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Articles 91 - 120 of 179
Full-Text Articles in Nuclear Engineering
Neutron Radiation Effects On Ge And Gesn Semiconductors, Christopher T. O'Daniel
Neutron Radiation Effects On Ge And Gesn Semiconductors, Christopher T. O'Daniel
Theses and Dissertations
Two different semiconductor materials received neutron radiation for assessment of radiation damage. The two materials are undoped bulk Ge and epitaxial Ge0.991Sn0.009, which is doped heavily with phosphorous. At room temperature, the Ge sample has direct and indirect bandgaps at 0.78 eV and 0.66 eV, respectively. The Ge0.991Sn0.009 sample has direct and indirect bandgaps at 0.72 eV and 0.63 eV, respectively. Two samples of each material were exposed to research reactor neutrons, delivering a 1 MeV equivalent neutron fluence of 2.52 × 1015 n/cm2. In order to assess the radiation …
Multidimensional Analysis Of Nuclear Detonations, Robert C. Slaughter
Multidimensional Analysis Of Nuclear Detonations, Robert C. Slaughter
Theses and Dissertations
The focus of this research is to develop the methods for 3-dimensional reconstructions and temperature distributions of early time nuclear fireballs. Initial developments have resulted in the first 2-dimensional temperature distribution of a nuclear fireball using digitized film. This same process was then extended to perform the first limb darkening calculations of nuclear fireballs. Limb darkening coefficients were then used to derive a temperature profile of the nuclear fireball as a function of optical path length. A 3-dimensional reconstruction was performed using a variation of a structure from illuminance technique in combination with limb darkening coefficients to produce structure using …
Coupling Nuclear Induced Phonon Propagation With Conversion Electron Mössbauer Spectroscopy, Michael J. Parker
Coupling Nuclear Induced Phonon Propagation With Conversion Electron Mössbauer Spectroscopy, Michael J. Parker
Theses and Dissertations
Mössbauer spectroscopy is a very sensitive measurement technique (10-8 eV) which prompted motivation for the experiment described in this thesis. Namely, can a sensitive detection system be developed to detect nuclear recoils on the order of 10 to 100 of eVs? The hypothesis that this thesis tests is: Nuclear induced phonon bursts caused by Rutherford scattered alphas, decayed from 241Am, in a type-310 stainless steel material can couple with 7.3 keV conversion electron Mössbauer events at the other end of the material which will have a statistically significant effect on a Mössbauer spectrum. The phonon bursts produced by …
Surface Geometry And Chemistry Of Hydrothermally Synthesized Single Crystal Thorium Dioxide, Scott W. Key
Surface Geometry And Chemistry Of Hydrothermally Synthesized Single Crystal Thorium Dioxide, Scott W. Key
Theses and Dissertations
The surface chemistry and geometry of hydrothermally grown, single crystal ThO2 was studied using X-ray Photoemission Spectroscopy (XPS) and Atomic Force Microscopy (AFM). The crystal was studied before and after sputter etching with Ar+, heating up to 675 K, and dehydration with dry nitrogen. The hydrothermal growth technique incorporated Cs and F into the near surface bulk. Heating to 675 K drove off the F, but did not the Cs. Sputtering with Ar+ at 75° cleaned the crystal and created a more uniform surface geometry. The Th 4f peak resolution, as measured by XPS improved by …
The Effect Of Anisotropic Scatter On Atmospheric Neutron Transport, Nicholas J. Mcintee
The Effect Of Anisotropic Scatter On Atmospheric Neutron Transport, Nicholas J. Mcintee
Theses and Dissertations
Anisotropy is present in the angular distributions of neutrons departing from a nuclear scattering event. This anisotropy cannot be defined in a closed-form solution, and it is dependent on the incident neutron energy, elastic or inelastic scatter, along with the inelastic level, and the species struck. The underlying question is, if anisotropic behavior is worth the computational cost to be included in certain simulations, and if so, what level of precision is effected by the inclusion of anisotropic scatter. A Watt spectrum of U235 fission neutrons was examined as it collided with species in a nitrogen-oxygen atmosphere. In a …
Ionizing And Non-Ionizing Radiation Effects In Thin Layer Hexagonal Boron Nitride, Brian L. Barnett
Ionizing And Non-Ionizing Radiation Effects In Thin Layer Hexagonal Boron Nitride, Brian L. Barnett
Theses and Dissertations
