Composition Of Neon Research Articles

The Lunar Breccia Dhofar 1442: Noble Gases, Nitrogen, and Carbon Released by Stepwise Combustion and Crushing

AbstractStepwise crushing and combustion methods were applied to study the KREEP-rich lunar breccia Dhofar 1442, the clastic material of which is cemented by porous matrix. The stepwise crushing released significant amount of gases of extraterrestrial origin from gas voids. Argon, nitrogen, and carbon are simultaneously released by stepwise combustion at 1100°С. The simultaneous high-temperature degassing of these gases, as well as the coincidence of С/N ratio and nitrogen and carbon contents in high-temperature combustion steps with those of crushing indicate that the gas carriers are voids in high-temperature phases (in particular, minerals, glasses), which are decomposed/melted at these temperatures. Helium and neon are released from the same positions at lower temperatures. The isotopic composition of neon obtained by stepwise combustion and crushing corresponds to the composition of fractionated solar wind. The fraction of argon in the first crushing steps is higher than that of any other of studied gases. The 40Ar/36Ar in the trapped lunar argon is ~18, which is not consistent with empirical model implying that 40Аr is implanted from lunar atmosphere (McKay et al., 1986; Eugster et al., 2001; Joy et al., 2011). We believe that the entrapment of volatile elements in gas voids of the meteorite Dhofar 1442 was caused by the redistribution of gases from one structural sites into others during impact events that accompanied the cratering, in particular, leading to the formation of the impact melt breccia Dhofar 1442. The trapped gases of the meteorite Dhofar 1442 contain not only typical volatile components (solar, radiogenic, cosmogenic, re-implanted 40Ar) of lunar breccias, but also nitrogen and carbon formed through the oxidation of organic matter of metamorphosed chondrites, which are present in the breccia. With increasing number of strokes and, correspondingly, a degree of crushing, the elemental ratios change. A slight decrease of 4He/20Ne ratio during crushing is likely related to the different diffusion ability and permeability of helium relative to neon under temperature influence and/or to the heterogeneous distribution of these gases in voids of different size. The 4He/36Ar, 20Ne/36Ar, 14N/36Ar, and 12С/36Ar ratios increase by factors of 10–100 during crushing. This can be explained by the combination of dynamically different processes leading to the argon fractionation relative to other gases and uneven redistribution of gases from different positions in voids of different sizes during impact metamorphism.

An inter-comparison of isotopic composition of neon via chemical assays and thermal analyses (IUPAC Technical Report)

Article An inter-comparison of isotopic composition of neon via chemical assays and thermal analyses (IUPAC Technical Report) was published on January 1, 2020 in the journal Chemistry International (volume 42, issue 1).

An inter-comparison of isotopic composition of neon via chemical assays and thermal analyses (IUPAC Technical Report)

Abstract In 2003–2014, a study on the effect of isotopic composition on the triple point temperature of neon was conducted under the framework of a Project involving laboratories from 11 countries. Natural neon from commercial sources of different isotopic composition, high-purity 20Ne and 22Ne isotopes, and certified artificial isotopic mixtures were used. The thermometric studies comprised: a) a total of 131 analytical assays from 3 laboratories on the isotopic composition of samples taken from 31 different bottles of neon with chemical gas purity 99.99 mol % to 99.9995+ mol %, including chemical impurities for some samples, with up to 12 assays per sample; b) multi-laboratory thermal analyses, with accuracies ranging up to better than 50 μK (k≈2), on 39 samples, almost all permanently sealed in metal cells, for the determination of the liquidus-point temperature of the triple point as a function of isotopic composition. The thermometric studies also constitute an international inter-comparison of thermal and analytical assays on the isotopic composition—and occasionally of the chemical impurities—of neon. These tests are critically needed for top-accuracy thermometry. The main results of the inter-comparison of the various chemical assays, and of the comparisons between the assays and the results of thermal analyses, are reported. They show discrepancies in x(20,21,22Ne), especially for x(22Ne), in ‘natural’ neon, for the same gas bottle, equivalent to an uncertainty of up to 165 μK (k = 1) in the triple point temperature, as measured by all testing laboratories, and of about 100 μK (k = 1) as measured from a single testing laboratory. This is an unsatisfactory situation for thermometry, since it is difficult to obtain a reliable and accurate isotopic assay for neon, thus limiting the accuracy of the realisation of the neon triple point temperature as a ITS-90 reference point to well above 50 μK. However, it also discloses a strong limitation in the relevant analytical chemistry.

