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Articles 61 - 90 of 96
Full-Text Articles in Nuclear
Characterization Of A Boron Carbide Heterojunction Neutron Detector, James E. Bevins
Characterization Of A Boron Carbide Heterojunction Neutron Detector, James E. Bevins
Theses and Dissertations
New methods for neutron detection have become an important area of research in support of national security objectives. In support of this effort, p-type B5C on n-type Si heterojunction diodes have been built and tested. This research sought to optimize the boron carbide (BC) diode by coupling the nuclear physics modeling capability of GEANT4 and TRIM with the semiconductor device simulation tools. Through an iterative modeling process of controllable parameters, optimal device construction was determined such detection efficiency and charge collection were optimized. This allows an estimation of expected charge collection and efficiency given a set of operating …
Ray Next Event Estimator Transport Of Primary And Secondary Gamma Rays, Whitman T. Dailey
Ray Next Event Estimator Transport Of Primary And Secondary Gamma Rays, Whitman T. Dailey
Theses and Dissertations
This thesis investigated the application of the ray next event estimation Monte Carlo method to the transport of primary and secondary gamma rays. The problem of interest was estimation of the free field flux at a distant point in a vacuum from a point source in the atmosphere. An existing Fortran code for neutron transport, Ray Next-Event Estimator v4.0, was adapted to perform photon transport computations including coherent scattering, incoherent scattering, photoelectric absorption, and pair production interactions. Production and transport of secondary gamma rays produced in bremsstrahlung, neutron inelastic scatter, and neutron absorption interactions was also implemented. A new version …
Tof-Sims For Rapid Nuclear Forensics Evaluation Of Uranium Oxide Particles, Hannah E. Hocking
Tof-Sims For Rapid Nuclear Forensics Evaluation Of Uranium Oxide Particles, Hannah E. Hocking
Theses and Dissertations
Because of nuclear proliferation concerns, nuclear material must be safeguarded, and peaceful intentions verified. The field of nuclear forensics addresses these concerns. While established nuclear forensic techniques exist, quicker, more accurate and less expensive methods are of interest for nonproliferation applications. Currently a host of different analytical techniques, requiring a week or longer, are employed to obtain isotopic ratios, chemical abundances and morphology for forensic particulate samples. Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) is a candidate technology for rapid evaluation of these properties for small amounts of nuclear materials. After a thorough investigation, this study found TOF-SIMS to be particularly …
Characterization Of Neutron-Induced Defects In Isotopically Enriched Lithium Tetraborate, Brant E. Kananen
Characterization Of Neutron-Induced Defects In Isotopically Enriched Lithium Tetraborate, Brant E. Kananen
Theses and Dissertations
Lithium Tetraborate (LTB) is assessed for use as a material for neutron detection. LTB isotopically enriched in either Li-6 or B-10 provides a medium that efficiently captures and transmutes neutrons into more readily detected forms of material or energy. Neutron detection is desirable to detect elicit movement of special nuclear material or nuclear weapons. Single crystals of LTB, Li-6 or B-10 enriched, were neutron irradiated, and electron paramagnetic resonance was used to detect point defects induced by the neutrons. Multiple defects were noted in the irradiated crystals. Two particular defects, perturbed lithium vacancies and lithium clusters are proposed as induced …
Investigation Of Gate Leakage Current In Nitrogen-Irradiated Algan/Gan Heterostructures, Rose E. May
Investigation Of Gate Leakage Current In Nitrogen-Irradiated Algan/Gan Heterostructures, Rose E. May
Theses and Dissertations
Due to commercial and government interest in devices capable of functioning in high-power, high-frequency space applications, radiation tolerant AlGaN/GaN devices have been under study in recent years. Passivation of the AlGaN surface by (Si3N4) prevents electron trapping and enhances the 2DEG, but it also increases gate leakage currents, which can lead to device failure. This study sought information about current leakage mechanisms by introducing displacement damage close to the Si3N4/AlGaN interface. The effects of irradiation damage around the Si3N4/AlGaN interface on irradiation-induced leakage current were investigated for three …
