No description available.

No description available.

Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 53-54). Also available on the World Wide Web.

University, Diss., 2004--Kiel.

The fundamental physics of spin-exchange optical pumping (SEOP) has been explained in detail by many brilliant scientists since its discovery in the 50’s and 60’s. Although some interactions remain only tenuously understood, mathematical relationships have been mapped across many trajectories with meticulous care. Despite these foundational descriptions, many of the larger scale dynamics remain capricious in practice, especially as SEOP strives to take advantage of rapidly developing laser technologies. This presents a difficulty for implementing the large-scale production of hyperpolarized gases that is required for clinical and some specific experimental applications. This research, performed over the past four years, was designed to shed light on some of the practical effects that become critical for scaling up production while keeping polarizations high, particularly in a “stopped-flow” polarizer environment. This dissertation is divided into eight main chapters. The first chapter is written to provide a historical context for the SEOP field and summarize the evolutionary stages that have led to current methodologies. The second chapter provides a brief summary of SEOP theory and mathematically outlines the transfer of quantum order from photon polarization, to electron polarization via optical pumping, and finally to long-lived nuclear polarizations via spin-exchange. Chapter 3 discusses the practical implementation of SEOP, and the specific designs and techniques used throughout this project to create and monitor polarization. Chapter 4 presents data with some unexpected trends collected by Dr. Nicholas Whiting and Dr. Peter Nikolaou using high densities of xenon and high resonant laser powers. This data inspired a set of simulations designed to locate the cause of these trends, and map the expected trajectory for further studies. Chapter 5 features a clinical-scale polarizer with 170 W of highly resonant cw laser power, capable of producing >0.8 L of hyperpolarized gas per SEOP cycle with 129Xe polarization values of ~30-90% (depending on the xenon density). Multidimensional data maps were created over various temperatures, gas mixes, and laser powers; the results are used to guide optimal performance and describe the conditions that cause SEOP to fail. Chapter 6 reintroduces helium into stopped-flow gas mixes to help mitigate the central difficulties found in Chapter 5 with thermal regulation, and discusses the improvements and difficulties observed as a result. Chapter 7 contrasts the tactics for high 129Xe polarization with the strategies that lead to high 131Xe polarization. Specifically this study is designed to assess whether 131Xe is capable of becoming polarized via SEOP to sufficient levels—and in sufficient amounts—to be used for some specific fundamental physics studies and other biomedical applications. Finally Chapter 8 presents a short proof of concept for the use of an aluminum optical pumping cell instead of the glass optical pumping cells predominantly used for SEOP.

No description available.

