Xe Data Research Articles

Presence of non-solar derived krypton and xenon unveiled by Chang'e-5 lunar soils

The extent of volatile elements on the surface and interior of the Moon remains a highly debated topic. Previous studies conducted on bulk lunar soil samples and solar wind samples collected by the Genesis mission indicate a discernible isotope mass- or non-mass-dependent fractionation of krypton and xenon. However, a detailed investigation of these processes is missing, particularly in determining the possible incorporation of cometary volatiles in the lunar regolith. New lunar soil samples returned by the Chang'e-5 mission provide a chance to answer these key questions. In this study, noble gas isotopes of nine subsamples from a Chang'e-5 scooped sample were analysed through stepwise-heating and total fusion laser extraction. The results reveal that a simple binary mixture of solar wind and cosmogenic components did not explain alone the isotopic composition of these samples. The Xe data shows insignificant amounts of atmospheric Xe and presents clear evidence of cometary contributions to the lunar regolith, with a significant depletion of 134,136Xe compared to that in the solar wind. Additionally, a meteoritic component is identified. Compared to the Apollo results, our findings further validate the theory of Earth's atmospheric escape, substantiate the plausibility of these exogenous admixtures to elucidate the isotopic fractionation mechanisms of Kr and Xe within the lunar regolith, and provide novel insights into long-term constancy in the solar wind composition.

Correlations between flow and transverse momentum in Xe+Xe and Pb+Pb collisions at the LHC with the ATLAS detector: A probe of the heavy-ion initial state and nuclear deformation

The correlations between flow harmonics $v_n$ for $n=2$, 3 and 4 and mean transverse momentum $[p_\mathrm{T}]$ in $^{129}$Xe+$^{129}$Xe and $^{208}$Pb+$^{208}$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.44$ TeV and 5.02 TeV, respectively, are measured using charged particles with the ATLAS detector. The correlations are sensitive to the shape and size of the initial geometry, nuclear deformation, and initial momentum anisotropy. The effects from non-flow and centrality fluctuations are minimized, respectively, via a subevent cumulant method and event activity selection based on particle production in the very forward rapidity. The results show strong dependences on centrality, harmonic number $n$, $p_{\mathrm{T}}$ and pseudorapidity range. Current models describe qualitatively the overall centrality- and system-dependent trends but fail to quantitatively reproduce all the data. In the central collisions, where models generally show good agreement, the $v_2$-$[p_\mathrm{T}]$ correlations are sensitive to the triaxiality of the quadruple deformation. The comparison of model to the Pb+Pb and Xe+Xe data suggests that the $^{129}$Xe nucleus is a highly deformed triaxial ellipsoid that is neither a prolate nor an oblate shape. This provides strong evidence for a triaxial deformation of $^{129}$Xe nucleus using high-energy heavy-ion collision.

Cosmic-ray sputtering of interstellar ices in the electronic regime

Aims. With this article, we aim to provide the sputtering yields for molecular species of potential astrophysical interest and in the electronic regime of interaction characteristic of cosmic rays. We specifically target molecules that are constitutive of interstellar ice mantles.Methods. We used a compendium of existing data on electronic sputtering to calculate the prefactors leading to the generalisation of the stopping-power-dependent sputtering yield for many species condensing at low temperature. In addition, we present new experimental results to constrain the yield for solid CH4, C6, and CH3CN.Results. Electronic sputtering is constrained using literature data for H2, HD, D2, Ne, N2, CO, Ar, O2, Kr, Xe, CO2, SO2, NH3, S, H2O, D2O, CH3OH, Leucine, C20H12, C24H12, and C60. A first-order relation with the sublimation enthalpy is derived, which allows us to predict the sputtering yield within an order of magnitude for most species. The fluctuations around the mean are partly assignable to the differences in resilience towards radiolysis for individual species, and partly to the micro-physics details of the energy transfer to the lattice.

Xenon-enhanced dual-energy tomosynthesis for functional imaging of respiratory disease-Concept and phantom study.

