Noble Gas Mixtures Research Articles

Commissioning of the MIGDAL detector with fast neutrons at NILE/ISIS

Many dark matter experiments are exploiting the Migdal effect, a rare atomic process, to improve sensitivity to low-mass (sub-GeV) WIMP-like dark matter candidates. However, this process is yet to be directly observed in nuclear scattering. The MIGDAL experiment aims to make the first unambiguous measurement of the Migdal effect in nuclear scattering. A low-pressure optical Time Projection Chamber is used to image in three-dimensions the characteristic signature of a Migdal event: an electron and a nuclear recoil track sharing a common vertex. Nuclear recoils are induced using fast neutrons from a D–D source, which scatter in the gaseous volume of the detector. The experiment is operated with 50 Torr of CF4 using two glass GEMs for charge amplification. Both light and charge are read-out, and these measurements are combined for track reconstruction. Commissioning data has been recorded with fast neutrons at the Neutron Irradiation Laboratory for Electronics (NILE) at Rutherford Appleton Laboratory in the UK. Results of the experiment’s commissioning and the performance of the detector with a high rate of highly ionising nuclear recoils are presented, along with results from low energy electrons. Initial results of light and charge read-out with low pressure noble gas mixtures are also presented.

The Bimodal Epithermal Astronuclear Reactor (BEAR): A Long-Lived, Universal Space Nuclear Powerplant

A neutronic model of a Nuclear Thermal Propulsion reactor based on the NERVA Peewee design using High Assay Low Enriched Uranium (HALEU) fuel in a Zirconium Carbide matrix has been thoroughly characterised and continuously modified over the last few years at the CSNR. The initial design (Emu, for the flightless bird) created in the summer of 2020 and presented at the NETS 2021 conference, has undergone significant adjustments in this time. Two major investigations have been undertaken and evolved over time; one into the requisites for the provision of electrical power to the propelled spacecraft via the circulation of a noble gas mixture in a closed Brayton cycle, and another into the use of planetary regolith as a reflector, reducing neutron leakage at what would otherwise be the reactor’s end of life in vacuo, rekindling it for an extended period of time as well as providing a very easy ultimate disposal solution, replacing the control drums with rods. It was determined that there are no insurmountable obstacles to performance in either mode.

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.

The Bimodal Epithermal Astronuclear Reactor (BEAR): A LONG-LIVED, Universal Space Nuclear Powerplant

A neutronic model of a Nuclear Thermal Propulsion reactor based on the NERVA Peewee design using High Assay Low Enriched Uranium (HALEU) fuel in a Zirconium Carbide matrix has been thoroughly characterised and continuously modified over the last few years at the CSNR. The initial design (Emu, for the flightless bird) created in the summer of 2020 and presented at the NETS 2021 conference, has undergone significant adjustments in this time. Two major investigations have been undertaken and evolved over time; one into the requisites for the provision of electrical power to the propelled spacecraft via the circulation of a noble gas mixture in a closed Brayton cycle, and another into the use of planetary regolith as a reflector, reducing neutron leakage at what would otherwise be the reactor’s end of life in vacuo, rekindling it for an extended period of time as well as providing a very easy ultimate disposal solution, replacing the control drums with rods. It was determined that there are no insurmountable obstacles to performance in either mode.

Two metasomatic events recorded by noble gas characteristics in the Finero mantle wedge: Extreme fractionation (He, Ar) and seawater penetration into the mantle deformation zone

