe limit of 1. These results reveal insignificant radiological health hazards for inhabitance within the study area hence murram is safe for use and also safe for quarriers.
Analysis of Telluric Currents on Miniature Electrical and Electronic Circuits in Nairobi City and Kajiado Counties, Kenya
(Kenyatta University, 2021) Odhiambo, Okoth Collins; Raphael Nyenge; Mathew Munji
The necessity for electrically ensured and trustworthy electrical and electronic contraptions or systems is growing in various business areas around the world, for instance, mechanical and manufacturing, vehicle, clinical, imperativeness, common science, information and correspondence development and sharp grid applications. The makers and end-customers of these contraptions or systems are depending on additional state-of-the-art headways that are electrically ensured, distortion free and pass on higher accuracy that grants action in under impeccable conditions. Perhaps the best region is the electronic devices, the science that incorporates the assessment and utilization of incredibly small scale systems and can be used over the entire science field. This assessment investigated the amplitudes of telluric currents in Embakasi, Nairobi City and Ongata Rongai, Kajiado counties, considering a locale of 10000 m2 as a result of obliged space available in each zone. Measurements were done by use of EX542:12 Multimeter and analysis conducted using informative sensible software known as Statistica. The measurements gave extents of constraining level of electrical hazard exhibited by telluric currents to electrical, electronic and media transmission devices or systems that rely upon these devices. The amplitudes of telluric currents measured and analyzed were seen as significant to present perilous electrical condition to underground structures, in this way measures to alleviate the risks were prescribed, such as electromagnetic shielding and earthing. To improve on the amplitudes of the measured telluric currents, the electrodes should be of high electrical properties such as silver coated electrodes. The choice of area of study was advised by higher concentration of underground installations in Nairobi county in relation to Kajiado county, hence basis of telluric currents measurement comparison.
Application of mass transport model to study temporal variation of concentration of lead in a riverine system
(2013-07-19) Njiru, Njoki Sophy
Heavy metal contamination within river systems is a major environmental problem around the world. An environmental model was developed to simulate the temporal variation of concentration of lead discharged into a riverine system. The model was developed by solving the transport equation which governs the concentration of lead. The equation has advection, dispersion, sink and source terms. The equation was discretised and converted into a language compatible with a computer. A computer program was developed using c++ programming language. The program divides the Nairobi River into blocks. Using the governing equations the program distributes the lead emitted from the source to all the blocks depending on the prevailing conditions. The resulting flow equations were solved by a suitable computer code developed in this work. There was a close agreement between the measured and simulated values. A correlation coefficient of 0.9124 was found. The data of lead concentration in Nairobi River is used to calibrate and validate the model as well as make its predictions.
Assessment of heavy metals concentration in soils at selected points on roads and sites around Nairobi using edxrf spectrometer
(2013-01-31) Wanjala, Felix Omonya
Increased exhaust emissions (gaseous and particulate), fuel leakage, damping and wear and tear of vehicle parts have resulted in environmental pollution by heavy metals especially along major roads with high traffic. This calls for constant monitoring to make sure that the levels of heavy metals do not go above the threshold limits recommended due to their adverse health effects on human beings, plants and animals. This research project focused on determining the present concentrations of heavy metals (Pb, Zn, Cu, and Ni) in soils at selected points on roads around Nairobi and some selected sites with respect to distance off-road and depth. The soil samples collected were ground into fine particles of size less than 100gm and prepared into pellet form for analysis using Energy dispersive X-ray fluorescence spectrometry. This analytic technique is fast, non-destructive and enables simultaneous determination of the concentrations of many elements in a sample with high sensitivity. It consists of a Si(Li) detector with energy resolution between 170eV to 190eV at 5.9KeV, MnKa-lines and a radioisotope source 109Cd (T1/2 =461.4 days) for sample excitation leading to emission of characteristic X-rays. Quantitative analysis was done using a software program called Quantitative X-ray Analysis System with a sub-routine program called Quantitative Analysis of Environmental Samples to finally obtain the concentrations of the different elements in the samples. The levels of the heavy metals obtained from the selected sampling sites C.Gar, K. Gar, K.R, G.B.P and Nai were 82.2±7.6,g /g to 236.1±9.2,g /g Pb, 273±9.2,g /g to 794±26,g /g Zn, 32.4±4.8,g /g to 221.8±6.8 g /g Cu, and 10.72.7 g /g to 33±4.8,g /g Ni. From the results, it was found that the concentrations of Pb, Zn, Cu, and Ni were very high at the garages followed by parking places for buses and heavy commercial vehicles and lastly at roundabouts. The concentrations of heavy metals on the selected roads at Roy, Cab, Kan, A.P and Len with respect to distance and depth were 26.2±2.5 g/g to 85±4.8 p/g Pb, 75.9±5.0 g/g to 337±18.2g/g Zn, 7.0 g/g to 49.6± 6.3 g/g Cu and 5.8 g/g to 31.1±4.4 g/g Ni. From the results obtained, the levels of heavy metals Pb, Zn, and Cu decreased with increasing distance off-road and depth. Soil sample collected during the dry season had higher concentrations of heavy metals on the surface soils than those collected during the wet season. This can be attributed to washing off of the top soils by heavy rains during the rainy season and also leaching. Although lead (Pb) emissions have dropped drastically with the phase-out of tetra-ethyl lead (TEL) as a fuel additive, Pb deposited along highway roads continues to be of concern because of its toxicity when inhaled, ingested or absorbed by both plants and animals. The levels of heavy metals Pb, Zn and Cu in soils along the roads decreasing with increasing distance off-road and depth indicate that automobile sources could be the possible source of the high concentrations of heavy metals in soils along the roads.
