Digital Commons Network^™

Beta-Delayed Neutron Data And Models For Scale, Kemper Dyar Talley

Doctoral Dissertations

Recent advancements in experimental and theoretical nuclear physics have yielded new data and models that more accurately describe the decay of fission products compared to historical data currently used for many applications. This work examines the effect of the adopting the Effective Density Model theory for beta-delayed neutron emission probability on calculations of delayed-neutron production and fission product nuclide concentrations after fission bursts as well as the total delayed neutron fraction in comparison with the Keepin 6-group model. We use ORIGEN within the SCALE code package for these calculations. We show quantitative changes to the isotopic concentrations for fallout nuclides …

Large Scale Brownian Dynamics Simulation Of Dilute And Semidilute Polymeric Solutions, Amir Saadat

Doctoral Dissertations

Excluded Volume (EV) and Hydrodynamic Interactions (HI) play a central role in static and dynamic properties of macromolecules in solution under equilibrium and nonequilibrium settings. The computational cost of incorporating HI in mesoscale Brownian dynamics (BD) simulations, particularly in the semidilute regime has motivated significant research aimed at development of high-fidelity and efficient techniques.

In this study, I have developed several algorithms for the mesoscale bead-spring representation of a macromolecular solution in dilute and semidilute regimes. The Krylov subspace method enables fast calculation of single chain dynamics with simulation time scaling of O(N_b²) [order N …

Optical Spectroscopy And The Contruction Of An Optimal Wannier Basis With Application To The Development Of Ab Initio Models, Robert Gerard Van Wesep

Doctoral Dissertations

Understanding the role of local orbital degrees of freedom in the behavior of solid state systems has long been understood as a key to unraveling the mysteries presented by complex transition metal compounds. A general approach to the many-body problem is density functional theory (DFT) and its time-dependent extension (TDDFT), which provide a realistic representation of the material-dependent symmetry and chemistry of a compound. Calculation of quantities in (TD)DFT are most often performed using the basis of Bloch states, which is not natural for investigating local degrees of freedom. The Wannier basis provides localized orbitals that retain all of the …

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 …

Development, Analysis, And Optimization Of A Swirl-Promoting Mean Flow Solution For Solid Rocket Motors, Andrew Steven Fist

Masters Theses

This work demonstrates and analyses a new flow candidate for describing the internal gaseous motion in simulated rocket motors. The fundamental features of this solution include the conservation of key system properties also incorporated in the classic Taylor-Culick (TC) system (i.e. inviscid, axisymmetric, steady and rotational properties), while allowing for the development of a swirling velocity component. The work compares the new solution to the development and formulation of the classic TC system, ultimately identifying that both the new and classic solutions are special cases of the Bragg-Hawthorne equation. Following this development, the text then explores the development of energy-optimized …

Correction To Luminosity Measurement For The Pixel Luminosity Telescope At Cms, Krishna Thapa

Masters Theses

The search for and detailed study of new particles and forces with the Compact Muon Solenoid (CMS) detector at the Large Hadron Collider (LHC) of CERN is fundamentally dependent on the precise measurement of the rate at which proton-proton collisions produce any particles, the so-called luminosity. Therefore, a new detector, the Pixel Luminosity Telescope (PLT), dedicated to measure the luminosity at high precision was added to the CMS experiment in 2015. It measures the inclusive charged particle production from each collision of proton bunches in the LHC. Additional charged particles which are observed by the instrument but produced from sources …

The Effect Of Attractive Polymer-Nanoparticle Interactions On The Local Segmental Dynamics Of Polymer Nanocomposites, Adam Prillaman Holt

Doctoral Dissertations

Considerable progress has been made in understanding the miscibility and morphology of polymer nanocomposites (PNCs). However, to date, there is little understood concerning the modification of segmental mobility at the polymer-nanoparticle interface, which due to prevalence of interfaces in PNCs, will predominately control the viscoelastic and mechanical properties of these materials.

