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Introduction: Apollo planned for the future, retaining a suite of specially curated pristine samples. One of these samples is an Apollo 17 double drive-tube core (73001/73002) [1], which samples down to 70 cm below the lunar surface within the ‘light mantle’ unit in the Taurus Littrow Valley (TLV) [2]. Models estimate a low temperature of ~250 K [3] at this depth, conducive for cold-trapping of volatiles. The lower core segment (73001) has been kept within a Core Sample Vacuum Container (CSVC) since 1972 when it was sealed under vacuum at the surface of the Moon [4]. On Earth, CSVC 73001 was sealed in a secondary outer vacuum container (OVC) at a pressure of ~6×10-2 mbar [5]. One of the science goals for Apollo 17 was to target samples that may have trapped gases released from the lunar interior via the Lee-Lincoln fault [1]. The vacuum sealed CSVC 73001 presents a prime opportunity to investigate for such gases. Here we present the preparation and execution of a unique gas extraction event of CSVC 73001, as part of the Apollo Next Generation Sample Analyses (ANGSA) Program. This activity was led by an ANGSA subteam including the European Space Agency (ESA), Washington University St Louis (WUStL), JSC Apollo Sample Curation Facility and University of New Mexico (UNM). Gas Extraction Set-Up & Challenges: A gas extraction set-up was created composed of two main hardware components: a piercing tool, designed and built by ESA, which interfaces with an ultra-high vacuum (UHV, order of pressure, ×10-9 mbar) gas extraction manifold developed and built by WUStL [6]. Technical and scientific challenges for the hardware design include: preserving the pristinity of the regolith and sample gases, avoiding contamination, preventing isotopic fractionation, capability to operate under UHV; accounting for limitations of dexterity when working within a dry N2 glovebox, and delivering on precision piercing of the CSVC stainless steel base without piercing the Teflon cap of the sample holder within. Design and Manufacture: Following a hardware literature review [e.g., 4,7], an ‘agile’ iterative design approach was undertaken. This included: deriving a set of design requirements based on science, curation and technical needs; experimentally deriving the required piercing force and piercing tip dimension; iterative breadboarding; and regular consultation with ANGSA team members. The piercing tool was machined and manufactured at ESA and the extraction manifold built and calibrated at WUStL. Mechanical testing of the piercing tool under ambient conditions aided operational refinement and piercing tip calibration. Subsequent extensive testing under UHV demonstrated efficient, repeatable use of the piercing tool in meeting the objectives and identified challenges and requirements. The tested hardware underwent stringent cleaning and baking (heated in a vacuum oven at 180ºC for 72 hours) prior to being installed at JSC. Outer Vacuum Container Gas Extraction: The OVC containing the CSVC and constituent sample was interfaced directly with the gas extraction manifold and a ‘blank’ sample of the background collected under UHV (order of ×10-9 mbar). A 100 cc ‘test’ aliquot and two gas samples were sequentially collected of the OVC gas, each for a duration of 15 minutes. The OVC gas could be important, if the CSVC may have leaked over the past 50 years. Initial (uncalibrated for system volume) pressures of the OVC sample (order of ×10-2 mbar) are consistent with that of the OVC when it was originally sealed. Piercing the CSVC: The CSVC was extracted from the OVC and rendered XCT images showed the most challenging scenario of the sample holder with the Teflon cap in direct contact with the CSVC base. The CSVC was transferred to the piercing tool and interfaced with the gas extraction manifold (Fig.1). Extensive He-leak testing indicated no atmospheric leaks. Monitoring of pressures and RGA spectra (using a quadrupole mass spectrometer) indicated that the CSVC may be leaking. The manifold was isolated with the system pressure at 8.7×10-9 mbar and the piercing commenced. A satisfying ‘pop’ marked successful piercing of the CSVC base. Test aliquots (100 cc); two ‘short’ 15 minute duration samples (uncalibrated pressure, ~6 mbar) and ‘long’ extraction (~1-2 week duration) samples were collected. Pressures and RGA spectra were monitored throughout from which a set of hypotheses on how well the OVC and the CSVC have performed have been made and will be tested as part of laboratory analyses of the gas. Analyses include determining general gas composition (Z. Sharp at UNM) and noble gas isotope ratios (R. Parai at WUStL). In particular, 20Ne/22Ne and 128Xe/130Xe can assess for presence of lunar gas [8]. Findings and Lessons Learned: The full performance of the piercing tool and CSVC is still to be fully assessed. First XCT and optical images of the CSVC base indicate a high-level of tool performance in terms of not having pierced the Teflon cap and producing an adequate size of hole. A baseline set of requirements and sequence of events have been demonstrated for a gas extraction procedure, which is informing a new generation of (volatile-rich) sample return missions (e.g., Artemis; Mars Sample Return). Synthesis of the CSVC performance will also inform development of easy to use containers with longer lasting, contaminant-free seals. Other lessons learned include recommendations to: produce physical duplicates and digital twins of flight hardware; further research into hardware degradation during flight and with time; ensure early definition of mission goals and consultation with science teams and curators (critical for providing clear driving requirements for hardware development); include flexibility in sample container designs and interfaces that account for the entire return sample life-time needs and not just at point of collection. Figure 1: Gas extraction setup composed of an UHV manifold and piercing tool. References: [1] Meyer C. (2011) Lunar Sample Compendium. [2] Schmitt et al. (2017) Icarus, 298, 2-33. [3] Keimh S.J. and Langseth M.G. (1973) Proc. 4th Lunar Sci. Conf. 2503-2513. [4] Allton J.A. (1989) JSC23454, NASA. [5] Butler P. (1973) Lunar Sample Info. Catalog, NASA JSC. [6] Parai. R et al. (2021) LPSC LII, Abs #2665. [7] NASA JSC (1971) CSVC Technical Drawing, M-11306. [8] Curran, N.M. et al. (2020) PSS, 182, 104823.

