Physics

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Electron Acceleration Mechanism and the Diffused Radio Emission in Galaxy Clusters
(Addis Ababa University, 2024-09) Hashim Jemal; Nagessa Tilahun (PhD)
The study of electron acceleration mechanisms in galaxy clusters is crucial for understanding the origin of diffused radio emission, which provides insights into the physical processes occurring in these massive cosmic structures. As massive structures in the Universe, galaxy clusters are sites of astrophysical processes that facilitate the acceleration of relativistic electrons. The diffuse radio emission, characterized by its synchrotron radiation. Our understanding of galaxy clusters, with implications for the broader study of cosmic evolution and large-scale structure formation is one of the fascinating topics Astrophysics. The extended diffuse radio emissions in clusters are referred to as halos, relics and mini halos. The numbers of these sources grown in recent years making them to discuss their properties and different models for their origin. The origin of these diffuse sources tightly connected to the process that leads to the cluster formation themselves.
The Role of Aerosols in the Earth's Atmosphere
(Addis Ababa University, 2024-09) Misanew Workye; Yitagesu Elfagd
In this project we have review the role of aerosols in the Earth's atmosphere. We considered an important source of aerosol particles in the atmosphere are the processes of physical and chemical interaction of substances, in particular the interaction of the main gas, and water vapour. In our work aerosol particles interact with sun radiation by reflection, scattering, or absorbing incoming radiation and the amount of reflection, scattering or absorbing we can explain the effect of aerosol in radiative transfer and also determine whether aerosol particles have a net warming or cooling effect on climate. This effect described by three related optical properties of aerosols. Aerosols play a crucial role in Earth's atmosphere, influencing climate, weather patterns, and air quality. These tiny particulate matter, which can be of natural or anthropogenic origin, act as cloud condensation nuclei, facilitating cloud formation and impacting precipitation processes.
Diffuse Radio Emission in Galaxy Clusters Insights With Primary Electron Model
(Addis Ababa University, 2024-09) Yadessa Chewaka; Negessa Tilahun
Diffuse extended radio sources are found as the number of galaxy clusters increases. The radio emission reveals the presence of cosmic rays and magnetic fields in the ICM. The relativistic electrons undergo diffuse radio emission and lose their energy via inverse-Compton and synchrotron losses in a short time, typically having lifetimes of about 0.1 Gyr. They could last for Gyr if significant re-acceleration is involved. Diffuse cluster radio sources are classified into radio halos, cluster radio shocks (relics), and revived AGN fossil plasma sources. This study summarizes the properties of diffuse cluster radio sources, providing significant insights and provides key insights into the complex interplay between relativistic electrons and the surrounding environment, enhancing our learning of cosmic structure formation.
Electrical Properties of two Hours Treated 4T1 Breast Cancer Cells and Effect of Magnetic Beads on Ionization of BT20 Breast Cancer Cells Using Optical Twezeers
(Addis Ababa University, 2024-09) Guta Korsa; Endris Mohammed
Study was undertaken to introduce the novel optical tweezers method for exploring the electrical charge developed and trap coefficient of pre-ionized 2 hour treated 4T1 breast cancer cells and to assess how magnetic beads affect the ionization properties of BT20 breast cancer cells. Specifically, the research focused on 4T1 breast cancer cells, which had been treated with the chemotherapy drug DMDD extracted from Averrhoa carambola L., and BT20 breast cancer cells mixed with 3.1 μm diameter polymer-coated magnetic beads. The trapping was achieved using an infrared diode-pumped Nd:YVO4 laser with a wavelength of 1064 nm, maximum output power of 8W, beam diameter of 4 mm, and a highly focused, linearly polarized beam. In experiments with the pre-ionized 2 hour treated 4T1 breast cancer cells, we recorded the following average values; the charge generated on cells in Z-numbers of 432.60±688.77, angular frequency of 72.12±30.12 rad ⁄s and trap coefficient of 8.32±4.55 un/m. As the cells approached to the center of the trap, their motion was influenced by the opposing of the drag force and the electrostatic force generated by the induced electric field, that resulted in their deceleration. When magnetic beads inserted in BT20 breast cancer cells they affected their ionization characteristics as the cells stayed in the trap.
