Noble Gas Research Articles

Determination of the polarization of Xe nuclear spin using transverse and longitudinal Rb in-situ magnetometers in NMR co-magnetometers

NMR co-magnetometers, as novel atomic sensors, can measure the angular velocity information in inertial measurements by detecting the spin precession of Xe nuclei. The Xe polarization plays a crucial role in the sensing unit of co-magnetometers, as it enhances the signal-to-noise ratio (SNR) and sensitivity of NMR sensors. Here we elucidated the Rabi dynamics of Xe nuclear spin and demonstrated two methods to determine the Xe polarization based on the classical Bloch equations. By detecting the optical rotation angle signal, we acquired the amplitude and the phase variations information in two methods, respectively. The transverse magnetometer relies on the amplitude of the free induction decay (FID) signal and applies a short pulse to flip the Xe fields into the transverse plane, enabling precise measurements. On the other hand, the longitudinal magnetometer offers an intuitive approach to measuring the demodulated phase variations by capturing the repetitive flips of longitudinal Xe fields. This paper discusses the advantages and disadvantages of both proposed methods, with the aim of enhancing the accuracy and authenticity of nuclear spin polarization measurements for noble gas atoms in atomic sensors.

Insights on the Formation Conditions of Uranus and Neptune from Their Deep Elemental Compositions

This study, placed in the context of the preparation for the Uranus Orbiter Probe mission, aims to predict the bulk volatile compositions of Uranus and Neptune. Using a protoplanetary disk model, it examines the evolution of trace species through vapor and solid transport as dust and pebbles. Due to the high carbon abundance found in their envelopes, the two planets are postulated to have formed at the carbon monoxide ice line within the protosolar nebula. The time evolution of the abundances of the major volatile species at the location of the CO ice line is then calculated to derive the abundance ratios of the corresponding key elements, including the heavy noble gases, in the feeding zones of Uranus and Neptune. Supersolar metallicity in their envelopes likely results from accreting solids in these zones. Two types of solids are considered: pure condensates (Case 1) and a mixture of pure condensates and clathrates (Case 2). The model, calibrated to observed carbon enrichments, predicts deep compositions. In Case 1, argon is deeply depleted, while nitrogen, oxygen, krypton, phosphorus, sulfur, and xenon are significantly enriched relative to their protosolar abundances in the two planets. Case 2 predicts significant enrichments for all species, including argon, relative to their protosolar abundances. Consequently, Case 1 predicts near-zero Ar/Kr or Ar/Xe ratios, while Case 2 suggests that these ratios are 0.1 and 0.5–1 times their protosolar ratios, respectively. Both cases predict a bulk sulfur-to-nitrogen ratio consistent with atmospheric measurements.

Temporal Variations of 222Rn Density Distributions in the Lunar Exosphere

Because of radiogenic processes, the lunar interior is a source of rare gases like helium (4He), argon (40Ar), and radon (222Rn) that might be released continuously, or impulsively during moonquakes. The detection of radon is therefore important in the sense that it can help trace the crustal dynamics on the Moon. In this study, we will introduce a Monte Carlo–based model designed to investigate the time-dependent transient dynamics of the lunar 222Rn exosphere. Our model accounts for the background emission and transient ejection of gas molecules from the lunar surface, encompassing loss processes such as radioactive decay, photoionization, and the cold trapping in permanently shadowed regions near the poles. Additionally, it incorporates the diurnal temperature fluctuations of the lunar surface, which significantly influence the condensation duration of the radon atoms and their subsequent release near the sunrise. This model also can support future observations in missions such as Chang’E 6 or other lunar explorations.

Cosmic pears from the Havelland (Germany): Ribbeck, the twelfth recorded aubrite fall in history