Noble gas composition of Indian carbonatites (Amba Dongar, Siriwasan): Implications on mantle source compositions and late-stage hydrothermal processes

Within a stepwise crushing study we determined the noble gas composition of several calcite separates, one aegirine and one pyrochlore-aegirine separate of the carbonatite ring dyke complex of Amba Dongar and carbonatite sill complex of Siriwasan, India. Both carbonatites are related to the waning stages of volcanic activity of the Deccan Igneous Province ca. 65 Ma ago. Major observations are a clear radiogenic 4He⁎ and nucleogenic 21Ne⁎ imprint related to in situ production from U and Th in mineral impurities, most likely minute apatite grains, or late incorporation of crustal fluids. However, in first crushing steps of most calcites from Amba Dongar a well-resolvable mantle neon signal is observed, with lowest air-corrected mantle 21Ne/22Ne-compositions equivalent to the Réunion hotspot mantle source. In case of the aegirine separate from Siriwasan we found a neon composition similar to the Loihi hotspot mantle source. This transition from a mantle plume signal in first crushing step to a more nucleogenic signature with progressive crushing indicates the presence of an external (crustal) or in situ nucleogenic component unrelated and superposed to the initial mantle neon component whose composition is best approximated by results of first crushing step(s). This contradicts previous models of a lithospheric mantle source of the carbonatitic magmas from Amba Dongar containing recycled crustal components which base on nucleogenic neon compositions. Instead, the mantle source of both investigated carbonatite complexes is related to a primitive mantle plume source that we tentatively ascribe to the postulated Deccan mantle plume. If, as is commonly suggested, the present location of the Deccan mantle plume source is below Réunion Island, the currently observed more nucleogenic neon isotopic composition of the Réunion hotspot might be obliterated by significant upper mantle contributions. In addition, compared with other carbonatite complexes worldwide a rather significant contribution of atmospheric noble gases is observed. This is documented in cut-off 20Ne/22Ne-ratios of ca. 10.2 (Amba Dongar) and 10.45 (Siriwasan) and cut-off 40Ar/36Ar-ratios of about 1500. This atmospheric component had been added at shallow levels during the emplacement process or later during hydrothermal alteration. However, understanding the late-stage interaction between atmospheric gases and magmatic mantle fluids still requires further investigation.

Neon isotopic composition of the mantle constrained by single vesicle analyses

The origin of volatiles on Earth is still a matter of debate. Noble gases are an efficient geochemical tool to constrain Earth formation processes due to their inertness. Several studies have focused on the neon isotopic composition of the lower mantle because the 20Ne/22Ne ratio is thought to reflect that of Earth's primordial components. Two models to explain the origin of light noble gases on Earth have been proposed: either solar wind implantation onto the Earth's solid precursors or dissolution into the mantle of a primordial atmosphere captured from solar nebula gas. In order to test these two models, we analyzed the noble gas compositions (helium, neon and argon) of two submarine oceanic island basalt glasses from Fernandina volcano (Galápagos archipelago), which have among the most primitive/unradiogenic terrestrial helium and neon isotopic compositions. Several sample pieces are studied both by step-crushing and by laser ablation analyses of single vesicles. Results of step-crushing are consistent with those of laser ablation analyses, but the latter results provide new insights into the origin of atmospheric contamination. The single-vesicle laser-ablation measurements overlap with the step crushing results, but have systematically higher 40Ar/36Ar, and 3He/36Ar, suggesting less atmospheric contamination using this method. The single vesicle data therefore suggest that atmospheric contamination is introduced by exposure to the modern atmosphere, after sample collection. 3He/4He values are about 23 times the atmospheric ratio (R/Ra) for the two Fernandina (Galápagos) samples, in agreement with previous studies. We obtain 20Ne/22Ne and 40Ar/36Ar isotopic ratios as high as 12.91 and 9400, respectively, for the mantle source of the Galápagos hotspot. The new data show that step-crushing and laser ablation analyses are complementary methods that should be used together to derive the noble gas ratios in uncontaminated samples. The results of neon compositions are consistent with previous hotspot studies and support the model of solar wind implantation associated with sputtering to explain helium and neon origins on Earth.

