NMR chemical shifts of129Xe dissolved in liquid haloalkanes and their mixtures

Xenon-129 NMR spectra have been measured for solutions containing Xe dissolved in a variety of linear 1-haloalkanes, α, ω-dihaloalkanes, and their mixtures. The data are found to be linearly related to solvent composition expressed as volume fraction of the constituent methyl groups, methylene groups, and halogen atoms. This behavior is consistent with a model in which the large dispersion force contributions to the chemical shift of¹²⁹Xe result from pair interactions between dissolved Xe atoms and the methyl, and methylene groups, and the halogen atom, from which the solvent molecules are composed.     

Imaging of a mixture of hyperpolarized 3He and 129Xe

With the use of hyperpolarized gases, a great number of experiments have been carried out in order to improve the diagnostics of the lung, both from a structural and a functional point of view. 3He is best suited for structural studies, whereas 129Xe gives more detailed information about the functionality of the lung because it enters the bloodstream. In this work, we propose the use of a gas mixture to perform consecutive analysis of lung structure and functionality upon the delivery of a single bolus of gas. We show images of a helium-xenon gas mixture in the presence of a small amount of liquid toluene in order to demonstrate how both nuclei can be detected independently, extracting the spectroscopic information provided by the 129Xe spectra and obtaining an image with high sensitivity for 3He. A second experiment performed on a dissected mouse lung was used to demonstrate how the mixture of gases can enhance sensitivity in the larger airways of the lung.     

Measurement of 129Xe frequency shift due to Cs–129Xe collisions

Enhancement factor K0, which characterizes NMR and EPR frequency shifts for Cs-129Xe, is measured for the first time. The enhancement factor r-o was measured to be （702±41） at 80 ℃ and （653±20） at 90 ℃, using the NMR frequency shift, detected by atomic magnetometer at a low magnetic field of 100 nT. This result is useful for predicting the EPR frequency shifts for Cs and the NMR frequency shifts for 129Xe in spin-exchange cells.     

Collisional frequency shifts in 133Cs fountain clocks

We present a theoretical analysis of the density dependent frequency shift in Cs fountain clocks using the highly constrained binary collision model described by Leo et al. [Phys. Rev. Lett. 85, 2721 (2000)]. We predict a reversal in the clock shift at temperatures near 0.08 microK. Our results show that s waves dominate the collision process. However, as a consequence of the large scattering lengths in Cs the clock shift is strongly temperature dependent and does not reach a constant Wigner-law value until temperatures are less than 0.1 nK.     

Hyperpolarised gas filling station for medical imaging using polarised 129Xe and 3He

We report the design, construction, and initial tests of a hyperpolariser to produce polarised ¹²⁹Xe and ³He gas for medical imaging of the lung. The hyperpolariser uses the Spin-Exchange Optical Pumping method to polarise the nuclear spins of the isotopic gas. Batch mode operation was chosen for the design to produce polarised ¹²⁹Xe and polarised ³He. Two-side pumping, electrical heating and a piston to transfer the polarised gas were some of the implemented techniques that are not commonly used in hyperpolariser designs. We have carried out magnetic resonance imaging experiments demonstrating that the ³He and ¹²⁹Xe polarisation reached were sufficient for imaging, in particular for in vivo lung imaging using ¹²⁹Xe. Further improvements to the hyperpolariser have also been discussed.     

Solvent-induced H/D isotope effect on129Xe chemical shifts

An effect of substitution of deuterium for protium in molecules of 17 solvents on^l29Xe NMR shifts was studied. The variation range of solvent-induced isotope xenon shifts σ _s ⁱ exceeds 5 ppm and lies in the range from ?1.18 ppm (in CH₃OD solution) to 3.92 ppm (in D₂O) at 28°C. Experimental results agree with the concept that interaction of xenon atoms with solvent molecules is determined predominantly by dispersion forces. Correlations of σ _s ⁱ with the isotope effect on polarizability, boiling point, and vapor pressure of solvents were established. Anomalous manifestation of properties of aqueous solution was detected.     

Atomic Electric Dipole Moment Measurement Using Spin Exchange Pumped Masers of 129Xe and 3He

We have measured the T-odd permanent electric dipole moment of 129Xe with spin exchange pumped masers and a 3He comagnetometer. The comagnetometer provides a direct measure of several systematic effects that may limit electric dipole moment sensitivity, and we have directly measured the effects of changes in leakage current that result when the applied electric field is changed. Our result, d(129Xe) = 0.7+/-3.3(stat)+/-0.1(syst)x10(-27)e cm, is a fourfold improvement in sensitivity.     