Investigation of the Propagation of Light in Spheroidal Core-Shell Nanoparticles with Passive and Active Dielectric Cores
(Addis Ababa University, 2024-05) Tolasa Tamasgen; Belayneh Mesfin
Nonlinear optics (NLO) is the study of the interaction of intense laser light with matter. In the last few years, a great deal of progress has been made in our comprehension of nonlinear polarization mechanisms and how they relate to the structural properties of materials. In our work, we studied the eﬀects of depolarization factor (L), metal fraction (p), permittivity of the host matrix (εh) and interfacial layer on the local ﬁeld enhancement factor (LFEF), induced optical bistability (IOB), and bistability domain (BD) of spheroidal core-shell nanocomposites (NCs) embedded in passive or active dielectric cores. Solving Laplace’s equation in the quasistatic limit, we obtained expressions of the electric potentials in the various regions of the NCs. Then, by introducing L and the Drude-Sommerfeld model into these expressions, we derived the equation of LFEF in the core of the NCs and studied their IOB as well as BD, theoretically and numerically. The results show that (i) ﬁrstly, whether L, p, and/or εh vary or kept constant, the LFEF of the spheroidal core-shell NCs possesses two sets of peaks with passive dielectric core, whereas there is one set of peaks with active dielectric core. In NCs with passive dielectric core, an increase in any of these parameters resulted in a more pronounced LFEF peaks in the ﬁrst set of resonances. With both passive and active dielectric cores, increasing L increases the peaks of LFEF, whereas increasing p decreases the peaks of LFEF of the same material with active dielectric core. Moreover, the highest peak of LFEF is obtained by increasing L than p or εh indicating that changing the geometry of NCs has the highest eﬀect on the LFEF. Equally increasing εh, intensities of LFEF of the NCs decrease, when the dielectric core is passive and increase when the dielectric core is active. (ii) Secondly, the study reveals that when L decreases, the bistable region of IOB of the NCs increases. However, when p increases at constant L and εh, the bistable region gets wider. When εh increases, the IOB region is achieved at larger values of the incident ﬁeld. Also, the IOB produced was narrower in the passive dielectric core than in the active one, showing that the type of core material also inﬂuences the IOB of the NCs. Moreover, when L changes, the region of BD also changes in both types of cores, while changing p or εh in both types of cores causes the BD to vanish or emerge. (iii) Thirdly, a system consisting of metal/dielectric spheroidal NCs with interfacial layer (I), the LFEF increased successively in the given frequency range with a single peak with an increase in thickness. Consequently, the LFEF in the passive medium is red-shifted with no appreciable change in peak magnitude as the radius (r) increases, whereas the LFEF in the active host medium increases. We also studied the possibility of LFEF increasing in passive and active dielectric host matrices as p grows. In brief, the LFEF, IOB, and BD in each core are sensitive to changes in the values of L, p, and εh. Hence, varying these parameters leads to the possibility of tuning the domains of the LFEF, IOB, and BD, which can be employed in potential applications such as optical sensing, nonlinear optics, and quantum optics.
Quantum Statistical Description of Thermal Radiation
(Addis Ababa University, 2024-11) Misahun Assefa; Yitagesu Elfagd
In this project we have studied and presented a review of the quantum statistical description of thermal radiation that o ers a comprehensive framework for understanding the emission and absorption of electromagnetic radiation from a microscopic perspective. This approach integrates principles of quantum mechanics and statistical mechanics to describe how radiation interacts with matter and how it is distributed across di erent frequencies or wavelengths. At the core of this description is the concept of photons quantized packets of energy whose distribution follows Bose-Einstein statistics due to their bosonic nature. Plancks law was pivotal in the development of quantum theory, as it introduced the concept of quantized energy levels to explain the observed spectral distribution, resolving the "ultraviolet catastrophe" predicted by classical physics. Together, the Stefan-Boltzmann law and Plancks law form the foundational principles of thermal radiation.
