Physical Sciences and Mathematics Commons^™

Pointing Control And Stabilization Of The High-Energy Uv Laser For Laser-Assisted Charge Exchange, Martin Joseph Kay

Doctoral Dissertations

Laser-Assisted Charge Exchange (LACE) is an experimental method of charge exchange injection into a proton accumulator ring that is being developed at the Spallation Neutron Source (SNS) in Oak Ridge National Laboratory (ORNL) as an alternative to hazardous injection foils. The current scheme of LACE requires a high-energy, low-repetition-rate UV (355 nm) laser beam (140 mJ pulses at 10 Hz) to be transported over 65 meters to the laser-particle interaction point (IP) in a high-radiation area of the accelerator. Thermal effects and other disturbances along the free-space laser transport line cause the beam to slowly drift away from the IP …

Fabrication Of Specialized Scintillators For Nuclear Security Applications, Cordell James Delzer

Doctoral Dissertations

Radiation detectors are important for a variety of fields including medical imaging, oil drilling, and nuclear security. Within nuclear security, they can serve a multitude of purposes whether that be imaging, localization, isotopic identification, or even just activity measurement. Even without directly seeing a nuclear material it is often able to notice their existence without a detector. Scintillators make up an important part of these detectors due to their large intrinsic efficiency, low cost, large volume, and relatively low upkeep. Due to the importance of the large number of purposes these scintillators may be used for, it can often be …

Laser-Induced Breakdown Spectroscopy And Plasmas Containing Cyanide, Christopher Matthew Helstern

Doctoral Dissertations

This dissertation focuses on laser-induced plasma of diatomic molecular cyanide. Optical breakdown plasma generation is produced by high-peak-power 1064 nm Q-switched nanosecond pulsed radiation. Laser-induced breakdown is performed on a 1:1 molar gas mixture of carbon dioxide and nitrogen held at a fixed pressure of 760 Torr, a 1:1 molar gas mixture of carbon dioxide and nitrogen held at a fixed pressure of 2069 Torr, and a flowing 1:1 molar gas mixture of carbon dioxide and nitrogen flowing at a rate of 100 mL per minute. Plasma shockwave measurements in laboratory air are shown to determine the shock front geometry …

High Resolution Validation Of Next Generation Turbulent Flow Models Using Neutron Beams, Laser Fluorescence, And Cryogenic Helium, Landen G Mcdonald

EURēCA: Exhibition of Undergraduate Research and Creative Achievement

Turbulent fluid flow is an incredibly unpredictable subject that continues to confound scientists and engineers. All of the empirical data that has been the basis of conventional turbulent computational fluid dynamics (CFD) models for decades only extends to roughly the equivalent turbulence created when Michael Phelps swims in a pool. The problem is that this data is then extrapolated out many orders of magnitude in order to design cruise ships, airplanes, and rockets which operate in significantly more turbulent flow regimes. This creates an incredible degree of uncertainty in the design process that demands over-engineering and increased expenditures.

The development …

Transport Of Water And Ions Through Single-Walled Armchair Carbon Nanotubes: A Molecular Dynamics Study, Michelle Patricia Aranha

Doctoral Dissertations

The narrow hydrophobic interior of a carbon nanotube (CNT) poses a barrier to the transport of water and ions, and yet, unexpectedly, numerous experimental and simulation studies have confirmed fast water transport rates comparable to those seen in biological aquaporin channels. These outstanding features of high water permeability and high solute rejection of even dissolved ions that would typically require a lot of energy for separation in commercial processes makes carbon nanotubes an exciting candidate for desalination membranes. Extending ion exclusion beyond simple mechanical sieving by the inclusion of electrostatics via added functionality to the nanotube bears promise to not …

On Laser-Induced Plasma Containing Hydrogen, Ghaneshwar Gautam

Doctoral Dissertations

Laser-induced micro-plasma dynamics are investigated in laboratory air, ultra-high-pure hydrogen gas, and hydrogen-nitrogen gas mixtures. The dissertation focuses on atomic spectroscopy of hydrogen in the visible region.

