Physics Commons^™

Quantum Computational Simulations For Condensed Matter Systems, Trevor Alan Keen

Doctoral Dissertations

In condensed matter physics, and especially in the study of strongly correlated electron systems, numerical simulation techniques are crucial to determine the properties of the system including interesting phases of matter that arise from electron-electron interactions. Many of these interesting phases of matter, including but not limited to Mott-insulating materials and possibly high-temperature superconducting systems, can be modeled by the Hubbard model. Although it is one of the simplest models to include electron-electron interactions, it cannot be solved analytically in more than one dimension and thus numerical techniques must be employed. Although there have been great strides in classical numerical …

Numerical Studies Of Correlated Topological Systems, Rahul Soni

Doctoral Dissertations

In this thesis, we study the interplay of Hubbard U correlation and topological effects in two different bipartite lattices: the dice and the Lieb lattices. Both these lattices are unique as they contain a flat energy band at E = 0, even in the absence of Coulombic interaction. When interactions are introduced both these lattices display an unexpected multitude of topological phases in our U -λ phase diagram, where λ is the spin-orbit coupling strength. We also study ribbons of the dice lattice and observed that they qualitative display all properties of their two-dimensional counterpart. This includes flat bands near …

Improving Sensitivities In 0𝒗ββ Decay Searches By Utilizing Pen As A Structural Scintillating Material, Brennan Theresa Hackett

Doctoral Dissertations

Neutrinoless double beta decay, 0nbb is currently the only experimental test to unambiguously determine the majorana nature of the neutrino. There is a large international effort to measure 0nbb decay, with several detector technologies being pursued. This dissertation will consider the LEGEND experiment (Large Enriched Germanium Experiment for Neutrinoless bb Decay), an international effort to measure 0nbb decay with ⁷⁶Ge as both the target isotope and the detecting material.

LEGEND has a 200 kg stage and a 1000 kg stage, each requiring extremely low levels of background radiation at Q_bb (E = 2.039 MeV). These ultra-low background levels …

Measurement Of Jet Constituent Yields In Pb-Pb Collisions At √Snn = 5.02 Tev Using The Alice Detector, Charles P. Hughes

Doctoral Dissertations

Hard partonic scatterings serve as an important probe of quark-gluon-plasma (QGP) properties. The properties of jets and their constituents can provide a tool for understanding the partonic energy loss mechanisms. Low momentum jets offer a unique window into partonic energy loss because they reconstruct the partons which have lost a significant amount of energy to the QGP medium. The main difficulty in studying low momentum jets in heavy ion collisions is the presence of a significant uncorrelated background of low momentum hadrons from soft processes. One way to deal with this background is to use jet- hadron correlations to fit …

Direct Calculation Of Configurational Entropy: Pair Correlation Functions And Disorder, Clifton C. Sluss

Doctoral Dissertations

Techniques such as classical molecular dynamics [MD] simulation provide ready access to the thermodynamic data of model material systems. However, the calculation of the Helmholtz and Gibbs free energies remains a difficult task due to the tedious nature of extracting accurate values of the excess entropy from MD simulation data. Thermodynamic integration, a common technique for the calculation of entropy requires numerous simulations across a range of temperatures. Alternative approaches to the direct calculation of entropy based on functionals of pair correlation functions [PCF] have been developed over the years. This work builds upon the functional approach tradition by extending …

Analysis Of Turbulent Flow Behavior In Helicopter Rotor Hub Wakes, Forrest Mobley

Masters Theses

The rotor hub is one of the most important features of all helicopters, as it provides the pilot a means for controlling the vehicle by changing the characteristics of the main and tail rotors. The hub also provides a structural foundation for the rotors and allows for the rotor blades to respond to aerodynamic forces while maintaining controllability and stability. Due to the inherent geometry and high rate of rotation, the rotor hub in its current form acts a large bluff body and is the primary source of parasite drag on the helicopter, despite its relatively small size. The rotor …

A Progress Report On Numerical Methods For Bgk-Type Kinetic Equations, Evan Habbershaw, Steven M. Wise