Xenon-enhanced dual-energy (DE) computed tomography (CT) and hyperpolarized noble-gas magnetic resonance imaging (MRI) provide maps of lung ventilation that can be used to detect chronic obstructive pulmonary disease (COPD) early in its development and predict respiratory exacerbations. However, xenon-enhanced DE-CT requires high radiation doses and hyper-polarized noble-gas MRI is expensive and only available at a handful of institutionsglobally. To present xenon-enhanced dual-energy tomosynthesis (XeDET) for low-dose, low-cost functional imaging of respiratory disease in an experimental phantomstudy. We propose using digital tomosynthesis to produce Xe-enhanced low-energy (LE) and high-energy (HE) coronal images. DE subtraction of the LE and HE images is used to suppress soft tissues. We used an imaging phantom to investigate image quality in terms of the area under the reciever operating characteristic curve (AUC) for the Non-PreWhitening model observer with an Eye filter and internal noise (NPWEi). The phantom simulated anatomic clutter due to lung parenchyma and attenuation due to soft tissue and lung tissue. Aluminum slats were used to simulate rib structures. A stepwedge consisting of an acrylic casing with sealed cylindrical air-filled cavities was used to simulate ventilation defects with step thicknesses of 0.5, 1, and 2cm and cylindrical radii of 0.5, 0.75, and 1cm. The phantom was ventilated with Xe and projection data were acquired using a flat-panel detector, a tube-voltage combination of 60/140kV with 1.2 mm of copper filtration on the HE spectrum and an angular range of in 1° increments. The AUC of a NPWEi observer that has access only to a single coronal slice was calculated from measurements of the three-dimensional noise power spectrum and signal template. The AUC was calculated as a function of ventilation defect thickness and radius for total patient entrance air kermas ranging from 1.42 to 2.84mGy with and without rib-simulating Al slats. For the AUC analysis, the observer internal noise level was obtained from an ad hoc calibration to a high-dose dataset. XeDET was able to suppress parenchyma-simulating clutter in coronal images enabling visualization of the simulated ventilation defects, but the limited angle acquisition resulted in residual clutter due to out-of-plane bone-mimmicking structures. The signal power of the defects increased linearly with defect radius and showed a ten-fold to fifteen-fold increase in signal power when the defect thickness increased from 0.5 to 2cm. These trends agreed with theoretical predictions. Along the depth dimension, the power of the defects decreased exponentially with distance from the center of the defects with full-width half maxima that varied from 1.85to 2.85cm depending on the defect thickness and radius. The AUCs of the 1-cm-radius defect that was 2cm in thickness ranged from good (0.8-0.9) to excellent (0.9-1.0) over the range of air kermasconsidered. Xenon-enhanced DE tomosynthesis has the potential to enable functional imaging of respiratory disease and should be further investigated as a low-cost alternative to MRI-based approaches and a low-dose alternative to CT-basedapproaches.

Absolute Double-Differential Cross Sections of Ultrasoft Isochromatic X-ray Radiation in Electron Scattering on Atoms

We calculate double-differential cross sections of ultrasoft X-ray bremsstrahlung in electron scattering by Ar, Kr, and Xe atoms in the soft-photon approximation. The calculations are done for the isochromatic spectra (i.e., dependence on the electron energy at a fixed photon energy of 165 and 177 eV). The results are consistent with the absolute values of the differential cross sections measured by Gnatchenko et al. (Phys. Rev. A 80, 022707 (2009)) for the above-mentioned photon energies. For low electron energies, our theoretical isochromatic spectra are in quantitative agreement with the experimental data for Ar. For Kr, the agreement is qualitative while agreement with the Xe data is poor.

Solubility Data and Computational Modeling of Baricitinib in Various (DMSO + Water) Mixtures.

