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Sample records for lead x-ray absorption

  1. X-ray Absorption Spectroscopy

    SciTech Connect

    Yano, Junko; Yachandra, Vittal K.

    2009-07-09

    This review gives a brief description of the theory and application of X-ray absorption spectroscopy, both X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), especially, pertaining to photosynthesis. The advantages and limitations of the methods are discussed. Recent advances in extended EXAFS and polarized EXAFS using oriented membranes and single crystals are explained. Developments in theory in understanding the XANES spectra are described. The application of X-ray absorption spectroscopy to the study of the Mn4Ca cluster in Photosystem II is presented.

  2. Identification of lead chemical form in mine waste materials by X-ray absorption spectroscopy

    SciTech Connect

    Taga, Raijeli L.; Ng, Jack; Zheng Jiajia; Huynh, Trang; Noller, Barry; Harris, Hugh H.

    2010-06-23

    X-ray absorption spectroscopy (XAS) provides a direct means for measuring lead chemical forms in complex samples. In this study, XAS was used to identify the presence of plumbojarosite (PbFe{sub 6}(SO{sub 4}){sub 4}(OH){sub 12}) by lead L{sub 3}-edge XANES spectra in mine waste from a small gold mining operation in Fiji. The presence of plumbojarosite in tailings was confirmed by XRD but XANES gave better resolution. The potential for human uptake of Pb from tailings was measured using a physiologically based extract test (PBET), an in-vitro bioaccessibility (BAc) method. The BAc of Pb was 55%. Particle size distribution of tailings indicated that 40% of PM{sub 10} particulates exist which could be a potential risk for respiratory effects via the inhalation route. Food items collected in the proximity of the mine site had lead concentrations which exceed food standard guidelines. Lead within the mining lease exceeded sediment guidelines. The results from this study are used to investigate exposure pathways via ingestion and inhalation for potential risk exposure pathways of Pb in that locality. The highest Pb concentration in soil and tailings was 25,839 mg/kg, exceeding the Australian National Environment Protection Measure (NEPM) soil health investigation levels.

  3. Identification of lead chemical form in mine waste materials by X-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Taga, Raijeli L.; Zheng, Jiajia; Huynh, Trang; Ng, Jack; Harris, Hugh H.; Noller, Barry

    2010-06-01

    X-ray absorption spectroscopy (XAS) provides a direct means for measuring lead chemical forms in complex samples. In this study, XAS was used to identify the presence of plumbojarosite (PbFe6(SO4)4(OH)12) by lead L3-edge XANES spectra in mine waste from a small gold mining operation in Fiji. The presence of plumbojarosite in tailings was confirmed by XRD but XANES gave better resolution. The potential for human uptake of Pb from tailings was measured using a physiologically based extract test (PBET), an in-vitro bioaccessibility (BAc) method. The BAc of Pb was 55%. Particle size distribution of tailings indicated that 40% of PM10 particulates exist which could be a potential risk for respiratory effects via the inhalation route. Food items collected in the proximity of the mine site had lead concentrations which exceed food standard guidelines. Lead within the mining lease exceeded sediment guidelines. The results from this study are used to investigate exposure pathways via ingestion and inhalation for potential risk exposure pathways of Pb in that locality. The highest Pb concentration in soil and tailings was 25,839 mg/kg, exceeding the Australian National Environment Protection Measure (NEPM) soil health investigation levels.

  4. Urban Airborne Lead: X-Ray Absorption Spectroscopy Establishes Soil as Dominant Source

    PubMed Central

    Pingitore, Nicholas E.; Clague, Juan W.; Amaya, Maria A.; Maciejewska, Beata; Reynoso, Jesús J.

    2009-01-01

    Background Despite the dramatic decrease in airborne lead over the past three decades, there are calls for regulatory limits on this potent pediatric neurotoxin lower even than the new (2008) US Environmental Protection Agency standard. To achieve further decreases in airborne lead, what sources would need to be decreased and what costs would ensue? Our aim was to identify and, if possible, quantify the major species (compounds) of lead in recent ambient airborne particulate matter collected in El Paso, TX, USA. Methodology/Principal Findings We used synchrotron-based XAFS (x-ray absorption fine structure) to identify and quantify the major Pb species. XAFS provides molecular-level structural information about a specific element in a bulk sample. Pb-humate is the dominant form of lead in contemporary El Paso air. Pb-humate is a stable, sorbed complex produced exclusively in the humus fraction of Pb-contaminated soils; it also is the major lead species in El Paso soils. Thus such soil must be the dominant source, and its resuspension into the air, the transfer process, providing lead particles to the local air. Conclusions/Significance Current industrial and commercial activity apparently is not a major source of airborne lead in El Paso, and presumably other locales that have eliminated such traditional sources as leaded gasoline. Instead, local contaminated soil, legacy of earlier anthropogenic Pb releases, serves as a long-term reservoir that gradually leaks particulate lead to the atmosphere. Given the difficulty and expense of large-scale soil remediation or removal, fugitive soil likely constrains a lower limit for airborne lead levels in many urban settings. PMID:19340295

  5. Lead uptake in diverse plant families: a study applying X-ray absorption near edge spectroscopy.

    PubMed

    Bovenkamp, Gudrun L; Prange, Alexander; Schumacher, Wolfgang; Ham, Kyungmin; Smith, Aaron P; Hormes, Josef

    2013-05-01

    The chemical environment of lead in roots and leaves of plants from four different plant families and a lichen from a former lead mining site in the Eifel Mountains in Germany was determined by Pb L3-edge XANES measurements using solid reference compounds and also aqueous solutions of different ionic strength simulating the plant environment. Pb(2+) ions in the plants were found to have two major coordinations, one with nine oxygen atoms in the first coordination shell similar to outer-sphere complexation and a second coordination with just three oxygen atoms similar to inner-sphere complexation. This can be interpreted assuming that lead is sorbed on the surface of cell walls depending on the concentration of lead in the soil solution. Pb L3-edge XANES spectra of dried and fresh plant samples are very similar because sorption does not change with removal of water but only because of the initial ionic strength. No bonding to biologically important groups (-S, - N) or precipitation (-PO4) was found. PMID:23517351

  6. Encapsulation of lead sulfide molecular clusters into solid matrices. Structural analysis with x-ray absorption spectroscopy

    SciTech Connect

    Moller, K.; Bein, T. ); Herron, N.; Mahler, W.; Wang, Ying )

    1989-07-26

    Molecular-size PbS species have been stabilized in the open-pore structure of zeolite Y and mordenite via ion exchange with Pb(II) and subsequent treatment with H{sub 2}S at 295 K. Detailed analysis of synchrotron x-ray absorption data of the Pb L{sub III}-edge shows that intrazeolite PbO{sub 2}(O{sub z} = zeolite oxygen) species in zeolite Y react with H{sub 2}S to form monomolecular S{sub 2}Pb(I{sub z}){sub 3} species that are still anchored to the zeolite framework. The intrazeolite PbS phase appears to be more ordered at high loading levels of lead in zeolite Y than at low loading levels. The coordination of Pb(II) and the structure of PbS in the mordenite host is less ordered but basically very similar to that of the monomolecular species in Y. Optical absorption data for these samples agree very well with the structural EXAFS results. Larger PbS clusters have been stabilized in 85% ethylene-15% methacrylic acid copolymer films by a similar preparation procedure. EXAFS data indicate that the reaction forms PbS clusters with several Pb coordination shells and that the conversion of PbS is a function of Pb(II) loading levels. 23 refs., 9 figs., 3 tabs.

  7. Determining copper and lead binding in Larrea tridentata through chemical modification and X-ray absorption spectroscopy

    SciTech Connect

    Polette, L.; Gardea-Torresdey, J.L.; Chianelli, R.; Pickering, I.J.; George, G.N.

    1997-12-31

    Metal contamination in soils has become a widespread problem. Emerging technologies, such as phytoremediation, may offer low cost cleanup methods. The authors have identified a desert plant, Larrea tridentata (creosote bush), which naturally grows and uptakes copper and lead from a contaminated area near a smelting operation. They determined, through chemical modification of carboxyl groups with methanol, that these functional groups may be responsible for a portion of copper(II) binding. In contrast, lead binding was minimally affected by modification of carboxyl groups. X-ray absorption spectroscopy studies conducted at Stanford Synchrotron Radiation Laboratory (SSRL) further support copper binding to oxygen-coordinated ligands and also imply that the binding is not solely due to phytochelatins. The EXAFS data indicate the presence of both Cu-O and Cu-S back scatters, no short Cu-Cu interactions, but with significant Cu-Cu back scattering at 3.7 {angstrom} (unlike phytochelatins with predominantly Cu-S coordination and short Cu-Cu interactions at 2.7 {angstrom}). Cu EXAFS of roots and leaves also vary depending on the level of heavy metal contamination in the environment from which the various creosote samples were obtained. In contrast, Pb XANES data of roots and leaves of creosote collected from different contaminated sites indicate no difference in valence states or ligand coordination.

  8. Micro-x-ray fluorescence, micro-x-ray absorption spectroscopy, and micro-x-ray diffraction investigation of lead speciation after the addition of different phosphorus amendments to a smelter-contaminated soil.

    PubMed

    Baker, Lucas R; Pierzynski, Gary M; Hettiarachchi, Ganga M; Scheckel, Kirk G; Newville, Matthew

    2014-03-01

    The stabilization of Pb on additions of P to contaminated soils and mine spoil materials has been well documented. It is clear from the literature that different P sources result in different efficacies of Pb stabilization in the same contaminated material. We hypothesized that the differences in the efficacy of Pb stabilization in contaminated soils on fluid or granular P amendment addition is due to different P reaction processes in and around fertilizer granules and fluid droplets. We used a combination of several synchrotron-based techniques (i.e., spatially resolved micro-X-ray fluorescence, micro-X-ray absorption near-edge structure spectroscopy, and micro-X-ray diffraction) to speciate Pb at two incubation times in a smelter-contaminated soil on addition of several fluid and granular P amendments. The results indicated that the Pb phosphate mineral plumbogummite was an intermediate phase of pyromorphite formation. Additionally, all fluid and granular P sources were able to induce Pb phosphate formation, but fluid phosphoric acid (PA) was the most effective with time and distance from the treatment. Granular phosphate rock and triple super phosphate (TSP) amendments reacted to generate Pb phosphate minerals, with TSP being more effective at greater distances from the point of application. As a result, PA and TSP were the most effective P amendments at inducing Pb phosphate formation, but caution needs to be exercised when adding large amounts of soluble P to the environment. PMID:25602650

  9. High pressure x-ray absorption studies of phase transitions

    SciTech Connect

    Tranquada, J.M.; Ingalls, R.; Crozier, E.D.

    1984-01-01

    High pressure generally changes all of the properties of substances, leading to phase transitions in many cases. This paper reviews how such phase changes reveal themselves in x-ray absorption spectra. Examples are given using the salts NaBr, RbCl, CuBr, and SnSe. (DLC)

  10. X-ray absorption fine structure combined with fluorescence spectrometry for monitoring trace amounts of lead adsorption in the environmental conditions.

    PubMed

    Izumi, Yasuo; Kiyotaki, Fumitaka; Minato, Taketoshi; Seida, Yoshimi

    2002-08-01

    The local structure of trace amounts of lead in an adsorbent matrix that contains a high concentration of iron and magnesium (Mg6Fe2(OH)16(CO3) x 3H2O) was successfully monitored by means of X-ray absorption fine structure spectroscopy combined with fluorescence spectrometry. A eutectic mixture of PbCO3 and Pb(OH)2 coagulated when Pb2+ was adsorbed from a 1.0 ppm aqueous solution, and in contrast, the major species was ion-exchanged Pb2+ in the case of adsorption from a 100 ppb aqueous solution. The difference was ascribed to the balance between the precipitation equilibrium for coagulation and the rate of the ion exchange reaction with surface hydroxyl groups. PMID:12175171

  11. Comparison of Lead Species in Household Dust Wipes, Soil, and Airborne Particulate Matter in El Paso, Texas, by X-Ray Absorption Spectroscopy

    NASA Astrophysics Data System (ADS)

    Pingitore, N. E.; Clague, J.; Amaya, M. A.

    2006-12-01

    Understanding the interplay of indoor and outdoor sources of lead in an urban setting is one foundation in establishing risk for lead exposure in children in our cities. A household may be the source for lead contamination due to the deterioration of interior lead-based paint, or a sink if lead particles are tracked or blown into the home from such potential ambient sources as yard soil or urban street dust. In addressing this issue, X-Ray Absorption Spectroscopy (XAS) presents the opportunity to directly and quantitatively speciate lead at low concentrations in bulk samples. We performed XAS analyses on dust wipes from window sills or floors from 8 houses that exceeded Federal standards for lead in dust. We entered these data into a Principal Components Analysis (PCA) that also included El Paso environmental samples: lead-based paints, soils, and airborne particulate matter. A simple two-component mixing system accounted for more than 95% of the variance of this data set. Paint and lead oxide appear to be the principal components, with all the samples falling in a compositional range from pure paint to 75% paint, 25% lead oxide. Note that several different lead compounds are possible constituents of a given lead-based paint. The paints spread from one end out along perhaps a fifth of the range of the compositional axis, followed closely, but not overlapped, by the soil samples, which covered the remainder of the compositional range. Two of the dust wipes plotted within the paint range, and the remaining 6 dust wipes plotted randomly through the soil range. Samples of airborne particulate matter plotted in both the paint and soil ranges. These observations suggest that the lead on most of the dust wipes originated outside the house, probably from deteriorated exterior lead-based paint deposited in adjacent yards. This paint mixed with lead oxide present in the soil and entered the houses by the airborne route. The probable source of the oxide in the soil is former

  12. X-ray Weak Broad-line Qquasars: Absorption or Intrinsic X-ray Weakness

    NASA Technical Reports Server (NTRS)

    Mushotzky, Richard (Technical Monitor); Risaliti, Guida

    2005-01-01

    XMM observations of X-ray weak quasars have been performed during 2003 and 2004. The data for all the observations have become available in 2004 (there has been a delay of several months on the initial schedule, due to high background flares which contaminated the observations: as a consequence, most of them had to be rescheduled). We have reduced and analyzed all the data, and obtained interesting scientific results. Out of the eight sources, 4 are confirmed to be extremely X-ray weak, in agreement with the results of previous Chandra observations. 3 sources are confined to be highly variable both in flux (by factor 20-50) and in spectral properties (dramatic changes in spectral index). For both these groups of objects we are completing a publication: 1) For the X-ray weak sources, a paper is submitted with a complete analysis of the X-ray spectra both from Chandra and XMM-Newton, and a comparison with optical and near-IR photometry obtained from all-sky surveys. Possible models for the unusual spectral energy distribution of these sources are also presented. 2) For the variable sources, a paper is being finalized where the X-ray spectra obtained with XMM-Newton are compared with previous X-ray observations and with observations at other wavelengths. It is shown that these sources are high luminosity and extreme cases of the highly variable class of narrow-line Seyfert Is. In order to further understand the nature of these X-ray weak quasars, we submitted proposals for spectroscopy at optical and infrared telescopes. We obtained time at the TNG 4 meter telescope for near-IR observations and at the Hobby-Eberly Telescope for optical high-resolution spectroscopy. These observations have been performed in early 2004. They will complement the XMM data and will lead to understanding of whether the X-ray weakness of these sources is an intrinsic property or is due to absorption by circum-nuclear material. The infrared spectra of the variable sources have been already

  13. Laser plasma x-ray source for ultrafast time-resolved x-ray absorption spectroscopy

    PubMed Central

    Miaja-Avila, L.; O'Neil, G. C.; Uhlig, J.; Cromer, C. L.; Dowell, M. L.; Jimenez, R.; Hoover, A. S.; Silverman, K. L.; Ullom, J. N.