Calcium–aluminium-rich inclusions (CAIs) are one of the first solids to have condensed in the solar nebula, while presolar grains formed in various evolved stellar environments. It is generally accepted that CAIs formed close to the Sun at temperatures above 1,500 K, where presolar grains could not survive, and were then transported to other regions of the nebula where the accretion of planetesimals took place. In this context, a commonly held view is that presolar grains are found solely in the fine-grained rims surrounding chondrules and in the low-temperature fine-grained matrix that binds the various meteoritic components together. Here we demonstrate, on the basis of noble gas isotopic signatures, that presolar SiC grains were incorporated into fine-grained CAIs in the Allende carbonaceous chondrite at the time of their formation, and have survived parent-body processing. This finding provides new clues on the conditions in the nascent Solar System at the condensation of the first solids.

Trinitite materials are the post-detonation glassy residues formed from melting and evaporation of arkosic sands during the first nuclear detonation at the Trinity test site, New Mexico on 16th July, 1945. These trinitites provide useful materials for studying elemental and isotopic behaviors associated with high temperature melting and evaporation that is otherwise difficult to achieve under laboratory conditions. Using a high-precision method, we measured the potassium (K) isotopic compositions of six bulk trinitite samples taken at different distances from the epicenter of detonation of the Gadget (ground zero). 15 leachates and etchates of trinitite samples were also analyzed to examine the distribution of K within the samples. All trinitites but IF_m (taken within 10 m from the epicenter) show no resolvable K loss and span a narrow range in K isotopic compositions (δ41K: −0.42 ± 0.05‰ to −0.48 ± 0.05‰), revealing no discernible K isotopic fractionation from the Bulk Silicate Earth (BSE) value (−0.48 ± 0.03‰). Residues and etchates of the trinitite material are identical in composition to the bulk samples implying that K isotopes were homogeneous within the arkosic sand at the Trinity test site prior to the nuclear detonation. The most strongly melted green trinitite IF_m, is the only trinitite that shows loss of K (~7%) coupled with a resolvable heavier K isotope composition (0.2‰ higher in δ41K than the BSE value). This coupled K loss and isotopic fractionation corresponds to a fractionation factor (αvapor-melt) between 0.995 and 0.998 during the Trinity nuclear detonation. These results confirm that K isotopic fractionation occurs through evaporation processes at high temperatures. We also show that, compared with Zn isotopes measured in the same samples, the isotopes of K were significantly less fractionated during evaporation, indicating that K is less volatile during processes such as magma ocean degassing, volcanic outgassing, and impact volatile loss. Our findings support the concept that the heavy K isotopic composition observed in lunar mare basalts reflects the primary signature imprinted by the Moon-forming giant impact event.

Here, we apply recently developed high-precision K isotope analyses to individual components of the LL4 chondrite Hamlet in order to investigate key processes which occurred during chondrite formation. The K isotopic compositions of all Hamlet chondrules range from −1.36‰ to −0.24‰ δ41K while the matrix and bulk samples show ranges of −0.89‰ to −0.80‰ and −0.86‰ to −1.08‰ δ41K, respectively. This range of δ41K values is significantly less than what was seen by in situ K isotopic analysis of Semarkona and Bishunpur chondrules, a likely effect of the different chondrite petrologic types, analytical artifacts in the SIMS analyses, and chondrule rim effects. Strong evidence for secondary parent-body alteration effects within Hamlet suggests its K fractionation and distribution are dominantly controlled by these processes. Interestingly, the strong correlation between δ41K and chondrule mass suggests that chondrule size played a significant role in the K isotopic distribution within Hamlet. This trend is likely a result of either inherited initial differences in the chondrule K isotopic ratios which were not completely overprinted or mechanisms involved in the metamorphism processes creating variations. This K isotope correlation with chondrule mass could also be suggestive of chondrule-forming nebular processes; nevertheless, it is currently unable to definitively favor any specific model. The K isotopic similarities between Hamlet and bulk ordinary chondrites suggest that all LL chondrites, if not all ordinary chondrites, may have formed via the same processes. Nevertheless, analysis of more pristine chondrules from chondrites of lower metamorphic grade is required to further assess any nebular processes of chondrule formation.