Assessment of Human Exposure to Natural Source of Radiation on the Soil in Tongaren Constituency of Bungoma County, Kenya
(Kenyatta University, 2016-01) Musamali, Enock Wanjala
Radionuclides are unstable nuclei with high ratio of proton to neutron. Natural activities like volcanic eruption and anthropogenic activities expose originally concealed radioactive elements in the rocks within the earth crust. Poor agricultural practices such as excessive use of fertilizers add radioactive elements in the soil. Transport agents like run-off water and rivers, spreads these radionuclides within the soil in Tongaren Constituency. The radionuclides disintegrate to form lighter atoms by emitting radiations like alpha, beta and gamma rays. Gamma rays penetrate in to human tissue causing cancer, tumor, fibroites and lens opacification. The greatest effect of radiations was felt during Nagasaki and Hiroshima bomb where more than 40,000 people lost life in 1945 (Murray et al., 2000). Tongaren constituency is situated between latitude 000 34’ 00’’ N and longitude 340 34’ 00’’ E. The increasing cases of cancer has been an issue of global concern and with little information on the level of radionuclides in Tongaren constituency this research is conducted out to find out whether the soil is safe for human being. Agriculture being a major source of income in Tongaren the use of inorganic fertilizers containing radioactive elements, in maize production may lead to gradual accumulation of radionuclides. When radionuclides accumulate beyond the threshold level they pose danger to health of human being. This study determined the concentration levels of radionuclides in Tongaren constituency of Bungoma county. Twenty samples of soil were collected from maize plantation areas. Three adjacent soil samples were mixed up from each sampling point to get twenty representative (composite) soil samples. The soil samples were dried at 1100C, grounded and sieved through wire mesh of diameter 0.5mm and packed in plastic beaker that were sealed to prevent leakage of radon. The soil samples were kept for 28 days for secular equilibrium to be reached between the activity of uranium, thorium, potassium, radium and their progeny. The activity concentration level for 226Ra, 232Th, 238U and 40K in soil samples were determined using gamma ray spectrometer with NaI (Tl). The average activity concentration for 232Th, 238U and 40K was found to be 85.0±4.3 BqKg-1 within the range (13.1-212.4), 260.3±13.0BqKg-1 within the range (34.6-484.8) and 981.5±49.1 BgKg-1 within the range (9.7-2178.5) respectively. The average radium equivalent activity was found to be 456.4±22.8 BqKg-1 while external and internal hazard indices were found to be 1.24±0.06 and1.94±0.10 respectively. According to European commission, (1999), values of index He≤ 2 corresponds to a dose rate criterion of 0.3 mSvy-1, whereas 2≤ He ≤ 6 correspond to 1.0 mSvy-1 and hence the hazard values are insignificant. The average dose rate was found to be 206.4±10 nGyh-1 within the range 36.4±1.8 nGyh-1 to 360.7±18 nGyh-1 which was below the hazard limit of 1500 nGyh-1. The annual effective dose rate was found to be 0.63±0.03 mSvy-1 within the range 0.11±0.01 mSvy-1 to 1.11±0.06 mSvy-1. These health hazard parameters were below the safe limit of 1.0 mSvy-1 since the maximum limit for annual effective dose rate is 1.0 mSvy-1 (UNSCEAR, 2001). These results reveal no significant radiological health hazards for inhabitance within the study areas.
Assessment of Natural Radio Activity Concentration Levels in Geological Samples Collected In Selected Areas in Makueni County
(Kenyatta University, 2018-11) Mutungi, Mutunga James
Natural radiation is the major contributor to the external dose and varies depending on the radioactivity concentration of naturally occurring radionuclides and their decay products in soil and rocks. Exposure to a high dose to human beings leads to health problems. Assessment of natural radioactivity concentration levels in geological samples collected in selected areas of Makueni County was carried out using gamma ray spectroscopy technique. Spectrum decomposition method was used to decompose the measured gamma ray spectra into spectral components of separate radionuclides. The measured peak intensities were used to calculate the activity concentration of the radionuclides in the samples. The average concentrations of 238U, 232Th and 40K measured in the soil samples collected in this study were 69 + 5 BqKg-1,53 + 3 BqKg-1 and 1098 + 69 BqKg-1 respectively while rocks were found to have concentrations of 139 + 6 BqKg-1, 73 + 3 BqKg-1, 1573 + 65BqKg-1 respectively. On average both rocks and soils were found to have activity concentrations of 104 + 5 BqKg-1, 63 + 3 BqKg-1, 1336 + 67 BqKg-1 for 238U, 232Th and 40K respectively. These values are above the global average values. To measure radiation hazard to the public, absorbed dose rate in air at a height of 1m above the ground surface was estimated. Absorbed dose rate in rocks was 175 + 7 nGyh-1 while in soil it was found to be 110 + 7 nGyh-1 These values are higher than the world average of 60 nGyh-1 (UNSCEAR, 2002).The effective dose rate calculated for human exposure from the ionizing radiations of 238U,232Th and40K in the soil samples collected were found to have 0.29 + 0.02 mSvy-1 while rocks registered 0.45 + 0.02 mSvy-1 These health hazard parameters were below the safe limit of 1.0 mSvy-1 (ICRP, 1991; UNSCEAR, 2002) and therefore do not indicate significant health hazard for the inhabitants of the selected area. The building materials from the study area are safe for use and I recommend that the government and other non- governmental organizations use this study as a baseline study in radioactivity concentration levels of the area.