Nuclear Weapon Yield Determination Through Nano Indentation Of Thermally Degraded Automobile Paint, Michael J. Richards
Nuclear Weapon Yield Determination Through Nano Indentation Of Thermally Degraded Automobile Paint, Michael J. Richards
Theses and Dissertations
This work investigated the suitability of automotive clearcoat as a nuclear weapon yield sensor, using the change in elastic modulus as the primary metric. The AFIT Xenon Thermal Simulator (AXTS) was used to simulate a nuclear thermal pulse. The elastic modulus of the clearcoat was measured using a nano indenter. During this research the power density of the AXTS beam was increased from 44.7 to 63.7 W/cm2. The morphological steps through which automobile paint proceeds as it thermally degrades were identified and correlated with temperatures. A computer model was created and used to ensure that the paint’s time-temperature …
A Comparison In The Accuracy Of Mapping Nuclear Fallout Patterns Using Hpac, Hysplit, Delfic Fpt And An Afit Fortran95 Fallout Deposition Code, April D. Miller
A Comparison In The Accuracy Of Mapping Nuclear Fallout Patterns Using Hpac, Hysplit, Delfic Fpt And An Afit Fortran95 Fallout Deposition Code, April D. Miller
Theses and Dissertations
Four nuclear fallout mapping tools are studied to determine which tool predicts the most accurate fallout dose-rate contours with low computation time and resources. The four programs consist of the FORTRAN95 based Fallout Deposition Code (FDC), the Hazard Prediction and Assessment Capability's (HPAC) Nuclear Weapon (NWPN), the Defense Land Fallout Interpretative Code (DELFIC) Fallout Planning Tool (FPT) and the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) Model. The models were compared to the Defense Nuclear Agency's (DNA) DNA 1251-1-EX, Compilation of Local Fallout Data from Test Detonations 1945-1962 Extracted from DASA 1251, using Warner and Platt's Measure of Effectiveness (MOE) method. …
Adaptive Imaging Methods Using A Rotating Modulation Collimator (Rmc), Daniel T. Willcox
Adaptive Imaging Methods Using A Rotating Modulation Collimator (Rmc), Daniel T. Willcox
Theses and Dissertations
The Rotating Modulation Collimator (RMC) belongs to a larger class of radiation imaging systems that rely on either temporal or spatial modulation of incident radiation through collimation to map the location of the incident radiation source. The strengths of these detection systems include their low cost and simplicity. A major drawback is the collection time required for low radiation intensities due especially to the loss of radiation information resulting from collimation. One method of addressing this drawback for the RMC is by applying an adaptive imaging approach. As with most system design theory, there are inherent design tradeoffs for the …
Directional Pair-Production Spectrometer Design For Airborne Stand-Off Detection Of Special Nuclear Material, William L. Harrell
Directional Pair-Production Spectrometer Design For Airborne Stand-Off Detection Of Special Nuclear Material, William L. Harrell
Theses and Dissertations
The purposes of this research are to experimentally and theoretically prove the concept of a directional pair-production spectrometer to detect and locate the tailings that are created when making Special Nuclear Material (SNM) at stand-off distances from a remotely piloted vehicle (RPV). A directional pair-production spectrometer uses the information garnered from the high energy gamma rays emitted by these SNM manufacturing tailings to perform pair-production spectroscopy and identify the isotope of interest. Through simultaneous operation as a Compton camera, the detection system will be able to measure rudimentary directional information from the medium energy gamma decays. The detector used for …
Combined Effects Of Radio Frequency And Electron Radiation On Cmos Inverters, Kristofer R. Dahl
Combined Effects Of Radio Frequency And Electron Radiation On Cmos Inverters, Kristofer R. Dahl
Theses and Dissertations
This research examines the measurement methodology, and the results of, the combined effects of electron and radio frequency irradiation (500kHz) on a CMOS Hex Inverter, CD4069UB. There have been many studies in recent years on the effects of electron radiation and electromagnetic interference on integrated circuits, however the combined effects have not been measured. A major obstacle for in-situ electron irradiation experiments is the over current hazard that exists to measurement equipment that comes from taking real-time, in-situ measurements. To overcome this, a test circuit was designed and built to allow for real-time in-situ measurement of the output voltage, current …
