Dissolved noble gases have been recognized for decades as ideal artificial hydro(geo)logical tracers, as they are chemically inert, invisible, and non-toxic. However, their widespread adoption has historically been limited by the difficulty of tracer injection, sampling, and analysis procedures. Developments in portable, high-resolution dissolved gas measurement technology over the last two decades have rekindled interest in the use of gas tracer methods for routine hydrogeological investigations, such as well-to-well tracer tests, intra-well tests, or studies of river infiltration towards alluvial aquifers. The application of gases in aqueous environments still poses unique challenges compared to other tracer methods, as potential exsolution and degassing need to be accounted for, and, if possible, avoided during tracer injection. Here, we present a simple and efficient methodology that addresses these challenges and allows the efficient, on-site preparation and injection of highly concentrated tracer solutions with controlled dissolved gas concentrations. We applied the method in a large drinking water wellfield and performed well-to-well tracer tests in an unconfined aquifer using helium-4 (4He), neon-20 (20Ne) and krypton-84 (84Kr). Known tracer quantities were injected together with fluorescent dyes into an observation well upgradient of a pumping well. Gas tracer breakthrough was monitored in the pumping well with a portable mass spectrometer. Breakthrough curves of 4He and 84Kr compared favorably with fluorescent dye tracers, and enabled reliable estimates of groundwater flow velocities, travel times, and tracer recovery. These findings illustrate how noble gases can substitute or complement other artificial tracer methods, even in large-scale settings. The methodology can be extended to other gases (e.g., neon-22, xenon isotopes, light hydrocarbons), significantly expanding the range of artificial tracers available for routine hydrogeological investigations.

Noble gases xenon (Xe) and argon (Ar) emerge as promising therapeutic agents. Extensive studies have validated their efficacy across various models of organ injury, positioning them as novel candidates for clinical translation in critical care and perioperative medicine. Xe and Ar exert protective effects through multiple mechanisms, including activation of hypoxia-inducible factor-1 (HIF-1) pathway, inhibition of regulated cell death pathways, such as apoptosis, necroptosis, ferroptosis, and pyroptosis, and suppression of pro-inflammatory signaling. By modulating these key signaling pathways, Xe and Ar have been shown to improve outcomes in neurological, cardiac, renal, and hepatic systems across diverse models of ischemia-reperfusion injury, traumatic brain injury, and systemic inflammation. Clinically, Xe has shown efficacy in anesthesia, neonatal neuroprotection, and cardiac arrest management. Ar, with greater availability and lower costs, holds promise for broader clinical use but remains in the early stage of translational research. Xe and Ar represent novel biologically active gases with the potential to provide promising therapies in perioperative and clinical care medicine. Overcoming current limitations, such as a lack of standardized delivery systems and optimized dosing strategies, is key to uncovering their clinical application.

Force fields based on the Mie (λ, 6) potential, combined with theoretical methods and molecular simulations, offer a promising framework for predicting the thermophysical properties of fluids. Despite this potential, the availability of reliable combining rules for unlike interaction parameters in mixtures remains limited, thereby constraining the broader application of Mie (λ, 6)-based force fields. In this study, a new set of combining rules for the Mie (λ, 6) potential is proposed, derived by using a distortion model for the repulsive interaction and a geometric mean approximation for the attractive interaction, combined with first-order mathematical approximations. The capability of the new combining rules was first evaluated for noble gas pairs modeled with the Lennard-Jones potential, a specific case of Mie (λ, 6) potential with λ = 12, for which experimentally derived data on unlike interaction parameters are available. The results showed noticeably better agreement with experimentally derived values than those obtained using the two commonly used combining rules. Further assessment was carried out through the evaluation of Henry's law constants, phase diagrams, and excess molar volumes, which are highly sensitive to cross-interactions, for various binary mixtures modeled using the Mie chain coarse-grained force field, obtained from NVT-GEMC, NPT-GEMC, and NPT-MC simulations, respectively. For mixtures with similar Mie (λ, 6) potential parameters for the components, all of the combining rules, including the new ones, yielded comparable predictions. In contrast, for asymmetric systems with significant force field parameter disparities, the new rules yielded substantially improved accuracy relative to experimental data for all considered thermodynamic properties, whereas the commonly used combining rules exhibited poor performance with markedly larger deviations. These findings highlight the improved robustness and broader applicability of the proposed combining rules for extending Mie (λ, 6)-based force fields to complex fluid mixtures.

