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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
91

AN EXPERIMENTAL STUDY OF STRUCTURAL DEFORMATION AND “GATE OPENING” OF ZEOLITIC IMIDAZOLATE FRAMEWORK-8 UPON GAS SORPTION: THERMODYNAMIC AND KINETIC EVIDENCE

Gallaba, Gallaba Mudiyanselage Dinuka Harshana 01 September 2020 (has links) (PDF)
Volumetric adsorption experiments were conducted over three sorbates in Zeolitic Imidazolate Framework – 8 (ZIF-8). The sorption isotherms were measured at low temperatures. The study included carbon monoxide sorption in ZIF-8, xenon in ZIF-8, and methane sorption in ZIF-8. As a metal-organic framework that has been investigated thoroughly for its remarkable characteristics, ZIF-8 interactions with the above three sorbates has revealed some new features. Each of these systems offered a unique opportunity to study the physical properties of the sorbate and ZIF-8 and the thermodynamic responses of the system for its unique characteristics. The fundamental understating of sorbents-sorbate not only reveals some of the remarkable properties but also opens up new frontiers for researches in practical applications such as gas storage separation and other sorption-based fields of interest. The investigation into CO-ZIF-8 system has confirmed some of the predictions made on a similar system and analysis on the ZIF-8 structure. The measured adsorption isotherms have confirmed the existence of three pre-saturation subs steps, which were explained in terms of effects from the structural transition and polarity of the sorbate. The behavior of isosteric heat of adsorption and the equilibration time revealed a strong connection between steps in the isotherm and the structural changes of ZIF-8 due to organic linker rotation and volume expansion, also known as “Gate-Opening” in some cases. In both Xe-ZIF-8 and CH4 -ZIF-8 systems, the sorption isotherms revealed two substeps before the saturation. This is the first time such a feature was resolved experimentally in these systems although many previous studies have predicted the feature. The experimental observations on characteristics of the Xe -ZIF-8 system are also verified by computer simulations. Unlike the CO-ZIF-8 system, Xe-ZIF-8 interactions do not trigger the organic linker rotation of ZIF-8 structure, but it influenced the expansion of the ZIF-8 structure. In CH4 – ZIF-8 system the isotherms’ substeps were not as steep as Xe system but the loading dependence of isosteric heat of adsorption and equilibration time revealed features that are similar to CO. The lack of sorption-combined structural analysis of CH4-ZIF-8 prevent us from concluding the actual nature of the changes occurring which are related to the substeps and other thermodynamic and kinetic features. In all three systems, our measurements of the adsorption kinetics, we observed a non-monotonic behavior of the equilibration time as a function of sorbent loading. For CO the loading dependence of equilibration time exhibit peaks at loadings that correspond to the intermediate and higher loading sub-steps, and CH4 showed similar behavior at the loading corresponds to its intermediate substep region. The sharp peaks can be interpreted as packing rearrangement of adsorbed phase molecule in both cases and for CO there may be some contributions from the linker flipping and structural transition. The structural effect of kinetics is yet to be confirmed by a structural analysis for the CH4 system.
92

The Effect of Xenon Pulsed-Light Technology on Biofilm Adhered to Stainless Steel Surfaces

Jacquez, Stephanie 01 March 2016 (has links) (PDF)
In food processing, inadequate surface sanitation procedures lead to the formation of biofilms in which bacteria attach and aggregate in a hydrated polymeric matrix of their own synthesis. Formation of these sessile communities and their inherent resistance to existing sanitation procedures and agents are at the root of the risk of bacterial infections for consumers. Due to this existing problem, an effective method for reducing biofilm formation in dairy processing equipment is necessary for dairy products processing. Ultraviolet Pulsed light Technology has shown a positive effect in eliminating microorganism populations on food products. The objective of this work is to evaluate the effect of Pulsed light Technology on a biofilm of different dairy component matrices (e.g. Water (control); whey protein isolates (WPI), lactose, and sweet whey). This evaluation will be performed using the three strains of spore forming Bacillus species most common in commercial milk powder (B. subtilis, B. coagulans, and B. licheniformis). The matrix in which the evaluation was made consisted on allowing the attachment of endospores to on to a square 2.5cm x 2.5cm ASI 304 stainless steel coupon. Four Xenon light treatment levels (no treatment, 5 bursts, 10 seconds, 20 seconds and 30 seconds) were applied to the coupon surfaces using the Xenon model RC847 machine. The attachment of Bacillus to stainless steel in water as matrix was 1000 to 3000/ sq cm as measured in our laboratory. Results showed that there was a significant difference in spore reduction depending on the matrix of the biofilm and with the intensity of the Xenon treatment. Reduction in spores ranged from 1 to 4.7 logarithmic reduction cycles depending on the material of the biofilm, the strain of spores and the intensity of treatment. We conclude that there is significant potential to use this technology in maintaining low spore counts in commercial dairy powders.
93