The Genesis mission captured Solar Wind (SW) and delivered it to Earth for laboratory analyses. Due to advanced mass spectrometric techniques developed specifically for analyses of returned Genesis SW-collectors, SW-oxygen, nitrogen and noble gas isotopes have been successfully measured providing new insights for cosmo- and geochemistry. SW-Xe collected by Genesis is the heaviest and the least abundant SW element analyzed. Here we describe in detail the experimental improvements we made over last 5 years and a latest refined SW-Xe isotopic composition. Combined with earlier, already published SW-Xe analyses, our new results provide the best current estimate for SW-Xe collected by Genesis: 136Xe/130Xe = 1.818 ± 0.004; 134Xe/130Xe = 2.242 ± 0.005; 132Xe/130Xe = 6.063 ± 0.010; 131Xe/130Xe = 5.010 ± 0.012; 129Xe/130Xe = 6.314 ± 0.013; 128Xe/130Xe = 0.510 ± 0.001; 126Xe/130Xe = 0.0256 ± 0.0004; 124Xe/130Xe = 0.0292 ± 0.0004 (all errors are 1σ). The achieved precision allows resolving small, but now statistically significant isotopic difference between solar wind Xe and Xe trapped in lunar regolith samples. This emerging difference, not apparent prior to this study, likely points to the composition of indigenous lunar Xe and to the temporal evolution of terrestrial Xe. Combining our Xe fluence with that for other high first ionization potential (FIP) elements, we find that the depletion of elements with the FIP greater than 12 eV is not constant but monotonically decreases as FIP increases.

We present the results of a coordinated NAUTILUS and NanoSIMS isotopic study of epsilon (e) phase metallic aggregates from the Oklo natural nuclear reactor zone (RZ) 13. We observed that fissionogenic Tc and Cs were heterogeneously sequestered within the aggregates. Isotopes of these elements are relevant for improving the safety of spent nuclear fuel storage and reactor operation on generational timescales. Like the noble metals, nearly all of the Tc was retained within the reactor, though its abundance relative to Ru in the metallic aggregates varied by a factor of 10. The neutron fluence estimated from the production of 100Ru from neutron capture on 99Tc was estimated to be up to 1.2 × 1021 n·cm-2. In contrast to Tc, nearly all of the fissionogenic Cs in the reactors was lost from the reactor fuel. The metallic aggregates contain the only phases yet identified to have sequestered radiocesium. Fissionogenic Cs isotopes decay over vastly different timescales, but were incorporated and retained within the e-phase in proportions similar to stable 133Cs. This indicates that retention began during criticality and sequestration lasted billions of years, despite local geologic activity and the presence of nearby magmatic dikes. Using fissionogenic Ba isotopes, we estimated that the metallic aggregates continually incorporated their radioactive Cs parents during criticality, though the majority of Cs was flushed out of the reactor on a characteristic timescale of 2.7 ± 0.6 years. We found that the abundance of Bi was correlated to Rh and Pd, and speculate that this may have been due to primary Np–Rh and Np–Pd alloys forming during or shortly after criticality. Using Pb–Pb data from uraninite and galena grains surrounding the metallic aggregates, we also inferred a final Pb mobility age of 298 Ma for RZ13, which is more recent than most estimates from other RZs.

Understanding the release and sequestration of specific radioactive signatures into the environment is of extreme importance for long-term nuclear waste storage and reactor accident mitigation. Recent accidents at the Fukushima and Chernobyl nuclear reactors released radioactive (137)Cs and (134)Cs into the environment, the former of which is still live today. We have studied the migration of fission products in the Oklo natural nuclear reactor using an isotope imaging capability, the NAval Ultra-Trace Isotope Laboratory’s Universal Spectrometer (NAUTILUS) at the US Naval Research Laboratory. In Oklo reactor zone (RZ) 13, we have identified the most depleted natural U of any known material with a (235)U/(238)U ratio of 0.3655 ± 0.0007% (2σ). This sample contains the most extreme natural burnup in (149)Sm, (151)Eu, (155)Gd, and (157)Gd, which demonstrates that it was sourced from the most active Oklo reactor region. We have discovered that fissionogenic Cs and Ba were captured by Ru metal/sulfide aggregates shortly following reactor shutdown. Isochrons from the Ru aggregates place their closure time at 4.98 ± 0.56 y after the end of criticality. Most fissionogenic (135)Ba and (137)Ba in the Ru migrated and was incorporated as Cs over this period. Excesses in (134)Ba in the Ru point to the burnup of (133)Cs. Cesium and Ba were retained in the Ru despite local volcanic activity since the reactor shutdown and the high level of activity during reactor operation.