AbstractIn 1889 the German poet and novelist Theodor Fontane wrote the popular literary ballad “Herr von Ribbeck auf Ribbeck im Havelland.” The Squire von Ribbeck is described as a gentle and generous person, who often gives away pears from his pear trees to children passing by and continued donating pears after his death. Now, 135 years later the rock called Ribbeck is giving us insight into processes that happened 4.5 billion years ago. The meteorite Ribbeck (official find location: 52°37′15″N, 12°45′40″E) fell January 21, 2024, and has been classified as a brecciated aubrite. This meteoroid actually entered the Earth's atmosphere at 00:32:38 UTC over Brandenburg, west of Berlin, and the corresponding fireball was recorded by professional all sky and video cameras. More than 200 pieces (two proved by radionuclide analysis to belong to this fresh fall) were recovered totaling about 1.8 kg. Long‐lived radionuclide and noble gas data are consistent with long cosmic ray exposure (55–62 Ma) and a preatmospheric radius of Ribbeck between 20 and 30 cm. The heavily brecciated aubrite consists of major (76 ± 3 vol%) coarse‐grained FeO‐free enstatite (En99.1Fs<0.04Wo0.9), with a significant abundance (15.0 ± 2.5 vol%) of albitic plagioclase (Ab95.3 An2.0Or2.7), minor forsterite (5.5 ± 1.5 vol%; Fo99.9) and 3.5 ± 1.0 vol% of opaque phases (mainly sulfides and metals) with traces of nearly FeO‐free diopside (En53.2Wo46.8) and K‐feldspar (Ab4.6Or95.4). The rock has a shock degree of S3 (U‐S3), and terrestrial weathering has affected metals and sulfides, resulting in the brownish appearance of rock pieces and the partial destruction of certain sulfides already within days after the fall. The bulk chemical data confirm the feldspar‐bearing aubritic composition. Ribbeck is closely related to the aubrite Bishopville. Ribbeck does not contain solar wind implanted gases and is a fragmental breccia. Concerning the Ti‐ and O‐isotope compositions, the data are similar to those of other aubrites. They are also similar to E chondrites and fall close to the data point for the bulk silicate Earth (BSE). Before the Ribbeck meteoroid entered Earth's atmosphere, it was observed in space as asteroid 2024 BX1. The aphelion distance of 2024 BX1's orbit lies in the innermost region of the asteroid belt, which is populated by the Hungaria family of minor planets characterized by their E/X‐type taxonomy and considered as the likely source of aubrites. The spectral comparison of an average large‐scale emission spectrum of Mercury converted into reflectance and of the Ribbeck meteorite spectrum does not show any meaningful similarities.

Calculation of electron scattering lengths on Ar, Kr, Xe, Rn and Og atoms

Abstract Focusing on the noble gases, we calculate the scattering potential using the Dirac–Coulomb Hamiltonian supplemented with a model polarization potential. We determine the scattering lengths using two methods, namely phase shifts for very small scattering energies and the shape of the wave function for zero scattering energy. We compare our theoretical electron scattering length results on Ar, Kr and Xe atoms with existing experimental and theoretical data. In turn, the results obtained for the first time for Rn and Og atoms require independent confirmation. The analysis conducted indicates that the source of the greatest uncertainty in the obtained results is the literature values of dipole polarizability. The study used the GRASP2018 computational package for bound states and the modified COWF code for continuum states.

Methodology for analyzing dose consequence using atmospheric dispersion code A2CDOSE

Abstract The experience of Fukushima brings out the importance of the emergency response plan during or after a severe nuclear power plant (NPP) accident. To deal with the accident emergency response situation, the National Atomic Research Institute (NARI) in Taiwan developed an emergent radiological dose evaluation system with the Central Weather Administration (CWA) called “A2CDOSE”. A2CDOSE can evaluate the eight-day projected dose after a nuclear accident and provide the predicted dose consequences for decision-making. Nevertheless, a source term generation method was still needed during the accident. This study chose MELCOR as the comparison target for the source term simulation issue with RASCAL. A MELCOR calculation of Maanshan NPP was built and a 5 % containment leakage was set for both MELCOR and RASCAL source term calculations. It seems the calculations of noble gases were consistent between MELCOR and RASCAL. However, the Cs-137 and I-131 calculated by MELCOR were twice compared to the RASCAL results, which may have a chance to cause different calculations of public protective actions during an accident. After the source term analysis, several atmospheric dispersion cases were simulated by A2CDOSE and RASCAL for further comparison.

Hyperdoping of germanium with argon toward strain-doping-induced indirect-to-direct bandgap transition in Ge

The first-principles calculations have recently shown that implanting sufficient noble gas atoms into germanium (Ge) can expand its lattice to achieve the desired tensile strain for indirect-to-direct bandgap transition to develop the on-chip high-efficient light emitter. Here, to experimentally prove this strain-doping concept, we implant argon (Ar) ions into Ge and then recrystallize the Ar-doped amorphous Ge (a-Ge) layer using nanosecond laser annealing (NLA) and furnace thermal annealing (FTA), respectively. The NLA effectively recrystallizes the 12 nm thick a-Ge layer with minimal loss of Ar dopants, while FTA fails to fully recrystallize it and results in significant loss of Ar dopants. The regrown Ge layer with Ar concentration above the critical value (0.8%) for bandgap transition is 3.8 nm thick, making it a challenge to distinguish the photoluminescence signal of strain-doped layer from the substrate. To overcome this, increasing the implantation energy and adding a capping layer may be necessary to further prevent Ar loss and achieve a strain-doped layer with sufficient depth. These findings provide promising view of the strain-doping concept for direct-bandgap emission from Ge.