The solubility and thermodynamic analysis of baricitinib (BNB) in various dimethyl sulfoxide (DMSO) + water mixtures were performed. The “mole fraction solubilities (xe)” of BNB in DMSO and water mixtures were determined at “T = 298.2–323.2 K” and “p = 0.1 MPa” using an isothermal saturation technique. “Hansen solubility parameters (HSPs)” of BNB, pure DMSO, pure water and “DMSO + water” mixtures free of BNB were also estimated. The xe data of BNB was regressed well by five different thermodynamics-based co-solvency models, which included “Apelblat, Van’t Hoff, Yalkowsky-Roseman, Jouyban-Acree and Jouyban-Acree-Van’t Hoff models” with overall deviations of <5.0%. The highest and lowest xe value of BNB was computed in pure DMSO (1.69 × 10−1 at T = 323.2 K) and pure water (2.23 × 10−5 at T = 298.2 K), respectively. The HSP of BNB was found to be closer to that of pure DMSO. Based on activity coefficient data, maximum solute–solvent molecular interactions were observed in BNB-DMSO compared to BNB-water. The results of “apparent thermodynamic analysis” indicated endothermic and entropy-drive dissolution of BNB in all “DMSO + water” combinations including mono-solvents (water and DMSO). “Enthalpy-entropy compensation analysis” showed enthalpy-driven to be the main mechanism of solvation of BNB.

Adsorbents and adsorption models for capture of Kr and Xe gas mixtures in fixed-bed columns

Off-gases produced during the reprocessing of used nuclear fuel (UNF) include 129I2, 3HHO, 14CO2, 85Kr, and 135Xe, which are volatilized out into the off-gas. In order to meet regulatory requirements for reprocessing plant emissions, these gases must be captured and removed from the off-gas stream prior to off-gas emission. Of particular interest are the noble gases, Kr and Xe, which can be fairly difficult to remove from the off-gas due to their low chemical reactivity. Thus, this work is focused on utilizing engineered adsorbents, AgZ-PAN and HZ-PAN, to capture Kr and Xe from a mixed-gas stream at relatively low temperatures (191–295 K) and various flow rates (50–2000 mL/min). Isothermal data for Kr and Xe on each adsorbent are analyzed to produce the Langmuir parameters needed to model the mixture adsorption capacities at relevant temperatures using the Extended Langmuir model. Those parameters are then incorporated into a fixed-bed adsorption model developed in this work using the Mulitphysics Object-Oriented Simulation Environment (MOOSE). That model is used to simulate breakthrough times for Kr and Xe in packed columns of AgZ-PAN and HZ-PAN, ranging in length from 6 to 20 in., at relevant temperatures and flow rates. Breakthrough times varied from nearly instantaneous for Kr in AgZ-PAN to 30 h for Xe in HZ-PAN. After the developed model was validated by comparisons with experimental breakthrough data, the model framework was used to simulate the performance of multiple fixed-bed columns connected in series.

Rapid single-breath hyperpolarized noble gas MRI-based biomarkers of airspace enlargement.

Multi-b diffusion-weighted hyperpolarized-gas MRI measures pulmonary airspace-enlargement using apparent diffusion coefficients (ADCs) and mean-linear-intercepts (Lm ). To develop single-breath 3D multi-b diffusion-weighted 3 He and 129 Xe MRI using k-space undersampling. Rapid, cost-efficient, single-breath acquisitions may facilitate clinical translation. Prospective. We evaluated 12 participants, including nine subjects (mean age = 69 ± 9) who were included in the retrospective experiment and three chronic pulmonary obstruction disease (COPD) patients (mean age = 81 ± 6) who participated in the prospective study. A whole-body 3 T 2D/3D fast gradient recall echo (FGRE) sequence. Hyperpolarized 3 He/129 Xe MRI, spirometry, plethysmography computed tomography (CT). We evaluated 129 Xe ADC/morphometry estimates by retrospectively undersampling previously acquired fully sampled multibreath, multi-b diffusion-weighted data. Next, we prospectively evaluated the feasibility of accelerated (AF = 7) 3 He MRI static-ventilation/T2 * (extra short-TE, b = 0 image) and ADC/morphometry (five b-values) maps using a single gas-dose and 16-second breath-hold. To conservatively evaluate cost-improvement, we compared total costs of single vs. multiple 129 Xe doses. Multivariate analysis of variance, independent t-tests and voxel-by-voxel basis difference test. For the retrospectively undersampled 129 Xe data, a nonsignificant mean difference for ADC/Lm of 14%/12%, 12%/8%, and 11%/9% was observed (all, P > 0.4) between the fully sampled and accelerated data for the never-smoker, COPD, and alpha-1 antitrypsin deficiency (AATD) groups, respectively. The control never-smoker group had significantly lower ADC (P < 0.001) and Lm (P < 0.001) than the COPD/AATD group for both fully sampled and accelerated data. For the prospectively acquired 3 He MRI data, static-ventilation, T2 *, ADC, and morphometry maps were acquired using a single 16-second breath-hold scan and single gas dose. Accelerated imaging resulted in cost savings of ~$US 1000/patient, a conservative estimate based on 129 Xe MRI dose savings (single vs. five doses). This is a proof-of-concept demonstration of accelerated (7×) morphometry that shows that less cost- and time-efficient multibreath methods that lead to variability and patient fatigue may be avoided in the future. 2 Technical Efficacy: Stage 5 J. Magn. Reson. Imaging 2018.