Triple-Point Temperature and the Isotopic Composition of Three Commercial Neon Gases

The triple-point temperature of neon, \(T_{\mathrm{tp-Ne}}\), is known to have dependence on the isotopic composition. Recently, the Technical Annex for the International Temperature Scale of 1990 was updated to specify the method of correction for the isotopic reference ratio of neon. In this study, to confirm this correction in the Technical Annex independently, the effects of the isotopic composition of neon on \(T_{\mathrm{tp-Ne}}\) for three commercial neon gas sources were studied. For the measurement of the isotopic composition, a gas mass spectrometer was used to compare the sample gases with a reference neon gas whose isotopic composition was known with high precision by a gravimetric method. For the measurement of \(T_{\mathrm{tp-Ne}}\), an open-cell type cryostat for the realization of low-temperature fixed points was used. The physical cell and the thermal environment around it remained very similar for all \(T_{\mathrm{tp-Ne}}\) measurements with the neon gases due to the nature of the open-cell type system. Therefore, the difference in \(T_{\mathrm{tp-Ne}}\) among different samples could be measured with a relatively low uncertainty, canceling many systematic effects that are common to all measurements. Our result was consistent with the correction in the Technical Annex. Furthermore, because one of the commercial neon gases was the bottle that was used for KRISS measurements in the international comparison CCT-K2, it is now possible to correct the measurement for the reference isotopic ratio and compare it with other measurements for which isotopic composition data are available.

Neon identifies two billion year old fluid component in Kaapvaal Craton

The deep gold mines of the Witwatersrand Basin, South Africa have gained recent attention not only because of investigations of the deep fracture water and associated CH 4- and H 2-rich gases found there, but because of recent reports of deep microbial communities persisting to depths of almost 3 km — an exotic outpost of the Earth's deep biosphere. While shallower fluids in the basin (to approximately 1 km) were found to contain abundant populations of methanogens and sulphate-reducing bacteria, the deepest, oldest, most saline fracture waters in the basin hosted hitherto unrecognised low biomass and low biodiversity chemoautotrophic ecosystems independent from the photosphere. Shallow and deep fluids also show distinct differences in gas and fluid geochemistry. Paleometeoric waters are dominated by hydrocarbon gases with compositional and isotopic characteristics consistent with production by methanogens utilising the CO 2 reduction pathway. In contrast the deepest, most saline fracture waters contain gases that are dominated by high concentrations of H 2 gas, and CH 4 and higher hydrocarbon gases with isotopic signatures attributed to abiogenic processes of water–rock reaction. The high salinities (up to hundreds of g/L), highly altered δ 18O and δ 2H signatures, and both 36Cl and measurements of co-occurring nucleogenic noble gases for these fracture waters are consistent with extensive water–rock interaction over geologically long time scales in these high rock/water ratio environments. While the ultimate origin of these fluids has been attributed alternately to saline waters that penetrated the crystalline basement, formation water, or hydrothermal fluids in some cases, their δ 18O and δ 2H isotopic signatures have typically been so profoundly overprinted by the effects of long-term water–rock interaction that, for the most saline end-members, little evidence of their primary composition remains. The key objective of the present study is to further investigate the origin of these fluids by integrating for the first time detailed neon isotope analyses on the dissolved gases. Helium isotopic analysis confirmed that there is no significant mantle-derived component associated with these fluids and gases. Neon isotope results show distinct differences in neon composition that correspond to the different fluid geochemical end-members previously identified. Typical crustal neon signatures (type A) are identified in the paleometeoric waters populated with abundant methanogens. In contrast, the deep more saline fracture waters contain an enriched nucleogenic neon signature unlike any previously reported in crustal fluids. These samples show the highest 21Ne/ 22Ne ratios (0.160 ± 0.003) ever reported in groundwater. Fluid inclusions in these rocks yield even higher 21Ne/ 22Ne ratios between 0.219 and 0.515, consistent with an extrapolated 21Ne/ 22Ne value of 3.3 ± 0.2 at 20Ne/ 22Ne = 0. We show that this enriched nucleogenic neon end-member represents a fluid component that was produced in the fluorine-depleted Archaean formations and trapped in fluid inclusions ≥ 2 Ga ago. The observation of enriched nucleogenic neon signatures in deep fracture water implies the release of this billion year old neon component from the fluid inclusions and its accumulation in exceptionally isolated fracture water systems. The observed association of this Archean neon signature with H 2-hydrocarbon-rich geogases of proposed abiogenic origin dissolved in the same deep groundwater suggests that the fracture systems have also allowed for the accumulation of various products of water–rock reactions throughout geologic times. One of these fracture systems contained the deepest characterised microbial ecosystems on earth — chemolithotrophs eking out an existence at maintenance levels independent from sunlight. Consequently, the enriched nucleogenic neon isotope signature may indicate regions in the Archaean crust where investigations of the deep biosphere might be focused.