Development of an X-ray ionization beam position monitor for PAL-XFEL soft X-rays.

The Pohang Accelerator Laboratory X-ray Free-Electron Laser (PAL-XFEL) operates hard X-ray and soft X-ray beamlines for conducting scientific experiments providing intense ultrashort X-ray pulses based on the self-amplified spontaneous emission (SASE) process. The X-ray free-electron laser is characterized by strong pulse-to-pulse fluctuations resulting from the SASE process. Therefore, online photon diagnostics are very important for rigorous measurements. The concept of photo-absorption and emission using solid materials is seldom considered in soft X-ray beamline diagnostics. Instead, gas monitoring detectors, which utilize the photo-ionization of noble gas, are employed for monitoring the beam intensity. To track the beam position at the soft X-ray beamline in addition to those intensity monitors, an X-ray ionization beam position monitor (XIBPM) has been developed and characterized at the soft X-ray beamline of PAL-XFEL. The XIBPM utilizes ionization of either the residual gas in an ultra-high-vacuum environment or injected krypton gas, along with a microchannel plate with phosphor. The XIBPM was tested separately for monitoring horizontal and vertical beam positions, confirming the feasibility of tracking relative changes in beam position both on average and down to single-shot measurements. This paper presents the basic structure and test results of the newly developed non-invasive XIBPM.

Anti-parasitic activity of garlic (Allium sativum) and onion (Allium cepa) extracts against Dactylogyrus spp. (Monogenean) in Nile tilapia (Oreochromis niloticus): Hematology, immune response, histopathological investigation, and inflammatory cytokine genes of gills

BackgroundGills monogenean infestation causes significant mortalities in cultured fishes as a result of respiratory manifestation. Medicinal plants are currently being heavily emphasized in aquaculture due to their great nutritional, therapeutic, antimicrobial activities, and financial value.MethodsThe current study is designed to assess the effect of garlic (Allium sativum) and onion (Allium cepa) extracts as a water treatment on the hematological profile, innate immunity, and immune cytokines expression besides histopathological features of gills of Nile tilapia (Oreochromis niloticus L.) infected with gills monogenetic trematodes (Dactylogyrus sp.). Firstly, the 96-hour lethal concentration 50 (96 h-LC50) of garlic extract (GE) and onion extract (OE) were estimated to be 0.4 g/ L and 3.54 g/ L for GE and OE, respectively. Moreover, the in-vitro anti-parasitic potential for (GE) was found between 0.02 and 0.18 mg/mL and 0.4 to 1.8 mg/mL for OE. For the therapeutic trial, fish (n = 120; body weight: 40–60 g) were randomly distributed into four groups in triplicates (30 fish/group, 10 fish/replicate) for 3 days. Group1 (G1) was not infected or treated and served as control. G2 was infected with Dactylogyrus spp. and not exposed to any treatment. G3, G4 were infected with Dactylogyrus sp. and treated with 1/10 and 1/5 of 96 h LC50 of OE, respectively. G5, G6 were infected with Dactylogyrus sp. and treated with 1/10 and 1/5 of 96 h LC50 of GE, respectively.ResultsNo apparent signs or behaviors were noted in the control group. Dactylogyrus spp. infected group suffered from clinical signs as Pale color and damaged tissue. Dactylogyrus spp. infection induced lowering of the hematological (HB, MCH, MCHC and WBCs), and immunological variables (lysozyme, nitric oxide, serum Anti- protease activities, and complement 3). the expression of cytokine genes IL-ß and TNF-α were modulated and improved by treatment with A. sativum and A. cepa extracts. The obtained histopathological alterations of the gills of fish infected with (Dactylogyrus spp.) were hyperplasia leading to fusion of the gill filament, lifting of epithelial tissue, aneurism and edema. The results indecated that G4 and G5 is more regenarated epithelium in compare with the control group.ConclusionA. sativum and A. cepa extracts enhance the blood profile and nonspecific immune parameters, and down-regulated the expression level of (IL-1β and TNF-α).