Synthesizing, Characterizing and Studying Structural and Optical Properties of Pure a: PbO, Sn: a: PbO, and Co: a: PbO Prepared by Co-Pricptation Method
(Addis Ababa University, 2024-08) Alehegn Bazezew; Fekadu Gashaw
In this study, undoped α-PbO and α-PbO nanoparticles doped with tin (Sn) and cobalt (Co) were synthesized using a co-precipitation technique. Characterization through XRD confirmed that the nanoparticles had a tetragonal α-PbO crystal structure, with average crystalline sizes ranging from 12.18 nm to 41.33 nm for Co and Sn doping. Reflectance spectroscopy showed that pure PbO had higher reflectance compared to Sn:α-PbO and Co:α-PbO. The optical band gaps were 1.86 eV for α-PbO, 2.86 eV for Sn:α-PbO, and 1.46 eV for Co:α-PbO, indicating a decrease in band gap with Co doping due to defect levels introduced by Co and Pb ions. Sn:α-PbO had a larger band gap than both pure PbO and Co:α-PbO. Photoluminescence studies showed lower emission for doped nanoparticles, indicating reduced electron-hole recombination. SEM revealed an average nanoparticle diameter of 5.50 nm for α-PbO, increasing to 7.8 nm with Sn doping. EDX analysis showed atomic percentages of Sn:α-PbO and Co:α-PbO as 0.63:55.15:44.22, respectively.
Momentum, Heat, and Mass Transport by Molecular Diffusion
(Addis Ababa University, 2024-10) Abraham Kebede; Yitagesu Elfagd
In this project we have presented a review of momentum, heat, and mass transport by molecular diffusion that takes place near interfaces and boundary layers. Specifically, we considered the thermodynamics of fluids, conductive heat and momentum transport mechanism by molecular collision, thermal conductivity and heat equation. Moreover, diffusive transport mechanisms and the associated uxes, coupled Heat and Mass Transport by Molecular Diffusion, and the equations that describe them. Fluid ow is governed by a coupled nonlinear system of partial differential equations. However, in many practical situations, the calculation of friction or energy losses in conduits, or the heat and mass transport at interfaces can be greatly simpli ed by using so called transport coefficient. These coefficients, which are based on analytical solutions are typically gathered as correlations based on dimensionless numbers.
Study of Natural Radioactivity Levels in Environmental Samples (Building Materials) in Dejen District, East Gojjam, Ethiopia
(Addis Ababa University, 2023-12) Gizachew Zihon; Tilahun Tesfaye
All materials derived from rock and soil contain varying levels of natural radioactive isotopes such as 238U and 232Th and their decay products as well as 40K. Therefore, whether willingly or unwittingly, humans are constantly exposed to radiation emitted by radionuclides. The purpose of this study is to determine the levels of naturally occurring radioactivity and their risk indices in raw gypsum, soil samples, and building-related raw materials (sand, limestone, clay, gypsum, pumice, and coal used in cement production) in East Gojjam, Dejen district, Ethiopia. Raw gypsum samples were collected from the production site of five gypsum factories, while soil samples were collected from agricultural and virgin lands. Raw building materials that are used for cement production were also collected from cement factories. All the samples were prepared and packed for measurement using standard methods [1]. The specific activities of 238U, 232Th, and 40K were computed using a p-type, coaxial, Canberra High Purity Germanium (HPGe) detector. The detector is used in conjunction with a multichannel analyzer that features an analog-to-digital converter for data acquisition and Genie 2000 multichannel analyzer software with 8192 channels to analyze spectra. In raw gypsum samples it was determined that 238U, 232Th, and 40K are found, with mean specific activities of 1.90 _ 0.33, 1.99 _ 0.39, and 28.16 _ 2.57 Bqkg􀀀1, respectively, which are significantly lower than the intercontinental approved values. All the radioactive risk indices calculated were significantly lower than the global recommended values. The results of various radioactive indices show that using gypsum powder obtained from studied samples in the construction of residences is safe. The calculated mean activity concentrations of 226Ra, 232Th, and 40K in agricultural soils were 33.44 _ 2.01, 66.02 _ 4.54, and 214.16 _ 8.90 Bqkg􀀀1, respectively, while in virgin soils they were 38.05 _ 2.48, 61.78 _ 4.76, and 240.32 _ 10.79 Bqkg􀀀1, respectively. The findings were discussed and compared to those of other studies. The mean values of absorbed dose rate, annual effective dose rate, radium equivalent activity, external hazard index, internal hazard index, radioactivity level index and excess lifetime cancer risk in agricultural land soils are 67.24 nGyh􀀀1, 0.083 mSvy􀀀1, 144.57 Bqkg􀀀1, 0.39, 0.48, 1.03 and 0.29_10􀀀3, and in virgin land soils are 67.53 nGyh􀀀1, 0.082 mSvy􀀀1, 144.90 Bqkg􀀀1, 0.39, 0.49, 1.03 and 0.29_10􀀀3, respectively. These results were compared and contrasted to the internationally recommended value. The activity concentrations of 226Ra, 232Th, and 40K, as well as their radiation risk indices, were measured in raw material samples (sand, limestone, clay, gypsum, pumice, and coal) used in cement production. 