Changes To Electrical Conductivity In Irradiated Carbon Nanocomposites, Nickolas A. Duncan
Changes To Electrical Conductivity In Irradiated Carbon Nanocomposites, Nickolas A. Duncan
Theses and Dissertations
Carbon nanotubes (CNT) and carbon nanofibers (CNF) are two nanoparticles incorporated in a polymer to create a composite material. These composites are two potential lightweight materials for use as replacements for aluminum structures on satellite systems. Both composite materials have a low resistivity that is consistent with conductive materials. However, the CNT composite is substantially more conductive than the CNF composite. The CNT and CNF composites were irradiated with electrons and neutrons to fluence levels of and. No changes were observed in the resistivity of the CNF composites following neutron and electron irradiation. A 3.7% increase in resistivity was observed …
Radiation Effects On The Electrical Properties Of Hafnium Oxide Based Mos Capacitors, Jesse C. Foster
Radiation Effects On The Electrical Properties Of Hafnium Oxide Based Mos Capacitors, Jesse C. Foster
Theses and Dissertations
Hafnium oxide-based MOS capacitors were investigated to determine electrical property response to radiation environments. In situ capacitance versus voltage measurements were analyzed to identify voltage shifting as a result of changes to trapped charge with increasing dose of gamma, neutron, and ion radiation. In situ measurements required investigation and optimization of capacitor fabrication to include dicing, cleaning, metalization, packaging, and wire bonding. A top metal contact of 200 angstroms of titanium followed by 2800 angstroms of gold allowed for repeatable wire bonding and proper electrical response. Gamma and ion irradiations of atomic layer deposited hafnium oxide on silicon devices both …
Characterization Of The Neutron Spectrum At The Indiana University Nrep Neutron Source, Matthew R. Halstead
Characterization Of The Neutron Spectrum At The Indiana University Nrep Neutron Source, Matthew R. Halstead
Theses and Dissertations
The neutron source at the Indiana University Cyclotron Facility produces neutrons via proton bombardment of a natural beryllium (100% 9Be) target. This source has two beam lines: the LENS and the NREP. The energy spectrum of the neutrons produced on the NREP beam line has not yet been characterized. Through simulation using the GEANT and MCNP particle transport codes as well as neutron activation analysis experiments, an attempt was made to characterize the energy spectrum of the neutron production source. First, the neutron production spectrum of beryllium, simulated using GEANT, was compared with literature; there are significant deviations. Next, foils …
Investigation Of Yag:Ce Scintillating Fiber Properties Using Silicon Photomultipliers, Bradley S. Jones
Investigation Of Yag:Ce Scintillating Fiber Properties Using Silicon Photomultipliers, Bradley S. Jones
Theses and Dissertations
The properties of thin, cerium activated, yttrium aluminum garnet (YAG:Ce), scintillating fiber-shaped crystals were investigated for particle tracking and calorimetric applications such as Compton imaging of Special Nuclear Material from remote platforms at standoff ranges. Silicon photomultipliers (SiPMs) are relatively new, efficient, single photon sensitive, solid-state photodiode arrays which are well suited for the readout of scintillating fibers. Using SiPMs, the scintillation decay time profiles of six 400 micrometers YAG:Ce fiber crystals were measured under alpha and gamma irradiation. Interestingly, the observed decay times in the thin fibers were substantially slower than values for bulk single crystal YAG:Ce reported in …
Improving The Efficiency Of Photon Collection By Compton Rescue, Alexander W. Stevenson
Improving The Efficiency Of Photon Collection By Compton Rescue, Alexander W. Stevenson
Theses and Dissertations