Here, we report that the Finero phlogopite peridotite massif, southern Italy, a sliver of the former subcontinental lithospheric mantle (SCLM), experienced two stages of fluid/melt percolation, which had different origins and scales in the mantle wedge based on noble gas analysis and the deformation structure. In the field investigation, we found a mylonite zone several tens of meters wide in the massif, inferred to have been caused by deformation in the mantle. Systematic differences in noble gas compositions between samples from inside and outside the mylonite zone reflect two stages of fluid/melt infiltration. In the first event, the fluid/melt with a noble gas mixture of seawater, radiogenic, and mantle components penetrated the Finero SCLM. It likely occurred simultaneously with the famous metasomatism that crystallized phlogopite and amphibole throughout the massif. This first event produced a 4He/40Ar ratio much higher than those of the convecting mantle and crustal components, probably during metasomatism by hydrous melt derived from the slab in the mantle wedge. The second event was probably synchronous with the development of mylonitization and locally supplied seawater-rich components. The 40Ar/36Ar ratios tend to be atmospheric as mylonitization progresses. Our results provide two insights: (i) the first demonstration of the formation of extremely high He/Ar ratios during mantle metasomatism of natural samples and (ii) differences in the deformation structure affecting the noble gas composition and distribution in the SCLM. Regarding (i), the elemental fractionation can be attributed to two factors: one is the difference in the solubility between noble gas elements in particular minerals in the slab, and the other is the difference in the diffusion coefficients of He and Ar. Our results imply that the recycling of volatiles within subduction zones is significantly influenced by the thermal structures of slabs. This is because these thermal structures control the stability of hydrous minerals on the slabs, temperature conditions, and potentially the efficiency of diffusion in mantle wedges.

Ab initio modelling of transport phenomena in multi-component mixtures of rarefied gases

The direct simulation Monte Carlo method based on ab initio potentials is applied to model transport phenomena in binary, ternary and quaternary mixtures of noble gases. To this end, the Couette and Fourier problems are solved over the whole range of the rarefaction parameter spanning the near free-molecular, transitional, and slip flow regimes. Moreover, analytical solutions are obtained in the limits of the free-molecular and continuous medium regimes of flow. As a result, the shear stress, heat flux through multi-component mixtures, distributions of velocity, temperature, and mole fractions of each species are calculated as a function of the gas rarefaction. An analysis of these data points out the properties which are strongly affected by the chemical composition. It is found that the largest deviations of characteristics of mixtures from those of a single gas are observed for the binary mixture of helium and krypton, while their deviations for the ternary and quaternary mixtures are smaller. A temperature variation in a mixture leads to non-uniform distributions of chemical composition due to the thermal diffusion phenomenon. Such redistributions are analyzed in both problems and their effect on the heat and momentum transfer is evaluated. The reported results can be used to evaluate the main factors determining transport phenomena in practical applications such as vacuum systems, microfluidics, gas separation technology, space research etc.

Simultaneous observation of noble gases and highly charged ions in an electron beam ion trap for accurate wavelength calibration of optical transitions

Spectral lines of buffer noble gases injected into an electron beam ion trap (EBIT) have recently been used as a reference to aid accurate determination of the wavelengths of optical transitions of highly charged ions (HCIs). Simultaneous observation of emission lines of HCIs along with those of neutral atoms or singly charged ions represents a reliable method for wavelength calibration that suppresses systematic uncertainties. Here, we present visible and infrared emission spectra of buffer Ne and Ar gases in an EBIT and briefly review the buffer gas calibration method. The experimental conditions required for implementing the calibration method are discussed by investigating the dependence of the emission spectra of mixtures of HCIs and noble gases on electron beam’s parameters and gas pressure.

Separation of Xenon from Noble Gas Mixtures of Argon, Krypton, and Xenon Using Gas Hydrate Technology

Separation of Xenon from Noble Gas Mixtures of Argon, Krypton, and Xenon Using Gas Hydrate Technology

Revised Enskog theory for Mie fluids: Prediction of diffusion coefficients, thermal diffusion coefficients, viscosities, and thermal conductivities.

Since the 1920s, the Enskog solutions to the Boltzmann equation have provided a route to predicting the transport properties of dilute gas mixtures. At higher densities, predictions have been limited to gases of hard spheres. In this work, we present a revised Enskog theory for multicomponent mixtures of Mie fluids, where the Barker-Henderson perturbation theory is used to calculate the radial distribution function at contact. With parameters of the Mie-potentials regressed to equilibrium properties, the theory is fully predictive for transport properties. The presented framework offers a link between the Mie potential and transport properties at elevated densities, giving accurate predictions for real fluids. For mixtures of noble gases, diffusion coefficients from experiments are reproduced within ±4%. For hydrogen, the predicted self-diffusion coefficient is within 10% of experimental data up to 200 MPa and at temperatures above 171K. Binary diffusion coefficients of the CO2/CH4 mixture from simulations are reproduced within 20% at pressures up to 14.7 MPa. Except for xenon in the vicinity of the critical point, the thermal conductivity of noble gases and their mixtures is reproduced within 10% of the experimental data. For other molecules than noble gases, the temperature dependence of the thermal conductivity is under-predicted, while the density dependence appears to be correctly predicted. Predictions of the viscosity are within ±10% of the experimental data for methane, nitrogen, and argon up to 300bar, for temperatures ranging from 233 to 523K. At pressures up to 500bar and temperatures from 200 to 800K, the predictions are within ±15% of the most accurate correlation for the viscosity of air. Comparing the theory to an extensive set of measurements of thermal diffusion ratios, we find that 49% of the model predictions are within ±20% of the reported measurements. The predicted thermal diffusion factor differs by less than 15% from the simulation results of Lennard-Jones mixtures, even at densities well exceeding the critical density.