226Ra, 232Th, and 40K activity concentrations in the tested samples ranged 4.90 _ 0.49 to 37.43 _ 2.57, 2.97 _ 0.42 to 72.08 _ 5.53, and 2.58 _ 1.28 to 208.78 _ 9.70 Bqkg􀀀1, respectively. For 226Ra, 232Th, and 40K, the clay sample had the highest activity concentration (37.33 _ 2.36, 71.06 _ 5.45, 208.66 _ 9.69 Bqkg􀀀1) and the gypsum sample had the lowest activity concentration (5.18 _ 0.55, 4.95 _ 0.61, 54.36 _ 3.40 Bqkg􀀀1). With the exception of clay samples for radium and thorium, these values are significantly lower than the corresponding worldwide mean values. The average results were compared to those of comparable studies conducted in other countries, as well as global average values. The received doses and radiological hazard characteristics were calculated and compared to global average values to determine the exposure risk associated with the use of these raw materials. Except for the increased lifetime cancer risk, the mean total estimated radiation hazard indices are below the recommended limits. This study demonstrated that the evaluated samples for raw gypsum; raw materials used in cement production and soil samples used in building construction are safe for residents and those involved in agricultural activities, and no additional radiological health risks are present in any of the studied samples.
Plasmonic Effects and Optical Properties of Core-Shell Nanoparticles
(Addis Ababa University, 2023-05) Garoma Dhaba; Belyaneh Mesfin; Teshome Senbeta
The applications in the real world require specific sizes, shapes, compositions, and structures. Hence, this dissertation is devoted to the theoretical and numerical investigations of the effects of size, shape, surface plasmons, and host medium on the optical properties of core-shell nanocomposites (NCs). Under the quasi-static approximation, we employed Laplace’s equation and the Drude-Lorentz model for electric potential distributions and dielectric functions, respectively. Then we calculated the local field enhancement factor (LFEF), polarizability, absorption, scattering, and extinction cross sections for spherical, cylindrical, prolate, and oblate core-shell NCs. The study reveals that when the core radius of spherical CdSe@Ag decreases, the resonance peaks of LFEF increase and are red shifted in the inner interface and blue-shifted in the outer interface of the shell. However, whether the shell radius is kept constant or decreased, increasing the core size produces a lower LFEF, showing that the core size is a crucial parameter to change the LFEF of nanoshells. Furthermore, an increase in the size of the core results in an increased resonance peaks of LFEF only in the presence of the spacer (ZnSe) between the core (CdSe) and the shell (Ag), demonstrating that the number of layers and the size of the spacer of core-shell NCs can affect the optical characteristics. When the metal shell thickness increases at a constant core radius, an enhancement in the local field factor is observed due to plasmonic effects. In addition, out of the four different shapes of CdSe@Au core-shell NCs studied, the LFEF, absorption, and extinction cross sections of the spherical and cylindrical structures possess two peaks, whereas oblate and prolate spheroids show three observable peaks. Moreover, the spherical and cylindrical core-shell NCs show higher peaks of LFEF and extinction cross sections, respectively. For the same composition, the differences in shapes of core-shell NCs determine the intensity, the number, and the positions of peaks of the LFEF and optical cross sections. The study also indicated that in different shapes of core-shell NCs, the change in the dielectric function of the embedding medium produces LFEF and extinction cross sections of different properties. Our analysis reveals that increasing the magnitude of the permittivity of the embedding medium greatly enhances the LFEF of nanoshells, than does increasing the metallic shell thickness. The possibility of obtaining adjustable LFEF by varying the sizes of the components of the core-shell NCs makes them attractive for applications in nonlinear optics, photocatalysis, and optoelectronics. Furthermore, shape dependent optical properties might be promising for applications in optical detection and bio-sensing. Especially, gold coated core-shell spheroids have good potential uses in multi-channel sensing.