Assessment of natural radioactivity levels and radiation risk due to the different rock types in the Kerio Valley region of Kenya
(2013-03-18) Agora, Jared Omari
Natural radioactivity levels and radiation risks due to different rock types in the Kerio Valley region of Kenya have been measured. Kerio Valley is one of the regions in Kenya suspected to be a high background radiation area (HBRA). This region is rocky and is occupationally characterized by quarrying activities of the various rocks for construction purposes both in the valley and neighbouring towns. All rocks are known to contain natural radionuclides of the 238U and 232Th series, as well as 4oK. The goal of this study was to analyse the natural radioactivity levels and distribution of natural radionuclides as well as assess the contribution of different rock types to the ambient gamma ray dose in the Kerio Valley region. The activity concentration levels of natural radionuclides (uranium, thorium, potassium) in rock samples were analysed using NaI(Tl) gamma ray spectrometry method. The associated radiological parameters (radium equivalent activity, external hazard index, dose rates) were calculated based on the obtained activity concentrations. The resulting activity concentrations were investigated by principal component analysis (peA) and hierarchical cluster analysis (HeA) to observe the nature of the association of the radionuclides and to identify the distribution patterns of the radionuclides in different subregions as well as to correlate radionuclides with the rock types. This would uniquely define the sources of HBRA in the region as well as provide regulatory information on the selection and use of rocks for construction in the Kerio Valley region. The activity concentration varied from 72.707±58.470 Bqkg-' (sandstone) to 116.l49±31.463 Bqkg' (marble) for 238U; 40.317±34.481 Bqkg' (limestone) to 83.652± 59.912 Bqkg-' (gneiss) for 232Th and 427.408±408 Bqkg-' (marble) to 1397.238±265.265 Bqkg' (granite) for 40K. For all the rock samples and' types, the activity concentration exceeded significantly the world average of 33 Bqkg-', 45 Bq/kg and 400 Bqkg' for 238U, 232Th and 4oK, respectively. The hazard indices were computed and used to determine the suitability of the rocks for building in the context of radiological hazard posed. The results obtained for the radium equivalent activity and the external hazard index show that all the rock types do not exceed the recommended limit of370 Bqkg-' and 1, respectively. The outdoor absorbed dose rate calculated ranged from 90.585 nGyh-' (limestone) to 159.085 nG/h (quartzite) while the indoor absorbed dose rate ranged from 66.696 nGyh-'(limestone) to 157.442 nGyh' (quartzite). These values for absorbed dose rate were above the world average value of 60nGy"'. The annual effective dose rate for all the rocks did not exceed the recommended limit of 1mSvy". Principal component analysis results show clustering of sampling sites based on rock types, which mean that the activity concentration of radionuclides in rocks from Kerio Valley depends on the type of rock as a result of the chemical and mineral composition of these rocks. Hierarchical cluster analysis technique (HeA) results showed different areas are distinguished in terms of average activity concentration of natural radionuclides with areas (sub regions) with close levels forming clusters. Rocks from areas to the southern part of the Valley (Kabiemit and Soy) where mining of fluorspar is done were found to have elevated activity concentration of all the measured radionuclides than other areas which are characterized by relatively low activity concentration.
Assessment of Radioactivity Concentration and Radiation Hazards Index for Building Materials Used in Babadogo Estate, Nairobi City County, Kenya
(Kenyatta University, 2022) Oborah, Amukah Kenneth; Nadir O. Hashim; Charles M. Migwi
Natural radioactive materials in certain conditions can get to hazardous radiological level. Some of these hazards are not prone to control as well as, they are usually referred to as the background radiation. The aim of my research work is to evaluate natural radioactivity concentration and radiological impacts on representative sampled building materials collected from different locations in Babadogo estate within Nairobi City County. The selected samples were crushed, sieved dried and store for four weeks after which, analysis done using gamma ray spectrometer was put into action for spectral data acquisition then analysis. The activity concentration levels of 238U, 232Th and 40K for the selected samples of building materials was measured by the use of gamma- ray spectrometry method. Radiological parameters were evaluated based on the prerequisite activity concentration obtained. The analyzed data compared with the standard acceptable values. The activity concentration in 40K varied from 55±3 to 2647±132 Bq/kg giving average value of 831 ±42 Bq/kg, 238U varied from 39±2 to 3602±180Bq/kg giving average figures of 378±19Bqkg¯1and 232Th ranged from 5.000±0.300 to 4213±211Bqkg¯1 giving mean figure of 290±15Bq/kg . Calculated mean figures for activity concentration surpassed the world mean figures of 420Bq/kg, 33Bq/kg, 45Bq/kg in 40K, 238U and 232Th respectively. Absorbed dose rate calculated ranges between 73±4 and 4777±239nGyh¯1 having average value of 540±27nGyh¯1 .The mean number for the absorbed dose rate was above the world acceptable mean value of 54nGyh¯1. The calculated annual effective dose rate varied from 0.040±0.002mSvy¯1 to 2.340±0.117mSvy¯1 having average figure of 0.260±0.013mSvy¯1 ,which was above the world average of 0.070mSvy¯1but below the maximum dose constraint of 1mSvy¯1.These results show that building materials in Babadogo estate are safe and can be used for construction of buildings and thus can be continued using as further research is done on other building materials not covered in my research work.
