Physics Commons^™

Speciation And Spectroscopy Of The Uranyl And Tetravalent Plutonium Nitrate Systems: Fundamental Studies And Applications To Used Fuel Reprocessing, Nicholas A. Smith

UNLV Theses, Dissertations, Professional Papers, and Capstones

This dissertation explores the use of UV-Visible spectroscopy and Time Resolved Laser Induced Fluorescence spectroscopy as near real time process monitors of uranium and plutonium concentrations in aqueous reprocessing trains. The molar absorptivities and linear ranges of these metals were investigated under total nitrate and acid concentrations similar to those found in current reprocessing systems. Concurrent to this, a new multiple wavelength monitor was derived that is capable of determining the total nitrate concentration spectroscopically. This method uses the uranium absorbance spectrum to calculate the nitrate concentration in solution. When used as part of an Advanced Safeguard suite, this technique …

Vibrational Spectroscopic Study Of The 1,3,5,7-Cyclooctatetraene At High Static Pressures, Edward Romano

UNLV Theses, Dissertations, Professional Papers, and Capstones

1,3,5,7-cyclooctatetraene (COT) is a single-ringed hydrocarbon that has not been studied extensively under high static pressures. It was the intent of this study to reveal its high-pressure behavior through its vibrational spectra. To this end, its infrared spectra as a function of pressure were collected at the National Synchrotron Light Source (NSLS) U2A beamline, as well as its Raman spectra over pressure using a micro-Raman spectrometer.

The spectra show the typical stiffening of force constants with increasing pressure for most peaks, particularly those which would theoretically exhibit a mode-softening behavior under hypotheses of molecular planarization and aromatization. Additionally, the data …

Spectroscopic Study Of Ultracold Rubidium Atoms In An Optical Dipole Force Trap, Eman Mohammed Ahmed

Physics Theses & Dissertations

The interaction of light with atoms and molecules is of fundamental interest in many branches of science. In atomic physics, this interaction can be used to cool and spatially confine (trap) atoms. These traps can be used as the starting point for other experiments, but the dynamics of the cooling and trapping processes is itself of interest. In order to better understand the physics of trapping atoms in an optical dipole force trap, we have conducted a series of spectroscopic measurements of ultracold rubidium atoms in such a trap. The trap was created at the focus of a Nd:YAG laser …

Design And Construction Of A Thermal Diffusion Cloud Chamber, Alexander Donoghue

Physics

This paper will cover the theory behind a thermal diffusion cloud chamber. In addition to that it will cover the process, thought and material used to construct two different cloud chambers. It will also discuss the effects of materials used in each chamber on the working of the chamber.

Optical Coherence: Recreation Of The Experiment Of Thompson And Wolf, David Collins

Physics

The purpose of our experiment is to recreate the experiment done by Thompson and Wolf in 1957 on the measurement of optical coherence. What is novel about our approach is that it allows one to view the effects of source size on optical spatial coherence in real time.

Partial Phonon Density Of States Of 57-Iron And 161-Dysprosium In Dyfe3 By Nuclear Resonant Inelastic X-Ray Scattering Under High Pressure, Elizabeth Anne Tanis

UNLV Theses, Dissertations, Professional Papers, and Capstones

The dual partial phonon density of states (DOS) from two different Mossbauer isotopes (161Dy and 57Fe) in the same material (DyFe3) was successfully measured using the nuclear resonant inelastic x-ray scattering (NRIXS) technique at high pressure. Nuclear inelastic scattering measurements yield an in-depth understanding of the element-specific dynamic properties. The Debye temperatures , the Lamb-Mossbauer factor, and the vibrational contributions to the Helmholtz free energy, specific heat , entropy and internal energy are calculated directly from the phonon density of states.