The separation of xenon (Xe) and krypton (Kr) is very important for industrial applications and environmental protection. However, the lack of permanent dipoles, low polarizabilities arising from their spherical nature, and similar kinetic diameters make their efficient separation by porous adsorbents exceptionally challenging. This study explored the effects of pore geometry and surface polarity of a series of aluminum-based metal-organic frameworks (CAU-10-H, MIL-160, KMF-1, CAU-23) on Xe/Kr separation performance using a heteroatom engineering strategy. These MOFs are composed of AlO6 clusters and bent dicarboxylic acid linkers, enabling us to systematically investigate the effects of pore size and heteroatom types on Xe/Kr separation performance. Among them, MIL-160 has a polar linker based on furan, showing the best balance performance. At 298 K and 1.0 bar, the uptake of Xe is 4.12 mmol g-1 and the IAST selectivity is 7.63 for a Xe/Kr (20/80) mixture. The practical performance was verified by dynamic breakthrough experiments, which yielded a long Xe breakthrough time of 42.9 min g-1. Grand Canonical Monte Carlo (GCMC) simulations and first-principles density functional theory (DFT) calculations revealed that the enhanced performance originates from cooperative confinement and polarization effects, with the furanyl oxygen atoms providing optimal Xe-binding sites. This work clarifies the structure-property relationships governing Xe/Kr separation in aluminum-based MOFs (Al-MOFs), highlighting the potential of heteroatom engineering for designing efficient noble gas adsorbents.

Abstract The ~1.27 Ga Mackenzie large igneous province is one of the largest preserved singular magmatic events in Earth history. It also hosts one of the most unusual glass flows (CM19) recognized, within the September Creek member of the Coppermine River flood basalt succession. The glass flow is dominantly composed of dacite glass (71 ±2 modal%) containing up to 15 wt.% H2O, with plagioclase (~15 modal%; An56-78), Mg-rich pyroxene (~12 modal%; orthopyroxene = En75Wo3, clinopyroxene = En46Wo37) and Cr-spinel (0.2 to 0.4 modal%), along with <0.1 modal% highly siderophile element-rich sulfides. This “split personality” mineral assemblage indicates a mixed heritage for the glass flow. Moderate weathering of the glass and the presence of a non-equilibrium mineral assemblage probably accounts for indeterminable plateau ages from 40Ar-39Ar measurements. The glass does not preserve coherent magnetic paleointensity. The CM19 glass flow is a product of magma and crystal mixing, with the Cr-spinel and sulfide representing materials from a mantle-derived mafic melt source and the dacite glass having trace element, noble gas and halogen abundances and ratios (e.g., Br/Cl = 2.7 × 10-2) consistent with formation from upper continental crust materials. These results are consistent with the glass flow representing the extrusive manifestation of Cr-spinel seam formation in the consanguineous Muskox intrusion that underlies the Coppermine River flood basalt succession. A further implication is that Muskox Cr-spinel seams resulted from crustal assimilation and magma mixing. This process may have occurred during interaction of a crustal melt lens above the existing mafic cumulates of the Muskox intrusion, where Cr-spinel crystallization was triggered by mixing of mafic and silicic melts. The Cr-spinel either descended to the floor of the melt lens as slurries or formed in situ, and some of this material, and associated mafic silicate minerals, were incorporated into the magmas that ultimately formed the glass flow. With models arguing for in situ crystallization of Cr-spinel seams in other layered intrusive complexes, our results show that transient melt lenses within crystal mushes that go on to form layered intrusions, rather than completely molten magma chambers, were important environments for producing Cr- and platinum-group element enrichment.