Mass-spectrometric analyses of Xe released from acid-treated U ore reveal that apparent Xe fission yields significantly deviate from the normal values. The anomalous Xe structure is attributed to chemically fractionated fission (CFF), previously observed only in materials experienced neutron bursts. The least retentive CFF-Xe isotopes, 136Xe and 134Xe, typically escape in 2:1 proportion. Xe retained in the sample is complimentarily depleted in these isotopes. This nucleochemical process allows understanding of unexplained Xe isotopic structures in several geophysical environments, which include well gasses, ancient anorthosite, some mantle rocks, as well as terrestrial atmosphere. CFF is likely responsible for the isotopic difference in Xe in the Earth's and Martian atmospheres and it is capable of explaining the relationship between two major solar system Xe carriers: the Sun and phase-Q, found in meteorites.

Using in situ laser analyses of a polished thin section from the IAB iron meteorite Campo del Cielo, we identified two silicate grains rich in radiogenic 129* Xe, Cr-diopside, and oligoclase, excavated them from the metal, and irradiated them with thermal neutrons for I-Xe dating. The release profiles of 129* Xe and 128* Xe are consistent with these silicates being diopside and oligoclase, with activation energies, estimated using Arrhenius plots, of � 201 and � 171 kcal mole � 1 , respectively. The 4556.4 � 0.4 Ma absolute I-Xe age of the more refractory diopside is younger than the 4558.0 � 0.7 Ma I-Xe age of the less refractory oligoclase. We suggest that separate impact events at different locations and depths on a porous initial chondritic IAB parent body led to the removal of the melt and recrystallization of diopside and oligoclase at the times reflected by their respective I-Xe ages. The diopside and oligoclase grains were later brought into the studied inclusion by a larger scale catastrophic collision that caused breakup and reassembly of the debris, but did not reset the I-Xe ages dating the first events. The metal melt most probably was

The preserved record of decay of now-extinct 129I into 129Xe forms the basis of the I-Xe chronometer. Comparison of the high precision I-Xe and Pb-Pb ages of chondrules and pure mineral phases separated from eight meteorites suggests the 17.5 ÷ 14.6 Ma range for the 129I half-life, assuming that the 235U and 238U half-lives are correct. The mean value of 16 Ma indicates that the 15.7 Ma half-life of 129I used here for the I-Xe age calculations is most probably correct. Since the 129I half-life value only affects the relative I-Xe ages, the few Ma relative to the Shallowater standard, the absolute I-Xe ages are almost immune to this uncertainty in the 129I half-life.

– Neon was measured in 39 individual olivine (or olivine-rich) grains separated from individual chondrules from Dhajala, Bjurbole, Chainpur, Murchison, and Parsa chondrites with spallation-produced 21Ne the result of interaction of energetic particle irradiation. The apparent 21Ne cosmic ray exposure (CRE) ages of most grains are similar to those of the matrix with the exception of three grains from Dhajala and single grains from Bjurbole and Chainpur, which show excesses, reflecting exposure to energetic particles prior to final compaction of the object. Among these five grains, one from chondrule BJ2A5 of Bjurbole shows an apparent excess exposure age of approximately 20 Ma and the other four from Dhajala and Chainpur have apparent excesses, described as an “age,” from 2 to 17 Ma. The precompaction irradiation effects of grains from chondrules do not appear to be different from the effects seen in olivine grains extracted from the matrix of CM chondrites. As was the case for the matrix grains, there appears to be insufficient time for this precompaction irradiation by the contemporary particle sources. The apparent variations within single chondrules appear to constrain precompaction irradiation effects to irradiation by lower energy solar particles, rather than galactic cosmic rays, supporting the conclusion derived from the precompaction irradiation effects in CM matrix grains, but for totally different reasons. This observation is consistent with Chandra X-Ray Observatory data for young low-mass stars, which suggest that our own Sun may have been 105 times more active in an early naked T-Tauri phase (Feigelson et al. 2002).

Detailed isotopic and mineralogical studies of silicate inclusions separated from a troilite nodule of the Toluca IAB iron meteorite reveal the presence of radiogenic 129 Xe in chlorapatite, plagioclase, perryite, and pyroxene grains. Subsequent I-Xe studies of 32 neutron-irradiated pyroxene grains indicate that high-Mg and low-Mg pyroxenes have distinctive I-Xe signatures. The I-Xe system in high-Mg pyroxenes closed at 4560.5 ± 2.4 Ma, probably reflecting exsolution of silicates from the melt, while the low-Mg pyroxenes closed at 4552.0 ± 3.7 Ma, 8.5 Ma later, providing a means for determining the cooling rate at the time of exsolution. If the host Toluca graphite-troilite- rich inclusion formed after the breakup and reassembly of the IAB parent body as has been suggested, the I-Xe ages of the high-Mg pyroxenes separated from this inclusions indicate that this catastrophic impact occurred not later than 4560.5 Ma, 6.7 Ma after formation of CAIs. The cooling rate at the time of silicates exsolution in Toluca is 14.5 ± 10.0 °C/Ma.

