99 research outputs found
PASSIVATED IMPLANTED PLANAR SILICON (PIPS) DETECTORS FOR MEASUREMENT OF RADIOXENON
No full textSilicon detectors are analyzed as an alternative to plastic scintillators for beta detection based on their higher energy resolution. A radioxenon detection setup was created with the intent of comparing the absolute efficiency of the beta-gamma coincidence measurements between a silicon detector (PIPS) with each a NaI(Tl) scintillator and a high purity germanium (HPGE) semiconductor detector. The absolute efficiencies of both setups are calculated and compared.M.S
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Compton suppression and gamma-gamma coincidence
No full texttextThis project aims to improve research in gamma-ray spectroscopy by using advanced detector systems. These systems are designed to reduce interference inherent in gamma-ray spectroscopy by rejecting Compton scattering events from high-energy gamma-rays, as well as look at cascading decays of gamma-rays through gamma-gamma coincidence counting. By combining these methods, one is able to lower detection limits for many elements than would otherwise be possible. This work also takes advantage of neutron activation analysis, which allows stable elements to be analyzed by activating them with neutrons, causing them to become unstable and decay with radioactive signatures. By analyzing these signatures, one is able to detect trace levels of elements with relatively small samples sizes (< 1g) and in a nondestructive manner.Mechanical Engineerin
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Long-term low-level Arctic aerosol trends, analysis, and climatological correlations at Alert, Canada
No full textThree decades of weekly winter low-level Arctic aerosol samples from Alert, Canada, are analyzed using Neutron Activation Analysis (NAA) in the TRIGA reactor at the University of Texas. The samples are from the longest currently-running Arctic aerosol data collection project and have received only limited analysis to date. The elemental composition (Aluminum, Bromine, Calcium, Chlorine, Copper, Iodine, Magnesium, Manganese, Sodium, Titanium, and Vanadium) is determined for each sample. The elemental results are characterized statistically and the results are compared to climatological data including temperature data, sea ice data, ice shelf data, and snow cover data. Positive Matrix Factorization (PMF) is performed on the complete data set to determine primary sources of the aerosol pollution. Other data from Alert, including Methanesulphonic Acid (MSA), Iron, and Sulphate data, is compared to the NAA results, and additional PMF is performed with the additional data. Results show many expected as well as unexpected trends and correlations including correlations with ice cover and temperature trends, correlations to decreasing anthropogenic pollution, and long-term trends of sea components and sea-component ratios in the aerosol. PMF results conclude that there are 5 predominant sources of the Arctic aerosol including two sea sources, two predominant anthropogenic sources (combustion and industrial), and a crustal component. This particular area of inquiry represents completely new information in the growing body of climate science and may influence studies that relate to the Arctic climate and environment, and should have an impact on the particular fields of Arctic Aerosol Monitoring, Atmospheric Transport, Global Diffusion and Dispersion, Arctic Climate Science, and Pollution Monitoring.Mechanical Engineerin
Source receptor modeling of airborne particles collected over the Great Lakes
No full textHigh-volume air samplers were used to collect aerosol samples on Whatman 41 air filters at the Canadian air sampling stations Burnt Island, Egbert and Point Petre. Once collected, the samples were analyzed for trace elements by neutron activation analysis. Air concentrations of over thirty trace elements were determined. A special focus was made to utilize Compton suppression gamma-ray spectroscopy and epithermal irradiations to enhance the detection limits of neutron activation analysis. These vanguard techniques allowed for the determination of trace elements at very low levels. Advancements were also made for the determination of Br through short-lived irradiations.After the air concentrations were determined for trace elements from the neutron activation analysis data, the trends, sources and origin of the atmospheric aerosols were investigated. Exploration of the seasonal trends revealed that elements from a salt source like Na, Cl and Br were highest in the winter while elements originating from crustal weathering like Al, Ca and Si were highest in the summer. Many elements of anthropogenic origin demonstrated no seasonal trend. Enrichment factor analysis revealed elements from non-crustal sources including the elements Ag, As, Br, Cl, I, In, Sb, Se, Sn and Zn. Factor analysis exhibited trends that indicate oil and coal combustion, mining, incineration, and smelting as anthropogenic sources to aerosols of the rural Great Lakes. Potential source contribution function analysis indicated that many of the anthropogenic atmospheric pollutants in the Great Lakes originate from industrial centers in the eastern and southeastern United States. Study of the trace metal dry deposition into Lakes Huron and Ontario indicated that the majority of the total deposition resulted from crustal materials. However, dry deposition is a significant pathway for many toxic anthropogenic trace metals into the Great Lakes.Made available in DSpace on 2011-05-07T12:00:13Z (GMT). No. of bitstreams: 2
