Physical Sciences and Mathematics Commons^™

Thick Target Yield Of Th-229 Via Low Energy Proton Bombardment Of Th-232, Justin Reed Griswold

Masters Theses

Actinium-225 is one of the more effective radioisotopes used in alpha radioimmunotherapy. Due to its ten-day half-life, it is more efficient to create its precursor, ²²⁹Th [Thorium-229] (t_1/2[half-life] = 7932 ± 55 years). In this work, ²²⁹Th was produced via 40 MeV [Mega electron Volts] proton bombardment of a thick ²³²Th [Thorium-232] target. The irradiation took place at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Lab (ORNL). The target, consisting of 23 stacked natural thorium foils (137 mg/cm² [milligrams per square centimeter] each), was irradiated with 50 nA [nanoamps] of …

The Isotope Effect On Proton Conduction And Glass Transition In Phosphoric Acid, Maximilian Ferdinand Heres

Masters Theses

Hydrogen fuel cells combine hydrogen and oxygen to create water and electricity. Polymer electrolyte membranes (PEM) make up barriers within the fuel cell allowing only protons to pass through, while keeping other components separate. Many PEM contain phosphoric acid (PA) as a building block due to its excellent proton conducting properties. Improved ionic conductivity in PEM can lead to the development of better, more efficient fuel cells.

While ionic conductivity in PA at high temperatures is extensively characterized, the low temperature dynamics are not so well explored. Below the glass transition, molecular motion is frozen and proton motion is forced …

Structure Analysis Of Sn Bilayer Films On Si (111), Weisong Tu

Masters Theses

Chemical doping is a well-established method for controlling the electronic properties of bulk semiconductors and, e.g, complex oxide materials. In this process, dopant atoms are located at substitutional lattice locations, from where they introduce free charge carriers to the host material. These carriers greatly improve the electrical conductivity of the host material and can even induce an insulator-metal transition at high doping levels. Dopants, however, also introduce scattering centers that are detrimental to conductivity, especially in low-dimensional systems such as nanowires and ultrathin films. These problems can be overcome by using a modulation doping approach in which the dopant atoms …

Radiation-Induced Radicals In Polyurea-Crosslinked Silica Aerogel, Benjamin Michael Walters

Masters Theses

Free radicals are atoms or molecules with an odd number of electrons in an outer shell. Since electrons typically occur in pairs, this leaves one electron that is unpaired. In seek of another electron to pair with, free radicals react with and steal electrons from neighboring molecules, which then become free radicals themselves. This can start a chain reaction, cascading into large scale damage.

Ionizing radiation can tear through molecules, just as bullets can tear through things that we see. If free radicals can be detected, and seen to increase in a material upon radiation exposure, this can indicate molecular …

Validation Of Weak Form Thermal Analysis Algorithms Supporting Thermal Signature Generation, Elton Lewis Freeman

Masters Theses

Extremization of a weak form for the continuum energy conservation principle differential equation naturally implements fluid convection and radiation as flux Robin boundary conditions associated with unsteady heat transfer. Combining a spatial semi-discretization via finite element trial space basis functions with time-accurate integration generates a totally node-based algebraic statement for computing. Closure for gray body radiation is a newly derived node-based radiosity formulation generating piecewise discontinuous solutions, while that for natural-forced-mixed convection heat transfer is extracted from the literature. Algorithm performance, mathematically predicted by asymptotic convergence theory, is subsequently validated with data obtained in 24 hour diurnal field experiments for …

Evaluation Of Tagging Techniques Gamma-Decay Probabilities Using The Surrogate Method, Timothy Lee Reed

Masters Theses

A detailed analysis of the statistical and discrete [gamma]-decay tagging techniques was conducted using the absolute surrogate and surrogate ratio method (SRM) to obtain the 92Mo(n,[gamma]) cross section in an equivalent neutron energy range of 80 to 880 keV. Excited 93Mo and 95Mo nuclei were populated using (d,p) reactions on 92Mo and 94Mo targets, respectively. The absolute surrogate 92Mo(n,[gamma]) cross sections disagreed with evaluated neutron capture cross section data by as much as a factor of 4 using the statistical tagging approach, whereas the discrete [gamma]-decay tag absolute surrogate cross section disagreed with the evaluated neutron capture cross section by …

