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Scintillation light, ionization yield and scintillation decay times have been measured in xenon and in its mixture with a 0.05% concentration of methane as a function of the reduced electric field (E/N)--the ratio of the electric field strength to the number density of gas--at a pressure of 21 atm. The measurements of scintillation decay times in the xenon-methane mixture have been made for the first time as a function of the reduced electric field (E/N). An ionization chamber has been constructed to simultaneously measure electrons and photons from a [sup.239]Pu source, which is placed in the center of a cathode in the chamber. The main peculiarity of the chamber is a movable cathode to measure scintillation light and ionization yield at various distances from the anode and monitor the purity of the investigated gas. It has been observed that both scintillation light and ionization yield decrease when methane is added into the xenon gas. Scintillation decay times in the xenon-methane mixture are observed to be longer than in the pure xenon when the electric field strength increases. Index Terms--High pressure xenon detectors, ionization yield, scintillation light, time protection chamber, xenon-methane mixture.

The use of appropriate mixtures of noble gases in proportional counters can take advantage of the Penning effect, a process of energy transfer between the two species which produces extra electrons. The Penning effect can occur in Xe-Ne mixtures and recent Monte Carlo simulation measurements have shown that a small percentage of Xe (below ~l%Xe) brings to a minimum the fluctuations in the formation of the primary electron cloud and decreases the [omega]-value to a magnitude near that for pure Xe. In addition, the excitation and ionization thresholds and the fluctuations in charge multiplication become lower and the ionization efficiency becomes higher than in pure Xe, indicating that improved energy resolution can be achieved at low applied voltages for a Xe-Ne filled proportional counter. In this work, we present an experimental study of the performance of a cylindrical proportional counter filled with several Xe-Ne mixtures at atmospheric pressure, for 5.9 keV x-rays. Results are presented for the energy resolution and gas multiplication factor and a discussion of the experimental results is made. Index Terms--Penning mixtures, proportional counters, Xenonneon mixtures, x-ray detectors.

We review the scintillation mechanism of liquid rare gases and estimate the absolute scintillation yield of liquid xenon in order to understand the superiority of liquid xenon as a detector medium. The decays of scintillation light from liquid xenon, which are faster than those of scintillation light from crystal scintillators, are summarized. New photomultipliers with high quantum efficiency that can operate at liquid xenon temperature were recently developed by Hamamatsu Photonics Co. Using these photomultipliers, a new gamma-ray calorimeter system, whose sensitive volume is surrounded by many photomultipliers was proposed. This new calorimeter system was applied to a [[micro].sup.+] [right arrow] [e.sup.+] [gamma] decay search experiment and then to liquid xenon scintillation time-of-flight positron-emission-tomography (TOF-PET). A third application, a new apparatus for detecting solar neutrinos and for use in the dark matter search experiment developed at Kamioka, Japan, is also presented. Index Terms--Scintillation mechanism, scintillation yield, liquid xenon, scintillation calorimeter, [[micro].sup.+] [right arrow] [e.sup.+] [gamma] decay search experiment, liquid xenon scintillation TOF-PET, dark matter search experiment.

The optical properties of liquid xenon (LXe) in the vacuum ultra violet (VUV), determining the performance of a scintillation calorimeter, are discussed in detail. The available data, measured in a wider spectral region from visible to UV light, and in a large range of Xe densities, from gas to liquid, are examined. It is shown that this information can be used for deriving the LXe optical properties in the VUV. A comparison is made with the few direct measurements in LXe for VUV light resulting from the LXe excitation by ionizing particles. A useful relation is obtained which connects the Rayleigh scattering length to the refractive index in LXe. Index Terms--Liquid xenon, VUV light.

The luminous efficiency characteristics of a new alternating current plasma display panel (ac PDP) structure with the segmented electrodes in delta color arrayed subpixels with enclosed barrier ribs (SDE) are investigated. The SDE structure which has a 4:3 horizontal to vertical cell dimension ratio showed higher luminance and luminous efficiency increment characteristics as the Xe partial pressure increased compared to those of the conventional stripe type with 1:3 ratio for a given resolution. The luminance and luminous efficiency increases with the electrode width, which provides a means to change the color temperature for the full color panel without using other method such as the subpixel size change. The driving feasibility of SDE structure panel with various electrode widths is confirmed by demonstrating the existence of sufficient driving voltage margin. Index Terms--High Xe contents, plasma display panel (PDP), segmented electrodes in delta color arrayed subpixels with enclosed barrier ribs (SDE).

