Physics Commons^™

Investigation Of Defect Production And Displacement Energies In Wurtzite Aluminum Nitride, Sean Anderson

Masters Theses

"Aluminum Nitride is an active element of sensors that monitor the performance and well-being of the nuclear reactors due to its piezoelectric properties. Yet, the variations of its properties under irradiation are largely unexplored. We report the results of the molecular dynamics simulations of the structural changes in AlN under irradiation via the knock-on atom technique. By creating and evolving the irradiation cascades due to energetic particle interaction with the atom of the crystalline lattice we determine the rate of the defect production as a function of the deposited energy. Further, we determine a displacement energy, a key characteristic that …

Numerical Investigations Of 2-D Magnetic Nozzles On Pulsed Plasma Plumes, Joshua Daniel Burch

Masters Theses

"This research presents studies of a novel type of magnetic nozzle that allows for three-dimensional (3-D) steering of a plasma plume. Numerical simulations were performed using Tech-X's USim® software to quantify the nozzle's capabilities. A2-D planar magnetic nozzle was applied to plumes of a nominal pulsed inductive plasma (PIP) source with discharge parameters similar to those of Missouri S&T's Missouri Plasmoid Experiment (MPX). Argon and xenon plumes were considered. Simulations were verified and validated through a mesh convergence study as well as comparison with available experimental data. Periodicity was achieved over the simulation run time and phase angle samples were …

Particle Swarm Optimization For Critical Experiment Design, Cole Michael Kostelac

Masters Theses

“Critical experiments are used by nuclear data evaluators and criticality safety engineers to validate nuclear data and computational methods. Many of these experiments are designed to maximize the sensitivity to a certain nuclide-reaction pair in an energy range of interest. Traditionally, a parameter sweep is conducted over a set of experimental variables to find a configuration that is critical and maximally sensitive. As additional variables are added, the total number of configurations increases exponentially and quickly becomes prohibitively computationally expensive to calculate, especially using Monte Carlo methods.

This work presents the development of a particle swarm optimization algorithm to design …

Several Problems In Nonlinear Schrödinger Equations, Tim Van Hoose

Masters Theses

“We study several different problems related to nonlinear Schrödinger equations….

We prove several new results for the first equation: a modified scattering result for both an averaged version of the equation and the full equation, as well as a set of Strichartz estimates and a blowup result for the 3d cubic problem.

We also present an exposition of the classical work of Bourgain on invariant measures for the second equation in the mass-subcritical regime”--Abstract, page iv.

A Simple Background Elimination Method For Miniaturized Fiber-Optic Raman Probe, Bohong Zhang

Masters Theses

"Raman scattering is called a photonic - molecular interaction based on the kinetic model of the analytic. Due to the uniqueness of the Raman scattering technique, it can provide a unique fingerprint signal for molecular recognition. However, a serious challenge often encountered in Raman measurement comes from the requirements of fast, real-time remote sensing, background fluorescence suppression, and micro-environmental detection.

A new Miniaturized Fiber-Optic Raman Probe (MFORP) for Raman spectroscopy, used especially for eliminating background fluorescence and enhancing sampling, is presented. Its main purpose is to provide an overview of excellent research on the detection of very small substances and …

A Compact Wavelength Meter Using A Multimode Fiber, Ogbole Collins Inalegwu

Masters Theses

“Wavelength meters are very important for precision measurements of both pulses and continuous-wave optical sources. Conventional wavelength meters employ gratings, prisms, interferometers, and other wavelength-sensitive materials in their design. Here, we report a simple and compact wavelength meter based on a section of multimode fiber and a camera. The concept is to correlate the multimodal interference pattern (i.e., speckle pattern) at the end-face of a multimode fiber with the wavelength of the input lightsource. Through a series of experiments, specklegrams from the end face of a multimode fiber as captured by a charge-coupled device (CCD) camera were recorded; the images …

