Department of Physical Sciences

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Radiometric assessment of natural radioactivity levels around Mrima Hill, Kenya
(International Journal of the Physical Sciences, 2011-07) Kebwaro, Jeremiah Monari; Rathore, I.V.S.; Hashim, N.O.; Mustapha, A.O.
Mrima Hill, located in the South coast of Kenya is known for high natural background radiation, due to the presence of radiogenic heavy minerals such as monazites and carbonatites. The activity concentration of 238U, 232Th and 40K in soil samples from the hill have been determined by gamma ray spectrometry using NaI(Tl) detector and decomposition of measured gamma-spectra. As a measure of radiation hazard to the public, gamma radiation dose rates were also estimated. The average activity concentrations of 238U, 232Th and 40K were 207.0±11.3, 500.7±20.0 and 805.4±20.0 Bqkg-1, respectively. The mean absorbed dose rate in air is 440.7±16.8 nGyh-1 while the estimated annual average effective dose rate is 1.11±0.01 mSvy-1. The absorbed dose rate due to gamma radiation from naturally occurring radioactive materials is above the global average value of 60 nGyh-1 (UNSCEAR, 2000)
The Challenges of Using Lesson Plan Formats for Effective Teaching of Chemistry in Kisii District, Kenya
(Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS), 2012) Olunga, Maureen Stella
The study sought to review the state of the use of lesson plans by teachers in teaching Chemistry in six secondary school s of Mosocho Division of Kisii District, namely Cardinal Otunga, Mosocho Academy, Raganga, Kioge, Nyatieko and Nyabururu. The research tool used was the questionnaire. The respondents included the headteachers, the heads of the Science departments and Chemistry teachers and, therefore, three types of questionnaires were administered. The Chemistry teachers’ questionnaire sought information regarding the problems that teachers faced in preparing and using the lesson plans. The heads of science department’s questionnaire solicited for information regarding problems they faced in trying to see that teachers prepared and used the lesson plan, if Chemistry teachers in one school used more than one lesson plan format and the format that was found easier to use. The head teachers’ questionnaire was used to collect information on how they carried out their duty of seeing that teachers prepared and used the lesson plan in teaching chemistry. The head teachers also made comments concerning the use of the lesson plan in teaching chemistry. From the findings of the study, it was noted that most teachers used the columnar format and understood the importance of the lesson plan. However, some were completely unable to use the lesson plan. This shows that there is need to employ qualified teachers. The study contributes useful knowledge to scholars and other education stakeholders that may help in improving teachers’ effectiveness in their teaching of Chemistry among other science subjects.
Critical temperature and condensate fraction of a bose – einstein condensate trapped in a finite volume
(Centre for Info Bio Technology, 2014) Mukoya, AK; Sakwa, TW; Khanna, KM; Ayodo, YK; Sarai, A; Rapondo, BW; Namwitako, J
Bose - Einstein Condensation, BEC, of an ideal gas is investigated for a finite number of particles trapped in a harmonic potential. The values of the critical temperature for Rb-87, its condensate fraction and the energy per particle are determined. The maxima appear to increase with the number of particles due to the fact that a smaller system has a larger available effective volume which concurs with the behavior of the critical temperatures.
Independent Measurement of θ13 via Neutron Capture on Hydrogen at Daya Bay
(Physical Review, 2014) Kebwaro, Jeremiah Monari
A new measurement of the θ13 mixing angle has been obtained at the Daya Bay Reactor Neutrino Experiment via the detection of inverse beta decays tagged by neutron capture on hydrogen. The antineutrino events for hydrogen capture are distinct from those for gadolinium capture with largely diﬀerent systematic uncertainties, allowing a determination independent of the gadolinium-capture result and an improvement on the precision of θ13 measurement. With a 217-day antineutrino data set obtained with six antineutrino detectors and from six 2.9 GWth reactors, the rate deﬁcit observed at the far hall is interpreted as sin2 2θ13 =0.083 ± 0.018 in the three-ﬂavor oscillation model. When combined with the gadolinium-capture result from Daya Bay, we obtain sin2 2θ13=0.089 ± 0.008 as the ﬁnal result for the six-antineutrino-detector conﬁguration of the Daya Bay experiment.