    2015-01-01

    We describe a laser-driven x-ray plasma source designed for ultrafast x-ray absorption spectroscopy. The source is comprised of a 1 kHz, 20 W, femtosecond pulsed infrared laser and a water target. We present the x-ray spectra as a function of laser energy and pulse duration. Additionally, we investigate the plasma temperature and photon flux as we vary the laser energy. We obtain a 75 μm FWHM x-ray spot size, containing ∼106 photons/s, by focusing the produced x-rays with a polycapillary optic. Since the acquisition of x-ray absorption spectra requires the averaging of measurements from >107 laser pulses, we also present data on the source stability, including single pulse measurements of the x-ray yield and the x-ray spectral shape. In single pulse measurements, the x-ray flux has a measured standard deviation of 8%, where the laser pointing is the main cause of variability. Further, we show that the variability in x-ray spectral shape from single pulses is low, thus justifying the combining of x-rays obtained from different laser pulses into a single spectrum. Finally, we show a static x-ray absorption spectrum of a ferrioxalate solution as detected by a microcalorimeter array. Altogether, our results demonstrate that this water-jet based plasma source is a suitable candidate for laboratory-based time-resolved x-ray absorption spectroscopy experiments. PMID:26798792

  14. Laser plasma x-ray source for ultrafast time-resolved x-ray absorption spectroscopy

    DOE PAGESBeta

    Miaja-Avila, L.; O'Neil, G. C.; Uhlig, J.; Cromer, C. L.; Dowell, M. L.; Jimenez, R.; Hoover, A. S.; Silverman, K. L.; Ullom, J. N.

    2015-03-02

    We describe a laser-driven x-ray plasma source designed for ultrafast x-ray absorption spectroscopy. The source is comprised of a 1 kHz, 20 W, femtosecond pulsed infrared laser and a water target. We present the x-ray spectra as a function of laser energy and pulse duration. Additionally, we investigate the plasma temperature and photon flux as we vary the laser energy. We obtain a 75 μm FWHM x-ray spot size, containing ~106 photons/s, by focusing the produced x-rays with a polycapillary optic. Since the acquisition of x-ray absorption spectra requires the averaging of measurements from >107 laser pulses, we also presentmore » data on the source stability, including single pulse measurements of the x-ray yield and the x-ray spectral shape. In single pulse measurements, the x-ray flux has a measured standard deviation of 8%, where the laser pointing is the main cause of variability. Further, we show that the variability in x-ray spectral shape from single pulses is low, thus justifying the combining of x-rays obtained from different laser pulses into a single spectrum. Finally, we show a static x-ray absorption spectrum of a ferrioxalate solution as detected by a microcalorimeter array. Altogether, our results demonstrate that this water-jet based plasma source is a suitable candidate for laboratory-based time-resolved x-ray absorption spectroscopy experiments.« less

  15. Laser plasma x-ray source for ultrafast time-resolved x-ray absorption spectroscopy.

    PubMed

    Miaja-Avila, L; O'Neil, G C; Uhlig, J; Cromer, C L; Dowell, M L; Jimenez, R; Hoover, A S; Silverman, K L; Ullom, J N

    2015-03-01

    We describe a laser-driven x-ray plasma source designed for ultrafast x-ray absorption spectroscopy. The source is comprised of a 1 kHz, 20 W, femtosecond pulsed infrared laser and a water target. We present the x-ray spectra as a function of laser energy and pulse duration. Additionally, we investigate the plasma temperature and photon flux as we vary the laser energy. We obtain a 75 μm FWHM x-ray spot size, containing ∼10(6) photons/s, by focusing the produced x-rays with a polycapillary optic. Since the acquisition of x-ray absorption spectra requires the averaging of measurements from >10(7) laser pulses, we also present data on the source stability, including single pulse measurements of the x-ray yield and the x-ray spectral shape. In single pulse measurements, the x-ray flux has a measured standard deviation of 8%, where the laser pointing is the main cause of variability. Further, we show that the variability in x-ray spectral shape from single pulses is low, thus justifying the combining of x-rays obtained from different laser pulses into a single spectrum. Finally, we show a static x-ray absorption spectrum of a ferrioxalate solution as detected by a microcalorimeter array. Altogether, our results demonstrate that this water-jet based plasma source is a suitable candidate for laboratory-based time-resolved x-ray absorption spectroscopy experiments. PMID:26798792

  16. Laser plasma x-ray source for ultrafast time-resolved x-ray absorption spectroscopy

    SciTech Connect

    Miaja-Avila, L.; O'Neil, G. C.; Uhlig, J.; Cromer, C. L.; Dowell, M. L.; Jimenez, R.; Hoover, A. S.; Silverman, K. L.; Ullom, J. N.

    2015-03-02

    We describe a laser-driven x-ray plasma source designed for ultrafast x-ray absorption spectroscopy. The source is comprised of a 1 kHz, 20 W, femtosecond pulsed infrared laser and a water target. We present the x-ray spectra as a function of laser energy and pulse duration. Additionally, we investigate the plasma temperature and photon flux as we vary the laser energy. We obtain a 75 μm FWHM x-ray spot size, containing ~106 photons/s, by focusing the produced x-rays with a polycapillary optic. Since the acquisition of x-ray absorption spectra requires the averaging of measurements from >107 laser pulses, we also present data on the source stability, including single pulse measurements of the x-ray yield and the x-ray spectral shape. In single pulse measurements, the x-ray flux has a measured standard deviation of 8%, where the laser pointing is the main cause of variability. Further, we show that the variability in x-ray spectral shape from single pulses is low, thus justifying the combining of x-rays obtained from different laser pulses into a single spectrum. Finally, we show a static x-ray absorption spectrum of a ferrioxalate solution as detected by a microcalorimeter array. Altogether, our results demonstrate that this water-jet based plasma source is a suitable candidate for laboratory-based time-resolved x-ray absorption spectroscopy experiments.

  17. Effects of Galactic absorption on soft X-ray surveys

    NASA Technical Reports Server (NTRS)

    Zamorani, G.; Gioia, I. M.; Maccacaro, T.; Wolter, A.

    1988-01-01

    A bias in the spectral distribution of X-ray sources detected in X-ray surveys is discussed which is due to the combination of the intrinsic characteristics of X-ray telescopes and the effects of low-energy photoelectric absorption within the Galaxy. A statistical method for obtaining information on the average spectrum of X-ray sources detected in well-defined surveys is presented. This method can be applied to surveys performed with X-ray telescopes working at relatively soft X-ray energies, such as Einstein, Exosat, and Rosat.

  18. Assessment of chemical species of lead accumulated in tidemarks of human articular cartilage by X-ray absorption near-edge structure analysis

    PubMed Central

    Meirer, Florian; Pemmer, Bernhard; Pepponi, Giancarlo; Zoeger, Norbert; Wobrauschek, Peter; Sprio, Simone; Tampieri, Anna; Goettlicher, Joerg; Steininger, Ralph; Mangold, Stefan; Roschger, Paul; Berzlanovich, Andrea; Hofstaetter, Jochen G.; Streli, Christina

    2011-01-01

    A highly specific accumulation of the toxic element lead was recently measured in the transition zone between non-calcified and calcified normal human articular cartilage. This transition zone, the so-called ‘tidemark’, is considered to be an active calcification front of great clinical importance. However, little is known about the mechanisms of accumulation and the chemical form of Pb in calcified cartilage and bone. Using spatially resolved X-ray absorption near-edge structure analysis (µ-XANES) at the Pb L 3-edge, the chemical state of Pb in the osteochondral region was investigated. The feasibility of the µ-XANES set-up at the SUL-X beamline (ANKA synchrotron light source) was tested and confirmed by comparing XANES spectra of bulk Pb-reference compounds recorded at both the XAS and the SUL-X beamline at ANKA. The µ-XANES set-up was then used to investigate the tidemark region of human bone (two patella samples and one femoral head sample). The spectra recorded at the tidemark and at the trabecular bone were found to be highly correlated with the spectra of synthetic Pb-doped carbonated hydroxyapatite, suggesting that in both of these very different tissues Pb is incorporated into the hydroxyapatite structure. PMID:21335911

  19. X-ray Attenuation and Absorption Calculations.

    Energy Science and Technology Software Center (ESTSC)

    1988-02-25

    This point-source, polychromatic, discrete energy X-ray transport and energy deposition code system calculates first-order spectral estimates of X-ray energy transmission through slab materials and the associated spectrum of energy absorbed by the material.

  20. Impacts of chemical amendment and plant growth on lead speciation and enzyme activities in a shooting range soil: an x-ray absorption fine structure investigation.

    PubMed

    Hashimoto, Yohey; Matsufuru, Hiroki; Takaoka, Masaki; Tanida, Hajime; Sato, Takeshi

    2009-01-01

    In situ chemical immobilization is a practical remediation technology for metal-contaminated soils because of its capability to reduce cost and environmental impacts. We assessed the immobilization effects of poultry waste amendment and plant growth (Panicum maximum Jacq.) on Pb speciation and enzyme activities in shooting range soils. Soil contaminated with Pb was obtained from the top 20 cm of a shooting range. To evaluate Pb mobility in the soil profile treated with plants and immobilizing amendment, we used large columns filled with Pb-contaminated soil (0-20 cm, surface soils) and non-contaminated soil (20-75 cm, subsurface soils). The column study demonstrated that the amendment reduced the toxicity characteristic leaching procedure-extractable Pb in the surface soil by 90% of the Control soil. Lead mobility from the surface to subsurface profiles was significantly attenuated by plant growth but was promoted by the amendment without plant application. The extended X-ray absorption fine structure analysis revealed that the amendment reduced the proportion of PbCO(3) and Pb-organic complexes and transformed them into a more geochemically stable species of Pb(5)(PO(4))(3)Cl with 30 to 35% of the total Pb species. Applications of plant and amendment increased activities of dehydrogenase and phosphatase in the surface soil with 2.7- and 1.1-fold greater than those in Control, respectively. The use of amendments in combination with plant growth may have potential as an integrated remediation strategy that enables Pb immobilization and soil biological restoration in shooting range soils. PMID:19465717

  1. Double conical crystal x-ray spectrometer for high resolution ultrafast x-ray absorption near-edge spectroscopy of Al K edge

    NASA Astrophysics Data System (ADS)

    Levy, A.; Dorchies, F.; Fourment, C.; Harmand, M.; Hulin, S.; Santos, J. J.; Descamps, D.; Petit, S.; Bouillaud, R.

    2010-06-01

    An x-ray spectrometer devoted to dynamical studies of transient systems using the x-ray absorption fine spectroscopy technique is presented in this article. Using an ultrafast laser-induced x-ray source, this optical device based on a set of two potassium acid phthalate conical crystals allows the extraction of x-ray absorption near-edge spectroscopy structures following the Al absorption K edge. The proposed experimental protocol leads to a measurement of the absorption spectra free from any crystal reflectivity defaults and shot-to-shot x-ray spectral fluctuation. According to the detailed analysis of the experimental results, a spectral resolution of 0.7 eV rms and relative fluctuation lower than 1% rms are achieved, demonstrated to be limited by the statistics of photon counting on the x-ray detector.

  2. Spatial distribution and speciation of lead around corroding bullets in a shooting range soil studied by micro-X-ray fluorescence and absorption spectroscopy.

    PubMed

    Vantelon, Delphine; Lanzirotti, Antonio; Scheinost, Andreas C; Kretzschmar, Ruben

    2005-07-01

    We investigated the spatial distribution and speciation of Pb in the weathering crust and soil surrounding corroding metallic Pb bullets in a shooting range soil. The soil had a neutral pH, loamy texture, and was highly contaminated with Pb, with total Pb concentrations in the surface soil up to 68 000 mg kg(-1). Undisturbed soil samples containing corroding bullets were collected and embedded in resin, and polished sections were prepared for micro-X-ray fluorescence (micro-XRF) elemental mapping and micro-X-ray absorption near edge structure (micro-XANES) spectroscopy. Bullet weathering crust material was separated from the metallic Pb cores and analyzed by powder X-ray diffraction analysis. Our results show a steep decrease in total Pb concentrations from the bullet weathering crust into the surrounding soil matrix. The weathering crust consisted of a mixture of litharge [alpha-PbO], hydrocerussite [Pb3(CO3)2-(OH)2], and cerussite [PbCO3], with litharge dominating near the metallic Pb core and cerussite dominating in the outer crust, which is in contact with the soil matrix. On the basis of these results and thermodynamic considerations, we propose that the transition of Pb species after oxidation of Pb(O) to Pb(II) follows the sequence litharge --> hydrocerussite --> cerussite. Consequently, the solubility of cerussite limits the activity of Pb2+ in the soil solution in contact with weathering bullets to < or =1.28 x 10(-6) at pH 7, assuming that the CO2 partial pressure (PCO2) in the soil is equal or larger than in the atmosphere (PCO2 > or = 0.000 35 atm). PMID:16053078

  3. X-RAY ABSORPTION OF HIGH-REDSHIFT QUASARS

    SciTech Connect

    Eitan, Assaf; Behar, Ehud E-mail: behar@physics.technion.ac.il

    2013-09-01

    The soft X-ray photoelectric absorption of high-z quasars has been known for two decades, but has no unambiguous astrophysical context. We construct the largest sample to date of 58 high-redshift quasars (z > 0.45) selected from the XMM-Newton archive based on a high photon count criterion (>1800). We measure the optical depth {tau} at 0.5 keV and find that 43% of the quasars show significant absorption. We aim to find which physical parameters of the quasars, e.g., redshift, radio luminosity, radio loudness, or X-ray luminosity, drive their observed absorption. We compare the absorption behavior with redshift with the pattern expected if the diffuse intergalactic medium (IGM) is responsible for the observed absorption. We also compare the absorption with a comparison sample of gamma-ray burst (GRB) X-ray afterglows. Although the z > 2 quasar opacity is consistent with diffuse IGM absorption, many intermediate-z (0.45 < z < 2) quasars are not sufficiently absorbed for this scenario, and are appreciably less absorbed than GRBs. Only 10/37 quasars at z < 2 are absorbed, and only 5/30 radio-quiet quasars are absorbed. We find a weak correlation between {tau} and z, and an even weaker correlation between {tau} and radio luminosity. These findings lead to the conclusion that although a diffuse IGM origin for the quasar absorption is unlikely, the optical depth does seem to increase with redshift, roughly as (1 + z){sup 2.2{+-}0.6}, tending to {tau} Almost-Equal-To 0.4 at high redshifts, similar to the high-z GRBs. This result can be explained by an ionized and clumpy IGM at z < 2, and a cold, diffuse IGM at higher redshift. If, conversely, the absorption occurs at the quasar, and owing to the steep L{sub x} {proportional_to}(1 + z){sup 7.1{+-}0.5} correlation in the present sample, the host column density scales as N{sub H}{proportional_to}L{sub x}{sup 0.7{+-}0.1}.

