Nuclear Commons^™

Measurement Of 18f(Alpha,P)21ne With The Array For Nuclear Astrophysics And Structure With Exotic Nuclei (Anasen), Keilah S. Davis

LSU Doctoral Dissertations

Certain (α,p) reactions on proton-rich nuclei are among the most important nuclear reactions occurring during Type I X-ray bursts, as well as being impactful in stellar explosions during the Asymptotic Giant Branch (AGB) phase and on accreting white dwarfs (WD). However, large uncertainties remain for reaction rates on some radioactive nuclei due to the lack of direct measurements. The Array for Nuclear Astrophysics and Structure with Exotic Nuclei (ANASEN) is a gas target and charged-particle detector designed for direct measurements of (α,p) reactions. ANASEN was redesigned with two hexagonal barrels of 100-µm-thick silicon strip surrounding the beam axis over a …

Determining The 17f(Α,P)20ne Reaction Rate For Application In Type I X-Ray Bursts, William Braverman

LSU Doctoral Dissertations

The ¹⁷F(α, p)²⁰Ne reaction has been identified as an alternate pathway for breakout from the hot-CNO cycle that can be important in some X-ray burst scenarios. The ¹⁷F(α, p)²⁰Ne reaction rate was previously determined through a parameterized exponential S-factor with a large enhancement from thermally-excited states based on statistical models with large uncertainties. We have measured the time-inverse ²⁰Ne(p,α)¹⁷F cross section at center-of-mass energies ranging from 5.50 to 7.10 MeV using an activation method with a proton beam on a neon gas cell. Coincident detections of 511-keV γ-rays, resulting from electron-positron …

How The Inter-Nucleon Force Shapes Emergent Collectivity And Imparts Uncertainties In Ab Initio Nuclear Observables, Kevin Becker

LSU Doctoral Dissertations

The importance of collective motion in atomic nuclei has been well-established for many decades. Even before the advent of the nuclear shell model and its much-needed answers to surprising empirical phenomena, collectivity and surface deformation have played a vital role in broadening our knowledge. Reconciling the collective and single-particle camps into a unified description required tremendous strides in the application of group theory and advances in high-performance supercomputing, and thanks to these efforts the symmetry-adapted no-core shell model, or SA-NCSM, has developed into a reliable model for the study of deformed light and medium-mass nuclei. State-of-the-art calculations reveal remarkably simple …

19ne Excited States In Explosive Nucleosynthesis, Khang Pham

LSU Doctoral Dissertations

Classical novae and Type I X-ray bursts are stellar explosions that occur in binary systems, where nuclear reactions involving ¹⁹Ne play a crucial role in nucleosynthesis. In novae, the destruction of ¹⁸F via the ¹⁸F(p,alpha)¹⁵O reaction significantly affects the amount of ¹⁸F remaining in the ejecta, directly influencing the detectability of predicted 511-keV gamma rays. However, discrepancies between observed and predicted ¹⁸F abundances highlight uncertainties in the reaction rates, primarily due to unknown properties of resonances in the compound nucleus ¹⁹Ne. In Type I X-ray bursts, the ¹⁵O(alpha,gamma)¹⁹Ne reaction …

Studying The Low-Lying Structure Of 9b Via The 10b(3he,A)9b Reaction, Rachel M. Shaffer

LSU Doctoral Dissertations

The unstable nature of ⁹B makes it a challenging isotope to study. The first-excited state of ⁹B has been particularly difficult to characterize. Since the first experimental observation of this state in 1955, many experimental and theoretical nuclear structure studies have sought to classify it, but with large discrepancies in the energy and width values from these results, the properties of the state remain inconclusive.

