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All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Early outgassing of Mars supported by differential water solubility of iodine and xenon

The Martian atmosphere has a high X-129/Xe-132 ratio compared to the Martian mantle. As Xe-129 is the daughter product of the extinct nuclide I-129, a means of fractionating iodine from xenon early in Martian history appears necessary to account for the X-129/Xe-132 ratios of its known reservoirs. A model is presented here to account for the Marian xenon data which relies on the very different solubilities of xenon and iodine in water to fractionate them after outgassing. Atmospheric xenon is lost by impact erosion during heavy bombardment, followed by release of Xe-129 produced from I-129 decay in the crust.

Musselwhite, Donald S.↗
NASA NTRS2003

I-Xe Ages and Trapped Xe Compositions

I-Xe isochrons are mixing lines between a single trapped and a single iodine derived component. The slope of this line establishes initial iodine and hence the I-Xe age. One end of the isochron is fixed by the composition of the trapped Xe component, which should be representative of the Xe that was present in the early solar system (Q-Xe or OC-Xe). Because the I/Xe ratio in the solar nebular was ~1, and the I-129/I-127 was about 10-4, the Xe-129 in trapped Xe cannot evolve appreciably with decay of I-129. While it may be possible for Xe in a closed system with elevated I/Xe ratios to evolve producing trapped components with higher Xe-129/Xe-132 ratios, trapped Xe compositions with lower (sub-planetary) Xe-129/Xe-132 ratios seem implausible.

Hohenberg, C. M.↗
NASA NTRS1986

Live 129I-129Xe dating

A technique of cosmic ray exposure age dating using cosmic ray produced I-129 and Xe-129 components is discussed. The live I-129 - Xe-129 method provides an ideal monitor for cosmic ray flux variations on the 10(7)y - 10(8)y time-scale. It is based on low-energy neutron reactions on Te, and these data, when coupled to those from other methods, may facilitate the detection of complex exposure histories.

Marti, K.↗
NASA NTRS1995

An NMR study of microvoids in polymers

An understanding of polymer defect structures, like microvoids in polymeric matrices, is crucial to their fabrication and application potential. In this project guest atoms are introduced into the microvoids in PMR-15 and NMR is used to determine microvoid sizes and locations. Xenon is a relatively inert probe that would normally be found naturally in polymer or in NMR probe materials. There are two NMR active xenon isotopes, Xe-129 and Xe-131. The Xe atom has a very high polarizability, which makes it sensitive to the intracrystalline environment of polymers. Interactions between the Xe atoms and the host matrix perturb the Xe electron cloud, deshielding the nuclei, and thereby expanding the range of the observed NMR chemical shifts. This chemical shift range which may be as large as 5000 ppm, permits subtle structural and chemical effects to be studied with high sensitivity. The Xe(129)-NMR line shape has been found to vary in response to changes in the pore symmetry of the framework hosts line Zeolites and Clathrasil compounds. Before exposure to Xe gas, the PMR-15 samples were dried in a vacuum oven at 150 C for 48 hours. The samples were then exposed to Xe gas at 30 psi for 72 hours and sealed in glass tubes with 1 atmosphere of xenon gas. Xenon gas at 1 atmosphere was used to tune up the spectrometer and to set up the appropriate NMR parameters. A single Xe-129 line at 83.003498 Mhz (with protons at 300 Mhz) was observed for the gas. With the xenon charged PMR-15 samples, a second broader line is observed 190 ppm downfield from the gas line (also observed). The width of the NMR line from the Xe-129 absorbed in the polymer is at least partially due to the distribution of microvoid sizes. From the chemical shift (relative to the gas line) and the line width, we estimate the average void sizes to be 2.74 +/- 0.20 angstroms. Since Xe-129 has such a large chemical shift range (approximately 5000 ppm), we expect the chemical shift anisotropy to contribute to the line width (delta upsilon = 2.5 kHz).

