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NASA NTRS1993

Cathodoluminescence properties of components in enstatite chondrites

As a group, the enstatite chondrites are notable by the extremely low FeO content of most of their silicates. This property predisposes many of these materials to emit Cathodoluminescence (CL). Since examination of the CL properties of meteoritic components in ordinary and carbonaceous chondrites have proven to be a useful technique, we have initiated a survey of the enstatite chondrites in order to better characterize the chemical and physical properties of their luminescing phases. Because of the diversity encountered in this study, it is first necessary to describe the number and types of materials observed to emit CL in these meteorites. Two CL techniques were used. First, the initial survey work was conducted at low magnification using a Nuclide (now MAAS) Luminoscope mounted to a Wild MP binocular microscope equipped for photomicroscopy. The beam conditions used were 14 +/- KeV and 7 +/- 1 milliamps, with the beam focussed to the diameter of the field of view of the microscope at 20x (appox. 1.25 cm). Photomosaics were produced for each section using Ecktar 1000 film and an exposure time of 15 to 30 seconds. Second, high magnification (400x) photos were obtained of individual components of interest by mounting a 35mm camera to the optical system of the Cameca Camebax microprobe located at the Johnson Space Center. Beam conditions used were 15 KeV and 600 nA. Ecktar 1000 film was also used, but exposure times of 6 minutes were necessary to produce a useful image. The components in E chondrites that produce CL can be divided into four broad categories. These are clasts and aggregates, chondrules, matrix components, and refractory objects. Components in each category are discussed.

Dehart, John M.↗

NASA NTRS1990

ASTP 15th Anniversary Clip-Media Release

This release is comprised of 5 separate clips, including the following: CL 762 Astronauts/Cosmonauts Visit to KSC and Walt Disney World; CL 739 ASTP Joint Crew Activities; CL 748 ASTP Astronauts/Cosmonauts Horlock Ranch Visit; CL 758 T-21 ASTP Training - US/USSR; and CL 743 ASTP Joint Crew Training in the Soviet Union.

Source record↗

NASA NTRS1995

Estimates of total organic and inorganic chlorine in the lower stratosphere from in situ and flask measurements during AASE 2

Aircraft sampling has provided extensive in situ and flask measurements of organic chlorine species in the lower stratosphere. The recent Airborne Arctic Stratospheric Expedition 2 (AASE 2) included two independent measurements of organic chlorine species using whole air sample and real-time techniques. From the whole air sample measurements we derive directly the burden of total organic chlorine (CCl(y)) in the lower stratosphere. From the more limited real-time measurements we estimate the CCl(y) burden using mixing ratios and growth rates of the principal CCl(y) species in the troposphere in conjunction with results from a two-dimensional photochemical model. Since stratospheric chlorine is tropospheric in origin and tropospheric mixing ratios are increasing, it is necessary to establish the average age of a stratospheric air parcel to assess its total chlorine (Cl(sub Total)) abundance. Total inorganic chlorine (Cl(y)) in the parcel is then estimated by the simple difference, Cl(y) = Cl(sub Total) - CCl(y). The consistency of the results from these two quite different techniques suggests that we can determine the CCl(y) and Cl(y) in the lower stratosphere with confidence. Such estimates of organic and inorganic chlorine are crucial in evaluating the photochemistry controlling chlorine partitioning and hence ozone loss processes in the lower stratosphere.

Woodbridge, E. L.↗

NASA NTRS2000

Terrestrial Ages of Antarctic Meteorites: Up Date 1999

We are continuing our ongoing study of cosmogenic nuclides in Antarctic meteorites. In addition to the studies of exposure histories of meteorites, we study terrestrial ages and pairing of Antarctic meteorites and desert meteorites. Terrestrial ages of Antarctic meteorites provide information on meteorite accumulation mechanisms, mean weathering lifetimes, and influx rates. The determination of Cl-36 (half-life=3.01 x 10(exp 5) y) terrestrial ages is one of our long-term on-going projects, however, in many instances neither Cl-36 or C-14 (5,730 y) yields an accurate terrestrial age. Using Ca-41 (1.04 x 10(exp 5) y) for terrestrial age determinations solves this problem by filling the gap in half-life between C-14 and Cl-36 ages. We are now applying the new Ca-41 - Cl-36 terrestrial age method as well as the Cl-36 - Be-10 method to Antarctic meteorites. Our measurements and C-14 terrestrial age determinations by the University of Arizona group are always complementary.

