Xe Gas Research Articles

Investigation of the complete encapsulation process of the noble gases by cryptophanes.

Based on DFT calculations (ωB97XD/def2-SVP/SVPfit), the ability and mechanism of noble gas encapsulation by series of cryptophanes were investigated. The focus was set to study the influence of different functionalization groups placed at the "gates" of cryptophanes cavity entrance by which the energy criteria were chosen as a main indicator for selective encapsulation of noble gases. Chosen functionalization groups were CH3, OCH3, OH, NH2, and Cl, and the encapsulation process of these cryptophanes was compared to a cryptophane without any functionalization group on its outer rim. Those groups were selected based on their different chemical properties and based on their size which will subsequently put additional steric restrictions on the cavity entrance. Chosen functionalization groups, beside their steric influence on the energy barrier magnitude, influence also the gating process through its chemical nature by which they can put an additional stabilization on noble gases encapsulation transition states enhancing the encapsulation process. Objective of this study was clearly to get better insights on the influence of those functional groups on the whole encapsulation process of noble gases. Large-size noble gases (Xe and Rn) from all noble gases are best accommodated in the cavities of selected cryptophanes, on the other hand these noble gases require to pass the highest energy barrier through the gating process. From the series of investigated cryptophanes, the cryptophane with the OCH3 functionalization group has been identified as the one with the best capabilities to host investigated noble gases, but on the other side this cryptophane puts the highest energy criteria required for the previous gating process.

The low primordial heavy noble gas and 244Pu-derived Xe contents of Earth's convecting mantle

Clues to unraveling the origin and history of terrestrial volatiles lie in the noble gas record of Earth's mantle. However, the low abundance of heavy noble gases (Ar-Kr-Xe) in mantle-derived rocks presents a major analytical challenge that limits our understanding of mantle volatile evolution. Here, we employ a new technique of ultrahigh precision dynamic mass spectrometry to measure Ar-Kr-Xe isotopes in mantle-derived gas collected from Mt. Etna (Italy) and Eifel (Germany), which both tap depleted convecting mantle reservoirs. We find that the fractions of primordial Kr-Xe from accretionary sources (≤ 7 % of non-radiogenic, non-fissiogenic isotopes) and 244Pu-derived 136Xe (≤ 9.8 ± 9.3 % of total fissiogenic Xe) are both markedly lower than previously estimated. For Mt. Etna, we find an apparent lack of detectable primordial Xe, which could reflect an additional contribution from recycled atmospheric volatiles from nearby subduction. In addition, slight excesses of 238U-derived fissiogenic Xe relative to the upper mantle composition may reflect the contribution of a crustal component related to the occurrence of a HIMU (“high μ” where μ = 238U/204Pb)-type source in Mt. Etna volcanic products. The low primordial heavy noble gas and 244Pu-derived Xe contents of Earth's convecting mantle, as derived from these new data, requires extensive volatile loss during terrestrial accretion, followed by long-term degassing and pervasive overprinting of primordial heavy noble gases by subduction recycling. In addition, we suggest that quantitative incompatible element (including Pu, U) extraction to the Hadean crust and subsequent reintroduction of U via subduction could have contributed to lowering the ultimate fraction of 244Pu-derived 136Xe in the upper mantle. The differences observed between this study and other upper mantle Xe studies may reflect mantle source heterogeneities (e.g. due to the heterogeneous overprinting of mantle volatiles by subduction) but could also result from analytical inconsistencies and/or subsurface isotope fractionation in natural systems. Future studies are crucial to gain insight into the origin of these different results.

Automated hyperpolarized 129Xe gas generator for nuclear magnetic resonance spectroscopy and imaging applications

We describe a method and an apparatus for producing hyperpolarized (HP) Xe gas of high concentration without Xe condensation. The HP Xe generator works under atmospheric pressure and employs a quasi-continuous method to provide a continuous supply of HP Xe gas by adopting technologies for supplying a highly pure gas, a gas control system and precise pressure control. The apparatus has a glass cell containing solid Rb metal and solid Xe in vacuum at a low temperature and is heated so that the Xe becomes a gas and Rb exists in a gas-liquid mixture. Then a magnetic field is applied with laser beam irradiation to produce polarized Xe gas of high concentration. The device was evaluated using a 2T magnetic resonance imaging (MRI) scanner. Long-term experimental operation demonstrated the continuous collection of 30 ml syringes of HP Xe gas with a sufficient polarization rate for fast one scan acquisition. A practical device for the automated manufacture of HP 129Xe gas was thus successfully developed.