Undesired radionuclides in 18F2 production by deuterons

In this paper, radionuclidic impurities generated during the bombardment of an 20Ne gaseous matrix in the routine production of [18F]-fluorodopa were studied. 18F2 is produced by the GE PETtrace cyclotron capable of accelerating negative deuteron ions to an energy of 8.4 MeV. The materials of the target and of the Havar foil, the stable fluorine added as carrier and the natural isotope composition of neon may interact with deuterons and produce undesired radionuclides. To measure them, a sampling system has been realized. Samples of the irradiated gas have been measured by gamma-ray spectrometry. The results show how the radionuclidic purity obtained is very high after a short time from the end of bombardment (EOB).

Progress Towards the Determination of the Relationship of Triple-Point Temperature versus Isotopic Composition of Neon

Following the finalization of the work performed to establish the triple-point temperature versus isotopic composition relationship for protium (Metrologia 42, 171 (2005)) adopted into the ITS-90 definition by the International Committee for Weights and Measures (CIPM) in 2005, and a preliminary exploration of the variability in the triple-point temperature of neon gas samples arising from differences in isotopic composition (Anal. Chem. 77, 5076 (2005)), this article reports further progress toward the determination of a similar comprehensive relationship for neon, to be included in a future revision of the Technical Annexe to the ‘mise en pratique’ of the kelvin. This progress article mainly concerns a set of gas samples used for the neon triple-point measurements during CCT-K2, and subsequently, others for which the isotopic compositions were recently measured. Recent high accuracy measurements of the corresponding thermal data are now available for many of these samples, but not yet for all of them.

Solar Wind Neon from Genesis: Implications for the Lunar Noble Gas Record

Lunar soils have been thought to contain two solar noble gas components with distinct isotopic composition. One has been identified as implanted solar wind, the other as higher-energy solar particles. The latter was puzzling because its relative amounts were much too large compared with present-day fluxes, suggesting periodic, very high solar activity in the past. Here we show that the depth-dependent isotopic composition of neon in a metallic glass exposed on NASA's Genesis mission agrees with the expected depth profile for solar wind neon with uniform isotopic composition. Our results strongly indicate that no extra high-energy component is required and that the solar neon isotope composition of lunar samples can be explained as implantation-fractionated solar wind.

Evidence of a Systematic Deviation of the Isotopic Composition of Neon from Commercial Sources Compared with Its Isotopic Composition in Air

Results are reported of a study concerning the variation in isotopic composition of a limited number of neon samples of commercial origin and the resulting influence on the temperature of the triple point of this element. All seven neon samples investigated were found to contain more 22Ne than neon in air, and the amount fraction of 22Ne varied by as much as 0.2% from sample to sample. This variation corresponds to a range of triple-point temperatures (Ttp) of more than 200 microK, much larger than the state-of-the-art uncertainty in the realization of this phase transition for metrological purposes. Deviations in the amount fractions of 21Ne were irrelevant, as far as their effect on T(tp) is concerned, though they may have relevance to other isotope studies. Ratios of amounts of neon isotopes at IRMM-Geel were obtained using the same measurement procedures, and instrumentation developed in the framework of the redetermination of the Avogadro constant and all significant sources of uncertainty were taken into account. The repeatability of the ion current ratio measurements on individual samples was 5 x 10(-5) relative. All uncertainty statements are made following the ISO/BIPM Guide to the Expression of Uncertainty in Measurements. Whereas these results proved unexpected, a more comprehensive study will follow incorporating a much wider range of samples of commercial origin.

Event‐to‐event variations in the isotopic composition of neon in solar energetic particle events

Using the Solar Isotope Spectrometer on the Advanced Composition Explorer, we have measured the isotopic composition of neon at 24–72 MeV/nucleon in nine solar energetic particle events between 4 November 1997 and 16 November 1998. The 22Ne/20Ne ratio varies from ∼0.7 to ∼2 times the solar wind value from event to event, indicating significant mass fractionation in the acceleration and/or transport of these particles. The mass fractionation is strongly correlated with the Fe/O and Na/Mg element abundance ratios, suggesting that elemental and isotopic fractionation are both governed by the ionic charge to mass ratio.

