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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Trapped noble gases indicate lunar origin for Antarctic meteorite

The isotopic abundances of the noble gases (He, Ne, Ar, Kr, Xe) are reported for Antarctic ALHA 81005. It contains solar wind-implanted gases whose absolute and relative concentrations are quite similar to lunar regolith samples but not to other meteorites. ALHA 81005 also contains a large excess Ar-40 component which is identical to the component in lunar fines implanted from the lunar atmosphere. Large concentrations of cosmogenic Ne-21, Kr-82, and Xe-126 in ALHA 81005 indicate a total cosmic ray exposure age of at least 200 million years. The noble gas data alone are strong evidence for a lunar origin of this meteorite.

Bogard, D. D.↗
NASA NTRS1983

Photographic observations of earth's airglow from space

A photographic-dispersion image of the earth limb airglow obtained during STS-5 using an S-20-photocathode image intensifier and a 300-line/mm holographic grating on the 55-mm f/1.4 objective lens of a standard 35-mm camera is presented and analyzed. The camera/intensifier spectral response and image wavelength are calibrated using a secondary standard continuum source and a mercury-lamp-illuminated slit, respectively. Features identified in the low-resolution spectrally dispersed image include the 7600-A 02 airglow (estimated intensity 200-300 kR), the 5577-A atomic-oxygen emission (4-6 kR), and the 7300-A Meinel-band OH continuum. The intensity of the O2 feature is in agreement with that found in oblique-rocket measurements by Megill et al. (1970).

Mende, S. B.↗
NASA NTRS1984

Where is the Earth's missing xenon?

Highly volatile elements (e.g., T1, Pb, B, C1, Br, etc.) in the Earth's crust occur in C-chondrite proportions, and so do the atmospheric noble gases Ne, Ar, and Kr. This has led to the suggestion that the Earth acquired its volatiles from a late veneer of C-chondrite-like material. A glaring exception is Xe, which is depleted approx. 20x relative to Ne, Ar, Kr. Three explanations are discussed for the depletion: (1) Xe is preferentially trapped in the crust, either in sediments (3) or in Antarctic ice (4); (2) the Earth's noble gas inventory is non-chondritic (5); or (3) Xe is incompletely outgassed from the mantle.

Wacker, J. F.↗
NASA NTRS1985

Measurement of collision-induced shift and broadening of the ultraviolet transitions of OH

Using a CW tunable laser, absorption measurements were made to determine for the first time the shift and broadening of the ultraviolet transitions of OH induced by collisions with molecular nitrogen and oxygen. Similar measurements were also made for collisions with air and inert gases He, Ne, Ar, and Kr. Both the shift and broadening due to these collisions were found to depend linearly upon pressures in the range from 50 Torr up to 1 atm. The homogeneous linewidth for the P2(2) transition of OH in ambient air is determined to be 0.20 + or - 0.005/cm. Results with Ar and Kr show contributions not accounted for by the polarizability of the colliding species.

Shirinzadeh, B.↗
NASA NTRS1986

The composition of lunar noble gases traped 2.5 AE and 3.5 AE ago

The times when the soils 74001 and 73261 were exposed on the lunar surface were determined by the U-235 - Xe-136 dating method. The isotopic composition of the trapped noble gases in these two soils is compared with that of the surface correlated noble gases in the young soils 12001 and in the present day solar wind. The surface correlated trapped gases are a mixture of implanted solar wind particles and retrapped lunar atmospheric gases. The observed changes are interpreted as a result of decreasing outgassing of radiogenic Ar-40 and perhaps He-4 and of fissiogenic Xe from the lunar crust. The old soils probably also contain surface correlated Kr-80 and Kr-82 produced by secondary cosmic ray neutron capture of adsorbed or retrapped bromine. To some extent the isotopic composition of the trapped gases in old lunar soil may also have been altered due to diffusion loss from material of low retentivity.