A method to improve the efficiency of photon collection in thin planar HPGe detectors was investigated. The method involved implementing a second HPGe detector to collect Compton scattered photons from the primary detector and incorporating coincident interactions in the two detectors that sum to the full energy event into the energy spectrum. This method is termed Compton rescue because the Compton scattered photons make a partial energy deposition in the primary detector and are added back to the spectrum after being detected by the second detector. This research has implications on improving the efficiency of positron annihilation spectroscopy (PAS) techniques …
Positron Annihilation Ratio Spectroscopy Study Of Electric Fields Applied To Positronium At Material Interfaces, Ariella C. Walker
Positron Annihilation Ratio Spectroscopy Study Of Electric Fields Applied To Positronium At Material Interfaces, Ariella C. Walker
Theses and Dissertations
The purpose of this research was to develop a new code to analyze the data from AFIT's positron annihilation of radiation spectrometer, PsARS, system. The PsARS was used to analyze positronium formation at the surface of a capillary tube coated with gold. Using energy and geometry filters, the PsARS code determined the ratio of ortho-positronium to para-positronium. An electric field applied across the capillary tube wall forced positrons to move towards the gold surface of the capillary tube and prevent them from dropping into the Ore gap before they reach the surface. Inside the Ore gap, the positrons are more …
The Combined Effects Of Radio Frequency And Gamma Irradiation On P-Channel Mosfets, Joshua D. Daniel
The Combined Effects Of Radio Frequency And Gamma Irradiation On P-Channel Mosfets, Joshua D. Daniel
Theses and Dissertations
The purpose of this research was to investigate the combined effects of continuous gigahertz radio frequency signals and gamma irradiation on the threshold voltage of metal oxide semiconductor field effect transistors. The combined effects of gigahertz radio frequency waves and gamma irradiation on electronics presents a new challenge in electronic warfare and little is known of the combined effect on threshold voltage damage and recovery. The Fairchild NDS352AP, a commonly used commercial device, was irradiated by a cobalt-60 source under a +5 V bias with and without a radio frequency signal applied to the gate. The threshold voltage was measured …
Three Dimensional Positron Annihilation Momentum Measurement Technique (3dpamm) Applied To Measure Oxygen-Atom Defects In 6h Silicon Carbide, Christopher S. Williams
Three Dimensional Positron Annihilation Momentum Measurement Technique (3dpamm) Applied To Measure Oxygen-Atom Defects In 6h Silicon Carbide, Christopher S. Williams
Theses and Dissertations
A three-dimensional Positron Annihilation Spectroscopy System (3DPASS) capable to simultaneously measure three-dimensional electron-positron (e--e+) momentum densities measuring photons derived from e--e+ annihilation events was designed and characterized. 3DPASS simultaneously collects a single data set of correlated energies and positions for two coincident annihilation photons using solid-state double-sided strip detectors (DSSD). Positions of photons were determined using an interpolation method which measures a figure-of-merit proportional to the areas of transient charges induced on both charge collection strips directly adjacent to the charge collection strips interacting with the annihilation photons. The subpixel resolution was measured for both double-sided strip detectors (DSSD) and …
In-Situ, Gate Bias Dependent Study Of Neutron Irradiation Effects On Algan/Gan Hfets, Janusz K. Mikina
In-Situ, Gate Bias Dependent Study Of Neutron Irradiation Effects On Algan/Gan Hfets, Janusz K. Mikina
Theses and Dissertations
AlGaN/GaN Heterostructure Field Effect Transistors (HFETs) have come under increased study in recent years due to their highly desirable material and electrical properties and survivability even during and after exposure to extreme temperature and radiation environments. In this study, unpassivated and SiN passivated Al0.27Ga0.73N/GaN HFETs were subjected to neutron radiation at 120 K. The primary focus of the research was the effects of neutron irradiation on drain current, gate leakage current, threshold voltage shift, gate-channel capacitance, and the effects of biasing the gate during irradiation. In-situ measurements were conducted on transistor current, gate-channel capacitance, and gate …
Thermal Neutron Point Source Imaging Using A Rotating Modulation Collimator (Rmc), Nathan O. Boyce
Thermal Neutron Point Source Imaging Using A Rotating Modulation Collimator (Rmc), Nathan O. Boyce
Theses and Dissertations