Primordial heavy noble gases in the pristine Paris carbonaceous chondrite.

The Paris carbonaceous chondrite represents the most pristine carbonaceous chondrite, providing a unique opportunity to investigate the composition of early solar system materials prior to the onset of significant aqueous alteration. A dual origin (namely from the inner and outer solar system) has been demonstrated for water in the Paris meteorite parent body (Piani et al. 2018). Here, we aim to evaluate the contribution of outer solar system (cometary‐like) water ice to the inner solar system water ice using Xe isotopes. We report Ar, Kr, and high‐precision Xe isotopic measurements within bulk CM 2.9 and CM 2.7 fragments, as well as Ne, Ar, Kr, and Xe isotope compositions of the insoluble organic matter (IOM). Noble gas signatures are similar to chondritic phase Q with no evidence for a cometary‐like Xe component. Small excesses in the heavy Xe isotopes relative to phase Q within bulk samples are attributed to contributions from presolar materials. CM 2.7 fragments have lower Ar/Xe relative to more pristine CM 2.9 fragments, with no systematic difference in Xe contents. We conclude that Kr and Xe were little affected by aqueous alteration, in agreement with (1) minor degrees of alteration and (2) no significant differences in the chemical signature of organic matter in CM 2.7 and CM 2.9 areas (Vinogradoff et al. 2017). Xenon contents in the IOM are larger than previously published data of Xe in chondritic IOM, in line with the Xe component in Paris being pristine and preserved from Xe loss during aqueous alteration/thermal metamorphism.

Extended atomic structure calculations for energy levels and radiative data of Xe XLIII

We report an extensive and elaborate theoretical study of atomic data for Xe XLIII. We have calculated energies for the lowest 141 fin. structure levels by using Multi-Configuration Dirac Fock (MCDF) method. We have also considered Quantum Electrodynamics (QED) and Breit corrections in our calculations. We have presented the radiative data for electric dipole (E1) transitions among lowest 141 levels. We have made comparisons of our calculated excitation energies and EUV (Extreme Ultraviolet) transition wavelengths with the theoretically computed and experimentally observed energy levels and wavelengths at Electron Beam Ion Trap (EBIT) and a good agreement is achieved. We have also computed energy levels by performing similar relativistic distorted wave calculations using Flexible Atomic Code (FAC). Additionally, we have provided new atomic data for Xe XLIII which are not published elsewhere in the literature. We believe that our results may be beneficial in fusion plasma research and detection and investigation of EUV and Soft X-ray (SXR) spectral lines.

Estimating carbon dioxide residence time scales through noble gas and stable isotope diffusion profiles