Characterization Of A Plasma Source Simulating Solar Wind Plasma In A Vacuum Chamber, Blake Anthony Folta

Masters Theses

"The United States has set an aggressive time line to not only return to the Moon, but also to establish a sustained human presence. In the Apollo missions dust was a significant factor, but the duration of those missions was short so dust and surface charging were problems, but they did not pose an immediate threat. For a long-term mission, these problems instead become incredibly detrimental. Because of this, research needs to be conducted to investigate these phenomena so that mitigation techniques can be developed and tested. To this end, this thesis serves to demonstrate the Gas and Plasma Dynamics …

Modulated Photothermal Radiometry: Detector Sensitivity Study And Experimental Setup, Jessica Nicole Seals

Masters Theses

"This thesis outlines the development of a system used for determining the surface thermal diffusivity of both non-irradiated and irradiated materials. The motivation for this work is to establish a modulated photothermal radiometry (PTR) system on the campus of Missouri University of Science and Technology. One of the main efforts described in this thesis is the design and construction of the physical apparatus. Along the way, it was necessary to perform a detailed sensitivity analysis of the system to determine whether the expected signal emitted from the sample falls within the bounds of detectivity for the HgCdTe (MCT) detector used …

Universal Wavefront Transmission Through Disordered Media, Jayson Robert Summers

Masters Theses

”When electromagnetic waves propagate through random dielectric media, they scatter in a predictable, deterministic way. The process is also fully reversible. If one sends an exiting wave backward through the same material, it will converge back to its original form and location in the same amount of time it took to originally propagate through the material. Due to this predictability, a great deal of research has went into studying these scattering processes in multimode fibers, diffusers, biological tissues, and other media. Scientists have turned random scattering material into focusing lenses, image transmitters, and highly transmitting media by controlling the impinging …

Customized Multi-Group Cross Section Generation With Njoy For Discrete Ordinates Computed Tomography And Radiography Simulation, Steven Michael Wagstaff

Masters Theses

"The purpose of this work was to explore the creation of photoatomic multi-group cross section libraries to be used with a software package DOCTORS (Discrete Ordinates Computed TOmography and Radiography Simulator). This software solves the linear Boltzmann equation using the discrete ordinates method [1]. To create these libraries, NJOY2016 was used, creating both fine and broad energy multi-group cross section files. The cross section's accuracy was tested against an equivalent Monte Carlo simulation using MCNP6.

Two simulation geometries were used. The first, a cylindrical water phantom with a single source projection placed in front, simulating an X-ray radiography. The second …

Developing Computational Models For Pulsed-Inductive Plasma Formation, Zachary Aaron Gill

Masters Theses

"Pulsed-inductive discharges are a common method of producing a plasma. They provide a mechanism for quickly and efficiently generating a large volume of plasma for rapid use and are seen in applications including propulsion, fusion power, and high-power lasers. However, some common designs see a delayed response time due to the plasma forming when the magnitude of the magnetic field in the device is at a minimum. New designs are difficult to evaluate due to the amount of time needed to construct a new geometry and the high monetary cost of changing the power generation circuit. To more quickly evaluate …

A Study Of The Potential Applications Of Am241, And Determining The Feasibility Of Using Gamma Spectroscopy For Future Physical Validation, Eric A. Feissle

Masters Theses

“Am241 is typically produced via Pu241 decay in a uranium fueled reactor. Presence of Am241 can be used as the age estimation tool for spent fuel, which is a focus of this thesis along with the interest of the measurement and the ratio of production rates of Am241’s activation products; Americium-242 and its first excited state of Americium-242m. MCNP models of the core and BEGe 3825 detector were built. These models were compared with established and physical measurements of gamma/x-ray standards that were available at the reactor. Thermal fluxes at 200 kW for potential foils centered in the source holder …

A Feasibility Study Of A Nuclear Power Plant With No Moving Parts, Jonathan Mark Schattke

Masters Theses

"In a nuclear reactor design, every moving part in a system is considered a failure point. In this study, a proposal is made for designing a nuclear reactor that has no moving parts by coupling an accelerator driven core (removing control system moving parts) to a magnetohydrodynamic generator (removing power generation moving parts) using mercury coolant (removing pumping system moving parts). Further safety is realized by using a subcritical core, where the core is never able to sustain a chain reaction on its own, obviating many safety systems. The design is verified with a Monte Carlo simulation "--Abstract, page iii.

