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Articles 121 - 150 of 179
Full-Text Articles in Nuclear Engineering
A Comparison Of Hazard Predication And Assessment Capability (Hpac) Software Dose-Rate Contour Plots To A Sample Of Local Fallout Data From Test Detonations In The Continental United States, 1945-1962, Richard W. Chancellor
A Comparison Of Hazard Predication And Assessment Capability (Hpac) Software Dose-Rate Contour Plots To A Sample Of Local Fallout Data From Test Detonations In The Continental United States, 1945-1962, Richard W. Chancellor
Theses and Dissertations
A comparison of Hazard Prediction and Assessment Capability (HPAC) software dose-rate contour plots to a sample of local nuclear fallout data from test detonations in the continental United States, 1945 - 1962, is performed. Fallout data from test detonations is obtained from "Compilation of Local Fallout Data from Test Detonations 1945- 1962 Extracted from DASA 1251, Volume I - Continental U.S. Tests." This report contains fallout plots and radiation contours for each test in the atmospheric nuclear test program conducted by the United States prior to 1963. These plots are compared with the plots resulting from Defense Threat Reduction Agency's …
Classification Of Battlespace Detonations From Temporally Resolved Mutli-Band Imagery And Mid-Infrared Spectra, Anthony N. Dills
Classification Of Battlespace Detonations From Temporally Resolved Mutli-Band Imagery And Mid-Infrared Spectra, Anthony N. Dills
Theses and Dissertations
The classification of battlespace detonations, specifically the determination of munitions type and size using temporal and spectral features, has been studied using near-infrared (NIR) and multi-color visible wavelength imagers. Key features from the time dependence of fireball size are identified for discriminating various types and sizes of detonation flashes. The five classes include three weights of trinitrotoluene (TNT) and two weights of an enhanced mixture, all of which are uncased and detonated with 10% C4. Using Fisher linear discriminant techniques, features are projected onto a line such that the projected points are maximally clustered for the different classes of detonations. …
Surface Oxidation Study Of Uranium Dioxide Under Wet And Dry Conditions, Gary T. Brett
Surface Oxidation Study Of Uranium Dioxide Under Wet And Dry Conditions, Gary T. Brett
Theses and Dissertations
The surface oxidation of pressed uranium dioxide (UO2) powder under controlled environmental conditions and the oxidation and reduction of pressed uranium trioxide (UO3) powder are presented. This is a continuing research project in the investigation of the oxidation of UO2 powder using Photoluminescence (PL) Spectroscopy. UO2 particles exposed to the ambient atmosphere will oxidize into a number of chemical complexes (specifically hydrates, hydroxides, and carbonates). During certain of these oxidation processes, the uranium ion can lose two of its electrons and change from uranous (UIV+) to uranyl (UVI+). This research …
Temperature Dependent Current-Voltage Measurements Of Neutron Irradiated Al0.27Ga0.73N/Gan Modulation Doped Field Effect Transistors, Troy A. Uhlman
Temperature Dependent Current-Voltage Measurements Of Neutron Irradiated Al0.27Ga0.73N/Gan Modulation Doped Field Effect Transistors, Troy A. Uhlman
Theses and Dissertations
In this research, the first ever neutron irradiation study of AlGaN/GaN MODFETs was conducted. Devices irradiated to a total 1 MeV Eq (Si) neutron fluence of 1.2x1016 n/cm2 demonstrated the temperature dependence of irradiation and annealing. Devices irradiated at 80 K exhibited significant persistent electrical degradation at only 5.4 rad (Si), whereas those irradiated at elevated temperatures exhibit transient increases in gate and drain current up to 400 krad (Si). I-V measurements indicate substantial radiation-induced increased gate and drain currents occur only at low-temperature irradiations. The introduction of a high-density of donor defects is hypothesized as the primary …
Lethality Of Bacillus Anthracis Spores Due To Short Duration Heating Measured Using Infrared Spectroscopy, Kristina M. Goetz
Lethality Of Bacillus Anthracis Spores Due To Short Duration Heating Measured Using Infrared Spectroscopy, Kristina M. Goetz
Theses and Dissertations