Chalconium cations are powerful Lewis acids containing a hypervalent chalcogen atom. They are utilized in the field of organocatalysis and crystal engineering. In the current work, the electrophilic force of these species has been examined. The [SF3]+ chalconium cation was selected for the current study, and its complexes with noble gas atoms were modeled. In this manner, a set of three [SF3(NCCH3)2Ng]+ and [SF3(Ng)2][SbF6] complexes (Ng = Ar, Kr, Xe) were computed. The Ng atom was substituted in place of the anion (in [SF3(NCCH3)2Ng]+) or neutral ligands (in [SF3(Ng)2][SbF6]). The computations were performed using a polarizable continuum model. The obtained tetramers were stable, true minima, characterized by weak interaction energies between -2 and -1 kcal mol-1. When the [SbF4]- anion was substituted by a noble gas atom, the interaction energy was significantly weakened compared to the full [SF3(NCCH3)2][SbF6] system, and its nature changed from electrostatic to dispersive. A comparable scenario was observed when the NCCH3 ligands were replaced with two noble gas atoms.

Identifying phytoremediation potential of ten tobacco varieties: Cadmium-induced hormesis, bioaccumulation and translocation.

Source and accumulation of helium in the Dongsheng gas Field, Ordos Basin, China: Insights from noble gas isotopes

Gas Proportional Scintillation Counters (GPSCs) are noble gas detectors in which the primary ionization charge generated by radiation interactions is amplified via electroluminescence (EL) in the gas. Under an external electric field, the primary ionization electrons drift into a region where the field exceeds the gas scintillation threshold. Compared to charge amplification via electron avalanches, EL amplification provides higher gain with improved signal-to-noise ratio, no space charge effects, and better immunity to radiofrequency noise and electrical discharges. GPSCs have been used in applications such as x-ray fluorescence analysis and x- and γ-ray astrophysics. Their high resistance to radiation damage, wide operational temperature range, simple yet flexible design, and large detection area capability are notable advantages. However, the solid angle subtended by the photosensor varies with the EL emission position, causing the detected signal to depend on the radiation interaction location. This limits the size of the detector's radiation window relative to the photosensor. To overcome these limitations, we recently proposed a novel and simple GPSC design that ensures a constant solid angle across the scintillation region. In this configuration, a single annular anode electrode, centered on the photosensor axis, defines a localized scintillation region near its surface. As a result, the entire region maintains a fixed solid angle with respect to the photosensor, making the EL signal independent of the interaction position. This design enables a large window-to-photosensor size ratio while maintaining uniform response. Previously, we developed a comprehensive simulation tool incorporating radiation absorption, electron drift, EL emission and light detection, which was validated against an annular-anode GPSC prototype. In this work, we use this simulation tool to explore the optimal geometrical parameters of the annular anode GPSC, aiming to balance energy resolution and the different parameters, mamely the detector window-to-photosensor radius ratio.

Abstract The abundance of elements in the interstellar medium is a key facet for many fields of astrophysical study. In the soft X-ray spectra, absorption by interstellar gas can result in deep absorption features that affect continuum measurements. In this paper, we focus on measuring the abundance of interstellar iron and neon from the column densities observed in soft spectra from XMM-Newton and Chandra for various low-mass X-ray binaries, which allows for a direct probe of elemental abundances. As a noble gas, neon will not deplete into solid form, thus providing a benchmark with abundances determined via UV spectroscopy. We find that, when assuming Fe is 90% depleted into grains, [Fe/Ne] = −0.523 ± 0.025, [Fe/H]+12 = 7.482 ± 0.016, and [Ne/H]+12 = 8.012 ± 0.022, which are the tightest observational constraints on these abundances to date, while being consistent with the literature, which uses protosolar abundances. We also test how depletion into solid grains and scattering affect the results. The choice of depletion fraction can affect the abundance measurement by roughly 5%, and the inclusion of a scattering component can affect abundance measurements by ∼1%–7%.