Nishiizumi, K.↗

NASA NTRS1997

Can Chlorine Anion Catalyze the Reaction fo HOCl with HCl?

The reaction of HOCl + HCl -> Cl2 + H20 in the presence of Cl has been studied using ab initio methods. This reaction has been shown to have a high activation barrier of 46.5 kcal/mol. The chlorine anion, Cl- is found to catalyze the reaction, viz. two mechanisms. The first involves Cl- interacting through the concerted four-center transition state of the neutral reaction. The other mechanism involves the formation of a HCl-HOCl-Cl- intermediate which dissociates into Cl2 + Cl- + H20. The steps are found to have no barriers. The overall exothermicity is 15.5 kcal/mol.

Richardson, S. L.↗

NASA NTRS1994

Low Ozone in the Marine Boundary Layer of the Tropical Pacific Ocean

Aircraft measurements of ozone, its key precursors, and a variety of chemical tracers were made in the troposphere of the western and central Pacific in October 1991. These data are presented and analyzed to examine the occurrence of low ozone concentrations in the remote marine boundary layer of the tropical and equatorial Pacific Ocean. The data from these flights out of Guam, covering an area extending from the equator to 20 N and from south of the Philippines to Hawaii, show average O3 concentrations as low as 8-9 ppb (ppb=10(exp-9)v/v) at altitudes of 0.3-0.5 km in the boundary layer. Individual measurements as low as 2-5 ppb were recorded. Low O3 concentrations do not always persist in space and time. High O3, generally associated with the transport of upper tropospheric air, was also encountered in the boundary layer. In practically all cases, O3 increased to values as large as 25-30 ppb within 2 km above the boundary layer top. Steady state model computations are used to suggest that these low O3 concentrations are a result of net photochemical O3 destruction in a low NO environment, sea-surface deposition, and extremely low net entrainment rates (1-2 mm per second) from the free troposphere. Day/night measurements of ethane, propane, gaseous and aerosol Cl suggest that daytime (morning) Cl atom concentrations in the vicinity of 10(exp 5) molecules per cubic centimeter may be present in the marine boundary layer. This Cl atom abundance can be rationalized only if sea salt aerosols can release free chlorine (Cl2) to the gas phase in the presence of sun light (and possibly O3). These Cl atom concentrations, however, are still insufficient and Cl (or Br) chemistry is not likely to be an important cause of the observed low O3.

Singh, Hanwant B.↗

NASA NTRS2011

The Atacama Cosmology Telescope: High-Resolution Sunyaev-Zel'dovich Array Observations of ACT SZE-Selected Clusters from the Equatorial Strip

We present follow-up observations with the Sunyaev-Zel'dovich Array (SZA) of optically-confirmed galaxy clusters found in the equatorial survey region of the Atacama Cosmology Telescope (ACT): ACT-CL J0022-0036, ACT-CL J2051+0057, and ACT-CL J2337+0016. ACT-CL J0022-0036 is a newly-discovered, massive (10(exp 15) Msun), high-redshift (z=0.81) cluster revealed by ACT through the Sunyaev-Zel'dovich effect (SZE). Deep, targeted observations with the SZA allow us to probe a broader range of cluster spatial scales, better disentangle cluster decrements from radio point source emission, and derive more robust integrated SZE flux and mass estimates than we can with ACT data alone. For the two clusters we detect with the SZA we compute integrated SZE signal and derive masses from the SZA data only. ACT-CL J2337+0016, also known as Abell 2631, has archival Chandra data that allow an additional X-ray-based mass estimate. Optical richness is also used to estimate cluster masses and shows good agreement with the SZE and X-ray-based estimates. Based on the point sources detected by the SZA in these three cluster fields and an extrapolation to ACT's frequency, we estimate that point sources could be contaminating the SZE decrement at the less than = 20% level for some fraction of clusters.