The research described in this Thesis investigates the coordination chemistry of pentafluorooxotellurate(VI) (F5TeO– or “teflate”) and [PnF6]– (Pn = As, F) derivatives of mercury(II), and expands the chemistry of Ng(II) (Ng = Kr, Xe) by characterizing several NgF2 coordination complexes with mercury, and the synthesis of a new xenon(II) oxide cation. The compounds discussed herein were characterized predominately by low-temperature single-crystal X-ray diffraction and Raman spectroscopy, and were frequently complemented by quantum-chemical calculations. The chemistry of the F5TeO–group was developed for Hg(II) derivatives by investigating the Lewis acid properties of Hg(OTeF5)2. Initial efforts investigated interactions with the nitrogen base NSF3, and resulted in the coordination complexes [Hg(OTeF5)2∙N≡SF3]∞, [Hg(OTeF5)2∙2N≡SF3]2, and Hg3(OTeF5)6∙4N≡SF3 at 0oC. Although the F5TeO–group often bonds in a monodendate fashion, these less sterically saturated salts result in oxygen bridging in the solid state. In Hg3(OTeF5)6∙4N≡SF3, oxygen bridging between three metal centers by the pentafluorooxotellurate(VI) group is observed for the first time. The nature of this new bonding was further analysed computationally for Hg3(OTeF5)6∙4N≡SF3 by natural bond orbital analyses (NBO). At room temperature, reactions of Hg(OTeF5)2 with NSF3 resulted in O/F metatheses to yield related F2OSN–derivatives, namely [Hg(OTeF5)(N=SOF2)∙N≡SF3]∞ and [Hg3(OTeF5)5(N=SOF2)-∙2N≡SF3]2, accompanied by the elimination of TeF6 as confirmed by 19F NMR spectroscopy. In related work, the acceptor properties of Hg(OTeF5)2 were further investigated in its reactions with M[OTeF5] (M = [N(CH3)4]+, [N(CH2CH3)4]+, Cs+) to form a series of teflate anion salts; [N(CH2CH3)4]2[Hg(OTeF5)4], [N(CH3)4]3[Hg(OTeF5)5], [N(CH2CH3)4]3[Hg(OTeF5)5], [N(CH3)4]2[Hg2(OTeF5)6], Cs2[Hg(OTeF5)4]•Hg(OTeF5)2, and {Cs3[Hg2(OTeF5)7]•Hg(OTeF5)2}•4SO2ClF. In comparison to their halide counterparts, the less basic and more sterically demanding teflate ligands of the Hg(II) anions show less tendency to extensively bridge. The Raman spectra of the [Hg(OTeF5)4]2−, [Hg(OTeF5)5]3−, and [Hg2(OTeF5)6]2− anions were fully assigned with the aid of their calculated gas-phase vibrational frequencies. NBO analyses further probed the bonding in the anions. The [Hg(OTeF5)5]3− anion provides an unusual square-pyramidal coordination sphere around mercury and the only presently known teflate-substituted anion with a net charge of 3–. In related work, the weakly coordination anion (WCA) [Sb(OTeF5)6]– was substituted in Hg2+ salts using weakly coordinating SO2ClF solvent to give the homoleptic solvent complex, [Hg(SO2ClF)6][Sb(OTeF5)6]2. The ability of this salt to function as a precursor for other ligands was demonstrated by the reaction with the nitrogen bases NCR (R = –CH3 or –CH2CH3) which resulted in the isolation and full characterization of the corresponding homoleptic nitrile complexes [Hg(NCR)5][Sb(OTeF5)6]2ꞏ2SO2ClF. Gas-phase energy-minimized calculation of the cations aided in the vibrational assignment of the Raman spectra, whereas NBO and counterpoise corrected binding energies give insights into the strength of the metal-ligand bonds and resulting electronic effects of these interactions. The established Lewis acidity of Hg(OTeF5)2, and known oxidative resistance of the F5TeO–group, were exploited to form rare examples of noble-gas difluoride adducts, Hg(OTeF5)2•1.5NgF2 (Ng = Xe, Kr). The isostructural complexes were fully characterized, and the KrF2 adduct provided only the second crystallographically characterized KrF2 complex and the first example of bridge coordination by KrF2¬. The chemistry of krypton was significantly extended by further exploring the little studied coordination of KrF2 with the salts Hg(PnF6)2 (Pn = As, Sb) and FHg(AsF6), leading to an important series of coordination complexes. The first homoleptic KrF2 coordination complex, [Hg(KrF2)8][AsF6]2•2HF, was thoroughly characterized by single-crystal X-ray diffraction, Raman spectroscopy, and quantum-chemical analyses. It provides the highest KrF2-to-metal ratio that is currently known for a coordination complex. The bonding was extensively analysed by NBO, calculated binding energies, energy decomposition analyses (EDA), and Extended Transition State Natural Orbitals for Chemical Valence (ETS-NOCV) analyses. This computational work suggests that both orbital interactions, which incorporate covalent bonding, and electrostatic contributions are important stabilization factors and that the 8σg (HOMO‒4) orbital and, to a lesser extent, a degenerate 4πu (HOMO) orbital, derived from free KrF2 (D∞h) are involved in adduct formation. This result helps to rationalize the observed M---F–Kr(F) coordination angles observed for most terminally coordinated NgF2 complexes. A series of related complexes with one to five KrF2 molecules per metal center were also characterized by single-crystal X-ray diffraction, namely Hg(KrF2)(HF)(AsF6)2 (1), Hg(KrF2)2(AsF6)2 (2), Hg(KrF2)3(HF)(SbF6)2 (3), [Hg(KrF2)4(HF)2(SbF6)]2[SbF6]2 (4), Hg(KrF2)5(AsF6)2 (5), Hg(KrF2)4(HF)2(AsF6)2•HF (6), FHg(μ3-FKrF)1.5(KrF2)0.5(AsF6) (7), and FHg(μ3-FKrF)0.5(KrF2)1.5(AsF6) (8). These complexes were unambiguously characterized by single-crystal X-ray diffraction which showed that the structures became more extensively linked due to bridging between mercury and the [PnF6]‒ anions as the number of coordinated KrF2 ligands decreased. While compounds (1)-(6) solely contain terminally coordinated KrF2 ligands, compound (7) also contains the second structurally characterized example of KrF2 bridging two metal centers through each of its fluorine atoms. Replacement of [AsF6]‒ by F‒ in compounds (7) and (8) also resulted in the first examples of a new bonding modality of KrF2, where only one of the fluorine atoms bridges two different metal centers. The Raman spectrum of (5) was assigned with the aid of calculated gas-phase vibrational frequencies. Natural bond orbital (NBO) analyses of [Hg(KrF2)5][AsF6]2 are consistent with coordinate covalent ligand-metal interactions. The nature of bonding for the unprecedented KrF2 bonding modality was further probed computationally with EDA and ETS-NOCV analyses and corroborate an MO description where electron density is donated from both the 8σg (HOMO‒4) and a degenerate 4πu (HOMO) molecular orbital of KrF2 to LUMOs involving the 6s and 6p orbitals of each mercury atom. To further expand the chemistry of the noble-gases, the second known xenon(II) oxide, [XeOXe]2+, was synthesized from the reaction of [FXeOXe---FXeF][AsF6] and acetonitrile at low-temperatures in anhydrous HF. The cation was isolated in macroscopic quantities as its well-isolated adduct-dication [CH3CN---XeOXe---NCCH3][AsF6]2 salt and was fully characterized by single-crystal X-ray diffraction and 16/18O isotopic enrichment Raman studies. The [XeOXe]2+ adduct-cation provides an important example of σ-hole bonding by a nitrogen base to a Xe(II) atom. The nature and strength of the Xe–O and Xe–N bonds in the calculated gas-phase [XeOXe]2+ and [CH3CN---XeOXe---NCCH3]2+ cations were extensively explored using a range of quantum-chemical (QC) methods, namely, NBO, atoms in molecules (AIM), electron localization function (ELF), and molecular electrostatic potential surface (MEPS) analyses. / Thesis / Doctor of Philosophy (PhD) / The coordination chemistry of pentafluorooxotellurate(VI) (F5TeO– or “teflate”) derivatives, as well as [PnF6]– (Pn = As, Sb) salts, of mercury(II), and the chemistry of Ng(II) (Ng = Kr, Xe), are the major focuses of this Thesis. The Lewis acid properties of Hg(OTeF5)2 were investigated using the nitrogen base, NSF3, and M[OTeF5] salts (M = Cs+, N(CH3)4+, N(CH2CH3)4+) which resulted in a series of NSF3 adducts, F2S(O)N– derivatives, and several anions. Reactions of Hg(OTeF5)2 with NgF2 also provided rare examples of bridging NgF2 coordination complexes. Routes to [Sb(OTeF5)6]– salts containing weakly-solvated Hg2+ cations was developed, which provided an important synthetic precursor to explore further ligand substitution reactions at Hg2+. The relatively unexplored chemistry of krypton was further advanced by synthesizing a series of coordination complexes of KrF2 with Hg(PnF6)2 and FHg(AsF6) salts, providing rare examples of terminally coordinated and bridging KrF2 ligands, and a new coordination mode for KrF2 molecules. Advances in the chemistry of Xe(II) were also made through the synthesis and characterization of the second known, and simplest, xenon(II) oxide species. Characterization methods employed in this Thesis predominantly were single-crystal X-ray diffraction and Raman spectroscopy. Quantum-chemical calculations aided with Raman assignments, and were used to further investigate the nature of chemical bonding in the compounds that had been synthesized. The research described in this Thesis significantly contributes to and extends the chemistry of the pentafluorooxotellurate(VI) ligand, to our knowledge and understanding of the reactivity and bonding of krypton(II) and xenon(II) species, and most notably, the coordination chemistry of KrF2.