Testing A Novel Technique To Improve Aluminum-26 Accelerator Mass Spectrometry Measurements For Earth Science Applications, Meghan Sarah Janzen

Masters Theses

The measurement of cosmogenic ²⁶Al [aluminum-26] in geological samples by accelerator mass spectrometry (AMS) is typically conducted on Al₂O₃ [aluminum oxide] targets. However, Al₂O₃ is not an ideal source material because it does not form a prolific beam of Al^- [negative atomic aluminum ions] required for measuring low-levels of ²⁶Al. This thesis presents the performance of AlN [aluminum nitride], AlF₃ [aluminum fluoride] and mixed AlN + Al₂O₃ as novel alternative source materials for the analysis of ²⁶Al. A negative ion cesium sputtering source at the Holifield …

Higher-Order Corrections In Effective Theory Of Deformed Nuclei, Jialin Zhang

Masters Theses

The low-energy excitation bands of open-shell heavy nuclei have been accounted for by collective motion of the constituting nucleons. Macroscopically, heavy nuclei can be looked upon as deformed rotors undergoing surface vibration and rotation. Traditionally, deformed nuclei are described within the Bohr-Mottelson geometric model or the interacting boson model. An effective theory that exploits spontaneous symmetry breaking has recently been developed for axially deformed nuclei. It describes the rotational and vibrational degrees of freedom in terms of Nambu-Goldstone bosons and quadrupole phonons respectively, with a power counting based on their different energy scales. A systematic way to construct the rotationally …

A High-Energy Neutron Flux Spectra Measurement Method For The Spallation Neutron Source, Nicholas Patrick Luciano

Masters Theses

The goal of this work was to develop a foil activation method to measure high-energy (∼1-100 MeV) neutron flux spectra at the Spallation Neutron Source by researching the scientific literature, assembling an experimental apparatus, performing experiments, analyzing the results, and refining the technique based on experience. The primary motivation for this work is to provide a benchmark for the neutron source term used in target station and shielding simulations Two sets of foil irradiations were performed, one at the ARCS beamline and one at the POWGEN beamline. The gamma radiation of the foil activation products was measured with a high …

Transverse Waves In Simulated Liquid Rocket Engines With Arbitrary Headwall Injection, Charles Toufic Haddad

Masters Theses

This work introduces a closed-form analytical solution for the transverse vorticoacoustic wave in a circular cylinder with arbitrary headwall injection. This particular configuration mimics the conditions leading to the onset of traveling radial and tangential waves in a simple liquid rocket engine (LRE). Assuming a short cylindrical chamber with an injecting headwall, regular perturbations are used to linearize the problem’s mass, momentum, energy, ideal gas and isentropic relations. A Helmholtz decomposition is subsequently applied to the first-order disturbance equations, thus giving rise to a compressible, inviscid and acoustic set that is responsible for driving the unsteady motion and to an …

Nuclear Modification Factor For Production Of Open Heavy Flavor At Forward Rapidity In Cu+Cu Collisions, Archil Garishvili

Masters Theses

The PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory with its muon spectrometer has the ability to detect muons over the range of pseudorapidity 1.1 < |eta| < 2.25. Single muon production is an important tool for studying heavy flavor production via semi-leptonic decays of open heavy flavor mesons. Because of their large mass, heavy quarks are produced in earlier stages of heavy ion collisions. Therefore, heavy flavor production can serve as an important probe of the Quark Gluon Plasma, a novel state of matter predicted to be created at RHIC. The measurement of the nuclear modification factor of open heavy flavor at forward rapidity in Cu+Cu collisions at sqrt{s_{NN}}=200 GeV is presented. Measurements of heavy flavor production in p+p collisions at sqrt{s_{NN}}=200 GeV will be also presented.