The I–Xe chronometer is based upon decay of now-extinct 129I where the ratio of accumulated daughter 129Xe to stable 127I reflects the iodine isotopic ratio at closure of the host mineral. Since none of the parent remains, I–Xe is by nature a relative chronometer but, when referenced by a standard mineral of known age, the I–Xe system becomes an absolute chronometer reflecting true closure times. Most iodine hosts are secondary minerals so the I–Xe system is unique in providing details of post-formational chronometry not readily available with other chronometers. The short half-life of 129I gives it exceptional precision. However, the secondary nature of iodine host minerals, combined with the inherent precision of I–Xe, were responsible for a large database of “whole-rock” I–Xe ages that were not easily interpreted. As this problem evolved historically, doubts were cast upon the viability of the I–Xe system as a chronometer which persisted until it was tested against other chronometers in single-mineral systems. Properly calibrated, absolute I–Xe ages reflect the true closure time of the host minerals, and sequences of closure times in different hosts provide cooling rates for the parent object.

The double beta decay half-lives of 130 Te measured in geological Te specimens of known age fall into two distinct groups: 2.5 ± 0.4 × 10 21 yr and 8 ± 1 × 10 20 yr. Discussion about which value is correct has lasted for more than 30 years without a satisfactory resolution. Since the ratio of the 130 Te half-life to that of 128 Te is known ( 3.74 ± 0.11 × 10 −4 ) , the 128 Xe half-life, which constrains the effective Majorana mass of the neutrino, also becomes uncertain within this factor of ∼3. Here we describe several experiments and observations, which lead us to the conclusion that the “short” half-lives are more likely to be correct. This is in agreement with preliminary results recently obtained in the direct counting NEMO-3 experiment.

Twenty-two dark inclusions (DIs) from Allende (18), Leoville (2), Vigarano (1) and Efremovka (1) were studied by the I-Xe method. All except two of these DIs (Vigarano 2226 and Leoville LV2) produce well-defined isochrons, and precise I-Xe ages. The Allende DIs formed a tight group about 1.6 Ma older than Shallowater (4.566 ± 0.002 Ga), about 5 Ma older than four previously studied Allende CAIs. Most of the dark inclusions require trapped Xe with less 129Xe (or more 128Xe) than conventional planetary Xe (well restricted in composition by Q-Xe or OC-Xe). Studies of an irradiated/unirradiated DI pair from Allende demonstrate that the 128Xe/132Xe ratio in trapped is normal planetary, so that a 129Xe/132Xe ratio below planetary seems to be required. Yet, this is not possible given constraints on 129Xe evolution in the early solar system. Trends among all of the Allende DIs suggest that an intimate mixture of partially decayed iodine and Xe formed a pseudo trapped Xe component enriched in both 129Xe and 127I, and subsequently in 128Xe after n-capture during reactor irradiation. Enrichment in radiogenic 129Xe, but with a 129Xe/127I ratio less than that observed in the iodine host phase, places closure of this trapped mixture ≥13 Ma after precipitation of the major iodine-bearing phase. Because the I-Xe isochron is a mixing line between iodine-derived and trapped Xe (pseudo or not), I-Xe ages, given by the slope of this mixing line, are not compromised by the presence of pseudo trapped Xe, and the precision of the I-Xe ages is given by the statistics of the line fit.

We report the results of a study of 81 micrometer-sized presolar SiC grains in the size range 0.5-2.6 m from the Murchison (CM2) carbonaceous chondrite. We describe a simple, nondestructive physical disaggregation technique used to isolate the grains while preserving them in their pristine state, as well as the scanning electron microscopy energy-dispersive X-ray mapping procedure used to locate them. Nine-tenths of the pristine SiCs are bounded by one or more planar surfaces consistent with cubic (3C polytype) crystal faces based on manifest symmetry elements. In addition, multiple polygonal depressions (generally 100 nm deep) are observed in more than half of these crystal faces, and these possess symmetries consistent with the structure of the 3C polytype of SiC. By comparison of these features with the surface features present on heavily etched presolar SiC grains from Murchison separate KJG, we show that the polygonal depressions on pristine grains are likely primary growth features. The etched SiCs have high densities of surface pits, in addition to polygonal depressions. If these pits are etched linear defects in the SiC, then defect densities are quite high (as much as 10 8 -10 9 /cm 2 ), about 10 3 -10 4 times higher than in typical synthetic SiCs. The polygonal depressions on crystal faces of pristine grains, as well as the high defect densities, indicate rapid formation of presolar SiC. No other primary minerals are observed to be intergrown with or overgrown on the pristine SiCs, so the presence of overgrowths of other minerals cannot be invoked to account for the survival of presolar SiC in the solar nebula. We take the absence of other primary condensates to indicate that further growth or back-reaction with the gas became kinetically inhibited as the gas-phase densities in the expanding asymptotic giant branch (AGB) stellar atmospheres (in which most of the grains condensed) became too low. However, we did observe an oxygen peak in the X-ray spectra of most pristine grains, implying silica coatings of as much as several tens of nm thickness, perhaps due to oxidation of the SiC in the solar nebula. We see little or no evidence on the pristine grains of the surface sputtering or cratering that are predicted theoretically to occur in the interstellar medium (ISM) due to supernova shocks. A possible implication is that the grains may have been protected during their residence in the ISM by surface coatings, including simple ices. Residues of such coatings may indeed be present on some pristine SiCs, because many (60%) are coated with an apparently amorphous, possibly organic phase. However, at present we do not have sufficient data on the coatings to draw secure inferences as to their nature or origin. A few irregular pristine SiCs, either fragments produced by regolith gardening on the Murchison parent body or by grain- grain collisions in the ISM, were also observed. Copyright © 2003 Elsevier Ltd