Irradiation records in regolith materials. I: isotopic compositions of solar-wind neon and argon in single lunar mineral grains

We have applied a stepwise pyrolytic extraction technique to eleven individual lunar regolith grains to investigate the compositions of light noble gases embedded in grain surfaces by solar wind irradiation, with emphasis on the rather poorly known isotopic composition of solar-wind argon. Results are intriguing: average 20Ne/ 22Ne ratios observed in early pyrolytic releases from ilmenite grains separated from lunar soils 71501, 79035 and 10084 agree very well with both direct measures of the solar wind neon composition in the Apollo foils and with values obtained in first releases from acid-etched ilmenites by the Zürich laboratory, whereas these same pyrolytic and acid-etch fractions carry argon isotopic signatures that significantly disagree—average 36Ar/ 38Ar ratios near 5.8 for thermal extraction compared to 5.4–5.5 for chemical etching at Zürich. Consideration of the isotopic and elemental data from these grains in the context of first-order diffusive modeling calculations points to gas release at low temperatures, without significant isotopic or elemental fractionation, from isolated grain-surface reservoirs of solar wind composition. The physical nature of these reservoirs is presently unknown. In this interpretation the preferred solar wind 20Ne/ 22Ne and 21Ne/ 22Ne ratios deduced from this study are respectively 13.81 ± 0.08 and 0.0333 ± 0.0003, both within error of the Zürich acid-etch values, and 36Ar/ 38Ar = 5.77 ± 0.08. It may be possible to reconcile the discrepancy between the acid-etch and pyrolytic estimates for the solar wind 36Ar/ 38Ar ratio in the context of arguments originally advanced by Benkert et al. (1993) to account for their He and Ne isotopic compositions. At the other, high-temperature end of the release profile from one of these grains there are clear isotopic indications of the presence of a Ne constituent with 20Ne/ 22Ne close to the 11.2 ratio found at Zürich and attributed by these workers to a deeply-sited component implanted by solar energetic particles.

Evolution of Earth's Noble Gases: Consequences of Assuming Hydrodynamic Loss Driven by Giant Impact

A simple analytic model of hydrodynamic escape is applied to atmospheric loss from Earth under conditions that are unproven but could plausibly have existed following deposition of thermal energy by a giant Moon-forming impact. Primordial xenon in the primary (pre-impact) atmosphere is readily fractionated to its contemporary nonradiogenic isotopic composition by appropriate selection of parameters in the equations governing the escape process. Subsequent mixing of the fractionated residuals of lighter primordial noble gases surviving in the post-escape atmosphere with solar-composition gases outgassed from the deep planetary interior yields close matches to the present-day abundances and isotopic compositions of atmospheric krypton and argon. Replication of present-day neon composition requires an additional later episode of hydrodynamic H 2escape, now powered by extreme-ultraviolet (EUV) solar radiation just intense enough for entrainment and loss of Ne but not of heavier species. Requirements for EUV flux intensity and planetary water inventory are substantially reduced compared to an earlier model of EUV-driven Xe loss from Earth. A noteworthy result of this approach is the close agreement of the noble gas elemental composition characterizing the pre-impact terrestrial atmosphere with that derived for Venus's primary atmosphere from a parallel evolutionary model involving only solar EUV radiation as an energy source. No claim is made that the modeling parameters used here adequately describe the complex and rapidly evolving physical nature of the post-impact terrestrial atmosphere, or that these solutions are unique. But they do suggest a basic unity in primordial noble gas distributions on the two planets, and point to separate mechanisms that could account for divergent evolution to their presently radically different compositional states.

Isotopes of the light noble gases in mineral waters in the eastern part of the Balkan peninsula, Bulgaria

The concentration and isotopic composition for the light noble gases in spontaneous gas from mineral waters in the eastern part of Balkan peninsula are presented in this paper. The isotopic ratio 3He 4He in dissolved gases varies within the range 0.15–1.1 × 10 −6 and the concentration of helium in these gases is between 0.002 and 3.14 vol%. It is determined that 86.7–98.8, 0.4–9.2 and <1% of 4He is derived from the crust, mantle and atmosphere, respectively. The main source of 3He is the Earth's mantle. The isotopic composition of neon is nearly the same as that in the atmosphere. Several samples show a slight excess of light isotopes, probably due to the mass fractionation of atmospheric neon. The isotopic composition of argon is also quite near to that in the atmosphere. In three cases argon contains 18.1, 12.3 and 7.9% of the radiogenic component. The ( Ar N 2 ) a ratios as a rule vary between 0.012 (air) and 0.027 (dissolved air), so that N 2 in most of the samples is also assumed to be of atmospheric origin. The ratio ΣC 3He in many sites is as low as 10 7, but this fact cannot be used to reveal unambiguously the origin of C-containing gases.

