Univ., Diss., 2004--Marburg

The adsorption isotherms can be used to study the properties of a sorbent and to determine the binding energy between a sorbent and a gas that is adsorbed on it. This study that was carried out on a metal organic framework called "Zeolitic imidazolate framework-8" (ZIF-8) as the sorbent. ZIF -8 is known to have a flexible structure and it has shown structural transformation during gas adsorption, at different temperatures. During this study, ZIF-8 was explored using Xenon adsorption. The range of temperatures for the Xenon adsorption isotherms was between 138 K and 157.56 K. During the adsorption of Xenon on ZIF -8 the lowest two isotherms (138 K and 140.39 K) showed two steps. The lower pressure step represents adsorption of Xenon on the "as - produced" ZIF-8. The extra step reflects the structural transition ("gate opening") that occurs due to the re-orientation of the organic linkers in ZIF-8. These changes increase the diameter of the apertures in the structure, and allow more gas molecules to enter in to the ZIF -8 structure. The Xenon adsorption isotherms were also used to determine the effective surface area of ZIF -8 by employing the "point B" method. The binding energy between Xenon and ZIF -8 was found using the isosteric heat for Xenon on ZIF-8 at low coverage. The kinetics of the Xenon adsorption was also studied during this experiment.

Galactical and cosmological evidence show that a quarter of the energy budget of our universe is made of collisionless, non-relativistic, and non-baryonic dark matter. Its potential coupling to standard model particles, however, has not yet been understood. One of the leading candidates - Weakly Interacting Massive Particles (WIMP) - allows the production of a dark matter relic density as observed today and couples to standard model particles at or below the weak scale. LUX-ZEPLIN (LZ) is a future tonne-scale two-phase xenon TPC aiming to detect WIMP recoils with xenon nuclei. The experiment will begin WIMP search data-taking in 2020 at the Sanford Underground Research Facility (SURF) in Lead, South Dakota and has a projected sensitivity of 3 × 10^-48 cm² or better in probing a 40 GeV/c² WIMP. The main observables of particle interactions in LZ are the primary scintillation (S1) and secondary scintillation (S2). However, optimising and achieving a stable S2 signal in such a tonne-scale TPC is non-trivial. Effects from the structural design of the S2 production region (top-corner structure), TPC tilt, and the xenon circulation system requires precise monitoring of the liquid surface. Such monitoring is achieved by the capacitive liquid level sensors developed within this thesis. The sensors are strategically placed to ensure that nonuniformity of the S2 signal due to the effects can be understood and corrected. In this thesis, the development of a monitoring system designed to optimise the quality of the S2 signal, based on the capacitive level sensors is discussed. A design of the electronics scheme based on a differential measurement allows femtofarad precision measurement of sensor's capacitance at picofarad level, even in the presence of cable capacitance at nanofarad level. A systematic study of the response of such a sensor to LXe and the application of the precision level sensors to two-phase TPC was carried out. Findings of intrinsic influences from LXe artefacts and LXe dielectric constant variation with its saturated temperature are identified; the result on the application of the sensors contributes to the designs of LZ circulation and the top-corner region. The final LZ level sensors show an artefact-free liquid level measurement and a 12 μm precision in measuring liquid nitrogen level (projection for LXe: ∼ 9 μm) over a 20 mm measurement range.

Orientador: Cesar José Bonjuani Pagan / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-26T12:37:33Z (GMT). No. of bitstreams: 1 Abrahao_RaphaelAkel_M.pdf: 16533697 bytes, checksum: be19936083fa8ed31271e3bbc975a3c1 (MD5) Previous issue date: 2014 / Resumo: Neste trabalho analisamos o espectro do xenônio cinco vezes ionizado obtido a partir de um tubo de descarga capilar, resultando na classificação de 146 novas linhas e 32 novos níveis. Calculamos a força de oscilador ponderada (gf), probabilidades de transição ponderadas (gA) e tempos de vida para todas as transições de dipolo experimentalmente conhecidas e níveis de energia do Xe VI. Os valores foram determinados pelo método Hartree-Fock, incluindo correções relativísticas e efeitos de polarização de caroço, com parâmetros de energia otimizados por um procedimento de mínimos quadrados a fim de obtermos níveis de energia ajustados aos valores experimentais correspondentes / Abstract: In the present work we analyze the spectrum of five time ionized xenon obtained in a discharge tube, resulting in the classification of 146 new lines and 32 energy levels. We calculated the weighted oscillator strengths (gf), weighted transition probabilities (gA) and lifetimes for all experimentally known dipole transitions and energy levels of Xe VI. These values were obtained using the Hartree-Fock method, including relativistic corrections and core polarization effects, and energy parameters optimized by a least-squares procedure in order to obtain energy levels adjusted to the corresponding experimental values / Mestrado / Eletrônica, Microeletrônica e Optoeletrônica / Mestre em Engenharia Elétrica

The present Book of Abstracts includes most of the contributions to the International Symposium XeMAT 2015, Xenon/hyperpolarized noble gases in magnetic resonance. This symposium took place from September 13-17, 2015 in Dresden in the new chemistry building of TU Dresden and covered all aspects of the use of xenon and hyperpolarized gases in magnetic resonance. This included for example materials science, biosensing, imaging, and molecular bioimaging as well as all aspects of gas hyperpolarization. The conference program included 15 invited lectures, 14 contributed talks as well as more than 20 posters.