There are a number of analytical and semi-empirical models that describe the behavior of particulate matter in the atmosphere. Many of these require modification for all types of weather, dry versus wet deposition, and overall effects can be quite non-linear. Rainfall (rate, drop size, etc.), snowfall (rate, flake size, etc.), humidity, pressure, temperature, and combination of these greatly affect particle settling and washout rates. To that end, a method for tracking released constituents using the Regional Atmospheric Modeling System (RAMS) microphysics package is developed by modifying one of the hydrometeor categories (hail) in the microphysics package. The RAMS microphysics package …
Development Of 2-Dimensional Cloud Rise Model To Analyze Initial Nuclear Cloud Rise, Karson A. Sandman
Development Of 2-Dimensional Cloud Rise Model To Analyze Initial Nuclear Cloud Rise, Karson A. Sandman
Theses and Dissertations
The objective of this research is to create a two-dimensional cloud rise model that could be used instead of the current one-dimensional cloud rise model in the Defense Land Fallout Intepretive Code (DELFIC) option of the Hazard Prediction and Assessment Capability (HPAC). The model includes numerical analysis of partial differential equations involving pressure, potential temperature, horizontal and vertical winds, and specific humidity. The 2-D model developed provides a much more detailed definition of the physical properties within the mushroom cloud than the 1-D DELFIC option. This is particularly useful in fallout studies on particle formation, fractionation, and particle location within …
A Comparison Of The Heft Subsurface And Delfic Particle Size Distributions And Effects In Hpac, Eric T. Skaar
A Comparison Of The Heft Subsurface And Delfic Particle Size Distributions And Effects In Hpac, Eric T. Skaar
Theses and Dissertations
The Heft subsurface three component lognormal fallout particle size distribution is compared and contrasted with the single lognormal fallout particle size distribution used by the Defense Land Fallout Interpretive Code (DELFIC). Comparison of the two distributions is accomplished with results from the AFIT smear code and the Hazard Prediction and Assessment Capability (HPAC). The effect of the distributions is explored in HPAC for varying yield weapons, varying surfaces, precipitation conditions, varying wind effects and varying dose rate times. The results from the two distributions are quantitatively compared using the concepts of grounded source normalization constant and the rate at which …
Excited States Of Silicon Carbide Clusters By Time Dependent Density Functional Theory, John E. Boyd
Excited States Of Silicon Carbide Clusters By Time Dependent Density Functional Theory, John E. Boyd
Theses and Dissertations
Previous AFIT research with density functional theory (DFT) has shown itself to be accurate for small SimCn (m,n ≤ 5) clusters at a fraction of the cost of other quantum mechanical methods, but it is only a ground state theory. Time dependent density functional theory (TDDFT), however, is able to calculate excited states as well. Evaluating the accuracy of these methods with respect to the excited states of these clusters was the focus of this research, specifically with respect to the excitation energies, geometries, and vibrational frequencies. It is shown that for the excited states that can …
Low Temperature Hall Measurements Of Neutron Irradiated Silicon Carbide, Angelo M. Bonavita
Low Temperature Hall Measurements Of Neutron Irradiated Silicon Carbide, Angelo M. Bonavita
Theses and Dissertations
The purpose of this research was to search for evidence of low temperature annealing from neutron irradiated 4H-silicon carbide. No features suggesting annealing were found below a temperature of 340K. Temperature dependant Hall effect measurements were taken over a range of 100K to 340K recording resistivity, carrier densities, and mobility. Resistivity was noted to increase with irradiations, and carrier densities appeared to decrease, while mobility appeared minimally affected by neutron irradiation. This suggests the creation of active acceptor defects decreasing carrier concentrations. N-type samples measured were 5mm x 5mm square with Nickel contacts, and irradiated to 1010 and 10 …
An Analysis Of The Potential For Using Over-The-Horizon Radar Systems For Space Surveillance, Matthew J. Colbert
An Analysis Of The Potential For Using Over-The-Horizon Radar Systems For Space Surveillance, Matthew J. Colbert
Theses and Dissertations
The Australian Defence Force is investigating the development of a space surveillance system. While several dedicated facilities for space surveillance are in operation around the world, Australia s Over-The-Horizon Radar (OTHR) network has some potential for this role. The OTHR operates in the HF band and is constrained by the propagation effects of the ionosphere. A spherically stratified ionospheric model and a model for a nominal OTHR antenna are developed that allow calculation of path propagation, power distribution, and clutter returns. A software-based radar receiver processing system is modeled to determine detection probabilities and the minimum detectable radar cross-section of …