  4. Lead Is Not Off Center in PbTe: The Importance of r-Space Phase Information in Extended X-Ray Absorption Fine Structure Spectroscopy

    NASA Astrophysics Data System (ADS)

    Keiber, T.; Bridges, F.; Sales, B. C.

    2013-08-01

    PbTe is a well-known thermoelectric material. Recent x-ray total scattering studies suggest that Pb moves off center along 100 in PbTe, by ˜0.2Å at 300 K, producing a split Pb-Te pair distribution. We present an extended x-ray absorption fine structure spectroscopy (EXAFS) study of PbTe (and Tl doped PbTe) to determine if Pb or Te is off center. EXAFS provides sensitive r- or k-space phase information which can differentiate between a split peak for the Pb-Te distribution (indicative of off-center Pb) and a thermally broadened peak. We find no evidence for a split peak for Pb-Te or Te-Pb. At 300 K, the vibration amplitude for Pb-Te (or Te-Pb) is large; this thermally induced disorder is indicative of weak bonds, and the large disorder is consistent with the low thermal conductivity at 300 K. We also find evidence of an anharmonic potential for the nearest Pb-Te bonds, consistent with the overall anharmonicity found for the phonon modes. This effect is modeled by a “skew” factor (C3) which significantly improves the fit of the Pb-Te and Te-Pb peaks for the high temperature EXAFS data; C3 becomes significant above approximately 150-200 K. The consequences of these results will be discussed.

  5. Soft X-ray Absorption Edges in LMXBs

    NASA Technical Reports Server (NTRS)

    2004-01-01

    The XMM observation of LMC X-2 is part of our program to study X-ray absorption in the interstellar medium (ISM). This program includes a variety of bright X-ray binaries in the Galaxy as well as the Magellanic Clouds (LMC and SMC). LMC X-2 is located near the heart of the LMC. Its very soft X-ray spectrum is used to determine abundance and ionization fractions of neutral and lowly ionized oxygen of the ISM in the LMC. The RGS spectrum so far allowed us to determine the O-edge value to be for atomic O, the EW of O-I in the ls-2p resonance absorption line, and the same for O-II. The current study is still ongoing in conjunction with other low absorption sources like Sco X-1 and the recently observed X-ray binary 4U 1957+11.

  6. X-Ray Absorption of High- Redshift Quasars

    NASA Astrophysics Data System (ADS)

    Behar, Ehud; Eitan, Assaf

    2012-09-01

    Soft X-ray absorption of high-z quasars has been known for more than a decade, but its astrophysical context remains a mystery. In order to better understand this absorption, we have constructed the largest to date high-S/N sample of high-z quasars (z > 0.5) from the XMM-Newton archive. We find that generally, z<2 and radio quiet objects provide only upper limits for the 0.5 keV optical depth (tau). Thus, we use censored statistics methods to seek correlations between tau and other quasar parameters. We find a dramatic increase of tau with z [(1+z)^{2.5}], although the correlation is rather weak. The correlation of tau with radio luminosity (or loudness) is even weaker. We also compare the absorption behavior with redshift with a large sample of GRBs, and with the pattern expected if the diffuse intergalactic medium (IGM) is responsible for the observed absorption. We find that although the z > 2 quasar opacity is consistent with a diffuse IGM effect and with the high-z GRB opacities, absorption of intermediate z (0.5 < z < 2) quasars is too low for this scenario, which leads to the conclusion that a simple IGM origin for this absorption is unlikely.

  7. TU-A-9A-07: X-Ray Acoustic Computed Tomography (XACT): 100% Sensitivity to X-Ray Absorption

    SciTech Connect

    Xiang, L; Ahmad, M; Nikoozadeh, A; Pratx, G; Khuri-Yakub, B; Xing, L

    2014-06-15

    Purpose: To assess whether X-ray acoustic computed tomography (XACT) is more sensitive to X-ray absorption than that of the conventional X-ray imaging. Methods: First, a theoretical model was built to analyze the X-ray absorption sensitivity of XACT imaging and conventional X-ray imaging. Second, an XACT imaging system was developed to evaluate the X-ray induced acoustic signal generation as well as the sensitivity improvement over transmission x-ray imaging. Ultra-short x-ray pulses (60-nanosecond) were generated from an X-ray source operated at the energy of 150 kVp with a 10-Hz repetition rate. The X-ray pulse was synchronized with the acoustic detection via a x-ray scintillation triggering to acquire the X-ray induced acoustic signal. Results: Theoretical analysis shows that X-ray induced acoustic signal is sensitive only to the X-ray absorption, while completely insensitive to out the X-ray scattering and fluorescence. XACT has reduced background and increased contrast-to-noise ratio, and therefore has increased sensitivity compared to transmission x-ray imaging. For a 50-μm size, gadolinium insertion in tissue exposed to 40 keV X-rays; the sensitivity of XACT imaging is about 28.9 times higher than that of conventional X-ray imaging. Conclusion: X-ray acoustic computer tomography (XACT) as a new imaging modality combines X-ray absorption contrast and high ultrasonic resolution in a single modality. It is feasible to improve the imaging sensitivity with XACT imaging compared with conventional X-ray imaging. Taking advantage of the high ultrasonic resolution, it is possible to perform 3-D imaging with a single x-ray pulse with arrays of transducers without any mechanical motion of the imaging system. This single-shot capability offers the potential of reducing radiation dose by a factor of 1000, and imaging 100 times faster when compared to the conventional X-ray CT, and thus revolutionizing x-ray imaging applications in medicine and biology. The authors

  8. X-Ray Absorption Spectra of Uranium by Synchrotron Radiation

    NASA Astrophysics Data System (ADS)

    Adachi, Hirohiko; Fujima, Kazumi; Taniguchi, Kazuo; Miyake, Chie; Imoto, Shosuke

    1981-08-01

    The X-ray absorption spectra of U, UO2 and UCl4 near the U OIV and OV thresholds have been measured by use of synchrotron radiation. The absorption peaks at about 100 eV and 110 eV are observed for all of these materials. However, the detailed structure of the spectra depend on the chemical state.

  9. Femtosecond x-ray absorption spectroscopy with hard x-ray free electron laser

    SciTech Connect

    Katayama, Tetsuo; Togashi, Tadashi; Tono, Kensuke; Kameshima, Takashi; Inubushi, Yuichi; Sato, Takahiro; Hatsui, Takaki; Yabashi, Makina; Obara, Yuki; Misawa, Kazuhiko; Bhattacharya, Atanu; Kurahashi, Naoya; Ogi, Yoshihiro; Suzuki, Toshinori

    2013-09-23

    We have developed a method of dispersive x-ray absorption spectroscopy with a hard x-ray free electron laser (XFEL), generated by a self-amplified spontaneous emission (SASE) mechanism. A transmission grating was utilized for splitting SASE-XFEL light, which has a relatively large bandwidth (ΔE/E ∼ 5 × 10{sup −3}), into several branches. Two primary split beams were introduced into a dispersive spectrometer for measuring signal and reference spectra simultaneously. After normalization, we obtained a Zn K-edge absorption spectrum with a photon-energy range of 210 eV, which is in excellent agreement with that measured by a conventional wavelength-scanning method. From the analysis of the difference spectra, the noise ratio was evaluated to be ∼3 × 10{sup −3}, which is sufficiently small to trace minute changes in transient spectra induced by an ultrafast optical laser. This scheme enables us to perform single-shot, high-accuracy x-ray absorption spectroscopy with femtosecond time resolution.

  10. X-Ray Weak Broad-Line Quasars: Absorption or Intrinsic X-Ray Weakness

    NASA Technical Reports Server (NTRS)

    Risaliti, Guido; Mushotzky, Richard F. (Technical Monitor)

    2004-01-01

    XMM observations of X-ray weak quasars have been performed during 2003. The data for all but the last observation are now available (there has been a delay of several months on the initial schedule, due to high background flares which contaminated the observations: as a consequence, most of them had to be rescheduled). We have reduced and analyzed these data, and obtained interesting preliminary scientific results. Out of the eight sources, 4 are confirmed to be extrimely X-ray weak, in agreement with the results of previous Chandra observations. 3 sources are confirmed to be highly variable both in flux (by factors 20-50) and in spectral properties (dramatic changes in spectral index). For both these groups of objects, an article is in preparation. Preliminary results have been presented at an international workshop on AGN surveys in December 2003, in Cozumel (Mexico). In order to further understand the nature of these X-ray weak quasars, we submitted proposals for spectroscopy at optical and infrared telescopes. We obtained time at the TNG 4 meter telescope for near-IR observations, and at the Hobby-Eberly Telescope for optical high-resolution spectroscopy. These observations will be performed in early 2004, and will complement the XMM data, in order to understand whether the X-ray weakness of these sources is an intrinsic property or is due to absorption by circumnuclear material.

  11. Soft X-ray induced damage in PVA-based membranes in water environment monitored by X-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Tzvetkov, George; Späth, Andreas; Fink, Rainer H.

    2014-10-01

    The effect of synchrotron X-ray flux in a soft X-ray scanning-transmission microspectroscope (STXM) instrument on the chemical structure of air-filled poly(vinyl alcohol) (PVA) based microbubbles and their stabilizing shell has been examined. Prolonged soft X-ray illumination of the particles in aqueous suspension leads to the breaking of the microbubbles' protective polymer shell and substantial chemical changes. The latter were clarified via a micro-spot C K-edge near-edge X-ray absorption fine structure (NEXAFS) spectroscopy with further respect to the absorbed X-ray doses. Our results revealed a continuous degradation of the PVA network associated with formation of carbonyl- and carboxyl-containing species as well as an increased content of unsaturated bonds. The observed effects must be taken into account in studies of micro- and nanostructured polymer materials utilizing X-rays.

  12. X-ray absorption spectroscopy of bacterial sulfur globules

    SciTech Connect

    George, Graham N.

    2002-08-01

    Sulfur K-edge X-ray absorption spectroscopy is a powerful in situ probe of sulfur biochemistry in intact cells and tissues. Under favorable circumstances the technique can provide quantitative information on the chemical identify of the sulfur species that are present in a sample. Prange et al. have recently reported an X-ray absorption spectroscopic study of bacterial sulfur storage globules. Unfortunately there are substantial problems with the experimental technique employed that, they contend, lead to completely erroneous conclusions. In the more recent of their two papers Prange et al. employed a curve-fitting method similar to that used by us (for more than 10 years). In essence, the method employs simply fitting a linear combination of the spectra of standard compounds to that of the unknown, in this case cultures of bacterial cells. This type of analysis can provide quantitative estimates of the individual sulfur types in the sample, but is critically dependent upon the choice of reference spectra. Prange et al. deduce substantial differences between the chemical forms of sulfur stored in the globules of different organisms; they conclude that the globules of Beggiatoa alba and Thiomargarita namibiensis contain cyclo-octasulfur (S{sub 8}), while those of other organisms contain polythionates (Acidithiobacillus ferrooxidans) and polymeric sulfur (e.g. Allochromatium vinosum). This is in contradiction with an earlier study, in which they found that sulfur in all globule species examined resembled that expected for various sized spherical particles of S{sub 8}. The discrepancy is due to an experimental artefact in the work of Prange et al. arising from their choice of transmittance detection, which is also discussed.

  13. High ionisation absorption in low mass X-ray binaries

    NASA Astrophysics Data System (ADS)

    Ponti, G.; Bianchi, S.; Muñoz-Darias, T.; De, K.; Fender, R.; Merloni, A.

    2016-05-01

    The advent of the new generation of X-ray telescopes yielded a significant step forward in our understanding of ionised absorption generated in the accretion discs of X-ray binaries. It has become evident that these relatively weak and narrow absorption features, sporadically present in the X-ray spectra of some systems, are actually the signature of equatorial outflows, which might carry away more matter than that being accreted. Therefore, they play a major role in the accretion phenomenon. These outflows (or ionised atmospheres) are ubiquitous during the softer states but absent during the power-law dominated, hard states, suggesting a strong link with the state of the inner accretion disc, presence of the radio-jet and the properties of the central source. Here, we discuss the current understanding of this field.

  14. Ultrafast absorption of intense x rays by nitrogen molecules

    SciTech Connect

    Buth, Christian; Liu Jicai; Chen, Mau Hsiung; Cryan, James P.; Fang Li; Hoener, Matthias; Berrah, Nora; Glownia, James M.; Coffee, Ryan N.

    2012-06-07

    We devise a theoretical description for the response of nitrogen molecules (N{sub 2}) to ultrashort and intense x rays from the free electron laser Linac Coherent Light Source (LCLS). We set out from a rate-equation description for the x-ray absorption by a nitrogen atom. The equations are formulated using all one-x-ray-photon absorption cross sections and the Auger and radiative decay widths of multiply-ionized nitrogen atoms. Cross sections are obtained with a one-electron theory and decay widths are determined from ab initio computations using the Dirac-Hartree-Slater (DHS) method. We also calculate all binding and transition energies of nitrogen atoms in all charge states with the DHS method as the difference of two self-consistent field (SCF) calculations ({Delta}SCF method). To describe the interaction with N{sub 2}, a detailed investigation of intense x-ray-induced ionization and molecular fragmentation are carried out. As a figure of merit, we calculate ion yields and the average charge state measured in recent experiments at the LCLS. We use a series of phenomenological models of increasing sophistication to unravel the mechanisms of the interaction of x rays with N{sub 2}: a single atom, a symmetric-sharing model, and a fragmentation-matrix model are developed. The role of the formation and decay of single and double core holes, the metastable states of N{sub 2}{sup 2+}, and molecular fragmentation are explained.