Toy, James↗
NASA NTRS1977

Comments on 'Extinct radioactivities: Trapped residuals of presolar grains'

It has recently been suggested that extinct I-129 and Pu-244 were trapped in primitive-solar-nebula ('presolar') grains and decayed into radiogenic Xe-129 and fission Xe before the grains were incorporated into meteorite bodies. This idea is reconsidered in light of the thermal and metamorphic history of meteorites. The criteria that parent and daughter species should never separate and that minerals or grains containing the anomalous xenon should not be subjected to temperatures exceeding 500 C are applied to iron meteorites, achondrites, and chondrites to determine whether presolar grains could be the carriers of rare-gas anomalies to meteorites. The results strongly indicate that the xenon anomaly could not have originated in presolar grains. Other difficulties with the presolar-grain model are discussed, including insufficiently small grain sizes, large variations in Xe-129/I-127 ratios in various meteorites, and apparently unrealistic meteorite formation times and locations.

Trivedi, B. M. P.↗
NASA NTRS1975

Krypton and xenon in Apollo 14 samples - Fission and neutron capture effects in gas-rich samples

Gas-rich Apollo 14 breccias and trench soil are examined for fission xenon from the decay of the extinct isotopes Pu-244 and I-129, and some samples have been found to have an excess fission component which apparently was incorporated after decay elsewhere and was not produced by in situ decay. Two samples have excess Xe-129 resulting from the decay of I-129. The excess is correlated at low temperatures with excess Xe-128 resulting from neutron capture on I-127. This neutron capture effect is accompanied by related low-temperature excesses of Kr-80 and Kr-82 from neutron capture on the bromine isotopes. Surface correlated concentrations of iodine and bromine are calculated from the neutron capture excesses.

Drozd, R.↗
NASA NTRS1988

I-Xe systematics in LL chondrites

A stepwise heating analysis of Ar and Xe data from five neutron-irradiated whole rock LL chondrites (Soko Banja, Alta Ameen, Tuxtuac, Guidder, and Olivenza) is presented, emphasizing the complicated thermal history of ordinary chondrites. None of the present meteorites show a well-defined (Ar-40)-(Ar-39) apparent age plateau comprised of more than two release fractions. Most of the samples are found to yield well-defined high-temperature correlations between Xe-129/Xe-130 and Xe-128/Xe-130, and thus determinations of I-129/I-127 and Xe-129/Xe-130 at the time of isotopic closure for Xe. As in the case of other ordinary chondrites, the I-Xe systematics for LL chondrites correlate neither with a metamorphic grade nor with chronologies based opon other methods.

Bernatowicz, T. J.↗
NASA NTRS1992

Forsterite/melt partitioning of argon and iodine: Implications for atmosphere formation by outgassing of an early Martian magma ocean

Argon and Xe in the Martian atmosphere are radiogenic relative to the Martian mantle if the SNC meteorites are from Mars. Decay of the short lived isotope I-129 to Xe-129 (t sub 1/2 = 16 m.y.) is the most plausible source of the radiogenic Xe. This short half life constrains any process responsible for the elevated Xe-129/Xe-132 ratio of the Martian atmosphere to occur very early in solar system history. Musselwhite et al. proposed that the differential solubility of I and Xe in liquid water played a key role in producing the radiogenic signature in the Martian atmosphere. Here we explore an alternative hypothesis involving purely igneous processes, and motivated in part by new experimental results on the partitioning of I and Xe between minerals and melt.

Musselwhite, Donald S.↗
NASA NTRS1994

Fractionated martian atmosphere in the nakhlites?

Considerable evidence points to a martian origin of the shergottite-nakhlite-chassignite (SNC) meteorites. Noble gas isotopic compositions have been measured in most SNC meteorites. The Xe-129/Xe-132 vs. Kr-84/Xe-132 ratios in Chassigny, most shergottites, and lithology C of EETA 79001 define a linear array. This array is thought to be a mixing line between martian mantle and martian atmosphere. One of the SNC meteorites, Nakhla, contains a leachable component that has an elevated Xe-129/Xe-132 ratio relative to its Kr-84/Xe-132 ratio when compared to this approximately linear array. The leachable component probably consists in part of iddingsite, an alteration product produced by interaction of olivine with aqueous fluid at temperatures lower than 150 C. The elevated Xe isotopic ratio may represent a distinct reservoir in the martian crust or mantle. More plausibly, it is elementally fractionated martian atmosphere. Formation of sediments fractionates the noble gases in the correct direction. The range of sediment/atmosphere fractionation factors is consistent with the elevated Xe-129/Xe-132 component in Nakhla being contained in iddingsite, a low temperature weathering product. The crystallization age of Nakhla is 1.3 Ga. Its low-shock state suggests that it was ejected from near the surface of Mars. As liquid water is required for the formation of iddingsite, these observations provide further evidence for the near surface existence of aqueous fluids on Mars more recently than 1.3 Ga.