Optical Properties Of Type Iii-V Semiconductor Spherical Quantum Dot Heterostructures, Nathan Haluska

Master's Theses - Daytona Beach

In recent years quantum dots (QD) have attracted increasing interest because of their wide variety of revolutionary applications. Such applications include high speed optical communication lasers, infrared photodetectors, and single photon emitters. One promising immediate application is QD solar cells. Proper analysis of the optical absorption characteristics in these solar cells requires a rigorous modeling of the electronic structure and optical properties of semiconductor heterostructures. Our emphasis will be on type III-V semiconductors. Such structures, have a great potential for increasing efficiencies, but they also possess highly degenerate and complex valence band structures. Therefore, we seek to develop a model …

Passive Ranging Using Infra-Red Atmospheric Attenuation, Douglas J. Macdonald

Theses and Dissertations

Methods of estimating range to an emissive target based on the depth of an atmospheric absorption band are demonstrated. The present work uses measurements of the CO2 absorption band centered at 2.0 µm where signal-to-background ratios are maximum for many applications. Model results, based on high-resolution transmission molecular absorption (HITRAN) database cross sections, are used to predict range accuracy at ranges of up to 50 km and are compared with short range (<5km) experimental results. The spectra of 23 high explosive events were used to validate the model. Using the assumption of a blackbody spectrum, extracted ranges consistently underestimated the true range by approximately 13%. By incorporating the stoichiometry of the fireball from previous research and using particulate contribution as a parameter, the error for the range estimates could be reduced to 3%.

Scene Change Artifacts In Fourier Transform Spectroscopy Of Temporally Changing Sources, Anthony M. Young

Theses and Dissertations

Improved understanding of midwave infrared (1-5 micron) spectral emissions from detonation fireballs is needed to develop phenomenological models for battle space optical forensics. The ability to measure radiance over a wide band pass at arbitrary resolutions make Fourier-transform spectrometers (FTS) an attractive tool. However, interferometer based spectroscopic measurements can be corrupted when the observed intensity changes during data acquisition. While small, random fluctuations in scene intensity translate into noise, systematic variations introduce scene-change artifacts (SCAs) into Fourier-transformed spectrum.

Positron Annihilation Ratio Spectroscopy (Psars) Applied To Positronium Formation Studies, Robert C. Slaughter

Theses and Dissertations

A Positron Annihilation of Radiation Spectrometer (PsARS) was developed and characterized. PsARS spectroscopy as well as digital Positron Annihilation Lifetime Spectroscopy (PALS) was applied to measure positronium formation on gold nanoparticles deposited through an evaporative method onto a thin capillary tube. This gold coated capillary tube was designed to be used for positronium lifetime studies in local electric field experiments. High local electric fields can polarize a positron-electron pair, which may result in an extended lifetime of the positron. These fields may be created through the interaction of an external electric field with silver nanoparticles deposited onto the surface of …

Hard Collisions In Rubidium Using Sub-Doppler Spectroscopy, Douglas E. Thornton

Theses and Dissertations

To better understand the laser kinetics of an alkali gain medium, hard collisions, or velocity-changing collisions, has been studied and a velocity-changing collisional rate has been calculated. Previous works have studied these collisions, but no rate has been calculated. Using the precise tool of sub-Doppler spectroscopy, atomic hard collisions can be observed. The collected spectra are fitted with two different line shapes to demonstrate the accuracy of this method. From the fits, the number of hard collisions can be extracted. The time scale of the hard collisions in rubidium is interpolated by varying the chopping frequency of the pump beam, …

Inelastic Collisions In Cold Dipolar Gases, Catherine A. Newell

University of Kentucky Doctoral Dissertations

Inelastic collisions between dipolar molecules, assumed to be trapped in a static electric field at cold (> 10⁻³K) temperatures, are investigated and compared with elastic collisions. For molecules with a Λ-doublet energy-level structure, a dipole moment arises because of the existence of two nearly degenerate states of opposite parity, and the collision of two such dipoles can be solved entirely analytically in the energy range of interest. Cross sections and rate constants are found to satisfy simple, universal formulas. In contrast, for molecules in a Σ electronic ground state, the static electric field induces a dipole moment in …

Pressure Induced Dynamical Instabilities In Body Center Cubic Crystals, Oscar Guerrero