A water cooled, high power, dielectric barrier discharge reactor for CO2 plasma dissociation and valorization studies

Aiming at the energy efficient use and valorization of carbon dioxide in the framework of decarbonization studies and hydrogen research, a novel dielectric barrier discharge (DBD) reactor has been designed, constructed and developed. This test rig with water cooled electrodes is capable of a plasma power tunable in a wide range from 20W to 2 kW per unit. The reactor was designed to be ready for catalysts and membrane integration aiming at a broad range plasma conditions and processes, including low to moderate high pressures (0.05–2 bar). In this paper, preliminary studies on the highly endothermic dissociation of CO2, into O2 and CO, in a pure, inert, and noble gas mixture flow are presented. These initial experiments were performed in a geometry with a 3 mm plasma gap in a chamber volume of 40cm3, where the process pressure was varied from few 200 mbar to 1 bar, using pure CO2, and diluted in N2. Initial results confirmed the well-known trade-off between conversion rate (up to 60%) and energy efficiency (up to 35%) into the dissociation products, as measured downstream of the reactor system. Improving conversion rate, energy efficiency and the trade-off curve can be further accomplished by tuning the plasma operating parameters (e.g. the gas flow and system geometry). It was found that the combination of a high-power, water-cooled plasma reactor, together with electronic and waveform diagnostic, optical emission and mass spectroscopies provides a convenient experimental framework for studies on the chemical storage of fast electric power transients and surges.

Distributions of Polydisperse Dust Grains in Noble Gas Mixtures

Distributions of Polydisperse Dust Grains in Noble Gas Mixtures

Direct simulation Monte Carlo method based on ab initio potential: Recovery of transport coefficients of multi-component mixtures of noble gases

The modeling of intermolecular collisions is the hardest and most time consuming part of the direct simulation Monte Carlo (DSMC) method. In order to reduce the computational cost of such modeling, lookup tables of deflection angle are calculated in the frame of quantum or classical theory of scattering. In the present work, the lookup tables for the noble gases, including helium-3, helium-4, neon, argon, krypton, and xenon, are calculated and provided in the supplementary material. The lookup tables for all possible mixtures of helium-4, neon, argon, and krypton are also provided. It is shown that the glancing collisions can be neglected reducing the computational cost without loss of numerical accuracy. Then, the lookup tables were revalidated via a recovery of the transport coefficients of multi-component mixtures, namely, viscosity, thermal conductivity, diffusion, and thermal diffusion. It is shown that the obtained tables recover the transport coefficients in a wide range of the temperature within the numerical error of the DSMC method.

Spectroscopy of high-pressure rubidium–noble-gas mixtures

Spectroscopy of alkali-metal--buffer-gas mixtures at high pressures from single-digit to several hundred bars in the regime of substantial collisional broadening is relevant in a wide range of fields, ranging from collisional redistribution cooling to laboratory astrophysics. Here we report on spectroscopic measurements of dense rubidium--noble-gas mixtures recorded in a pressure cell equipped with soldered sapphire optical viewports, which allows for the controlled realization of extreme conditions of high temperature and high pressure in a table top laboratory experiment. In the gas cell, we have recorded absorption and emission spectra of rubidium subject to 188 bars of helium buffer-gas pressure at 548-K temperature. The spectra to good accuracy follow a Boltzmann-type Kennard-Stepanov frequency scaling of the ratio of absorption and emission spectral profiles. Further, the long optical path length in the cell allowed us to both record spectra of rubidium-argon mixtures at moderate temperatures and high pressures and observe redistributional laser cooling in this system.