  15. Photoelectron and X-ray Absorption Spectroscopy Of Pu

    SciTech Connect

    Tobin, J; Chung, B; Schulze, R; Farr, J; Shuh, D

    2003-11-12

    We have performed Photoelectron Spectroscopy and X-Ray Absorption Spectroscopy upon highly radioactive samples of Plutonium at the Advanced Light Source in Berkeley, CA, USA. First results from alpha and delta Plutonium are reported as well as plans for future studies of actinide studies.

  16. Determining the Uncertainty of X-Ray Absorption Measurements

    PubMed Central

    Wojcik, Gary S.

    2004-01-01

    X-ray absorption (or more properly, x-ray attenuation) techniques have been applied to study the moisture movement in and moisture content of materials like cement paste, mortar, and wood. An increase in the number of x-ray counts with time at a location in a specimen may indicate a decrease in moisture content. The uncertainty of measurements from an x-ray absorption system, which must be known to properly interpret the data, is often assumed to be the square root of the number of counts, as in a Poisson process. No detailed studies have heretofore been conducted to determine the uncertainty of x-ray absorption measurements or the effect of averaging data on the uncertainty. In this study, the Poisson estimate was found to adequately approximate normalized root mean square errors (a measure of uncertainty) of counts for point measurements and profile measurements of water specimens. The Poisson estimate, however, was not reliable in approximating the magnitude of the uncertainty when averaging data from paste and mortar specimens. Changes in uncertainty from differing averaging procedures were well-approximated by a Poisson process. The normalized root mean square errors decreased when the x-ray source intensity, integration time, collimator size, and number of scanning repetitions increased. Uncertainties in mean paste and mortar count profiles were kept below 2 % by averaging vertical profiles at horizontal spacings of 1 mm or larger with counts per point above 4000. Maximum normalized root mean square errors did not exceed 10 % in any of the tests conducted. PMID:27366627

  17. Simultaneous surface plasmon resonance and x-ray absorption spectroscopy.

    PubMed

    Serrano, A; Rodríguez de la Fuente, O; Collado, V; Rubio-Zuazo, J; Monton, C; Castro, G R; García, M A

    2012-08-01

    We present an experimental setup for the simultaneous measurement of surface plasmon resonance (SPR) and x-ray absorption spectroscopy (XAS) on metallic thin films at a synchrotron beamline. The system allows measuring in situ and in real time the effect of x-ray irradiation on the SPR curves to explore the interaction of x-rays with matter. It is also possible to record XAS spectra while exciting SPR in order to study changes in the films induced by the excitation of surface plasmons. Combined experiments recording simultaneously SPR and XAS curves while scanning different parameters can be also carried out. The relative variations in the SPR and XAS spectra that can be detected with this setup range from 10(-3) to 10(-5), depending on the particular experiment. PMID:22938268

  18. Simultaneous surface plasmon resonance and x-ray absorption spectroscopy

    SciTech Connect

    Serrano, A.; Rodriguez de la Fuente, O.; Collado, V.; Rubio-Zuazo, J.; Castro, G. R.; Monton, C.; Garcia, M. A.

    2012-08-15

    We present an experimental setup for the simultaneous measurement of surface plasmon resonance (SPR) and x-ray absorption spectroscopy (XAS) on metallic thin films at a synchrotron beamline. The system allows measuring in situ and in real time the effect of x-ray irradiation on the SPR curves to explore the interaction of x-rays with matter. It is also possible to record XAS spectra while exciting SPR in order to study changes in the films induced by the excitation of surface plasmons. Combined experiments recording simultaneously SPR and XAS curves while scanning different parameters can be also carried out. The relative variations in the SPR and XAS spectra that can be detected with this setup range from 10{sup -3} to 10{sup -5}, depending on the particular experiment.

  19. A method for normalization of X-ray absorption spectra

    SciTech Connect

    Weng, T.-C.; Waldo, G.S.; Penner-Hahn, J.E.

    2010-07-20

    Accurate normalization of X-ray absorption data is essential for quantitative analysis of near-edge features. A method, implemented as the program MBACK, to normalize X-ray absorption data to tabulated mass absorption coefficients is described. Comparison of conventional normalization methods with MBACK demonstrates that the new normalization method is not sensitive to the shape of the background function, thus allowing accurate comparison of data collected in transmission mode with data collected using fluorescence ion chambers or solid-state fluorescence detectors. The new method is shown to have better reliability and consistency and smaller errors than conventional normalization methods. The sensitivity of the new normalization method is illustrated by analysis of data collected during an equilibrium titration.

  20. X-ray absorption spectroscopy of liquid surface

    NASA Astrophysics Data System (ADS)

    Watanabe, Iwao; Tanida, Hajime; Kawauchi, Sigehiro; Harada, Makoto; Nomura, Masaharu

    1997-09-01

    An apparatus has been constructed for x-ray absorption spectroscopy of elements at air/aqueous solution interface. Its surface sensitivity is gained from glancing incidence of synchrotron radiation under total reflection condition. The absorption is detected by total conversion He ion-yield method. This apparatus was operated at the beam line 7C of Photon Factory, where the incident photon beam comes from a sagittal focus double-crystal monochromator via a 70-cm-long bent mirror. The mirror focuses the beam vertically and changes the beam direction downward by 1 mrad to irradiate solution surface. The essential requirement of this technique, ripple-free liquid surface at accurate position, was attained by introducing a trough on a floating boat, continuous surface level monitoring, and an automatic Z-stage control. The x-ray absorption edge jump demonstrated that surface concentration of bromide ion follows the Langmuir type adsorption for tetraalkylammonuim bromide solution. By comparing the jump values for surface-active and -inactive bromide salt solutions, the detecting depth of the present technique was determined to be 8.8 nm. An extended x-ray absorption fine structure analysis of bromide ion segregated to the surface by stearyltrimethylammonium cation indicated that its solvation structure is different from that of bulk.

  1. An x-ray absorption spectroscopy study of Mo oxidation in Pb at elevated temperatures

    SciTech Connect

    Liu, Shanshan; Olive, Daniel; Terry, Jeff; Segre, Carlo U.

    2009-06-30

    The corrosion of fuel cladding and structural materials by lead and lead-bismuth eutectic in the liquid state at elevated temperatures is an issue that must be considered when designing advanced nuclear systems and high-power spallation neutron targets. In this work, lead corrosion studies of molybdenum were performed to investigate the interaction layer as a function of temperature by X-ray absorption spectroscopy. In situ X-ray absorption measurements on a Mo substrate with a 3-6 {micro}m layer of Pb deposited by thermal evaporation were performed at temperatures up to 900 C and at a 15{sup o} angle to the incident X-rays. The changes in the local atomic structure of the corrosion layer are visible in the difference extended X-ray absorption fine structure and the linear combination fitting of the X-ray absorption near-edge structure to as-deposited molybdenum sample and molybdenum oxide (MoO{sub 2} and MoO{sub 3}) standards. The data are consistent with the appearance of MoO{sub 3} in an intermediate temperature range (650-800 C) and the more stable MoO{sub 2} phase dominating at high and low temperatures.

  2. Extended X-ray absorption fine structure of bimetallic nanoparticles

    PubMed Central

    2011-01-01

    Summary Electronic and magnetic properties strongly depend on the structure of the material, especially on the crystal symmetry and chemical environment. In nanoparticles, the break of symmetry at the surface may yield different physical properties with respect to the corresponding bulk material. A useful tool to investigate the electronic structure, magnetic behaviour and local crystallographic structure is X-ray absorption spectroscopy. In this review, recent developments in the field of extended X-ray absorption fine structure measurements and in the analysis methods for structural investigations of bimetallic nanoparticles are highlighted. The standard analysis based on Fourier transforms is compared to the relatively new field of wavelet transforms that have the potential to outperform traditional analysis, especially in bimetallic alloys. As an example, the lattice expansion and inhomogeneous alloying found in FePt nanoparticles is presented, and this is discussed below in terms of the influence of employed density functional theory calculations on the magnetic properties. PMID:21977436

  3. Operando X-ray absorption and infrared fuel cell spectroscopy

    SciTech Connect

    Lewis, Emily A.; Kendrick, Ian; Jia, Qingying; Grice, Corey; Segre, Carlo U.; Smotkin, Eugene S.

    2011-11-17

    A polymer electrolyte fuel cell enables operando X-ray absorption and infrared spectroscopy of the membrane electrode assembly catalytic layer with flowing fuel and air streams at controlled temperature. Time-dependent X-ray absorption near edge structure spectra of the Pt and Ni edge of Pt based catalysts of an air-breathing cathode show that catalyst restructuring, after a potential step, has time constants from minutes to hours. The infrared Stark tuning plots of CO adsorbed on Pt at 100, 200, 300 and 400 mV vs. hydrogen reference electrode were obtained. The Stark tuning plots of CO adsorbed at 400 mV exhibit a precipitous drop in frequency coincident with the adsorption potential. The turn-down potential decreases relative to the adsorption potential and is approximately constant after 300 mV. These Stark tuning characteristics are attributed to potential dependent adsorption site selection by CO and competitive adsorption processes.

  4. X-ray absorption spectroscopy of chicken sulfite oxidase crystals

    SciTech Connect

    George, G.N.; Pickering, I.J.; Kisker, C.

    1999-05-17

    Sulfite oxidase catalyzes the physiologically vital oxidation of sulfite to sulfate. Recently, the crystal structure of chicken sulfite oxidase has been reported at 1.9 {angstrom} resolution. In contrast to the information available from previous X-ray absorption spectroscopic studies, the active site indicated by crystallography was a mono-oxo species. Because of this the possibility that the crystals did in fact contain a reduced molybdenum species was considered in the crystallographic work. The authors report herein an X-ray absorption spectroscopic study of polycrystalline sulfite oxidase prepared in the same manner as the previous single-crystal samples, and compare this with data for frozen solutions of oxidized and reduced enzyme.

  5. X-ray absorption studies of yeast copper metallothionein

    SciTech Connect

    George, G.N.; Byrd, J.; Winge, D.R.

    1988-06-15

    The local structures of the metal sites in copper metallothionein from Saccharomyces cerevisiae have been investigated by x-ray absorption spectroscopy at the copper and sulfur K edges. Analysis of the EXAFS (extended x-ray absorption fine structure) data indicates that each copper is trigonally coordinated to sulfur at a distance of 2.23 A. Cu-Cu interactions at 2.7 and 3.9 A have also been tentatively identified. Sulfur K edge data are compatible with cysteinyl thiolates bridging each of the eight Cu(I) ions. The data support a model for the copper cluster in yeast metallothionein consisting of a Cu8S12 core. EXAFS data on two specifically engineered carboxyl-terminal truncated mutants reveal that the copper coordination in the mutants is similar to that observed in the wild-type protein.

  6. MODELING BROADBAND X-RAY ABSORPTION OF MASSIVE STAR WINDS

    SciTech Connect

    Leutenegger, Maurice A.; Zsargo, Janos; Martell, Erin M.; Owocki, Stanley P.; Gagne, Marc; Hillier, D. John

    2010-08-20

    We present a method for computing the net transmission of X-rays emitted by shock-heated plasma distributed throughout a partially optically thick stellar wind from a massive star. We find the transmission by an exact integration of the formal solution, assuming that the emitting plasma and absorbing plasma are mixed at a constant mass ratio above some minimum radius, below which there is assumed to be no emission. This model is more realistic than either the slab absorption associated with a corona at the base of the wind or the exospheric approximation that assumes that all observed X-rays are emitted without attenuation from above the radius of optical depth unity. Our model is implemented in XSPEC as a pre-calculated table that can be coupled to a user-defined table of the wavelength-dependent wind opacity. We provide a default wind opacity model that is more representative of real wind opacities than the commonly used neutral interstellar medium (ISM) tabulation. Preliminary modeling of Chandra grating data indicates that the X-ray hardness trend of OB stars with spectral subtype can largely be understood as a wind absorption effect.

  7. Modeling Broadband X-Ray Absorption of Massive Star Winds

    NASA Technical Reports Server (NTRS)

    Leutenegger, Maurice A.; Cohen,David H.; Zsargo, Janos; Martell, Erin M.; MacArthur, James P.; Owocki, Stanley P.; Gagne, Marc; Hillier, D. John

    2010-01-01

    We present a method for computing the net transition of X-rays emitted by shock-heated plasma distributed throughout a partially optically thick stellar wind from a massive star. We find the transmission by an exact integration of the formal solution, assuming the emitting plasma and absorbing plasma are mixed at a constant mass ratio above some minimum radius, below which there is assumed to be no emission. This model is more realistic than either the slab absorption associated with a corona at the base of the wind or the exospheric approximation that assumes all observed X-rays are emitted without attenuation from above the radius of optical depth unity. Our model is implemented in XSPEC as a pre-calculated table that can be coupled to a user-defined table of the wavelength dependent wind opacity. We provide a default wind opacity model that is more representative of real wind opacities than the commonly used neutral ISM tabulation. Preliminary modeling of Chandra grating data indicates that the X-ray hardness trend of OB stars with spectral subtype cars largely be understood as a wind absorption effect.

  8. X-ray absorption studies of battery materials

    SciTech Connect

    McBreen, J.

    1996-10-01

    X-ray absorption spectroscopy (XAS) is ideal for {ital in}{ital situ} studies of battery materials because both the probe and signal are penetrating x rays. The advantage of XAS being element specific permits investigation of the environment of a constituent element in a composite material. This makes it very powerful for studying electrode additives and corrosion of individual components of complex metal hydride alloys. The near edge part of the spectrum (XANES) provides information on oxidation state and site symmetry of the excited atom. This is particularly useful in study of corrosion and oxidation changes in cathode materials during charge/discharge cycle. Extended fine structure (EXAFS) gives structural information. Thus the technique provides both chemical and structural information. Since XAS probes only short range order, it can be applied to study of amorphous electrode materials and electrolytes. This paper discusses advantages and limitations of the method, as well as some experimental aspects.