The study of natural carbon dioxide reservoirs provides fundamental insight into processes involved in carbon capture and storage. However, the calculations of process rates such as dissolution of CO2 into formation water remain uncertain due to indirectly determined ages of the CO2 influx. The proposed ages for the Bravo Dome gas field in New Mexico, USA, vary from 56 ka to 1.5 Ma. Here we demonstrate that residence times can be estimated from simple modeling of noble gas and stable isotope diffusion profiles from the gas-water contact through the gas column. The Bravo Dome gas field shows a gradient in noble gas concentrations and isotopic ratios from east to west across the 70-km-wide field. A mantle-like end member with a 3He/4He (R/RA) ratio of up to 4.7 is found in the west in contrast to a groundwater end member with high concentrations of air- and crustal-derived noble gases in the east. The air- and crustal-derived noble gases decrease gradually toward the west. Stable isotope compositions (C and O) also vary across the field. Diffusion modeling of He, Ne, Ar, Kr, Xe, and δ13C data yield residence times for the CO2 between 14.1 ± 0.2 ka and 16.9 +1.1/–0.5 ka. This is far less than the previous estimates of 1.2–1.5 Ma based on apatite (U-Th)/He thermochronology, leading to a dissolution rate of 29,900 +11,800/–10,700 t/a to 35,900 ± 12,300 t/a, implying that 28% of the total emplaced CO2 dissolved. This new method can be applied to a wide variety of gas fields with variation in the concentration of groundwater-derived noble gases and allow a better assessment of the time scale of other diffusive fluid-fluid interactions.

Ultraviolet discharges from a radio-frequency system for potential biological/chemical applications

In this work, we describe a new electrode-less radio-frequency (RF) excitation technique for generating excimers in the vacuum ultraviolet (VUV) and ultraviolet (UV) spectral regions for potential biological/chemical applications. Spectra data of Xe, XeI, and KrI generated by this new technique are presented. Optical efficiency of the lamp system ranges from 3% to 6% for KrI, 7% to 13% for XeI, and 15% to 20% for Xe. Also, results of irradiating E-coli with XeI discharge from this lamp system is presented to show one of the promising applications of such electrode-less apparatus. This new RF lamp system offers an interesting addition to the already existing technologies for generating VUV and UV light for various biological, physical, and chemical processes especially those requiring large area for high productivity.

I–Xe systematics of the impact plume produced chondrules from the CB carbonaceous chondrites: Implications for the half-life value of 129I and absolute age normalization of 129I–129Xe chronometer

It is inferred that magnesian non-porphyritic chondrules in the CB (Bencubbin-type) carbonaceous chondrites formed in an impact generated plume of gas and melt at 4562.49±0.21Ma (Bollard et al., 2015) and could be suitable for the absolute age normalization of relative chronometers. Here xenon isotopic compositions of neutron irradiated chondrules from the CB chondrites Gujba and Hammadah al Hamra (HH) 237 have been analyzed in an attempt to determine closure time of their I–Xe isotope systematics. One of the HH 237 chondrules, #1, yielded a well-defined I–Xe isochron that corresponds to a closure time of 0.29±0.16Ma after the Shallowater aubrite standard. Release profiles and diffusion properties of radiogenic 129*Xe and 128*Xe, extracted from this chondrule by step-wise pyrolysis, indicate presence of two iodine host phases with distinct activation energies of 73 and 120kcal/mol. In spite of the activation energy differences, the I–Xe isotope systematics of these two phases closed simultaneously, suggesting rapid heating and cooling (possibly quenching) of the CB chondrules. The release profiles of U-fission Xe and I-derived Xe correlate in the high temperature host phase supporting simultaneous closure of 129I–129Xe and 207Pb–206Pb systematics.The absolute I–Xe age of Shallowater standard is derived from the observed correlation between I–Xe and Pb–Pb ages in a number of samples. It is re-evaluated here using Pb–Pb ages adjusted for an updated 238U/235U ratio of 137.794 and meteorite specific U-isotope ratios. With the addition of the new data for HH 237 chondrule #1, the re-evaluated absolute I–Xe age of Shallowater is 4562.4±0.2Ma. The absolute I–Xe age of the HH 237 chondrule #1 is 4562.1±0.3Ma, in good agreement with U-corrected Pb–Pb ages of the Gujba chondrules (Bollard et al., 2015) and HH 237 silicates (Krot et al., 2005).All I–Xe data used here, and in previous estimates of the absolute age of Shallowater, are calculated using 15.7±0.6Ma value for 129I half-life. The slopes of I–Xe – Pb–Pb correlation lines plotted for different sets of samples for Shallowater normalization are always ⩽1. Assuming uranium half-life values are correct; this restricts the half-life of 129I to ⩽15.7Ma.