Assessment of the geothermal potential of Lake Baringo area using magnetic method
(Kenyatta University, 2018-07) Seurey, Paul
ABSTRACT Ground magnetic survey in Lake Baringo area was carried out to examine underlying geology in relation to anomalies in the magnetic field of the earth arising from the magnetic properties of subsurface lithology. This has been done to delineate areas associated with high temperature reservoir in the study area and establish if it relates with the occurrence of geothermal manifestations. The field stations were selected carefully along a profile in the study area and were positioned using Global Positioning System (GPS). The profile and station separation was set at about 800m and 500m respectively. The vertical magnetic field intensities were then measured using Flux Gate magnetometer. Data reduction was done to correct for diurnal and geomagnetic variations. Surfer 8.0 software was then used for gridding and to plot contour map to establish the anomaly signature of the area. Qualitative and quantitative interpretations has been done using the reduced vertical magnetic field intensity. Qualitative interpretation from the magnetic intesity contour map of the area showed that NE region is more dominated by long-wavelength component, that could be caused by deeper sources of magnetic anomalies. The Euler deconvolution method has been effectively used in estimating depth to the top of magnetic bodies. 2D Euler solutions revealed subsurface faulting activities and the presence of fluid-filled zones within the survey area which are marked by the absence of magnetic sources. Quantitative interpretation by forward modeling using Mag2dc software, has been used along selected profiles in the study area. The average modeled depth for the near surface magnetic anomaly sources of the area is 86.57m, while that of the deep seated anomaly sources is 349.25m. The bodies display susceptibility as high as 0.5301 SI units to as low as –0.841 SI units. The models show extensive lava flows. They are interpreted to be basaltic sills and dykes of different types based on geologic unit of the area. They may be possible heat source causing a thermal anomaly in the area west of Lake Baringo and such may have been magmatic intrusive that remained at the subsurface.
Calculation of cross selection for elastic scattering of electrons by a magnesium atom at intermediate energies
(2011-08-01) Kariuki, Kinuthia Peter
Elastic electron-atom collision data from experimental and theoretical studies is useful in the interpretation of spectra obtained in X-ray photoelectron spectroscopy and Auger electron spectroscopy as well as in the Monte Carlo simulation of conduction electrons in solids. In principle the behavior of an electron-atom collision system is predicted by solving the Schrodinger equation. However this task is far from simple in that the equation can only be solved exactly for a two-body collision problem and consequently approximation methods are necessary for electron-atom scattering. In this study the Optical Model Potential method was used to calculate cross sections for elastic scattering of electrons by a magnesium atom at intermediate energies. Computer program PSCATT was developed to solve the Schrodinger equation numerically. Through use of a complex optical potential which accounts for possibility of inelastic processes at intermediate energies, the results obtained were found to be in fairly good agreement with recent measured results. The present results were also found to be comparable to, and in some cases better than, theoretical results obtained using sophisticated multi-channel methods. The computer program used in this study is much less demanding on computer power than the computer codes associated with multi-channel methods which has implications in terms of reducing research costs.