Reese, Erik D.↗

NASA NTRS2011

The Atacama Cosmology Telescope: High-Resolution Sunyaev-Zeldovich Array Observations of ACT SZE-Selected Clusters from the Equatorial Strip

We present follow-up observations with the Sunyaev-Zel'dovich Array (SZA) of optically-confirmed galaxy clusters found in the equatorial survey region of the Atacama Cosmology Telescope (ACT): ACT-CL J0022-0036, ACT-CL J2051+0057, and ACT-CL J2337+0016. ACT-CL J0022-0036 is a newly-discovered, massive ( approximately equals 10(exp 15) Solar M), high-redshift (z = 0.81) cluster revealed by ACT through the Sunyaev-Zeldovich effect (SZE). Deep, targeted observations with the SZA allow us to probe a broader range of cluster spatial scales, better disentangle cluster decrements from radio point source emission, and derive more robust integrated SZE flux and mass estimates than we can with ACT data alone. For the two clusters we detect with the SZA we compute integrated SZE signal and derive masses from the SZA data only. ACT-CL J2337+0016, also known as Abell 2631, has archival Chandra data that allow an additional X-ray-based mass estimate. Optical richness is also used to estimate cluster masses and shows good agreement with the SZE and X-ray-based estimates. Based on the point sources detected by the SZA in these three cluster fields and an extrapolation to ACT's frequency, we estimate that point sources could be contaminating the SZE decrement at the approx < 20% level for some fraction of clusters.

galaxies↗

NASA NTRS2016

Calibration of the Fluorine, Chlorine and Hydrogen Content of Apatites With the ChemCam LIBS Instrument

Determining the composition of apatites is important to understand the behavior of volatiles during planetary differentiation. Apatite is an ubiquitous magmatic mineral in the SNC meteorites. It is a significant reservoir of halogens in these meteorites and has been used to estimate the halogen budget of Mars. Apatites have been identified in sandstones and pebbles at Gale crater by ChemCam, a Laser-Induced Breakdown Spectroscometer (LIBS) instrument onboard the Curiosity rover. Their presence was inferred from correlations between calcium, fluorine (using the CaF molecular band centered near 603 nm, whose detection limit is much lower that atomic or ionic lines and, in some cases, phosphorus (whose detection limit is much larger). An initial quantification of fluorine, based on fluorite (CaF2)/basalt mixtures and obtained at the LANL laboratory, indicated that the excess of F/Ca (compared to the stoichiometry of pure fluorapatites) found on Mars in some cases could be explained by the presence of fluorite. Chlorine was not detected in these targets, at least above a detection limit of 0.6 wt% estimated from. Fluorapatite was later also detected by X-ray diffraction (with CheMin) at a level of approx.1wt% in the Windjana drill sample (Kimberley area), and several points analyzed by ChemCam in this area also revealed a correlation between Ca and F. The in situ detection of F-rich, Cl-poor apatites contrasts with the Cl-rich, F-poor compositions of apatites found in basaltic shergottites and in gabbroic clasts from the martian meteorite NWA 7034, which were also found to be more Cl-rich than apatites from basalts on Earth, the Moon, or Vesta. The in situ observations could call into question one of the few possible explanations brought forward to explain the SNC results, namely that Mars may be highly depleted in fluorine. The purpose of the present study is to refine the calibration of the F, Cl, OH and P signals measured by the ChemCam LIBS instrument, initiated for F, for Cl in soils, for P, and estimate their limit of detection. For this purpose, different types of apatites and mixtures of basalt powder and apatites were analyzed using ChemCam Engineering Qualification Model (EQM) at IRAP, Toulouse. The present abstract presents the initial results from the laboratory analyses. Differences between the response function of the EQM and the Flight Model of ChemCam are still to be refined to apply these new results to the Martian dataset.