We investigated the effect of Xe content variation on the luminous efficiency of two different subpixel types, i.e., segmented electrode in delta color arrayed, enclosed subpixel (SDE) and conventional stripe barrier type, in an alternating current plasma display panel through three-dimensional (3-D) numerical simulations. The simulation result agreed well with the experimental result where the SDE structure showed to have higher luminous efficiency improvement with increasing Xe content than the conventional structure did. The conventional cell type was found to have higher vacuum ultraviolet (VUV) generation efficiency at low Xe content as compared with SDE structure, but as the Xe content increased, the SDE type showed a higher improvement in efficiency due to the lower plasma loss to the enclosing surfaces. Using the ray-optics code in conjunction with the 3-D plasma simulation, the transport efficiency of visible light from phosphor through the front plate in the SDE structure, which has a higher aperture ratio, was higher than that of the conventional structure with much increased improvement with the increase of Xe content Index Terms--High Xe content, luminous efficiency, plasma display panel (PDP), segmented electrode in delta color arrayed, enclosed subpixel (SDE).

High-pressure xenon (HPXe) gas is a desirable radiation detection medium for many reasons, including its large atomic number, high density, low mean energy to produce an electron-ion pair, and the ability to produce devices with large detection volumes. While past work in HPXe has produced relatively successful detectors with energy resolution at 662 keV as good as approximately 2% FWHM, an expected limitation of these chambers in field operation is resolution degradation due to the vibration of their Frisch grids. Progress on a detector without a Frisch grid is reported in this submission; it is expected that the proposed anode design will provide competitive energy resolution with minimal degradation from mechanical vibration. Simulations accounting for charge carrier statistics, changes in the charge induced on the anode as a function of interaction location, and electronic noise predict a best-case energy resolution of 2.3% FWHM at 662 keV. Experimental data is compared with these simulations. Index Terms--Coplanar anodes, gas detectors, Geant, ionization chambers, single polarity charge sensing, xenon.

NMR experiments of [sup.129]Xe adsorbed on an iridium single crystal surface are reported. Very high nuclear polarization ([P.sub.z] [approximately equal to] 0.7) makes the experiment possible. A coverage of less then one monolayer is investigated on the Ir(111) surface with an area of 0.8 [cm.sup.2]. The observed resonance line shifts are very large and highly anisotropic. We find [[sigma].sub.iso] = 1,032 [+ or -] 11 ppm and [[sigma].sub.an] = 291 [+ or -] 33 ppm, which are far above the typical range of physisorption. The highly ordered substrate leads to homogeneous conditions for the xenon atoms, as seen in the narrow linewidth of 20 ppm. Chemical shifts under physisorption conditions are not large enough to totally explain the results. Knight shift can clearly be identified as the cause of the findings. This shift shows the presence of conduction electrons of the metallic substrate at the xenon nucleus and thus the mixing of metallic and atomic states at the Fermi level. Such mixing is in accordance with recent Hartree-Fock and density functional calculations of similar van der Waals adsorption systems. Quantitative comparisons, however, fail completely. The size and ratio of [[sigma].sub.an] and [[sigma].sub.iso] are pure ground-state properties in a structurally simple system. They are accessible to theory and provide detailed local information that can serve as a benchmark for theory.

Longitudinal relaxation times T(sub 1) of laser-polarized xenon in water solutions containing alpha-cylodextrin and wheat nonspecific lipid transfer protein are measured. It reveals that even with an atom of high polarizability, such as xenon, the van der Waals energy is not sufficiently predominant to avoid large amplitude motions of an apolar guest around its average sites.

Characterization of SBA-15 samples prepared at several different temperatures by hyperpolarized 129Xe NMR spectroscopy is presented. Results reveal that the evolution of the chemical shift with the NMR measurement temperature allows evaluation of the heat of adsorption of xenon, which increases for SBA-15 synthesized at higher temperature, in parallel with the decrease of the size of the surface micropores.