A goniometric measurement system for reflection, diffusion, and transmission characterization in the VUV range

The characterization in the Vacuum Ultraviolet (VUV) range of reflection, diffusion and transmission of mechanical components plays a crucial role in understanding and optimizing the performance of particle detectors exploiting the scintillation light coming from liquefied noble gases. To this purpose a goniometric measurement system has been realized. In this presentation, the main technical characteristics and performances of the system are shown together with results coming from preliminary tests on different materials. © 2001 Elsevier Science. All rights reserved.

High resolution identification and quantification of diffuse deep groundwater discharge in mountain rivers using continuous boat-mounted helium measurements

Discharge of deeply sourced groundwater to streams is difficult to locate and quantify, particularly where both discrete and diffuse discharge points exist, but diffuse discharge is one of the primary controls on solute budgets in mountainous watersheds. The noble gas helium is a unique identifier of deep groundwater discharge because groundwater with long residence times is commonly enriched in helium. In this study, a portable mass spectrometer was used to measure longitudinal variation in dissolved helium concentrations in two mountainous rivers at high spatial resolution not feasible with traditional sampling techniques. Helium profiles were then simulated using a mass-balance model to quantify longitudinal variation in groundwater discharge to the receiving rivers. Results indicate helium concentrations were enriched by multiple orders of magnitude above atmospheric equilibrium in both rivers and that this persisted for up to 18 km below observed pulse inputs in the Colorado River. Helium mass-balance models match observed longitudinal patterns with the exception of sharp initial increases in helium observed in the rivers. Increased longitudinal groundwater discharge rates correspond to mapped geologic structures in both watersheds that likely transport deep geothermal water. Models show variable sensitivity to spatial assignment of input variables representing the groundwater source, illustrating the importance of collecting data from discrete groundwater discharges where possible. The methodology shows promise for field experiments designed to assess air–water exchange rates and to quantify total groundwater discharge from a combination of discrete and diffuse sources.

Theoretical Study of Ground-State Barium-Rare Gas Van der Waals Complexes: Combining Rule Modeling and Ab Initio Calculations.

The present study aims to generate the potential energy curves (PECs) and spectroscopic constants for barium alkaline earth (AE) atoms interacting with rare gas (RG) atoms (He, Ne, Ar, Kr, and Xe). The study focuses on investigating the van der Waals bonds that characterize the interactions between alkaline-earth metals and RG atoms, with a specific emphasis on employing the Tang and Toennies (TT) potential model, known to accurately describe such interactions. The TT potential model was employed in conjunction with combining rules to calculate its parameters, which include dispersion coefficients C 2n and Born-Mayer constants A and b. Additionally, we have conducted high-level ab initio calculations at the CCSD(T) level for all Ba-RG ground states. Obtained PECs from both methods have been used to evaluate the spectroscopic properties D e, R e, ωe, B e, and ωeχe. Our findings reveal that the derived spectroscopic constants from the TT model exhibit good agreement with the results obtained from CCSD(T) calculations and with other available theoretical studies. Furthermore, to gain insights into the relative differences among AE-RG species, we calculated the κ parameter for AE-RG and AE+-RG (AE = Sr, Ca, Mg, Ba; RG = He-Xe) complexes. It is found that except for the case of Ba-RG and Ba+-RG, the κ values within the same series, AE-RG and AE+-RG, are remarkably close to each other.

A Simple Model for the Pauli Repulsion with Possible Utility in QM, MM and Chemical Education.

The Pauli repulsion is the intermolecular force responsible for the volume and low compressibility of condensed-phase matter at normal conditions. A simple model for this force is presented, wherein per-atom electron densities are represented as spherical charge distributions that are prevented from significantly overlapping. In the example of two noble gas atoms approaching one another beyond their van der Waals radii, the distance between the centers of the electronic charge distributions becomes larger than the distance between the nuclei, giving rise to an unfavorable electrostatic interaction. For the purpose of calculating this interaction, the model is further simplified by representing the per-atom electron density as a negative point charge, loosely inspired by the classical Drude oscillator. The dispersion interaction is simplified to an R-6 term, centered on the aforementioned point charges. Despite the gross simplicity of the resulting formalism, near-quantitative agreement with high-level QM interaction energies of noble gas dimers is achieved. Accordingly, the present model is thought to have utility in force fields, in post-HF and post-DFT dispersion corrections, and in chemical education.