Probing interlayer interactions between graphene and metal substrates by supersonic rare-gas atom scattering

We demonstrate that highly surface-sensitive supersonic rare-gas (He, Ar, and Xe) atom scattering, in both the quantum and classical regimes, can probe and quantify the interlayer interactions between graphene monolayers and metal substrates in terms of the Debye temperature corresponding to the surface normal vibration, and the surface effective mass. As models of the strongly and weakly interacting graphene, we investigated two systems, graphene on Ru(0001) and Pt(111), respectively. The experimental data for Ar and Xe are compared with the results from theoretical simulations based on the classical smooth surface model. For gr/Pt(111) we find that the scattering pattern of the rare-gas beam, including the Debye-Waller attenuation of the He beam, are quite similar to that from highly oriented pyrolytic graphite (HOPG); this suggests that the graphene-Pt(111) interaction is much like a van der Waals interaction. On the contrary, for the gr/Ru(0001) system, we find a smaller Debye-Waller attenuation and a larger surface effective mass, indicating that graphene on Ru(0001) is tightly bonded to the substrate. Furthermore, asymmetrical spectral shapes in the Ar and Xe scattering spectra from gr/Ru(0001) are interpreted as a result of the lateral distribution of the interlayer interaction corresponding to the moir\'e pattern. It is found that the ``valley'' region of the moir\'e pattern has high effective mass reflecting stronger bonding to the substrate, contributing to the high reflectivity of the He beam reported for this system. On the other hand, the effective mass of the ``hill'' region is found to be similar to that of HOPG, indicating that this region is well decoupled from the substrate. These results demonstrate a unique capability of atom scattering to probe and evaluate the molecule-substrate interaction and its spatial distributions.

Modern atmospheric signatures in 4.4 Ga Martian meteorite NWA 7034

The NWA 7034 Martian basaltic breccia, dated at ∼4.4 Ga, represents an entirely new type of Martian meteorite. However, due to the unique make-up of NWA 7034 compared to other Martian meteorite types (including its anomalous oxygen isotope ratios), noble gas analyses – a key tool for Martian meteorite identification – are important to confirm its Martian origin. Here, we report the first noble gas results for NWA 7034, which show the presence of a trapped component that resembles the current Martian atmosphere. This trapped component is also similar in composition to trapped gases found in the much younger shergottites (∼150–600 Ma). Our formation ages for the sample suggest events at ∼1.6 Ga (K–Ar), and ∼170 Ma (U–Th/He), which are considerably younger than those observed by Rb–Sr (2.1 Ga), and Sm–Nd (4.4 Ga; zircons ∼4.4 Ga). However, our K–Ar age is similar to a disturbance in the U–Pb zircon data at ∼1.7 Ga, which could hint that both chronometers have been subjected to disturbance by a common process or event. The U–Th/He age of ∼170 Ma could relate to complete loss of radiogenic 4He at this time, and is a similar age to the crystallisation age of most shergottites. While this may be coincidental, it could indicate that a single event is responsible for both shergottite formation and NWA 7034 thermal metamorphism. As for cosmic ray exposure ages, our favoured age is ∼5 Ma, which is outside the ranges for other Martian meteorite groups, and may suggest a distinct ejection event. NWA 7034 shows evidence for neutron capture on Br, which has caused elevations in Kr isotopes 80Kr and 82Kr. These elevated abundances indicate significant shielding, and could relate to either a large meteoroid size, and/or shielding in relation to a regolithic origin. We have also applied similar neutron capture corrections to Ar and Xe data, which further refine the likelihood of a modern atmospheric component, though such corrections remain speculative. Cosmogenic production rates and noble gas data are consistent with a meteoroid radius of >50 cm. Fission contributions are clear in the Xe data, with evidence to suggest that NWA 7034 contains both 238U and 244Pu derived fission Xe components. If the gas in NWA 7034 was trapped at its ancient igneous formation, this would suggest little evolution of the Martian atmosphere between ∼4.4 Ga and present day. However, as NWA 7034 is a regolith breccia with multiple lithologies and a strong compositional similarity to Gusev soils, the timing and incorporation of trapped atmospheric gases is unclear. With hints of resetting events at ∼1.5–2.1 Ga, the atmospheric component may have been incorporated during breccia formation – possibly in the Amazonian, though it could also have been incorporated on ejection from the surface.