Pressure-responsive, or breathing, metal-organic frameworks (MOFs) that exhibit step-shaped gas adsorption isotherm behavior are highly promising materials for gas capture and separations. Utilizing porous materials to separate the noble gases Xe and Kr has been recognized as an energy-saving and cost-effective alternative to the traditional separation method of cryogenic distillation. Herein, a series of isoreticular flexible benzimidazolate-based (bim) zeolitic imidazolate frameworks (ZIFs) of the form M(bim)2 (M = Zn (ZIF-7), Co (ZIF-9), and Cd (CdIF-13)) were examined to elucidate the effects of metal identity on the pressure-responsive-phase changes during Xe and Kr gas adsorption. Phase transition pressure threshold positions, prestep gas uptakes, and step uptake capacities were compared across multiple temperatures. The well studied Zn analog ZIF-7 was used as the baseline material for comparison and determination of metal substitution effects. Compared to ZIF-7, metal substitution to form ZIF-9 and CdIF-13 resulted in substantially improved Xe adsorption performance. Notably, metal identity dramatically influenced prestep adsorption and threshold adsorption pressure, decreasing the prestep adsorption and increasing the threshold pressure needed to induce the phase transition. Remarkably, CdIF-13 showed negligible prestep adsorption of Xe and a Xe capacity of more than 4 mmol/g at 1 bar and 193 K. Comparison of the estimated usable capacities resulted in a ranking of CdIF-13 > ZIF-9 > ZIF-7. Lastly, the Xe adsorption capacity and Xe/Kr selectivity are compared to other promising MOFs for noble gas capture.

Interest in interstellar noble gas chemistry has been stimulated by the recent detection of ArH+ and HeH+ in a variety of astrophysical environments ranging from diffuse clouds to supernova remnants. In this context, it seems timely to explore or revisit chemical reactions involving noble gas ions, such reactions being an efficient way to form noble gas bearing molecules in the interstellar medium. The reaction of Ar+ ions with methane, CH4, and ethylene, C2H4, at low temperatures, i.e., 24.1 and 71.6K, was investigated in the laboratory with the help of a dedicated instrument combining a uniform supersonic flow reactor with a mass selective ion source. Computational flow dynamics and ion trajectory simulations were conducted to assess the thermalization of the ions in the flow. Ab initio and transition state theory calculations were employed to complement, at a microphysical scale, the interpretations derived from the macroscopic measurements of the Ar+ + CH4 and Ar+ + C2H4 reactions. The branching between the products is reasonably well explained by theoretical calculations.

We introduce circular under-threshold RABBITT (cuRABBITT) as a new interferometric method to probe discrete electronic excitations in atoms with attosecond resolution. By combining circularly polarized attosecond pulses with broadband ("rainbow") spectral analysis, we directly access two-photon ionization amplitudes and their relative phases. Time-dependent Schrödinger simulations, supported by Green's function theory, reveal strong resonances in helium and argon and a Cooper-like minimum in xenon. These results demonstrate that cuRABBITT provides continuous spectral mapping of bound-state resonances and extends Fano's propensity rule into the under-threshold regime. Our Letter establishes cuRABBITT as a powerful attosecond metrology technique, opening the way to polarization-resolved studies of resonant dynamics in atoms and molecules.