Line-of-sight measurements are analyzed to obtain spatial distributions of electron densities and excitation temperatures. The studies include evaluation of self-absorption phenomena. The plasma dynamics occur initially well above re-entry speeds and diminish to hypersonic and then supersonic expansions. Expansion velocities are measured that are above three hundred times the speed of sound in standard atmosphere. Optical breakdown is induced by using pulsed laser radiation. Emission spectra are collected by employing a spectrometer equipped …

Improving Predictive Capabilities Of Classical Cascade Theory For Nonproliferation Analysis, David Allen Vermillion

Doctoral Dissertations

Uranium enrichment finds a direct and indispensable function in both peaceful and nonpeaceful nuclear applications. Today, over 99% of enriched uranium is produced by gas centrifuge technology. With the international dissemination of the Zippe archetypal design in 1960 followed by the widespread illicit centrifuge trafficking efforts of the A.Q. Khan network, traditional barriers to enrichment technologies are no longer as effective as they once were. Consequently, gas centrifuge technology is now regarded as a high-priority nuclear proliferation threat, and the international nonproliferation community seeks new avenues to effectively and efficiently respond to this emergent threat.

Effective response first requires an …

Experiment And Simulation Of Single-Molecule Recycling, Bo Wang

Doctoral Dissertations

This dissertation presents theoretical, numerical, and experimental research into a technique for extending the observation time of a single molecule in solution, while also enabling measurement of its diffusion coefficient. A confocal microscope is used to observe the fluorescently labelled molecule in aqueous solution, which is confined within a nanochannel. By focusing a laser beam into the nanochannel and applying electrokinetic flow along the tube, a molecule passes through the laser beam and emits a burst of photons. The molecule then passes back and forth through the focus while the voltage is repeatedly reversed at a fixed delay after each …

Experimental Study On The Production Of Negative Ion Copper Clusters And Applications, Ran Chu

Masters Theses

At the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratories (ORNL), we investigated the formation, production and potential application of negative-ion copper clusters using mass distributions of negative-ion copper clusters obtained by bombarding various copper samples with Cs ions. The Cu samples – in very large mass-selected clusters Cu (e.g. n=54) – included natural Cu, isotopically enriched copper-63 and copper-65, and electroformed ultra-clean Cu. Mass spectra of negative copper cluster produced by Cs sputter source size up to 50 are shown for the first time.

Three main features were observed for all four copper samples: the intensity …

Spectroscopic Imaging Of Aluminum Containing Plasma, David Michael Surmick

Doctoral Dissertations

This dissertation aims to characterize laser-induced plasma from a physics point of view as warm, dense matter. Use of nominal nanosecond pulsed laser radiation initiates a plasma with electron temperatures of the order of 10 electron volts and electron densities of the order of air species densities at standard ambient temperature and pressure. For laser ablation and/or optical breakdown at or near a solid surface, the electron density can amount to be 1000 times greater. Spectroscopic investigations of the plasma emissions provide a method by which the electron density, temperature, and shockwave expansion may be determined. Of particular interest are …

Strontium Monoxide Measurements In Methane-Air Flames, Bobby J. Wimberly

Masters Theses

The spectroscopy of alkaline earth metal compounds has been an area of active research for several decades. This is at least in part stimulated by the application of these compounds to practical areas ranging from technology to medicine. The use of these compounds in the field of pyrotechnics was the motivation for a series of flame emission spectroscopy (FES) experiments with strontium containing compounds. Specifically, strontium monoxide (SrO) is studied as a candidate radiator for the diagnostic of methane-air flames.

SrO emissions have been observed in flames with temperatures in the range of 1200-1600-K for two compounds: strontium hydroxide and …

Measurements Of Methyl Radicals And Temperatures By Using Coherent Microwave Rayleigh Scattering From Resonance Enhanced Multiphoton Ionization, Yue Wu

Doctoral Dissertations

This thesis includes two main parts: (I) The CH₃[methyl radical] detection in methane/air flames and (II) the rotational temperature measurement of O₂[molecular oxygen] in a variety of environments by using coherent microwave Rayleigh scattering from resonance enhanced multiphoton ionization (Radar REMPI).