Eugster, O.↗
NASA NTRS1986

The dating of pre-exposure times of lunar rocks and soils

Xenon produced by fission of uranium, thorium and plutonium has repeatedly been observed in lunar rocks and soils. In two basaltic rocks and in two soils Xe was found originating from fission of U-235 induced by neutrons which are due to the interactions of cosmic ray particles with lunar matter. Two facts lead to this conclusion: (1) fission Xe is present in excess of that expected for the U, Th, and Pu concentrations and for the gas retention age of the samples; and (2) the Xe-134/Xe-136 ratio of excess fission Xe is close to 1.25 as expected for neutron induced fission of U-235. Information on the duration of the exposure to cosmic rays was obtained from the Kr-81-Kr systematics whereas the effective shielding conditions were derived from the depth sensitive cosmogenic ratio Xe-131/Xe-126. For the four samples the exposure to cosmic rays in the lunar regolith is described by a two stage exposure model. The history of the four samples was derived in terms of duration and shielding depth of the two stages.

Eugster, O.↗
NASA NTRS1986

Release of noble gases and nitrogen from grain-surface sites in lunar ilmenite by closed-system oxidation

Noble gases and nitrogen were extracted from a 100 to 150 microns ilmenite separate from lunar soil 71501 by closed system stepped heating in approx. 10 torr O2 at 300 C, 400 C, 500 C, 600 C and 630 C, followed by stepped pyrolysis at ten temperatures between 680 C and approx. 1500 C. The five oxidation steps together liberated approx. 65% of the total He-4, 45% of the Ne-20, 23% of the N-14 and Ar-36, 12% of the Kr-84 and 8% of the Xe-132 in the sample; Ne-20/Ar-36 and Ne-20/Ne-22 ratios agree with the solar wind composition experiment, and Kr-84/Ar-36 and Xe-132/Ar-36 are within approx. 10% of Cameron's estimates for the sun and solar wind. The remaining gases, released above 630 C by pyrolysis, are strongly fractionated with respect to the SWC-Cameron solar wind elemental composition. Large concentrations of fractionated noble gases in grain interiors, their virtual absence in the relatively unfractionated surface gas reservoir, and the high N/noble gas ratio all imply that most of the solar wind noble gases initially implanted in grain surfaces are eventually lost by diffusion. Loss limits can be estimated by considering two given scenarios. It is concluded tat approx. 70 to 97% or more of the Ar implanted in 71501 ilmenite grains has diffusively escaped.

Frick, U.↗
NASA NTRS1986

Altitude variation of EUV emissions and evidence for proton precipitation at low latitudes in the Saturnian atmosphere

Extreme ultraviolet observations of Saturn from Voyager 1 and 2 are analyzed. The Lyman alpha and H2 band emissions extend throughout the upper atmosphere, from the hydrocarbon homopause to well above the exobase. Analysis of the Lyman alpha emissions with a radiative transfer model indicates that the Lyman alpha source temperature is very high. This suggests that energetic protons or hydrogen atoms are responsible for a fraction of the emissions. Calculation of the solar-scattered component of the emissions based on the neutral atmosphere of Smith et al. (1983) reveals that only 1-2 kR out of a total of 3.5 kR of the observed Lyman alpha intensity is due to solar scatter for the Voyager 2 disk observations; the remainder of the Lyman alpha emissions are collisionally excited. The Lyman alpha and H2 bands are constant in longitude but decrease in local time by a factor of 2 from dawn to dusk. This correlation of the Lyman alpha and H2 band intensities is further evidence that most of the Lyman alpha is collisionally excited.

Yelle, R. V.↗
NASA NTRS1987

Development of an effusive inlet for mass spectrometric gas analysis of hypersonic boundary layer

The use of a microchannel plate (MCP) as a mass spectrometer inlet device to allow nonintrusive sampling of flight vehicle boundary layers is investigated. Two possible configurations for mounting the inlet are studied: (1) flow coaxial with the channels; and (2) flow perpendicular to the channel axis. The test gases are pure Kr; pure Ne; and a mixture of 10 pct Kr, 10 pct Ne, and 80 pct N2. The pressure ranges studied vary from 500 to 10 microns. A mass discrimination at the quadrupole mass spectrometer is observed, indicating an enrichment in the heavier gas. Possible explanations for this enrichment are discussed. It is shown that an MCP is capable of acting as a nonintrusive sampling device. Further work that will enable quantitative determination of the species at the surface is discussed.