Investigation the Effect of Nikel and Lithuim Dopping on the Structural and Optical Properties Pure Beta Lead Oxide Nanoparticles Prepared by Co Precipitation Techniques
(Addis Ababa University, 2024-08) Berhanu Muluneh; Fekadu Gashaw
The impact of doping pure beta lead oxide (β-PbO) nanoparticles, produced by co-precipitation methods, with nickel (Ni) and lithium (Li) on their optical and structural characteristics. Li doping causes lattice expansion and decreases dislocation density, while Ni doping causes lattice contraction and increases dislocation density, according to structural analysis. Ni doping enhanced and Li doping attenuated the photoluminescence in the 450-550 nm region, according to optical investigations, which showed small changes in band gap energy but considerable fluctuations in photoluminescence intensity. Scanning electron microscopy (SEM) was used to better clarify the morphological effects of the dopants. This study offers significant perspectives on modifying the characteristics of β-PbO nanoparticles for prospective uses in environmental sensing, optoelectronics, and catalysis. Future directions include for creating prototype devices, investigating various synthesis techniques, and working with business to commercialize the results.
Light Curve Characteristic of Gamma-Ray Burst
(Addis Ababa University, 2024-03) Temam Beyan; Feraol Fana
The long-lasting afterglow emissions, which shift from a higher energy X-ray band to a lower energy radio band, are produced by the interaction between the relativistic jet and the surrounding medium. Our understanding of afterglow, both theoretically and observationally, was fundamentally altered with the launch of the Swift satellite. One of Swift’s observational findings was the identification of an X-ray afterglow’s canonical behavior, in which the light curves generally comprise four different power law segments: initial steep decay, followed by a very shallow decay, a normal decay followed by late steep decay. Here we aimed to verify the consistency of our sampled Swift / XRT data with theoretically proposed canonical X -ray model. For this purpose, a sample of nine afterglow data randomly identified from Swift / XRT data catalogues that detected over the past ten to fifteen years. The data analysed using jupyter lab software, and various fitting parameters are generated and interpreted to justify our objectives. The results of temporal analysis show that, the dominant fraction (67%) of sampled data consistent with the shallow phase [0.5 < 2 < -1] and normal phase [1 < 3 < 1.5]. On the other hand, the analysis of data tells us, the majority of long afterglow GRBs (80 %) characterized by larger amplitudes, that indicates long afterglows associated with higher energy than short afterglows. Results of analysis also show, 67% of the sampled has R2 value nearly closer to 1, which implies the data distributed about best fitting line. Similarly, correlation coefficients of all the sampled range between -0.98 and -1.00, which indicates there is a strong negative relationship between the variables, and agreed with power law decay. Error bars on the top of histograms tell the fluctuation of photons count about mean value. On our histograms, fluctuation of photons in short GRBs afterglow higher than that of long GRBs, that ensures both classes from different sources.
Computational Study of Electronic Properties of Carbon-Homo Doped Silicene Monolayer
(Addis Ababa University, 2024-08) Desea Mamiru; Chernet Amente
Silicene, two dimensional form of silicon atom, has attractive considerable attention due to its promising applications in nanoelectronics. This study, investigates how doping carbons at different concentrations alters and improve its properties as well as intensify its applications. Inorder to investigate structural and electronic modifications produced by doping carbon atom in to silicene lattice, we use Density Functional Theory ( DFT). Our findings indicate that substituting carbon atoms leads to significant changes, starting with the emergence of a band gap at a dopant concentration of x = 0.22 in super cell of eighteen(18) silicon atoms. This transition converts silicene from a semimetal to a semiconductor. Furthermore, at both carbon dopant concentrations of x= 0.22 and x = 0.33, a direct band gap material is produced.The study provides understanding of how carbon doping influence the electronic properties of silicene, open the way for development of next generation technology.
Solar Variability: the Connection Between Solar Surface Magnetic Flux Density and Solar UV Variability
(Addis Ababa University, 2024-07-30) Mbonteh Roland; Negessa Tilahun
The strength of Solar surface magnetic flux plays an important role in the variability of solar UV irradiance. Several proxies of magnetic activity such as MgII, CaII, and f10.7 have been introduced to correlate solar UV irradiance variability. Daily weak flux densities (WFDs) during solar minimum in 2010 and solar maximum in 2014 calculated from the Solar Dynamic Observatory/Helioseismic Magnetic Imager was used. SSI measurements are from the Solar Stellar Irradiance Comparison Experiment (SOLSTICE). The influence of the magnetic flux density variation on the SSI has been characterized using Spearman, Pearson, and wavelet analysis. The Pear- son’s correlation shows that the SSI has a significant positive correlation with weak flux density (WFD) in 2010 and less in 2014; Spearman shows the same. Wavelet analysis also supports the idea that the WFD and SSI have a moderate causality linkage (in both 2010 and 2014) and that the WFD influences solar UV variability on the rotational timescale. The CWT also shows a significant correlation in 2010 than in 2014, while correlogram analysis follows suit and shows more sensitivity between SSI and CaII K lines, indicating a potential shift in solar activity mechanisms and signifying that other external factors are affecting solar activity.