  9. A new X-ray Absorption Model for the Interstellar Medium

    NASA Astrophysics Data System (ADS)

    Gatuzz, E.; Kallman, T.; García, J.; Gorczyca, T.; Mendoza, C.

    2014-07-01

    Absorption from the interstellar medium (ISM) affects every X-ray observation. Its effects are usually removed or studied using models which assume that the gas is neutral. However, spectra show that ions are present in most or many lines of sight. We present a model for interstellar X-ray absorption, which we call ismabs, that includes both ions and neutral elements and which uses the most accurate atomic data available for abundant elements. We have benchmarked ismabs using high-resolution spectra from X-ray binary sources obtained with the High Energy Transmission Grating Spectrometer (HETGS) on the Chandra X-ray observatory. The oxygen and neon K edge absorption regions as well as the iron L edge absorption region have been studied in detail. Although the neutral component is dominant in these spectra, the inclusion of ions leads to better fits to observed data, compared with previous work which only included neutral elements. The use of ismabs allows the determination of column densities of abundant elements, and their mean ionization states. Ismabs is fast and has relatively few free parameters. It has been developed for use with common X-ray spectral fitting packages such as XSPEC or ISIS.

  10. A laboratory-based hard x-ray monochromator for high-resolution x-ray emission spectroscopy and x-ray absorption near edge structure measurements

    SciTech Connect

    Seidler, G. T. Mortensen, D. R.; Remesnik, A. J.; Pacold, J. I.; Ball, N. A.; Barry, N.; Styczinski, M.; Hoidn, O. R.

    2014-11-15

    We report the development of a laboratory-based Rowland-circle monochromator that incorporates a low power x-ray (bremsstrahlung) tube source, a spherically bent crystal analyzer, and an energy-resolving solid-state detector. This relatively inexpensive, introductory level instrument achieves 1-eV energy resolution for photon energies of ∼5 keV to ∼10 keV while also demonstrating a net efficiency previously seen only in laboratory monochromators having much coarser energy resolution. Despite the use of only a compact, air-cooled 10 W x-ray tube, we find count rates for nonresonant x-ray emission spectroscopy comparable to those achieved at monochromatized spectroscopy beamlines at synchrotron light sources. For x-ray absorption near edge structure, the monochromatized flux is small (due to the use of a low-powered x-ray generator) but still useful for routine transmission-mode studies of concentrated samples. These results indicate that upgrading to a standard commercial high-power line-focused x-ray tube or rotating anode x-ray generator would result in monochromatized fluxes of order 10{sup 6}–10{sup 7} photons/s with no loss in energy resolution. This work establishes core technical capabilities for a rejuvenation of laboratory-based hard x-ray spectroscopies that could have special relevance for contemporary research on catalytic or electrical energy storage systems using transition-metal, lanthanide, or noble-metal active species.

  11. A laboratory-based hard x-ray monochromator for high-resolution x-ray emission spectroscopy and x-ray absorption near edge structure measurements.

    PubMed

    Seidler, G T; Mortensen, D R; Remesnik, A J; Pacold, J I; Ball, N A; Barry, N; Styczinski, M; Hoidn, O R

    2014-11-01

    We report the development of a laboratory-based Rowland-circle monochromator that incorporates a low power x-ray (bremsstrahlung) tube source, a spherically bent crystal analyzer, and an energy-resolving solid-state detector. This relatively inexpensive, introductory level instrument achieves 1-eV energy resolution for photon energies of ∼5 keV to ∼10 keV while also demonstrating a net efficiency previously seen only in laboratory monochromators having much coarser energy resolution. Despite the use of only a compact, air-cooled 10 W x-ray tube, we find count rates for nonresonant x-ray emission spectroscopy comparable to those achieved at monochromatized spectroscopy beamlines at synchrotron light sources. For x-ray absorption near edge structure, the monochromatized flux is small (due to the use of a low-powered x-ray generator) but still useful for routine transmission-mode studies of concentrated samples. These results indicate that upgrading to a standard commercial high-power line-focused x-ray tube or rotating anode x-ray generator would result in monochromatized fluxes of order 10(6)-10(7) photons/s with no loss in energy resolution. This work establishes core technical capabilities for a rejuvenation of laboratory-based hard x-ray spectroscopies that could have special relevance for contemporary research on catalytic or electrical energy storage systems using transition-metal, lanthanide, or noble-metal active species. PMID:25430123

  12. Near Edge X-Ray Absorption Fine Structure Spectroscopy with X-Ray Free-Electron Lasers

    SciTech Connect

    Bernstein, D.P.; Acremann, Y.; Scherz, A.; Burkhardt, M.; Stohr, J.; Beye, M.; Schlotter, W.F.; Beeck, T.; Sorgenfrei, F.; Pietzsch, A.; Wurth, W.; Fohlisch, A.; /Hamburg U.

    2009-12-11

    We demonstrate the feasibility of Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy on solids by means of femtosecond soft x-ray pulses from a free-electron laser (FEL). Our experiments, carried out at the Free-Electron Laser at Hamburg (FLASH), used a special sample geometry, spectrographic energy dispersion, single shot position-sensitive detection and a data normalization procedure that eliminates the severe fluctuations of the incident intensity in space and photon energy. As an example we recorded the {sup 3}D{sub 1} N{sub 4,5}-edge absorption resonance of La{sup 3+}-ions in LaMnO{sub 3}. Our study opens the door for x-ray absorption measurements on future x-ray FEL facilities.

  13. High Resolution X-Ray Absorption Spectroscopy: Distribution of Matter in and around Galaxies

    NASA Astrophysics Data System (ADS)

    Schulz, Norbert; MIT/CAT Team

    2015-10-01

    The chemical evolution of the Universe embraces aspects that reachdeep into modern astrophysics and cosmology. We want to know how present and past matter is affected by various levels and types of nucleo-synthesis and stellar evolution. Three major categories were be identified: 1. The study of pre-mordial star formation including periods of super-massive black hole formation, 2. The embedded evolution of the intergalactic medium IGM, 3. The status and evolution of stars and the interstellar medium ISM in galaxies. Today a fourth category relates to our understanding of dark matter in relationwith these three categories. The X-ray band is particularly sensitive to K- and L-shell absorption and scattering from high abundant elements like C, N, O, Ne, Mg, Si, S,Ar, Ca, Fe, and Ni. Like the Lyman alpha forest in the optical band, absorbers in the IGM produce an X-ray line forest along the line of sight in the X-rayspectrum of a background quasar. Similary bright X-ray sources within galaxies and the Milky Way produce a continuum, which is being absorbed by elements invarious phases of the ISM. High resolution X-ray absorption surveys are possible with technologies ready for flight within decade. == high efficiency X-ray optics with optical performance 3== high resolution X-ray gratings with R 3000 for E 1.5 keV== X-ray micro-calorimeters with R 2000 for E 1.5 keV. The vision for the next decade needs to lead to means and strategies which allows us to perform such absorption surveys as effectively as surveys are now or in very near future quite common in astronomy pursued in other wave length bands such as optical, IR, and sub-mm.

  14. A History of X-ray absorption fine structure

    NASA Astrophysics Data System (ADS)

    Stumm von Bordwehr, R.

    This historical account of X-ray absorption fine structure (XAFS) spectroscopy from the origin to 1975 begins with the first observations of X-ray absorption edges and the experimental setups used at the turn of the century. Then, the discovery of XAFS and Kossel's early interpretation are discussed. A close look is taken at the three outstanding papers written by Kronig to explain XAFS in solids and molecules. Petersen's development of XAFS in molecules and Smoluchowski's investigation of XAFS in crystals during the thirties are reviewed. Then, the Japanese and Soviet contributions to X-ray absorption spectroscopy up to the sixties are described. We conclude with the advent of the present understanding of XAFS developed in the early seventies. Although many experiments are presented, we emphasize the conceptual evolution of the interpretation of XAFS, including false steps and overlooked works. Cette histoire de la spectroscopie de structure fine des seuils d'absorption X (XAFS) des origines à 1975 commence par présenter les premières observations de seuils d'absorption X ainsi que les dispositifs expérimentaux utilisés au début du siècle. Puis on décrit la découverte des structures fines et l'interprétation qu'en donne Kossel. On discute en details les trois remarquables articles écrits par Kronig pour expliquer les XAFS dans les solides et les molécules. On montre comment Petersen a développé la théorie des XAFS des molécules et Smoluchowski celle des cristaux. Puis on passe en revue les contributions japonaises et soviétiques à cette spectroscopie jusqu'aux années soixante. On conclut par la description de la théorie actuelle des XAFS qui s'est développée au début des années soixante-dix. Bien que décrivant des nombreuses expériences, ce travail met l'accent sur l'évolution conceptuelle de l'interprétation des XAFS, en tenant compte des faux pas et des contributions négligées.

  15. Note: Construction of x-ray scattering and x-ray absorption fine structure beamline at the Pohang Light Source

    SciTech Connect

    Lee, Ik-Jae; Yu, Chung-Jong; Yun, Young-Duck; Lee, Chae-Soon; Seo, In Deuk; Kim, Hyo-Yun; Lee, Woul-Woo; Chae, Keun Hwa

    2010-02-15

    A new hard x-ray beamline, 10B KIST-PAL beamline (BL10B), has been designed and constructed at the Pohang Light Source (PLS) in Korea. The beamline, operated by Pohang Accelerator Laboratory-Korean Institute of Science and Technology consortium, is dedicated to x-ray scattering (XRS) and x-ray absorption fine structure (XAFS) experiments. X rays with photon energies from 4.0 to 16.0 keV are delivered to the experimental station passing a collimating mirror, a fixed-exit double-crystal Si(111) monochromator, and a toroidal mirror. Basic experimental equipments for XAFS measurement, a high resolution diffractometry, an image plate detector system, and a hot stage have been prepared for the station. From our initial commissioning and performance testing of the beamline, it is observed that BL10B beamline can perform XRS and XAFS measurements successfully.

  16. X-ray-induced photo-chemistry and X-ray absorption spectroscopy of biological samples

    PubMed Central

    George, Graham N.; Pickering, Ingrid J.; Pushie, M. Jake; Nienaber, Kurt; Hackett, Mark J.; Ascone, Isabella; Hedman, Britt; Hodgson, Keith O.; Aitken, Jade B.; Levina, Aviva; Glover, Christopher; Lay, Peter A.

    2012-01-01

    As synchrotron light sources and optics deliver greater photon flux on samples, X-ray-induced photo-chemistry is increasingly encountered in X-ray absorption spectroscopy (XAS) experiments. The resulting problems are particularly pronounced for biological XAS experiments. This is because biological samples are very often quite dilute and therefore require signal averaging to achieve adequate signal-to-noise ratios, with correspondingly greater exposures to the X-ray beam. This paper reviews the origins of photo-reduction and photo-oxidation, the impact that they can have on active site structure, and the methods that can be used to provide relief from X-ray-induced photo-chemical artifacts. PMID:23093745

  17. X-Ray Absorption Spectroscopy Imaging of Biological Tissues

    NASA Astrophysics Data System (ADS)

    Pickering, Ingrid J.; George, Graham N.

    2007-02-01

    X-ray absorption spectroscopy (XAS) is proving invaluable in determining the average chemical form of metals or metalloids in intact biological tissues. As most tissues have spatial structure, there is great additional interest in visualizing the spatial location of the metal(loid) as well as its chemical forms. XAS imaging gives the opportunity of producing maps of specific chemical types of elements in vivo in dilute biological systems. X-ray fluorescence microprobe techniques are routinely used to study samples with spatial heterogeneity. Microprobe produces elemental maps, with chemical sensitivity obtained by recording micro-XAS spectra at selected point locations on the map. Unfortunately, using these procedures spatial detail may be lost as the number of point spectra recorded generally is limited. A powerful extension of microprobe is XAS imaging or chemically specific imaging. Here, the incident energy is tuned to features in the near-edge which are characteristic of the expected chemical forms of the element. With a few simple assumptions, these XAS images can then be converted to quantitative images of specific chemical form, yielding considerable clarity in the distributions.

  18. ISMabs: A COMPREHENSIVE X-RAY ABSORPTION MODEL FOR THE INTERSTELLAR MEDIUM

    SciTech Connect

    Gatuzz, E.; Mendoza, C.; García, J.; Kallman, T. R.; Gorczyca, T. W. E-mail: claudio@ivic.gob.ve E-mail: timothy.r.kallman@nasa.gov

    2015-02-10

    We present an X-ray absorption model for the interstellar medium, to be referred to as ISMabs, that takes into account both neutral and ionized species of cosmically abundant elements, and includes the most accurate atomic data available. Using high-resolution spectra from eight X-ray binaries obtained with the Chandra High Energy Transmission Grating Spectrometer, we proceed to benchmark the atomic data in the model particularly in the neon K-edge region. Compared with previous photoabsorption models, which solely rely on neutral species, the inclusion of ions leads to improved spectral fits. Fit parameters comprise the column densities of abundant contributors that allow direct estimates of the ionization states. ISMabs is provided in the appropriate format to be implemented in widely used X-ray spectral fitting packages such as XSPEC, ISIS, and SHERPA.

  19. ISMabs: A Comprehensive X-Ray Absorption Model for the Interstellar Medium

    NASA Astrophysics Data System (ADS)

    Gatuzz, E.; García, J.; Kallman, T. R.; Mendoza, C.; Gorczyca, T. W.

    2015-02-01

    We present an X-ray absorption model for the interstellar medium, to be referred to as ISMabs, that takes into account both neutral and ionized species of cosmically abundant elements, and includes the most accurate atomic data available. Using high-resolution spectra from eight X-ray binaries obtained with the Chandra High Energy Transmission Grating Spectrometer, we proceed to benchmark the atomic data in the model particularly in the neon K-edge region. Compared with previous photoabsorption models, which solely rely on neutral species, the inclusion of ions leads to improved spectral fits. Fit parameters comprise the column densities of abundant contributors that allow direct estimates of the ionization states. ISMabs is provided in the appropriate format to be implemented in widely used X-ray spectral fitting packages such as XSPEC, ISIS, and SHERPA.

  20. The x-ray absorption spectra of water and ice

    NASA Astrophysics Data System (ADS)

    Kong, Lingzhu; Wu, Xifan; Car, Roberto

    2012-02-01

    We calculate the x-ray absorption spectra of liquid water at STP, hexagonal ice and amorphous low- and high-density ice at T=269K, using the static Coulomb-hole and screened exchange self energy approach ootnotetextW. Chen, X. Wu and R. Car, PRL 105, 017802 (2008) . We take the nuclear quantum effects into account by averaging over the Feynman path-integral replicas. We find that quantum disorder is particularly important in liquid water where it substantially improves the structure ootnotetextJ. Morrone and R. Car, PRL 101, 017801 (2008) Compared to Ref. 2, we use an improved screening model that includes the approximate local field correction ootnotetextM. Hybertsen and S. G. Louie, PRB 37, 2733 (1988). The resulting spectra are in significantly better agreement with experiments than in previous calculations.