Atomistic Insights into Carbon Dioxide Sequestration in Natural Gas Hydrates in the Presence of Mixture of Flue and Noble Gases

AbstractThe exchange of carbon dioxide with methane in natural gas hydrates (NGHs) is one of the sustainable approaches for the sequestration of carbon dioxide in NGHs. However, the formation of mixed CH4─CO2 hydrates during CH4─CO2 exchange in NGHs reduces the rate of CH4─CO2 exchange in NGHs. It is reported that molecular level insights into CH4─CO2 exchange in NGHs using quaternary‐gas systems of CH4, CO2, and a mixture of flue (H2S and N2) and noble (Ne, Ar, Kr, and Xe) gases in heterogeneous medium using molecular dynamics simulation techniques. The sequestration of gases other than CH4 in the new hydrate cages besides the interface is the highest in CO2:H2S:Ar (2:1:1) system among all the reported quaternary‐gas systems. The results show that Ar enhances CO2 sequestration in NGHs in the presence of H2S rather than N2. The hydrate growth occurs due to the formation of dual hydrate cages. Among the methane molecules released from the hydrate slab in a binary‐gas (CH4─CO2) system, > 60 % of the released methane molecules reform new cages beside the interface. On the other hand, only ≈ 50 % of the released methane molecules reform new hydrate cages besides the interface in CO2:H2S:Ar (2:1:1) system.

Radiation induced non-linear oscillations in ITER baseline scenario plasmas in DIII-D

This work shows how the radiation brought about by metals or metal-equivalent radiators such as Kr and Xe produces non-linear dynamics on otherwise stationary β N flattops of DIII-D ITER Baseline Scenario demonstration discharges. The Kr and Xe gases are used to reproduce the radiative loss rates of W in present machines that operate at core temperatures much lower than the expected ITER temperature. Experiments on DIII-D with injection of Kr and Xe, as well as with sources of intrinsic metals reach the range of radiated fraction values expected in the ITER core and experience slow oscillations in temperature and radiated power. In many cases of high radiated fraction, the core temperature decreases enough for the safety factor profile to rise above the 1/1 rational surface, naturally eliminating sawteeth and occasionally producing a persistent helical core. The oscillations can be reproduced by a modified Lotka–Volterra system for temperature and radiated fraction if diffusion and noise are included, which indicates that the interplay between temperature and radiation can be the main cause of the cyclic nature of the system. A new physics based model which includes equations for temperature, density and input power can also reproduce the oscillations observed in the experiments. The present results suggest that the non-linearity of the system can be increased by the inclusion of the inherently non-linear alpha heating term, which is proportional to ∼n e 2 T i 2, and obtains oscillations in the model when added to an otherwise more stationary system.

Self-Assembly of Chiral Porous Metal-Organic Polyhedra from Trianglsalen Macrocycles.

Metal-organic polyhedra (MOPs) can exhibit tunable porosity and functionality, suggesting potential for applications such as molecular separations. MOPs are typically constructed by the bottom-up multicomponent self-assembly of organic ligands and metal ions, and the final functionality can be hard to program. Here, we used trianglsalen macrocycles as preorganized building blocks to assemble octahedral-shaped MOPs. The resultant MOPs inherit most of the preorganized properties of the macrocyclic ligands, including their well-defined cavities and chirality. As a result, the porosity in the MOPs could be tuned by modifying the structure of the macrocycle building blocks. Using this strategy, we could systematically enlarge the size of the MOPs from 26.3 to 32.1 Å by increasing the macrocycle size. The family of MOPs shows experimental surface areas of up to 820 m2/g, and they are stable in water. One of these MOPs can efficiently separate the rare gases Xe from Kr because the prefabricated macrocyclic windows of MOPs can be modified to sit at the Xe/Kr size cutoff range.