NMR chemical shifts of129Xe dissolved in various oxygen and nitrogen substituted straight chain aliphatic compounds

Xenon-129 NMR spectra have been measured for dilute solutions of¹²⁹Xe dissolved in a series of n-alcohols and primary n-alkyl amines, as well as ethylene glycol and water. The chemical shifts recorded for¹²⁹Xe in the alcohols and amines are found to be linearly related to solvent composition expressed in terms of the individual methyl and methylene groups as well as the nitrogen and oxygen bearing functional groups making up these compounds. This behavior is consistent with a simple model which considers the van der Waals contribution to the chemical shift of¹²⁹Xe to result from pair interactions between a dissolved Xe atom and the individual methyl, methylene, and functional groups from which the solvent molecules are derived. The¹²⁹Xe chemical shifts caused by the ?CH₂?, ?NH₂, and ?OH groups are found to be quite similar in magnitude, each being approximately twice that of a ?CH₃ group.     

NMR chemical shifts of129Xe dissolved in liquid ethers, secondary amines, and alkyl sulfides

Xenon-129 NMR spectra have been measured for solutions containing Xe dissolved in a variety of linear aliphatic ethers, secondary amines, and alkyl sulfides. The chemical shifts obtained from these data are found to be linearly related to the composition of the solvent molecules expressed as volume fraction of the constituent methyl groups, methylene groups, and the respective oxygen, nitrogen, and sulfur atoms. These results support a model used previously to interpret chemical shifts measured for¹²⁹Xe dissolved in a variety ofn-alkanes and their terminally substituted derivatives. This model treats dispersion force contributions to the chemical shift as resulting from pairwise additive interactions between each dissolved Xe atom and the individual constituent groups of each solvent molecule.     

Density dependence of 129Xe N.M.R. chemical shifts in O2 and NO

For neutral species it is possible to choose a gauge in which the molecular hamiltonian is translationally invariant. Here it is shown that for charged species this is not entirely possible, but that, if molecular coordinates are employed, the lack of invariance may be confined to the translational part of the hamiltonian.     

129Xe contact shift in oxygen gas

We have determined the temperature dependence of σ₁ of ¹²⁹Xe in oxygen gas. These results were obtained by measurement of the resonance frequency of ¹²⁹Xe in gas samples of known densities in Xe and O₂. The shift of the resonance frequency due to Xe-Xe interactions has been measured in pure Xe gas samples with improved precision. This allows the determination of σ₁(Xe-O₂) by subtracting out the known effect of Xe-Xe interactions in mixed Xe-O₂ samples. σ₁(Xe-O₂) values are reported here for the temperature range 220 to 440 K. The values of σ₁(Xe-O₂) are adequately described by the polynomial function in p.p.m. amagat^-1 σ₁(Xe-O₂) = - 1·061 + 3·64 × 10^-3τ - 2·19 × 10^-5τ² + 9·58 × 10^-8τ³ - 2·08 × 10^-10τ⁴, where τ = (T - 300 K). It is found that the temperature dependence of σ₁(Xe-O₂) can be interpreted in terms of a contact interaction between Xe and the paramagnetic O₂ molecule.     

Effective interactions in dilute mixtures of3He in4He

Nonlocal pseudopotentials which describe the effective interaction between³He quasiparticles, and between these quasiparticles and the background⁴He liquid, are obtained as a function of concentration and pressure by generalizing the Aldrich-Pines pseudopotentials for pure³He and⁴He to dilute mixtures. The hierarchy of physical effects which determine these pseudopotentials is established. Interaction-induced short-range correlations are the dominant physical feature; next in order of importance is the greater zero point motion associated with the replacement of a⁴He atom by a³He atom, while spin-induced Pauli principle correlations play a significantly smaller, albeit still important role. We find a consistent trend in the change of the effective direct quasiparticle interactions with increasing concentration, and show how the Aldrich-Pines pseudopotentials for pure³He quasiparticles represent a natural extension of our results for dilute mixtures. Our calculated nonlocal pseudopotential for³He quasiparticles is qualitatively similar to that proposed by Bardeen, Baym, and Pines; it changes sign at somewhat lower momentum transfers than the BBP result, varies little with concentration, and provides a physical basis for understanding the BBP result. The effective interaction between quasiparticles of parallel spin, here determined for the first time, is essentially repulsive in the very dilute limit; as the concentration increases, it becomes increasingly attractive at low momentum transfers, and resembles closely that between antiparallel spin quasiparticles at 5% concentration. The concentration-dependent transport properties calculated from these pseudopotentials (which involve only one phenomenological parameter) are in good agreement with experiment at saturated vapor pressure (SVP), 10 atm, and 20 atm. Maxima in the thermal conductivity and spin diffusion are predicted to occur at concetrations somewhat less than 4%. Because the effective quasiparticle interactions are somewhat more repulsive than those previously proposed, we find the transition of the³He quasiparticles to the superfluid state takes place at significantly lower temperatures than many previous estimates; our predicted maximum superfluid transition temperature is 2×10^–8 K (for a 0.6% mixture at 20 atm).     