Evaluation of permutite for removal of radiocobalt from nuclear wastewater
(Journal of Radioanal Nucl Chem, 2014-07) Zhao, Xianghai; Luo, Yong; He, Chaohui; Zong, Pengfei; Zhang, Kai; Kebwaro, Jeremiah Monari; Li, Kui; Fu, Baofeng; Zhao, Yaolin
A synthetic zeolite, commercially available as permutite was tested for removing radiocobalt from aque- ous solutions by sorption. The sorption process was studied as a function of contact time, pH, ionic strength and solid content by batch technique. The results revealed that the process is dependent on the pH and ionic strength under ambient conditions. The kinetic sorption was fitted well by a pseudo-second-order rate equation. The thermodynamic parameters (DH0, DS0, DG0) suggested that sorption behavior of Co(II) is a spontaneous and endothermic pro- cess. The study shows that permutite has excellent potential for disposal of wastewaters containing radiocobalt.
Developments of oil-free Bakelite resistive plate chambers for particle physics experiments
(Journal of Instrumentation; IOP Publishing, 2014-07) Zhang, Q; Lv, Z.; Zhang, J.; Xie, Y.; Qian, S.; Ning, Z.; Xu, J.; Guan, M.; Kebwaro, J.M.; Yan, J.; Xu, M.; Chen, Y.
In this paper, we sumarized a Bakelite Resistive Plate Chamber (RPC) with non-oil surface treatment. This type of RPC has been installed and run smoothly in BESIII Muon identification system and Daya Bay cosmic Muon veto system. Based on its good performances, it has been futher studied as the sensitive detector of a digital hadron calorimeter for measuring the energies of particles in a hadron jet and as a thermal neutron detector. In addition, since the bulk resistivity of Bakelite plates can be controlled, futher developments with low bulk resistivity are being undertaken to guarantee high rate capability in experiments.
Search for a Light Sterile Neutrino at Daya Bay
(PHYSICAL REVIEW LETTERS, 2014-07) Kebwaro, Jeremiah Monari
A search for light sterile neutrino mixing was performed with the ﬁrst 217 days of data from the Daya Bay ReactorAntineutrinoExperiment. Theexperiment’suniqueconﬁgurationofmultiplebaselinesfromsix2.9GWth nuclear reactors to six antineutrino detectors deployed in two near (effective baselines 512 m and 561 m) and one far (1579 m) underground experimental halls makes it possible to test for oscillations to a fourth (sterile) neutrino in the 10−3 eV2 < |∆m241| < 0.3 eV2 range. The relative spectral distortion due to electron antineutrinodisappearancewasfoundtobeconsistentwiththatofthethree-ﬂavoroscillationmodel. Thederivedlimits on sin2 2θ14 cover the 10−3 eV2 .|∆m2 41|. 0.1 eV2 region, which was largely unexplored.
Simulation of (16)O (n, p) (16)N reaction rate and nitrogen-16 inventory in a high performance light water reactor with one pass core
(Applied Radiation and Isotopes; Elsevier, 2014-12) Kebwaro, Jeremiah Monari; Zhao, Yaolin; He, Chaohui
The rate of activation of the isotope (16)O to (16)N in a typical HPLWR one pass concept was calculated using MCNP code. A mathematical model was used to track the inventory of the radioisotope (16)N in a unit mass of coolant traversing the system. The water leaving the moderator channels has the highest activity in the circuit, but due to interaction with fresh coolant at the lower plenum, the activity is downscaled. The calculated core exit activity is higher than values reported in literature for commercial boiling water reactors.
Evaluation of candidate materials for SCWR turbine and balance of plant shielding
(Progress in Nuclear Energy; ScienceDirect, 2015-03) Kebwaro, Jeremiah Monari; Zhao, Yaolin; He, Chaohui
Since the coolant leaving the SCWR core contains an assortment of radioisotopes, it is necessary to identify appropriate materials for shielding ex-core components. Photon attenuation characteristics, photo-neutron production capacity and cost effectiveness of candidate materials were investigated in this study. WinXcom computer code was used for attenuation studies while other properties were surveyed in literature. High Z materials (lead and tungsten) show excellent gamma attenuation properties however they are expensive and could be vulnerable to photo-neutron production if used for shielding turbines or the pressure vessel exit steam-line. Barite concrete which is a moderate attenuator could also be susceptible to photo-neutron production if used for shielding components with high Nitrogen-16 activity. Heavy concretes with iron aggregates on the other hand show fair attenuation and are not susceptible to photo-neutron production in the energy range of photons released from reactor water. In terms of cost, concretes are cheaper and easy to fabricate compared to high Z materials especially when a shield of intricate shape is required. Depending on the available space for the shield, heavy concretes would be the most appropriate materials for shielding the SCWR turbine and balance of plant. However in case of space limitation, their attenuation capacity can be enhanced by introducing high Z materials in reasonable proportions.