Positron Emission Tomography (Pet) For Flow Measurement, Bi Yao Zhang

Masters Theses

Positron Emission Tomography (PET) is frequently used for medical imaging. Maturity and flexibility of PET as an imaging technique has expanded its utility beyond the medical domain. It can be used as a tool for fluid flow studies in opaque fluids and for flow within complex geometry where conventional optical flow measurement approaches fail. This study explores the capabilities of PET as flow measurement tool suited to validation of computational fluid dynamic (CFD) predictions.

The MicroPET P4 scanner was used to image the diffusion process in flow around a rod bundle geometry similar to that found in a nuclear reactor …

A Study Of The Release Properties Of Sn And Sns From An Isol-Type Target/Ion Source System, Ronald Earl Goans

Masters Theses

Radioactive ion beams (RIBs) provide a method for studying the properties of increasingly exotic nuclei. For many nuclei, the intensity of the RIB available in the isotope separation on-line (ISOL) technique is limited by the relatively long delay time in the target/ion source system (TISS). New techniques are needed to decrease this delay time, thereby increasing the intensity of the RIBs available for study.

The sulfide molecular sideband was discovered in 2001 as a way to greatly enhance the quality of Sn beams. Holdup measurements were performed at the Holifield Radioactive Ion Beam Facility (HRIBF) to determine the extent to …

On The Behavior Of The Asymptotics Of Robertson-Walker Cosmologies As A Function Of The Cosmological Constant, Noah Thomas Schaefferkoetter

Masters Theses

An analysis of the Einstein Field Equations within a Robertson-Walker Cosmology. More specifically, what values of the cosmological constant will result in a Big Bang.

Analytical Computation Of Proper Orthogonal Decomposition Modes And N-Width Approximations For The Heat Equation With Boundary Control, Tasha N. Fernandez

Masters Theses

Model reduction is a powerful and ubiquitous tool used to reduce the complexity of a dynamical system while preserving the input-output behavior. It has been applied throughout many different disciplines, including controls, fluid and structural dynamics. Model reduction via proper orthogonal decomposition (POD) is utilized for of control of partial differential equations. In this thesis, the analytical expressions of POD modes are derived for the heat equation. The autocorrelation function of the latter is viewed as the kernel of a self adjoint compact operator, and the POD modes and corresponding eigenvalues are computed by solving homogeneous integral equations of the …

Elastic And Magnetic Properties Of Tb6fe(Sb,Bi)2 Using Resonant Ultrasound Spectroscopy., David Michael Mccarthy

Masters Theses

Tb6FeSb2 and Tb6FeBi2 are novel rare earth compounds with little prior research. These compounds show high and variable curie temperatures for rare-earth compounds. This has lead to a literature review which includes the discussion of: elasticity, resonance, and magnetism. This review is used to discuss the theory and methodology which can relate these various properties to each other. Furthermore, synthesis, x-ray analysis, and RUS sample preparation of Tb6FeSb2 and Tb6FeBi2 were completed.

Resonant Ultrasound Spectroscopy (RUS) elastic studies were taken for Tb6FeSb2 and Tb6FeBi2 as a function temperature from 5-300K, in various magnetic fields ranging from 0-9T. Tb6FeSb2’s and Tb6FeBi2’s …

Nonlinear Acoustics Of Piston-Driven Gas-Column Oscillations, Andrew William Wilson

Masters Theses

The piston-driven oscillator is traditionally modeled by directly applying boundary conditions to the acoustic wave equations; with better models re-deriving the wave equations but retaining nonlinear and viscous effects. These better models are required as the acoustic solution exhibits singularity near the natural frequencies of the cavity, with an unbounded (and therefore unphysical) solution. Recently, a technique has been developed to model general pressure oscillations in propulsion systems and combustion devices. Here, it is shown that this technique applies equally well to the piston-driven gas-column oscillator; and that the piston experiment provides strong evidence for the validity of the general …

Three Dimensional Localization With Time-Gated Photon Counting And Maximum Likelihood Analysis, James Andrew Germann