Cross-calibration of quantum atomic sensors for pressure metrology

Quantum atomic sensors have shown great promise for vacuum metrology. Specifically, the density of gas particles in vacuum can be determined by measuring the collision rate between the particles and an ensemble of sensor atoms. This requires preparing the sensor atoms in a particular quantum state, observing the rate of changes of that state, and using the total collision rate coefficient for state-changing collisions to convert the rate into a corresponding density. The total collision rate coefficient can be known by various methods, including quantum scattering calculations using a computed interaction potential for the collision pair, measurements of the post-collision sensor-atom momentum recoil distribution, or empirical measurements of the collision rate at a known density. Observed discrepancies between the results of these methods call into question their accuracy. To investigate this, we study the ratio of collision rate measurements of co-located sensor atoms, 87Rb and 6Li, exposed to natural abundance versions of H2, He, N2, Ne, Ar, Kr, and Xe gases. This method does not require knowledge of the test gas density and is, therefore, free of the systematic errors inherent in efforts to introduce the test gas at a known density. Our results are systematically different at the level of 3% to 4% from recent theoretical and experiment measurements. This work demonstrates a model-free method for transferring the primacy of one atomic standard to another sensor atom and highlights the utility of sensor-atom cross-calibration experiments to check the validity of direct measurements and theoretical predictions.

Atom probe tomography of segregation at grain boundaries and gas bubbles in neutron irradiated U-10 wt% Mo fuel

During neutron irradiation to fission densities > 5.2 × 1021 fiss/cm3, Xe agglomerates forming gas bubbles of varying size within the U-Mo fuel matrix. Herein, segregation of fission products to Xe bubbles and grain boundaries (GB) were studied using atom probe tomography (APT). Segregation behavior was found to vary among GBs, small bubbles (<10 nm), and larger bubbles (>10 nm). Solid fission products were enriched at GBs and larger bubbles, but not at small bubbles. A denuded zone was identified adjacent to a > 10 nm Xe gas bubble and a GB.

Adsorptive separation of Xe/Kr mixtures by microporous lanthanide metal-organic frameworks with high thermal stability

Efficient separation of Xenon (Xe) and Krypton (Kr) is a significant process for their wide industrial applications and potential environmental concerns. Owing to the inert atomic gases (Xe and Kr) nature with similar physical and chemical properties, it is a great challenge to achieve efficient separation of the Xe/Kr mixture. Herein, we report a series of microporous lanthanide based metal-organic frameworks Ln (BTC) (H2O)·(DMF)1.1 (Ln-MOF) (Dy-BTC (1), Er-BTC (2), and Yb-BTC (3)) with ultrahigh thermal stability for adsorptive Xe/Kr separation. These three isostructural Ln-MOFs consisted of lanthanide metal ions and 1,3,5-benzene dicarboxylate ligands that possess a square channel with pore sizes of 6–7 Å. By substitution of Ln ions, Yb-BTC shows the smallest pore size among the three compounds which enables its obvious higher Xe/Kr selectivity compared with the other two Ln-MOFs. Yb-BTC exhibits a moderately high Xe uptake of 2.5 mmol/g (298 K and 1 bar), and a significantly high Xe/Kr uptake ratio of 3.8, indicative of its great potential for separation of Xe/Kr mixture. The effective Xe/Kr separation ability of Yb-BTC was also confirmed by a breakthrough experiment.

Assessing the potential for CO2 storage in shallow coal seams using gas geochemistry: A case study from Qinshui Basin, North China