The radiation response of 14nm h-BN/Si metal insulator semiconductor (MIS) devices was investigated using current-voltage and capacitance-voltage measurements indicating Frenkel Poole (FP) and Fowler-Nordheim tunneling (FNT) are the primary current mechanisms before and after irradiation. The data were fit to a composite model of FP and FNT currents. Irradiations to 33.1, 99.3, and 331 krad(Si) from a cobalt-60 source causes a negative voltage shift to the current-voltage measurements of -0.14, -0.45, and -0.46 V respectively. The negative shift indicates radiation induced production of positive space charge at the h-BN/Si interface. No device characteristic changes were observed following gamma irradiation. Fitting …
Two-Dimensional Temperature Analysis Of Nuclear Fireballs Using Digitized Film, Robert C. Slaughter, Tyler R. Peery, John W. Mcclory
Two-Dimensional Temperature Analysis Of Nuclear Fireballs Using Digitized Film, Robert C. Slaughter, Tyler R. Peery, John W. Mcclory
Faculty Publications
Researchers at Lawrence Livermore National Laboratory have begun digitizing technical films spanning the atmospheric nuclear testing operations conducted by the United States from 1945 through 1962. Each atmospheric nuclear test was filmed by Edgerton, Germeshausen, and Grier, Inc., using between 20 to 40 cameras per test. These technical film test data represent a primary source for advancing the knowledge of nuclear weapon output as well as the understanding of nonnuclear high-temperature gases. This manuscript outlines the procedures followed in order to perform two-dimensional temperature calculations for early time nuclear fireballs using digitized film. The digitized optical densities of the film …
Measurements Of Dna Damage And Repair In Bacillus Anthracis Sterne Spores By Uv Radiation, Chelsea C. Marcum
Measurements Of Dna Damage And Repair In Bacillus Anthracis Sterne Spores By Uv Radiation, Chelsea C. Marcum
Theses and Dissertations
Spores of Bacillus anthracis (Ba) sterne were irradiated with 267nm UV light using small light emitting diodes. The pRB373 plasmid with a red fluorescent protein was transformed into Ba sterne cells prior to irradiation. Following irradiation, germination media was added and the spores were incubated for various times, to allow for DNA repair. The pRB373 plasmid was isolated and analyzed using real-time PCR. Primers were designed across the RFP in the plasmid yielding two amplicons, 245bp and 547bp long. PCR amplification was not achieved for germinated samples. Spore samples isolated using bead beating methods were amplified. Results indicate a quicker …
Copper Doping Of Zinc Oxide By Nuclear Transmutation, Matthew C. Recker
Copper Doping Of Zinc Oxide By Nuclear Transmutation, Matthew C. Recker
Theses and Dissertations
This research verifies that neutron irradiation of zinc oxide leads to Cu-doping of the material by nuclear transmutation. After irradiation, both 65Zn and 69mZn were detected and positively identified. 65Zn was visible at all times while 69mZn was visible when the samples were measured within a few Zn-69m half-lifes. All decay paths of 65Zn lead to 65Cu and the detection of the 1115.5 keV characteristic gamma ray from this decay clearly indicated that 65Cu was being created. Previous electron paramagnetic resonance (EPR) spectroscopic results were replicated to determine the spectrum of copper impurities …
Searching For Stable SiNCN Clusters: Combination Of Stochastic Potential Surface Search And Pseudopotential Plane-Wave Car-Parinello Simulated Annealing Simulations, Xiaofeng F. Duan, Lingyu Huang, Larry W. Burggraf
Searching For Stable SiNCN Clusters: Combination Of Stochastic Potential Surface Search And Pseudopotential Plane-Wave Car-Parinello Simulated Annealing Simulations, Xiaofeng F. Duan, Lingyu Huang, Larry W. Burggraf
Faculty Publications
To find low energy SinCn structures out of hundreds to thousands of isomers we have developed a general method to search for stable isomeric structures that combines Stochastic Potential Surface Search and Pseudopotential Plane-Wave Density Functional Theory Car-Parinello Molecular Dynamics simulated annealing (PSPW-CPMD-SA). We enhanced the Sunders stochastic search method to generate random cluster structures used as seed structures for PSPW-CPMD-SA simulations. This method ensures that each SA simulation samples a different potential surface region to find the regional minimum structure. By iterations of this automated, parallel process on a high performance computer we located hundreds to …
Theoretical Study Of The Effects Of Di-Muonic Molecules On Muon-Catalyzed Fusion, Eugene V. Sheely
Theoretical Study Of The Effects Of Di-Muonic Molecules On Muon-Catalyzed Fusion, Eugene V. Sheely
Theses and Dissertations