Xenon Transient Studies for a CANDU Reactor / PART B: MCMASTER (OFF-CAMPUS) PROJECT

Kotlarz, Joseph 08 1900 (has links)
Part B of two parts. Part A found at: http://hdl.handle.net/11375/18745 / <p> This report studies the xenon transient behaviour in a CANDU reactor as a function of time after shutdown, start-up and power setbacks. In addition, load cycling transients were obtained for typical daily load requirements. </p> / Thesis / Master of Engineering (MEngr)
94

Rare Gas Fission Yields of Am241 and Am242

Pleva, James Francis 05 1900 (has links)
The yields of xenon and krypton from the neutron- induced fission of Am241 and Am242 have been measured with a mass spectrometer. This was accomplished by irradiating samples of Am241 for different lengths of time so that the effect of the growth of highly fissionable Am242 could be determined. These studies reveal that both the degree of fine structure in the mass yield curve and the fission-product charge distribution are dependent on the energy of the incident neutrons. This has not been previously observed for any fissioning nuclide. These studies also reveal effects of the 50-neutron shell and of the neutron-proton ratio of the fissioning nuclide on the mass yield curve. / Thesis / Doctor of Philosophy (PhD)
95

Synthesis and Structural Characterization of New Xenon(II) Compounds and the use of an Oxidant for the Preparation of Halogenated Carbocations

