Chemistry & Biochemistry Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/2752

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Now showing 1 - 6 of 6
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    DIRECTED AND ELLIPTIC FLOW MEASUREMENTS: A COMPARISON BETWEEN THE PARTICIPANT AND SPECTATOR PLANES IN Pb+Pb COLLISIONS AT √sNN = 5.02 TeV WITH CMS AT THE LHC
    (2024) Lascio, Samuel Andrew; Mignerey, Alice C.; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Directed and elliptic flow of unidentified charged hadrons at mid-rapidity are measured as a function of transverse momentum (pT) and pseudorapidity (η) in ultra-relativistic PbPb collisions at √sNN = 5.02 TeV with the Large Hadron Collider (LHC) at CERN. The reaction plane (RP) angle is approximated using participants and spectator neutrons measured with the Compact Muon Solenoid (CMS) detector and the newly installed Spectator Reaction Plane Detector (SRPD), respectively. The SRPD is the latest addition to the existing Zero Degree Calorimeter (ZDC) designed to measure spectator neutrons +/- 140 m from the interaction point at CMS. The Event Plane (EP) Method is used to calculate the v1odd, v1even, and v2 harmonic flow parameters as functions of η and pT. The directed flow measurements using participants and spectators with CMS are compared and contrasted. Overall results are in good agreement between participants and spectators, however v1even(pT) measurements using spectators begin to show the opposite trend to those using participants at pT > 2 GeV/c. Results are compared to those obtained by A Large Ion Collider Experiment (ALICE), which is another experiment at the CERN LHC. Directed flow results do not agree with those obtained by ALICE. Additionally, the first elliptic flow measurements using the EP Method and mixed harmonics with the SRPD are reported. A slight asymmetry in v2(η) is observed using spectators. The elliptic flow results do agree with ALICE. Tracking efficiency as determined by the CMS collaboration is applied to the data and potential corruption as a result is discussed. Results strongly support continued use of the SRPD as a spectator neutron detector for reaction plane determination within the CMS ZDC.
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    Cryogenic Design and Thermal Analysis of the CURIE CryoTrap
    (2022) Osborn, Rebecca Caroline; Koeth, Timothy W; Chemical Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The decay rates of electron capture (EC) radioisotopes, such as 7Be, are demonstrativelysusceptible to alteration with change to the electron orbital structure [1] [2] [3] [4]. The Cryogenic Ultra-high vacuum Radioactive Isotope Experiment (CURIE) Project aims to isolate the various charge states of the low-Z radioisotope 7Be stably to perform novel half-life measurements. To achieve this, the system must be cooled to 4K to reach extreme high vacuum (XHV) conditions in excess of 10E−15 mbar and to ensure single ion resolution detection. The cryogenic design which achieves this is presented here. The design consists of the actively cooled 45K radiation shield, and the 4K stage which houses the Penning trap. The 4K stage is brought to XHV and maintained at these pressures through the design of a rotary “cryovalve”. This thesis details the entire apparatus, the heat loads incident on both stages through simulation, and outlines an experimental method for testing the “cryovalve”.
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    Jet Production Cross Section Measurement In √ s = 5.02 Tev pp Collisions
    (2021) Baron, Owen David Cadwalader; Mignerey, Alice C; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The study of jets offers insights into the nature of the basic partons composing matter, and enables further studies into the nature of the universe. This analysis presents the double-differential production cross section of radius parameter R = 0.3 proton-proton jets in units of pseudorapidity and transverse momentum at √ s = 5.02 TeV, measured in the Compact Muon Solenoid detector at the Large Hadron Collider experiment located at CERN. Jets are reconstructed using Particle Flow and the anti-kT algorithms. The methodology of correcting the detector response through Jet Energy Corrections and Bayesian unfolding is described with a detailed explanation. The results from data recorded in CMS in 2015 are shown and compared with leading-order theory-based simulated PYTHIA8 Monte Carlo events.
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    Nuclear Structure Studies of ${^78,80}$Ge and Adjacent Nuclei
    (2018) Forney, Anne Marie; Walters, William B; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The main topic of this thesis concerns the unusual features of the nuclear structure of $^{78}$Ge. The discovery of a sequence of levels separated by one unit of angular momentum for which the expected crossover transitions carrying two units of angular momentum are not observed. This result stands in contrast to the neighboring even-even Ge and Se nuclei, as well as the results of most model calculations. The level structures of adjacent $^{82,80}$Ge are also studied to place the results for $^{78}$Ge in context. Likewise, shell-model calculations are performed as comparisons with the structures for all three nuclei. The data come from experiments at Argonne National Laboratory using the Gammasphere detector array. These experiments are important because of the broad interest in the structure of $^{76}$Ge and neighboring nuclei, owing to a world-wide effort in the search for neutrinoless double $\beta$ decay. Owing to the unusual features of this level sequence, it is labelled as a $\kappa$ band, taken from the Greek word καινουργιος, meaning new. The results pose a challenge to theorists to find ways to develop models that can fit both these features, as well as the other aspects of the structure of $^{78}$Ge. In addition, this study is important determining why no sequence like this has been found in any of the adjacent nuclei.