Faculty Publications and Other Works -- Mathematics

In this report we review some preliminary work on the numerical solution of BGK-type kinetic equations of particle transport. Such equations model the motion of fluid particles via a density field when the kinetic theory of rarefied gases must be used in place of the continuum limit Navier-Stokes and Euler equations. The BGK-type equations describe the fluid in terms of phase space variables, and, in three space dimensions, require 6 independent phase-space variables (3 for space and 3 for velocity) for accurate simulation. This requires sophisticated numerical algorithms and efficient code to realize predictions over desired space and time scales. …

Liquid-Liquid Transition In Ionic Liquids, Matthew Albert Harris

Doctoral Dissertations

The properties of liquids have been linked to the existence of the liquid-liquid transition (LLT), a first-order thermodynamic transition from one liquid phase to another in a single- component liquid. LLT is fundamental to the understanding of the liquid state and has been theorized to manifest from a two-state feature of local order in the liquid. LLT has been reported in a variety of liquids with computer simulations comprising the bulk of the evidence. Experimental evidence for LLT remains controversial because it frequently manifests in the supercooled state, obscured by crystallization. In this dissertation, evidence is presented revealing LLT in …

Beta-Delayed Neutron Emission Spectroscopy In The 78ni Region And Development Of Yso-Based Implantation Detector, Maninder Singh

Doctoral Dissertations

Decays of Cu isotopes provide a laboratory to study the properties for nearly doubly-magic nuclei with a significant neutron excess which are also relevant for the r-process models. The beta-decay properties of doubly-magic ⁷⁸Ni (N=50) are imprinted in the neighboring Cu decay, nuclei with a single proton outside the Z=28 core. The investigated isotopes ^79,80,81Cu are strong beta-delayed neutron precursors, suggesting that their decay strength distribution lies above neutron separation energies in ^79,80,81Zn daughters.

For decay studies, a segmented scintillator YSO (Y₂SiO₅ : Ce doped) based implantation detector was developed at the University of …

Tokamak 3d Heat Load Investigations Using An Integrated Simulation Framework, Thomas Looby

Doctoral Dissertations

Reactor class nuclear fusion tokamaks will be inherently complex. Thousands of interconnected systems that span orders of magnitude in physical scale must operate cohesively for the machine to function. Because these reactor class tokamaks are all in an early design stage, it is difficult to quantify exactly how each subsystem will act within the context of the greater systems. Therefore, to predict the engineering parameters necessary to design the machine, simulation frameworks that can model individual systems as well as the interfaced systems are necessary. This dissertation outlines a novel framework developed to couple otherwise disparate computational domains together into …

Towards The Production Of A Self-Consistent Phase Space Distribution, Austin Hoover

Doctoral Dissertations

A self-consistent phase space distribution is a charged particle beam in which the electric field has a linear dependence on the particle coordinates, and in which the linearity of the electric field is conserved as the beam is transported through arbitrary linear focusing fields. These features could increase the possible beam intensity in a circular accelerator by minimizing/eliminating the space charge tune shift/spread. Additionally, the uniform density of known self-consistent distributions would be ideal for fixed-target applications. Finally, certain self-consistent distributions can be flattened by exploiting the relationships between their phases space coordinates and would therefore be useful in a …

The Upgraded Measurement Of The Neutron Lifetime Using The In-Beam Method, Jimmy P. Caylor

Doctoral Dissertations

Precision measurements of neutron beta decay can provide answers to some of the most fundamental questions in particle physics, astrophysics and cosmology. Neutron beta decay is the simplest semi-leptonic decay; therefore, it provides a clean test of the charged current sector of the Standard Model (SM). A precise measurement of the neutron lifetime and λ, the ratio of axial vector and vector coupling constants of the weak interaction, allows for a determination of the Cabibbo-Kobayashi-Moskawa (CKM) matrix element V_ud that is free from nuclear structure effects. The SM predicts that the CKM matrix is unitary; therefore, the measurement of …

Emergent Phenomenon In Jeff=1/2 Iridate, Junyi Yang

Doctoral Dissertations

Recent work on various quantum materials has led to fruitful result including unconventional magnetic states, topological properties, and exotic emergent phenomenon. High T_c superconductivity is one of the prominent properties discovered in quantum materials like strong correlated systems. Though the efforts on understanding this exotic behavior have lasted for years, the mechanism remains elusive owing to the many-body nature of the system and the research scope limitation within cuprates. Recent unravel of J_eff=1/2 state in the iridate square lattice offers alternative to study the complicated many body physics and potentially achieve high T_c superconductivity. In addition, …