Neon and xenon isotopes in MORB: implications for the earth-atmosphere evolution

The isotopic composition of neon and xenon measured in MORB glasses confirm significant deviations from atmospheric values. These are (1) 21Ne excesses which are attributed to nucleogenic reactions in the mantle: (2) 20Ne/ 22Ne ratios higher than the air ratio interpreted as an evidence for the occurrence of solar-type Ne at depth: (3) 129Xe and 131–136Xe excesses, attributed to both extinct ( 129I and 244Pu) and present ( 238U) radioactivities. Ne and Xe isotopic signatures in the mantle can hardly be explained in the framework of classical models for the atmospheric evolution (which postulate a mantle origin for atmospheric gases) and appeal for at least two sources of gases. Ne isotopic differences between air and MORB appear too large to be accounted for by any reasonable fractionation process in the mantle. They imply either fractionation of neon during hydrodynamic escape of a primary atmosphere or different degrees of mixing between primordial Ne components, which, in turn imply isolation of the surface reservoir (air) and deep reservoir (mantle) from the accretional period (except for mantle outgassing through volcanism, the contribution of which is 41% at best for 20Ne). 129I 129Xe, 244Pu 238U 136Xe systematics for atmospheric and MORB-type xenon suggest that either atmospheric gases derived from a source whose formation was delayed (⩾ 17 Ma) with respect to the mean accretion time of the mantle source and/or atmospheric gases and MORB-type gases derived from chemically distinct sources. These features are consistent with heterogeneous accretion models for the Earth. Volatile degassing was probably contemporaneous to accretional events, following impact degassing, and might have been most efficient during the late stages of Earth formation.

Neon isotope studies of Fayetteville and Kapoeta meteorites and clues to ancient solar activity

Pyroxene grain-size separates, from both dark (D) and light (L) portions of two gas-rich meteorites, Fayetteville and Kapoeta, were chemically etched to remove the surficial solar wind (SW). These samples were studied mass spectrometrically for neon to decipher the long-term average solar flare (SF) neon composition and fluxes as well as the solar cosmic ray (SCR) proton fluxes from the ancient Sun during the solar system formation. Based on the results from Fayetteville and Kapoeta, we deduce that the SF-Ne composition from the ancient Sun is 20 22 = 11.6 ± 0.2 and 21 22 = 0.030 , which is similar to that deduced from our lunar sample studies (Nautiyal et al., 1981, 1986). The SF, SCR and galactic cosmic ray (GCR) produced neon isotopes are resolved into their individual components in the neon mixtures of these etched pyroxenes under the assumption that GCR-produced neon in pyroxenes from the dark and light phases of Fayetteville and Kapoeta are similar. We find significant excess of 21Ne produced by SCR protons ( p) in these etched pyroxenes. This observed excess 21Ne can be explained if the SCR proton fluxes from the ancient Sun are considered to be about three orders of magnitude higher than those from the contemporary Sun. This inference is supported by the significant excess of implanted SF- 20Ne ( E > 1 MeV/amu) observed here in the irradiated pyroxenes of Fayetteville and Kapoeta. The agreement of p ( E > 10 MeV/amu)/ Ne ( E > 1 MeV/amu) ratio for the ancient solar flares deduced in this study with the same ratio for the contemporary solar flares deduced from lunar sample studies suggests that these observed neon excesses were most probably produced by the solar flare irradiation of these grains during surface irradiation on the regolith of the meteorite parent bodies during the early solar system.