An Experimental Design For Measuring In Situ Radiation Damage To A Piezoelectric Transducer, Michael R. Severson
An Experimental Design For Measuring In Situ Radiation Damage To A Piezoelectric Transducer, Michael R. Severson
Theses and Dissertations
An experiment was conducted investigating the use of an acoustic pulse waveguide to collect response measurements from three piezoelectric acoustic emission (AE) transducers while the transducers were exposed to an active nuclear reactor neutron flux ranging from 1 x 1011 to 2.4 x 1012 neutrons per cm2. Material, mechanical, and radiation studies were performed to determine a practical design for the construction of the experiment. Discreet frequency pulses generated by an Arbitrary Waveform Generator were transmitted by an aluminum waveguide to the core of the Ohio State University Research Reactor (OSURR). Three AF transducers coupled to …
Special Nuclear Material Imaging Using A High Purity Germanium Double Sided Strip Detector, Clifford V. Sulham
Special Nuclear Material Imaging Using A High Purity Germanium Double Sided Strip Detector, Clifford V. Sulham
Theses and Dissertations
The purpose of this research is to investigate the feasibility of using a High Purity Germanium Double Sided Strip Detector (HPGeDSSD) to image Special Nuclear Material (SNM) for use in the field of nuclear nonproliferation. SNM shape can be determined by using a gamma ray imaging system that is capable of imaging either Pu-239 or U-235. The detector used for this research is a liquid-nitrogen cooled germanium detector with five charge collection strips on both faces. The strips on the two faces are orthogonal to each other, creating a five by five array of data collection pixels. When the detector …
An Analysis Of The Effects Of Low Energy Electron Radiation Of AlXGa1-XN/Gan Modulation-Doped Field-Effect Transistors, James M. Sattler
An Analysis Of The Effects Of Low Energy Electron Radiation Of AlXGa1-XN/Gan Modulation-Doped Field-Effect Transistors, James M. Sattler
Theses and Dissertations
The effects of radiation on AlxGa1-xN/GaN MODFETs is an area of increasing interest to the USAF as these devices become developed and integrated in satellite-based systems Irradiation is also a valuable tool for analyzing the quantum-level characteristics and properties that are responsible for device operation AlxGa1-xN/GaN MODFETs were fabricated and irradiated at liquid nitrogen temperatures by 0,45-1,2MeV electrons up to doses of 6*1016 e/cm2. Following irradiation, low temperature I-V measurements were recorded providing dose-dependent measurements Temperature-dependent I-V measurements were also made during room temperature annealing following irradiation I-V measurements …
Electron Paramagnetic Resonance Spectroscopy And Hall Effect Studies Of The Effects Of Low Energy Electron Energy On Gallium Nitride (Gan), Kevin D. Greene
Electron Paramagnetic Resonance Spectroscopy And Hall Effect Studies Of The Effects Of Low Energy Electron Energy On Gallium Nitride (Gan), Kevin D. Greene
Theses and Dissertations
The nature of native donors in GaN, types and interactions of radiation-induced defects, and damage creation coefficients for 1.0 MeV electron irradiation have been ascertained by the concerted application of electron paramagnetic resonance spectroscopy and Hall effect measurements to virgin and electron-irradiated GaN epilayers. Samples produced via molecular beam epitaxy and hydride vapor phase epitaxy, both silicon doped and nominally undoped, were subjected to Van de Graff generator produced monoenergtic electron beams with total fluences of 1016- 1018 electrons/cm2. Nitrogen vacancies are rejected as a possible cause of n-type conductivity in nominally undoped GaN due …
Theoretical Comparison Of The Excited Electronic States Of The Linear Uranyl (Uo22+) And Tetrahedral Uranate (Uo42-) Ions Using Relativistic Computational Methods, Eric V. Beck
Theses and Dissertations
This thesis examines the ground and excited electronic states of the uranyl (UO2+) and uranate (UO42-) ions using Hartree-Fock self-consistent field (HF SCF), multi-configuration self-consistent field (MCSCF) and multi-reference single and double excitation configuration interaction (MR- CISD) methods. The MR-CISD SD calculation included spin-orbit operators. Molecular geometries were obtained from self-consistent field (SCF ) second-order perturbation theory (MP2), and density functional theory (DFT) geometry optimizations using the NWChem 4.01 massively parallel ab initio software package. COLUMBUS version 5.8 was used to perform in-depth analysis on the HF SCF MCSCF and MR-CISD potential energy surfaces. Excited …