Characterization of Cattle Anal Odour Blend Responsible for Repellency against Rhipicephalus Appendiculatus, the Vector of East Coast Fever
(2014-03-06) Kariuki, Margaret Wangechi; Hassanali, Ahmed; Ng'ang'a, Margaret Mwihaki
East Coast fever (ECF) is one of the most devastating livestock diseases in east, central and southern Africa, and remains the major health hindrance to the development and improvement of the livestock industry. Although synthetic chemical acaricides have made a tremendous impact over the years in the control and management of the vectors on livestock, ticks have developed resistance to most of them In addition, these chemicals are toxic to non-target organisms. Previous on-host behavior studies of adult R. appendiculatus showed preference to feed mainly inside and around the ear of their hosts. Combination of a repellent blend from the anal region and attractive blend at the ear has been sho-wn to play natural "push" and "pull" roles, respectively, to guide these ticks to the cattle ears. The present study aimed at characterizing and evaluating the constituents and blend in cattle anal odour responsible for repelling adults of brown ear tick. The anal odours, and for comparison, odours emanating from fresh dung were analyzed by gas chromatography-linked mass spectrometry (GC-MS). The individual constituents were identified by comparing their mass spectra with those in the National Institute of Standards and Technology (NIST) libraries. The major constituents of the anal odour were diisobutylphthalate (41.27%), o-xylene (9.2%), 4-hydroxy-4-methyl-2- pentanone (4.6%), 4-methyl-2-methoxyphenol (4.3%), ethyl benzene (2.7%), 2,6,6- trimethyl-[IS(la,~,5a)]bicycloheptanes (0.6%), 5-ethoxydihydro-2(3H)-furanone (0.5%), 3-methylene-2-pentanone, (0.5%), 5-methyl-2-phenyl-1H-indole (0.4%), and 3-pentanone (0.2%). Three compounds namely 4-hydroxy-4-methyl-2-pentanone, N- (3-methyl-l-oxobutyl)-alanine methyl ester and 2,4-dimethyl-benzo[h ]quinoline) were common in both anal and dung odours. The repellency of odours, selected constituents, blends and DEET was evaluated using two choice climbing assay. The anal and fresh dung odour had comparable repellence (RD50 2.7 and 2.9, respectively). Of the individual compounds tested, 4-methyl-2-methoxyphenol was found to be most repellent (RD75 =0.56) while 3-pentanone was least active (RD75 = 622.7). The two blends evaluated were more repellent than the anal and dung odours. One of the blends (made up of 4-methyl-2-methoxyphenol, 3-pentanone, 3-methyl-2- pentanone, and 4-hydroxy-4-methyl-2-pentanone) tested gave RD75 of 0.032. The other blend (without 3-pentanone) was more repellent (RD75= 0.019; P ::S 0.05, SNK). In addition, of the analogues tested, 2,4-dimethylphenol was most repellent (RD75= 0.0089) while 3,4-methylenedioxytoluene was inactive. The study lays down the groundwork for characterizing compounds and/or blends with potent repellence against the Brown Ear Tick on cattle.
Characterization of cdxse1-xs/pbs thin films deposited by chemical bath deposition for p-n junction solar cell application
(2017-09) Njeru, Ephantus Nyaga
The CdS and PbS are of great research interest due to their outstanding electronics and optical properties such as winder energy band gap phase and good antireflective properties respectively. CdS has been earlier doped by Zn and used as a window layer combined with PbS as the absorber material using the CBD method. It realised an efficiency of 0.9. It is for this reason in my research, I doped CdS with Se in the fabrication of CdxSe1-xS/PbS PN junction for solar cell application to see whether the efficiency could be enhanced still employing the CBD method. The chemicals used in preparation of CdxSe1-xS were; Solutions of 0.004M Cadmium nitrate, 0.008M Ammonium nitrate, and 0.008M Thiourea. Doping of the CdS films with Se was done using varying volumes of uniform concentration of Sodium Selenosulphate (Na2SeSO3) solutions by volume at a constant deposition temperature of 80 ± 20C. The PbS films were prepared from an alkaline bath using aqueous solutions of lead nitrate solution (Pb(NO3)2.3H2O) and Thiourea (CS(NH2)2) which acted as a source of Pb2+ and S2- ions, respectively. The Tri-ethanolamine solution was used as a complexing agent during the deposition process. The CdxSe1-xS thin film deposition was done at a temperature of 80oC ± 2oC for 25 minutes while PbS deposition was done at room temperature of 27oC ± 2oC, both at normal atmospheric pressure utilizing aqueous conditions for approximately 120 minutes. In the deposition of both window and absorber layers, chemical bath deposition method (CBD) was employed. The precursor solution pH level was maintained at 9 using pH meter. Optical optimization of the thin films was done using DUV UV-VIS-NIR spectrophotometer 3700. Electrical characterization was done using four point probe connected to a Keithley2400 source meter interfaced with computer respectively for both thin films. The Cd0.5Se0.5S film was selected as the best candidate for cell fabrication with Eg of 2.83 eV and transmittance of 89.7%, low absorbance of 1.77% and Resistivity of 1.97×104 Ω-cm in the VIS region was noted. The PbS from a 0.5M concentration was selected as the best candidate with a transmittance of 26.8%, Absorbance of 38.79% and band gap of 1.43eV. The Cd0.5Se0.5S/PbS fabricated cell had the following cell parameters: Open voltage (VOC) of 0.36V Short circuit current (Is) of 0.031A, Fill factor (FF) of 0.65 and cell efficiency of 1.15%. In conclusion, the Cd0.5Se0.5S/PbS P-N junction is appropriate for photovoltaic applications and especially in the VIS and IR region of the electromagnetic spectrum.
