Physical Sciences and Mathematics Commons^™

Methodology For Generating Simplified Cross Section Data Sets For Neutron Transport Calculations, Thomas Jay Harrison

Doctoral Dissertations

Neutron shielding problems involve radiation transport calculations over a wide range of energies. Fission neutrons have initial energy on the order of MeV, fusion neutrons have initial energy on the order of 10s of MeV, and space-origin neutrons have initial energy on the order of 100s of MeV or higher. Shielding calculations must track the neutrons from their initial energies until they are no longer of interest; for deep-penetration neutrons, this final energy can be on the order of eV before the neutron is no longer tracked. Thus, for deep-penetration space radiation shielding problems, the calculation may require tracking the …

Effective Field Theory Approach To Collective Motion In Atomic Nuclei, Eduardo Antonio Coello Perez

Doctoral Dissertations

Collective motion in heavy nuclei has been studied within collective and algebraic models, and within density functional theory. While they reproduce the energy spectra of these systems, their predictions for some electromagnetic transitions and moments do not lie within experimental uncertainty; in other words, these predictions are inconsistent with experimental data. An effective field theory approach to collective motion in heavy nuclei solves this long standing problem. Based on symmetry arguments only, the effective field theories, constructed as expansions in powers of a small parameter, consistently describe the energy spectra of nuclei exhibiting collective motion at low order in the …

Voxel-Level Absorbed Dose Calculations With A Deterministic Grid-Based Boltzmann Solver For Nuclear Medicine And The Clinical Value Of Voxel-Level Calculations, Justin Mikell

Dissertations & Theses (Open Access)

Voxel-level absorbed dose (VLAD) is rarely calculated for nuclear medicine (NM) procedures involving unsealed sources or 90Y microspheres (YM). The current standard of practice for absorbed dose calculations in NM utilizes MIRD S-values, which 1) assume a uniform distribution in organs, 2) do not use patient specific geometry, and 3) lack a tumor model. VLADs overcome these limitations. One reason VLADs are not routinely performed is the difficulty in obtaining accurate absorbed doses in a clinically acceptable time. The deterministic grid-based Boltzmann solver (GBBS) was recently applied to radiation oncology where it was reported as fast and accurate for both …

Installation And Alignment Of The N3he Experiment, Eric Lee Plemons

Masters Theses

The n3He experiment is designed to probe the hadronic weak interaction by measuring the parity violating asymmetry between the spin of incoming neutrons and the momentum of outgoing protons following the nuclear break up of a helium three upon absorbing a neutron. Cold neutrons from the SNS are first polarized then allowed to impact a target chamber filled with helium three where the reaction occurs. Energetic particles resulting from the nuclear breakup ionize the helium three gas and are thereby detected as currents by an array of signal wires within the target chamber. In order to make a statistics limited …

Predictive Modeling Of Terrestrial Radiation Exposure From Geologic Materials, Daniel A. Haber

UNLV Theses, Dissertations, Professional Papers, and Capstones

Aerial gamma ray surveys are an important tool for national security, scientific, and industrial interests in determining locations of both anthropogenic and natural sources of radioactivity. There is a relationship between radioactivity and geology and in the past this relationship has been used to predict geology from an aerial survey. The purpose of this project

is to develop a method to predict the radiologic exposure rate of the geologic materials in an area by creating a model using geologic data, images from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), geochemical data, and pre-existing low spatial resolution aerial surveys …

Hyperpolarized 129xe Magnetic Resonance Imaging Of Radiation-Induced Lung Injury, Ozkan Doganay

Electronic Thesis and Dissertation Repository

Lung cancer is the largest contributor to cancer-related mortality worldwide. Only 20% of stage III non-small cell lung cancer patients survive after 5-years post radiation therapy (RT). Although RT is an important treatment modality for lung cancer, it is limited by Radiation-Induced Lung Injury (RILI). RILI develops in two phases: (i) the early phase (days-weeks) referred to radiation pneumonitis (RP), and (ii) the late phase (months). There is a strong interest in early detection of RP using imaging to improve outcomes of RT for lung cancer. This thesis describes a promising approach based on ¹²⁹Xe gas as a contrast …

Low Intensity Gamma-Ray Spectroscopy Of The Lake Labyrinth Meteorite, Tristan C. Paul

Physics

A 23.7g fragment of the Lake Labyrinth Meteorite (fell in 1924, collected in 1934 at Lake Labyrinth in South Australia, Australia) was re-investigated for evidence of the presence of 98Tc using a two dimensional low-intensity gamma-ray spectrometer. A new calibration technique using 26Al sources found the gamma-rays previously thought to be due to 98Tc are more likely from 166Ho. The presence of 166Ho is most likely due to activation of the stable 165Ho in the meteorite from terrestrial background sources where it was stored.