In first the part, from Chapter I to Chapter III, the methyl radical detection and quantitative measurements have been conducted in hydrocarbon flame with one-dimensional and two-dimensional spatial-resolved concentration distribution. Due to the proximity of the argon resonance state (4+1 REMPI by 332.5 nm) with the CH₃ state (2+1 REMPI by 333.6 nm), in …

Diatomic Carbon Measurements With Laser-Induced Breakdown Spectroscopy, Michael Jonathan Witte

Masters Theses

In this thesis, investigation of well-known carbon Swan spectra is of primary interest. Combustion processes and/or explosion of hydrocarbon fuels cause occurrence of the Swan band system that originates from diatomic carbon. Physical characteristics of low-temperature stars and the interstellar medium can also reveal the Swan bands. The diatomic carbon molecule shows that its lowest rotational levels are sensitive to temperature variation, and higher rotational levels are sensitive to the surrounding gas density and the radiation field. In addition, carbon is a crucial element for life and is the 4th most abundant element; therefore, it is important to ascertain accurately …

Nonlocal Polarization Interferometry And Entanglement Detection, Brian P. Williams

Doctoral Dissertations

At present, quantum entanglement is a resource, distributed to enable a variety of quantum information applications such as quantum key distribution, superdense coding, and teleportation. Necessarily, the distribution and characterization of entanglement is fundamental to its application. This dissertation details three research efforts to enable nonlocal entanglement detection, distribution, and characterization. Foremost of these efforts, we present the theory and demonstration of a nonlocal polarization interferometer capable of detecting entanglement and identifying Bell states statistically. This is possible due to the interferometer’s unique correlation dependence on the anti-diagonal elements of the density matrix, which have distinct bounds for separable states …

Hi-Fidelity Simulation Of The Self-Assembly And Dynamics Of Colloids And Polymeric Solutions With Long Range Interactions, Mahdy Malekzadeh Moghani

Doctoral Dissertations

Modeling the equilibrium properties and dynamic response of the colloidal and polymeric solutions provides valuable insight into numerous biological and industrial processes and facilitates development of novel technologies. To this end, the centerpiece of this research is to incorporate the long range electrostatic or hydrodynamic interactions via computationally efficient algorithms and to investigate the effect of these interactions on the self-assembly of colloidal particles and dynamic properties of polymeric solutions. Specifically, self-assembly of a new class of materials, namely bipolar Janus nano-particles, is investigated via molecular dynamic simulation in order to establish the relationship between individual particle characteristics, such as …

Laser-Induced Breakdown Spectroscopy For Analysis Of High Density Methane-Oxygen Mixtures, Matthew Dackman

Masters Theses

The applicability of laser-induced breakdown spectroscopy (LIBS) toward greater than atmospheric density combustion diagnostics is examined. Specifically, this involves ascertaining the feasibility of measuring chemical equivalence ratios directly from atomic emission spectra at high density. The need for such measurement arises from the desire to quantify real time, localized combustion performance in weakly mixed flows. Insufficiently mixed flows generally result in unwanted byproducts, possess the propensity for overall combustion instability, and are increasingly likely to experience localized flame extinction.

We simulate methane/oxygen combustion in ambient pressures ranging 1 to 4 atmospheres, demonstrating these results to be analogous to what would …

Atomic And Molecular Laser-Induced Breakdown Spectroscopy Above A Titanium Target, Alexander Charles Woods

Doctoral Dissertations

The goal of this research is to use optical emission spectroscopy to investigate the processes occurring subsequent to laser ablation of a titanium sample. Laser-induced breakdown spectroscopy provides a procedure for atomic and molecular identification for particular constituents of a laser-induced plasma. Atomic spectral line shapes provide a diagnostic tool for characterizing laser induced plasma, particularly within the first hundreds of nanoseconds. Molecular recombination and/or excitation of selected molecules can lead to simultaneous detection of atomic and molecular species via spectral analysis. Nonlinear fitting of synthetic molecular spectra, calculated via diatomic quantum theory, provides tools for identification, temperature measurement, and …