LXeGRIT is a liquid xenon time projection chamber (LXeTPC) used as balloon-borne Compton telescope for imaging cosmic sources in the MeV energy band. The three-dimensional position sensitive charge readout is triggered by the xenon scintillation light. In the original chamber design, the light is detected by four UV sensitive, 2' PMT's (EMI 9813), coupled to the liquid xenon vessel by quartz windows. In order to improve the trigger efficiency and uniformity, a new light readout system has been studied. It consists of 12 UV sensitive, compact 2' PMT's (Hamamatsu R6041Q), mounted in Teflon frames which cover the four sides of the LXeTPC active volume. These all-metal PMT's were especially developed to work at liquid xenon temperature and up to 3.5 atm overpressure. Light simulations promise an increase in light collection efficiency by more than a factor of ten for the new readout. We present simulations of the light collection efficiency and initial results from the successful operation of the new PMT fully immersed in liquid xenon. Index Terms--Compton telescope, gamma-rays, liquid xenon, scintillation, time projection chamber (TPC), trigger.

The mechanism of adsorption and the initial stage of absorption of a Van der Waals particle into crystalline ice are investigated. It is shown that the potential of mean force (PMF) can be used to illustrate the degree of disruption of the crystalline structure of the ice.

The study of strong-field excitation of condensed xenon, both solid and liquid is presented. Focused 60 femtosecond pulses at 400 and 800 nm are used for this purpose and the intense fields generated with focused femtosecond pulses provide an efficient method for nonresonant access to excitonic states in condensed Xe.

This work describes a new method for the correction of signal drift of a MS-based sensor by standard gas addition (SGA). It consists of introducing a gaseous He--Xe mixture continuously and independently of the carrier gas into the mass spectrometer source. To mimic the disturbances generated by periodical tuning of the mass detector, three series of adjustments were made to the main acquisition parameters. The influence of the SGA signal correction on the discriminating power of the data was evaluated from the analysis of three batches of cheeses by dynamic headspace coupled to mass spectrometry. SGA afforded a good correction of the main types of drift classically observed in mass spectrometry.

The purpose of this study was to examine the [sup.133]xenon washout technique as a viable method for measuring adipose tissue blood flow (ATBF) in swine. Using a total of 32 female Yucatan miniature swine (Sus scrofa), the partition coefficient for [sup.133]xenon in swine subcutaneous adipose tissue was determined and ATBF was measured at rest and under various physiological conditions. These conditions included feeding, anesthesia, epinephrine infusion, and acute exercise. The effects of epinephrine and acute exercise were examined in both sedentary and exercise-trained swine. The partition coefficient value for [sup.133]xenon in swine subcutaneous adipose tissue was 9.23 [+ or -] 0.26 mL/ g (mean [+ or -]SD, n = 10). The average value for resting ATBF in swine was 3.98 [+ or -] 2.72 mL/(100 g tissue*min) (n = 19). Feeding increased ATBF by approximately fivefold over fasting values, and isoflurane anesthesia significantly decreased ATBF compared to rest (1.64 [+ or -] 1.12 vs 3.92 [+ or -] 4.22 mL/[100 g*min], n = 10). A 30-min epinephrine infusion (1 [micro]g/[kg BW*min]) significantly increased ATBF from a resting value of 3.13 [+ or -] 2.61 to 10.35 [+ or -] 5.31 mL/(100 g*min) (n = 12). Epinephrine infusion into exercise-trained swine increased ATBF to the same extent as when infused into sedentary swine. An acute, 20-min bout of exercise significantly increased ATBF in swine, and the sedentary swine showed a larger increase in ATBF than their exercise-trained littermates relative to rest: 7.83 vs 2.98 mL/(100 g*min). In conclusion, the [sup.133]xenon washout technique appears to be a viable method for measuring ATBF in swine; our findings are comparable to swine ATBF values reported using the microsphere method and are consistent with values reported in animal and human studies. Key Words: Adipose Tissue, Anesthesia, Epinephrine, Exercise, Pigs, Xenon

Research is presented concerning the measurement of the electrical characteristics and vacuum ultraviolet emission of two planar cylindrical electrodes subjected to dc voltage. Various He/Xe pressures and mixtures were used.

Research has been conducted on the protein cavities. The role of these cavities in the substrate facilitating movement has been investigated by determining the X-ray structures of the soluble methane monooxygenase hydroxylase from Methylococcus capsulatus.