Measurement Of Neutrino-Induced Neutron Production In Lead, Brandon J. Becker

Doctoral Dissertations

The COHERENT Collaboration is an experimental effort to make the first measurement of coherent elastic neutrino-nucleus scattering (CE𝜈NS). The Spallation Neutron Source (SNS) at Oak Ridge National Laboratory provides an intense, timed source of neutrinos from the decay of pions and muons produced during the spallation of mercury by 1 GeV protons generated in a particle accelerator. COHERENT seeks to make an unambiguous measurement by using a variety of low-threshold detectors capable of measuring the low-energy nuclear recoils resulting from CE𝜈NS interactions. This already challenging task is further complicated with the presence of backgrounds. Consequently, we must seek to reduce …

Control And Calibration Strategies For Quantum Simulation, Paul M. Kairys

Doctoral Dissertations

The modeling and prediction of quantum mechanical phenomena is key to the continued development of chemical, material, and information sciences. However, classical computers are fundamentally limited in their ability to model most quantum effects. An alternative route is through quantum simulation, where a programmable quantum device is used to emulate the phenomena of an otherwise distinct physical system. Unfortunately, there are a number of challenges preventing the widespread application of quantum simulation arising from the imperfect construction and operation of quantum simulators. Mitigating or eliminating deleterious effects is critical for using quantum simulation for scientific discovery. This dissertation develops strategies …

Transverse Energy Analysis In Small Collision Systems, Alexander L. Aukerman

Masters Theses

Heavy Ion Collisions performed in the LHC at Cern are capable of generating a new phase of nuclear matter known as the Quark Gluon Plasma. In addition to running heavy ion collisions, the detectors dedicated to studying the QGP perform collisions utilizing smaller collision systems for the sake of comparing key measurements associated with the creation of a QGP. The transverse energy of the particles generated from the collision is one such key measurement. For the sake of comparison an analysis is performed on the transverse energy measurements taken from proton-proton collisions.

Enigma - Ongoing Development Towards Novel Beta-Decay Spectroscopy Station At Isolde, Philipp Wagenknecht

Masters Theses

Beta decay and collinear laser spectroscopy are proven efficient tools to study nuclear structure far from stability. Two areas of significance are investigations into nuclear deformation and shape coexistence, as well as delayed neutron emissions used in nuclear energy applications. This contribution presents the ongoing development towards a novel beta-decay spectroscopy station for the VITO experiment at CERN’s radioactive ion beam facility ISOLDE. The setup will utilize both collinear laser spectroscopy and beta-decay spectroscopy to measure the energy and spin-parities of the ground and excited states of radioactive beams. Initial designs of the support structure, magnetic field, and detector array …

Study Of One-Nucleon Transfer Reactions, Jerome Mathew Kovoor

Doctoral Dissertations

The structure of nuclei away from the line of stability and near the driplines in the nuclear chart has been of huge interest since the arrival of radioactive ion beam facilities. The properties of nuclei evolve as a function of proton and neutron numbers and understanding the mechanisms behind this is one of the keys to explaining the strong nuclear force. Single-nucleon transfer reactions using deuteron targets are powerful probes of nuclear structure when the emitted proton or neutron is measured with high fidelity.

A variety of structure phenomena are observed in the beryllium isotopes marking them particularly attractive for …

A High Rate Pixelated Neutron Detector For Neutron Reflectometry At The Spallation Neutron Source, Su-Ann Chong

Doctoral Dissertations

This work presents the development of a high-rate 6Li-based pixelated neutron detector for neutron reflectometry instruments at the Spallation Neutron Source (SNS), Oak Ridge National Laboratory. The current detector technology falls short on the instrument requirements, particularly on the counting rate capability. This detector was designed specifically to overcome the limitation in counting rate by having a fully pixelated design from neutron conversion layer to photodetector and readout system. For the neutron converting layer, a 6Li-based neutron scintillator was used. Each scintillator element was coupled to a photodetector, in this case, a silicon photomultiplier (SiPM). The output of each SiPM …