Theoretical and Numerical Investigation of InAs/GaAs Quantum Dot Solar Cell to Improve the Power Conversion Effciency
(Addis Ababa University, 2024-05) Tewodros Adaro; Teshome Senbeta
The concept of introducing an intermediate band to overcome the e ciency limit of single-bandgap solar cells was proposed by Luque and Mart in 1997. It is predicted that utilising the intermediate band for multi-photon absorption can signi cantly improve the pho-tocurrent generation without accompanying output voltage loss. Quantum dots (QDs) have been proposed as a means for implementing intermediate band solar cells (IBSCs) to absorb low energy photons, due to their quantum con nement of carriers. The work reported in this thesis is concerned with the theoretical and numerical investigation of quantum dot solar cell (QDSC) using InAs QD multi-layers embedded in the i-region of a GaAs n+ 􀀀 i 􀀀 p+ structure. In particular, the dependence of QDSC parameters on the number of QD layers, QD size, and size dispersion and the impact of inserting InAs QD multi-layers in the middle subcell of Ga0:51In0:49P=GaAs=Ge triple-junction quantum dot solar cell (3J-QDSC). Numerical simulations show that, the solar cell parameters are strongly dependent on the number of QD layers, the average size and size dispersion of QDs. A maximum e ciency is obtained at optimum number of QD layers, QD size, and size dispersion. Above or below this optimal value degrades the e ciency of QDSC. The current density-voltage characteristics have been simulated and discussed for triple junction solar cell with and without InAs QD. Inserting InAs QDs increases the short circuit current and e ciency of 3J-QDSC (40.1% ) with small degradation in open circuit voltage. In general, inserting optimized size, size dispersion, number of InAs QD layers in the i-region of a GaAs solar cell as well as in the middle subcell of triple-junction Ga0:51In0:49P=GaAs=Ge solar cell improves both the short circuit current density and the eciency of the solar cell with a small degradation in open circuit voltage.
A Monte Carlo Study on a 3-Dimensional Comb Polymer Translocation Through a Nanopore Driven by an Electric Field
(Addis Ababa University, 2024-01) Bruh Tesfa; Tatek Yergou
A lattice Monte Carlo study of comb polymers translocation through a nanopore subject to an electric field is presented. Our approach is universal in a sense that we are not limited to single file translocations. Instead, we investigated single file translocations as a particular case in this universal approach. In this way, we have made an extensive study on the translocation dynamics of comb polymers as a function of field strength, pore size, and the comb polymer’s topology. We were able to show the existence of a critical field strength for any particular system. The difference between the most probable translocation time and the mean translocation time is minimum at the critical field strength. Also, the critical field strength helped us to identify two regimes of translocations with different properties. We named them as smooth and chaotic translocations. These results should also be valid for linear polymers because linear polymers are comb polymers without side chains. In addition, we took advantage of the side chains of comb polymers to study the pore-polymer interaction in an unprecedented way by varying the side chain lengths. This enabled us explain the varied values of _ in h_ i _ N_, where h_ i is the mean translocation time and N is the chain length of a linear polymer, in the literature.