Shallow coal seams are a target reservoir for CO2 sequestration. So far efforts to trace CO2 sequestration by coal beds have largely focussed on short-term monitoring or theoretical modelling. To evaluate the feasibility of safe long-term storage of CO2 in shallow coal beds, we report the first systematic gas geochemical study at a shallow injection site in Shizhuang, Qinshui Basin, one year after CO2 injection ceased. The injected CO2 is isotopically distinctive and appears to be enriched in heavy noble gases (Kr and Xe). The high CO2 content and light δ13CCO2 of gases from production wells confirm the migration of injected gas to the northeast and east of the main injection well previously tracked by geophysical studies. The migration of injected gas to the southeast has not been identified before, and exceeds that to the northeast, implying that gas geochemistry provides a more robust method of tracking migration. Less than 1 % of the total injected CO2 has been extracted from production wells in the year since injection ceased. We estimate that the target coal seam in the study area can store about 0.08 billion tonnes of CO2. Scaling up we estimate that the Qinshui Basin has the potential to store about 19 billion tonnes of CO2. This is significantly more than previous estimates. This study demonstrates the importance of geochemical tracers in quantifying and monitoring CO2 sequestration and also implies that unmined coal seams have high potential for the long-term storage of CO2.

Size limits and fission channels of doubly charged noble gas clusters.

Small, highly charged liquid droplets are unstable with respect to spontaneous charge separation when their size drops below the Rayleigh limit or, in other words, their fissility parameter X exceeds the value 1. The absence of small doubly charged atomic cluster ions in mass spectra below an element-specific appearance size na has sometimes been attributed to the onset of barrierless fission at X = 1. However, more realistic models suggest that na marks the size below which the rate of fission surpasses that of competing dissociative channels, and the Rayleigh limit of doubly charged van der Waals clusters has remained unchartered. Here we explore a novel approach to form small dicationic clusters, namely by Penning ionization of singly charged noble gas (Ng) clusters that are embedded in helium nanodroplets; the dications are then gently extracted from the nanodroplets by low-energy collisions with helium gas. We observe Ngn2+ ions that are about 40% smaller than previously reported for xenon and krypton and about 20% for argon. These findings suggest that fission barriers have been underestimated in previous theoretical work. Furthermore, we measure the size distributions of fragment ions that are produced by collisional excitation of mass-selected dications. At lowest collision gas pressure, dicationic Kr and Xe clusters that are smaller than previously observed are found to evaporate an atom before they undergo highly symmetric fission. The distribution of fragments resulting from fission of small dicationic Ar clusters is bimodal.

Efficient Xe Filling of MEMS Vapor Cells Empowered by Customized Triple Stack Wafer Bond Processing

Nuclear-magnetic-resonance (NMR) gyroscopes based on MEMS vapor cell technology are currently being investigated worldwide and show superior advantages over current MEMS gyroscopes. However, there are still challenges in the upscaling and further deployment of NMR gyroscopes, due to the extremely high cost of the required gases (i.e. 129Xe, 131Xe), size, and high power consumption. To tackle these bottlenecks, in this study, a miniaturized, chip-scale, and low-cost NMR gyroscope has been conceptualized and fabricated. Here, a cost-effective and scalable filling of MEMS vapor cells with isotropic Xe filling was developed via an innovative microfabrication and wafer stacking process flow. By utilizing ultra-thin glass wafers, Taiko-processed silicon wafers, and an external gas flow system integrated into the wafer bonders, a sequential anodic bonding technique was executed to create a hermetically sealed chamber through which Xe gas can flow in a minimal volume. Fig. 1 shows the configuration of the triple-stack bonded wafer featuring the sealed chamber, the gas inlet, and the outlet. The Xe mass flow rate during the efficient filling process was 3.2528 *10-7 kg/s with a total filling time of <100 sec, as verified by the two-way Fluid-Structure Interactions (FSI) simulation data. As a result, it was demonstrated that the consumption of Xe gas during device filling can be dramatically reduced, which has a substantial impact on the total cost of the MEMS vapor cell. Figure 1. A demonstration of the triple-stack bonded wafer (glass-Silicon-glass) with an efficient Xe gas-filling process Figure 1

‘Self-calibration’ method for TALIF measurement of O atoms by full photofragmentation of O3 using a 226 nm UV laser