Design and optimization of HPLWR high pressure Turbine gamma ray shield
(Nuclear Engineering and Design; Elsevier, 2015-04) Kebwaro, Jeremiah Monari; Zhao, Yaolin; He, Chaohui
This work proposes the optimum gamma ray shield thickness around the HPLWR high pressure turbine for different occupancy periods in the turbine building. Monte Carlo method was employed in the design process and only radioactive nitrogen-16 was considered as the source of radiation. Five grades of concrete (ordinary, magnetite, heavy magnetite, steel magnetite and barite) were used as shielding materials. The isotope source term in the high pressure turbine was estimated by modeling the HPLWR three pass core in MCNP and tracking the inventory using a simple algorithm. The high pressure turbine was thereafter modeled in MCNP with a concrete shield arrayed in layers around it. The surface flux tally and ICRP74 dose conversion coefficients were employed to estimate the dose profile across the shield. For some shielding materials, exponential functions were fitted on the calculated data to extrapolate dose values beyond the model thickness. The optimum shield thickness was determined by comparing the calculated dose profiles with dose limit proposals in the IAEA standard (NS-G-1.13) on radiation protection considerations during nuclear power plant design. It was observed that with a 120 cm thick heavy concrete shield, the turbine building would be safe for most occupancy periods. However for ordinary concrete the shield would require some extension to guarantee safety. For very long occupancy (more than 10 person hours per week), magnetite shield may also require slight extension. It can therefore be concluded that the shield thickness recommended for BWR turbines (which operate on a direct cycle like HPLWR) could be sufficient for HPLWR if high density concretes are used.
New Measurement of Antineutrino Oscillation with the Full Detector Configuration at Daya Bay
(PHYSICAL REVIEW LETTERS, 2015-05) Kebwaro, Jeremiah Monari
We report a new measurement of electron antineutrino disappearance using the fully-constructed Daya Bay Reactor Neutrino Experiment. The ﬁnal two of eight antineutrino detectors were installed in the summer of 2012. Including the 404 days of data collected from October 2012 to November 2013 resulted in a total exposure of 6.9×105 GWth-ton-days, a 3.6 times increase over our previous results. Improvements in energy calibration limited variations between detectors to 0.2%. Removal of six 241Am-13C radioactive calibration sources reduced the background by a factor of two for the detectors in the experimental hall furthest from the reactors. Direct prediction of the antineutrino signal in the far detectors based on the measurements in the near detectors explicitly minimized the dependence of the measurement on models of reactor antineutrino emission. The uncertainties in our estimates of sin2 2θ13 and |∆m2 ee| were halved as a result of these improvements.Analysisoftherelativeantineutrinoratesandenergyspectrabetweendetectorsgave sin2 2θ13 = 0.084±0.005and |∆m2 ee| = (2.42±0.11)×10−3 eV2 in the three-neutrino framework.
Investigation of photoneutron and capture gamma-ray production in Pb and W under irradiation from 16N decay radiation
(Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms; Elsevier, 2015-09) Kebwaro, Jeremiah Monari; Zhao, Yaolin; He, Chaohui
Lead and tungsten are potential alternative materials for shielding reactor ex-core components with high 16N activity when available space limits application of concrete. Since the two materials are vulnerable to photonuclear reactions, the nature and intensity of the secondary radiation resulting from (γ,n) and (n,γ) reactions when 16N decay radiation interact with these materials need to be well known for effective shielding design. In this study the MCNP code was used to calculate the photoneutron and capture gamma-ray spectra in the two materials when irradiated by 16N decay radiation. It was observed that some of the photoneutrons generated in the two materials lie in the low-energy range which is considered optimum for (n,γ) reactions. Lead is more transparent to the photoneutrons when compared to tungsten. The calculations also revealed that the bremsstrahlung generated by the beta spectrum was not sufficient to trigger any additional photoneutrons. Both energetic and less energetic capture gamma-rays are observed when photoneutrons interact with nuclei of the two materials. Depending on the strength of the 16N source term, the secondary radiation could affect the effectiveness of the shield and need to be considered during design.