This thesis demonstrates a previously untested capability of the Rotating Modulation Collimator (RMC) to image a point-like neutron source. The encouraging results, achieved using low-energy neutrons, provide motivation for further refinement and continued research with higher-energy neutrons. The detector and the masks on an existing RMC imaging system were exchanged to function with neutrons. The source in this research produced a poly-energetic spectrum of neutrons through the reaction. The source of alpha particles was a 72.7 mCi 239Pu source. The RMC detector was located 250 cm from the bare source and operated for three hours to generate a modulation …
Time Dependent Channel Packet Calculation Of Two Nucleon Scattering Matrix Elements, Brian S. Davis
Time Dependent Channel Packet Calculation Of Two Nucleon Scattering Matrix Elements, Brian S. Davis
Theses and Dissertations
A new approach to calculating nucleon-nucleon scattering matrix elements using a proven atomic time-dependent wave packet technique is investigated. Wave packets containing centripetal barrier information are prepared in close proximity to nuclear well. This is accomplished by first using an analytic equation to determine the wave packets in a suitable intermediate asymptotic state where the centripetal barrier is negligible. Then, the split operator technique is used to propagate the wave packets back to their original positions under the full Hamiltonian. Here, one wave packet is held stationary while the other is allowed to evolve and explore the nuclear well. Scattering …
Uncertainty Quantification Of Multi-Component Isotope-Separation Cascade Model, Khoi D. Tran
Uncertainty Quantification Of Multi-Component Isotope-Separation Cascade Model, Khoi D. Tran
Theses and Dissertations
Monte Carlo uncertainty quantification (UQ) capability has been added to a code for modeling multi-component steady-state isotope-separation enrichment cascades to characterize the propagation of uncertainties in input data that define the cascade and the feed. Random samples of error for every computational input are drawn from its individual uncertainty distribution and added to the inputs, creating a set of enrichment cascade problems with perturbed inputs. The set of problems is solved using the verified code. The cascade outputs are then characterized using the empirical cumulative distribution. The uncertainty output data are analyzed to gain new insights into the behaviors of …
Nuclear Forensics: Measurements Of Uranium Oxides Using Time-Of-Flight Secondary Ion Mass Spectrometry (Tof-Sims), Wesley A. Schuler
Nuclear Forensics: Measurements Of Uranium Oxides Using Time-Of-Flight Secondary Ion Mass Spectrometry (Tof-Sims), Wesley A. Schuler
Theses and Dissertations
Over the past decade, law enforcement, governmental and public agencies have been stymied by the threat of the trafficking of nuclear materials. During this time span, reports from the International Atomic Energy Agency of illicit trafficking have increased eightfold from 20 to 160. For this reason, nuclear forensics is a burgeoning science focused on the identification of seized special nuclear materials. Identification of these materials is based upon the wealth of information that can be obtained by applying multiple analytical and measurement technologies. All of the information gained from each sample can then be used to further characterize other samples …
Effect Of Advanced Synthetically Enhanced Detector Resolution Algorithm On Specificity And Sensitivity Of Portable High Purity Germanium Gamma Detector Spectra, Latosha M. Bell
Theses and Dissertations
The ability to identify special nuclear material is one of the necessary prevention mechanisms for preventing proliferation of special nuclear materials. Additionally, if a nuclear event were to occur, information about the nuclear material used may be extracted from gamma spectra, provided it is obtained quickly and accurately. This can be made possible with the use of the exceptional resolution of the HPGe detector. This experiment applied the Advanced Synthetically Enhanced Detector Resolution Algorithm (ASEDRA) to a portable HPGe detector's spectra, to investigate whether improvements in specificity and sensitivity can be obtained. This method has been used to improve performance …
Estimation Of Weapon Yield From Inversion Of Dose Rate Contours, Buckley E. O'Day Iii
Estimation Of Weapon Yield From Inversion Of Dose Rate Contours, Buckley E. O'Day Iii
Theses and Dissertations