Xenon properties of carbon nanotubes were studied using 129Xe nuclear magnetic resonance spectroscopy.

Series operation of direct current xenon chloride excimer sources is investigated.

A theoretical and experimental study involving a full investigation into neutral xenon hydrides in solid neon.

Computational studies and an FTIR spectroscopy were used to fully investigate the rare-gas-containing compound HXeNCO in solid Xenon.

A model of xenon resonance radiation transportation in a plasma display panel cell is presented.

(Super129)Xe NMR spectroscopy can discriminate between xenon complexes of cryptophane-A and deuterated congeners in solution.

Two-photon excitation of xenon atoms with concomitant amplified emission used to prepare Xe(5d[3/2] (sub)1) resonance state atoms in Xe has been examined. Results indicate that a slow quenching rate of the Xe(5d[3/2] (sub)1) atoms enhance emission intensity.

A hyperpolarized 129Xe NMR was used to examine the binding interactions of xenon to the surface of various proteins in the solution and lyophilized solid states. A comparison of the NMR results with N2, Xe and CH4 gas isotherms revealed that lipoxygenase possesses unique properties among the other proteins studied. Lipoxygenase is found to have a relatively high affinity for gas molecules and displays the most clearly adsorbed 129Xe NMR peak in the lyophilized state.

A study was conducted to analyze the construction of an apparatus for optical pumping of 129XE in a circulating gas system linked to a probe for static high-field nuclear magnetic resonance. The optimal working environment for the optical pumping under flow was also examined. The performance of the system was then evaluated by monitoring signal intensities of the gas at room temperature.

A study was conducted to analyze a novel probe-coupled 2.45 GHz microwave arrangement designed to drive a xenon excimer lamp. The maximum in-range optical power was pegged at 60 W. Model computations and experimental measurements of the angular distribution of emission revealed considerable intensity well away from the surface normal. Results indicated a good agreement between the predicted and theoretical electrical efficiencies.

One- and two-dimensional NMR spectra of 129Xe sorbed in NaY zeolite at a loading of about 1 Xe atom/4 alpha-cages were investigated as a function of temperature. The data were fitted to the simple statistical mechanical cylindrical pore model of Cheung producing a van der Waals adsorption energy of 3.3 kJ/mol. Two-dimensional data indicated that the intercrystalline diffusion is slow compared to intracrystalline diffusion. Findings showed that the Xe atoms spend most of their time in the alpha-cages and at the lower temperatures, near the cage walls.

Research was conducted to examine the manifestations of bridgehead-bridgehead interactions in the bicyclo(1.1.1)pentane ring system. The reactions were performed in 5 mm NMR tubes and their progress was monitored by 1H NMR. Results demonstrate that their reactions with xenon difluoride cover a wide range of reactivities. The peak potential data and acidity constants bear significantly on the nature and transmission of substituent electronic effects in the (1.1.1) system.

A study was conducted to correlate the dynamics of rare gases in zeolites with an equilibrium property of the system - the instantaneous normal mode spectrum. Specifically, xenon adsorption was examined in all-silica polymorphs of four zeolites, namely, silicalite, faujasite, mordenite and Na-A. Among other results, it was found that short-time dynamics in a zeolite especially at low sorbate concentrations is largely ballistic and controlled by the sorbate-wall interactions.

The nuclear spin polarization of 129Xe can be enhanced by several orders of magnitude by using optical pumping techniques. The increased sensitivity of xenon NMR has allowed imaging of lungs as well as other in vivo applications. The most critical parameter for efficient delivery of laser-polarized xenon to blood and tissues is the spin-lattice relaxation time ([T.sub.1]) of xenon in blood. In this work, the relaxation of laser-polarized xenon in human blood is measured in vitro as a function of blood oxygenation. Interactions with dissolved oxygen and with deoxyhemoglobin are found to contribute to the spin-lattice relaxation time of 129Xe in blood, the latter interaction having greater effect. Consequently, relaxation times of 129Xe in deoxygenated blood are shorter than in oxygenated blood. In samples with oxygenation equivalent to arterial and venous blood, the 129Xe [T.sub.1]s at 37 [degrees] C and a magnetic field of 1.5 T were 6.4 s [+ or -] 0.5 s and 4.0 s [+ or -] 0.4 s, respectively. The 129Xe spin-lattice relaxation time in blood decreases at lower temperatures, but the ratio of [T.sub.1] in oxygenated blood to that in deoxygenated blood is the same at 37 [degrees] C and 25 [degrees] C. A competing ligand has been used to show that xenon binding to albumin contributes to the 129Xe spin-lattice relaxation in blood plasma. This technique is promising for the study of xenon interactions with macromolecules.