Moran, Matthew D. January 2007 (has links)
<p>The chemistry of Xe(II) has been significantly extended to include the first examples of a neutral Xe(II) oxide fluoride species, O(XeF)<sub>2</sub>, as well as the first nitrate derivative of Xe(II), FXeONO<sub>2</sub>. Until recently, neutral oxide fluorides were known for all formal oxidation states of xenon except Xe(II). The synthesis of the missing oxide fluoride of Xe(II), O(XeF)<sub>2</sub>, has been accomplished by reaction of the [FXeOXeFXeF][AsF<sub>6</sub>] salt with NOF and characterized by NMR spectroscopy in CH<sub>3</sub>CN solution at -78 °C and by Raman spectroscopy. Reaction of NO<sub>2</sub>F with [FXeOXeFXeF][AsF<sub>6</sub>] has provided the first structurally characterized noble-gas nitrate, FXeONO<sub>2</sub>, which slowly decomposes (-78 °C) to XeF<sub>2</sub>·N<sub>2</sub>O<sub>4</sub>. X-ray crystal structures have been determined for FXeONO<sub>2</sub>, XeF2·N<sub>2</sub>O<sub>4</sub>, and XeF2·HNO<sub>3</sub>. The preparation of the XeONO<sub>2</sub><sup>+</sup> cation was attempted by the reaction of FXeONO<sub>2</sub> with AsF<sub>5</sub> at -78 °C, but was not directly observed. It is presumed that the cation initially forms, but rapidly decomposes to give Xe, O<sub>2</sub>, and [NO<sub>2</sub>][AsF<sub>6</sub>].</p> <p>The salt, [XeOTeF<sub>5</sub>][Sb(OTeF<sub>5</sub>)<sub>6</sub>], is a strong, low-temperature oxidant capable of oxidizing halomethanes in SO<sub>2</sub>ClF solvent at -78 °C. The CCl<sub>3</sub><sup>+</sup> and CBr3<sup>+</sup> cations have been synthesized by oxidation of CCl<sub>4</sub> and CBr<sub>4</sub>, respectively. The CBr<sub>3</sub><sub></sub><sup>+</sup> cation reacts with BrOTeF<sub>5</sub>, produced in the initial redox reaction, to give CBr(OTeF<sub>5</sub>)<sub>2</sub><sup>+</sup>, C(OTeF<sub>5</sub>)<sub>3</sub><sup>+</sup> , and Br<sub>2</sub>. The XeOTeF<sub>5</sub><sup>+</sup> cation also reacts with BrOTeF<sub>5</sub> to give the Br(OTeF<sub>5</sub>)<sub>2</sub><sup>+</sup> cation. The X-ray crystal structures of [CCl<sub>3</sub>][Sb(OTeF<sub>5</sub>)<sub>6</sub>], [CBr<sub>3</sub>][Sb(OTeF<sub>5</sub>)<sub>6</sub>]•SO<sub>2</sub>ClF, and [C(OTeF5)3][Sb(OTeF5)6]·3SO<sub>2</sub>ClF have been determined and show that the carbocations are trigonal planar about the central atom.</p> <p>Reactions of chlorofluoro-and bromofluoromethanes with [XeOTeF<sub>5</sub>][Sb(OTeF<sub>5</sub>)<sub>6</sub>] have also been investigated in SO<sub>2</sub>ClF solvent by <sup>13</sup>C and <sup>19</sup>F NMR spectroscopy at -80 °C. The CFCl<sub>2</sub><sup>+</sup> and CFCl(OTeF<sub>5</sub>)<sup>+</sup> cations are among the carbocations that have been obtained by reactions of CFCl<sub>3</sub> and CF<sub>2</sub>Cl<sub>2</sub> with XeOTeF<sub>5</sub><sup>+</sup>. The CF<sub>2</sub>Br<sup>+</sup> cation is an intermediate in the reaction of XeOTeF<sub>5</sub><sup>+</sup> with CF<sub>2</sub>Br<sub>2</sub>, undergoing rapid halogen exchange with CF<sub>2</sub>Br<sub>2</sub> to form CFBr<sub>2</sub><sup>+</sup> and CF<sub>3</sub>Br. The CFBr<sub>2</sub><sup>+</sup> cation undergoes further halogen exchange over several hours to form the CBr<sub>3</sub><sup>+</sup> cation and CF<sub>3</sub>Br. Although the highly electrophilic CF<sub>3</sub><sup>+</sup> cation has not been isolated by the reaction of CF<sub>3</sub>Br with XeOTeF<sub>5</sub><sup>+</sup>,<sup> 13</sup>C and <sup>19</sup>F NMR spectroscopy indicates the CF<sub>3</sub><sup>+</sup> cation reacts with BrOTeF<sub>5</sub> to form F<sub>3</sub>CBrOTeF<sub>5</sub><sup>+</sup> and/or abstracts an OTeF<sub>5</sub> group from the Sb(OTeF<sub>5</sub>)<sub>6</sub><sup>- </sup>anion to yield CF<sub>3</sub>OTeF<sub>5</sub> and, ultimately, [SbBr<sub>4</sub>][Sb(OTeF<sub>5</sub>)<sub>6</sub>].</p> <p>The synthesis of C(OTeF<sub>5</sub>)<sub>4</sub> has been accomplished by reaction of CBr4 with Br0TeF5 in SO<sub>2</sub>ClF solution, and has been fully characterized by NMR spectroscopy, Raman spectroscopy, and single-crystal X-ray diffraction, and its geometric parameters have been compared with those of the isoelectronic B(OTeF<sub>5</sub>)<sub>4</sub><sup>-</sup>anion in order to assess the symmetry of the E(OTe)<sub>4</sub><sup>-/0</sup> (E = B, C) subgroup.</p> / Doctor of Philosophy (PhD)
96