Models used for permeability predictions of nanoporous materials revisited for H2/CH4 and H2/CO2 mixtures

High throughput screening of new generation nanoporous materials, e.g. metal organic frameworks (MOFs) and zeolitic imidazolate frameworks (ZIFs), for gas mixture separations have produced large amounts of data. Reported gas permeabilities have been mainly calculated using a simplified (approximate) approach. Permeability predictions of an alternative method (new method), proposed previously by our group, have shown to significantly improve the predictions of the approximate method for noble gas mixtures. Permeabilities calculated using Onsager coefficients, detailed method, are accepted as correct answers, however constructing Onsager coefficient matrix is computationally cumbersome and not feasible especially for the high throughput screening purposes. In this work, we question in what accuracy the approximate and new methods can predict gas permeabilities and permeation selectivities of gases with respect to the detailed method. We perform Grand Canonical Monte Carlo and Molecular Dynamics simulations for six ZIFs, namely ZIF-6, ZIF-10, ZIF-60, ZIF-69, ZIF-79, and ZIF-81. Permeabilities of H2/CH4 and H2/CO2 mixtures are selected as cases, since the dominating interactions of the gas species with the pores of the membranes are different. For the H2/CH4 mixture, approximate and new methods predict H2 permeability results of the detailed method sufficiently good. CH4 permeabilities of the approximate method reveal deviations from the correct answers, yet the new method improves the predictions of the approximate approach. In the case of H2/CO2 mixture, H2 permeabilities calculated by the approximate approach are in agreement with the detailed method, except for ZIF-60 and ZIF-79. For the CO2 permeability, approximate and new methods give significant deviations from the results calculated using the detailed method.

Novel Time-of-Flight Residual Gas Analyzer (TOF-RGA) for in situ Real-time Process Monitoring

Sensitive gas analyses, in particular in industrial processes, are nowadays performed either via spectroscopy or using quadrupole mass spectrometers; the first method provides a fast but indirect measurement, whereas the second provides in situ measurements of only one species at a time. In this article, we present a novel time-of-flight residual gas analyzer (TOF-RGA) built by the Swiss company Spacetek Technology AG, and show the results of measurements such as the characterization of the FC5311 calibration compound, the detection of naturally abundant noble gases in air, the measurement of a noble gas mixture in the ultra-high vacuum facilities of CERN, and measurements acquired in a X-ray Photoelectron Spectroscopy facility in Germany, to demonstrate the capability of this new TOF-RGA to compete with already existing techniques for the monitoring of the composition of gases in real time (10 times per second), at high resolution (m/?m = 1 200 measured at m/z 132), and with a high sensitivity at ppb level.

Aeroseparation of gas mixture during supersonic outflow in vacuumed reservoir with skimmer

Present paper presents the theoretical study of aeroseparation effect. Simulation is performed using the event-driven molecular dynamics (EDMD) method. Considered problem is a noble gas mixture outflow into vacuum through convergent–divergent micronozzle. In present paper two practical aspects were studied: (1) enhancement of binary mixture separation by adding third light carrier component; (2) influence of position, orientation and shape of flow separator (skimmer) located in the outlet (vacuumed) reservoir on separation efficiency. It was shown that, despite separation results of actual skimmers differ from predictions of virtual ones located in the same place, those predictions can still be used to evaluate the performance of real skimmers. It is also shown that position, orientation and shape of skimmer can influence separation performance but can be chosen in a way to minimize the deviation from predictions made using virtual skimmers.