The arrangement of Xe atoms incorporated in the cavities of a fully dehydrated zeolite A with a unit composition of Cs3Na8HSi12Al12O48 (Cs3-A) has been studied. A Cs3-A crystal was exposed to 255 atm of Xe at 400 degrees C for 7 days and then cooled at pressure to trap the Xe atoms. A second crystal received the same treatment at 450 atm and a third crystal at 1020 atm. Single-crystal x-ray diffraction methods were used in determining the crystal structures in the cubic space group Pm3m at 21 degrees C and 1 atm.

A study was conducted to examine the dynamics associated with a low pressure xenon discharge plasma using a collisional-radiative framework. Computations were carried out to generate the main properties of the temporal evolution of xenon spontaneous emission lines under a pulsed environment. Results indicated that the collisional-radiative model effectively interpreted the stimulated emission mechanisms for the ionic xenon laser in the ultraviolet-visible region.

Absorption spectroscopy and emission spectroscopy were used to examine the afterglow from radio frequency inductive excited discharges in Xe and I2 mixtures. The findings show that exciplex XeI* results in the afterglow when ground state Xe and highly excited I2 are combined. Ion-ion neutralization was also found to be an important precursor reaction for the development of I*(2P3/2) as well as of Xe*, Xe**, I2*, I2** and other excited species found in the afterglow.

A study was conducted to examine the generation of products of C-C and C-F cleavage in self-assembled fluorocarbon monolayers during collisions of XE+ and I+ ions over a 15-80 eV collision energy range. Theoretical computations were carried out to determine the geometry of reaction products and reaction enthalpies. Results indicated the occurrence of charge exchange with liberation of fluorocarbon cations from the surface at low collision energies.

Modeling was used to examine the mechanism of negative differential conductivity (NDC) in an electron-beam sustained gas discharge of pure xenon. Calculations of the drift velocity of electrons in xenon involved the self-consistent solution of the Boltzmann equation for electron energy distribution function and a set of rate equations in the discharge plasma. Findings showed that the main factor responsible for the NDC effect is Coulomb interaction between electrons.

A study was conducted to analyze the diffusion of a mixture of methane and xenon in the zeolite silicalite using molecular dynamics simulations and pulsed field gradient nuclear magnetic resonance. The interactions were modeled by 12-6 Lennard-Jones pair potentials. Experimental results indicated that the limited rnage of the spin-echo attenuation and the finite contribution of long-range and restricted diffusion hindered the determination of the principal values of the diffusion tensor.

A study relating to research on the synthesis of various compounds of XeF2 with strong fluoride ion acceptors presents the results of an experimental and theoretical investigation of the structure of new Xe(II) species, namely, the XeNO3+ and XeNO2+ ions prepared for the first time ever in the gas phase. These synthesized ions were characterized by mass spectroscopic and theoretical techniques. Experimental methods and data are discussed.

The synthesis, crystal structures and other properties of the compounds XeF2.2CrF4 and XeF5+CrF5- are described. XeF2.2CrF4 was synthesized by the solvolysis of XeF2.CrF4 in anhydous hydrogen fluoride, followed by decantation of the dissolved XeF2. Chain-like arrangements were observed in the resulting structure of the compounds, while additional six fluorine bridges were formed in the tetravalent chromium. Each nonbridging fluorine contributed different bond orders to the resulting compounds.

Experiments in bath fluid mixtures were conducted for a further testing of the quantitative approach in the collisional deactivation of vibrationally highly excited azulene in equimolar supercritical mixtures of xenon and ethane at 385 K from gas- to liquid-phase densities. An isolated binary collision model was used to describe the density dependence of the collisional deactivation rate constant k(sub c) of highly excited azulene in binary mixtures of ethane and xenon. Results have led to the quantitative understanding of collisional energy transfer of highly excited azulene from the dilute gas to the compressed liquid phase.