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    MODELING AND VALIDATION OF NEUTRON ACTIVATION AND GAMMA-RAY SPECTROSCOPY MEASUREMENTS AS AN EXPLORATORY TOOL FOR NUCLEAR FORENSIC ANALYSIS
    (2018) Goodell, John; Mignerey, Alice C; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The continued success of nuclear forensic analysis relies on the development of new material and process signatures. However, the unique safety hazards and strict controls concerning nuclear materials and operations limit the practicality of experimental scenarios. To bypass these limitations, the nuclear science community is increasingly reliant on simulation-based tools. In this dissertation, neutron activation and gamma-ray spectroscopy measurements are simulated to explore the activation network of stainless steel and its components using two neutron sources. The goal is to identify nuclides or ratios that are indicative of the neutron source and test their measurability in complex samples. The neutron sources are a critical assembly, providing fission spectrum neutrons, and a beryllium (Be) neutron converter, producing neutrons through various deuteron induced reactions. Simulated neutron energy distributions are calculated using the Monte Carlo N-Particle (MCNP) radiation transport code. Neutron activation has an inherent neutron energy dependence, making nuclide production rates contingent on the neutron energy distribution. Activation calculations performed by hand and with the FISPACT-II code are compared against experiments to validate the neutron energy distributions and assess available reaction cross-section data. Additionally, ratios of activation products common to both neutron sources are investigated to determine if they are indicative of the neutron source. Gamma-ray spectroscopy with high-purity germanium (HPGe) detectors is the leading passive assay technique for radioactive samples, providing detailed qualitative and quantitative information while preserving sample integrity. A simple HPGe detector is modeled using MCNP to assess the measurability of different activation product ratios. The HPGe model is validated against its real counterpart to determine if the level of complexity is sufficient for this work. Activation calculations were able to validate the critical assembly neutron energy distribution but showed significant errors in the Be converter model. Additionally, validation of activation calculations identified shortcomings in the 60Ni(n,p)60Co reaction cross section. Absent interferences, HPGe simulation performance was equivalent to the real detector. The HPGe model also showed that decay time can affect measurement accuracy when significant interferences are present. Activation product ratios identified in this work that are indicative of the neutron source are 57Co/54Mn, 51Cr/54Mn, 57Co/59Fe, and 51Cr/59Fe.
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    A Probe of Colored Medium Effects on Quarkonia Polarization in √s = 7 TeV pp collisions at CMS
    (2017) Ferraioli, Charles Christopher; Mignerey, Alice C; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The suppression of quarkonia mesons is one of the signature indications of the presence of a quark-gluon plasma, the colored, asymptotically free state of matter believed to have existed moments after the Big Bang, and recreated by colliding heavy-ions. Two S-wave charmonia states, the J/ψ and the ψ(2S), along with three S-wave bottomonia states, the Υ(1S), Υ(2S), and Υ(3S), have been studied in heavy-ion collisions at both the Relativistic Heavy Ion Collider and the Large Hadron Collider (LHC), showing clear sequential suppression patterns, with the most tightly bound states less suppressed than the others, relative to scaled proton-proton (pp) collisions. Yet, the results remain difficult to interpret, owing to a combination of complicated feed-down processes from P-wave χ states, as well as regeneration of quarkonia occurring well after the initial collision. Further, the basic production mechanism of quarkonia is still far from certain, leaving open the possibility that changing mechanisms could affect the scaling of pp yields. This thesis aims to be the first in a line of studies into the effects of a colored medium on the basic production mechanism of quarkonia by measuring quarkonia polarization. Polarization can be measured using the angular distributions of dimuons emanating from quarkonia decays, and the Compact Muon Solenoid detector is well suited for these measurements. The polarizations of the three Υ(nS) and two ψ(nS) states were measured versus event multiplicity using a dimuon data sample collected during the 2011 LHC run of √s = 7 TeV pp collisions, with a total integrated luminosity of 4.9 fb−1. The measurements were integrated over the available rapidity range, for transverse momentum up to 35 GeV/c. All quarkonia states showed small polarizations, which were cross checked across several reference frames, and are consistent with multiplicity-integrated analyses. In the states for which a precise measurement could be made, the J/ψ and the Υ(1S), there was no variation with multiplicity, but these states are strongly affected by feed-down, preventing any definitive conclusions. Ultimately, this study leads the way for a polarization measurement in heavy-ion collisions, which would provide a more decisive look into the affect of a colored medium on quarkonium production.