Drake, Michael J.↗
NASA NTRS2004

Calibration of the Galactic Cosmic Ray Flux

We report first Xe data on the cross-calibration of I-129-Xe-129(sub n) ages with conventional CRE ages, a method which is expected to provide information on the long-term constancy of the galactic cosmic ray (GCR) flux. We studied isotopic signatures of Xe released in stepwise heating, decomposition and melting of troilites in the Cape York iron meteorite to identify isotopic shifts in Xe-129 and Xe-131 due to neutron capture in Te-128 and Te-130. We also resolve components due to extinct 129I, spallation and fission Xe. There has recently been much speculation on the constancy of GCR over long time scales, as may be inferred from iron meteorites. If GCRs originate from supernova events, this provides the basis for postulating increased fluxes at locations with higher than average densities of supernovae, specifically in OB-associations. The solar system at present appears to be inside a local bubble between spiral arms and may experience an increased GCR flux.

Mathew, K. J.↗
NASA NTRS1973

Low temperature mechanical properties, fractographic and metallographic evaluation of several alloy steels

The mechanical properties are presented of alloy steels, 4130, 4140, 4340, 6150, and 8740. Test specimens were manufactured from approximately 1.00 inch (2.54 cm) diameter bar stock which had been heat treated to two different hardness levels. The following mechanical tests were performed at temperatures of 80 F (+26.7 C), 0 F (-17.8 C), -100 F (-73 C), and -200 F (-129 C): (1) tensile test (Ultimate, yield, modulus, elongation, and reduction of area), (2) notched tensile test, (3) charpy V-notched impact test (impact energy), and (4) double shear strength test (ultimate and yield). The test data indicate excellent tensile strength, notched/unnotched tensile ratios, ductility, impact, and shear properties at all test temperatures, except at -200 F (-129 C) where the impact strength of the higher strength group of alloy steels, 4130 (Rc-37) and 4140 (Rc-44) decreased to approximately 9 ft. lbs. (12 joules) and 6 ft. lbs. (8 joules), respectively. Chemical, metallographic, and fractographic analyses were also performed to evaluate microstructure, microhardness and the effect of decrease in temperature on the ductile to brittle failure transition.

Montano, J. W.↗
NASA NTRS1972

The origin and chemical composition of the earth's core

The process of core formation in the earth is subject to the constraints that it be nearly simultaneous with accretion and yet occur in a manner that the mantle retains radiogenic Xe-129 produced from the extinct radioactivity of I-129 with a half life of 17.6 million y. From these constraints, it appears that the only feasible mechanism is the segregation of an Fe-FeS melt. Trace element abundances in major classes of meteorites and the silicate fractions of the earth show that not only there is a high depletion of sulphur in the crust and the mantle, but that it is even more highly depleted than the rare gases, water and the halogens. From the nature of this depletion pattern and the fact that any model of accretion of the earth will necessarily produce an Fe-FeS melt, it is concluded that the light element in the core is largely sulphur with minor amounts of carbon. A consequence of this mode of core formation is found to be the availability of K-40 radioactive heat production in the liquid core, estimated at about 10 to the 19th power erg/s at the present time.

Murthy, V. R.↗
NASA NTRS1976

A target for production of radioxenons

A liquid cesium target has been developed which permits the production and identification of the neutron deficient isotopes of xenon. The thick target yields of Xe-127 and Xe-129 m were measured for proton energies between 28 and 40 MeV. Production of Xe-129 m, as indicated by the presence of a 196 keV line in the gamma ray spectra, occurred at all proton energies; Xe-127 was produced at proton energies above 33 MeV. Both accumulated on the target with the same time constant, and the cross sections were comparable in magnitude. The radioxenons were removed from the target by a stream of carrier gas so that chemical separation was unnecessary.