Meta-Heuristic Optimization Techniques For The Production Of Medical Isotopes Through Special Target Design, Cameron Ian Salyer

Masters Theses

Medical isotopes are used for a variety of different diagnostic and therapeutic purposes Ruth (2008). Due to recent newly discovered applications, their production has become rapidly more scarce than ever before Charlton (2019). Therefore, more efficient and less time consuming methods are of interest for not only the industry’s demand, but for the individuals who require radio-isotope procedures. Currently, the primary source of most medical isotopes used today are provided by reactor and cyclotron irradiation techniques, followed by supplemental radio-chemical separations Ruth (2008). Up until this point, target designs have been optimized by experience, back of the envelope calculations, and …

An Overview Of Approaches To Nuclear Security In Ghana, Raymond Agalga, Paul Atta Amoah, Daniel Nii Adjei, Daniel Frederick Charles, Emmanuel Ofori Darko

International Journal of Nuclear Security

Ghana has significantly improved its nuclear security infrastructure over the years. However, as threats increase by the day and new applications of nuclear and radiological technology are designed and implemented, Ghana must develop a rigid and comprehensive approach to mitigating the negative impacts on its nuclear security while improving prevention, detection, and deterrence of nuclear and radiological terrorism within its geographical space. This paper overviews the approaches adopted by Ghana to build a strong nuclear security regime within the past decade. These include improving legal frameworks for nuclear security by establishing an independent Nuclear Regulatory Authority; assessing nuclear security culture …

Unconventional Computation Including Quantum Computation, Bruce J. Maclennan

Faculty Publications and Other Works -- EECS

Unconventional computation (or non-standard computation) refers to the use of non-traditional technologies and computing paradigms. As we approach the limits of Moore’s Law, progress in computation will depend on going beyond binary electronics and on exploring new paradigms and technologies for information processing and control. This book surveys some topics relevant to unconventional computation, including the definition of unconventional computations, the physics of computation, quantum computation, DNA and molecular computation, and analog computation. This book is the content of a course taught at UTK.

Design Of An Accelerator-Based Shielding Experiment At The Nasa Space Radiation Laboratory Relevant To Enclosed, Shielded Environments In Space, Lawrence H Heilbronn, Michael Sivertz, Adam Rusek, Charlie Pearson, Martha Clowdsley, Luis Castellanos, Natalie Mcgirl, Ashwin Srikrishna, Cary Zeitlin

Faculty Publications and Other Works -- Nuclear Engineering

Recent calculations indicate that the dose equivalent in an enclosed, shielded environment in a galactic cosmic ray field will increase or remain unchanged when shielding thickness increases beyond 20 to 30 g/cm2. This trend is seen out to 100 g/cm2, beyond which calculations were not run since depths greater than this are not envisioned for human missions in deep space. If these calculations are accurate, then an optimal shielding thickness (or narrow range of thicknesses) exists, with important implications for spacecraft and habitat design. Crucially, the calculation reveals a minimum dose equivalent value that cannot be reduced with added shielding, …

There From The Beginning: The Women Of Los Alamos National Laboratory Supporting National And International Nuclear Security, Olga Martin, Laura Mcclellan, Octavio Ramos, Heather Quinn

International Journal of Nuclear Security

From the beginning of the Manhattan Project in the early 1940s, the women of what would become Los Alamos National Laboratory (LANL) worked in technical positions alongside their male counterparts, played a key role as computers, and worked in administrative jobs as secretaries, phone operators, bookkeepers, and on behalf of the U.S. Army in the Women’s Army Corps.