Quantification of atomic oxygen through the method of two-photon absorption laser-induced fluorescence (TALIF) is common in the fields of plasma fundamental research and application treatments. Fluorescence signal calibration is required to absolutely quantify the O amount and normally achieved with the help of TALIF measurement of a known-density Xe gas. In this study, an alternative calibration method is proposed based on the full photofragmentation (FPF) of O3 with a known density in a known gas composition by the same UV laser beam as that of the TALIF detection of atomic O. This is achieved by an equivalent amount of O fragment contributing the same fluorescence intensity as that of the O3 FPF-TALIF process under the same experimental conditions. The validity of this calibration method is proved by comparing it to the TALIF measurement of the Xe gas. It provides a ‘self-calibration’ method for the TALIF detection of O atoms without any need to change the laser optical arrangements including the laser wavelength. In addition, it only requires a gas flow with known O3 density through the studied medium reactor or chamber (such as plasma discharges). Detailed theoretical and practical principles of this self-calibration approach are presented and discussed in this study.

Frequency-Dependent Quadratic Response Properties and Two-Photon Absorption from Relativistic Equation-of-Motion Coupled Cluster Theory.

We present the implementation of quadratic response theory based upon the relativistic equation-of-motion coupled cluster method. We showcase our implementation, whose generality allows us to consider both time-dependent and time-independent electric and magnetic perturbations, by considering the static and frequency-dependent hyperpolarizability of hydrogen halides (HX, X = F-At), providing comprehensive insights into their electronic response characteristics. Additionally, we evaluated the Verdet constant for noble gases Xe and Rn and discussed the relative importance of relativistic and electron correlation effects for these magneto-optical properties. Finally, we calculate the two-photon absorption cross sections of transition [ns1S0 → (n + 1)s1S0] of Ga+ and In+, which are suggested as candidates for new ion clocks. As our implementation allows for the use of nonrelativistic Hamiltonians as well, we have compared our EOM-QRCC results to the QR-CC implementation in the DALTON code and show that the differences between CC and EOMCC response are in general smaller than 5% for the properties considered. Collectively, the results underscore the versatility of our implementation and its potential as a benchmark tool for other approximated models, such as density functional theory for higher-order properties.

The effect of inert gases (Xe, Ar, Ne, He) on decomposition reactions of N2O, CH4 and CO2 at high pressures

In a pulsed compression reactor (PCR) experiments were done with N2O (4%mol), CH4 (1%mol) and CO2 (2%mol) diluted in the inert gases Xe, Ar, Ne and He. The mixtures were compressed up to 250 bar, reaching temperatures of up to 4000 K. At equal temperature, pressure and volume, significant differences (up to 20%) were measured in the conversion of the three species in different noble gases. The measurements with N2O decomposition showed that the reaction is the fastest in the most heavy noble gas tested. The conversion decreased as the molar mass of the noble gas decreased. Likewise, methane pyrolysis was measured to be the fastest in xenon and slowed down in accordance with the mass of the inert molecule. A reverse trend was measured for the decomposition of CO2 to CO and O⋅, which is explained by the dominant role of the reverse reaction. As a result, the CO2 data is also explained by conversion rates that are higher in heavier gases. This paper provides a first attempt to understand the observed influence of the molar mass of the inert bathing gas on the reaction rate in the high pressure domain. A theory is proposed based on a Newtonian description of reactant activation by the inert bathing gas.

Continuous Nanospace in Nanoporous Liquid Crystal Investigated by 129 Xe NMR Spectroscopy.

Continuous nanopores within fluid materials could be used for novel chemical events such as the accommodation of guest molecules, unique arrays of the entrapped molecules, and chemical reactions in a dynamic molecular assembly. Columnar liquid crystals composed of a one-dimensionally stacked assembly of shape-persistent macrocycles form nanochannels owing to the intrinsic nanospace in the column. However, the existence of substantial nanoporosity has not been confirmed experimentally thus far. In this study, for the first time in the literature, we confirmed the presence of discrete and spatiotemporally continuous voids in a liquid-crystalline material. In 129 Xe NMR spectroscopy of liquid crystalline columnar assembly of imine-bridged shape-persistent macrocycles under Xe atmosphere, the NMR signals of the Xe atoms entrapped in the liquid-crystalline macrocycle depended on the gas pressure and phase-transition temperatures. These results indicate that the encapsulation of Xe gas molecules within the discrete and oriented nanospaces of nanoporous liquid crystals is different from the homogeneous dissolution of the solute in an ordinary solution.