Oxide and Oxide Fluoride Chemistry of Xenon(VIII), Xenon(VI), and Iridium

Goettel, James T. January 2017 (has links)
This Thesis extends our fundamental knowledge of high-oxidation-state chemistry and in particular compounds of Xe(VIII), Xe(VI), and Ir(V). The crystal structure of XeVIIIO4 was obtained and provides important information on this fundamentally interesting endothermic and shock-sensitive compound. Macroscopic amounts of XeO3F2 have been prepared for the first time. Although the low-temperature Raman spectrum of solid XeO3F2 exhibits some frequency shifts and band splittings of the bending modes, the spectrum is similar to the Raman spectrum of the previously reported matrix-isolated compound. The crystal structures of decomposition and byproducts resulting from the syntheses of XeO3F2 have been obtained for [XeF5][HF2]∙XeOF4 and XeF2∙XeO2F2. The solid-state structure of xenon trioxide, XeO3, was reinvestigated by low-temperature single-crystal X-ray diffraction and shown to exhibit polymorphism that is dependent on crystallization conditions. The previously reported α-phase (orthorhombic, P212121) only forms upon evaporation of aqueous HF solutions of XeO3. In contrast, two new phases, β-XeO3 (rhombohedral, R3) and gamma-XeO3 (rhombohedral, R3c) have been obtained by slow evaporation of aqueous solutions of XeO3. The extended structures of all three phases result from Xe=O----Xe bridge interactions among XeO3 molecules that arise from the amphoteric donor-acceptor nature of XeO3. The Xe atom of the trigonal pyramidal XeO3-unit has three Xe---O secondary bonding interactions. The orthorhombic α-phase displays the greatest degree of variation among the contact distances and has a significantly higher density than the rhombohedral phases. The ambient-temperature Raman spectra of solid α- and gamma-XeO3 have also been obtained and assigned for the first time. Xenon trioxide interacts with CH3CN and CH3CH2CN to form O3XeNCCH3, O3Xe(NCCH3)2, O3XeNCCH2CH3, and O3Xe(NCCH2CH3)2. Their low-temperature single-crystal X-ray structures show that the xenon atoms are consistently coordinated to three electron-donor atoms which result in pseudo-octahedral environments around their xenon atoms. The adduct series provides the first examples of a neutral xenon oxide bound to nitrogen bases. Energy-minimized gas-phase geometries and vibrational frequencies were obtained for the model compounds O3Xe(NCCH3)n (n = 1−3) and O3Xe(NCCH3)n∙[O3Xe(NCCH3)2]2 (n = 1, 2). The natural bond orbital (NBO), quantum theory of atoms in molecules (QTAIM), electron localization function (ELF), and molecular electrostatic potential surface (MEPS) analyses were carried out to further probe the nature of the bonding in these adducts. Xenon trioxide forms adducts with the polytopic nitrogen base ligands: hexamine, DABCO, 2,2’-bipyridine, 1,10-phenanthroline, and 4,4’-bipyridine. The adducts were conveniently synthesized in aqueous or CH3CN solutions and are stable at room temperature. The crystal structures of hexamine∙2XeO3, hexamine∙XeO3∙H2O, 2,2’-bipyridine∙XeO3, 1,10-phenanthroline∙XeO3, and 4,4’-bipyridine∙XeO3 have been determined by low-temperature single-crystal X-ray diffraction. The structures consist of XeO3 molecules bridged by the ligands to form extended supramolecular networks with Xe---N bonds which range from 2.634(3) to 2.829(2) Å. Raman spectroscopy was used to characterize and probe the room-temperature stabilities of these adducts. The reaction of 1,4-diazabicyclo[2.2.2]octane (DABCO) with XeO3 in aqueous solutions yields thin, plate-shaped crystals which are severely twinned whereas the reaction of DABCO with XeO3 in the presence of HF forms [DABCOH]2[F2(XeO3)2]∙H2O and [DABCOH2][F][H2F3] which were also characterized by low-temperature X-ray crystallography and Raman spectroscopy. A reversible temperature-dependent phase transition occurred for [DABCOH]2[F2(XeO3)2]∙H2O. The structures of 2,2’-bipy∙XeO3 and 1,10-phen∙XeO3 provide the first examples of noble-gas chelates. The structure of hexamine∙XeO3∙H2O provides the first instance in which a noble-gas centre is coordinated by water. These compounds also represent the first examples of sp2- and sp3-hybridized N---Xe(VI) bonds and are rare examples of noble-gas compounds that are air-stable at ambient temperatures. Adducts between XeO3 and three molar equivalents of the nitrogen bases, pyridine and 4-dimethylaminopyridine (4-DMAP), have been synthesized and characterized. The crystal structures of (C5H5N)3XeO3, {(CH3)2)2NC5H4N}3XeO3∙H2O have been determined by low-temperature single-crystal X-ray diffraction. The reaction of hydrolyzed XeF6 in acetonitrile with pyridine or 4-DMAP afforded [C5H5NH]4[HF2]2[F2(XeO3)2] and [(CH3)2NC5H4NH][HF2]∙XeO3 which were characterized by low-temperature X-ray crystallography and Raman spectroscopy. The structures contain pyridinium cations that are hydrogen bonded to the fluoride coordinated to XeO3 and can be viewed as pyridinium fluoroxenates. The structure of (CH3)2NC5H5N∙XeO3∙H2O contains a water molecule that is hydrogen bonded to two oxygen atoms of two adjacent XeO3 molecules. The pyridine