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Archived Theses
Application of group theory to quantum information and quantum computation
The method of group theory leads to the very simple and elegant description of the synthesis of quantum information and quantum computation processes. For example reversible quantum logic gates can be analyzed by using group theory. It is known that quantum entanglement can be also formulated by using group theory. The algorithms for quantum computations can be constructed in the framework of hidden subgroup. The Quantum Fourier Transform which can be used to solve some logarithm problems also closely related to the hidden subgroup and finite groups. There is also an interesting link between SU(2) symmetry and quantum beam splitter transformation, as well as n-qudit systems and quantum codes. We also found some fingerprints of quantum entanglements- in exceptional groups such as E6, E7 and E8- generating by Quantum Gates and that concisely related with Clifford Groups, Coxeter Groups. During realization of Quantum Gates it is very important establishing connection between Coxeter Groups and qubit symmetries ( e.g. unitary transformation). We would like to mention here that formalism of quantum information and quantum computation lies in the clever use of group theory. We also point out that quantum information and quantum computation theory are young sciences but they are very fast moving and very popular because of their fascinating beauty. Consequently, all this group theoretical analysis would be worth to solve the complicated problems in quantum information and computation theory.
Application of variational method and supersymmetric technique to the fokker-planck equation
The time dependent probability density for the one-dimensional Fokker-Planck equation is determined by the variational method within the context of the Supersymmetric Quantum Mechanics. Using an ansatz function for the superpotential, one can obtain the trial wavefunctions of the variational method and then the construction of the hierarchy of the effective Hamiltonians allows us to obtain the variational eigenfunctions and energies of the excited states to the evaluation of the probability. The symmetric bistable potentials, whose energy eigenvalues are calculated for some potential parameters, are studied. The numerical results obtained in this study are in very good agreement with the eigenvalues obtained by numerical integration in previous studies. The error percent is also presented in all calculations.
Partitation of the excitation energy between the fission fragment in spontaneous fission of Cf252
in this thesis experimental data on mass distribution of fission fragments, kinetic energy distribution of fission fragments, neutron avaerage multiplicity distribution of fission fragments, and neutron average emission energy from fission fragments in spontaneous fission of Cf252 were analayzed in order to calculate correlation in neutron average number distribution and correlation in fission fragment average excitation energy distribution. To fulfill this task the most probable charge values for complementary light and heavy fragments in spontaneous fission of Cf252, neutron binding energy of fission fragments and the average gamma ray energy from fission fragments has been estimated. The average fission fragment excitation energy then is estimated. Results of calculations are in satisfactory agreement with corresponding experimental results.
Calculation of prompt neutron energy spectrum in laboratory system from spontaneous fission of Cf-252
In this work, we discuss the influence of the different forms of prompt fission neutron energy spectrums in the fission fragment center of mass system to the laboratory spectrum of neutrons in spontaneous fission of Cf-252. We show that the Le Couteur spectrum which takes into account multiple neutron emission of neutron emission of neutrons in the center of mass system well describes the observed neutron energy spectrum when transformed to the laboratory system. The Le Couteur in laboratory spectrum, in addition to Watt spectrum, can be used for the representation of observed prompt neutron spectrum of Cf-252 spontaneous fission.
Properties of electrodeposited metalic systems(Schottky diodes) on semiconductor substrates
In this study, by using n-type Si substrate with (100) orientation, 150 nm thickness and 10-20 ?m resistivity and chromium doped, thin film Schottky diode system (Cr/n-Si SBHs which is electrochemically formed on n-type Si) is constructed and characterized.In the electrical characterization of this diodes, the current ?voltoge (I-V) and the capacitance ? voltage (C-V) measurements are done.The basic diode parameters such as ideality factor (n) and barrier height (?b) were consequently extracted from electrical measurements. It has been shown that the ideality factors increased and barrier heights decreased with the decreasing temperatures, on the basis of the thermionic emission (TE) theory.The homogeneity or the uniformity of the Schottky BH is an issue with important implications on the theory of Schottky barrier formation and important ramifications for the operation of Schottky barrier diodes and contacts. Thus, provided semiconductor substrate is well characterized, the homogeneous Schottky BH may be obtained even from the I-V characteristics of one contact. For this purpose ,Cr/n-type Si SBHs with a doping density of about 1.25x1015 cm-3 is prepared and the linear region with large BHs is used. The electrical characterisitics of Cr/n-type structures were investigated in the wide temperature range (80-320 K) by steps of 20 K.Key words: Silicon, Schottky barrier diodes, Electrodeposition Method.