On The Spin Evolution Of Isolated Pulsars, Oliver Quinn Hamil

Doctoral Dissertations

Neutron stars are the remnants of supernova explosions, and harbor the densest matter found in the universe. Because of their extreme physical characteristics, neutron stars make superb laboratories from which to study the nature of matter under conditions of extreme density that are not reproducible on Earth. The understanding of QCD matter is of fundamental importance to modern physics, and neutron stars provide a means of probing into the cold, dense region of the QCD phase diagram.

Isolated pulsars are rotating neutron stars that emit beams of electromagnetic radiation into space which appear like lighthouses to observers on Earth. Observations …

Nucleosynthesis In Self-Consistent Core-Collapse Supernova Models Using Multidimensional Chimera Simulations, James Austin Harris

Doctoral Dissertations

Observations of nuclear abundances in core-collapse supernova (CCSN) ejecta, highlighted by γ-ray [gamma-ray] observations of the ⁴⁴Ti [titanium-44] spatial distribution in the nearby supernova remnants Cassiopeia A and SN 1987A, allow nucleosynthesis calculations to place powerful constraints on conditions deep in the interiors of supernovae and their progenitor stars. This ability to probe where direct observations cannot makes such calculations an invaluable tool for understanding the CCSN mechanism. Unfortunately, despite knowing for two decades that supernovae are intrinsically multi-dimensional events, discussions of CCSN nucleosynthesis have been predominantly based on spherically symmetric (1D) models, which employ a contrived energy source …

Studies Of Two-Nucleon Interactions And Few-Body Electromagnetic Structure In Chiral Effective Field Theory, Maria Piarulli

Physics Theses & Dissertations

A coordinate-space nucleon-nucleon potential is constructed in chiral effective field theory (χEFT) retaining pions, nucleons and Δ-isobars as explicit degrees of freedom. The calculation of the potential is carried out by including one-and two-pion-exchange contributions up to next-to-next-to-leading order (N2LO) and contact interactions tip to next-to-next-to-next-to-leading order (N3LO). The low-energy constants multiplying these contact interactions are fitted to the 2013 Granada database in the laboratory-energy range 0–300 MeV. Three versions of this chiral potential, corresponding to three different cutoffs, have been developed. The cutoff regularizes the one- and two-pion exchange as well as the contact part of the potential. A …

Event Localization In Bulk Scintillator Crystals Using Optical Coded Apertures, Joshua Brian Braverman

Doctoral Dissertations

Scintillation-based radiation detectors provide an effective method to detect radioactive materials. In medical physics, astrophysics, and national security technology oftentimes it is optimal to have the ability to localize a radioactive interaction in a scintillator to as small a region as possible within the crystal. Current methods rely on the ability to centroid a light spot as read onto a phototransducer (commonly a photomultiplier tube), and due to the typical width of the light spot when it reaches the phototransducer, the resolution is generally limited to several millimeters. One method to achieve a finer resolution is to use a segmented …

Computational Framework For Small Animal Spect Imaging: Simulation And Reconstruction, Sang Hyeb Lee

Doctoral Dissertations

Small animal Single Photon Emission Computed Tomography (SPECT) has been an invaluable asset in biomedical science since this non-invasive imaging technique allows the longitudinal studies of animal models of human diseases. However, the image degradation caused by non-stationary collimator-detector response and single photon emitting nature of SPECT makes it difficult to provide a quantitative measure of 3D radio-pharmaceutical distribution inside the patient. Moreover, this problem exacerbates when an intra-peritoneal X-ray contrast agent is injected into a mouse for low-energy radiotracers.