First Principles Study of Novel Properties of Pristine and Carbon Supported Gax (X=P, As, Sb)
(Addis Ababa University, 2023-11) Demmilash Kassa; Kenate Nemera
Utilizing the most recent Density Functional Theory(DFT), the electronic struc- ture,optical properties, and new characteristics of pristine and carbon-supported GaX (X=P, As, Sb) in cubic zinc-blende (ZB) phase are investigated. For the purpose of predicting the ZB phase , the lattice parameters, bulk mod- ulus,cohesive energy , formation energy as well as energy band nature and band gap values, and optical properties were analyzed. Where accessible, the experi- mental data are quite compatible with our _ndings and results. As compared to the experimental data, our estimated values for the equilibrium lattice parameter, bulk modulus, energy band gap, cohesive energy, and formation energy. GaP, GaAs, and GaSb results were provided as 5.54 _A, 5.65 _A, 6.21 _A, and 77.3 GPa, 52.4 GPa, and 46.0 GPa respectively for lattice parameter values and bulk mod- ules, which are in good agreement with the experimental values. The computed cohesive energy and formation energy 1.43 eV, 3.74 eV,3.24 eV & -0.57 eV, 0,81 eV, -0.56 eV respectively, which are in a good agreement with the experimental values. Projector augmented-wave pseudo-potential (PAW) was used in the GGA,PBE, and DFT+U approximations to treat the interaction between the core and va- lence electrons for the minimal energy emerges. DOS and PDOS were analyzed in the electronic characteristics of the graphene/GaX (X=P, As, Sb) heterostructure from better charge. The _ndings indicate that there is charge transfer between graphene and GaX (X=P, As, Sb) and that the combination/junction is a conduc- tor with no band gap. The refractive index, optical conductivity, and refelectivity of the optical characteristics studied are in good agreement with the experimen- tal values. The most favorable adsorptions have adsorption energies in the range [-58.47,-17.07, 8.15]eV for a carbon adsorbate at 1 ML adsorbate coverage. With the adsorption of graphene, these values are in the range of [22.16,34.76, 48.63]eV. The fact that carbon has comparatively lower adsorption energies than graphene may mean that the two ions are more mobile in the electrolyte. Additionally, with higher fuel supplies, GaSb is a more favorable and reactive sur- face with the adsorbates as a result, it more accurately depicts the usual surface of the GaAs alloy. Each carbon atom appears to emit roughly 0.261e of charge, which contributes power to the system. Finally, since graphene's Dirac point is unaltered despite its adsorption on GaX, its interaction with GaX has no bearing on the signi_cance of its higher conduc- tivity excited electrons in hybrid systems are largely accumulated on graphene with energies between 0 and 3eV (versus Fermi energy). The calculations provide a theoretical defense for the e_cient performance of graphene/GaX hybrid mate- rials as photocatalysts and solar cells.
Evaluation of Reaction Cross-Section for Deuteron Induced Radioisotope [125I,62ZN,15o and 103PD] at Different Energy Ranges Using the PACE 4 CODE
(Addis Ababa University, 2024-06) Anteneh Getachew; Tilahun Tesfaye
This thesis work emphasize on theoretical evaluating reaction cross sections of deuteron induced nuclear reactions for the production of therapeutic radionuclide using PACE4 statistical model code , which is a code based on the statistical model of nuclear reactions. PACE4 statistical model code is used to calculate the theoretical nuclear cross section in the production processes of 125I, 62Zn, 15O and 103Pd, while experimentally decoded nuclear cross sections data of these radionuclide were taken from ENDF(Evaluated nuclear data file) IAEA database, to compute a reliable result, PACE4 statistical model code performed at level density parameter(K=8, K=10 and K=12 ) and the number of cascades(events in monte carlo calculation) is set at 100,000. The target radioisotopes are 124T, 63Cu, 14N and 103Rh are taken for the production of medical useful radioisotope 125I, 62Zn, 15O and 103Pd respectively. Deuteron energies ranging from 4.5MeV to 20MeV were considered for the production of 125I, 17MeV to 35MeV for the production of 62Zn, 1MeV to 20MeV for the production of 15O and energy range from 6.5MeV to 23.5MeV were considered for the production of 103Pd, and then experimental and theoretical outputs of nuclear cross sections of these radionuclide production were analyzed and compared. The maximum experimental and theoretical nuclear cross section computed at different energy range is stated below respectively: for 124T (d,n)125I reaction the maximum cross section at deuteron incident energy of 9.0MeV was 232 mb and 555 mb at 9.5MeV ( at K=12), for 63Cu(d,3n)62Zn reaction 50.5 mb at 33MeV and 63.9 mb at 31.5MeV ( at K=8), for the reaction 14N(d,n)15O the maximum cross section was 213 mb at 3.5MeV and 214 mb at 12.5MeV ( at K=12) and for the reaction 103Rh(d,2n)103Pd the maximum cross section was 1056 mb at 13.5MeV and 1390 mb at 18.5MeV ( at K=12). The PACE4 code slightly gives good agreement with ENDF determined excitation function at some computed radionuclide production considered under this study,while the rest results are unfitted with the ENDF data. It has been observed that complete fusion, incomplete fusion and pre-equilibrium emission processes play important roles in heavy ion reactions at these energies. The observed disagreement may be credited to the contribution from the incomplete fusion reaction, pre-equilibrium emission processes and light particle reaction is not well taken into account by PACE4 statistical model code.