Brown, Kenneth G.↗
NASA NTRS1988

S-process krypton of variable isotopic composition in the Murchison meteorite

Data are reported which, for the first time, permit the derivation of the full isotopic spectrum of s-process krypton with reasonable precision. It is shown that this s-Kr in a residue from the Murchison meteorite did not originate in one single s-process but rather is a mixture of contributions from stellar environments where the density of free neutrons was not the same. The astrophysical conditions under which this krypton was produced were distinct from those that have been invoked to explain the solar system s-process abundance. Similar to the C-13-rich carbon component in an aliquot of the same residue, the s-process Kr from different astrophysical sites has retained its identity during the accumulation and subsequent history of the meteorite.

Ott, Urlich↗
NASA NTRS1989

A novel array antenna for MSAT applications

The issue of reducing the cost of phased array vehicle antennas through the use of a lens feeding arrangement instead of phase shifters at each element is addressed. In particular, the economic viability of a mobile satellite system (MSAT) is largely dependent on the efficient use of the allocated scarce spectrum and orbit as well as the satellite power. the type of vehicle antenna used will play a critical role in achieving this efficiency. A standard design approach for an electronically steered array uses phase shifters at each element to provide beam steering. A method for reducing the required number of phase shifters by using an R-KR lens feed network is outlined. The authors briefly discuss the phase shifter approach to beam steering, examine various lens feed techniques, and describe the R-KR lens approach. The lens feed network architecture is examined, a computer model for simulation of the array is presented, and the results of analysis of a suggested design for the MSAT application are given. In addition, satellite acquisition and tracking considerations are investigated.

Bodnar, Donald G.↗
NASA NTRS1991

Solar-wind krypton and solid/gas fractionation in the early solar nebula

The solar-system Kr abundance is calculated from solar-wind noble-gas ratios, determined previously by low-temperature oxidations of lunar ilmenite grains, normalized to Si by spacecraft solar-wind measurements. The estimated Kr-83 abundance of 4.1 + or - 1.5 per million Si atoms is within uncertainty of estimates assuming no fractionation, determined from CI-chondrite abundances of surrounding elements. This is significant because it is the first such constraint on solid/gas fractionation, though the large uncertainty only confines it to somewhat less than a factor of two.

Wiens, Roger C.↗
NASA NTRS1993

Thermodynamic data for fifty reference elements

This report is a compilation of thermodynamic functions of 50 elements in their standard reference state. The functions are C(sub p)(sup 0), (H(sup 0)(T) - H(sup 0)(0)), S(sup 0)(T), and -(G(sup 0)(T) - H(sup 0)(O)) for the elements Ag, Al, Ar, B, Ba, Be, Br2, C, Ca, Cd, Cl2, Co, Cr, Cs, Cu, F2, Fe, Ge, H2, He, Hg, I2, K, Kr, Li, Mg, Mn, Mo, N2, Na, Nb, Ne, Ni, O2, P, Pb, Rb, S, Si, Sn, Sr, Ta, Th, Ti, U, V, W, Xe, Zn, and Zr. Deuterium D2 and electron gas e(sup -) are also included. The data are tabulated as functions of temperature as well as given in the form of least-squares coefficients for two functional forms for C(sub p)(sup 0) with integration constants for enthalpy and entropy. One functional form for C(sub p)(sup 0) is a fourth-order polynomial and the other has two additional terms, one with T(exp -1) and the other with T(exp -2). The gases Ar, D2, e(sup -), H2, He, Kr, N2, Ne, O2, and Xe are tabulated for temperatures from 100 to 20,000 K. The remaining gases Cl2 and F2 are tabulated from 100 to 6000 K and 1000 to 6000 K. The second functional form for C(sub p)(sup 0) has an additional interval from 6000 to 20,000 K for the gases tabulated to 20,000 K. The fits are constrained so that the match at the common temperature endpoints. The temperature ranges for the condensed species vary with range of the data, phase changes, and shapes of the C(sub p)(sup 0) curves.

Mcbride, Bonnie J.↗
NASA NTRS1992

Heavy-element abundances from a neutron burst that produces Xe-H

We examine quantitatively the suggestion that the heavy anomalous isotopes of Xe-HL found in meteoritic diamonds were produced by a short intense neutron burst and then implanted into the diamonds. Using a large nuclear reaction network we establish one (out of many) neutron irradiation hostories that successfully reproduces the heavy isotopes of Xe-HL, and then evaluate what that same history would produce in every heavy element. This has become more relevant following recent measurement of anomalous Ba and Sr in those same diamond samples. Therefore we offer these calculations as a guide to the anomalies to be expected in all elements if this scenario is correct. We also discuss several other aspects of the problem, especially the established contradictions for Ba, the observed Kr pattern, the near normalcy of Xe-129 and some related astrophysical ideas. In particular we argue from p-process theory that the observed deficit of Kr-78 in correlation with Xe-(124-126) excess implicates Type II supernovae as the diamond sources.