Anti-Pyretic Properties of Methanolic Bark Extracts of Terminalia brownii in Wistar Rats (Rattus novegicus)
(Journal of oJ Pharmacognosy & Natural Products, 2016) Mbinda, Wilton; Kasili, Sichangi; Mbiri, Jane W; Kisangau, Patrick D; Piero, Ngugi M
The conventional drugs used to manage fever are usually not affordable, not easily available and have adverse side effects. Alternative therapeutic agents, like medicinal plant derivatives, should therefore be developed because they have been reported to be more affordable, more readily available and have lesser side effects. Terminalia brownii is traditionally used to manage fever but this ethno-medicinal claim lacks scientific validation. The present study therefore evaluated the anti-pyretic activity of T. brownii in Wistar rats. Fresh bark samples of T. brownii were collected from Kitui County, Kenya. This study used 30 adult male Wister rats that were 2-3 months old and weighing 140-180 g was used for the experiments. Steam-distilled turpentine was the pyrogen used to induce pyrexia and Aspirin was used as the reference drug. The extract reduced the elevated rectal temperatures by between 1.15- 4.38% while aspirin reduced the elevated rectal temperatures by between 0.00-4.85%. The present study showed a significant dose-dependent anti-pyretic activity of methanolic bark extracts of T. brownii hence validating its folklore use as a fever remedy.
Anti-Pyretic Properties of Methanolic Bark Extracts of Terminalia brownii in Wistar Rats ( Rattus novegicus )
(J Pharmacogn Nat Prod, an open access journal, 2016) Mbinda, Wilton; Kasili, Sichangi; Mbiri, Jane W; Kisangau, Patrick D; Piero, Ngugi M
The conventional drugs used to manage fever are usually not affordable, not easily available and have adverse side effects. Alternative therapeutic agents, like medicinal plant derivatives, should therefore be developed because they have been reported to be more affordable, more readily available and have lesser side effects. Terminalia brownii is traditionally used to manage fever but this ethno-medicinal claim lacks scientific validation. The present study therefore evaluated the anti-pyretic activity of T. brownii in Wistar rats. Fresh bark samples of T. brownii were collected from Kitui County, Kenya. This study used 30 adult male Wister rats that were 2-3 months old and weighing 140-180 g was used for the experiments. Steam-distilled turpentine was the pyrogen used to induce pyrexia and Aspirin was used as the reference drug. The extract reduced the elevated rectal temperatures by between 1.154.38% while aspirin reduced the elevated rectal temperatures by between 0.00-4.85%. The present study showed a significant dose-dependent anti-pyretic activity of methanolic bark extracts of T. brownii hence validating its folklore use as a fever remedy.
Reproducibility of (n,γ) gamma ray spectrum in Pb under different ENDF/B releases
(Elsevier, 2016-02) Kebwaro, Jeremiah Monari
Radiative capture reactions are of interest in shielding design and other fundamental research. In this study the reproducibility of (n,γ) reactions in Pb when cross-section data from different ENDF/B releases are used in the Monte-Carlo code, MCNP, was investigated. Pb was selected for this study because it is widely used in shielding applications where capture reactions are likely to occur. Four different neutron spectra were declared as source in the MCNP model which consisted of a simple spherical geometry. The gamma ray spectra due to the capture reactions were recorded at 10 cm from the center of the sphere. The results reveal that the gamma ray spectrum produced by ENDF/B-V is in reasonable agreement with that produced when ENDF/B-VI.6 is used. However the spectrum produced by ENDF/B-VII does not reveal any primary gamma rays in the higher energy region (E > 3 MeV). It is further observed that the intensities of the capture gamma rays produced when various releases are used differ by a some margin showing that the results are not reproducible. The generated spectra also vary with the spectrum of the source neutrons. The discrepancies observed among various ENDF/B releases could raise concerns to end users and need to be addressed properly during benchmarking calculations before the next release. The evaluation from ENDF to ACE format that is supplied with MCNP should also be examined because errors might have arisen during the evaluation.