  1. A X-Ray Absorption Spectroscopy Study of Manganese Containing Compounds and Photosynthetic Spinach Chloroplasts.

    NASA Astrophysics Data System (ADS)

    Kirby, Jon Allan

    The manganese sites in chloroplasts, long thought to be involved in photosynthetic oxygen evolution have been examined and partially characterized by X-ray Absorption Spectroscopy (XAS) using synchrotron radiation. The local environment about the manganese atoms is estimated from an analysis of the extended X-ray Absorption Fine Structure (EXAFS). Comparisons with and simulations of the manganese EXAFS for several reference compounds leads to a model in which the chloroplast manganese atoms are contained in a binuclear complex similar to di-u-oxo -tetrakis-(2,2'-bipyridine) dimanganese. It is suggested that the partner metal is another manganese. The bridging ligands are most probably oxygen. The remaining manganese ligands are carbon, oxygen, or nitrogen. A roughly linear correlation between the X-ray K edge onset energy and the "coordination charge" of a large number of manganese coordination complexes and compounds has been developed. Entry of the chloroplast manganese edge energy onto this correlation diagram establishes that the active pool of manganese is in an oxidation state greater than +2. If the manganese is in a dimeric form the oxidation states are most probably (II,III). Underlying these results is an extensive data analysis methodology. The method developed involves the use of many different background removal techniques, Fourier transforms and ultimately curve fitting to the modulations in the x-ray absorption cross sections. A large number of model compounds were used to evaluate the analysis method. These analyses are used to show that the two major curve fitting models available are essentially equivalent. Due to its greater versatility, the theoretical model of Teo and Lee is preferred (J. Am. Chem. Soc. (1979), 101, 2815). The results are also used to determine the informational limitations of XAS within the limits of the present understanding of X-ray absorption phenomena by inner shell electrons for atoms with atomic number greater than that

  2. Weak Hard X-Ray Emission from Broad Absorption Line Quasars: Evidence for Intrinsic X-Ray Weakness

    NASA Astrophysics Data System (ADS)

    Luo, B.; Brandt, W. N.; Alexander, D. M.; Stern, D.; Teng, S. H.; Arévalo, P.; Bauer, F. E.; Boggs, S. E.; Christensen, F. E.; Comastri, A.; Craig, W. W.; Farrah, D.; Gandhi, P.; Hailey, C. J.; Harrison, F. A.; Koss, M.; Ogle, P.; Puccetti, S.; Saez, C.; Scott, A. E.; Walton, D. J.; Zhang, W. W.

    2014-10-01

    We report NuSTAR observations of a sample of six X-ray weak broad absorption line (BAL) quasars. These targets, at z = 0.148-1.223, are among the optically brightest and most luminous BAL quasars known at z < 1.3. However, their rest-frame ≈2 keV luminosities are 14 to >330 times weaker than expected for typical quasars. Our results from a pilot NuSTAR study of two low-redshift BAL quasars, a Chandra stacking analysis of a sample of high-redshift BAL quasars, and a NuSTAR spectral analysis of the local BAL quasar Mrk 231 have already suggested the existence of intrinsically X-ray weak BAL quasars, i.e., quasars not emitting X-rays at the level expected from their optical/UV emission. The aim of the current program is to extend the search for such extraordinary objects. Three of the six new targets are weakly detected by NuSTAR with <~ 45 counts in the 3-24 keV band, and the other three are not detected. The hard X-ray (8-24 keV) weakness observed by NuSTAR requires Compton-thick absorption if these objects have nominal underlying X-ray emission. However, a soft stacked effective photon index (Γeff ≈ 1.8) for this sample disfavors Compton-thick absorption in general. The uniform hard X-ray weakness observed by NuSTAR for this and the pilot samples selected with <10 keV weakness also suggests that the X-ray weakness is intrinsic in at least some of the targets. We conclude that the NuSTAR observations have likely discovered a significant population (gsim 33%) of intrinsically X-ray weak objects among the BAL quasars with significantly weak <10 keV emission. We suggest that intrinsically X-ray weak quasars might be preferentially observed as BAL quasars.

  3. Weak hard X-ray emission from broad absorption line quasars: evidence for intrinsic X-ray weakness

    SciTech Connect

    Luo, B.; Brandt, W. N.; Scott, A. E.; Alexander, D. M.; Gandhi, P.; Stern, D.; Teng, S. H.; Arévalo, P.; Bauer, F. E.; Boggs, S. E.; Craig, W. W.; Christensen, F. E.; Comastri, A.; Farrah, D.; Hailey, C. J.; Harrison, F. A.; Koss, M.; Ogle, P.; Puccetti, S.; Saez, C.; and others

    2014-10-10

    We report NuSTAR observations of a sample of six X-ray weak broad absorption line (BAL) quasars. These targets, at z = 0.148-1.223, are among the optically brightest and most luminous BAL quasars known at z < 1.3. However, their rest-frame ≈2 keV luminosities are 14 to >330 times weaker than expected for typical quasars. Our results from a pilot NuSTAR study of two low-redshift BAL quasars, a Chandra stacking analysis of a sample of high-redshift BAL quasars, and a NuSTAR spectral analysis of the local BAL quasar Mrk 231 have already suggested the existence of intrinsically X-ray weak BAL quasars, i.e., quasars not emitting X-rays at the level expected from their optical/UV emission. The aim of the current program is to extend the search for such extraordinary objects. Three of the six new targets are weakly detected by NuSTAR with ≲ 45 counts in the 3-24 keV band, and the other three are not detected. The hard X-ray (8-24 keV) weakness observed by NuSTAR requires Compton-thick absorption if these objects have nominal underlying X-ray emission. However, a soft stacked effective photon index (Γ{sub eff} ≈ 1.8) for this sample disfavors Compton-thick absorption in general. The uniform hard X-ray weakness observed by NuSTAR for this and the pilot samples selected with <10 keV weakness also suggests that the X-ray weakness is intrinsic in at least some of the targets. We conclude that the NuSTAR observations have likely discovered a significant population (≳ 33%) of intrinsically X-ray weak objects among the BAL quasars with significantly weak <10 keV emission. We suggest that intrinsically X-ray weak quasars might be preferentially observed as BAL quasars.

  4. High energy X-ray phase and dark-field imaging using a random absorption mask

    NASA Astrophysics Data System (ADS)

    Wang, Hongchang; Kashyap, Yogesh; Cai, Biao; Sawhney, Kawal

    2016-07-01

    High energy X-ray imaging has unique advantage over conventional X-ray imaging, since it enables higher penetration into materials with significantly reduced radiation damage. However, the absorption contrast in high energy region is considerably low due to the reduced X-ray absorption cross section for most materials. Even though the X-ray phase and dark-field imaging techniques can provide substantially increased contrast and complementary information, fabricating dedicated optics for high energies still remain a challenge. To address this issue, we present an alternative X-ray imaging approach to produce transmission, phase and scattering signals at high X-ray energies by using a random absorption mask. Importantly, in addition to the synchrotron radiation source, this approach has been demonstrated for practical imaging application with a laboratory-based microfocus X-ray source. This new imaging method could be potentially useful for studying thick samples or heavy materials for advanced research in materials science.

  5. A Comprehensive X-Ray Absorption Model for Atomic Oxygen

    NASA Technical Reports Server (NTRS)

    Gorczyca, T. W.; Bautista, M. A.; Hasoglu, M. F.; Garcia, J.; Gatuzz, E.; Kaastra, J. S.; Kallman, T. R.; Manson, S. T.; Mendoza, C.; Raassen, A. J. J.; de Vries, C. P.; Zatsarinny, O.

    2013-01-01

    An analytical formula is developed to accurately represent the photoabsorption cross section of atomic Oxygen for all energies of interest in X-ray spectral modeling. In the vicinity of the K edge, a Rydberg series expression is used to fit R-matrix results, including important orbital relaxation effects, that accurately predict the absorption oscillator strengths below threshold and merge consistently and continuously to the above-threshold cross section. Further, minor adjustments are made to the threshold energies in order to reliably align the atomic Rydberg resonances after consideration of both experimental and observed line positions. At energies far below or above the K-edge region, the formulation is based on both outer- and inner-shell direct photoionization, including significant shake-up and shake-off processes that result in photoionization-excitation and double-photoionization contributions to the total cross section. The ultimate purpose for developing a definitive model for oxygen absorption is to resolve standing discrepancies between the astronomically observed and laboratory-measured line positions, and between the inferred atomic and molecular oxygen abundances in the interstellar medium from XSTAR and SPEX spectral models.

  6. A comprehensive X-ray absorption model for atomic oxygen

    SciTech Connect

    Gorczyca, T. W.; Bautista, M. A.; Mendoza, C.; Hasoglu, M. F.; García, J.; Gatuzz, E.; Kaastra, J. S.; Raassen, A. J. J.; De Vries, C. P.; Kallman, T. R.; Manson, S. T.; Zatsarinny, O.

    2013-12-10

    An analytical formula is developed to accurately represent the photoabsorption cross section of O I for all energies of interest in X-ray spectral modeling. In the vicinity of the K edge, a Rydberg series expression is used to fit R-matrix results, including important orbital relaxation effects, that accurately predict the absorption oscillator strengths below threshold and merge consistently and continuously to the above-threshold cross section. Further, minor adjustments are made to the threshold energies in order to reliably align the atomic Rydberg resonances after consideration of both experimental and observed line positions. At energies far below or above the K-edge region, the formulation is based on both outer- and inner-shell direct photoionization, including significant shake-up and shake-off processes that result in photoionization-excitation and double-photoionization contributions to the total cross section. The ultimate purpose for developing a definitive model for oxygen absorption is to resolve standing discrepancies between the astronomically observed and laboratory-measured line positions, and between the inferred atomic and molecular oxygen abundances in the interstellar medium from XSTAR and SPEX spectral models.

  7. X-ray absorption fine structure and X-ray excited optical luminescence studies of II-VI semiconducting nanostructures

    NASA Astrophysics Data System (ADS)

    Murphy, Michael Wayne

    2010-06-01

    Various II-VI semiconducting nanomaterials such as ZnO-ZnS nanoribbons (NRs), CdSxSe1-x nanostructures, ZnS:Mn NRs, ZnS:Mn,Eu nanoprsims (NPs), ZnO:Mn nanopowders, and ZnO:Co nanopowders were synthesized for study. These materials were characterized by techniques such as scanning electron microscopy, transmission electron microscopy, element dispersive X-ray spectroscopy, selected area electron diffraction, and X-ray diffraction. The electronic and optical properties of these nanomaterials were studied by X-ray absorption fine structure (XAFS) spectroscopy and X-ray excited optical luminescence (XEOL) techniques, using tuneable soft X-rays from a synchrotron light source. The complementary nature ofthe XAFS and XEOL techniques give site, element and chemical specific measurements which allow a better understanding of the interplay and role of each element in the system. Chemical vapour deposition (CVD) of ZnS powder in a limited oxygen environment resulted in side-by-side biaxial ZnO-ZnS NR heterostructures. The resulting NRs contained distinct wurtzite ZnS and wurtzite ZnO components with widths of 10--100 nm and 20 --500 nm, respectively and a uniform interface region of 5-15 nm. XAFS and XEOL measurements revealed the luminescence of ZnO-ZnS NRs is from the ZnO component. The luminescence of CdSxSe1-x nanostructures is shown to be dependent on the S to Se ratio, with the band-gap emission being tunable between that of pure CdS and CdSe. Excitation of the CdSxSe 1-x nanostructures by X-ray in XEOL has revealed new de-excitation channels which show a defect emission band not seen by laser excitation. CVD of Mn2+ doped ZnS results in nanostructures with luminescence dominated by the yellow Mn2+ emission due to energy transfer from the ZnS host to the Mn dopant sites. The addition of EuCl3 to the reactants in the CVD process results in a change in morphology from NR to NP. Zn1-xMnxO and Zn1-xCOxO nanopowders were prepared by sol-gel methods at dopant concentrations

  8. Communication: On the difficulty of reproducibly measuring PbCl2 X-ray absorption spectra

    NASA Astrophysics Data System (ADS)

    Schwartz, Craig P.; Prendergast, David

    2015-09-01

    Previous measurements of the X-ray absorption spectra of PbCl2 at the chlorine K-edge have shown significant variation between different studies. Herein, using first principles simulations of X-ray absorption spectroscopy, we show that the observed spectral variations are due to the generation of Cl2 gas and depletion of chlorine from PbCl2, consistent with what is observed during ultraviolet absorption for the same compound. We note that Cl2 gas generation can also be initiated using higher resonant X-ray energies, including Pb X-ray absorption edges. While this casts doubt on previous interpretations of certain measurements, it does indicate a means of generating chlorine gas during in situ experiments by passing high energy x-rays through a hard x-ray transparent medium and onto PbCl2.

  9. Communication: On the difficulty of reproducibly measuring PbCl2 X-ray absorption spectra.

    PubMed

    Schwartz, Craig P; Prendergast, David

    2015-09-21

    Previous measurements of the X-ray absorption spectra of PbCl2 at the chlorine K-edge have shown significant variation between different studies. Herein, using first principles simulations of X-ray absorption spectroscopy, we show that the observed spectral variations are due to the generation of Cl2 gas and depletion of chlorine from PbCl2, consistent with what is observed during ultraviolet absorption for the same compound. We note that Cl2 gas generation can also be initiated using higher resonant X-ray energies, including Pb X-ray absorption edges. While this casts doubt on previous interpretations of certain measurements, it does indicate a means of generating chlorine gas during in situ experiments by passing high energy x-rays through a hard x-ray transparent medium and onto PbCl2. PMID:26395677

  10. Examination of the local structure in composite and lowdimensional semiconductor by X-ray Absorption Spectroscopy

    SciTech Connect

    Lawniczak-Jablonska, K.; Demchenko, I.N.; Piskorska, E.; Wolska,A.; Talik, E.; Zakharov, D.N.; Liliental-Weber, Z.

    2006-09-25

    X-ray absorption methods have been successfully used to obtain quantitative information about local atomic composition of two different materials. X-ray Absorption Near Edge Structure analysis and X-Ray Photoelectron Spectroscopy allowed us to determine seven chemical compounds and their concentrations in c-BN composite. Use of Extended X-ray Absorption Fine Structure in combination with Transmission Electron Microscopy enabled us to determine the composition and size of buried Ge quantum dots. It was found that the quantum dots consisted out of pure Ge core covered by 1-2 monolayers of a layer rich in Si.