Unique chemistry of a diamond-bearing pebble from the Libyan Desert Glass strewnfield, SW Egypt: Evidence for a shocked comet fragment

We have studied a small, very unusual stone, here named “Hypatia”, found in the area of southwest Egypt where an extreme surface heating event produced the Libyan Desert Glass 28.5 million years ago. It is angular, black, shiny, extremely hard and intensely fractured. We report on exploratory work including X-ray diffraction, Raman spectroscopy, transmission electron microscopy, scanning electron microscopy with EDS analysis, deuteron nuclear reaction analysis, C-isotope and noble gas analyses. Carbon is the dominant element in Hypatia, with heterogeneous O/C and N/C ratios ranging from 0.3 to 0.5 and from 0.007 to 0.02, respectively. The major cations of silicates add up to less than 5%. The stone consists chiefly of apparently amorphous, but very hard carbonaceous matter, in which patches of sub-μm diamonds occur. δ13C values (ca. 0‰) exclude an origin from shocked terrestrial coal or any variety of terrestrial diamond. They are also higher than the values for carbonaceous chondrites but fall within the wide range for interplanetary dust particles and comet 81P/Wild2 dust. In step heating, 40Ar/36Ar ratios vary from 40 to the air value (298), interpreted as a variable mixture of extraterrestrial and atmospheric Ar. Isotope data of Ne, Kr and Xe reveal the exotic noble gas components G and P3 that are normally hosted in presolar SiC and nanodiamonds, while the most common trapped noble gas component of chondritic meteorites, Q, appears to be absent. An origin remote from the asteroid belt can account for these features.We propose that the Hypatia stone is a remnant of a cometary nucleus fragment that impacted after incorporating gases from the atmosphere. Its co-occurrence with Libyan Desert Glass suggests that this fragment could have been part of a bolide that broke up and exploded in the airburst that formed the Glass. Its extraordinary preservation would be due to its shock-transformation into a weathering-resistant assemblage.

129Xe nuclear resonance scattering on solid Xe and 129Xe clathrate hydrate

Nuclear inelastic and nuclear forward-scattering experiments utilizing the 129Xe Mössbauer resonance were performed on solid Xe and enriched 129Xe clathrate hydrate. The lifetime and energy of the nuclear resonance were determined to be and , respectively. Nuclear inelastic scattering spectra could be obtained with an instrumental resolution of . Despite low Lamb-Mössbauer factors, Xe specific densities of phonon states were derived for solid Xe and Xe clathrate hydrate. Their reliability was investigated using 1-phonon terms obtained by fixing Lamb-Mössbauer factor values within the applied Fourier-Log decomposition. ABINIT calculations of the density of phonon states in solid Xe supplement the interpretation of the experimental data for fcc Xe and good agreement with published densities of phonon states could be achieved below . Results for the Xe clathrate hydrate essentially confirm the rattling nature of the Xe guests and indicate that Xe modes do not contribute to lattice dynamics above .

Porosity of Pillared Clays Studied by Hyperpolarized 129Xe NMR Spectroscopy and Xe Adsorption Isotherms

