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Articles 1 - 19 of 19
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Source Normalization Constants For Ground Distributed Fallout Fields, Justin M. Smith
Source Normalization Constants For Ground Distributed Fallout Fields, Justin M. Smith
Theses and Dissertations
Five assumptions regarding a first order model developed to calculate dose rate at a detector above a fallout field are analyzed. The omission of scattering is relaxed by the method of successive scatters resulting in a build up factor of 1.1. The use of a single average photon energy to represent a fallout distribution is analyzed using the Oak Ridge National Laboratory Isotope Generator (ORIGEN) Fallout Analysis Tool. An average photon energy of 0.81MeV is calculated and shown to be an accurate approximation of the fallout field energy distribution. A Gaussian distribution is used to calculate the minimal impact of …
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 …
Background And Source Term Identification In Active Neutron Interrogation Methods, David A. Anthony
Background And Source Term Identification In Active Neutron Interrogation Methods, David A. Anthony
Theses and Dissertations
The detection and tracking of special nuclear material (SNM) is vitally important in order to know where these materials are and prevent them from being used in a harmful manner. Active neutron interrogation is a sought after method for this since the resulting high energy gamma rays produced by inelastic scattering and neutron capture reactions can pass through denser shielding than natural decay gammas, and their energy spectra are unique to each isotope. Using Monte Carlo N Particle (MCNP) simulations, this research investigated the characterization of gamma ray sources created by active neutron interrogation. Ring detector and mesh tallies within …
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 …
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 …
Cathodoluminescence And Photoemission Of Doped Lithium Tetraborate, Christina L. Dugan
Cathodoluminescence And Photoemission Of Doped Lithium Tetraborate, Christina L. Dugan
Theses and Dissertations
Lithium tetraborate (Li2B4O7) crystals are being developed for possible use in solid state neutron detectors. The 6Li(n,α)3H and 10B(n,α)7Li reactions are the basis for neutron detection, and a Li2B4O7 crystal enriched with Mn should show improved efficiency for neutron detection. There is a lack of fundamental characterization information regarding this useful material, particularly with regard to its electronic configuration. Photoemission spectroscopy was used to determine the energy level structure of the Mn doped Li2B4O7 crystals. …
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 …
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 …
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 …
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 …
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 …
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 …
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 …
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. …
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 …
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 …