adduct, (C5H5N)3XeO3, was found to be relatively insensitive to shock, whereas the 4-DMAP adduct was extremely shock sensitive. The number of isolable compounds which contain different noble-gas−element bonds is limited for xenon and even more so for krypton. Examples of Xe−Cl bonds are rare and prior to this work, no definitive evidence for a Xe−Br bonded compound existed. The syntheses, isolation, and characterization of the first compounds to contain Xe−Br bonds ([N(C2H5)4]3[Br3(XeO3)3] and [N(CH3)4]4[Br4(XeO3)4]) and their chlorine analogues are described. The bromo- and chloroxenate salts are stable in the atmosphere at room temperature and were characterized in the solid state by Raman spectroscopy, low-temperature single-crystal X-ray diffraction, and in the gas phase by quantum-chemical calculations. They are the only known examples of cage anions that contain a noble-gas element. The Xe−Br and Xe−Cl bonds are weakly covalent and can be viewed as σ-hole interactions, similar to halogen bonds. Xenon trioxide reacts with alkali metal fluorides and chlorides to form a variety of room-temperature stable fluoro- and chloroxenate salts. The reaction of XeO3 with various ratios of KF in water afforded three new compounds. The crystal structures of α-K[F(XeO3)2], β-K[F(XeO3)2], α-K[FXeO3], K2[F2(XeO3)] have been determined. The reaction of XeO3 with aqueous CsF resulted in Cs3[F3(XeO3)2]. The XeVI−F bond lengths range from 2.3520(18) to 2.5927(17) Å. No stable product was isolated when [N(CH3)4]F was the fluoride source, but in the presence of HF, crystals of [N(CH3)4]3[HF2]2[H2F3]∙2XeO3 were obtained. The reaction of KCl with XeO3 in equimolar amounts resulted in the formation of K[ClXeO3] whereas the analogous reaction with CsCl yielded Cs3[Cl3(XeO3)4]. Attempts to synthesize Xe–P and Xe–S bonded compounds were unsuccessful and instead resulted in adducts between XeO3 and O-bases such as the phosphine oxide adduct, {(C6H5)3PO}2XeO3 and dimethylsulfoxide (DMSO) adduct {(CH3)2SO}3(XeO3)2. Although DMSO was found to be resistant to oxidation by XeO3, no significant Xe---S bonding interactions were observed. Acetone was found to be highly resistant to oxidation by XeO3 and forms {(CH3)2CO}3XeO3 at low temperatures. The reaction of pyridine-N-oxide yielded large crystals of (C5H5NO)3(XeO3)2 in which the structure contains short chains in contrast with ((CH3)2SO)3(XeO3)2 whose structure consists of discrete dimers. The reaction of XeO3 with the oxidatively resistant main-group oxide anion source, [N(CH3)4][OTeF5] in CH3CN solvent afforded [N(CH3)4][F5TeOXeO3(CH3CN)2]. Xenon trioxide reacts with potassium hydroxide to form the previously known K4[XeO6]∙2XeO3 salt which was characterized by Raman spectroscopy and low-temperature X-ray crystallography. The reaction of MgO with XeO3 yielded single crystals of [Mg(OH2)6]4[XeO6(XeO3)12O2]∙12H2O, which also contains perxenate-XeO3 interactions. Alkali metal carbonates also incorporate XeO3 into their crystal lattices. Raman spectra of M2[CO3(XeO3)n]∙xH2O (M = Na, K, Rb) were recorded and contain intense bands assigned to the XeO3 stretching modes and very weak bands assigned to the [CO3]2− modes. The reaction of dilute aqueous solutions of XeO3 with RbOH and atmospheric CO2 afforded single crystals of Rb2[CO3(XeO3)2]∙2H2O which were characterized by low-temperature X-ray crystallography. Attempts to incorporate XeO3 into other polyatomic anion salts such as KMnO4, NaClO3, and NaNO3 were unsuccessful. The reaction of IrO2 with XeF6 in aHF provided [Xe2F11][IrF6], whereas the reaction of IrO2 with KrF2 with ClF3 in anhydrous HF solvent provided [ClO2][Ir2F11] and [ClO2][(μ-OIrF4)3]. The structure of [(μ-OIrF4)3]− consists of a six membered Ir3O3 ring with four terminal fluorine atoms on each Ir atom. It was also found that ClF3 forms an adduct with [Xe2F11][HF2] in which the structural parameters of ClF3 are very similar to that of solid ClF3. The [ClO2][Ir2F11] salt provides the first structural information on the [Ir2F11]− anion and the [(μ-OIrF4)3]− anion represents the first isolated iridium oxide fluoride species. / Thesis / Doctor of Philosophy (PhD) / Xenon is a noble-gas element which is located in the far right-hand column of the periodic table and was previously thought to be chemically unreactive and incapable of forming compounds. In 1962, it was shown that xenon reacts with the most reactive compounds, such as elemental fluorine, but the resulting xenon compounds are themselves highly reactive. This Thesis extends the chemistry of some of the most unstable and chemically reactive xenon compounds that are currently known. One such compound, xenon trioxide, tends to easily detonate unless carefully handled. Methods of stabilizing xenon trioxide were developed and its behaviour with compounds which resulted in formation of new xenon compounds was studied. The molecular structures of these compounds were investigated in the solid with particular emphases on their chemical bonding. Iridium is one of the most chemically resistant metals known. Highly reactive xenon and krypton compounds were used synthesize new iridium compounds.
97