Complex I-Xe and mineralogical studies have been performed on four heavily-altered Allende fine-grained spinel-rich Ca, Al-rich inclusions (CAIs) and four Allende dark inclusions (DIs) showing various degrees of iron-alkali metasomatic alteration. The CAIs are largely composed of Fe-rich spinel, Al-diopside, and secondary nepheline and sodalite. The DIs consist of chondrules and Allende-like matrix composed of lath-shaped fayalitic olivine, nepheline, sodalite, and Ca, Fe-rich pyroxene ± andradite ± FeNi-sulfide nodules. Chondrule phenocrysts are extensively or completely replaced by fayalitic olivine, nepheline, and sodalite; metal nodules are replaced by FeNi-sulfides, andradite and Ca, Fe-rich pyroxenes. The chondrules and matrices are crosscut by Ca, Fe-rich pyroxene ± FeNi-sulfide ± fayalitic olivine veins. DIs are surrounded by continuous Ca-rich rims composed of andradite, wollastonite, kirschsteinite, and Ca, Fe-rich pyroxenes, whereas the outer portions of the inclusions are depleted in Ca. Three CAIs yield well-defined I-Xe isochrons with ages 3.1 ± 0.2, 3.0 ± 0.2 and 3.7 ± 0.2 Ma younger than the Shallowater internal standard (4566 ± 2 Ma). Similar release profiles suggest the same iodine carrier (most probably sodalite) for all four CAIs. The Allende DIs yield I-Xe ages from 0.8 ± 0.3 to 1.9 ± 0.2 Ma older than Shallowater. Based on the petrographic observations, we infer that the DIs experienced at least two-stage alteration. During an early stage of the alteration, which took place in an asteroidal setting, but not in the current location of the DIs, chondrule silicates were replaced by secondary fayalitic olivine, nepheline, and sodalite. Calcium lost from the chondrules was redeposited as Ca, Fe-rich pyroxene veins and Ca, Fe-rich pyroxene ± andradite nodules in the matrix. The second stage of alteration resulted in mobilization of Ca from the DIs and its re-deposition as Ca-rich rims composed of Ca, Fe-rich pyroxenes, andradite, and wollastonite, around the DIs. We interpret I-Xe ages of the DIs as time of their alteration prior incorporation into Allende. The younger I-Xe ages of the fine-grained spinel-rich CAIs may reflect hydrothermal alteration of the Allende host, which could have occurred contemporaneously with the second stage of alteration of the Allende DIs. The lack of evidence for the disturbance of I-Xe system in the Allende DIs may suggest that fluid responsible for the alteration of the Allende CAIs was in equilibrium with the I- and Xe-bearing phases of the DIs.

A 28 g sample of the Qingzhen enstatite (EH3) chondrite was subjected to chemical and physical separation procedures to yield several grain-size residues. Ion mapping of isotopes of Si, O, and C in the ion microprobe of two size fractions (QZR4: 0.4-0.8 μm; QZR5: 0.8-2 μm) identified 55 30Si-depleted candidates out of 37,917 Si-rich grains and six 18O-depleted grains out of 54,410 oxides. Subsequent isotopic analyses of C, N, and Si of 48 grains of the 30Si-depleted candidates and additional randomly selected SiC and Si3N4 grains confirmed 36 of X-type SiC, nine of X-type Si3N4, and one of A+B-type SiC. The isotopic compositions of most X grains overlap those of previously measured X grains from the Murchison carbonaceous chondrite, but ~25% show more pronounced 29Si deficits, suggestive of multiple stellar origins of X grains. Presolar Si3N4 grains have isotopic compositions similar to those of X SiC grains, except that their C isotopic ratios are close to solar. The relative abundances of various presolar grain types in Qingzhen are different from those in Murchison, suggestive of heterogeneity and/or size sorting in the primitive solar nebula.

The extremely old I-Xe ages of Orgueil and Murchison magnetites, difficult to integrate into conventional meteorite evolutionary models, are not confirmed. New measurements indicate that Orgueil magnetite is 3 Ma younger than the Shallowater reference sample rather than 7 Ma older as previously reported by Lewis and Anders (1975) . If these differences are due to difficulties with the irradiation monitors in the earlier studies, there are wider implications because the same KI monitor was used to establish the I-Xe age of Murchison magnetite, which is used, in turn, as a reference sample in many subsequent I-Xe studies. Confirmation of these new results and a careful review of existing I-Xe age data are therefore in order. The old I-Xe age of Allegan feldspar, reported by Brazzle et al. (1999) may also be an artifact of shock disturbance.