Influences of Bacillus pumilus SA388 as an environmentally friendly antibiotic alternative on growth performance, blood biochemistry, immunology, cecal microbiota, and meat quality in broiler chickens

The widespread use of antibiotics causes the development of antibiotic-resistant bacterial strains, which have a severe impact on poultry productivity and human health. As a result, research is continuing to develop safe natural antibiotic alternatives. In the current study, Bacillus pumilus SA388 was isolated from the chicken feces and confirmed to be a probiotic. The selected strain was tested for its antimutagenic and antioxidant capabilities before being employed as a probiotic food supplement and antibiotic alternative. The effect of B. pumilus SA388 impact on broiler chickens' growth performance, gut microbiome, blood biochemical markers, immunological response, and meat quality was also studied. B. pumilus SA388 showed significant bactericidal activity against Streptococcus pyogenes, Listeria monocytogenes, Staphylococcus aureus, Escherichia coli, Salmonella typhi, and Klebsiella pneumonia. A total of 200 chickens were used in the present study, divided equally among four experimental groups (ten birds per group with 5 replicates): group 1 (control, G1) received a basal diet without B. pumilus SA388, group 2 (G2) received a basal diet supplemented with 0.4 mg/kg of B. pumilus SA388, group 3 (G3) received a basal diet supplemented with 0.8 mg/kg of B. pumilus SA388, and group 4 (G4) received a basal diet supplemented with 1.6 mg/kg of B. pumilus SA388. Over 35 d, the B. pumilus SA388-supplemented groups outperformed the G1 in terms of body weight gain, performance index, and feed conversion ratio, with a preference for the G4 treatment. The levels of alanine aminotransferase (ALT), aspartate transaminase (AST), low-density lipoprotein (LDL), and total cholesterol decreased significantly (P < 0.05) with increasing B. pumilus SA388 dosages compared to the control G1 group. Dietary supplementation of B. pumilus SA388 at 1.6 mg/kg (G4) significantly (P < 0.05) resulted in improved lipid profile, immunological response, thyroid function, and gut microbiota compared to the control group (G1). Compared to the broilers in the control treatment (G1), the addition of B. pumilus SA388 to broilers in G4 significantly (P < 0.05) enhanced juiciness, tenderness, aroma, and taste. Adding B. pumilus SA388 to chicken feed at different doses significantly (P < 0.05) decreased average feed intake while increasing economic and relative efficiency measures. In conclusion, B. pumilus SA388 has been proven to be an effective antibiotic and nutritional supplement.

A study of 222Rn/220Rn exhalation rate and indoor 222Rn/220Rn levels in higher Himalayan terrain.

The noble radioactive gas radon and its isotope thoron dominate terrestrial radiation in the indoor environment. These gases eventually disintegrate generating radioactive ions that readily adhere to aerosol particles. This study was conducted in a tectonically active location with significant radon concentrations. The obtained average values of radon mass exhalation and thoron surface exhalation rate from this study are higher than the global average values of 56 mBq kg-1h-1 and 1000 mBq m-2s-1, respectively. As the exhalation rates are higher, naturally the average radon and thoron concentrations are also greater than the worldwide average values of 40 and 10Bqm-3, respectively. No significant correlation was observed between 222Rn and 220Rn exhalation rate and indoor 222Rn/220Rn concentration. The exposure dose due to 222Rn, 220Rn and their progenies shows no significant health risk.

Suitable Pore Confinement with Multiple Interactions in a Low-Cost Zeolitic Imidazolate Framework for Efficient Xe Capture and Separation

The increasing industrial demand for the noble gases xenon (Xe) and krypton (Kr), along with growing environmental concerns on their radionuclides, has made the efficient separation and purification of Xe and Kr a critical issue. Leveraging advanced porous materials to achieve highly efficient adsorptive Xe/Kr separation has been recognized as an energy-saving and economical alternative to the widely used cryogenic distillation technology. Herein, we present a stable, low-cost, and easily scalable zeolitic imidazolate framework (ZIF) material, ZIF-4, for effective xenon adsorption and separation. ZIF-4 possesses uniformly distributed pore cavities with ideally matched pore size (4.3 Å) with that of Xe atom (4.047 Å), providing appropriate pore confinement for Xe binding. Sorption isotherms of ZIF-4 demonstrate the remarkably high Xe uptake (1.64 mmol/g at 0.2 bar and 298 K) and excellent Xe/Kr separation selectivity (16.2 for IAST selectivity of 20/80 Xe/Kr gas mixtures). Breakthrough experiments further validate the efficient separation performance of ZIF-4 in both binary Xe/Kr (20/80) gas mixtures and under dilute conditions. Single-crystal X-ray diffraction studies of activated and Xe-loaded ZIF-4 crystals reveal that the flexible pore cavities of ZIF-4 can self-adaptively adsorb and accommodate Xe atoms through the rotation of imidazolate rings, forming multiple Xe···H and Xe···π interactions to create strong binding sites for Xe capture and discrimination. The stability, economic feasibility, and scalability of ZIF-4 underscore its significant potential for industrial Xe/Kr separation.