The Effect of Anisotropy Field on the Dispersion Relation and Thermodynamic Properties of Antiferromagnetic Materials : Employing the Quantum Field theory
(Addis Ababa University, 2024-08) Desalegne Tefera; Chernet Amente
In this thesis, we look at the complex dynamics of spin waves in a two-sublattice antiferromagnetic (AFM) system, with an emphasis on spin interactions and the magnon dispersion relation. The main purpose of this study was to examine spin wave interaction and how anisotropy field influence on dispersion relation and characteristics of (AMF) systems. The theoretical framework is based on the Heisenberg Hamiltonian model, which was specifically built to manage a uniaxial anisotropy field within an antiferromagnetic system. To overcome the problem, we employ quantum field theory, namely the double-time temperature-dependent Green function technique to achieve magnon dispersion. A random phase approximation is used to decouple and diagonalize higher order components. The discovery of a relationship between the anisotropy field and the dispersion relation for the wave vector k at low temperatures is particularly interesting. The findings indicate that as the anisotropic field becomes stronger, the magnon dispersion progressively shifts from a curved trajectory to linearity, finally adopting a sinusoidal form with further expansion into the first Brillouin zone. Furthermore, we investigate the thermodynamic parameters of magnetization and heat capacity within the uniaxial symmetric AFM crystal lattice, concentrating on excitation temperature at low temperatures and utilizing the long-wavelength approximation. The results show that AFM magnetization and heat capacities are sensitive to anisotropic fields, with magnetization trending upward and the greatest peak of heat capacity dropping as anisotropy increased. The findings provide understanding of the complicated relationship between anisotropy and exchange fields in antiferromagnetic systems, indicating their significant impact on magnetization, heat capacity, and other thermodynamic parameters. Furthermore, this model gives information on the variations in susceptibility and heat capacity between transition metal antiferromagnetic fluorides. Further investigation may be necessary in this situation.
Measurement of Radioactivity Concentrations and Analysis of Radiation Hazards for Environmental and Industrial Samples Collected from Different Parts of Ethiopia
(Addis Ababa University, 2025-01) Yared Birhane; Tilahun Tesfaye
In this study, the activity concentrations of 238U, 226Ra, 232Th, and 40K in various environmental and industrial product samples were determined using a gamma detection system. The industrial samples analyzed included cement raw materials and finished products, while the environmental samples comprised soil samples and medicinal plants. The measured mean activity concentrations of 226Ra, 232Th, and 40K in the cement raw materials and products were found to be 21.1 ± 0.995, 53.2±2.9, and 304±13.8Bqkg−1, respectively. For soil samples from Mekelle City, the corresponding mean activity concentrations were 25.035±1.788, 53.091±4.22, and 371.34±14.26Bqkg−1, respectively. The mean specific activity concentrations of 238U, 232Th, and 40K in soil samples from the districts ofMenge, Sherkole, Assosa, and Bambasiwere determined as follows: for Menge, 24±1.2, 36.15±2, and 275.5±13.3Bqkg−1; for Sherkole, 35.14±1.77, 47.3±2.7, and 146±7.2Bqkg−1; for Assosa, 45.2±2.3, 70±3.8, and 238.8±11.6Bqkg−1; and for Bambasi, 61±3.2, 89.2±5.3, and 237.7±12.7Bqkg−1. Regarding the medicinal plants, the mean activity concentrations of 238U, 232Th, and 40K were found to be 7.82±0.04, 28.67±2.66, and 579.4±1.37Bqkg−1, respectively. The study also estimated the absorbed dose rate (D(nGyh−1)), the annual effective dose rate (E (mSvy−1)), the gamma index (Iγ), the hazard indices (Hex and Hin), and the excessive lifetime cancer risk (ELCR). Notably, the specific activity concentration of 40K in Moringa oleifera exceeded the recommended safe limit. Meanwhile, the measured mean radioactivity concentrations in the Mekelle soil, Messebo cement raw materials, and cement products were below the safe values of 35, 30, and 400 Bqkg−1 for 226Ra/238U, 232Th, and 40K, respectively. However, the mean concentrations in soil samples from the Assosa, Bambasi, Menge, and Sherkole districts exceeded these safe values. Consequently, such elevated concentrations pose potential health risks, and continuous monitoring is recommended.

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