Continuous Nanospace in Nanoporous Liquid Crystal Investigated by 129Xe NMR Spectroscopy

AbstractContinuous nanopores within fluid materials could be used for novel chemical events such as the accommodation of guest molecules, unique arrays of the entrapped molecules, and chemical reactions in a dynamic molecular assembly. Columnar liquid crystals composed of a one‐dimensionally stacked assembly of shape‐persistent macrocycles form nanochannels owing to the intrinsic nanospace in the column. However, the existence of substantial nanoporosity has not been confirmed experimentally thus far. In this study, for the first time in the literature, we confirmed the presence of discrete and spatiotemporally continuous voids in a liquid‐crystalline material. In 129Xe NMR spectroscopy of liquid crystalline columnar assembly of imine‐bridged shape‐persistent macrocycles under Xe atmosphere, the NMR signals of the Xe atoms entrapped in the liquid‐crystalline macrocycle depended on the gas pressure and phase‐transition temperatures. These results indicate that the encapsulation of Xe gas molecules within the discrete and oriented nanospaces of nanoporous liquid crystals is different from the homogeneous dissolution of the solute in an ordinary solution.

Numerical investigation on flow and heat transfer characteristics of helium–xenon gas mixture in rod bundles

The helium-xenon(He–Xe) gas mixture with low Prandtl number and good heat transfer characteristics suits for the advanced high heat flux and compact gas-cooled reactors. A numerical simulation was conducted on the flow, heat transfer, and turbulent mixing characteristics of He–Xe gas mixture in a tightly arranged triangular rod bundle subchannel. The transition characteristics of He–Xe gas mixture in rod bundle structure were obtained. The friction resistance coefficient, Nusselt number(Nu), and turbulent mixing factor β was corrected within the Reynolds number(Re) range of 3 × 102 - 1.8 × 105. The research results indicate that the transition occurs at Re equal to 2000 and forms a transition zone within the Re range of 2000–5000; The Blasius correlation can describe the wholly turbulent flow precisely, but it is suitable to adopt a new formula in the transition zone; The local Nu prediction performance of the modified Peckett correlation is in good agreement with the numerical simulation results, and the Petukhov correlation with shape correction and temperature correction factors has good prediction results on global Nu; The turbulent mixing factor using Re and shape parameters can better describe the mixing characteristics. This study has reference value for the design of rod bundle reactors using He–Xe gas mixtures as working fluids.

PROPORTIONAL DETECTORS OF GAMMA-RADIATION BASED ON HIGH PURITY XENON GAS FOR RADIATION MONITORING

This article is dedicated to a detailed investigation of properties of a proportional counter based on the Xe+2%CH4 mixture. A setup for filling the detectors with high purity Xe gas and Xe-based gas mixtures was designed and made. An optimized design of the proportional counters was developed and investigated. The design parameters, such as the material and diameter of the anode, the number and material of the gas mixture inlets, composition and pressure of the gas were improved. The operating regimes of the proportional counters, as well as their thermal stability, were investigated.

INCREASING THE CONVERSION ACCURACY OF MODEL GAS (Ar) CONSUMPTION INTO XENON CONSUMPTION WHEN USING CAPILLARY TUBES IN THE WORKING SUBSTANCE FEED SYSTEMS OF ELECTRIC PROPULSION

The article discusses the possibility of improving the method of converting the mass flow rate of the model gas (Ar) to the mass flow rate of the working gas (Xe) in capillary tubes. The well-known method of such conversion, which is used in electric propul- sion systems, is based on Poiseuille’s law for laminar flow. The results of the experimental verification of the method showed the accuracy from 21 % to 30 %. On the basis of the conducted experimental studies, it was proposed to enter a correction factor depending on the inner diameter of the capillary into the existing methodology of mass flow recalculation, which made it pos- sible to significantly reduce the error of recalculation of Ar mass flow rate into Xe mass flow rate to ±4 %. Increasing the accuracy of the calculation allows the wide use of argon model gas in the selection of capillary flow restrictors for feed systems of low- and medium-power electric propulsion systems and during testing of assembled systems at various stages of development and testing.