This document presents a theoretical study di-muonic hydrogen and helium molecules that have the potential of enhancing the muon-catalyzed fusion reaction rate. In order to study these di-muonic molecules a method of non-adiabatic quantum mechanics referred to as a General Particle Orbital (GPO) method was developed. Three mechanisms that have the possibility of enhancing the muon-catalyzed fusion rate were discovered. Two involve the formation of di-muonic hydrogen molecules, and the other uses di-muonic molecules to liberate muons stuck to 3He nuclei. The effects of muon spin on dimuonic hydrogen molecules was studied. The nuclear separation in di-muonic hydrogen molecules …
A Programmable Liquid Collimator For Both Coded Aperture Adaptive Imaging And Multiplexed Compton Scatter Tomography, Jack G. M. Fitzgerald
A Programmable Liquid Collimator For Both Coded Aperture Adaptive Imaging And Multiplexed Compton Scatter Tomography, Jack G. M. Fitzgerald
Theses and Dissertations
A novel, fully reconfigurable collimator device for gamma-ray and X-ray imaging was built and tested as a coded aperture. The device consisted of 10x10, 5x5x5 mm3 chambers. Each chamber either was filled with an attenuating liquid, stopping photons, or evacuated of the attenuating liquid, allowing the photons to pass through. As the pattern of on and off chambers was manipulated, different, semi-independent views of the gamma-ray source were found. Noise in reconstructed images decreased in all tests. Image reconstruction was performed with correlation methods and Maximum Likelihood Expectation Maximization (ML-EM). Using 10 mask patterns, the signal-to-noise ratio (SNR) in …
Neutron Detection Using Gadolinium-Based Diodes, Benjamin R. Thomas
Neutron Detection Using Gadolinium-Based Diodes, Benjamin R. Thomas
Theses and Dissertations
P-n heterojunction diodes consisting of a thin n-type layer of Gd2O3 deposited on both p-type Si and p-type 4H SiC substrates were explored as possible solid-state neutron detectors. 79 keV internal conversion electrons from the de-excitation of the meta-stable Gd-158 nucleus can create ionization in the depletion region of the reverse-biased diodes resulting in a detectable signal. The diodes were modeled with Davinci software to determine the feasibility of signal detection above the reverse-bias leakage current. A CASINO simulation showed that less than one percent of the internal conversion electrons deposit their full energy within the achievable …
Gadolinium Oxide/Silicon Thin Film Heterojunction Solid-State Neutron Detector, Christopher M. Young
Gadolinium Oxide/Silicon Thin Film Heterojunction Solid-State Neutron Detector, Christopher M. Young
Theses and Dissertations
The internal conversion electron emission from the de-excitation of the Gd-158m nucleus was explored as a means for neutron detection. Thin film gadolinium oxide (Gd2O3) and p-type silicon heterojunction diodes were produced using a supercritical water deposition process. Pulse height spectroscopy was conducted on the novel diodes while they were subjected to a moderated plutonium-beryllium (PuBe) source flux of 104 thermal neutrons/cm2 s. Coincident gamma spectroscopy was employed to verify the 1107.6 keV photon emissions from the diode indicative of successful neutron capture by Gd-157 and the subsequent de-excitation of the Gd-158m nucleus. Neutron …
The Effects Of Temperature And Electron Radiation On The Electrical Properties Of Algan/Gan Heterostructure Field Effect Transistors, Jeffrey T. Moran
The Effects Of Temperature And Electron Radiation On The Electrical Properties Of Algan/Gan Heterostructure Field Effect Transistors, Jeffrey T. Moran
Theses and Dissertations
AlxGa1-xN/GaN Heterostructure Field Effect Transistors (HFETs) have come under increased study, in recent years, owing to their highly desirable material and electrical properties, ruggedness, and survivability even during and after exposure to extreme temperature and radiation environments. These devices or similar devices constructed of AlGaN and/or GaN materials are being researched for their potential applications in many military and space based systems. In this study, unpassivated and SiN passivated Al0.27Ga0.73N/GaN HFETs were subjected to electron radiation at incident energies of 0.5MeV and 1.0MeV and fluences from 5x1014 to 5x1015 [e-/cm …
Electrostatic Discharge Properties Of Irradiated Nanocomposites, Joshua D. Mcgary
Electrostatic Discharge Properties Of Irradiated Nanocomposites, Joshua D. Mcgary
Theses and Dissertations
Modernization in space systems requires employment of new light-weight, high performance composite materials that reduce bulk weight and increase structural integrity. This thesis explored the behavior of one such material prior to and following a 35-year simulated space radiation life-cycle. Select electrical properties of nickel nanostrandTM-carbon composites in seven configurations were characterized prior to electron irradiation via surface and bulk resistivity measurements and contact electrostatic discharge (ESD) measurements. Following irradiation at a fluence of 1016 e-/cm2 at an average energy of 500 keV, measurements were repeated and compared against pre-irradiation data. Configuration D is …