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<p> A new dating method has been developed which uses fission product xenon in a manner similar to radiogenic argon in the 40Ar - 39Ar method. Measurable quantities of spontaneous fission xenon accumulate with time in rocks and minerals containing approximately 1 ppm or more of uranium as a result of the spontaneous fission of 238u. In the past, attempts have been made to date this type of sample by measuring the absolute amount of fission product xenon and the uranium content. In the new method a sample is irradiated in a thermal neutron flux to implant xenon from the neutron induced fission of 235u in amounts proportional to the uranium content. After a short cooling period (before radioactive 133xe has decayed) the sample is placed in a high vacuum system and the xenon is released by heating in a series of temperature steps. For each step the isotopic composition of the xenon is measured using a high sensitivity mass spectrameter and the ratio of spontaneous fission xenon to neutron fission xenon is calculated. Fission xenon ages for all steps are then calculated from the spontaneous to neutron fission xenon ratios and the measured integrated neutron flux. </p> <p> The method has several advantages over the conventional U - Xe technique. {a) The measurement of isotope ratios is inherently more precise than the measurement of absolute quantities. (b) Whereas the conventional U - Xe technique measures the sample date only once, the method described in this thesis measures the sample date several times. (c) If a geological disturbance has caused loss of fission xenon a valid date can still be obtained using the low mobility xenon released at high temperatures. (d) In some samples disturbed dates as well as initial formation dates can be measured. </p> <p> The method was developed and evaluated by a series of experiments which dated four zircon samples, one sphene sample, and a carbonatite sample. The zircon and sphene samples had been dated in other laboratories by the conventional u - Th - Pb and Rb - Sr methods. Fission xenon dating of these samples provided valuable new geochronological information. The experiments also showed that in addition to the advantages mentioned, the new method appears to be better able to see past metamorphic events than other methods. </p> / Thesis / Candidate in Philosophy

<p> The relative cumulative yields of krypton and xenon isotopes from the thermal neutron fission of 237Np and Np238 and from the fast neutron fission of Np237 have been measured by means of a mass spectrometer. These are the first fission yield results for 238Np, and the first for 237Np at thermal neutron energies. The results are compared with those from other fissioning nuclides.</p> <p> Independent yields of the shielded nuclides 80Br, 82Br, 128I, and 130I from the thermal neutron fission of 235U, 233U, 239Pu, and 238Np have been determined by mass spectrometric analyses of the krypton and xenon β-decay products. The results are discussed in terms of conventional charge distribution theories, and also in terms of neutron emission effects.</p> / Thesis / Doctor of Philosophy (PhD)

This work presents results on the study of the scintillation of high-pressure Xenon gas irradiated by various sources. Noble gases such as Xenon give off characteristic scintillation light when irradiated. The goal of the study was to develop a characteristic based on the scintillation time response of Xenon gas that would reliably discriminate between events from different types of primary radiation (neutron or gamma). A reliable discrimination characteristic would enable the development of room temperature, gas phase detectors for use in the search for Galactic Dark Matter. The surprising result of the present work was that a reliable discrimination characteristic existed for distinguishing x-ray, gamma ray, and alpha particle events. Results for neutrons were negative. This was due to several factors: Ionization tracks in xenon generally form two roughly cylindrical regions. A region near the center of the track, called the core, has very dense ionization. An outer region, called the penumbra, has sparse ionization. In Xenon, recombination of ions and the subsequent scintillation from the penumbra region happens slowly and can be easily distinguished from scintillation that happens in the core region. Nuclear recoils resulting from neutron collisions that give recoil energies in the same range as that predicted for WIMP-nuclear collisions are of such low energy that they do not produce a significant penumbra region in Xenon gas. As such, the scintillation time response for these events is similar to that of high-energy gamma rays. Other results of the present work include: The amount of energy deposited in the gas needed to produce a scintillation photon was measured for gamma rays and was found to be in agreement with results from other experiments. Low-energy gamma rays appeared to produce more scintillation photons for an equal amount of energy deposited than high-energy gamma rays. The decay of the singlet and triplet molecular states of xenon was observed and the lifetimes of these states were measured. The singlet state lifetime was found to be independent of pressure while the triplet state lifetime was dependent on pressure. The lifetimes were measured and compared to previous results. A better understanding of the ionization, recombination, and scintillation processes of gaseous Xenon was achieved. Argon gas has been proposed as an alternative to Xenon gas for use in a high-pressure gas scintillation detector due to its lower mass and its property of forming a core ionization region that is much less dense than the core region of xenon. This substitution may allow for a reliable discrimination characteristic to be developed. / Physics