Investigation Of A Passive, Temporal, Neutron Monitoring System That Functions Within The Confines Of Start I, Stephanie Vaughn
Investigation Of A Passive, Temporal, Neutron Monitoring System That Functions Within The Confines Of Start I, Stephanie Vaughn
Theses and Dissertations
This study is an investigation of the theoretical and experimental possibilities of using activation foils to detect and monitor special nuclear material for treaty monitoring purposes. None of the experiments demonstrated sufficient sensitivity to detect the target flux of 0.5 neutrons/cm3-sec. The target flux could be detectable, if the limit of detection had been reduced by a factor of 4 to 6. However, many issues identified could enhance the sensitivity including: increasing foil size, increasing detector efficiency, and optimizing foil selection. The theoretical portion focused on gold, silver, indium, europium, and gadolinium foils and determined the minimum flux …
Detection Of Special Nuclear Material With High Purity Germanium (Hpge) And Mercuric Iodide (Hgi2) Gamma Detectors, Michael B. Nelson
Detection Of Special Nuclear Material With High Purity Germanium (Hpge) And Mercuric Iodide (Hgi2) Gamma Detectors, Michael B. Nelson
Theses and Dissertations
The Defense Threat Reduction Agency (DTRA) contracted for two gamma radiation detectors: mercuric iodide (HgI2) and electromechanically cooled (EMC) high purity germanium (HPGe) to support arms control inspection efforts. This project investigated whether these detectors could measure the quality and quantity of special nuclear material (SNM), particularly Pu-239 for the treaty verification mission. The project investigated two areas of detector capabilities: 1) HgI2 and HPGe detector performance necessary to characterize the quality of plutonium and the presence of shielding materials and 2) HgI2 and EMC HPGe detector performance degradation by high noise levels and EMC HPGe …
Total Dose Effects Of Ionizing And Non-Ionizing Radiation On Piezoresistive Pressure Transducer Chips, Samuel J. Willmon
Total Dose Effects Of Ionizing And Non-Ionizing Radiation On Piezoresistive Pressure Transducer Chips, Samuel J. Willmon
Theses and Dissertations
The effects of ionizing and non ionizing radiation on the resistivity of silicon based, piezoresistive bulk micro-machined chips from pressure transducers were examined. Standard current-voltage (I-V) measurements were taken in-situ and post-irradiation during isothermal annealing at room temperature. One group of chips was irradiated to a maximum total gamma dose of lMrad(Si) in the 11,000 Ci (60) Co gamma cell at Ohio State University. The second group of chips was irradiated at the Ohio State University Research Reactor facility to a maximum total neutron dose of 4 Mrad(Si) using beam port Hi. The resistivity was shown to decrease during gamma …
An Evaluation Of The Hazard Prediction And Assessment Capability (Hpac) Software's Ability To Model The Chornobyl Accident, Dirk E. Plante
An Evaluation Of The Hazard Prediction And Assessment Capability (Hpac) Software's Ability To Model The Chornobyl Accident, Dirk E. Plante
Theses and Dissertations
A parameter study was conducted for a space nuclear reactor radiation shield. The focus of this research was to explore alternatives to current radiation shield designs to reduce the mass while maintaining the same shielding performance. MCNP4C was used to determine the parameters necessary to build an optimum shield. A design known as the split scatter shield offered some potential for reductions in shield mass. In theory, less material is required for this type of shield, which uses thin shield sections to scatter radiation away from the dose plane. The parameters for this shield design are the shield geometry, number …
Characterization Of The Optical And Electrical Properties Of Proton-Irradiated 4h-Silicon Carbide, Heather C. Crockett
Characterization Of The Optical And Electrical Properties Of Proton-Irradiated 4h-Silicon Carbide, Heather C. Crockett
Theses and Dissertations
Epitaxial n-type 4H-silicon carbide (SiC) is irradiated with 2 MeV protons to evaluate the dislocation damage effects on the optical and electrical characteristics of the material. Semiconductor materials with a high tolerance to radiation fields have applications in several aerospace power and satellite systems. SiC is under investigation due to its potential for such space material applications. The optical properties of the material are investigated using temperature-dependent photoluminescence (PL) and the effects of proton irradiation on the electrical properties are evaluated using current-voltage measurements and constant-voltage deep level transient spectroscopy (CV-DLTS). Subsequent high-temperature thermal annealing and recovery of the irradiated …