Masters Theses

The localization of particles is an important step for the study of nanoscale objects and systems. Research is ongoing on techniques to find the position of particles moving about freely or interacting with other objects, especially below the diffraction limit of optical microscopy. The method of particle localization under development here arranges four laser beam foci created from a femtosecond pulsed Ti-Sapphire laser into a tetrahedron. The microscope constructed for this thesis includes optics to split each Ti-Sapphire laser pulse into four temporally and spatially separated pulses at the focus of the objective. Maximum likelihood analysis of the time-gated fluorescence …

Digital Aperture Photometry Utilizing Growth Curves, William Chandler Overcast

Masters Theses

Point source extraction is critical to proper analysis of images containing point sources obtained by focal plane array cameras. Two popular methods of extracting the intensity of a point source are aperture photometry and point spread function fitting. Digital aperture photometry encompasses procedures utilized to extract the intensity of an imaged point source. It has been used by astronomers in various forms for calculating stellar brightness. It is also useful for doing analysis of data associated with other unresolved radiating objects. The various aperture photometry methods include the two-aperture method, aperture correction, and growth curve method.

The growth curve method …

An Investigation Of Gas Bubble Generation And Measurement In Water And Mercury, Stuart A Walker

Masters Theses

The pressure increase attributed to the energy deposition in the liquid metal target of the Spallation Neutron Source results in cavitation and pitting erosion of the target pressure boundary. Introducing compressibility in the form of small gas bubbles will extend the lifetime of the target vessel. The pressure rise caused by the beam energy deposition occurs in one microsecond, which encourages use of bubbles of radius less than 20 microns, such that the bubble response to pressure change is adequately fast. Gas volume fraction near 0.5% is sufficient to accommodate the mercury volumetric expansion and reduce the pressure rise. Bubble …

Polarimetry Studies For The Npdgamma Experiment At The Sns, Mostafa Jon Dadras

Masters Theses

The NPDGamma collaboration aims to measure a parity{violating directional gamma-ray asymmetry from the capture of polarized cold neutrons on protons. The asymmetry, predicted to be on the order of 50 ppb, is a result of the weak interaction between mesons and nucleons during the neutron capture reaction. The experiment is designed to make a statistics limited measurement of the asymmetry at the level of about 20%. The experiment will be carried out at the Fundamental neutron Physics Beamline (FnPB) at the Spallation Neutron Source (SNS). The neutron beam is polarized by a super{mirror polarizer. A 9.5 G magnetic field guides …

High-Sensitivity Spectral Fluorescence Lifetime Imaging For Resolving Spectroscopically Overlapping Species, Justin Lee Crawford

Masters Theses

The capability to resolve the contributions from spectroscopically overlapping fluorophores has enabled significant breakthroughs in cellular imaging. However, commercial microscopes for this purpose use analog light detection with least squares curve-fitting analysis and improvements in sensitivity are needed. To this end, a microscope has been constructed with high throughput and single-photon detection capability. The fluorescence is separated through use of a prism spectrometer or a series of dichroic mirrors into four spectral bands and detected using four single-photon avalanche diode (SPAD) detectors, which provide high-quantum efficiency in the red spectral region. The detectors are connected to a time-correlated single photon …

An Automated Approach To The Study And Classification Of Colliding And Interacting Galaxies, Steven Alvaro Boada

Masters Theses

Colliding galaxies are perhaps the greatest events changing and evolving our Universe. Consequently, the need for an understanding of how that interaction originated is very important. This thesis presents a framework in which the study of these events can be conducted in a timely and efficient manner. A genetic algorithm coupled with an initial conditions generator, a physics engine and an analysis package performs an automated search to visually match an unknown galactic interaction with a known event, thus providing the starting conditions that created such an interaction.

Microfluidic Device For The Electrokinetic Manipulation Of Single Molecules, Jason Keith King

Masters Theses

Manipulation and trapping of single molecules in solution is a useful tool for studies of biological molecules and molecular dynamics, but has to date been implemented in only one or two dimensions. The goal of the research in this thesis is to develop a microfluidic device to address the need for three-dimensional manipulation of single fluorescent molecules in solution. The device consists of two pairs of platinum electrodes deposited onto two standard borosilicate glass coverslips via ultraviolet microlithography and ionic sputtering. The two coverslips are sandwiched together such that the electrode tips form a tetrahedral configuration, and by applying appropriate, …