Anti-inflammatory properties of methanolic bark extracts of terminalia Brownii in wistar albino rats
(Innovare academic sciences pvt ltd., 2016-06) Wilton, Mbinda; Wanja, Mbiri J.; Sichangi, Kasili; Kisangau, Patrick; Ngugi, M. Piero
Evaluation of In vivo Toxicity of Methanolic Leaf Extract of Vernonia lasiopus (O. Hoffman)
(Journal of Pharmacognosy & Natural Products, 2017) Mbinda, Wilton M; Ngugi, Mathew P; Koech, Samson C; Muthoni, Beatrice G; Musila, Michael N
The main objective of this study was to evaluate the in vivo toxicity of methanolic leaf extract of Vernonia lasiopus. To provide information on the safety of V. lasiopus, we evaluated its acute and sub-chronic toxicity in Wistar rats. For evaluation of acute toxicity of the plant extract, five Wistar rats were orally dosed with 2000 mg/kg body weight sequentially. Sub-chronic toxicity was tested in twenty Wistar rats using three extract doses 100, 300 and 1000 mg/kg body weight. They were orally administered for 28 days. Mortality and toxicity signs were monitored during the study period. At the end of the experiment, the animals were sacrificed, their internal organs weighed and blood samples collected for haematology and biochemical analysis. In acute toxicity, no single death was reported; leading to conclusion that the median lethal dose (LD50) of methanolic leaf extract of V. lasiopus is beyond 2000 mg/kg body weight. In sub-chronic toxicity studies, V. lasiopus lowered total proteins in all the study groups significantly. Albumin was also lowered at extract dose of 1000 mg/kg body weight. In addition, it resulted to significant neutropenia, lymphocytosis and thrombocytosis in the group administered with dose extract of 1000 mg/kg body weight (P˂0.05). It was therefore concluded that methanolic leaf extract of V. lasiopus is safe for use when administered at therapeutic doses. The plant extract may also be useful in the management of haematological disorders especially thrombocytopenia.
Hydromagnetic Turbulent Flow Between Two Parallel Infinite Plates
(Science Journal of Applied Mathematics and Statistics, 2017) Karimi, Kennedy John Mwangi; Kinyua, Dickson Kande
In this study we shall investigate hydromagnetic turbulent unsteady flow of an incompressible electrically conducting fluid between two parallel infinite plates. The flow variables such as velocity and thermodynamic properties at every point of fluid vary with respect to time. The effect of an applied transverse magnetic field normal to the main flow direction on the dynamic behavior of the fluid when the lower plate is stationary and the upper plate is impulsively started in opposite direction at constant velocity shall be investigated. Further, we shall investigate how the various parameters such as Peclet Number and Eckert Number affect the flow; in particular, velocity and temperature profiles. A finite difference method shall be used to solve the coupled non-liner and dimensionless partial differential equations governing this problem
Water Resources and Management under Increasing Urban Demography: A Kenyan Perspective—A Review
(Journal of Water Resource and Protection, 2018) Ondigo, Deziline Adhiambo; Kebwaro, Jeremiah; Kavoo, Agnes Mumo
The United Nations classifies Kenya as a water-scarce country since it has less than 1000 m3 per capita of renewable freshwater supplies. Numerous factors including global warming, contamination of drinking water, and a lack of investment in water resources have aggravated the water crisis in Kenya. Estimates indicate that only about 56% of its population has access to safe water supply. Like many developing countries, Kenya recognizes the crucial role of water in realizing its development goals. Its economic performance and poverty reduction are critically dependent on clean water availability for agriculture, industrialization, energy production and tourism among others. Similar to most developing countries, Kenya suffers from lack of human, monetary and institutional capabilities to efficiently provide clean and sufficient water to its citizens. The water shortage in the major cities is acute and chronic and has continued to worsen with increasing urbanization, water pollution and encroachment of water catchment areas by humans and invasive plant species. Despite the water challenges facing the urban populations, Kenya possesses sufficient water resources to meet demand if the available resources are properly managed. Several initiatives are being put in place in Kenya to mitigate the water challenges and protect water resources in Kenya. These include enacting of water policies to protect water catchment areas, reduce pollution and enhance access to clean water.
Validation of Popular Models used in the Analysis of Specific Activities of Primordial Radionuclides in Environmemtal Samples trough 1-D Analytical Modeling.
(Radiation Enviroment and Medicine, 2019) Kebwaro, J. M.; Chege, M. W.