Characterization of Cu2S / SnO2: F P-N Junction for Solar Cell Applications
(Kenyatta University, 2019) Omwoyo, Jared Gisemba
Due to industrialization and increase in population, there is need for clean, green and renewable source of electrical energy. Traditional sources of electrical energy like fossil fuels are getting depleted, on the other hand silicon based solar cells are expensive hence the need for low cost and reliable alternative source of energy. Photovoltaic is a reliable energy source which is renewable. Photovoltaic is a process of conversion of solar energy to electricity directly using solar cells. For this study Copper (I) Sulphide (Cu2S) thin films were deposited on glass substrates by Chemical Bath Deposition (CBD) technique. Copper sulphate (CuSO4) was used as a source of copper ions, thiourea (CS (NH2)2) as a source of sulphide ions and tartaric acid as a complexing agent, ammonia solution was used to regulate the pH. SnO2: F thin films were deposited using spray pyrolysis technique (SPT) on glass substrates at substrate temperature of 3500 C using pentahydrated stannous chloride (SnCl4∙5H2O) and ammonium fluoride (NH4F) as precursors. Optical transmittance and reflectance of all film samples prepared in the range of 200 nm-1100 nm were measured using UVVIS- NIR spectrophotometer. The optical measurements were simulated using SCOUT software to obtain optical constants. Cu2S deposited at 0.15 M Cu2+ exhibited low average transmittance of 20.91 %, high average absorbance of 51.29 % and narrow optical band gap of 2.33 eV hence a good absorber material to be used as ptype layer in solar cells applications. On the other hand, SnO2: F had high average transmittance of 79.94 % and wide optical band gap of 4.04 eV at 4 % concentration of fluorine. This shows that SnO2: F is a suitable n-type layer for solar cell applications. Cu2S had lowest refractive index of 1.44 at 0.15 M Cu2+. The four point probe was used to measure the sheet resistivity of all thin films. SnO2: F had lowest resistivity of 40.3 Ω cm at 4% concentration of fluorine while Cu2S had low resistivity of 0.40x103 Ω cm at 0.15 M Cu2+. .The Cu2S/SnO2: F p-n junction was fabricated in phases. First the n-type layer of SnO2: F was deposited onto the glass substrate by spray pyrolysis method and then the p-type layer of Cu2S thin films was deposited onto SnO2: F thin film to form a p-n junction. The solar simulator was used to measure the I-V characteristics of the fabricated cell. The fabricated cell had open circuit voltage (Voc) of 0.4075 V, short circuit current (Isc) of 0.00219 A, fill factor (FF) of 0.61 and efficiency (η) of 0.303 %. Therefore, Cu2S and SnO2: F thin films are suitable materials for fabrication of Cu2S/SnO2: F p-n junction solar cell.
Characterization of Cu2S / SnO2: F P-N Junction for Solar Cell Applications
(Kenyatta University, 2019) Omwoyo, Jared Gisemba
Due to industrialization and increase in population, there is need for clean, green and renewable source of electrical energy. Traditional sources of electrical energy like fossil fuels are getting depleted, on the other hand silicon based solar cells are expensive hence the need for low cost and reliable alternative source of energy. Photovoltaic is a reliable energy source which is renewable. Photovoltaic is a process of conversion of solar energy to electricity directly using solar cells. For this study Copper (I) Sulphide (Cu2S) thin films were deposited on glass substrates by Chemical Bath Deposition (CBD) technique. Copper sulphate (CuSO4) was used as a source of copper ions, thiourea (CS (NH2)2) as a source of sulphide ions and tartaric acid as a complexing agent, ammonia solution was used to regulate the pH. SnO2: F thin films were deposited using spray pyrolysis technique (SPT) on glass substrates at substrate temperature of 3500 C using pentahydrated stannous chloride (SnCl4∙5H2O) and ammonium fluoride (NH4F) as precursors. Optical transmittance and reflectance of all film samples prepared in the range of 200 nm-1100 nm were measured using UV-VIS-NIR spectrophotometer. The optical measurements were simulated using SCOUT software to obtain optical constants. Cu2S deposited at 0.15 M Cu2+ exhibited low average transmittance of 20.91 %, high average absorbance of 51.29 % and narrow optical band gap of 2.33 eV hence a good absorber material to be used as p-type layer in solar cells applications. On the other hand, SnO2: F had high average transmittance of 79.94 % and wide optical band gap of 4.04 eV at 4 % concentration of fluorine. This shows that SnO2: F is a suitable n-type layer for solar cell applications. Cu2S had lowest refractive index of 1.44 at 0.15 M Cu2+. The four point probe was used to measure the sheet resistivity of all thin films. SnO2: F had lowest resistivity of 40.3 Ω cm at 4% concentration of fluorine while Cu2S had low resistivity of 0.40x103 Ω cm at 0.15 M Cu2+. .The Cu2S/SnO2: F p-n junction was fabricated in phases. First the n-type layer of SnO2: F was deposited onto the glass substrate by spray pyrolysis method and then the p-type layer of Cu2S thin films was deposited onto SnO2: F thin film to form a p-n junction. The solar simulator was used to measure the I-V characteristics of the fabricated cell. The fabricated cell had open circuit voltage (Voc) of 0.4075 V, short circuit current (Isc) of 0.00219 A, fill factor (FF) of 0.61 and efficiency (η) of 0.303 %. Therefore, Cu2S and SnO2: F thin films are suitable materials for fabrication of Cu2S/SnO2: F p-n junction solar cell.
Characterization of CuxNy AND CdO:Al thin films for solar cell applications
(Kenyatta University, 2016-05) Mosoti, Obare B.