An experiment using the ¹⁰B(³He,α)⁹B reaction was performed at the John D. Fox Superconducting Linear Accelerator Laboratory at Florida State University in an effort to populate and characterize …

Decay Spectroscopy Of 134sb Using X-Array And Saturn, Graeme E. Morgan

LSU Doctoral Dissertations

The ground-state decay of ¹³⁴Sb is reported by the current evaluated nuclear data to be dominated by a 0^-→0⁺ first-forbidden Gamow-Teller transition to the ground state of ¹³⁴Te. In 2013, a recoil-ion time-of-flight (RI-TOF) spectroscopy measurement of ¹³⁴Sb with the Beta-decay Paul Trap (BPT) indicated that the ground-state feeding of ¹³⁴Te is weaker than reported. Simulation work of ¹³⁴Sb ground-state decays replicated the RI-TOF results with the addition of a theorised 5-MeV state that was fed with ~17% of the total β-decay strength. To search for higher energy states and transitions that …

Measurement Of The Β-Decay Properties Of A=105 Isotopes Using The Modular Total Absorption Spectrometer And The Development Of The Beta Spectrum Module, Thomas J. Ruland

LSU Doctoral Dissertations

Nuclear reactors produce an extremely diverse population of beta-decaying isotopes. Accurate and precise knowledge of the beta-decay properties of these isotopes is vital to safe reactor operations as well as informing next-generation reactor design. These beta-decay properties not only impact the design and operation of nuclear reactors, but they influence the expected antineutrino flux and spectrum measured from nuclear reactors. Historical measurements of many of these isotopes are subject to a systematic bias referred to as the Pandemonium Effect, because the low-efficiency, high-precision detectors used to perform the measurements results in misinterpreting weak gamma cascades from high- energy levels as …

Measurement Of Near-Threshold Proton Branching Ratios In 31s Important For Novae, Sudarsan Balakrishnan

LSU Doctoral Dissertations

Classical novae are stellar explosions that contribute to the nucleosynthesis of isotopes on the proton-rich side of the valley of stability up to ⁴⁰Ca. In ONe novae, the incompletely understood reaction rate of ³⁰P(p,γ)³¹S is known to strongly influence the production rate of several stable isotopes such as ³⁰Si, ³¹P, and ^32,33,34S. A precise measurement of this reaction rate has several potential implications towards matching astrophysical observables to the physical composition of the nova site -- the observed elemental abundance ratios of O/S and S/Al have been suggested as useful `thermometers' to gauge …

Deformed No-Core Shell Model And Symplectic Effective Field Theory, David Kekejian

LSU Doctoral Dissertations

Most nuclei are deformed! This simple fact has been established since Bohr and Mot- telson, and successfully demonstrated from first principles by nuclear structure calculations carried out using the ab-initio Symmetry-Adapted No-Core Shell Model (SA-NCSM) us- ing realistic interactions. This simple fact has been the main driver towards understanding the underlying physics; namely, that symplectic symmetry describes deformation and is a dominant symmetry in all nuclei independent of A (nucleon number) and of the realistic interaction used. These two simple observations laid the foundation of this thesis work to explore the applications of symplectic symmetry towards defining a deformed symplectic …

Electromagnetic Transitions And Beta Decays In Nuclei From The Ab Initio Symmetry-Adapted No-Core Shell Model, Grigor Sargsyan

LSU Doctoral Dissertations

Nuclear physics today is a diverse field, involving research that extends from the minus- cule scales of neutrons and protons to the colossal dimensions of astrophysical objects in the universe. And since the ab initio methods in nuclear physics use realistic internucleon interactions, nuclear modeling has gained predictive capabilities that enable us to probe ever more deeply into the fundamental nature of matter. One of these models – the symmetry- adapted no-core shell model (SA-NCSM) – is capable of reaching the medium-mass region of the chart of the nuclides, by exploiting the emergent symmetries of nuclei, and is therefore well-suited …

Structural Shielding Considerations For Vmat, Ana Lucia Dieguez

LSU Master's Theses

Introduction: As noted in National Council on Radiation Protection and Measurements (NCRP) Report 151, the medical physicist or other qualified expert has the responsibility to keep abreast of any new technology or treatment method that could potentially impact structural shielding design. Volumetric arc therapy (VMAT) became prevalent after the publication of Report 151 and thus was not explicitly addressed in Report 151. If the shielding-related characteristics of VMAT differ enough from the expectations of Report 151, especially in the circumstance of a vault utilized exclusively for VMAT, a shielding design based on Report 151 could potentially be inadequate. The …

A Study Of 26al(P, Γ)27si With The Silicon Array For Branching Ratio Experiments (Sabre), Erin Courtney Good