Attenuation Properties Of Cement Composites: Experimental Measurements And Monte Carlo Calculations, Raul Florez

Masters Theses

"Developing new cement based materials with excellent mechanical and attenuation properties is critically important for both medical and nuclear power industries. Concrete continues to be the primary choice material for the shielding of gamma and neutron radiation in facilities such as nuclear reactors, nuclear waste repositories, spent nuclear fuel pools, heavy particle radiotherapy rooms, particles accelerators, among others. The purpose of this research was to manufacture cement pastes modified with magnetite and samarium oxide and evaluate the feasibility of utilizing them for shielding of gamma and neutron radiation. Two different experiments were conducted to accomplish these goals. In the first …

Intensity Control Of Dielectric Barrier Discharge Filaments, Matthew Crawford Paliwoda

Masters Theses

"When operated in a filamentary mode, a volume dielectric barrier discharge (DBD) is known to produce patterned plasma structures. These structures are currently being explored for reconfigurable metamaterial applications. In this work the presence and intensity of a single filament, within an array of filaments, was controlled by adjusting the voltage to that filament's individual needle electrode. The current, voltage, and time-averaged normalized light intensity were measured while varying the voltage of the needle through a self-biasing resistance. For a 7.5 kV, 3.2 kHz DBD in air, the needle-controlled filament intensity varies from that of the surrounding filaments to zero …

Microwave Assisted Reconstruction Of Optical Interferograms For Distributed Fiber Optics Sensing & Characterization Of Pcb Dielectric Properties Using Two Striplines On The Same Board, Lei Hua

Masters Theses

"A new concept, the microwave-assisted reconstruction of an optical interferogram for distributed sensing, was developed to resolve both the position and reflectivity of each sensor along an optical fiber. This approach involves sending a microwave-modulated optical signal through cascaded fiber optic interferometers. The optical spectrum of each sensor can be reconstructed by sweeping the optical wavelength and detecting the modulation signal. A series of cascaded fiber optic extrinsic Fabry-Perot interferometric sensors was used to prove the concept. The microwave-reconstructed interferogram matched well with those recorded individually from a traditional optical spectrometer. The application of distributed strain measurement was also investigated. …

Novel Transparent Conductive Materials: Understanding And Prediction, Yaou Song

Masters Theses

"Transparent conductive oxides (TCOs) such as doped In₂O₃, ZnO, SnO₂ or CdO are highly attractive due to their special properties, which are electrical conductivity and optical transparency. The lack of complete understanding of the fundamentals behind this unique phenomena and rapidly increasing commercial demand draw a lot of interest in investigating this kind of materials. More efficient, environmentally friendly and less expensive transparent conductive materials are needed for a variety of applications, and a general understanding of the origins of the unusual behavior would help further search for potential transparent conductive (TC) candidates. Understanding the basic properties of conventional TCOs …

Model Correction For The Formation Of Amorphous Silicon By Ion Implantation, John Robert Dennis

Masters Theses

"ESR has been used to study the formation of an amorphous layer in silicon by ion implantation. The room temperature implants were done at 20 keV with low dose rates. The critical dose was determined as a function of ion mass for six different ion species. Our experimental heavy ion results agree with those found by other ESR investigators at higher energy, but are not the same for light ions. However, our light and heavy ion results agree with electron microscope measurements for low energy implants. An energy-independent model for the formation of amorphous silicon by ion implantation has …

The Design And Calibration Of A Vibrating Sample Magnetometer, Donald Dwight Hoffman

Masters Theses

"The design and calibration of a vibrating sample magnetometer is described. The sample motion was in the direction of the external magnetic field which was produced by a superconducting solenoid. The maximum external magnetic field was 70 kilogauss. Sample temperature could be varied from 77°K to 1000°K with a vacuum jacketed furnace. The maximum temperature was obtained with approximately 27 watts. The instrument was calibrated to 1% with a spherical nickel sample"--Abstract, page ii.