The existence of a significant non-baryonic component to the Universe is widely accepted, with worldwide efforts underway trying to detect this so-called dark matter. The ZEPLIN-III detector utilises liquid xenon (Xe) as a target medium in the search for the expected rare interactions of Weakly Interacting Massive Particles, or WIMPs, with ordinary baryonic matter. The neutralino, arising in supersymmetric extensions to the standard model of particle physics, provides a particularly well-motivated candidate. The ZEPLIN-III experiment, operating in two-phase (liquid/gas) mode, measures both the scintillation and ionisation signatures produced during an interaction. The first science run (FSR) of ZEPLIN-III was performed during three months in 2008. The run culminated in a published result which excluded a WIMP-nucleon interaction cross-section above 8:1 x 10-8 pb for a 60 GeVc-2 WIMP at the 90% confidence level. ZEPLIN-III then entered an upgrade period where the photomultiplier tube (PMT) array, previously the dominant source of background, was replaced with new, ultra-low background, PMTs. The radio-contamination of components used to make these PMTs has been thoroughly studied and their impact on the background rates in ZEPLIN-III characterised. Additionally, a new 1.5 tonne plastic scintillator veto detector was constructed, increasing the ability to reject WIMPlike signals caused by neutron induced nuclear recoil events and improving the γ-ray discrimination capability of ZEPLIN-III. The second science run (SSR) of ZEPLIN-III began in June 2010 and continued for 6 months, with a projected upper limit for the interaction cross-section of 1:52 x 10-8 pb for a 55 GeVc-2 WIMP at the 90% confidence level.