LSU Doctoral Dissertations

The observation of the radioisotope ²⁶Al is an indicator of ongoing nucleosynthesis in the Galaxy due to its short lifetime (t_1/2 = 7.2 × 10⁵ yr) on Galactic timescales. It is thought to be synthesized in several different environments in our Galaxy, one of which is in classical novae. Classical novae are stellar explosions that occur on the surface of a white dwarf in a binary system with a main sequence star. The isotopic production resulting from the nucleosynthesis that drives these explosions can be modeled with the input of nuclear reaction rates. In recent years, many …

Stellar Nucleosynthesis: Direct Measurement Of The Neutron-Capture Cross Sections Of Stable Germanium Isotopes And Design Of A Next Generation Ion Trap For The Study Of Beta-Delayed Neutron Emission, Alexander Laminack

LSU Doctoral Dissertations

Knowledge of stellar nuclear reaction rates is critical to understanding the cosmic origins of the abundances of elements. In order to determine these reaction rates, accurate measurements of nuclear cross sections are needed. This thesis presents the results of an experiment to directly measure the neutron capture cross sections of 70-Ge, 72-Ge, 74-Ge, and 76-Ge. These measurements were performed at the Los Alamos Neutron Science CEnter (LANSCE) using the Detector for Advanced Neutron Capture Experiments (DANCE). This is the first direct measurement for many of these isotopes across the neutron energy spectrum of 10 eV to 1 MeV using the …

Measurements Of The 16c + 12c And 16c + 13c Fusion Cross Sections With Implications For Astrophysics, Ashley Ann Hood

LSU Doctoral Dissertations

The fusion of neutron-rich nuclei is of interest to nuclear astrophysics and nuclear structure. X-ray superbursts are powered by runaway thermonuclear burning deep inside of a neutron star, where heating from the pycnonuclear fusion of neutron-rich isotopes is an important heat source. Experimental measurements of fusion cross sections of neutron-rich isotopes have provided insights regarding nucleon transfer and nuclear structure properties affecting fusion. Recently, the ¹⁵C + ¹²C total fusion cross section was measured using a ¹⁵C beam produced by the in-flight beam production facility, which is part of the Argonne Tandem LINAC Accelerator System (ATLAS) at …

Alpha Capture Reaction Rates For Nucleosynthesis Within An Ab Initio Framework, Alison Constance Dreyfuss

LSU Doctoral Dissertations

Clustering in nuclear systems has broad impacts on all phases of stellar burning, and plays a significant role in our understanding of nucleosynthesis, or how and where nuclei are produced in the universe. The role of alpha particles in particular is extremely important for nuclear astrophysics: ⁴He was one of the earliest elements produced in the Big Bang, it is one of the most abundant elements in the universe, and helium burning -- in particular, the triple-alpha process -- is one of the most important ``engines'' in stars. To better understand nucleosynthesis and stellar burning, then, it is important …

Electromagnetic Sum Rules And Response Functions From The Symmetry-Adapted No-Core Shell Model, Robert Byron Baker

LSU Doctoral Dissertations

Recent developments in ab initio nuclear structure have provided us with a variety of many-body methods capable of describing nuclei into the medium-mass region of the chart of nuclides. One of these, the symmetry-adapted no-core shell model (SA-NCSM), capitalizes on inherent symmetries of the nucleus and is uniquely suited to examine the underlying physics of dynamical quantities, such as the response function.

We examine the applicability of the SA-NCSM to calculations of these quantities and assess the quality of its inputs by calculating electromagnetic sum rules and response functions with the Lanczos sum rule method and Lanczos response function method, …

Studying The Reaction 34ar(Alpha,P)37k And Its Impact On Xrb Nucleosynthesis And Observables, Amber C. Lauer

LSU Doctoral Dissertations

Type I X-Ray bursts (XRB’s) are a site of nucleosynthesis for some proton-rich elements up to A=100. These stellar explosions occur on the surface of a neutron star in a Low- Mass X-ray Binary accreting H- and He-rich material. During accretion nuclear burning occurs through stable processes such as the hot CNO (HCNO) cycles, but at some critical accretion condition the the HCNO cycles are bypassed through a breakout reaction. This triggers the thermonuclear runaway of the XRB. During the burst, nucleosynthesis on certain proton-rich nuclei, called (α, p) waiting points, can stall which could stall the energy generation and …