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 …

Aluminum Monoxide Emission Measurements Following Laser-Induced Breakdown For Plasma Characterization, David Michael Surmick

Masters Theses

In this work, spectroscopic emissions from laser ablated aluminum samples are used to characterize the time dependent decay of laser-induced plasma. The plasma is created by tightly focusing nanosecond pulsed laser radiation. Time resolved measurements of the plasma are made with a gated, intensified linear diode array coupled to an optical multichannel analyzer and/or an intensified charged coupled device. Time resolution is achieved by synchronizing the laser with the measurement rate of the array detector.

Computed diatomic molecular aluminum monoxide emissions were used to infer the temperature of the plasma as a function of time. This was completed by comparing …

Neutron Polarimetry With Polarized 3he For The Npdgamma Experiment, Matthew Martin Musgrave

Doctoral Dissertations

Cold neutrons enable the study of the fundamental interactions of matter in low-energy, low-background experiments that complement the efforts of high-energy particle accelerators. Neutrons possess an intrinsic spin, and the polarization of a beam of neutrons defines the degree to which their spins are oriented in a given direction. The NPDGamma experiment uses a polarized beam of cold neutrons to make a high precision measurement, on the order of one part in 100 million, of the parity-violating asymmetry in the angular distribution of emitted gamma-rays from the capture of polarized neutrons on protons. This asymmetry is a result of the …

Tracking Real-Time Nanoparticle Positions And Measuring Three-Dimensional Solution Flow With A Four-Focus Confocal Microscope, James Andrew Germann

Doctoral Dissertations

This dissertation presents the development of instrumentation for measuring the position of a single emitter within the sample volume of a confocal fluorescence microscope with sub-diffraction limited precision in three dimensions together with applications for determining solution flow and for tracking a fluorescent nanoparticle as it undergoes Brownian diffusion. The localization method is based on comparing photon counts from alternating excitation of the emitter by four laser beams, which are focused at slightly offset positions in a tetrahedral pattern within the confocal volume. Two experimental set-ups are constructed. In the first, the four beams are from a femtosecond laser, which …

A Study Of The Optical And Negative Ion Properties Of Selected Chiral Molecules, Jason Michael Lambert

Doctoral Dissertations

Chirality is subtle geometric property where objects lack reflection plane symmetry. In this thesis I study three chiral molecules using a combination of experimental and theoretical methods to elucidate the relationships between conformation freedom, solvent choice, and temperature. The importance of nuclear motion when predicting the optical rotation is explored. For carvone, corrections with each nuclear mode coordinate is important. Predictions of the ORD have the incorrect sign without the inclusion of vibrational corrections. For the case of two newly synthesized amino acid derivatives the vibrational corrections did not correct the sign of the calculated ORD to bring it into …

Three-Dimensional Electrokinetic Trapping Of A Single Fluorescent Nanoparticle In Solution, Jason Keith King

Doctoral Dissertations

This dissertation presents the development of an instrument for effectively trapping a single fluorescent nanoparticle that is freely diffusing in solution in all three dimensions. The instrument is expected to have applications for studies of single nanoparticles or molecules for which prolonged observations are required, but without immobilization or proximity to a surface, which may alter behavior. The trapping technique depends on rapid three-dimensional position measurements of the nanoparticle with sub-micron precision, which are used for real-time control of induced electrokinetic motion, so as to counteract Brownian motion. While anti-Brownian electrokinetic trapping experiments in one and two dimensions have previously …

Towards A Unification Of Supercomputing, Molecular Dynamics Simulation And Experimental Neutron And X-Ray Scattering Techniques, Benjamin Lindner

Doctoral Dissertations

Molecular dynamics simulation has become an essential tool for scientific discovery and investigation. The ability to evaluate every atomic coordinate for each time instant sets it apart from other methodologies, which can only access experimental observables as an outcome of the atomic coordinates. Here, the utility of molecular dynamics is illustrated by investigating the structure and dynamics of fundamental models of cellulose fibers. For that, a highly parallel code has been developed to compute static and dynamical scattering functions efficiently on modern supercomputing architectures. Using state of the art supercomputing facilities, molecular dynamics code and parallelization strategies, this work also …