High-temperature corrosion testing of titanium beryllides in the presence of water vapor and oxygen

Beryllium-based intermetallics are promising materials for the blankets of future fusion reactors and have potential applications in other areas of the nuclear industry, such as fission reactor reflectors and space technology. Understanding the high-temperature corrosion behavior of these materials in a noble gas medium containing chemically active impurities is essential for evaluating their suitability and guiding their application.This study investigates the high-temperature corrosion of titanium beryllide Be12Ti in the form of plate and grinded samples, produced by JSC “Ulba Metallurgical Plant” (Ust-Kamenogorsk, Kazakhstan). The corrosion tests were conducted under non-isothermal vapor-gas mixture (Ar + D2O or Ar + H2O flowing atmospheres) purging conditions using thermogravimetric (TG) analysis, differential scanning calorimetry (DSC), and mass-spectrometry of the gas phase.As a result of the corrosion tests, new experimental data on thermal effects have been obtained, describing the corrosion processes of Be12Ti samples across a wide range of temperatures and various heating rates in the presence of water vapor in the purge gas. The dependencies of sample mass change under heating conditions have been determined, and the characterization results of the samples before and after high-temperature corrosion tests are presented.Corrosion of titanium beryllides, both for Be12Ti plate and grinded samples, follows similar mechanisms. At around 500 °C, the mass of the samples begins to increase, and hydrogen isotopes are released. The test results indicate that corrosion of titanium beryllides with varying surface inhomogeneities proceeds similarly within the temperature range of 500–900 °C, showing a linear dependence on temperature.The results revealed significant insights into the oxidation mechanisms and the formation of corrosion products, which are crucial for optimizing the material's performance in fusion reactor environments.

Modeling hydrogeological conditions of noble gases in water and aqueous electrolyte solutions

Dissolved noble gases in water hold significant potential as tracers and precursors in various hydrogeological and geological applications, particularly in understanding surface water-groundwater interactions. These applications necessitate precise solubility predictions. Employing the fugacity-fugacity approach, our study models the solubilities of Neon, Argon, Krypton, Xenon, and Radon in both pure water and electrolyte solutions. Leveraging the Cubic-Plus-Association Equation of State, we achieve remarkable accuracy, with average deviations below 2.5 % for vapor pressure, liquid, and vapor-phase densities. Additionally, in water–gas binary systems, deviations in gas solubilities within pure water remain under 5.0 %. Extending our analysis to water–gas-salt ternary systems, our model demonstrates deviations smaller than 5.6 %. Alongside discussing the gas dissolution mechanism, this work emphasizes the adaptability of the model, informed by robust experimental and modeling data. The interpretations derived from modeling hydrogeological conditions are poised to enhance our understanding of hydrological processes, thereby assisting planners and water managers in achieving sustainable development and management of water resources.

Soft ionization mechanisms in flexible µ-tube plasma—elucidation of He-, Ar-, Kr-, and Xe-FµTP

The soft ionization mechanism of helium-based plasma seems to be understood while it still remains challenging in argon-based plasma, although many studies have used argon plasmas as a soft ionization source with good ionization efficiencies. In this study, helium, argon, krypton, and xenon were fed into the same discharge geometry, a flexible micro-tube plasma (FµTP), to determine the ionization mechanisms. The FµTPs operated with the named noble gases obtained comparable ionization efficiencies by MS measurements. The optical emission results showed that N2+ were the dominant ions within the helium-FµTP and noble gas ions were dominant for the other plasmas. These ions support the development of excitation and eventually stop at the end of the capillary. Therefore, Penning ionization and charge transfer between plasma and ambient air/analytes in the open atmosphere have been proven not to be the primary soft ionization mechanism. Furthermore, it was found that photoionization played a minor role in soft ionization. Using helium as a diagnosis gas in front of the discharge capillary nozzle of the FµTP, where the sample is usually positioned, shows that helium can be ignited by all of these FµTPs. This demonstrates that the excitation of a diagnosis gas as well as the ionization of analytes is independent of the type of the discharge gas. An alternative mechanism that a transient potential created by the ions is responsible for the soft ionization is subsequently proposed.

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.