  11. X-Ray Absorption Spectroscopy of Dinuclear Metallohydrolases

    PubMed Central

    Tierney, David L.; Schenk, Gerhard

    2014-01-01

    In this mini-review, we briefly discuss the physical origin of x-ray absorption spectroscopy (XAS) before illustrating its application using dinuclear metallohydrolases as exemplary systems. The systems we have selected for illustrative purposes present a challenging problem for XAS, one that is ideal to demonstrate the potential of this methodology for structure/function studies of metalloenzymes in general. When the metal ion is redox active, XAS provides a sensitive measure of oxidation-state-dependent differences. When the metal ion is zinc, XAS is the only spectroscopic method that will provide easily accessible structural information in solution. In the case of heterodimetallic sites, XAS has the unique ability to interrogate each metal site independently in the same sample. One of the strongest advantages of XAS is its ability to examine metal ion site structures with crystallographic precision, without the need for a crystal. This is key for studying flexible metal ion sites, such as those described in the selected examples, because it allows one to monitor structural changes that occur during substrate turnover. PMID:25229134

  12. X-ray Absorption Spectroscopy of the Rare Earth orthophosphates

    SciTech Connect

    Shuh, D.K.; Terminello, L.J.; Boatner, L.A.; Abraham, M.M.

    1993-06-01

    X-ray Absorption Spectroscopy (XAS) of the Rare Earth (RE) 3d levels yields sharp peaks near the edges as a result of strong, quasi-atomic 3d{sup 10}4f{sup n} {yields} 3d-{sup 9}4f{sup n+1} transitions and these transitions exhibit a wealth of spectroscopic features. The XAS measurements of single crystal REPO{sub 4} (RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er) at the 3d edge were performed in the total yield mode at beam line 8-2 at the Stanford Synchrotron Radiation Laboratory (SSRL). The XAS spectra of the RE ions in the orthophosphate matrix generally resemble the XAS of the corresponding RE metal. This is not unexpected and emphasizes the major contribution of the trivalent state to the electronic transitions at the RE 3d edges. These spectra unequivocally identify the transitions originating from well-characterized RE cores and correlate well with previous theoretical investigations.

  13. X-Ray Continua of Broad Absorption Line Quasars

    NASA Technical Reports Server (NTRS)

    Mathur, S.

    1999-01-01

    The targets for this program, PG1416-129 and LBQS 2212-1759 were known to be Broad Absorption Line Quasars (BALQSOs). BALQSOs are highly absorbed in soft X-rays. Good high energy response of Rossi-XTE made them ideal targets for observation. We observed LBQS 2212-1759 with PCA. We have now analyzed the data and found that the source was not detected. Since our target was expected to be faint, reliable estimate of background was very important. With the release of new FTOOLS (version 4.1) we were able to do so. We also analyzed a well known bright object and verified our results with the published data. This gave us confidence in the non-detection of our target LBQS 2212-1759. We are currently investigating the implications of this non-detection. Due to some scheduling problems, our second target PG1416-129 was not observed in A01. It was observed on 06/26/98. This target was detected with RXTE. We are now working on the spectral analysis with XSPEC.

  14. Insights into the mechanism of X-ray-induced disulfide-bond cleavage in lysozyme crystals based on EPR, optical absorption and X-ray diffraction studies

    SciTech Connect

    Sutton, Kristin A.; Black, Paul J.; Mercer, Kermit R.; Garman, Elspeth F.; Owen, Robin L.; Snell, Edward H.; Bernhard, William A.

    2013-12-01

    Electron paramagnetic resonance (EPR) and online UV–visible absorption microspectrophotometry with X-ray crystallography have been used in a complementary manner to follow X-ray-induced disulfide-bond cleavage, to confirm a multi-track radiation-damage process and to develop a model of that process. Electron paramagnetic resonance (EPR) and online UV–visible absorption microspectrophotometry with X-ray crystallography have been used in a complementary manner to follow X-ray-induced disulfide-bond cleavage. Online UV–visible spectroscopy showed that upon X-irradiation, disulfide radicalization appeared to saturate at an absorbed dose of approximately 0.5–0.8 MGy, in contrast to the saturating dose of ∼0.2 MGy observed using EPR at much lower dose rates. The observations suggest that a multi-track model involving product formation owing to the interaction of two separate tracks is a valid model for radiation damage in protein crystals. The saturation levels are remarkably consistent given the widely different experimental parameters and the range of total absorbed doses studied. The results indicate that even at the lowest doses used for structural investigations disulfide bonds are already radicalized. Multi-track considerations offer the first step in a comprehensive model of radiation damage that could potentially lead to a combined computational and experimental approach to identifying when damage is likely to be present, to quantitate it and to provide the ability to recover the native unperturbed structure.

  15. Geometric Structure Determination of N694C Lipoxygenase: a Comparative Near-Edge X-Ray Absorption Spectroscopy And Extended X-Ray Absorption Fine Structure Study

    SciTech Connect

    Sarangi, R.; Hocking, R.K.; Neidig, M.L.; Benfatto, M.; Holman, T.R.; Solomon, E.I.; Hodgson, K.O.; Hedman, B.

    2009-05-27

    The mononuclear nonheme iron active site of N694C soybean lipoxygenase (sLO1) has been investigated in the resting ferrous form using a combination of Fe-K-pre-edge, near-edge (using the minuit X-ray absorption near-edge full multiple-scattering approach), and extended X-ray absorption fine structure (EXAFS) methods. The results indicate that the active site is six-coordinate (6C) with a large perturbation in the first-shell bond distances in comparison to the more ordered octahedral site in wild-type sLO1. Upon mutation of the asparigine to cystiene, the short Fe-O interaction with asparigine is replaced by a weak Fe-(H{sub 2}O), which leads to a distorted 6C site with an effective 5C ligand field. In addition, it is shown that near-edge multiple scattering analysis can give important three-dimensional structural information, which usually cannot be accessed using EXAFS analysis. It is further shown that, relative to EXAFS, near-edge analysis is more sensitive to partial coordination numbers and can be potentially used as a tool for structure determination in a mixture of chemical species.

  16. Quantitative analysis of deconvolved X-ray absorption near-edge structure spectra: a tool to push the limits of the X-ray absorption spectroscopy technique.

    PubMed

    D'Angelo, Paola; Migliorati, Valentina; Persson, Ingmar; Mancini, Giordano; Della Longa, Stefano

    2014-09-15

    A deconvolution procedure has been applied to K-edge X-ray absorption near-edge structure (XANES) spectra of lanthanoid-containing solid systems, namely, hexakis(dmpu)praseodymium(III) and -gadolinium(III) iodide. The K-edges of lanthanoids cover the energy range 38 (La)-65 (Lu) keV, and the large widths of the core-hole states lead to broadening of spectral features, reducing the content of structural information that can be extracted from the raw X-ray absorption spectra. Here, we demonstrate that deconvolution procedures allow one to remove most of the instrumental and core-hole lifetime broadening in the K-edge XANES spectra of lanthanoid compounds, highlighting structural features that are lost in the raw data. We show that quantitative analysis of the deconvolved K-edge XANES spectra can be profitably used to gain a complete local structural characterization of lanthanoid-containing systems not only for the nearest neighbor atoms but also for higher-distance coordination shells. PMID:25171598

  17. Photon interference effect in x-ray absorption spectra over a wide energy range

    NASA Astrophysics Data System (ADS)

    Nishino, Y.; Ishikawa, T.; Suzuki, M.; Kawamura, N.; Kappen, P.; Korecki, P.; Haack, N.; Materlik, G.

    2002-09-01

    We consider fundamental structures in x-ray absorption spectra over a wide energy range. We formulate the elastic scattering in addition to the photoelectric absorption in recently reported photon interference x-ray absorption fine structure (πXAFS). The simulations show excellent agreement with experimental x-ray absorption spectra for platinum and tungsten powders far above and below the L absorption edges. πXAFS can be as big as in the order of 10% of XAFS, and cannot be easily neglected in detailed analysis of XAFS and related phenomena.

  18. Enhancement of X-ray dose absorption for medical applications

    NASA Astrophysics Data System (ADS)

    Lim, Sara; Nahar, S.; Pradhan, A.; Barth, R.

    2013-05-01

    A promising technique for cancer treatment is radiation therapy with high-Z (HZ) nanomoities acting as radio-sensitizers attached to tumor cells and irradiated with X-rays. But the efficacy of radiosenstization is highly energy dependent. We study the physical effects in using platinum (Pt) as the radio-sensitizing agent, coupled with commonly employed broadband x-ray sources with mean energies around 100 keV, as opposed to MeV energies produced by clinical linear accelerators (LINAC) used in radiation therapy. Numerical calculations, in vitro, and in vivo studies of F98 rat glioma (brain cancer) demonstrate that irradiation from a medium energy X-ray (MEX) 160 kV source is far more effective than from a high energy x-ray (HEX) 6 MV LINAC. We define a parameter to quantify photoionization by an x-ray source, which thereby provides a measure of subsequent Auger decays. The platinum (Z = 78) results are also relevant to ongoing studies on x-ray interaction with gold (Z = 79) nanoparticles, widely studied as an HZ contrast agent. The present study should be of additional interest for a combined radiation plus chemotherapy treatment since Pt compounds such cis-Pt and carbo-Pt are commonly used in chemotherapy.

  19. X-ray phase imaging using a Gd-based absorption grating fabricated by imprinting technique

    NASA Astrophysics Data System (ADS)

    Yashiro, Wataru; Kato, Kosuke; Sadeghilaridjani, Maryam; Momose, Atsushi; Shinohara, Takenao; Kato, Hidemi

    2016-04-01

    A high-aspect-ratio absorption grating with a pitch of several µm is a key component of X-ray grating interferometery, which is an X-ray phase imaging technique that allows for highly sensitive X-ray imaging with a compact laboratory X-ray source. Here, we report that X-ray phase imaging was successfully performed at 15 keV by using a 23 ± 1-µm-height, 9-µm-pitch absorption grating (10 × 10 mm2) based on Gd (Gd60Cu25Al15) fabricated by a metallic glass imprinting technique. The imprinting technique is cost-efficient and has a high-production rate, and will be widely used for fabricating gratings not only for X-rays but also neutrons in the near future.

  20. X-ray-absorption-spectroscopy study of manganese-containing compounds and photosynthetic spinach chloroplasts

    SciTech Connect

    Kirby, J.A.

    1981-05-01

    The manganese sites in chloroplasts, long thought to be involved in photosynthetic oxygen evolution have been examined and partially characterized by x-ray Absorption Spectroscopy (XAS) using synchrotron radiation. The local environment about the manganese atoms is estimated from an analysis of the extended X-ray Absorption Fine Structure (EXAFS). Comparisons with and simulations of the manganese EXAFS for several reference compounds leads to a model in which the chloroplast manganese atoms are contained in a binuclear complex similar to di-u-oxo-tetrakis-(2,2'-bipyridine) dimanganese. It is suggested that the partner metal is another manganese. The bridging ligands are most probably oxygen. The remaining manganese ligands are carbon, oxygen, or nitrogen. A roughly linear correlation between the X-ray K edge onset energy and the coordination charge of a large number of manganese coordination complexes and compounds has been developed. Entry of the chloroplast manganese edge energy onto this correlation diagram establishes that the active pool of manganese is in an oxidation state greater than +2.

  1. Enhancement of X-ray dose absorption for medical applications

    NASA Astrophysics Data System (ADS)

    Lim, Sara; Montenegro, Maximiliano; Nahar, Sultana; Pradhan, Anil; Barth, Rolf; Nakkula, Robin; Bell, Erica; Yu, Yan

    2012-06-01

    Interaction of high-Z (HZ) elements with X-rays occurs efficiently at specific resonant energies. Cross sections for photoionization rapidly decrease after the K-edge; higher energy X-rays are mostly Compton-scattered. These features restrict the energy range for the use of HZ moities for radiosensitization in cancer therapy. Conventional X-ray sources such as linear accelerators (LINAC) used in radiotherapy emit a broad spectrum up to MeV energies. We explore the dichotomy between X-ray radiotherapy in two ranges: (i) E < 100 keV including HZ sensitization, and (ii) E > 100 keV where sensitization is inefficient. We perform Monte Carlo numerical simulations of tumor tissue embedded with platinum compounds and gold nanoparticles and compute radiation dose enhancement factors (DEF) upon irradiation with 100 kV, 170 kV and 6 MV sources. Our results demonstrate that the DEF peak below 100 keV and fall sharply above 200 keV to very small values. Therefore most of the X-ray output from LINACs up to the MeV range is utilized very inefficiently. We also describe experimental studies for implementation of option (i) using Pt and Au reagents and selected cancer cell lines. Resultant radiation exposure to patients could be greatly reduced, yet still result in increased tumoricidal ability.

  2. Microanalysis of iron oxidation state in iron oxides using X Ray Absorption Near Edge Structure (XANES)

    NASA Technical Reports Server (NTRS)

    Sutton, S. R.; Delaney, J.; Bajt, S.; Rivers, M. L.; Smith, J. V.

    1993-01-01

    An exploratory application of x ray absorption near edge structure (XANES) analysis using the synchrotron x ray microprobe was undertaken to obtain Fe XANES spectra on individual sub-millimeter grains in conventional polished sections. The experiments concentrated on determinations of Fe valence in a suite of iron oxide minerals for which independent estimates of the iron speciation could be made by electron microprobe analysis and x ray diffraction.

  3. Detection of X-ray photons by solution-processed lead halide perovskites

    NASA Astrophysics Data System (ADS)

    Yakunin, Sergii; Sytnyk, Mykhailo; Kriegner, Dominik; Shrestha, Shreetu; Richter, Moses; Matt, Gebhard J.; Azimi, Hamed; Brabec, Christoph J.; Stangl, Julian; Kovalenko, Maksym V.; Heiss, Wolfgang

    2015-07-01

    The evolution of real-time medical diagnostic tools such as angiography and computer tomography from radiography based on photographic plates was enabled by the development of integrated solid-state X-ray photon detectors made from conventional solid-state semiconductors. Recently, for optoelectronic devices operating in the visible and near-infrared spectral regions, solution-processed organic and inorganic semiconductors have also attracted a great deal of attention. Here, we demonstrate a possibility to use such inexpensive semiconductors for the sensitive detection of X-ray photons by direct photon-to-current conversion. In particular, methylammonium lead iodide perovskite (CH3NH3PbI3) offers a compelling combination of fast photoresponse and a high absorption cross-section for X-rays, owing to the heavy Pb and I atoms. Solution-processed photodiodes as well as photoconductors are presented, exhibiting high values of X-ray sensitivity (up to 25 μC mGyair-1 cm-3) and responsivity (1.9 × 104 carriers/photon), which are commensurate with those obtained by the current solid-state technology.