Single Molecule Detection Of Near-Infrared Phthalocyanine Dyes, You Li

Masters Theses

The major advantage associated with near-infrared monitoring is the fact that few compounds show intrinsic fluorescence in this region of the spectrum and hence background from other molecules is reduced. Phthalocyanine dyes provide emission at deep red and near infrared wavelengths but have excellent photostability and hence are an attractive candidate for near-infrared fluorescence bioassay applications. However, because of their small Stokes shifts, non-standard methods are needed for optimum separation of fluorescence from scattered laser light. This thesis reports the development of a custom confocal microscope that uses a lowcost laser diode operating at 667 nm for sample excitation and …

Geometrical Effects On Electromagnetic Enhancement To Sers From Metal Nanoparticle Dimer Arrays, Abigail Laurel Gaddis

Masters Theses

Much recent effort has been devoted to the study of the optical properties of metal nanoparticle substrates. In such finely ordered structures, surface plasmons can be induced by incident light. These collective excitations of the electrons in the nanoparticle create localized areas of high electromagnetic field intensity. The intense local fields generated are of interest for various applications, including Surface-enhanced Raman Scattering (SERS) for molecular detection and sensing. In this thesis, the optical properties of various nanoparticle dimer and array geometries are considered, including gold triangular prism dimers and silver spherical dimers. The effect of SERS due to electromagnetic interaction …

Environmental Analysis And White Cell Applications Ftir Spectroscopy, Maria Gabriela Oliveros

Masters Theses

The research is concerned with atmospheric chemistry & physics, and analyzing the environment with respect to the quantity of molecules is in the air we breathe. Fourier Transform Infrared Spectroscopy is used to identify the IR active molecules in our atmosphere. FTIR Spectrometer determines the intensity loss for molecules that have absorbed IR light. The FTIR spectroscopy is performed using the light from the sun or a carbon rod light source in the lab. A Sun-tracking device was employed to direct the sunlight into the spectrometer. Open-path measurements were made using multiple mirror reflections of the carbon rod light source …

Experimental Determination Of Emissivity And Resistivity Of Yttria Stabilized Zirconia At High Temperatures, Howard Mosley Frederick

Masters Theses

The emissivity and resistivity of yttria stabilized zirconia (YsZ), Y₂O₃-ZrO₂, a ceramic material that has been specially fabricated for use as an electrically powered high temperature air heater are determined for temperatures above 2000 K. Published results of measurements of emissivity and resistivity of yttria, zirconia, and their alloys at temperatures above 2000 K are rare in the technical literature. A survey of literature describing the properties of YsZ, particularly literature concerning the ionic conduction process at high temperatures, is assembled to provide a theoretical basis for the formulation of a temperature and resistivity …

Simulation Of Single Molecule Trapping In A Nanochannel, William Neil Robinson

Masters Theses

Trapping of single fluorescent molecules in solution is numerically simulated. Optical trapping provides insufficient force for trapping molecules much smaller than the optical wavelength. Instead, a means for trapping by sensing the molecule position and applying real-time feedback of flow to compensate diffusional displacement is used. The solution is contained in a nanochannel, reducing the problem to one spatial dimension. The position of the molecule is estimated from the fluorescence signals generated by two focused laser beams, which originate from a single laser source that is split and temporally alternated between the two focal spots. Photon collection is time gated, …

Fusion Reaction Cross-Section Measurements Near 100Sn, Elton Lewis Freeman

Masters Theses

This thesis describes the measurement of production rates of A=109 isobars produced with beams of ⁵⁴Fe ions accelerated to 207 MeV bombarding ⁵⁸Ni target. The reaction products have been electromagnetically separated according to their mass over charge ratio and implanted into a semiconductor detector. The spontaneous decay radiation from the implanted radioactive isobars has been measured in a detection system with known detection efficiency, enabling to determine absolute intensities of observed isotopes. Known branching ratios of alpha decays of ¹⁰⁹Xe, ¹⁰⁹Te, proton decay of ¹⁰⁹I and beta delayed gamma radiation of ¹⁰⁹Te and ^{109 …}