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Theses and Dissertations

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Browsing Theses and Dissertations by Author "Bartels, Randy, committee member"

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    Detection of small numbers of barium ions implanted in solid xenon for the EXO experiment
    (Colorado State University. Libraries, 2012) Cook, Shon, author; Fairbank, William, advisor; Lee, Siu Au, committee member; Roberts, Jacob, committee member; Bartels, Randy, committee member
    In an effort to discover the yet-unknown absolute masses of neutrinos, the goal of the Enriched Xenon Observatory is to observe neutrinoless double beta decay of 136Xe. Identification of this very rare decay may be difficult even with the best conventional efforts to reduce and reject radioactive background, thus requiring additional background rejection via detection of the daughter 136Ba nucleus. One method of detection is laser-induced fluorescence of the barium atom in solid xenon. Spectra of very small numbers of barium atoms in solid xenon, as few as 3 atoms, are reported for the first time. Demonstration of detection of Ba atoms with large fluorescence efficiencies gives promise for detecting single atoms in the near future. Results from experiments involving implantation of Ba+ ions in solid xenon are discussed. One narrow excitation peak was discovered from ion beam deposition that was not found in neutral deposits. Five new emission lines are found with this same excitation spectrum. Bleaching, annealing, and laser dependence of these lines are studied. The identification of the new Ba species as Ba+ or as a barium molecule is discussed.
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    Experimental realization of two-isotope collision-assisted Zeeman cooling
    (Colorado State University. Libraries, 2013) Hamilton, Mathew, author; Roberts, Jacob, advisor; Lundeen, Stephen, committee member; Gelfand, Martin, committee member; Bartels, Randy, committee member
    The work presented in this thesis focuses on the demonstration and initial evaluation of a novel non-evaporative cooling method called collision-assisted Zeeman cooling. For this realization, an ultracold gas consisting of a mixture of 87Rb and 8Rb was used. Cooling was accomplished through interisotope inelastic spin-exchange collisions that converted kinetic energy into magnetic energy. Continual optical pumping spin polarized the 85Rb which ensured that only kinetic energy reducing collisions occurred and the scattered pump photons carried entropy out of the system. Thus, cooling of the ultracold gas can be achieved without requiring the loss of any atoms in order to do so. This represents a theoretical advantage over forced evaporative cooling, which is the current state-of-the-art cooling technique in most experiments. This thesis discusses the details of collision-assisted Zeeman cooling, as well as how the theory of the technique has been extended from cooling a single species to cooling with two species. There are many predicted advantages from using two rather than one species of atom in this type of cooling: greater flexibility in finding favorable spin-exchange collision rates, easier requirements on the magnetic fields that must be used, and an additional means to mitigate reabsorption (the primary limitation in many if not most non-evaporative cooling techniques). The experimental considerations needed to prepare a system that simultaneously trapped two isotopes to be able to perform collision-assisted Zeeman cooling are discussed. Because this cooling scheme is highly reliant on the initial conditions of the system, a focused experiment examining the loading of the optical trap with both isotopes of Rb was conducted and the results of that experiment are described here. The first experimental observations of spin-exchange collisions in an ultracold gas mixture of Rb are described as a part of this work. The experiments where collision-assisted Zeeman cooling were demonstrated are then described and evaluated. In this first implementation of the cooling technique the initial densities were too low and optical-pump-induced heating and loss too high for achieving the full predicted performance of the cooling technique. Through additional modeling, these limitations were understood and the necessary improvements for the next iteration of CAZ cooling experiments are laid out at the end of this work.
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    Precision measurement and symmetry properties of metastable hydrogen
    (Colorado State University. Libraries, 2022) Rasor, Cory M., author; Yost, Dylan, advisor; Roberts, Jacob, committee member; Mooney, Michael, committee member; Bartels, Randy, committee member
    Hydrogen has been an indispensable system to study during the development of quantum mechanics due to the simplicity of its atomic structure. Hydrogen maintains its utility today as an important tool for determining fundamental values such as the Rydberg and fine structure constants, as well as the proton charge radius. The work described in this thesis aims to use hydrogen for determining the proton Zemach radius, to search for anomalous spin-dependent forces, and to provide means for measuring the degree of parity violation within this simple system. An overview of a 2S1/2 hyperfine interval measurement is described, followed by a description of the apparatus used and finally a discussion of the systematic effects to be characterized. A proposed parity violation experiment is also described.