The Contribution Of Phonon-Induced Tunneling To Donor Esr Spectral Narrowing In Semiconductors, David Lawrence Meier

Masters Theses

"The narrowing of donor electron spin resonance spectra with increasing donor concentration N_D and increasing temperature T has been observed in semiconductors in the past. One proposed explanation for this phenomenon has been narrowing due to electron motion caused by phonon-induced tunneling (hopping) between donor sites. According to the Anderson narrowing theory, the line width of the narrowed line can be expressed in terms of the average square spread of the non-narrowed spectrum, < H²>_ave, and the average frequency of electron motion, ω_n. Previous work has been done on narrowing by hopping, but rigorous expressions for ω …

Temperature Dependence Of The Formation Of An Amorphous Layer In Ion-Implanted Silicon, Gary Keith Woodward

Masters Theses

"Electron spin resonance (ESR) has been used to study the temperature dependence of the formation of an amorphous damaged layer produced by ion implantation in silicon.

Undoped silicon wafers were implanted with N⁺, Ar⁺, and Kr⁺ ions at 20 keV and dose rates less than .36 µa/cm². Implant temperatures ranged from room temperature to 250°C. ESR measurements were made at room temperature on these wafers. The only ESR signal found was that associated with amorphous silicon. The ESR signal amplitude for a given ion and temperature increased approximately linearly with dose up to …

Gas-To-Particle Conversions Of So₂-No₂-H₂O-Air Gas Mixtures Under Specific Uv Irradiation, James Leonard Fowler

Masters Theses

"In these series of experiments, mixtures of sulfur dioxide and nitrogen dioxide were irradiated in an absorption cell with monochromatic radiation found in the tropospheric region of the atmosphere. The irradiated mixtures were then introduced into a Wilson type cloud chamber to investigate the effects of these specific wavelength induced gas to particle conversions on nucleation. Results showed that sulfur dioxide could not be the sole agent for the formation of condensation nuclei. A mixture of sulfur dioxide and nitrogen dioxide irradiated at 3660 angstroms produced copious droplet formation identifying nitrogen dioxide as an integral reactant in nuclei production"--Abstract, page …

Thermal Expansivity And Refractive Index Determinations For Some Hydrosol Systems And Their Similarity To Properties Ascribed To "Anomalous" Water, Gerald Wayne Chappue

Masters Theses

"The characteristic thermal expansion and refractive index of aqueous dispersions of SiO₂ and NaOH were determined for samples contained in quartz micro-capillaries. Comparison is made with the expansivity and refractive properties of anomalous water or polywater as reported by other investigators. The similarity between the properties and behavior of various hydrosol systems and those ascribed to anomalous water is cited as a serious challenge to the hypothesized existence of an allotropic modification of water"--Abstract, page ii.

Application Of The Weiss Molecular Field Theory To The Lattice Of The B-Site Spinel, Wayne Edmund Holland

Masters Theses

"The Weiss molecular field theory has been applied to the lattice of the B-site spinel. The forms of the ordering temperatures and the asymptotic Curie temperature have been determined for a sixteen-sublattice model with collinear spins. The theory has been applied to the problem of determining the exchange integrals for systems of the form Aa₁₋ₓAbₓCr₂X₄ and ACr₂Xa_4(1-y)Xb_4y. The theoretical results have been compared to the experimental data for the systems Hg₁₋ₓCdₓCr₂S₄, Zn₁₋ₓCdₓCr₂Se₄, and CdCr₂S_4(1-y)Se_4y in an attempt to determine the exchange integrals"--Abstract, page ii.