Distribution Iteration: A Robust Alternative To Source Iteration For Solving The Discrete Ordinates Radiation Transport Equations In Slab And Xy- Geometries, Nicholas J. Prins
Distribution Iteration: A Robust Alternative To Source Iteration For Solving The Discrete Ordinates Radiation Transport Equations In Slab And Xy- Geometries, Nicholas J. Prins
Theses and Dissertations
The discrete ordinates method is widely used to solve the Boltzmann transport equation for neutral particle transport for many engineering applications. Source iteration is used to solve the discrete ordinates system of equations, but can be slow to converge in highly scattering problems. Synthetic acceleration techniques have been developed to address this shortcoming; however, recent research has shown synthetic acceleration to lose effectiveness or diverge for certain problems. LTC Wager introduced an alternative to source iteration and demonstrated it in slab geometry. Here the method is further developed, enhancing efficiency in various ways, and demonstrated in XY-geometry as well as …
Neutron Detection Utilizing Gadolinium Doped Hafnium Oxide Films, Bryan D. Blasy
Neutron Detection Utilizing Gadolinium Doped Hafnium Oxide Films, Bryan D. Blasy
Theses and Dissertations
Gadolinium (Gd) doped hafnium oxide (HfO2) was deposited onto a silicon substrate using pulsed laser deposition. Synchrotron radiation was used to perform Gd L3-edge extended X-ray absorption fine structure (EXAFS) measurements on 3%, 10%, and 15% doped HfO2 samples. The interatomic distances determined from Fourier transformation and fitting the data show Gd occupying the hafnium site in the HfO2 lattice, there was no clustering of Gd atoms, and the Gd ion retains monoclinic local symmetery for all levels of doping. Current as a function of voltage experiments identified the films as having poor diode characteristics with …
Evaluating The Response Of Polyvinyl Toluene Scintillators Used In Portal, Kelly D. Rakes
Evaluating The Response Of Polyvinyl Toluene Scintillators Used In Portal, Kelly D. Rakes
Theses and Dissertations
The goal of this research work was to determine if there exists, and to what extent, variability in the pulse-height spectrum, and resolution produced by ɤ-photon induced scintillation events in polyvinyl toluene scintillators. Scintillator panels of the same type as those used in portal detector units currently operated by the Department of Homeland Security, made of polyvinyl toluene and measuring 12 x 15 x 2 in were purchased from three vendors. Each vendor supplied two scintillators, one wrapped by the vendor with aluminum foil coated mylar, and two unwrapped. The scintillators where exposed to an ≈ 8µCi source collimated …
Micro-Etched Platforms For Thermal Inactivation Of Bacillus Anthracis And Bacillus Thuringiensis Spores, Leslie S. Hawkins
Micro-Etched Platforms For Thermal Inactivation Of Bacillus Anthracis And Bacillus Thuringiensis Spores, Leslie S. Hawkins
Theses and Dissertations
This research developed and applied microlithography techniques to etch microscope slide platforms in order to measure thermal inactivation of Bacillus thuringiensis and Bacillus anthracis spores, two closely related Bacillus species. B.t. is widely used as a surrogate for B.a. in response studies and in some field studies. This work addressed the previously identified problem of measuring both spore growth and spore thermal kill threshold using the traditional method of spreading a diluted spore solution on a plate. The micro-etched platforms forced spore separation thereby preventing neighbor growth from obscuring germination and initial vegetative growth measurements using a microscope. The technique …
Discrete Counting Of Short Lived Isotopes With Low Background Detectors, David E. Mather
Discrete Counting Of Short Lived Isotopes With Low Background Detectors, David E. Mather
Theses and Dissertations
We consider radiation counting experiments used to measure quantities of materials that are short-lived with respect to the count durations. The HPS 13.31 statistical analysis seriously overestimates the uncertainty when the quantity and background are very low. We consider the case in which the objective is to quantify the number of atoms, n, that were present in a sample when it was drawn. Mathews and Gerts [JRNC, 2008] analyzed this case and developed formulas for the probability distribution of n, in order to develop experiment design processes that minimize the smallest detectable quantity of material, thus maximizing sensitivity for the …