The influence of the layer charge on the microstructure was studied for a series of three hybrid pillared interlayered clays based on the organic dication Me(2)DABCO(2+) and charge reduced synthetic fluorohectorites. To get a detailed picture of the local arrangements within the interlayer space, multinuclear solid-state NMR spectroscopy was performed in conjunction with high-resolution (129)Xe MAS NMR, temperature-dependent wide-line 1D and 2D (129)Xe NMR, and Ar/Ar(l) and Xe/Xe(l) physisorption measurements. The resulting layer charge (x) for the three samples are 0.48, 0.44, and 0.39 per formula unit (pfu). The samples exhibit BET equivalent surfaces between 150 and 220 m(2)/g and pore volumes which increase from 0.06 to 0.11 cm(3)/g while the layer charge reduces. 1D and 2D (1)H, (13)C, (19)F, and (29)Si MAS data reveal that the postsynthetic charge reduction induces regions with higher defect concentrations within the silicate layers. Although the pillars tend to avoid these defect-rich regions, a homogeneous and regular spacing of the Me(2)DABCO(2+) pillars is established. Both the Ar/Ar(l) physisorption and (129)Xe NMR measurements reveal comparable pore dimensions. The trend of the temperature-dependent wide-line (129)Xe spectra as well as the exchange in the EXSY spectra is typical for a narrow 2D pore system. (129)Xe high-resolution experiments allow for a detailed description of the microstructure. For x = 0.48 a bimodal distribution with pore diameters between 5.9 and 6.4 Å is observed. Reducing the layer charge leads to a more homogeneous pore structure with a mean diameter of 6.6 Å (x = 0.39). The adsorption enthalpies ΔH(ads) determined from the temperature-dependent (129)Xe chemical shift data fit well to the ones derived from the Xe/Xe(l) physisorption measurements in the high-pressure limit while the magnitude of ΔH(ads) in the low-pressure limit is significantly larger. Thus, the (129)Xe data are influenced by adsorbate-adsorbent as well as adsorbate-adsorbate interactions.

Excitation and emission spectra of rubidium in rare-gas thin-films

To understand the optical properties of atoms in solid state matrices, the absorption, excitation, and emission spectra of rubidium doped thin-films of argon, krypton, and xenon were investigated in detail. A two-dimensional spectral analysis extends earlier reports on the excitation and emission properties of rubidium in rare-gas hosts. We found that the doped crystals of krypton and xenon exhibit a simple absorption-emission relation, whereas rubidium in argon showed more complicated spectral structures. Our sample preparation employed in the present work yielded different results for the Ar crystal, but our peak positions were consistent with the prediction based on the linear extrapolation of Xe and Kr data. We also observed a bleaching behavior in rubidium excitation spectra, which suggests a population transfer from one to another spectral feature due to hole-burning. The observed optical response implies that rubidium in rare-gas thin-films is detectable with extremely high sensitivity, possibly down to a single atom level, in low concentration samples.

Using 3He/4He isotope ratios to identify the source of deep reservoir contributions to shallow fluids and soil gas

One strategy to counteract rising atmospheric CO2 levels is the capture and subsequent geological storage of anthropogenic CO2. Legislation will require the monitoring and early identification of any leakage to the near surface from the storage site. Owing to their low concentrations and unreactive nature, noble gases are well established as key tracers of crustal fluid systems (Ballentine et al., 2002). The 3He/4He and noble gas content of soil gases and groundwater may provide the opportunity to detect, identify and quantify a weak, deep-sourced signal that contributes to a larger, near-surface biological signal. We present 3He/4He, Ne, Ar, Kr, and Xe data from near-surface soil gases, two of which exhibit hydrocarbon microseepage from deeper oil reservoirs from the Teapot Dome oil field, Wyoming, USA. We also present a noble gas characterisation of the oil reservoirs beneath the seepages. A helium excess (4Heexcess up to 37.7 ppm) relative to air concentrations (4Heair = 5.24 ppm) is found in soil gases at both microseepage sites. Error propagation demonstrates that it is possible to unambiguously resolve the 3He/4He of the deep helium source and allows us to explore the limits of this technique. At one seep the resolved deep 3He/4He = 0.055 ± 0.009Ra (where Ra = 1.40 × 10− 6) is indistinguishable from the range observed in the subsurface hydrocarbon system of 0.046 to 0.109Ra. Notably the soil gas 4He/CH4 = 1.8 × 10− 3 at this microseepage site compares similarly with the lower subsurface source 4He/CH4 = 1.4 to 3.4 × 10− 4 and demonstrates the conservative nature of helium as a tracer. We show that the sensitivity of helium as a deep fluid tracer should be increased by up to two orders of magnitude in groundwater compared to soil gases studied here due to the low solubility of helium in water. Groundwater rather than soil gas should be the priority in any monitoring strategy that plans to use helium as an early indicator of deep fluid microseepage.