A Study Of The Evaporation Rates Of Small Freely Falling Water Droplets, Hugh Alan Duguid

Masters Theses

"The evaporation rates of small (radium 3-9µ), freely falling water droplets were determined. the droplets, produced in a diffusion cloud chamber, were allowed to fall through air of known relative humidity (95-100%) and at three ambient temperatures (25C, 30C, and 35C) in a vertical drift tube. the rates of evaporation were ascertained by recording the drop positions on film at fixed time intervals. The results are compared with several existing theories, and are found to lie between the formulation of Kinzer and Gunn, and the quasistationary theory based on Maxwell's equation"--Abstract, page ii.

Infrared Cooling Near Atmospheric Temperature Inversions And Absorber Concentration Variations, Joey Keith Tuttle

Masters Theses

"Cooling due to infrared radiation near temperature inversions is investigated. Temperature inversions tend to hold pollution below the inversion level. The pollution itself may contribute to the stability of the inversion by selectively cooling certain portions of the atmosphere. A method is developed for evaluating infrared cooling rates at discreet points in the atmosphere. Several sample calculations are given to demonstrate the effects of variations of absorber concentration and lapse rate"--Abstract, page i.

A Low Frequency Phase Shift Method, Ronnie Carroll Mcmillan

Masters Theses

"The phase shift method of measuring atomic lifetimes is particularly useful because it allows us to make measurements in the steady state mode instead of in the transient mode. High frequency phase shift techniques cause many problems. The equipment, which was designed and built to make low frequency phase shift techniques possible, is shown schematically and discussed. The new experimental techniques employed in our apparatus are a phase multiplier and a unique method of using a photomultiplier as a mixer. In the photomultiplier the final dynode is used as the grid of a triode. The next to the last dynode …

An Experimental Comparison Of Various Nuclei Counters, Joel William Mansell

Masters Theses

"A series of simultaneous nuclei concentration measurements, with four different nuclei counters, have been made. these counters were a Pollak and a Gardner counter supplied by Mr. Paul Allee of the Environmental Science Services Administration, Boulder, Colorado, and a Pollak and a G.E. counter supplied; by Mr. Norman White of the National Center for Air Pollution Control, Cincinnati, Ohio. In the absence of any knowledge of the absolute concentrations in the samples, the data for each of the individual counters have been compared to the averages computed from all four counters. The results of these comparisons indicate the following: (1) …

A Study Of Bifeo₃ And The Hall Effect In Bifeo₃ And Cds, Fred Hoerger Taylor

Masters Theses

"Pure samples of BiFeO₃ were heat treated in oxygen and nitrogen atmospheres in an attempt to reduce the conductivity of the samples. Dielectric constant and dissipation factor measurements, as a function of frequency, were made to determine whether the samples had been altered. A special high temperature Hall effect apparatus was constructed. Using this apparatus an upper limit for the Hall mobility in BiFeO₃ was established. The apparatus was also used for room temperature measurements of Ga-doped CdS samples. Resistivity measurements to be used with the Hall effect results were made on both the BiFeO₃ and the CdS samples. Hot-Point …

Absolute Specification Of X-Ray Spectra By Laplace Transform Analysis Of Attenuation Data, Gerald Robert Lusk

Masters Theses

"A well characterized, variable plate separation ion chamber was utilized as a detector to collect x-ray attenuation data for generating information on the Laplace transform predicted spectrum of a 50 KvCP conventional x-ray tube. The variable plate separation feature allows one to include a wavelength dependent correction to the detector response which is associated with the hardening of the x-ray spectrum as it traverses the attenuating material. With this correction, the conventional two-term Laplace transform was shown to approximate independently the bremsstrahlung and characteristic L radiation from the tungsten target. The detector provides an absolute statement of the target-referenced x-ray …