Laser-Atom Interactions: A Multiresolution Approach, Nicholas Eric Vence

Doctoral Dissertations

Isolated, attosecond laser pulses have allowed real-time measurement and control of electrons on atomic time scales. We present an explicit time-evolution scheme solving the time dependent Schro ̈dinger equation, which employs an adaptive, discontinuous, spectral-element basis that automatically refines to accommodate the requested precision providing efficient computation across many length scales in multiple dimensions. This method is illustrated through time evolution studies of single electron atoms and molecular ions in three and four dimensions under the influence of intense, few-cycle laser pulses.

Atomistic Simulations Of The Fusion-Plasma Material Interface, Mostafa Jon Dadras

Doctoral Dissertations

A key issue for the successful performance of current and future fusion reactors is understanding chemical and physical processes at the Plasma Material Interface (PMI). The material surfaces may be bombarded by plasma particles in a range of impact energies (1 eV - a few keV) and kept at a range of temperatures (300 - 1000 K). The dominant processes at the PMI are reflection and retention of impacting particles and sputtering (chemical and physical). Sputtering leads to surface erosion and pollution of the plasma, both of which degrade reactor performance. Retention influences the recycling of the plasma, and in …

Water Ice Films In Cryogenic Vacuum Chambers, Jesse Michael Labello

Doctoral Dissertations

The space simulation chambers at Arnold Engineering Development Complex (AEDC) allow for the testing and calibration of seeker sensors in cryogenic, high vacuum environments. During operation of these chambers, contaminant films can form on the components in the chamber and disrupt operation. Although these contaminant films can be composed of many molecular species, depending on the species outgassed by warm chamber components and any leaks or virtual leaks (pockets of gas trapped within a vacuum chamber) that may be present, water vapor is most common, and it will be the focus of this dissertation. In this dissertation, some properties of …

Optical Modeling Of Schematic Eyes And The Ophthalmic Applications, Bo Tan

Doctoral Dissertations

The objectives of this dissertation are to advance and broaden the traditional average eye modeling technique by two extensions: 1) population-based and personalized eye modeling for both normal and diseased conditions, and 2) demonstration of applications of this pioneering eye modeling.The first type of representative eye modeling can be established using traditional eye modeling techniques with statistical biometric information of the targeted population. Ocular biometry parameters can be mathematically assigned according to the distribution functions and correlations between parameters. For example, the axial dimension of the eye relates to age, gender, and body height factors. With the investigation results from …

Direct Observation Of H2 Binding To A Metal Oxide Surface, J. Z. Larese, T. Arnold, L. Frazier, R. J. Hinde, A. J. Ramirez-Cuesta

Chemistry Publications and Other Works

Inelastic neutron scattering is used to probe the dynamical response of H₂ films adsorbed on MgO(100) as a function of film thickness. Concomitant diffraction measurements and a reduced-dimensionality quantum dynamical model provide insight into the molecule-surface interaction potential. At monolayer thickness, the rotational motion is strongly influenced by the surface, so that the molecules behave like quasiplanar rotors. These findings have a direct impact on understanding how molecular hydrogen binds to the surface of materials used in catalytic and storage applications.

A Six-Dimensional H2–H2 Potential Energy Surface For Bound State Spectroscopy, Robert Hinde

Chemistry Publications and Other Works

We present a six-dimensional potential energy surface for the (H₂)₂ dimer based on coupled-cluster electronic structure calculations employing large atom-centered Gaussian basis sets and a small set of midbond functions at the dimer’s center of mass. The surface is intended to describe accurately the bound and quasibound states of the dimers (H₂)₂, (D₂)₂, and H₂–D₂ that correlate with H₂ or D₂ monomers in the rovibrational levels (v, j) =(0,0), (0,2), (1,0), and (1,2). We employ a close-coupled approach to compute the …