Collisional shifts in an optical-lattice atomic clock

The effects of elastic collisions in optical-lattice atomic clocks are analyzed. Calculations are presented using a separated oscillatory fields clock arrangement. The interactions of atoms in multiply occupied lattice sites cause a linear frequency shift, and also generate asymmetric Ramsey fringe patterns, both complicate the determination of the resonance frequency and reduce the fringe visibility due to interparticle entanglement. A method of reducing these collisional effects in an optical lattice clock containing bosonic atoms by introducing a phase difference of π between the Ramsey driving fields in adjacent sites is developed. This configuration suppresses site-to-site hopping due to the interference of two tunneling pathways, without degrading the fringe visibility. The probability of double occupancy is, thereby, reduced and collisional shifts are, thus, ameliorated.     

Sub-Coulomb transfer and fission in collisions of129Xe,132Xe and136Xe with238U

Integral cross sections for fission and for one- and two-neutron transfer reactions in the system¹³²Xe+²³⁸U were measured radiochemically in the energy range 0.7≦E/E _Coul≦1. The excitation functions for fission and transfer are found to be essentially parallel below 0.85×E _Coul. Even at the lowest energies the transfer cross sections exceed the fission cross section by more than one order of magnitude. With the other projectiles¹²⁹Xe and¹³⁶Xe different transfer cross sections illustrating their sensitivity for the ground stateQ-values,Q _gg , are observed while the fission cross sections are the same as in the¹³²Xe +²³⁸U reaction. The fission data are interpreted in terms of a continuous transition between Coulomb fission and several transfer-induced fission processes.     

129Xe NMR in study of tissues and plants

The high sensitivity of the¹²⁹Xe nuclear magnetic resonance (NMR) chemical shift to the environment was used for characterization of biological tissues and plants. The xenon gas was dissolved under moderate pressure by means of a special device in small pieces of human and animal tissues (heart, muscle, lung, kidney, liver, spleen, brain, sinew, cartilage and hypodermic fat) or plants (leaves, stems, grains, fruits) and the NMR parameters were measured in vitro. The observed line with the chemical shift ～ 180 ppm was attributed to the xenon located in various cellular structures such as lipid shells, intracellular formations. A xenon spectrum in the lungs obtained in vitro coincides with that in the lungs of a mouse measured in vivo by other investigators. The NMR parameters were found to reveal noticeable distinctions between normal and tumour-affected tissues. The analysis of the¹²⁹Xe NMR spectra of the sinew and the cartilage revealed the dependence of the magnetic parameters on the age of the substance. This fact could be accounted for by the changes of the absorption ability of a biological system due to age transformations. The results obtained in comparison with biochemical data reveal the promissory outlook of¹²⁹Xe NMR for the investigation of the state of biological tissues and for medical diagnostics.     

129Xe diffusion in a ferroelectric liquid crystal

Measurements of ¹²⁹Xe self-diffusion and shielding as a function of temperature were performed to cover the different phases of the ferroelectric liquid crystal FELIX-R&;D. The shielding data prove untwisting of the helical structure in the nematic phase (i.e. non-chiral nematic phase) of FELIX-R&;D. Self-diffusion measurements were carried out in a direction parallel to the main magnetic field of the NMR spectrometer. However, in order to yield the anisotropy of the xenon self-diffusion tensor a few measurements also were performed in the perpendicular direction. A special technique, based on the observation of the second spin echo instead of the conventional first one, was applied to avoid convection problems. The experiments reveal all the phase transitions and a continuous decrease in the self-diffusion constant along the external magnetic field, D‖, when moving from the isotropic to the smectic C? phase. The respective activation energy E‖ appears to vary remarkably, however, being about the same in the isotropic and smectic C? phases. In the smectic mesophases significantly faster xenon self-diffusion was detected in the perpendicular direction than in the parallel direction. The detected self-diffusion constant D ⊥ in the perpendicular direction seems to remain almost constant in the smectic mesophases and close to the value of the self-diffusion constant in the isotropic phase. The results are in agreement with the structural features of smectic phases and indicate redistribution of xenon atoms towards the interlayer space of smectic mesophases.