In this dissertation, we design and develop a complete computational framework for the entire SPECT scan procedure from the radio-pharmaceutical …

Beta Decay Of Neutron-Rich Isotopes Of Zinc And Gallium, Mohammad Faleh M. Al-Shudifat

Doctoral Dissertations

Beta-decays of neutron-rich nuclei near the doubly magic ⁷⁸Ni [78Ni] were studied at the Holifield Radioactive Ion Beam Facility. The half-life and the gamma-gamma coincidence spectra were used to study the nuclear structure. A new ^82,83Zn [82Zn, 83Zn] decay-scheme was built, where a 71±7% beta-delayed neutron branching ratio was assigned in ⁸²Zn [82Zn] decay. New gamma-ray lines and energy levels observed in ^82,83Ga [82Ga, 83Ga] beta-decay were used to update previously reported decay-schemes. The experimental results were compared to shell model calculations, which postulate the existence of Gamow-Teller transitions in these decays. The half-lives of 155±17 …

Relativistic And Non-Relativistic Proton-Nucleus Scattering, Kinsey Ann Elisabeth Zarske-Williamson

Honors Theses

Calculations for proton-nucleus scattering often rely on transition amplitudes. We implement new transition amplitudes [7] with the relativistic equations. We can find the matrix elements of the operators between the usual Dirac spinor basis or the helicity spinor basis. The operators can also be written as a linear combination of non-relativistic spin operators. To transform from one basis to another, we need to find a transformation matrix. We must establish what one of the factors that appears in the transformed expression means in order to correctly complete our transformation matrix. Once this is resolved, our transformation matrix will be complete.

Mass Table Calculations With Nuclear Density Functional Theory, Noah Watson Birge

Masters Theses

To better understand nuclei and the strong nuclear force, it is useful to analyze global nuclear properties and trends across the nuclear chart. To this end, we utilized Nuclear Density Functional Theory with Skyrme Energy Density Functionals in conjunction with high-performance computing to perform large-scale mass table calculations for even-even nuclei. Using the binding energy, pairing gap, root-mean-square radius, and deformation data from these tables we were able to analyze the two-proton and two-neutron drip lines, neutron skin depth, two-proton radioactivity, and the effect of nuclear deformation on mass filters. We used numerous energy density functionals to assess the statistical …

An Investigation Into The Phenomenological Relation Between Solar Activity And Nuclear Beta-Decay Rates, Tasneem M. Mohsinally

Open Access Dissertations

We investigate experimental evidence for time-varying nuclear decay rates, in contrast to the widely-accepted view that nuclear decaying isotopes disintegrate at a constant rate unaffected by external conditions. We study several past cases of radioactive isotopes exhibiting annual periodicities in their decay rates, presumably related to the annual variation in Earth-Sun distance. Following recent indications of shorter-lived anomalies in ⁵⁴Mn decay rates concomitant with an X-class flare in 2006, we attempt to design and develop a series of unique signal detection algorithms to identify regions of anomalous activity in a nuclear decay signal. With stringent threshold cut-offs and filtering …

Fission Fragment Tracking And Identification In The Neutron-Induced Fission Fragment Tracking Experiment’S Time Projection Chamber, Eric Song

Physics

The Neutron-Induced Fission Fragment Tracking Experiment (NIFFTE) built a novel Time Projection Chamber (TPC), the FissionTPC, for measuring neutron-induced fission cross-sections to unprecedented precision. We investigated data from a 2014 run (400010151) at the Los Alamos Neutron Science Center (LANSCE) with a double-sided U235/Pu239 target. Our particle identification studies will aid in the development of improved tracking algorithms.

Measurement Of The Dμd Quartet-To-Doublet Molecular Formation Rate Ratio (Λq : Λd) And The Μd Hyperfine Rate (Λqd) Using The Fusion Neutrons From Μ− Stops In D2 Gas, Nandita Raha

Theses and Dissertations--Physics and Astronomy

The MuSun experiment will determine the μd capture rate (μ−+d ->n+n+ν_e) from the doublet hyperfine state Λ_d, of the muonic deuterium atom in the 1S ground state to a precision of 1.5%. Modern effective field theories (EFT) predict that an accurate measurement of Λ_d would determine the two-nucleon weak axial current. This will help in understanding all weak nuclear interactions such as the stellar thermonuclear proton-proton fusion reactions, the neutrino reaction ν+d (which explores the solar neutrino oscillation problem). It will also help us understand weak …