Open Access Theses & Dissertations

Large-scale atomistic simulations of shock-wave propagation in single crystals exhibit large anisotropies in the elastic-plastic and solid-liquid transitions. Characteristic of this type of simulations are the large strains at which the crystal yields plastically, regardless of crystal orientation. At these large strains, uniaxial deformations, such as those produced in planar shock loading generate dynamical instabilities. We have investigated the directional anisotropy of the elastic limit in bcc crystals, in particular Tantalum (Ta), employing molecular dynamics (MD) simulations. We show that the elastic - plastic transition in BCC defect-free crystals is caused by the appearance of soft-phonon modes and not via …

Understanding The Promotion Effect: A Density Functional Theory Study Based On High Resolution Transmission Electron Microscopy Images For Mos2-Cobalt Promoted Interfaces, Manuel A. Ramos

Open Access Theses & Dissertations

Many studies had been done in order to understand promotion effect and structure/function in unsupported catalyst. Results indicated that d-electrons play an important role promoting catalytical active sites at the edges of MoS2 catalytically structures. Sulfur removal from crude oil, occurs on the edge of molybdenum di-sulfide (MoS2) nano structures, due to promotion of MoS2 nano structures with nickel or cobalt in sulfur-terminated or molybdenum-terminated edge planes. The promotion leads to formation of so-called CoMoS phase (MoS2/Co9S8) first discovered by meaning of Mössbauer spectroscopy, much more CoMoS phase usually called unsupported catalytical particles, have been topic of great interest in …

Spectroscopic Study Of The Inhibition Of Calcium Oxalate Calculi By Larrea Tridentata, Luis Alonso Pinales

Open Access Theses & Dissertations

The causes of urolithiasis include such influences as diet, metabolic disorders, and genetic factors which have been documented as sources that aggravate urinary calculi depositions and aggregations, and, implicitly, as causes of urolithiasis. This study endeavors to detail the scientific mechanisms involved in calcium oxalate calculi formation, and, more importantly, their inhibition under growth conditions imposed by the traditional medicinal approach using the herbal extract, Larrea tridentata. The calculi were synthesized without and with Larrea tridentata infusion by employing the single diffusion gel technique. A visible decrease in calcium oxalate crystal growth with increasing amounts of Larrea tridentata herbal infusion …

A Measurement Of The Neutron Electric Form Factor At Very Large Momentum Transfer Using Polarized Electrons Scattering From A Polarized Helium-3 Target, Aidan Michael Kelleher

Dissertations, Theses, and Masters Projects

Knowledge of the electric and magnetic elastic form factors of the nucleon is essential for an understanding of nucleon structure. of the form factors, the electric form factor of the neutron has been measured over the smallest range in Q2 and with the lowest precision. Jefferson Lab experiment 02-013 used a novel new polarized 3He target to nearly double the range of momentum transfer in which the neutron form factor has been studied and to measure it with much higher precision. Polarized electrons were scattered off this target, and both the scattered electron and neutron were detected. GEn was measured …

An Ab-Initio Study Of The Elastic Properties Of Important Group Iv Diborides At High Temperatures, Manny Gonzales

Open Access Theses & Dissertations

Presented is an ab-initio Molecular Dynamics (MD) study, employing the Density Functional Theory (DFT), of the lattice parameter, thermal expansion coefficients and elastic constants of ZrB₂, TiB₂ and HfB₂ as a function of temperature. The MD trajectories provide the equilibrium lattice parameters at finite temperatures, and the gradient of the energy from these equilibrium solutions is then used to calculate the components of the stiffness tensor. The results for ZrB₂ are shown to agree well with reported experimental results for the lattice parameters and elastic constants as a function of temperature.

Preparing A Vacuum Chamber To Trap Atoms, And The Principles Of A Magneto-Optical Trap, Grant Rayner

Physics

No abstract provided.

Reflectivity Of A Cholesteric Liquid Crystal, Justin Lawson

Physics

In this paper we investigate the light properties of a chiral liquid crystal or a crystal for which the director angle relative to some fixed axis changes as a function of the crystal depth. Sometimes a dopant can introduce a chirality or "twist" in a nematic liquid crystal. For such cases of non-linear depth dependence (where chirality is determined by a diffusion equation) we may use this research to work backwards from a crystal's light properties to intensity and duration of dopant exposure.