Comparisons of I-Xe and Pb-Pb relative ages are made for phosphate and feldspar separates from 12 different meteorites. In all cases where I-Xe ages can be measured in phosphate, I-Xe and Pb-Pb chronometers agree within experimental uncertainty. No discordant phosphate samples are observed. With the exception of Allegan, I-Xe ages for feldspar separates generally agree with Pb-Pb ages for the corresponding phosphate. The general concordancy observed between I-Xe and Pb-Pb chronometers suggests that the I-Xe system is a reliable and interpretable chronometer when applied to single minerals systems. Allegan feldspar differs from the other feldspar separates, predating its phosphate by ∼17 Ma, with an I-Xe age indistinguishable from those of Orgueil and Murchison magnetites, among the oldest observed.

To evaluate the isotopic composition of the solar nebula from which the planets formed, the relation between isotopes measured in the solar wind and on the Sun's surface needs to be known. The Genesis Discovery mission returned independent samples of three types of solar wind produced by different solar processes that provide a check on possible isotopic variations, or fractionation, between the solar-wind and solar-surface material. At a high level of precision, we observed no significant inter-regime differences in 20 Ne/ 22 Ne or 36 Ar/ 38 Ar values. For 20 Ne/ 22 Ne, the difference between low- and high-speed wind components is 0.24 ± 0.37%; for 36 Ar/ 38 Ar, it is 0.11 ± 0.26%. Our measured 36 Ar/ 38 Ar ratio in the solar wind of 5.501 ± 0.005 is 3.42 ± 0.09% higher than that of the terrestrial atmosphere, which may reflect atmospheric losses early in Earth's history.

129Xe, from the decay of the now-extinct 16.7 Ma129I, accumulates in iodine-bearing sites and since most iodine host phases are secondary, the I-Xe system is typically a chronometer for post-formational processes. The validity of the I-Xe chronometer is confirmed by comparison with Pb-Pb ages on phosphate and feldspar separates from twelve meteorites. Phosphate separates are found to be concordant with Pb-Pb for all six samples in which useful I-Xe data were obtained. Feldspar is a better iodine host than apatite in H chondrites, typically providing good I-Xe isochrons. These too are concordant with the Pb-Pb ages of the corresponding phosphates for five out of six feldspar separates. The exception is Allegan whose feldspar yields one of the oldest I-Xe ages observed, similar to those for CI and CM magnetites. We attribute this to a more primary mineralization, predating the secondary phosphate from which the comparison Pb-Pb age was obtained. Absolute I-Xe ages, found using the reported Pb-Pb age of Acapulco phosphate provide an absolute I-Xe age of 4.566 ± 0.002 Ga for both Shallowater and Bjurbole irradiation standards. This allows relative I-Xe ages to be interpreted in the context of absolute ages.

One of the major goals of the Genesis Mission was to refine our knowledge of the isotopic composition of the heavy noble gases in solar wind and, by inference, the Sun, which represents the initial composition of the solar system. This has now been achieved with permil precision: ^(36)Ar/^(38)Ar = 5.5005 ± 0.0040, ^(86)Kr/^(84)Kr = .3012 ± .0004, ^(83)Kr/^(84)Kr = .2034 ± .0002, ^(82)Kr/^(84)Kr = .2054 ± .0002, ^(80)Kr/^(84)Kr = .0412 ± .0002, ^(78)Kr/^(84)Kr = .00642 ± .00005, ^(136)Xe/^(132)Xe = .3001 ± .0006, ^(134)Xe/^(132)Xe = .3691 ± .0007, ^(131)Xe/^(132)Xe = .8256 ± .0012, ^(130)Xe/^(132)Xe = .1650 ± .0004, ^(129)Xe/^(132)Xe = 1.0405 ± .0010, ^(128)Xe/^(132)Xe = .0842 ± .0003, ^(126)Xe/^(132)Xe = .00416 ± .00009, and ^(124)Xe/^(132)Xe = .00491 ± .00007 (error-weighted averages of all published data). The Kr and Xe ratios measured in the Genesis solar wind collectors generally agree with the less precise values obtained from lunar soils and breccias, which have accumulated solar wind over hundreds of millions of years, suggesting little if any temporal variability of the isotopic composition of solar wind krypton and xenon. The higher precision for the initial composition of the heavy noble gases in the solar system allows (1) to confirm that, exept ^(136)Xe and ^(134)Xe, the mathematically derived U–Xe is equivalent to Solar Wind Xe and (2) to provide an opportunity for better understanding the relationship between the starting composition and Xe-Q (and Q-Kr), the dominant current “planetary” component, and its host, the mysterious phase-Q.