In this dissertation, static and dynamic experimental techniques are combined to identify the specific parameters controlling the modification of segmental dynamics at the polymer-nanoparticle interface in the model system of poly(2-vinyl pyridine)/silica nanocomposites. In general, the experimental results clearly demonstrate that the segmental dynamics at the polymer-nanoparticle interface are …

A Generalized Method For Fissile Material Characterization Using Short-Lived Fission Product Gamma Spectroscopy, Justin Richard Knowles

Doctoral Dissertations

Characterizing the fissile content of nuclear materials is of particular interest to the safeguards and nuclear forensics communities. Short-lived fission product gamma spectroscopy offers a significant reduction in analysis time and detection limits when compared to traditional non-destructive assay measurements. Through this work, a fully generalizable method that can be applied to variations in fissile compositions and neutron spectra was developed for the modeling and measurement of short-lived fission product gamma-rays. This method uses a 238-group neutron flux that was characterized for two pneumatic tube positions in the High Flux Isotope Reactor using flux monitor irradiations. This flux spectrum was …

Characterizing Local Order And Physical Properties Of Rare Earth Complex Oxides, Thomas Jacob Shamblin

Doctoral Dissertations

With more than 500 compositions, materials possessing the pyrochlore structure have a myriad of technological applications and physical phenomena. Three of the most noteworthy properties are the structure’s ability to resist amorphization making it a possible host matrix for spent nuclear fuel, its exotic magnetic properties arising from geometric frustration, and fast ionic conductivity for solid-oxide fuel cell applications. This work focuses on these three aspects of the pyrochlore’s many potential uses. Structural characterization revealed that pyrochlore-type oxides have a tendency to disorder from a high symmetry cubic structure to a lower symmetry orthorhombic arrangement in response to a variety …

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 …

Actinium-225 Production Via Proton Irradiation Of Thorium-232, Justin Reed Griswold

Doctoral Dissertations

High energy proton spallation reactions on natural thorium metal targets have been utilized to produce multi mCi [milliCurie] quantities of Actinium-225. Theoretical cross sections for actinium and thorium isotopes as well as for a select number of the fission products produced in these reactions were generated by the Monte Carlo radiation transport code PHITS to simulate the experimental data obtained from sixteen irradiations of thorium metal targets with 25-210 µA [microampere] proton beams ranging in energies from 77 to 192 MeV. Irradiations were conducted at Brookhaven National Laboratory (BNL) and Los Alamos National Laboratory (LANL), while target dissolution and processing …

Control System Requirements For A Nuclear Thermal Propulsion System, Adam Hasse, Michael Smith, Bradley Pershke, Andrew Adams, Stephen GilliAm

Chancellor’s Honors Program Projects

No abstract provided.

Toward A Precision Measurement Of The Theta_13 Mixing Angle With The Double Chooz Detectors, Ben Thomas Rybolt

Doctoral Dissertations

Neutrinos are the most numerous and least understood particle in the universe. In the last few decades numerous experiments have been devoted to discovering their properties. The Double Chooz experiment was designed to make a precise measurement of θ₁₃ [theta 13], the neutrino mixing parameter which describes flavor oscillations governing short baselines. To accomplish this measurement, two identical neutrino detectors have been deployed at a near and far baseline outside two commercial nuclear reactors. The neutrino flux and spectrum at the near and far detector sites will determine the disappearance of anti-neutrinos created inside the reactors.

I have contributed …

Symbiotic Plasmonic Nanomaterials: Synthesis And Properties, Abhinav Malasi

Doctoral Dissertations

Metal particles of the dimensions of the order of 1 to 100's of nanometers show unique properties that are not clearly evident in their bulk state. These nanoparticles are highly reactive and sensitive to the changes in the vicinity of the particle surface and hence find applications in the field of sensing of chemical and biological agents, catalysis, energy harvesting, data storage and many more. By synthesizing bimetallic nanoparticles, a single nanoparticle can show multifunctional characteristics. The focus of this thesis is to detail the synthesis and understand the properties of bimetallic nanomaterial systems that show interesting optical, chemical, and …

Biophysical Studies Of Cell Division Protein Localization Mechanisms In Escherichia Coli, Matthew Wayne Bailey