The case for a martian origin of the shergottites, II. Trapped and indigenous gas components in EETA 79001 glass

Analysis of nitrogen and light noble gases in a large sample of glass (lithology C) from the antarctic shergottite EETA 79001 yields a minimum δ 15N > +300‰ for the isotopic composition of nitrogen trapped in the glass. The new data fall on the mixing line through the martian atmospheric composition defined by δ 15N vs. 40Ar/ 14N for two smaller samples analyzed previously. The results from all three samples are consistent with a two-component nitrogen system in which ∼ 84 ppb of trapped martian atmospheric N is mixed in variable proportions with another, more thermally labile N component during stepped heating. This second component, which appears to be indigenous to the glass rather than adsorbed from air and is present in amounts that vary by more than a factor of 3 from sample to sample, may represent volatiles from the martian interior. Data from crystalline phases of several SNC meteorites indicate that the indigenous gas may have δ 15N < −35‰ and 36Ar/ 14N≲ 3 × 10 −6 , similar to the enstatite chondrites. Neon compositions in EETA 79001 glass samples suggest an earth-like value of ∼ 10.1 ± 0.7 for the unknown 20Ne/ 22Ne ratio in the martian atmosphere. The nitrogen-argon correlation systematics yield trapped 40Ar/ 36Ar= 2260 ± 200 , within error of the Viking value. There is evidence that 36Ar/ 38Ar in the martian atmosphere is 4.1 ± 0.2, strikingly different from terrestrial or typical chondritic ratios near 5.3. Attribution of this low value to excess 38Ar generated over martian history by galactic cosmic-ray (GCR) spallation of surface materials would be difficult for a number of reasons, among them the excessive GCR fluences required and the absence of a corresponding 21Ne excess.

Solar flare neon composition and solar cosmic-ray exposure ages based on lunar mineral separates

view Abstract Citations (8) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Solar Flare Neon Composition and Solar Cosmic-Ray Exposure Ages Based on Lunar Mineral Separates Nautiyal, C. M. ; Padia, J. T. ; Rao, M. N. ; Venkatesan, T. R. Abstract Etched pyroxene grain-size separates from lunar soils 14148 and 24087 and etched feldspar grain-size separates from soil 61221 are analyzed for neon isotopic and elemental composition, and the procedures to isolate the implanted solar flare (SF) neon and solar and Galactic cosmic-ray (SCR and GCR)-produced Ne components in these samples are discussed. These results indicate that the SF neon composition is Ne-20/Ne-22 = 11.6 + or - 0.2. The surface exposure ages are determined from the resolved SCR-produced Ne contents in the mineral separates from soils 14148, 24087, and 69921 using the appropriate SCR-Ne-21 production rates for feldspars and pyroxenes, based on the SCR proton flux of J (equal to or greater than 10 MeV) = 100 protons/sq cm per sec and R(0) = 100 MV. These SCR ages agree with those determined by particle track methods within a factor of 2. Publication: The Astrophysical Journal Pub Date: February 1986 DOI: 10.1086/163915 Bibcode: 1986ApJ...301..465N Keywords: Abundance; Chronology; Lunar Composition; Neon; Solar Cosmic Rays; Solar Flares; Lunar Soil; Minerals; Pyroxenes; Radiation Dosage; MOON; SOLAR FLARES; NEON; COMPOSITION; COSMIC RAYS; EXPOSURE AGE; SOIL; MINERALS; SAMPLES; LUNAR; PYROXENE; 14148; 24087; FELDSPAR; 61221; APOLLO MISSIONS; ISOTOPES; ELEMENTS; TECHNIQUES; ISOTOPIC RATIOS; FLUX; 69921; PRODUCTION RATES; DATING METHODS; COMPARISONS; EXPERIMENTS; Lunar and Planetary Exploration; Moon; COSMIC RAYS: ABUNDANCES; MOON; SUN: ABUNDANCES; SUN: FLARES full text sources ADS |

A hollow cathode arc in neon: Simultaneous laser probing and molecular-beam sampling of metastable atoms as a plasma diagnostic

The mean free path of metastable rare-gas atoms in a plasma can be determined by simultaneous sampling of a beam of metastable atoms through an orifice in the wall and optically pumping of the metastable atoms in the plasma with a cw dye laser beam perpendicular to the atomic beam axis. This method gives very accurate results for the absolute value and the velocity dependence (using a time-of-flight detection technique) of this mean free path. With a simple model the contributions of collisions with electrons and with heavy particles to the experimental mean free path can be determined from the velocity dependence. We have applied this method to the external plasma column of a hollow cathode arc in neon. The experimentally determined mean free path of 2–10 mm points unambiguously to a surprisingly low degree of ionization of 2% or less. At these conditions the plasma column is fully transparent for the background atoms in the vacuum chamber. This all means that the character of the plasma of a hollow cathode arc in neon is totally different from argon and helium, which is probably caused by the isotope composition of neon.