Time Dependent Discrete Ordinates Neutron Transport Using Distribution Iteration In Xyz Geometry, James R. Dishaw
Time Dependent Discrete Ordinates Neutron Transport Using Distribution Iteration In Xyz Geometry, James R. Dishaw
Theses and Dissertations
The DI algorithm is an alternative to source iteration that, in our testing, does not require an accelerator. I developed a formal verification plan and executed it to verify the results produced by my code that implemented DI with the above features. A new, matrix albedo, boundary condition treatment was developed and implemented so that infinite-medium benchmarks could be included in the verification test suite. The DI algorithm was modified for parallel efficiency and the prior instability of the refinement sweep was corrected. The testing revealed that DI performed as well or faster than source iteration with DSA and that …
A Multireference Density Functional Approach To The Calculation Of The Excited States Of Uranium Ions, Eric V. Beck
A Multireference Density Functional Approach To The Calculation Of The Excited States Of Uranium Ions, Eric V. Beck
Theses and Dissertations
An accurate and efficient hybrid Density Functional Theory (DFT)/Multireference Configuration Interaction (MRCI) model for computing electronic excitation energies in heavy element atoms and molecules was developed. This model incorporated relativistic effects essential for accurate qualitative and quantitative spectroscopic predictions on heavy elements, while simultaneously removing spin-multiplicity limitations inherent in the original model on which it is based. This model was used to successfully compute ground and low-lying electronic states for atoms in the first two rows of the period table, which were used for calibration. Once calibrated, calculations on carbon monoxide, bromine fluoride, the bromine atom, uranium +4 and +5 …
Precise Calculation Of Complex Radioactive Decay Chains, Logan J. Harr
Precise Calculation Of Complex Radioactive Decay Chains, Logan J. Harr
Theses and Dissertations
This thesis documents a new approach to investigate the gamma radiation activity of the fission products of three different fuels (U-235, U-238, and U-239) exposed to three different incident neutron energy spectra (thermal, fast spectrum, and high energies). An application of the exponential moments function is used with a transmutation matrix in the calculation of complex radioactive decay chains to achieve greater precision than can be attained through current methods. The result of this research is a code which can calculate the decay products from complex radioactive decay chains with a high degree of precision while quantifying the uncertainty in …
High Resolution Mesoscale Weather Data Improvement To Spatial Effects For Doserate Contour Plot Predictions, Christopher P. Jones
High Resolution Mesoscale Weather Data Improvement To Spatial Effects For Doserate Contour Plot Predictions, Christopher P. Jones
Theses and Dissertations
Reanalysis weather data is obtained for dates surrounding historical nuclear tests and processed through Regional Atmospheric Modeling System (RAMS) software to produce a high-resolution weather forecast. Output from RAMS is visualized to check for validity and input into Hazard Prediction and Assessment Capability (HPAC) software and modeled predictions are compared to historical observation data. Simulations are conducted using constant high resolution weather and varying terrain resolution. The HPAC prediction is numerically compared to historical observation data. The result of this research culminated in the knowledge that early-time, low-altitude wind data was neglected by HPAC's incorporation of the Defense Land Fallout …
Terrain And Spatial Effects On Hazard Prediction And Assessment Capability (Hpac) Software Dose-Rate Contour Plot Predictions As Compared To A Sample Of Local Fallout Data From Test Detonations In The Continental United States, 1945-1962, Kevin D. Pace
Theses and Dissertations
Hazard Prediction and Capability (HPAC) Software is validated by comparing modeled predictions to historical test data. Reanalysis weather data is acquired and reformatted for use in HPAC. Simulations are made using various amounts of weather data by use of a spatial domain. Simulations are also varied by levels of terrain resolution. The predicted output of the software is numerically compared to historical test data. The result of this research culminated in the knowledge that HPAC prediction accuracy is improved by using terrain resolutions beyond the flat earth assumption. Furthermore, this research establishes that domain size variation produces no significant advantage …
Improved Multinuclide Imaging Of Special Nuclear Material Using A High Purity Germanium Double Sided Strip Detector, Fred D. Rothenbush Jr.