A solar cell is a device that converts light energy into electricity by photovoltaic effect. The photovoltaic effect refers to photons of light exciting electrons into a higher state of energy, allowing them to act as charge careers for an electric current. Materials presently used for solar cell fabrication include silicon, gallium arsenide (GaAs) among others. However, these materials are expensive and not readily available. As a result, there is need to search for alternative materials which are readily available and give a high conversion coefficient. The purpose of this research was to prepare and study the optical and electrical properties of CuxNy and CdO:Al thin films so as to optimize them for solar cell applications. CuxNy and CdO:Al thin films were deposited by dc magnetron sputtering and reactive evaporation techniques respectively using Edwards Auto 306 vacuum coater system. CuxNy films were deposited at Nitrogen flow rates between 2 sccm and 10 sccm. CdO:Al films were deposited with Al doping concentrations of 0%, 1%, 3%, 5%, 7% and 9% atomic weight. The optical measurements were done using spectrophotometer Solid Spec 3700 DUV in the range (300-2000nm) while electrical characterization was done by four point probe method. Transmittance of CuxNy films was found to increase with increase in wavelength and was below 20% in the 300-2000 nm range. For CdO:Al thin films, integrated transmittance was above 78% in the 400-800 nm range for all samples prepared. Reflectance of CuxNy thin films was found to be below 30% in the 300-2000 nm range while that of CdO:Al thin films was below 15% in 400-800 nm range. From scout software, optical properties such as absorption coefficient, refractive index and extinction coefficient of the thin films were also obtained. For both CuxNy and CdO:Al thin films, absorption coefficient decreased with increase in wavelength of incident radiation. Optical band gap of CuxNy thin films increased with increase in Nitrogen flow rate to a maximum of 1.72 ± 0.02 eV at 10 sccm. For CdO:Al thin films, optical band gap increased with increase in Al doping to a maximum of 3.10 ± 0.06 eV at 5% Al doping, after which it started to decrease with increase in Al doping. Electrical resistivity of CuxNy ranged from 31.70 Ωcm to 87.46 Ωcm while that of CdO:Al thin films ranged from 5.526 x 10-2 Ωcm to 11.33 x 10-2 Ωcm. Optimized deposition parameters such as nitrogen flow rate and Al doping concentration were used to fabricate a thin film solar cell on transparent glass slide. I-V characteristics of the solar cell were measured using a Keithley 2400 source meter interfaced with a computer running Labview program. An open circuit voltage of 476 mV, short circuit current density of 0.48 mA/cm2, fill factor of 0.54 and conversion efficiency of 0.21 % were obtained. From these results, CuxNy and CdO:Al thin films serve as potential alternative materials to the widely used silicon solar cells.
Characterization of CuxOy - ZnO:A1 P-N junction for solar cell applications
(2012-04-17) Keheze, Fanuel Mugwang'a; Partrick M. Karimi; Walter K. Njoroge
Semiconductors thin films have found applications in various optoelectronics devices. Of much interest is the application in solar cells. Consequently, this has led to a continuous search for new semiconductor materials for solar cell applications. Various elements and compourids have been used to fabricate thin film semiconductors for solar cell applications like Si, AI, GaAs, CuInSe2, CuO among others. In this work, Cu.O, and ZnO:Al thin films on plain glass substrates have been deposited as single thin films for property characterization by reactive DC Magnetron Sputtering and evaporation techniques using an Edward Auto 306 Magnetron Sputtering System respectively. A CuXOy-ZnO:Al p-n junction was fabricated by reactive DC magnetron sputtering and reactive thermal evaporation technique on a glass slide with silver as contacts. Transmittance and reflectance data in the range 300 nm-2500 nm were obtained using UV-VIS NIR Spectrophotometer Solid State 3700 DUV for all the thin films samples that were prepared. Transmittance values of above 70% for Copper Oxide and above 80 % for AlO were observed. The optical measurements were simulated using SCOUT 98 software to determine optical constants and optical bad gap of the thin films. Band gap values of 1.62 eV _ 2.54 eV are observed for Copper Oxide and 3.18 eV - 3.42 eV for AlO. The surface sheet resistivities at room temperature of 298 K were found to vary with the deposition parameters and film thickness. Urbach energy for AlO was found to increase with doping levels from 2.08 x 10-4 to 2.18x 10-4 and varied between 0.6 x 10-4 to 1.92 x 10-4 for Copper Oxide. Current-Voltage (I-V) characteristic of the fabricated pn junction was obtained using solar simulator. From the I-V characteristic the following parameters were determined; open circuit voltage Voc = 0.579 V and the short circuit current Isc = 1.12 mA/m2 resulting in 0.42 % solar cell efficiency.
Characterization of CuᵪOᵧ - ZnO:Sn P-N Junction for solar cell applications
(2014-05-02) Omayio, Enock Osoro; Karimi, P. M.; Njoroge, W. K.