Growth and treatment of hydrogenated amorphous carbon nanoparticles in a low‐pressure plasma

AbstractA parallel‐plate, low‐pressure plasma for fundamental nanodusty plasma research is used to grow hydrogenated amorphous carbon nanoparticles using an argon‐acetylene gas mixture. The particles stay confined in the volume of the argon plasma after turning off the gas flow and the effects of prolonged treatment with noble gas (Ar) and reactive gas mixtures (Ar/, Ar/, or Ar/) are investigated using in situ infrared absorption spectroscopy. Additionally, ex situ scanning electron microscopy imaging of extracted nanoparticles is used to analyze their size and surface morphology. In 45 min of argon treatment, a size increase of about 50% is seen together with a decrease in bonds and an increase in C═O bonds, indicating incorporation of oxygen from gas impurities into the particle material. All reactive gas mixtures lead to the expected etching of the nanoparticle material without any exchange reactions between gas‐phase deuterium and surface‐bonded hydrogen atoms. These results are important for in situ studies of nanoparticle clouds such as dust density wave diagnostics, but they also provide fundamental information about plasma interaction with a‐C:H material.

Gas discharge sustained by powerful THz and sub-THz gyrotrons in the mixtures of noble gases with nitrogen

The discharge propagation velocity towards electromagnetic radiation of sub-THz and THz bands was measured in various noble gases (argon, krypton) mixtures with nitrogen in the wide pressure range (0.1 – 2 atm) for various field intensities into the focal spot (from dozen of kW/cm2 to several MW/cm2). In the experimental setups two different gyrotrons were used. In case of 263 GHz it was CW gyrotron with power up 1 kW, in case of 670 GHz – pulsed gyrotron (20 μs) with power up to 40 kW. In both cases the focusing system provided the size of the focal spot of (2–3)·λ, which ensured the investigation of discharge phenomena in a wide pressure range (0.1 – 2 atm). In both cases discharge appeared in the focal spot spread towards heating radiation into the area with the field intensity much less than one in the focal spot. Velocity of the discharge propagation was measured by using photos from speed camera with small exposure (down to 20 ns) and streak camera. It was demonstrated that discharge velocity increase along with pressure decrease and drops with electric field decrease as it moves away from the focal spot.

Optical Radiation from the Sputtered Species under Excitation of Ternary Mixtures of Noble Gases by the 6Li(n,α)3H Nuclear Reaction Products

The present paper examines the luminescence of ternary Ar-Kr-Xe and Ne-Ar-Kr mixtures of noble gases in the spectral range from 300 to 970 nm, excited by the 6Li(n,α)3H nuclear reaction products in the core of a nuclear reactor. A thin layer of lithium applied on the walls of the experimental device, stabilized in the matrix of the capillary-porous structure, serves as a source of gas excitation. During in-pile tests, conducted at the IVG.1M research reactor, thermal neutrons interact via the 6Li(n,α)3H reaction, and the emergent alpha particles with a kinetic energy of 2.05 MeV and tritium ions with a kinetic energy of 2.73 MeV excite gaseous medium. The study was carried out in a wide temperature range. The temperature dependence of the intensity of the emission of the atoms of noble gases and alkali metals, heteronuclear ionic molecules of noble gases were studied. The obtained values of the activation energy of the emission process 1.58 eV for lithium and 0.72 eV for potassium agree well with the known values of evaporation energy. Excitation of alkali metals atoms occurs consequently of the Penning process of alkali metals atoms on noble gas atoms in the 1s-states and further ion-molecular reactions.

Properties of CaP coatings produced by reactive RF-magnetron sputtering in a mixture of nitrogen and noble gases

Calcium phosphate coatings are widely used to increase the biocompatibility of metal implants. Nowadays various dopants in the structure of calcium phosphate coatings are actively studied. Nitric oxygen is known as an essential mediator of blood flow. Its presence in the structure of calcium phosphate coating can stimulate angiogenesis and promote osseointegration of the implant. This article is dedicated to the study of morphology and physico-chemical properties of the calcium phosphate coatings formed via reactive RF-$$$magnetron sputtering of hydroxyapatite in the mixture of noble gases (Ne, Ar and Xe) and nitrogen with the same volume concentrations. There is a decrease in grain size and an increase in roughness with the growth of the atomic mass of noble gas in the mixture with nitrogen. The Ca/P ratio also decreases with the increase in the atomic mass of noble gas. Coatings formed in Ne + N2 and Xe + N2 gas mixtures are characterized by higher surface free energy in comparison with the ones formed in Ar + N2. It allows us to suggest that the coatings formed in Ne + N2 and Xe + N2 are more biocompatible than ones formed in Ar + N2, however, additional studies are needed to prove it.