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INVESTIGATING THE RESPONSE OF YTTRIUM HYDRIDE MODERATOR DUE TO CHANGES IN STOICHIOMETRY AND TEMPERATURE
No full textMicroreactors are designed to be compact, truck-transportable, and self-regulating with power levels rated anywhere between 1 kWe to 10 MWe. Microreactors are envisioned to be utilized for terrestrial as well as space power applications. Originally, microreactors were envisioned to use HEU fuel with fast spectrum core operation, however, this poses regulatory concerns. As such, recent endeavors rely on the application of Low Enriched Uranium (LEU) fuel. In order to maintain a relatively compact reactor-core with LEU fuel, effective neutron moderation is required; and hence LEU mandates the use of moderators. Solid metal hydrides are being considered due to their structural, neutronic, and containment benefits. Out of all the metal hydrides, Yttrium Hydride (YH_(2-x)) is considered as the primary candidate as it provides relatively high hydrogen density combined with high maximum operating temperature. However, hydrogen dissociation and migration at higher temperatures within the YH_(2-x) element raises concerns as it changes the reactor behavior during operation. The diffusion of hydrogen within the YH_(2-x) matrix under a temperature-gradient causes local shifts in the material properties as YH_(2-x) is altered to YH_((2-x)±Δ). As such, stoichiometric and temperature responses of the YH_(2-x) moderator properties are investigated in this dissertation. To create these properties, atomistic simulations, using Density Functional Theory (DFT), are performed. Furthermore, thermal scattering laws (TSLs) are generated using DFT phonon density of states and NJOY2016 for sub-stoichiometric YH_(2-x) to account for shifts in neutron cross sections at thermal energies. The properties generated from atomistic modeling is further validated with the neutron diffraction experiments performed by Los Alamos Neutron Science Center (LANSCE) and available literature. Finally, a coupling capability is developed and implemented using the Monte-Carlo code MCNP along with the Finite Element based code ABAQUS. The coupled framework is realized via Picard iterations, and allows the investigation of neutronics, heat transfer, and hydrogen mass diffusion. This dissertation provides a general framework to model the design space and performance of YH_(2-x) moderated reactors.Ph.D
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Essential physics for fuel cycle modeling
No full texttextNuclear fuel cycles (NFC) are the collection of interconnected processes which generate electricity through nuclear power. Due to the high degree of coupling between components even in the simplest cycles, the need for a dynamic fuel cycle simulator and analysis framework arises. The work presented herein develops essential physics models of nuclear power reactors and incorporate them into a NFC simulation framework.
First, a one-energy group reactor model is demonstrated. This essential physics model is then to simulate a sampling fuel cycles which are perturbations of well known base-case cycles. Because the NFC may now be simulated quickly, stochastically modeling many fuel cycle realizations dramatically expands the parameter space which may be analyzed. Finally, a multigroup reactor model which incorporates spectral changes as a function of burnup is presented to increase the fidelity of the original one-group reactor.
These methods form a suite of modeling technologies which reach from the lowest levels (individual components) to the highest (inter-cycle comparisons). Prior to the development of this model suite, such broad-ranging analysis had been unrealistic to perform. The work here thus presents a new, multi-scale approach to fuel cycle system design.Mechanical Engineerin
Development Of A Nuclear Certificate For Nuclear Safety, Nuclear Security, And Nuclear Environmental Protection Within A Mechanical Engineering Department
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Critical thickness of high structural quality SrTiO3 films grown on orthorhombic (101) DyScO3
No full textStrained epitaxial SrTiO{sub 3} films were grown on orthorhombic (101) DyScO{sub 3} substrates by reactive molecular-beam epitaxy. The epitaxy of this substrate/film combination is cube on cube with a pseudocubic out-of-plane (001) orientation. The strain state and structural perfection of films with thicknesses ranging from 50 to 1000 {angstrom} were examined using x-ray scattering. The critical thickness at which misfit dislocations was introduced was between 350 and 500 {angstrom}. These films have the narrowest rocking curves (full width at half maximum) ever reported for any heteroepitaxial oxide film (0.0018{sup o}). Only a modest amount of relaxation is seen in films exceeding the critical thicknesses even after postdeposition annealing at 700{sup o}C in 1 atm of oxygen. The dependence of strain relaxation on crystallographic direction is attributed to the anisotropy of the substrate. These SrTiO{sub 3} films show structural quality more typical of semiconductors such as GaAs and silicon than perovskite materials; their structural relaxation behavior also shows similarity to that of compound semiconductor films
Barium Titanate and Barium Orthotitanate Powders Through An Ethylene Glycol Polymerization Route
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