Four uraninite separates from different reefs from in and above the Central Rand Group (Upper Witwatersrand Supergroup) were obtained from gold mines in the East Rand, West Rand, and Welkom Goldfields of the Witwatersrand Basin in South Africa. These samples were dated by the Xes-Xen spectrum technique. All four age spectra have a typical stepup form with plateaux for high temperature Xe release. The plateau ages are 0.832 ± 0.026 Ga for the Carbon Leader Reef sample from Blyvooruitzicht Gold Mine, 1.043 ± 0.024 Ga for the Basal Reef sample from Free State Geduld Gold Mine, 1.115 ± 0.036 Ga for the Main Reef uraninite concentrate from Sub Nigel Gold Mine, and 1.300 ± 0.058 Ga for the Ventersdorp Contact Reef sample from Kloof Gold Mine. No apparent ages in excess of 1600 Ma were observed. It is obvious from the general Witwatersrand chronological database that these fission xenon dating results do not correspond to primary crystallization ages for the uraninites. Instead, they most likely represent resetting events that affected the UXe isotopic system in these samples. Comparison with other recent chronological results obtained on rocks from the region of and around the Witwatersrand Basin indicates that the region was affected by magmatotectonic activity at 1.3 to 1 Ga ago, which, thus, was not only localized along the southern margin of the Kaapvaal Craton, the so-called Namaqua-Natal Thrust Front, but also affected other parts of the craton.

It is generally accepted that the primitive Sun, which contains the vast majority of the mass of the solar system, has the same composition as the primitive solar nebula, and that the contemporary Sun has a similar composition except perhaps for light elements modified in main sequence hydrogen burning. The diversity of isotopic and elemental compositions now observed in various solar system reservoirs is most likely the result of subsequent modification and noble gases can provide us with valuable tools to understand the evolutionary paths leading to these different compositions. However, to do this we need to know the composition of the Sun with sufficient precision to delineate the different paths and processes leading to the variations observed and how the present solar wind noble gases may differ from that composition.

Using selective laser extraction technique combined with sensitive ion-counting mass spectrometry, we have analyzed the isotopic structure of fission noble gases in U-free La-Ce-Sr-Ca aluminous hydroxy phosphate associated with the 2 billion yr old Oklo natural nuclear reactor. In addition to elevated abundances of fission-produced Zr, Ce, and Sr, we discovered high (up to $0.03\text{ }\text{ }{\mathrm{c}\mathrm{m}}^{3}\text{ }\mathrm{S}\mathrm{T}\mathrm{P}/\mathrm{g}$) concentrations of fission Xe and Kr, the largest ever observed in any natural material. The specific isotopic structure of xenon in this mineral defines a cycling operation for the reactor with 30-min active pulses separated by 2.5 h dormant periods. Thus, nature not only created conditions for self-sustained nuclear chain reactions, but also provided clues on how to retain nuclear wastes, including fission Xe and Kr, and prevent uncontrolled runaway chain reaction.

We review the development of the I-Xe technique and how its data are interpreted, and specify the best current practices. Individual mineral phases or components can yield interpretable trends in initial 129I/127I ratio, whereas whole-rock I-Xe ages are often hard to interpret because of the diversity of host phases, many of which are secondary. Varying standardizations in early work require caution; only samples calibrated against Shallowater enstatite or Bjurble can contribute reliably to the emerging I-Xe chronology of the early solar system.Although sparse, data for which I-Xe and Mn-Cr can be compared suggest that the two systems are concordant among ordinary chondrite samples. We derive a new age for the closure of the Shallowater enstatite standard of 4563.3 ± 0.4 Myr from the relationship between the I-Xe and Pb-Pb systems. This yields absolute I-Xe ages and allows data from this and other systems to be tested by attempting to construct a common chronology of events in the early solar system.Absolute I-Xe dates for aqueous and igneous processes are consistent with other systems. Consideration of the I-Xe host phases in CAIs and dark inclusions demonstrates that here the chronometer records aqueous alteration of pre-existing material. The ranges of chondrule ages deduced from the Al-Mg and I-Xe systems in Semarkona (LL3.0) and Chainpur (LL3.4) are consistent. Chainpur I-Xe data exhibit a greater range of ages than Semarkona, possibly reflecting a greater degree of parent body processing. However individual chondrules show little or no evidence of such processing. Determining the host phase(s) responsible for high temperature correlations may resolve the issue.

The Hayabusa2 spacecraft returned to Earth from the asteroid 162173 Ryugu on 6 December 2020. One day after the recovery, the gas species retained in the sample container were extracted and measured on-site and stored in gas collection bottles. The container gas consists of helium and neon with an extraterrestrial ³He/⁴He and ²⁰Ne/²²Ne ratios, along with some contaminant terrestrial atmospheric gases. A mixture of solar and Earth’s atmospheric gas is the best explanation for the container gas composition. Fragmentation of Ryugu grains within the sample container is discussed on the basis of the estimated amount of indigenous He and the size distribution of the recovered Ryugu grains. This is the first successful return of gas species from a near-Earth asteroid., 「はやぶさ2」ミッションによる世界初の小惑星からのガスサンプル：リュウグウからのたまて箱. 京都大学プレスリリース. 2022-10-21.