The interactions of noble gases (Ng = He, Ne, Ar, Kr) with highly electron-deficient main-group fragments are systematically investigated by using high-level CCSD and CCSD(T) calculations. A broad set of electrophilic acceptors is considered, spanning six-electron (O, S, F+, Cl+, Br+, OH+, SH+, NH2+), four-electron (BF2+, AlF2+), and two-electron (BeF+, MgF+) centers. Optimized geometries, interaction energies, and electronic descriptors reveal a continuous evolution of Ng binding behavior across the series from weak polarization-dominated interactions for He and Ne, to donor-acceptor bonding for Ar, and to strongly covalent-like coordination in Kr complexes. The analysis, supported by natural bond orbital (NBO), quantum theory of atoms in molecules (QTAIM), symmetry-adapted perturbation theory (SAPT), and molecular electrostatic potential (MESP) descriptors, demonstrates that the strength and multiplicity of Ng binding are governed primarily by the electrophilicity and valence-electron deficiency of the acceptor fragment with noble-gas polarizability modulating the interaction strength. Within this context, a unified 2e-4e-6e valence-electron framework is employed as a descriptive tool to rationalize why six-electron centers preferentially bind one Ng atom, four-electron centers stabilize two Ng atoms, and highly electron-deficient two-electron centers accommodate three Ng atoms. Among the multi-noble-gas complexes examined, BeF+ and MgF+ are found to stabilize tri-noble-gas adducts across the He-Kr series, with Kr3BeF+ exhibiting the strongest overall binding. Trihelium coordination to BeF+, with interaction energies of several kcal mol-1 per He atom, highlights the remarkable stabilization that can arise in extreme electron-deficient environments. Overall, the results provide a unified and internally consistent framework for organizing mono-, di-, and tri-noble-gas binding motifs across the noble-gas series, clarifying the electronic factors that govern noble-gas coordination in highly electrophilic chemical regimes.

Under hyperbaric conditions, the elevated concentrations of the ambient gases may elicit a range of behavioral responses in various animals. A substantial portion of these behaviors represents changes in cognitive states that are yet poorly understood. One notable example is general anesthesia. The behavioral effect of several gases under hyperbaric conditions in general anesthesia, or narcosis, has been a long-lasting scientific inquiry, despite the overwhelmingly frequent use of the drugs in medicine. Xenon, classified as a noble gas and an anesthetic agent, is regarded as one of the safest options for general anesthesia in humans. However, it does not anesthetize flies under normobaric conditions. Here, we established a simple experimental setup that increases the ambient pressure up to ~3 atm and allows the study of xenon anesthesia in one of the most popular model organisms, Drosophila melanogaster. This experimental setup further facilitates the study of other gases and their effect under hyperbaric conditions.

ABSTRACT Thermodynamic properties of a fluid governed by the Carra-Konowalow potential were calculated using Monte Carlo simulations. The study characterises both the single-phase region and vapour-liquid equilibrium. From the simulation data, analytical expressions for the critical point parameters, saturated vapour pressure, coexistence densities, and a single-phase equation of state were derived. The behaviour of the Zeno line was analysed. Parameters for the potential were fitted to some real substances, demonstrating good agreement with the properties of noble gases.

The geodynamic mechanisms underlying the development of the southeastern margin of the Tibetan Plateau (SETP) remain unclear. Several models of deformation have been proposed and have primarily been assessed by GPS and geophysical data. In recent years, an increasing amount of geochemical data pertaining to geothermal gases in the vicinity of the SETP has been collected. Upon examining and analyzing the He inventory and its spatial variation patterns, we determined that the transportation mode for deep volatiles in the SETP corroborates the existence of crustal flow. Gas samples from the Sichuan basin and the middle section of the Anninghe-Xiaojiang fault system exhibit typical crustal He degassing (RC/RA < 0.1 RA, where RA is atmospheric [air] 3He/4He, and RC is air-corrected 3He/4He), whereas mantle-derived fluids are unequivocally detected in the remainder of the SETP (RC/RA > 0.1 RA). This process involves the lateral movement of crustal flows, which convey mantle noble gas signals from the Tibetan Plateau to the Yangtze craton. The significant mantle signal in the bending section of the Xianshuihe fault system is attributed to the swift migration of mantle fluids through the crust, demonstrating that crustal movement can exert additional impacts on vertical movement of mantle fluids. Our results are supportive of the existence of crustal flow, supporting the hypothesis that the uplift and expansion of the SETP are relevant to the crustal flows. At the same time, our study also emphasizes that the influence of crustal movement on deep fluid migration cannot be ignored.