Cold dark matter in the form of weakly interacting massive particles (WIMPs) is a favoured explanation to the galactic dark matter puzzle and could account for a large proportion of the missing mass of the Universe. There are currently numerous detectors around the world attempting to observe a WIMP signal. The ZEPLIN-III detector is one such device. Utilising liquid xenon as a target medium, identification is based on extraction of scintillation and electroluminescence signals from the two-phase xenon target caused when WIMPs scatter and has recently completed its first science run (FSR). With no WIMP signal observed, ZEPLIN-III has excluded a WIMP-nucleon spin-independent cross section above 8.1 × 10−8 pb (90% confidence limit) for a WIMP mass of 60 GeV/c2 and also set a 90% confidence upper limit of a pure WIMP-neutron spin-dependent cross section of 1.9 × 10−2 pb for a 55 GeV/c2 WIMP mass. However, the focus of this thesis is the future of the ZEPLIN-III detector with regards to the second science run (SSR). As with all dark matter detectors, background reduction from neutrons and gamma-rays plays a significant part in obtaining competitive WIMP detection sensitivities. The author has contributed significantly to the design, development and testing of a low radioactivity veto for the ZEPLIN-III detector, to be retrofitted in time for the SSR. It will detect neutrons and gamma-rays in coincidence with the ZEPLIN-III target allowing these events to be removed as candidate WIMP events. This thesis describes the author’s contribution to the design, construction, testing and evaluation of the veto. Also discussed is the development of a comprehensive Monte Carlo simulation, utilised to aid in the design process, to determine the background rates emanating from the veto components (and therefore possible impact on the low sensitivity running of ZEPLIN-III), and to provide an accurate estimation of the overall veto efficiency to reject coincident neutrons and gamma-rays. The veto will have a neutron rejection factor of 67%, reducing the expected neutron background in ZEPLIN-III from 0.4 neutrons/year to 0.14 neutrons/year, a significant factor in the event of a possible WIMP observation. In addition to the work performed on the ZEPLIN-III veto, the author has also contributed to the first science run analysis program by profiling the historical evolution of the electron lifetime throughout the FSR, and implementing consideration of this to improve the data quality.

An ever-growing body of evidence suggests that dark matter exists and is abundant in our universe. Although the direct detection of dark matter has yet to be realized, the intensity of the experimental and theoretical search continues to amplify. The question is no longer whether dark matter exists, but rather what is its fundamental nature and how can it be known. Many large-scale, international experiments are actively searching for one class of dark matter candidates, weakly interacting massive particles (WIMPs). While indirect searches, such as those looking for the creation of dark matter in particle accelerators or for the Standard Model byproducts of dark matter annihilation, are contributing significantly to our understanding of the properties WIMPs may have, direct searches, such as those using cryogenic liquids and solids to look for scattering, have produced the most stringent limits on the properties of WIMPs. Liquid xenon (LXe) detectors continue to lead the field in the search for the direct detection of WIMPs. The success of experiments using LXe relies upon decades of measurements of the fundamental properties of LXe itself, as well as thorough characterization of the detectors that utilize this amazing element. One frontier of LXe detectors is at low energies. Next-generation LXe detectors, such as XENON1T, require a better understanding of the response of LXe to particle interactions as a function of electric field, as well as more precise measurements of the radioactive backgrounds that contribute to low-energy electronic recoil interactions. In this thesis, I describe details of efforts to characterize the stability of the XENON100 detector during its primary dark matter search periods in 2010-2012. I examine the electronic recoil data for any indications of periodic behavior, and compare the XENON100 result with a dark matter annual modulation claim by DAMA/LIBRA. I also describe the design, construction, and performance of a dedicated experiment to measure the low-energy properties of LXe, in particular the energy and electric field dependence of the response of LXe to electronic recoils. Finally, I describe the design and performance of an atom trap trace analysis device for assaying the levels of radioactive krypton in LXe dark matter detectors.