This research studies the uncertainty in yield estimation from inversion of dose rate contours. The Hazard Prediction and Assessment Capability (HPAC) and a simple FORTRAN95 based Fallout Deposition Code (FDC) are used to recreate dose rate contours from historic nuclear tests. Fallout footprints from six atomic tests are recreated using balloon wind soundings and high resolution mesoscale weather reanalysis data. Dose rate contour plots are created for different yields for a single set of weather conditions. Dose rate contours are compared to determine uncertainty in yield estimation from inversion of dose rate contour plots. Results of these dose rate recreations …
Phenomenological Model For Infrared Emissions From High-Explosive Detonation Fireballs, Kevin C. Gross
Phenomenological Model For Infrared Emissions From High-Explosive Detonation Fireballs, Kevin C. Gross
Theses and Dissertations
Time-resolved infrared spectra were recently collected via a Fourier-transform spectrometer (FTS) from the detonation fireballs of two types of conventional military munitions (CMM) as well as uncased TNT and four types of enhanced novel explosives (ENEs). The CMM spectra are dominated by continuum emission, and a single-temperature Planckian distribution, modified for atmospheric attenuation, captures most of the variation in the data. Some evidence of selective emission is identified by systematic patterns in the fit residuals. The behavior of these systematic residuals affords a distinction between the two types of CMMs studied. The uncased TNT and ENE spectra appear strongly influenced …
Efficient And Accurate Computation Of Elastic Cross Sections In The Single-Level Breit-Wigner Resonance Region, Edward L. Hobbs
Efficient And Accurate Computation Of Elastic Cross Sections In The Single-Level Breit-Wigner Resonance Region, Edward L. Hobbs
Theses and Dissertations
The use of piecewise cubic Hermite polynomials to approximate resonance region cross sections provides a means to accomplish the same task with increased accuracy and fewer points that require exact cross section calculation. Once the derivative of the cross section formula is derived and the interpolating cubic is appropriately shifted and scaled for numerical stability, use of the piecewise cubic Hermite polynomial is easily inserted into computer codes that depend on cross section calculation in the resonance energy region.
Characterization Of Detonation Phenomena Observed In High-Speed Visible Imagery, Trevor W. Warren
Characterization Of Detonation Phenomena Observed In High-Speed Visible Imagery, Trevor W. Warren
Theses and Dissertations
Measurements for radius, angular velocity, initial time of observation, and final time of observation were made for turbulent vortices around detonation fireballs. A proxy for vortex power, determined through unit analysis, was found to correlate well to initial (and final) time of observation with R2 equal to 0.8572. The linear trend on a log10-log10 plot was indicative of a rapid decrease (over 10-1 s) in power associated with the decay of the fireball. Predictions, based on turbulent spectral theory were made for root-mean-square velocity fluctuations and Reynolds numbers, both as functions of time. In addition, …
In-Line Particulate Transport And Dispersion Modeling Using The Regional Atmospheric Modeling System (Rams), John W. Englert
In-Line Particulate Transport And Dispersion Modeling Using The Regional Atmospheric Modeling System (Rams), John W. Englert
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 …
Efficient And Accurate Computation Of Non-Negative Anisotropic Group Scattering Cross Sections For Discrete Ordinates And Monte Carlo Radiation Transport, David W. Gerts
Theses and Dissertations
A new method for approximating anisotropic, multi-group scatter cross sections for use in discretized and Monte Carlo multi-group neutron transport is presented. The new method eliminates unphysical artifacts such as negative group scatter cross sections and falsely positive cross sections. Additionally, when combined with the discrete elements angular quadrature method, the new cross sections eliminate the lack of angular support in the discrete ordinates quadrature method. The new method generates piecewise-average group-to-group scatter cross sections. The accuracy and efficiency for calculating the discrete elements cross sections has improved by many orders of magnitude compared to DelGrande and Mathews previous implementation. …