Blue, J. W.↗
NASA NTRS1979

Clues to the origin of sulfide minerals in CI chondrites

The dominant sulfide in CI carbonaceous chondrites is an Fe-deficient pyrrhotite containing about 1% Ni, Alais, Ivuna, and Orgueil also contain minor cubanite, CuFe2S3, and Alais minor pentlandite, (Fe,Ni)9S8. All pyrrhotites contain 39.4 + or - 0.1% S; Ni contents range from 0.7 to 1.3%. The phase diagrams reveal no temperature at which the observed pentlandite-pyrrhotite assemblage is at equilibrium. Similarly, the pyrrhotite composition alone are inconsistent with equilibrium formation from a gas of solar composition. In Xe from high-purity submilligram Orgueil pyrrhotite separates, the ratios Xe-129/Xe-132 are not significantly larger than those in trapped meteoritic Xe. The lack of positive evidence for extinct I-129 in pyrrhotite does not permit any inferences regarding cooling rates in the early solar nebula. It is concluded that sulfides in CI chondrites cannot be nebular condensates formed under equilibrium conditions. Argon isotopic abundances reveal the presence of significant spallation and trapped gas components in Orgueil pyrrhotite. The Orgueil exposure age is calculated to be at least about 10 m.y.

Kerridge, J. F.↗
NASA NTRS1979

Xenon component organization in 14301

Xe in 14301 is a superposition of in situ spallation and presumably also fission Xe, of trapped solar wind, and of trapped fission Xe and Xe-129 redistributed after origin elsewhere on the moon. Some and probably most of the trapped fission originates from Pu-244. All of the components of various origins are released independently in stepwise heating, indicating that they were acquired by different means and remain in different sites within the sample. This applies to the excess fission and to the excess Xe-129, which fail to correlate quantitatively with each other; they must thus have been trapped by different mechanisms or at different times. In spite of their independent behavior in stepwise heating, the various trapped components contribute in constant proportion to the total Xe contents of the various size fractions. This quantitative correlation between excess Xe and solar wind Xe indicates that the same circumstances control the acquisition of both. The variation of the ratio of excess to solar wind Xe among different breccias thus can be ascribed more confidently to compositional variation in total Xe available for trapping rather than to the details of the trapping process.

Bernatowicz, T. J.↗
NASA NTRS1980

I-Xe age and trapped Xe components of the Murray /C-2/ chondrite

A neutron-irradiated bulk sample of the Murray (C-2) carbonaceous chondrite was etched with H2O2 and then divided into colloidal and non-colloidal fractions. The H2O2 treatment removed about 80% of the trapped Xe and greatly increased variations in the Xe-129/Xe-132 ratio measured in stepwise heating. The colloid showed very little excess Xe-129, but the anti-colloid gave a fairly good I-Xe correlation corresponding to formation 3.7 + or - 2.1 m.y. after Bjurbole. Variations in the trapped Xe component were also observed; most notably the 550 C anti-colloid fraction has large deficiencies relative to AVCC at the heavy isotopes.

Niemeyer, S.↗
NASA NTRS1981

Isotopically anomalous xenon in meteorites - A new clue to its origin

The CCF xenon component in primitive meteorites, which has been attributed either to fission of a superheavy element or to nucleosynthesis in a supernova, does not show the large enrichment in Xe-129 (from decay of 16 Myr I-129) expected for supernova ejecta. Although this problem can be circumvented by ad hoc assumptions, a fission origin of CCFXe seems more likely.

Lewis, R. S.↗
NASA NTRS1986

Xenon and other noble gases in shergottites

The isotopic composition of the xenon component trapped in EETA 79001's lithologies B and C has been determined, and other noble gases were measured in some samples. The Xe component was found to have light isotope ratios indistinguishable from those of the terrestrial atmosphere. The trapped component has a Xe-129/Xe-132 ratio of about 2.4, and is enhanced in Xe-134 and Xe-136 relative to the terrestrial atmosphere or the average carbonaceous chondrite. Similarities between values for Ar-40/Ar-36, Xe-129/Xe-132, and N-15/N-14 and the corresponding Martian atmospheric values suggest Martian origin of the trapped gases.

Swindle, T. D.↗