Meslin, P.-Y.↗

NASA NTRS2017

Oxychlorine Species in Gale Crater and Broader Implications for Mars

Of 15 samples analyzed to date, the Sample Analysis at Mars (SAM) instrument on the Mars Science Laboratory (MSL) has detected oxychlorine compounds (perchlorate or chlorate) in 12 samples. The presence of oxychlorine species is inferred from the release of oxygen at temperatures less than 600degC and HCl between 350-850degC when a sample is heated to 850degC. The O2 release temperature varies with sample, likely caused by different cations, grain size differences, or catalytic effects of other minerals. In the oxychlorine-containing samples, perchlorate abundances range from 0.06 +/- 0.03 to 1.15 +/- 0.5 wt% Cl2O7 equivalent. Comparing these results to the elemental Cl concentration measured by the Alpha Particle X-ray Spectrometer (APXS) instrument, oxychlorine species account for 5-40% of the total Cl present. The variation in oxychlorine abundance has implications for their production and preservation over time. For example, the John Klein (JK) and Cumberland (CB) samples were acquired within a few meters of each other and CB contained approximately1.2 wt% Cl2O7 equivalent while JK had approximately 0.1 wt%. One difference between the two samples is that JK has a large number of veins visible in the drill hole wall, indicating more post-deposition alteration and removal. Finally, despite Cl concentrations similar to previous samples, the last three Murray formation samples (Oudam, Marimba, and Quela) had no detectable oxygen released during pyrolysis. This could be a result of oxygen reacting with other species in the sample during pyrolysis. Lab work has shown this is likely to have occurred in SAM but it is unlikely to have consumed all the O2 released. Another explanation is that the Cl is present as chlorides, which is consistent with data from the ChemCam (Chemical Camera) and CheMin (Chemistry and Mineralogy) instruments on MSL. For example, the Quela sample has approximately1 wt% elemental Cl detected by APXS, had no detectable O2 released, and halite (NaCl) has been tentatively identified in CheMin X-ray diffraction data. These data show that oxychlorines are likely globally distributed on Mars but the distribution is heterogenous depending on the perchlorate formation mechanism (production rate), burial, and subsequent diagenesis

Ming, Douglas W.↗

NASA NTRS2022

Unexpected Repartitioning of Stratospheric Inorganic Chlorine after the 2020 Australian Wildfires

The inorganic chlorine (Cl y ) and odd nitrogen (NO y ) chemical families influence stratospheric O 3 . In January 2020 Australian wildfires injected record-breaking amounts of smoke into the southern stratosphere. Within 1-2 months ground-based and satellite observations showed Cl y and NO y were repartitioned. Compared to decadal means, lower stratospheric (LS) HCl columns declined by ~30% between March and May while ClONO 2 columns increased by 40-50%. The Cl y perturbations recovered from June to October. The LS NO 2 decreased from February to April, consistent with sulfate aerosol reactions, but returned to typical values by June - months earlier than the Cl y recovery. Transport tracers show an air mass change explains the observed O 3 decrease after April. Simulations assuming wildfire smoke behaves identically to sulfate aerosols couldn’t reproduce observed Cl y changes, suggesting that their composition and chemistry differs from sulfate aerosols. This undermines our ability to predict ozone in a changing climate.

middle atmosphere chemistry and composition↗

NASA NTRS2022

Development Towards Stable Chlorine Isotope Measurements of Astromaterials Using the Modified Middleton Source of an Accelerator Mass Spectrometer

The volatile element Cl can be lost during the formation and evolution of planetary bodies, leading to fractionation of its two stable isotopes 35Cl and 37Cl. Chlorine isotope variations (reported as δ37Cl in parts per thousand (‰) relative to Standard Mean Ocean Chloride, SMOC) are documented to exceed 80‰ between different lunar rock samples and have been variably interpreted as the fingerprint of degassing during accretion, magma ocean, or volcanic portions of lunar history. The large intersample and intrasample variations observed by both bulk isotope ratio mass spectrometry (IRMS) and in-situ secondary ion mass spectrometry (SIMS) methods are difficult to interpret in part because of a paucity of bulk Cl isotope measurements. This lack of high-precision bulk data is due to the relative rarity of IRMS laboratories capable of making these high precision measurements on small samples of precious planetary materials such as those returned by human or robotic exploration. Here we present a new method for performing high precision δ37Cl measurements using the modified Middleton ion source of an existing accelerator mass spectrometer. For samples with as little as 1 μg Cl–the equivalent of 2–4 mm3 of a typical lunar rock sample–the average cathode accuracy is ∼1‰. Cathode reproducibility is typically ∼1‰ (2σ) for samples with at least 10 μg of Cl, increasing to ∼3–6‰ for aliquots with ∼1–2 μg Cl, similar to published SIMS results and sufficient to study astromaterials from the Moon, Mars, or 4 Vesta, which have tens of ‰ observed variations.