The structural and dynamic properties of chlorine and bromine ions and atoms in xenon clusters were investigated. A search method based on a genetic algorithm was utilized to determine the lowest energy structure of Xe(sub n)Y (Y = Cl(super -), Br(super -) and Br) microclusters. Experimental results showed that both Cl and Cl(super -) were found inside the Xe cluster while Br and Br(super -) adsorb onto the cluster surface. It was also found that for most clusters, the lowest energy structures of the lighter halogen appear to be independent of its charge state.

129Xe nuclear magnetic resonance spectroscopy was used to examine the adsorption and distribution of xenon in AgA zeolite. Results showed a slow exchange of xenon between the alpha-cages of AgA zeolite treated in a vacuum at 380 or 410 K and the appearance of separate lines in the 129Xe NMR spectrum for the cages with different populations of xenon. As many as 10 different Xe(sub n) clusters with n between 1 and 8 are distinguishable. Any charged silver clusters are believed located inside the sodalite cages, since large xenon clusters up to Xe(sub 8) can reside in the alpha cage.

The ligation of atomic gold(I) cation Au+ by different kinds of inorganic and organic ligands with heteroatoms was investigated empirically and theoretically. The best theoretical estimate for the binding energy was D0(Au+ -Xe) = 30.1 kcal/mol. This value was employed to related computed and empirically grouped binding energies of Au(L)+ complexes with a relative gold(I) cation affinity scale for heteroatom ligands L. The gold(I) cation was unique because its binding energy was exceptionally high.

A study was conducted on the interaction of xenon with cryptophane-A in 1,1,2,2-tetrachloroethane-d2 using 129Xe and 1H NMR spectroscopy. The stability of the xenon complex seems to be much greater than that of the previously described xenon complex of alpha-cyclodextrin in water. The findings indicate that the incoming xenon atom must displace the departing one to enter the cryptophane cavity. Moreover, the results suggest that the complexation equilibrium does not involve the empty cryptophane.

The Monte Carlo simulation model was used to investigate the distributions of the number of primary electrons produced per incident mono-energetic x-rays in the 1- to 41-keV energy range comprising the xenon L- and K-absorption edges. The results of the simulation results were compared with recent data and experimental values measured with a gas proportional scintillation counter. Findings indicate a discontinuous behavior with incident x-ray energy which results in an ambiguity in the determination of the x-ray energy in certain narrow ranges containing the edges.

Although xenon becomes metallic at pressures above about 100 gigapascals, a combination of quantum mechanical calculations and high pressure-temperature experiments reveals no tendency on the part of xenon to form a metal alloy with iron or platinum to at least 100 to 150 gigapascals. The transformation of xenon from face-centered cubic (fcc) to hexagonal close-packed (hcp) structures is kinetically hindered, the differences in volume and bulk modulus between the two phases being smaller than we can resolve (less than 0.3 percent and 0.6 gigapascals, respectively). The equilibrium fcc-hcp phase boundary is at 21 (± 3) gigapascals, which is a lower pressure than was previously thought, and it is unlikely that Earth's core serves as a reservoir for primordial xenon., Like the other noble elements, Xe is characterized by a reluctance to form chemical bonds. Indeed, chemical inertness makes the noble gases useful as tracers that help reveal the evolution [...]

XeF2 has been examined in terms of its reaction behavior toward isocyanates and azides, using both aHF and aqueous solution. An intermediate formation of FXe(N3) and FXe(NCO) seems to be a better explanation than a simple isocyanate and azide fluorination. There are minimum structures for xenon isocyanate fluoride and xenon azide fluoride. In addition, FXe(OCN) represents true minima at MP2 and HF levels, though, compared to the isocyanate species, this isomer has higher energy.

The heavy atom effects of xenon in the photochemistry of organic compounds were determined by investigating the photolysis of 2,3-diazabicyclo[2.2.2]oct-2-ene in sodium Y (NaY) zeolite containing adsorbed xenon. The results revealed showed that xenon is an effective heavy atom perturbant, giving a 3:1 product ratio of triplet electron spin states and a singlet spin state either in the diazenyl diradical or on the surface of 1,4-cyclohexanediyl.