Howard, W. M.↗
NASA NTRS1992

Filamentary and hierarchical pictures - Kinetic energy criterion

We present a new criterion for formation of second-generation filaments. The criterion called the kinetic energy ratio, KR, is based on comparison of peculiar velocities at different scales. We suggest that the clumpiness of the distribution in some cases might be less important than the 'coldness' or 'hotness' of the flow for formation of coherent structures. The kinetic energy ratio is analogous to the Mach number except for one essential difference. If at some scale KR is greater than 1, as estimated at the linear stage, then when fluctuations of this scale reach nonlinearity, the objects they produce must be anisotropic ('filamentary'). In the case of power-law initial spectra the kinetic ratio criterion suggests that the border line is the power-spectrum with the slope n = -1.

Klypin, Anatoly A.↗
NASA NTRS1977

Mariner 9 Ultraviolet Spectrometer Experiment: Mars Atomic Oxygen 1304-A Emission

Selected results are presented for an analysis of Mariner 9 1304-A data from the first 100 passes. Based on a comparison of limb data, the exospheric temperature appears lower on several Mariner 9 passes than when Mariner 6 and 7 encountered the planet in 1969. Temperatures of 300 and 350 K are considered in the atmospheric modeling. At 300 K, derived values of the atomic oxygen concentration are typically between 0.5 and 1 percent of the total density at 135 km, based on fitting theoretical intensities to limb data from several passes. Structure in the limb data below 200 km suggests the possibility that approximately 0.2 kR of the observed approximately 0.8 kR near 150 km is due to dissociative excitation of CO2. There is variability in limb profiles indicating changes in the O distribution with time. The variability does not appear to follow a recognizable pattern. Interpretation of the 1304-A disc data shows a correlation in intensity with the 10.7 cm solar flux and larger O concentrations in the afternoon than in the morning. The correlation in intensity with the 10.7 cm flux is probably due largely to variation in the solar 1304-A fluxes. Selected disc data show localized and random enhancements in the intensity.

Strickland, D. J.↗
NASA NTRS1993

A long-term change of the AR/KR/XE fractionation in the solar corpuscular radiation

Solar noble gases in an ilmenite separate from breccia 79035 (antiquity greater than 1 Ga) were analyzed by closed system stepped etching (CSSE). All five gases show the familiar two-component structure: first solar-wind (SW) gases are released, followed by gases from solar energetic particles (SEP). Element patterns in 79035 are similar to those of 71501 ilmenite. SW-He-Ne were partly lost, but SEP-He-Ne-Ar are retained (nearly) unfractionated. Constant Ar/Kr/Xe ratios indicate that ilmenites contain an unfractionated sample of the heavy SW-SEP noble gases. Ar/Kr/Xe ratios in the solar corpuscular radiation are, however, different from 'solar system' values, whereby the Kr/Xe difference in 79035 is about twice as large as in 71501. We propose that Xe is less fractionated than Kr and Ar, though its first ionization potential (FIP) is higher than the 'cutoff' at approximately 11.5 eV, above which all elements in SEP are usually assumed to be depleted by a roughly constant factor. SW-Ne may be isotopically slightly heavier in the ancient SW trapped by 79035, as proposed earlier. In this work we extend our previous CSSE studies of solar noble gases including Kr and Xe to a lunar sample irradiated at least 1 Ga ago (breccia 79035, ilmenite separate, 42-64 microns). This sample was particularly gently etched in the first steps. Surprisingly, the first three steps, each releasing less than or equal to 0.5% of the total 36-Ar, showed an SEP-like trapped component plus relatively large concentrations of cosmogenic gases. Steps 4ff contain much less cosmogenic and more solar gas with a SW-like isotope pattern. Thus, a very minor easily etchable phase that has completely lost its SW-gases must be responsible for steps 1-3. We will not discuss these steps here and refer to the actual step 4 as the 'initial' etching step.

Wieler, R.↗
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.↗