The Cu.O, - ZnO:Sn p-n junction solar cell has been fabricated in steps. Cu.O, and ZnO:Sn thin films were first deposited by reactive de magnetron sputtering and reactive evaporation techniques respectively using Edwards Auto 306 vacuum coater system .Cu.O, films were deposited at oxygen flow rates between 5-30 seem, ZnO:Sn films were deposited with Sn doping concentrations reaching 6%. Transmittance of ZnO:Sn films was above 70% for Sn doping less than 5% whereas reflectance was below 40% within the visible range. For Cu.O, films, transmittance increased with increase in wavelength and reflectance was below 35 % within the visible range. From simulation of optical spectra of films using scout software absorption coefficient, refractive index and optical band gap of thin films were obtained. For both Cu.O, and ZnO:Sn films, absorption coefficient decreases with increase in wavelength of incident radiation. Optical band gap of CuxOy films increased with increase in oxygen flow rate to a maximum of 2.64 eV at 10 seem of O2 flow after which it started to decrease. For ZnO:Sn films, optical band gap decreased with increase in Sn doping to a minimum of 2.48 eV at 4% Sn doping after which it started to increase with increase in Sn doping. Electrical resistivity of Cu.O, films increased slightly with increase in 02 flow whereas for ZnO:Sn film's resistivity decreased with increase in Sn doping concentration with minimum resistivity of 21.1 ncm. Solar cell was fabricated on transparent glass slide from 250nm thick p-type Cu.O, film deposited at oxygen flow of 5 seem and 140 nm thick n-type ZnO:Sn film deposited with 2% Sn doping concentration. I-V characteristics of the solar cell were measured by Keithley 2400 sourcemeter interfaced with computer running labview program. It had Voc of 480 mV and fill factor of 0.63 which is higher than those of other cells in literature. The fabricated solar cell had conversion efficiency of 0.232%.
Characterization of p-SnO2:Al /n-ZnO:Al p-n junction deposited by spray pyrolysis technique for led applications
(Kenyatta University, 2015-06) Nyangaresi, Onkundi Paul
Thin films of SnO2:Al and ZnO: Al were deposited under different deposition parameters. Effect of substrate temperature, Carrier gas pressure, substrate to nozzle distance and doping percentages were investigated to obtain optimum conditions for deposition of p-SnO2:Al for LED applications. Optimized film of SnO2:Al was deposited at temperature of 408 o C, nozzle substrate distance of 4.75 cm, carrier gas pressure of 1.88 bars and aluminium doping atomic percent of 5.37 %. Solid spectrophotometer DUV 3700 was used to obtain the transmittance data that was between 75% - 78% in the visible range. Four point probe was used to obtain electrical resistivity of the films which was found to be of the order of 10-3 Ωcm. The band gap of the film was The band gap of the film was The band gap of the film was The band gap of the film was The band gap of the film was The band gap of the film was The band gap of the film was The band gap of the film was The band gap of the film was The band gap of the film was The band gap of the film was The band gap of the film was The band gap of the film was 3.96 eV. For n-ZnO: Al, deposition was done at a temperature of 400 o C, carrier gas pressure of 1.5 bars, nozzle substrate distance of 4.5cm. Aluminium doping atomic percent of 2.42 %. Solid spectrophotometer DUV 3700 was used to obtain the transmittance data. The average transmittance was found to be between 82% - 89% in the visible range. The films had resistivity of the order 10-1 Ωcm and a band gap of a band gap of a band gap of a band gap of a band gap of a band gap of a band gap of a band gap of a band gap of a band gap of a band gap of 3.71eV. The p-n junction of p-SnO2:Al and n-ZnO:Al that was fabricated had a turn-on voltage of 0.6V with a maximum current of 0.75μA at 4 V. These results show that films of p-SnO2:Al and n-ZnO:Al can be used in opto-electronic devices such as light emitting diodes (LEDs).
Characterization of Radiation Protection X-Ray Beam for Secondary Standard Dosimetry Laboratory at Kenya Bureau of Standards
(kenyatta University, 2021) Omondi, Collins; Nadir O. Hashim; David Otwoma
The need for specification of X-ray beam quality arises from the fact that several parameters are required to realize and measure operational quantities accurately. X-ray measurements are affected by target material, tube potential, monitor chamber, absorber material and thickness, collimation shape, calibration factors and the source-chamber distance. The aim of this research is to analyze the performance of X-ray source (dosimetry) by indirectly specifying the radiation beam quality and quantity through measurements of half value layer (HVL), homogeneity coefficient and air-kerma. The work involve determination of quality of X-ray of photon field, physical characteristic and calibration radiation protection equipment. The air kerma quantity is useful for calibration of reference photon radiation fields and calibration of radiation protection instruments. Ionization chamber is used as primary reference instrument for ionizing radiation measurement. The reference ionization chamber is connected to an electrical electrometer and is capable of accurately measuring charge. The corrections are applied to account for the effects of air pressure, air temperature, ionic recombination and other influence parameters. The measurements were carried out at the Secondary Standard Dosimetry Laboratory (SSDL) at Kenya Bureau of Standards (KEBS). The X-ray beam were generated from bombardment of tungsten anode, at tube voltages between 40-200 kV, for radiation protection level. The investigation were done following inter-comparison measurements that showed variation of results in operational quantities at KEBS facility. Different HVL X-ray beams measurements results were obtained by introducing various filters across the beam and compared to international standard, ISO 4037-1, 2019. The operational quantities and physical properties were then established and used to calibrate survey meter. Uncertainty of measurement was then tabulated after identification of parameters that contribute to measurement errors. The homogeneity coefficient results were found to be consistent with ISO 4037-1, 2019 recommendations. However errors and inconsistencies were found in beam qualities, operational quantities and physical characteristics. The calibrated survey meter had a relative error of 10%, and therefore calibration factor was derived for error correction. Three beam qualities errors namely N-40, N-80 and N-200 were found to be outside the permissible range of 5% limit. Therefore, it is recommended that the beam errors be minimized within the required range and radiation protection equipment be issued with correction factors after calibration for rectifying of errors.