Measurements Of Neutron Induced Surface And Bulk Defects In 4h Silicon Carbide, Kent T. Jones
Measurements Of Neutron Induced Surface And Bulk Defects In 4h Silicon Carbide, Kent T. Jones
Theses and Dissertations
Epitaxial n-type 4H-silicon carbide (SiC) is irradiated with 2 MeV protons to evaluate the dislocation damage effects on the optical and electrical characteristics of the material. The optical properties of the material are investigated using temperature-dependant photoluminescence (PL) and the effects of proton irradiation on the electrical properties are evaluated using current-voltage measurements and constant-voltage deep level transient spectroscopy (CV-DLTS). Subsequent high-temperature thermal annealing and recovery of the irradiated material is investigated over the temperature range of 900-1500°C. Proton-induced irradiation damage is apparent in the 4H-SiC material, affecting both the optical and electrical characteristics of the devices. The radiative behavior …
Parameter Study For Optimizing The Mass Of A Space Nuclear Power System Radiation Shield, Benjamin R. Kowash
Parameter Study For Optimizing The Mass Of A Space Nuclear Power System Radiation Shield, Benjamin R. Kowash
Theses and Dissertations
A parameter study was conducted for a space nuclear reactor radiation shield. The focus of this research was to explore alternatives to current radiation shield designs to reduce the mass while maintaining the same shielding performance. MCNP4C was used to determine the parameters necessary to build an optimum shield. A design known as the split scatter shield offered some potential for reductions in shield mass. In theory, less material is required for this type of shield, which uses thin shield sections to scatter radiation away from the dose plane. The parameters for this shield design are the shield geometry, number …
Assessment Of The Effects Of Entrainment And Wind Shear On Nuclear Cloud Rise Modeling, Daniel E. Zalewski
Assessment Of The Effects Of Entrainment And Wind Shear On Nuclear Cloud Rise Modeling, Daniel E. Zalewski
Theses and Dissertations
The Missile Defense Agency (MDA) plans to construct, during a two-week period, an X-Band Radar (XBR) on Shemya, AK. Wind speeds must not, at any time during the construction, exceed a 25 knot limit set by the MDA for lifting the massive dome panels into place. The goal of this research was to explore the possibilities of long-range forecasts to determine the feasibility of predicting any upcoming two-week windows of opportunity, well in advance, that will ensure the successful completion of constructing the XBR on Shemya. In order to reach this goal, the following objectives were achieved; (1) a climatological …
Electronic Quenching Of The A(0+U) State Of Bi2, Joseph L. Cox
Electronic Quenching Of The A(0+U) State Of Bi2, Joseph L. Cox
Theses and Dissertations
Temporally-resolved laser induced fluorescence ofhigh vibrational levels in Bi2 A(0+u) above and below the predissociation limit of v'=22 were investigated by observing total fluorescence from a wavelength tunable, pulsed dye laser. Electronic quenching ofBi2 A(0+u) by five collision partners (Ne, Ar, Kr, Xe, N2) was examined for four vibrational levels (v'=22,23,24,25). Electronic quenching by a sixth collision partner (He) was examined for eight vibrational levels (v'=18 through 25). The quenching from stable vibrational levels (v'≤22) was independent ofvibrational quantum number. A significant increase in quenching occurs for the predissociated level …
Aircrew Ionizing Doses From Nuclear Weapon Bursts, Fred E. Garcia Ii
Aircrew Ionizing Doses From Nuclear Weapon Bursts, Fred E. Garcia Ii
Theses and Dissertations
Total radioactive doses to aircrew members have been calculated in the past using different methods. The methodologies include smearing models, disk-tosser codes, and puff models. This study uses output data from the Hazard Prediction and Assessment Capability (HPAC) code as input into a FORTRAN program written by the author to calculate total dose to aircrew members through sky-shine and cabin ingestion. A description of the input parameters and new project setup in the Nuclear Weapon (NWPN) module within HPAC is given. The various aspects of controlling the project and plotting the data are also described. This information is presented essentially …