Improved Multinuclide Imaging Of Special Nuclear Material Using A High Purity Germanium Double Sided Strip Detector, Fred D. Rothenbush Jr.
Theses and Dissertations
The purpose of this research is to improve the ability to image Special Nuclear Material (SNM) using a High Purity Germanium Double Sided Strip Detector (HPGeDSSD) for use in the field of nuclear nonproliferation. When used for gamma spectrometry, HPGe detectors can efficiently distinguish various isotopes because of their good energy resolution. The detector used for this research is a liquid nitrogen cooled germanium detector with five charge collection strips on each face. The strips are orthogonal to each other, creating a five by five array of data collection pixels. When the 25 mm by 25 mm detector array is …
Capacitance-Voltage Study On The Effects Of Low Energy Electron Radiation On Al0.27Ga0.73N/Gan High Electron Mobility Transistor, Thomas D. Jarzen
Capacitance-Voltage Study On The Effects Of Low Energy Electron Radiation On Al0.27Ga0.73N/Gan High Electron Mobility Transistor, Thomas D. Jarzen
Theses and Dissertations
The effects of radiation on semiconductors are extremely important to the Department of Defense since the majority of the defense informational, navigational and communications systems are now satellite-based. Due to the high radiation tolerance of gallium nitride and a plethora of high temperature, high power and high frequency applications, the prospect that gallium nitride based devices will become key components in a multitude of military satellite-based systems is highly probable. AlGaN/GaN HEMTs were irradiated at low temperature (~80 K) by 0.45 – 0.8 MeV electrons up to fluences of 1×1015 e-/cm2. Following irradiation, low temperature capacitance-voltage measurements …
Feasibility Analysis Of A Compton Spectrometer System For Identification Of Special Nuclear Material, Chad C. Schools
Feasibility Analysis Of A Compton Spectrometer System For Identification Of Special Nuclear Material, Chad C. Schools
Theses and Dissertations
Current operational needs require the deployment of radiation detection equipment with the ability to accurately and reliably identify special nuclear materials and their byproducts without dependence on cryogenics. This requires a resolution of 0.5% or less over a range of 200 to 700 keV. The feasibility of a Compton spectrometer to achieve this resolution is examined. The Compton spectrometer system used consists of two detectors. The Compton scatter event occurs in a CdTe detector where the Compton electron energy is collected. Gamma rays scattered out of the CdTe at an angle determined by a conical collimator, are collected in a …
Manufacture And Testing Of An Activation Foil Package For Use In Afids, Warren E. Kimmel
Manufacture And Testing Of An Activation Foil Package For Use In Afids, Warren E. Kimmel
Theses and Dissertations
This study used simulation and experiment to design and test foil packets for use in the Activation Foil Integrated Detection System (AFIDS). The initial plan to activate foil packets outside with the pulse reactor at White Sands Missile Range (WSMR) was not possible due to WSMR not having safety approval to take the reactor outside. As an alternative, the concept of using liquid nitrous oxide inside a reactor to simulate large volumes of air was investigated. Simulation using the Standardized Computer Analyses for Licensing Evaluation (SCALE) program was used to select ten foils to be included in the foil packet. …