Doctoral Dissertations

How nanometer-scale proteins position accurately within micron-scale bacteria has intrigued both biologists and physicists alike. A critical process requiring precise protein localization is cell division. In most bacteria, cell division starts with the self-assembly of the FtsZ proteins into filaments that form a ring-like structure encircling the cell at its middle, the Z-ring. The Z-ring is a scaffold for additional proteins that synthesize the lateral cell wall which separates the two daughter cells. If division planes are misplaced relative to bacterial chromosomes, also called nucleoids, daughter cells with incomplete genetic material can be produced. In Escherichia coli, research carried out …

Pulsed-Laser Induced Dewetting Of Metallic Nanostructures, Christopher Aidan Hartnett

Doctoral Dissertations

This dissertation explores the fluid dynamics of nano and microscale liquid metal filaments, with an emphasis on experimentally investigating the influences and causes of filament breakup and metallic nanostructure formation. Understanding and manipulating the liquid state properties of materials, especially metals, have the potential to advance the development of future technology, particularly nanoscale technology. The combination of top-down nanofabrication techniques with bottom-up, intrinsic self-assembly mechanisms are a powerful fusion, because it permits new and unusual nanostructures to be created, whilst revealing interesting nanoscale physics.

In fluid dynamics, wetting and dewetting is the spontaneous natural process that occurs when a liquid …

Fundamental Physics With Cold Neutron Beams, Kyle Brandon Grammer

Doctoral Dissertations

The neutron exhibits rich physics both as a tool for studying materials, particle and nuclear physics, as well as the object of experimental study. The neutron lifetime is an important input to Big Bang Nucleosynthesis models and is currently known only to approximately 0.3\% with the most precise measurements from two different experimental techniques in disagreement by more than 3$\sigma$ [sigma]. Parity violation has been the subject of study since its discovery in 1957. Parity violation experiments provide access to studying the hadronic weak interaction, which is otherwise suppressed by several orders of magnitude below that of the strong interaction. …

Spin Flipper, Neutron Polarimetry, And Simulation, For The N3he Experiment, Christopher Bradshaw Hayes

Doctoral Dissertations

The n3He experiment constructed on FnPB [Fundamental neutron Physics Beamline-13] probes the PV [parity violating] nuclear force by measuring the statistical distribution of decay protons which result from the interaction of helium-3 nuclei with a beam of cold neutrons. Pulses of neutrons at 60 Hz are generated by the SNS [Spallation Neutron Source] from a 1 GeV proton beam colliding with a liquid Mercury target. Spalled neutrons are then focused into an intense cold neutron beam thru the use of a liquid hydrogen moderator and a neutron guide making the beam an effective tool as a low energy probe of …

Investigation Of Langmuir Probes In Non-Maxwellian Plasma Using Particle-In-Cell (Pic) Modeling, Densu Aktas Lister

Doctoral Dissertations

This dissertation explores the development of a capability for simulating the plasma dynamics of Langmuir probes (LP) in complex plasmas where the velocity distributions are non-equilibrium and the electron energy spectrum is non-Maxwellian with respect to laboratory and space experiments. The results of this investigation are interpreted to give recommendations for design and use of LPs. This work is conducted using computational techniques to create the exact plasma conditions of the experimental testing environments. The investigations address the following topics:

• development of a technique to model non-Maxwellian physics,
• modification of a baseline-technique and optimization of it for this application,
• creation …

Improving Ventricular Catheter Design Through Computational Fluid Dynamics, Sofy Hefets Weisenberg

Masters Theses

Cerebrospinal fluid (CSF) shunts are fully implantable medical devices that are used to treat patients suffering from conditions characterized by elevated intracranial pressure, such as hydrocephalus. In cases of shunt failure or malfunction, patients are often required to endure one or more revision surgeries to replace all or part of the shunt. One of the primary causes of CSF shunt failure is obstruction of the ventricular catheter, a component of the shunt system implanted directly into the brain's ventricular system. This work aims to improve the design of ventricular catheters in order to reduce the incidence of catheter obstruction and …