Tyler S. Anderson↗

NASA NTRS1977

Kinetics of the reactions of ClO with O and with NO

The rate constants k1, k2, and k3 for the reactions Cl + O3 yields ClO + O2 (1), ClO + O yields Cl + O2 (2), and ClO + NO yields Cl + NO2 (3), respectively, were measured by the discharge-flow technique, in which chlorine atoms are added to a flow of O3 and either O or NO in a helium carrier gas. The conditions of the experiment were such that the steady-state concentration ratios of Cl to ClO are simply interpretable in terms of the rate constant ratios k2/k3 or k3/k1. These rate constant ratios were measured over the range 220 to 298 K and combined with the directly determined k1 value to yield k2 and k3. The results are: k1 = 2.12 x 10 to the -11th exp(-157/T); k2 = 3.38 x 10 to -11th exp(75 plus or minus 40/T); and k3 = 1.13 x 10 to the -11th exp(200 plus or minus 30/T) cu cm/sec.

Zahniser, M. S.↗

NASA NTRS1984

Crack layer theory

A damage parameter is introduced in addition to conventional parameters of continuum mechanics and consider a crack surrounded by an array of microdefects within the continuum mechanics framework. A system consisting of the main crack and surrounding damage is called crack layer (CL). Crack layer propagation is an irreversible process. The general framework of the thermodynamics of irreversible processes are employed to identify the driving forces (causes) and to derive the constitutive equation of CL propagation, that is, the relationship between the rates of the crack growth and damage dissemination from one side and the conjugated thermodynamic forces from another. The proposed law of CL propagation is in good agreement with the experimental data on fatigue CL propagation in various materials. The theory also elaborates material toughness characterization.

Chudnovsky, A.↗

NASA NTRS1987

Crack layer theory

Chudnovsky, A.↗

NASA NTRS1987

An intercomparison technique for measuring thermal attachment cross sections and rate constants in distinct final channels

A new technique is introduced for comparing negative-ion signal rates in which a common ion is produced by dissociative attachment in a series of molecules. Measurements are carried out at electron energies less than 100 MeV and at resolutions of 6-8 MeV (FWHM). The technique is demonstrated by detection of the Cl(-) signal in CFCl3, CCl4, CF2Cl2, 1,1,2-C2Cl3F3, 1,1,1-C2Cl3F3 and C2Cl4. Measurements for 1,1,1-C2Cl3F3 show that there is a significant open channel, other than Cl(-) formation, which accounts for about 60 percent of negative-ion formation in thermal-multiple-collision (swarm) experiments. Channel cross sections and rate constants are given for the process Cl(-)/1,1,1-Cl2Cl3F3, as well as in C2Cl4, for the separate channels Cl(-)/C2Cl4 and C2Cl4(-)/C2Cl4.

Alajajian, S. H.↗

NASA NTRS1988

Chemistry of chlorinated species in the Antarctic stratosphere

The chemistry of Cl sub 2 O sub 2, the chlorine monoxide dimer, has been further investigated in order to better asses its potential role in catalytic ozone destruction cycles. The dimer has been generated in a flow system, in the 200 to 250 K temperature range, by using ozone and chlorine atoms as ClO precursors. The Cl-atoms are produced by a microwave discharge of either Cl sub 2, or of F sub 2 with subsequent addition of HCl. With this later scheme the dimer can be generated in the absence of Cl sub 2. The Fourier transform infrared spectra of the products clearly indicates the presence of two isomers, in agreement with earlier results (J. Phys. Shen., 91, 433, 1987). None of the observed IR bands can be attributed to a ClO-OClO adduct, since they all appear in the absence of any detectable amount of OCl. It is likely that the particles in the polar stratospheric clouds will have a relatively dilute nitric acid outer layer, even if the core is the nitric acid monohydrate, since the particles are in equilibrium with the ambient water vapor, which is present at levels of a few parts per million.

Molina, Mario J.↗

NASA NTRS1989

Compositions of isolated forsterites in Ornans (C3O)

The Ornans (C3O) carbonaceous chondrite shows many examples of isolated olivine grains which are Mg-rich and show cathodoluminescence (CL). Using backscattered electron imaging to scan and select Mg-rich isolated olivine grains, and a CL detector, the chemical zoning within these grains was investigated together with its relation to CL and to chemical zoning of grains within a Fe-rich chondrule. Composition profiles from the core to the rim of five isolated forsterites showed details of Al, Ca, Sc, Ti, V, Cr, Mn, and Fe zoning with respet ot position and CL color.

Steele, Ian M.↗