A Measurement Of The Prompt Fission Neutron Energy Spectrum For 235U(N,F) And The Neutron-Induced Fission Cross Section For 238U(N,F), Zachariah W. Miller

Theses and Dissertations--Physics and Astronomy

Two measurements have been made, addressing gaps in knowledge for ²³⁵U(n,f) and ²³⁸U(n,f). The energy distribution for prompt fission neutrons is not well-understood below 1 MeV in ²³⁵U(n,f). To measure the ²³⁵U(n,f) prompt fission neutron distribution, a pulsed neutron beam at the WNR facility in Los Alamos National Laboratory was directed onto a ²³⁵U target with neutron detectors placed 1 m from the target. These neutron detectors were designed specifically for this experiment and employed a unique geometry of scintillating plastic material that was designed to reject backgrounds. Fission fragments were detected using an avalanche …

An Analysis Of The Parity Violating Asymmetry Of Polarized Neutron Capture In Hydrogen From The Npdgamma Experiment, Elise Tang

Theses and Dissertations--Physics and Astronomy

The NPDGamma Experiment is used to study the n + p to d + g reaction for the purpose of examining the hadronic weak interaction. The nucleon-nucleon interaction is overwhelmingly mediated by the strong force, however, the weak part can be extracted by a study of its parity violating manifestations. When neutrons are incident on protons, deuterons and 2.2 MeV gamma rays are produced. If the incoming neutrons are polarized, the parity violating weak interaction gives rise to a measured spatial asymmetry, A_g, in the outgoing gamma rays, as s_n · k_g is parity odd.

At …

The N-P Scattering Cross Section From 90 Kev To 1.8 Mev, Hongwei Yang

Theses and Dissertations--Physics and Astronomy

There have been very few measurements of the total cross section for n-p scattering below 500 keV. In order to differentiate among NN potential models, improved cross section data between 20 and 600 keV are required. We measured the n-p and n-C total cross sections in this energy region by transmission; a collimated neutron beam was passed through CH₂ and C samples and transmitted neutrons were detected by a BC-501A deuterated liquid scintillator. Cross sections were obtained by taking the ratios of normalized neutron yields with the samples in the beam and with no sample in the beam. Both …

Search For A Permanent Electric Dipole Moment Of 225Ra, Mukut R. Kalita

Theses and Dissertations--Physics and Astronomy

The observation of a permanent electric dipole moment (EDM) in a non-degenerate system would indicate the violation of discrete symmetries of Time reversal (T) or combined application of Charge (C) and Parity (P) symmetry violation through the CPT theorem. The diamagnetic ²²⁵Ra atom with nuclear spin I=1/2 is a favorable candidate for an EDM search. Experimental sensitivity to its EDM is enhanced due to its high atomic mass and the increased Schiff moment of its octupole deformed nucleus. An experimental setup is developed where laser cooled neutral radium atoms are collected in a …

Studies Of Molecular Dynamics Of Fmoc Amino Acids Using Solid State Deuteron Nuclear Magnetic Resonance Spectroscopy, Wei Xu

Dissertations, Theses, and Masters Projects

The purpose of devising and validating models for intramolecular motions for FMOC amino acids is to quantify side chain motion in proteins which plays an important role in understanding biological structure function relations of proteins. In this thesis, spin lattice relaxation times (Ti) of FMOC amino acids were m easured under both static and magic angle spinning (MAS) condition at variable tem peratures. Lower activation energies of the relaxation times than the normal amino acids observed indicate a less sterically crowded environment for the rotation methyl group. A three-site jump model for the methyl group w as developed to fit …

Consequence Management: Evaluating And Developing International Responses To Nuclear And Radiological Disasters, Timothy Taylor

Dissertations and Theses

No abstract provided.

Some Properties Of Meson Excited States From Lattice Qcd, Ekaterina V. Mastropas

Dissertations, Theses, and Masters Projects

The work presented here is devoted to the calculations of the decay constants of the pion and its excited states. All calculations were carried out in the framework of lattice quantum chromodynamics, a well-established formalism of strong interactions enabling the ab initio solution of the theory. After a short introduction and review of the fundamental approaches and methods commonly used in lattice QCD, I provide a detail description of the numerical simulations which were performed at three values of the pion mass between 400 and 700 MeV, using an anisotropic clover fermion action with three flavors of quarks. The results …