We develop a semi-analytic theory for describing nonadiabatic bound-bound, free-bound, bound-free, and free-free photoprocesses in heteronuclear ions in the regime of the superlinear potential energy curve crossing. It extends the previous semiclassical method for calculating the absorption and emission spectra of strongly and moderately bound diatomic species based on the linear curve crossing model and can be used for molecules and ions with small dissociation energies, D0 ≲ kBT. The use of quasicontinuum approximation for rovibrational levels allows us to give a unified description of the integral contributions of the discrete and continuous spectra of the molecular species with linear and superlinear crossings to the effective cross sections and rate coefficients of the radiative processes in the systems studied. Specific calculations were performed for the excimer-like NeXe+ ion (DeNeXe+=37.3 meV). Potential energy curves and dipole transition matrix elements are evaluated using abinitio multi-reference calculations with a perturbative description of relativistic effects. In contrast to ArXe+ and KrXe+ ions studied previously, the main contributions to the absorption spectra of NeXe+ are due to bound-bound transitions and photoassociation. The emission spectra at room temperatures are determined predominantly by the bound-bound transitions, while at temperatures above 450K, the most significant contribution to the radiation is made by bound-free phototransitions. Our calculations are in good agreement with the available experimental data. The results obtained are of interest for chemical physics, spectroscopy of weakly bound molecular systems, and physics of radiative processes in gases and plasmas, as well as for the kinetics of active media of excilamps and gas lasers based on noble gas mixtures.

We demonstrate that classical density functional theory (DFT) based on the PC-SAFT equation of state is a fast, accurate, and predictive model to predict multicomponent adsorption in porous materials, which is an essential step toward the design of next-generation adsorbents for relevant applications. Using GPU acceleration, adsorption isotherms and adsorption enthalpies can be obtained in a matter of seconds, which is several orders of magnitude faster than grand canonical Monte Carlo (GCMC) simulations. Using metal-organic frameworks as adsorbents and non- or weakly polar molecules as adsorbates, we validate our approach by performing GCMC simulations for binary, ternary, and quaternary mixtures with practically relevant applications, such as noble gas separations (Kr/Xe, Ar/Kr/Xe), direct dry air capture (CO2/N2), hydrogen enrichment (CH4/H2, CH4/H2/N2) and adsorbed natural gas (CH4/C3H8, CH4/C2H6/C3H8, CH4/C2H6/C3H8/N2). Classical DFT reproduces loadings and adsorption enthalpies of the mixtures in close agreement with results from GCMC simulations. Thus, classical DFT expands our toolbox for studying multicomponent adsorption.

Abstract Noble gases such as argon, neon, and helium are widely used in low-temperature plasma research and applications. Owing to its lower ionization energy, argon plasma is generally expected to exhibit a higher electron density than neon or helium. Here, we report an anomalous electron density behavior in high-pressure E-mode inductively coupled plasma (ICP), where helium and neon plasmas achieve higher electron densities than argon plasma. At 220 mTorr, the electron density of helium exceeds that of argon by a factor of 2.4. It is found that, under these conditions, argon exhibits a Druyvesteyn electron energy probability function (EEPF) due to the Ramsauer effect, whereas neon and helium maintain Maxwellian distributions. This difference leads to larger collisional energy losses in argon, thereby suppressing its electron density compared to helium and neon. At low pressures or in H-mode operation, this anomalous behavior is absent, and the conventional trend is recovered. These findings highlight the critical role of electron energy distributions in determining plasma density in ICP discharges, and they provide new insight into the use of noble gases for plasma source design under high-pressure conditions.