Throughout the history of the Laboratory, women experts at LANL helped establish and lead important national and international security programs, with careers in science, technology, engineering, and mathematics. Over time, the women of Los Alamos have come together under various Employee Resource …

Evaluation And Improvement Of Nuclear Security Measures At A Radiological Facility In Morocco, Halima Jemmal, Abdelmajid Choukri, Mohammed Mouhib

International Journal of Nuclear Security

Nuclear security combines both concepts of physical security and security culture within a nuclear facility to protect people, property, society and the environment from harmful effects of ionization radiation. Physical security means prevention, detection, and response to unauthorized removal, sabotage, and/or illegal transfer involving radioactive sources and nuclear material. Nuclear security culture is the human factor within the nuclear field which is considered a principal means to support and enhance nuclear security system. This paper presents a study of nuclear security system already established within a radiological facility considering concepts such as: deter, detect, delay, and response layers. This study …

Impurity Production And Transport In The Prototype Material Plasma Exposure Experiment, Clyde J. Beers

Doctoral Dissertations

The Prototype Material Plasma Exposure eXperiment (Proto-MPEX) is a linear pulse plasma device at Oak Ridge National Laboratory with the purpose of doing the research and development for the heating concepts on the planned full MPEX device. The goal of MPEX is to perform material studies at fusion relevant conditions. To understand the conditions at the material target for performing plasma-material interaction studies the ion temperature and density, the electron temperature and density, and the particle flux and fluence must be known. Impurities within Proto-MPEX can alter the desired conditions at the material target and need to be understood for …

Electroweak Interactions And Fundamental Symmetries In Light Nuclei With Short-Range Effective Field Theories, Zichao Yang

Doctoral Dissertations

Effective field theories(EFTs) are powerful tools to study nuclear systems that display separation of scales. In this dissertation, we present halo EFT results for the $\beta$-delayed proton emission from $^{11}$Be, and pionless EFT results for three-nucleon systems. Halo nuclei are simply described by a tightly bound core and loosely bound valence nucleons. Using the halo EFT, we calculate the rate of the rare decay $^{11}$Be, which is a well-known halo nucleus, into $^{10}\text{Be} + p +e^- + \bar{\nu}_e$. We assume a shallow $1/2 ^+$ resonance in the $^{10}$Be$-p$ system with an energy consistent with a recent experiment by Ayyad {\it …

Search For New Physics In Rare Higgs Boson Decays With The Cms Detector At The Large Hadron Collider, Himal Acharya

Doctoral Dissertations

A new boson with a mass of 125 GeV was discovered at the large hadron collider (LHC) in July 2012. The properties of this particle are so far consistent with the standard model (SM) expectation. Differences in the Higgs boson decay rates and predicted by the SM might indicate the presence of new particles and forces between them. Particularly, rare exclusive decays of the Higgs boson are a promising laboratory to study physics beyond the standard model. Searches for decays of the Higgs boson into a Z boson and a J/ψ meson or into pairs of J/ψ or Υ mesons …

Production Of Protactinium-229 Via Deuteron Irradiation Of Thorium-232, Naser Burahmah

Doctoral Dissertations

²²⁵Ac [Actinium-225] is a promising radionuclide for targeted alpha therapy of cancer. ²²⁹Pa can lead to the production of ²²⁹Th [Thorium-229] and ²²⁵Ac [Actinium-225]. Deuteron bombardment on natural thorium targets has been investigated to measure cross sections of protactinium isotopes. In this work, ²²⁹Pa [Protactinium-229] excitation function was measured via deuteron energies up to 50 MeV [Mega electron volt] of thin thorium foils. The irradiation took place at Lawrence Berkeley National Laboratory’s (LBNL) 88-Inch Cyclotron. The target processing and analysis were performed at Oak Ridge National Laboratory (ORNL). The target consisted of 4 thin foils …

Accelerating Dynamical Density Response Code On Summit And Its Application For Computing The Density Response Function Of Vanadium Sesquioxide, Wileam Y. Phan

Masters Theses

This thesis details the process of porting the Eguiluz group dynamical density response computational platform to the hybrid CPU+GPU environment at the Summit supercomputer at Oak Ridge National Laboratory (ORNL) Leadership Computing Center. The baseline CPU-only version is a Gordon Bell-winning platform within the formally-exact time-dependent density functional theory (TD-DFT) framework using the linearly augmented plane wave (LAPW) basis set. The code is accelerated using a combination of the OpenACC programming model and GPU libraries -- namely, the Matrix Algebra for GPU and Multicore Architectures (MAGMA) library -- as well as exploiting the sparsity pattern of the matrices involved in …