A nonlinear diffusion theory model for xenon-induced flux oscillations

Teachman, John David January 1981 (has links)
A nonlinear model is developed for the xenon induced flux oscillation problem that occurs in nuclear power plants. The model is based on Galerkins' method of weighted residuals applied to multigroup diffusion theory. A similar linear model is developed by the same methods in order to consider the effects of the nonlinearities of the system. The effects of multi- and single-energy group considerations are also examined. Finally, the effects of various number of basis functions used to approximate the flux, iodine, and xenon concentrations is determined. A partial listing of the computer program XORA, developed from the nonlinear and linear models, is given along with representative input and output from this program. / Ph. D.
98

Zeolite membranes for the separation of krypton and xenon from spent nuclear fuel reprocessing off-gas

Crawford, Phillip Grant 13 January 2014 (has links)
The goal of this research was to identify and fabricate zeolitic membranes that can separate radioisotope krypton-85 (half-life 10.72 years) and xenon gas released during spent nuclear fuel reprocessing. In spent nuclear fuel reprocessing, fissionable plutonium and uranium are recovered from spent nuclear fuel and recycled. During the process, krypton-85 and xenon are released from the spent nuclear fuel as process off-gas. The off-gas also contains NO, NO2, 129I, 85Kr, 14CO2, tritium (as 3H2O), and air and is usually vented to the atmosphere as waste without removing many of the radioactive components, such as 85Kr. Currently, the US does not reprocess spent nuclear fuel. However, as a member of the International Framework for Nuclear Energy Cooperation (IFNEC, formerly the Global Nuclear Energy Partnership), the United States has partnered with the international nuclear community to develop a “closed” nuclear fuel cycle that efficiently recycles all used nuclear fuel and safely disposes all radioactive waste byproducts. This research supports this initiative through the development of zeolitic membranes that can separate 85Kr from nuclear reprocessing off-gas for capture and long-term storage as nuclear waste. The implementation of an 85Kr/Xe separation step in the nuclear fuel cycle yields two main advantages. The primary advantage is reducing the volume of 85Kr contaminated gas that must be stored as radioactive waste. A secondary advantage is possible revenue generated from the sale of purified Xe. This research proposed to use a zeolitic membrane-based separation because of their molecular sieving properties, resistance to radiation degradation, and lower energy requirements compared to distillation-based separations. Currently, the only commercial process used to separate Kr and Xe is cryogenic distillation. However, cryogenic distillation is very energy intensive because the boiling points of Kr and Xe are -153 °C and -108 °C, respectively. The 85Kr/Xe separation step was envisioned to run as a continuous cross-flow filtration process (at room temperature using a transmembrane pressure of about 1 bar) with a zeolite membrane separating krypton-85 into the filtrate stream and concentrating xenon into the retentate stream. To measure process feasibility, zeolite membranes were synthesized on porous α-alumina support discs and permeation tested in dead-end filtration mode to measure single-gas permeance and selectivity of CO2, CH4, N2, H2, He, Ar, Xe, Kr, and SF6. Since the kinetic diameter of krypton is 3.6 Å and xenon is 3.96 Å, zeolites SAPO-34 (pore size 3.8 Å) and DDR (pore size 3.6 Å) were studied because their pore sizes are between or equal to the kinetic diameters of krypton and xenon; therefore, Kr and Xe could be separated by size-exclusion. Also, zeolite MFI (average pore size 5.5 Å) permeance and selectivity were evaluated to produce a baseline for comparison, and amorphous carbon membranes (pore size < 5 Å) were evaluated for Kr/Xe separation as well. After permeation testing, MFI, DDR, and amorphous carbon membranes did not separate Kr and Xe with high selectivity and high Kr permeance. However, SAPO-34 zeolite membranes were able to separate Kr and Xe with an average Kr/Xe ideal selectivity of 11.8 and an average Kr permeance of 19.4 GPU at ambient temperature and a 1 atm feed pressure. Also, an analysis of the SAPO-34 membrane defect permeance determined that the average Kr/Xe selectivity decreased by 53% at room temperature due to unselective defect permeance by Knudsen diffusion. However, sealing the membrane defects with polydimethylsiloxane increased Kr/Xe selectivity by 32.8% to 16.2 and retained a high Kr membrane permeance of 10.2 GPU at ambient temperature. Overall, this research has shown that high quality SAPO-34 membranes can be consistently fabricated to achieve a Kr/Xe ideal selectivity >10 and Kr permeance >10 GPU at ambient temperature and 1 atm feed pressure. Furthermore, a scale-up analysis based on the experimental results determined that a cross-flow SAPO-34 membrane with a Kr/Xe selectivity of 11.8 and an area of 4.2 m2 would recover 99.5% of the Kr from a 1 L/min feed stream containing 0.09% Kr and 0.91% Xe at ambient temperature and 1 atm feed pressure. Also, the membrane would produce a retentate stream containing 99.9% Xe. Based on the SAPO-34 membrane analysis results, further research is warranted to develop SAPO-34 membranes for separating 85Kr and Xe.
99