Modeling Pressurized Water Reactor Kinetics, William H. Harman
Modeling Pressurized Water Reactor Kinetics, William H. Harman
Theses and Dissertations
A computer model of a pressurized water reactor (PWR) was developed for use as a teaching tool in graduate level nuclear reactor courses. The development, based on the diffusion equation, includes the methodology for solving the steady state spatial dependence of the neutron power output in a homogeneous right circular cylinder unreflected PWR system. This includes a two dimensional one energy group model, a three dimensional one energy group model, and a three dimensional two energy group model. To solve the homogeneous diffusion equation, a method was developed to search for criticality of the reactor based on the geometry and …
Simulating Wet Deposition Of Radiocesium From The Chernobyl Accident, Aaron M. Kinser
Simulating Wet Deposition Of Radiocesium From The Chernobyl Accident, Aaron M. Kinser
Theses and Dissertations
In response to the Chernobyl nuclear power plant accident of 1986, a cesium-137 deposition dataset was assembled. Most of the airborne Chernobyl cesium was wet deposited, either via interception by falling raindrops or via absorption into cloud droplets destined to become raindrops. The Hybrid Single-Particle Lagrangian rated Transport (HYSPLIT) model, developed at Air Resources Laboratory, is used to simulate the transport and deposition of Chernobyl cesium-137. A cloud base parameterization modification is tested and appears to slightly improve the accuracy of one HYSPLIT simulation of daily Chernobyl cesium-137 deposition over the course of the accident at isolated European sites, and …
Positive Anisotropic Group Scattering Cross Sections For Radiation Transport, J. Mark Delgrande
Positive Anisotropic Group Scattering Cross Sections For Radiation Transport, J. Mark Delgrande
Theses and Dissertations
In solving the Boltzmann transport equation, most discrete ordinates codes calculate the source term by first approximating the scattering cross section using a Legendre polynomial expansion. Such expansions are insufficient when scattering is anisotropic and the Legendre expansion is truncated prematurely. This can lead to nonphysical negative cross sections, negative source terms and negative angular fluxes. While negative sources are problematic for standard discrete ordinates methods leading to poor convergence or convergence to incorrect results, they are of particular concern to exponential methods, causing such calculations to fail. We've developed and tested a new technique to solve this problem called …
An Investigation Into The Noninvasive Assessment Of Bone Density Using Multiplexed Compton Scattered Tomography, Marc J. Sands
An Investigation Into The Noninvasive Assessment Of Bone Density Using Multiplexed Compton Scattered Tomography, Marc J. Sands
Theses and Dissertations
The purpose of this research is to investigate the application of a Compton scatter imaging technique to measure bone density. A demonstration Multiplexed Compton Scatter Tomograph (MCST) was assembled to demonstrate the feasibility of detecting osteoporosis by modifying a system originally designed to detect hidden corrosion in aluminum aircraft wings. Measurements were performed on an aluminum phantom representing a wrist bone containing varying densities in the center and varying thickness of the cortical shell. The densities in the center are comparable to normal trabecular bone, sixty-percent of normal trabecular bone and a void. The MCST images of the phantom were …
Development Of A Discrete Ordinates Code System For Unstructured Meshes Of Tetrahedral Cells, With Serial And Parallel Implementations, Rodney L. Miller
Development Of A Discrete Ordinates Code System For Unstructured Meshes Of Tetrahedral Cells, With Serial And Parallel Implementations, Rodney L. Miller
Theses and Dissertations
A numerically stable, accurate, and robust form of the exponential characteristic (EC) method, used to solve the time-independent linearized Boltzmann Transport Equation, is derived using direct affine coordinate transformations on unstructured meshes of tetrahedra. This quadrature, as well as the linear characteristic (LC) spatial quadrature, is implemented in our transport code, called TETRAN. This code solves multi-group neutral particle transport problems with anisotropic scattering and was parallelized using High Performance Fortran and angular domain decomposition. A new, parallel algorithm for updating the scattering source is introduced. The EC source and inflow flux coefficients are efficiently evaluated using Broyden's rootsolver, started …