Thermal and optical characteristics of radiation induced defect centers in alkali Halide crystals (TLD-100)
Abstract Thermal and Optical Characteristics of Radiation Induced Defect Centers in Alkali Halide Crystals (TLD-100) " YAZICI Ahmet Necmeddin Ph.D. in P.E., University of Gaziantep Supervisor: Asst.Prof.Dr. Zihni öztürk October 1996, 168 Pages The exact cause of sensitivity loss in TLD LiF:Mg,Ti has not been completely understood yet. If a used TLD is not annealed at an elevated temperature prior to reuse, residual deep defect centers still present in dosimeter. These centers will interact with new incoming radiations and produce further centers. This will introduce significant errors in low dose measurements. If the structure, thermal and optical characteristics of these defects were better understood, then a better model could be proposed to overcome sensitivity loss. Therefore, the samples were, firstly, irradiated by p-rays to produce sufficient concentration of defect centers, then optical absorption, phototransferred thermoluminescence, and thermoluminescence measurements were made to identify defect structures in LiF:Mg,Ti with appropriate heat treatments. The changes in the optical absorption band and mglow peak areas were determined as a function of various heat treatments using a computerised deconvolution program. The similarities in the variation of curves of glow peak 5 and OA band at 310 nm suggest that they may be belong to the same traps, namely Mg-trimer/Ti complex. The lack of correspondence between peak 2 and 380 nm band indicates that peak 2 is not related to Mg-dipoles as previously suggested, but related to Ti-related/F- center complex. Deconvolution analysis of OA and glow curves produced by annealing at and above 125 °C for long times before irradiation permits the identification of a new peak at 1 75 °C and OA band at 282 nm. Due to their similar thermal decaying properties, it is thought that they may be belong to the Z2-type centers. The effects of pre-irradiation annealing on the values of trapping parameters of LiF:Mg,Ti were determined as a function of durations at 125 °C by computerized glow curve analysis. The application of pre-annealing with different durations made significant changes on the activation energies of peaks 1 to 5, especially of peak 4. These variations are due to the interactions of defects with each other during heat treatments. A new simple model was developed to describe TL emission bands of luminescent centers in solids. TL emission spectra measurements of LiF:Mg.Ti showed one main emission band at 420 nm. The individual emission bands were separated using the developed model to investigate the success of the developed model. According to this model, the emission spectrum of whole glow peaks can be successfully fitted with two emission bands. Keywords: Alkali halide, LiF:Mg,Ti, thermoluminescence, optical absorbance, emission spectra, trapping parameters. IV
Calculation of alpha half-lives of radiosotopes by using different techniques
AbstractCalculation of Alpha Half-Lives of Radioisotopes byUsingDi¤erent TechniquesSÜR, SerapM. Sc in Engineering PhysicsSupervisor: Prof. Dr. Zihni ÖZTÜRKJuly 2005The estimations and comparisions of alpha half-lives of alphaemitting isotopes of odd-odd, even-even, odd-even and even-odd nu-clei are made by using di¤erent methods. Tunnelling probabilitiesare determined by the breaking the Coulomb barrier into segments.The obtained succesive tunnelling probabilities are multiplied toobtain tunnelling probability utilized to determine alpha half-lives.The advantages and disadvantages of the model are discussed. Itis observed that an application of the simple model based on thetunnelling probability provides quite satisfactory results comparedto some other techniques.Key words: Alpha Decay, Tunnelling Probability, Half-life.1
The effect of various experimental parameters on glow peaks and TL kinetics of some dosimetric materials
Either natural fluride which contains, depending on its origin, a wide variety of different impurities acting as activators, or synthetic CaF2 as a host lattice with artificial dopants such as Tm, Dy, and Mn have been used as dosimeter. The samples used in this study were CaF2:Dy (TLD-200), CaF2:Tm (TLD-300) and CaF2:Mn (TLD- 400) crystal chips obtained from Harshaw Chemical Company, Ohio, USA. In this study we have investigated the effect of heating rate on the dose response and linearities of these samples by evaluating their supra / super linearity indexes, f(D) and g(D) respectively. Also the fading characteristics of the samples both in the dark and under tungsten filament lamp and the effect of heating rate on shape of the glow curves and total peak areas of the glow curves have been investigated in detail.Lithium triborate, (LiB3O5, LBO), is one of the most known lithium borates. It is a newly developed nonlinear optical crystal. In this work, the trapping parameters of Al- doped LiB3O5, synthesized in Middle East Technical University, were evaluated by using different experimental methods, namely; the additive dose repeated initial rise, variable heating rate, peak shape, isothermal decay, three points methods and the computerized glow curve deconvolution method.
Theoretical investigation of the effect of nitrogen on optical and electronic properties of GaInAsN semiconductors
The investigation of profound of nitrogen containing III-V semiconductors in fundamental properties proven experimentally and device applications and to propose new device materials are the aim of this thesis. We have presented an overview of the fundamental properties of nitrogen incorporated GaInAs semiconductor and the physics behind of unusual characteristics of GaInAsN. We have compared the band alignments of the nitrogen-free and nitrogen-included laser devices on GaAs and InP substrates. We have presented the calculations to investigate the role of N and Sb on the critical thickness hc of strained GaInAsNSb QWs on GaAs and InP substrate for (001) and (111) orientations.We have presented a new analytical method to investigate the effect of nitrogen on intrinsic carrier density, screening parameter, effective Bohr radius and binding energy of shallow donors in GaAsN alloys. We have investigated the relation between the binding energy of hydrogenic shallow donor in bulk GaAsN alloys for different screening parameter and nitrogen concentrations. We have investigated the refractive indices and the corresponding optical confinement factors of the proposed GaInAsN laser material systems on GaAs substrate. We have compared conventional and N-based quantum well laser systems to find which has better optical confinement.