Mitigation of the radioxenon memory effect in beta-gamma detector systems by deposition of thin film diffusion barriers on plastic scintillator

Fay, Alexander Gary 16 February 2011 (has links)
The significance of the radioxenon memory effect in the context of the International Monitoring System of the Comprehensive Nuclear-Test-Ban Treaty is introduced as motivation for the project. Existing work regarding xenon memory effect reduction and thin film diffusion barriers is surveyed. Experimental techniques for radioxenon production and exposure, as well as for thin film deposition on plastic by plasma enhanced chemical vapor deposition (PECVD), are detailed. A deposition rate of 76.5 nm min⁻¹ of SiO₂ is measured for specific PECVD parameters. Relative activity calculations show agreement within 5% between identically exposed samples counted on parallel detectors. Memory effect reductions of up to 59±1.8% for 900 nm SiO₂ films produced by plasma enhanced chemical vapor deposition and of up to 77±3.7% for 50 nm Al₂O₃ films produced by atomic layer deposition are shown. Future work is suggested for production of more effective diffusion barriers and expansion to testing in operational monitoring stations. / text
100

Production of [beta-gamma] coincidence spectra of individual radioxenon isotopes for improved analysis of nuclear explosion monitoring data

Haas, Derek Anderson, 1981- 01 October 2012 (has links)
Radioactive xenon gas is a fission product released in the detonation of nuclear devices that can be detected in atmospheric samples far from the detonation site. In order to improve the capabilities of radioxenon detection systems, this work produces [beta-gamma] coincidence spectra of individual isotopes of radioxenon. Previous methods of radioxenon production consisted of the removal of mixed isotope samples of radioxenon gas released from fission of contained fissile materials such as ²³⁵U. In order to produce individual samples of the gas, isotopically enriched stable xenon gas is irradiated with neutrons. The detection of the individual isotopes is also modeled using Monte Carlo simulations to produce spectra. The experiment shows that samples of [superscript 131m]Xe, ¹³³Xe, and ¹³⁵Xe with a purity greater than 99% can be produced, and that a sample of [superscript 133m]Xe can be produced with a relatively low amount of ¹³³Xe background. These spectra are compared to models and used as essential library data for the Spectral Deconvolution Analysis Tool (SDAT) to analyze atmospheric samples of radioxenon for evidence of nuclear events. / text

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