  4. Sensitivity of in vivo X-ray fluorescence determination of skeletal lead stores

    SciTech Connect

    Sokas, R.K.; Besarab, A.; McDiarmid, M.A.; Shapiro, I.M.; Bloch, P. )

    1990-09-01

    Eighteen patients with known past occupational lead exposure underwent parenteral diagnostic chelation with ethylenediaminetetraacetic acid and x-ray fluorescent determination of in vivo skeletal lead stores at the distal styloid process of the ulna and at the temporal base bone using a cobalt 57 source and measuring lead Ka x-rays. X-ray fluorescent lead measurements in both locations correlated with results of diagnostic chelation. Using a post-chelation urinary excretion of greater than 600 micrograms lead/24 h as the definition of high-lead stores, sensitivity of x-ray fluorescence at the wrist and temple was 56% and 39%, respectively.

  5. An energy and intensity monitor for X-ray absorption near-edge structure measurements

    NASA Astrophysics Data System (ADS)

    de Jonge, Martin D.; Paterson, David; McNulty, Ian; Rau, Christoph; Brandes, Jay A.; Ingall, Ellery

    2010-07-01

    An in-line X-ray beam energy and intensity monitor has been developed for use in focussed X-ray absorption near-edge spectroscopy (XANES) measurements. The monitor uses only the X-ray intensity that would otherwise bypass our zone-plate focussing optic and relies on a measurement of photoemission current. The monitor is inexpensive, easy to align, and provides valuable feedback about the X-ray energy. Operation of the monitor is demonstrated for measurements of phosphorus XANES. The precision of the energy determination is around 0.5 eV.

  6. X-ray diffraction study of lead chloride

    NASA Astrophysics Data System (ADS)

    Nitsch, K.; Knížek, K.; Rodová, M.

    1994-08-01

    PbCl 2 was examined by X-ray diffraction in order to test information about polymorphism in this compound. X-ray diffraction patterns of PbCl 2 crystallized from the aqueous solution, as well as of PbCl 2 molten and quenched, are the same. Two modifications in PbCl 2 were not found and polymorphism was not confirmed.

  7. Discovery of an X-ray Violently Variable Broad Absorption Line Quasar

    NASA Technical Reports Server (NTRS)

    Ghosh, Kajal K.; Gutierrez, Carlos M.; Punsly, Brian; Chevallier, Loic; Goncalves, Anabela C.

    2006-01-01

    In this letter, we report on a quasar that is violently variable in the X-rays, XVV. It is also a broad absorption line quasar (BALQSO) that exhibits both high ionization and low ionization UV absorption lines (LoBALQSO). It is very luminous in the X-rays (approximately 10(exp 46) ergs s(sup -l) over the entire X-ray band). Surprisingly, this does not over ionize the LoBAL outflow. The X-rays vary by a factor of two within minutes in the quasar rest frame, which is shorter than 1/30 of the light travel time across a scale length equal to the black hole radius. We concluded that the X-rays are produced in a relativistic jet beamed toward earth in which variations in the Doppler enhancement produce the XVV behavior.

  8. Improved self-absorption correction for extended x-ray absorption fine-structure measurements

    SciTech Connect

    Booth, C.H.; Bridges, F.

    2003-06-04

    Extended x-ray absorption fine-structure (EXAFS) data collected in the fluorescence mode are susceptible to an apparent amplitude reduction due to the self-absorption of the fluorescing photon by the sample before it reaches a detector. Previous treatments have made the simplifying assumption that the effect of the EXAFS on the correction term is negligible, and that the samples are in the thick limit. We present a nearly exact treatment that can be applied for any sample thickness or concentration, and retains the EXAFS oscillations in the correction term.

  9. Phase Effects on Mesoscale Object X-ray Absorption Images

    SciTech Connect

    Martz, Jr., H E; Aufderheide, M B; Barty, A; Lehman, S K; Kozioziemski, B J; Schneberk, D J

    2004-09-24

    At Lawrence Livermore National Laboratory particular emphasis is being placed on the nondestructive characterization (NDC) of 'mesoscale' objects.[Martz and Albrecht 2003] We define mesoscale objects as objects that have mm extent with {micro}m features. Here we confine our discussions to x-ray imaging methods applicable to mesoscale object characterization. The goal is object recovery algorithms including phase to enable emerging high-spatial resolution x-ray imaging methods to ''see'' inside or image mesoscale-size materials and objects. To be successful our imaging characterization effort must be able to recover the object function to one micrometer or better spatial resolution over a few millimeters field-of-view with very high contrast.

  10. X-Ray Absorption Characterization of Diesel Exhaust Particulates

    SciTech Connect

    Nelson, A J; Ferreira, J L; Reynolds, J G; Roos, J W

    1999-11-18

    We have characterized particulates from a 1993 11.1 Detroit Diesel Series 60 engine with electronic unit injectors operated using fuels with and without methylcyclopentadienyl manganese tricarbonyl (MMT) and overbased calcium sulfonate added. X-ray photoabsorption (XAS) spectroscopy was used to characterize the diesel particulates. Results reveal a mixture of primarily Mn-phosphate with some Mn-oxide, and Ca-sulfate on the surface of the filtered particulates from the diesel engine.

  11. Improvement of filling bismuth for x-ray absorption gratings through the enhancement of wettability

    NASA Astrophysics Data System (ADS)

    Lei, Yaohu; Liu, Xin; Li, Ji; Guo, Jinchuan; Niu, Hanben

    2016-06-01

    Filling materials with high x-ray linear absorption coefficients in high aspect-ratio (HAR) structures is a key process for the fabrication of absorption gratings used in x-ray differential phase-contrast imaging. Bismuth has been chosen as an effective filling material in micro-casting technology, because of its low cost both in price and facility use. However, repellence on structure surfaces against molten bismuth leads to an obstacle in terms of completely filling bismuth into the small-aperture and HAR microstructure formed by photo-assisted electrochemical etching in 5 inch silicon wafers. We propose and implement a novel method of surface modification to completely fill bismuth into these structures with periods of 3 μm and 42 μm, respectively, and as deep as 150 μm. The modified surface with a Bi2O3 layer covering the structure surface, including the side walls, induces an enhanced bismuth filling ratio. The superiority of the method is demonstrated by micrographs which show filled microstructures compared to the previously used method, where only a layer of 100 nm SiO2 was covered. Furthermore, we have observed that the improved micro-casting makes the absorption gratings clean surfaces, and no post treatment is needed.

  12. X-Ray Attenuation and Absorption for Materials of Dosimetric Interest

    National Institute of Standards and Technology Data Gateway

    SRD 126 X-Ray Attenuation and Absorption for Materials of Dosimetric Interest (Web, free access)   Tables and graphs of the photon mass attenuation coefficient and the mass energy-absorption coefficient are presented for all of the elements Z = 1 to 92, and for 48 compounds and mixtures of radiological interest. The tables cover energies of the photon (x-ray, gamma ray, bremsstrahlung) from 1 keV to 20 MeV.

  13. Theory of x-ray absorption by laser-aligned symmetric-top molecules.

    SciTech Connect

    Buth, C.; Santra, R.; Chemical Sciences and Engineering Division

    2008-01-01

    We devise a theory of x-ray absorption by symmetric-top molecules which are aligned by an intense optical laser. Initially, the density matrix of the system is composed of the electronic ground state of the molecules and a thermal ensemble of rigid-rotor eigenstates. We formulate equations of motion of the two-color (laser plus x rays) rotational-electronic problem. The interaction with the laser is assumed to be nonresonant; it is described by an electric dipole polarizability tensor. X-ray absorption is approximated as a one-photon process. It is shown that the equations can be separated such that the interaction with the laser can be treated independently of the x rays. The laser-only density matrix is propagated numerically. After each time step, the x-ray absorption is calculated. We apply our theory to study adiabatic alignment of bromine molecules (Br2). The required dynamic polarizabilities are determined using the ab initio linear response methods coupled-cluster singles (CCS), second-order approximate coupled-cluster singles and doubles (CC2), and coupled-cluster singles and doubles (CCSD). For the description of x-ray absorption on the {sigma}g1s-->{sigma}u4p resonance, a parameter-free two-level model is used for the electronic structure of the molecules. Our theory opens up novel perspectives for the quantum control of x-ray radiation.

  14. Weak Hard X-Ray Emission from Two Broad Absorption Line Quasars Observed with NuStar: Compton-Thick Absorption or Intrinsic X-Ray Weakness?

    NASA Technical Reports Server (NTRS)

    Luo, B.; Brandt, W. N.; Alexander, D. M.; Harrison, F. A.; Stern, D.; Bauer, F. E.; Boggs, S. E.; Christensen, F. E.; Comastri, A.; Craig, W. W..; Fabian, A. C.; Farrah, D.; Fiore, F.; Fuerst, F.; Grefenstette, B. W.; Hailey, C. J.; Hickox, R.; Madsen, K. K.; Matt, G.; Ogle, P.; Risaliti, G.; Saez, C.; Teng, S. H.; Walton, D. J.; Zhang, W. W.

    2013-01-01

    We present Nuclear Spectroscopic Telescope Array (NuSTAR) hard X-ray observations of two X-ray weak broad absorption line (BAL) quasars, PG 1004+130 (radio loud) and PG 1700+518 (radio quiet). Many BAL quasars appear X-ray weak, probably due to absorption by the shielding gas between the nucleus and the accretion-disk wind. The two targets are among the optically brightest BAL quasars, yet they are known to be significantly X-ray weak at rest-frame 2-10 keV (16-120 times fainter than typical quasars). We would expect to obtain approx. or equal to 400-600 hard X-ray (is greater than or equal to 10 keV) photons with NuSTAR, provided that these photons are not significantly absorbed N(sub H) is less than or equal to 10(exp24) cm(exp-2). However, both BAL quasars are only detected in the softer NuSTAR bands (e.g., 4-20 keV) but not in its harder bands (e.g., 20-30 keV), suggesting that either the shielding gas is highly Compton-thick or the two targets are intrinsically X-ray weak. We constrain the column densities for both to be N(sub H) 7 × 10(exp 24) cm(exp-2) if the weak hard X-ray emission is caused by obscuration from the shielding gas. We discuss a few possibilities for how PG 1004+130 could have Compton-thick shielding gas without strong Fe Ka line emission; dilution from jet-linked X-ray emission is one likely explanation. We also discuss the intrinsic X-ray weakness scenario based on a coronal-quenching model relevant to the shielding gas and disk wind of BAL quasars. Motivated by our NuSTAR results, we perform a Chandra stacking analysis with the Large Bright Quasar Survey BAL quasar sample and place statistical constraints upon the fraction of intrinsically X-ray weak BAL quasars; this fraction is likely 17%-40%.

  15. WEAK HARD X-RAY EMISSION FROM TWO BROAD ABSORPTION LINE QUASARS OBSERVED WITH NuSTAR: COMPTON-THICK ABSORPTION OR INTRINSIC X-RAY WEAKNESS?

    SciTech Connect

    Luo, B.; Brandt, W. N.; Alexander, D. M.; Hickox, R.; Harrison, F. A.; Fuerst, F.; Grefenstette, B. W.; Madsen, K. K.; Stern, D.; Bauer, F. E.; Boggs, S. E.; Craig, W. W.; Christensen, F. E.; Comastri, A.; Fabian, A. C.; Farrah, D.; Fiore, F.; Hailey, C. J.; Matt, G.; Ogle, P.; and others

    2013-08-01

    We present Nuclear Spectroscopic Telescope Array (NuSTAR) hard X-ray observations of two X-ray weak broad absorption line (BAL) quasars, PG 1004+130 (radio loud) and PG 1700+518 (radio quiet). Many BAL quasars appear X-ray weak, probably due to absorption by the shielding gas between the nucleus and the accretion-disk wind. The two targets are among the optically brightest BAL quasars, yet they are known to be significantly X-ray weak at rest-frame 2-10 keV (16-120 times fainter than typical quasars). We would expect to obtain Almost-Equal-To 400-600 hard X-ray ({approx}> 10 keV) photons with NuSTAR, provided that these photons are not significantly absorbed (N{sub H} {approx}< 10{sup 24} cm{sup -2}). However, both BAL quasars are only detected in the softer NuSTAR bands (e.g., 4-20 keV) but not in its harder bands (e.g., 20-30 keV), suggesting that either the shielding gas is highly Compton-thick or the two targets are intrinsically X-ray weak. We constrain the column densities for both to be N{sub H} Almost-Equal-To 7 Multiplication-Sign 10{sup 24} cm{sup -2} if the weak hard X-ray emission is caused by obscuration from the shielding gas. We discuss a few possibilities for how PG 1004+130 could have Compton-thick shielding gas without strong Fe K{alpha} line emission; dilution from jet-linked X-ray emission is one likely explanation. We also discuss the intrinsic X-ray weakness scenario based on a coronal-quenching model relevant to the shielding gas and disk wind of BAL quasars. Motivated by our NuSTAR results, we perform a Chandra stacking analysis with the Large Bright Quasar Survey BAL quasar sample and place statistical constraints upon the fraction of intrinsically X-ray weak BAL quasars; this fraction is likely 17%-40%.

  16. High energy X-ray phase and dark-field imaging using a random absorption mask

    PubMed Central

    Wang, Hongchang; Kashyap, Yogesh; Cai, Biao; Sawhney, Kawal

    2016-01-01

    High energy X-ray imaging has unique advantage over conventional X-ray imaging, since it enables higher penetration into materials with significantly reduced radiation damage. However, the absorption contrast in high energy region is considerably low due to the reduced X-ray absorption cross section for most materials. Even though the X-ray phase and dark-field imaging techniques can provide substantially increased contrast and complementary information, fabricating dedicated optics for high energies still remain a challenge. To address this issue, we present an alternative X-ray imaging approach to produce transmission, phase and scattering signals at high X-ray energies by using a random absorption mask. Importantly, in addition to the synchrotron radiation source, this approach has been demonstrated for practical imaging application with a laboratory-based microfocus X-ray source. This new imaging method could be potentially useful for studying thick samples or heavy materials for advanced research in materials science. PMID:27466217

  17. High energy X-ray phase and dark-field imaging using a random absorption mask.

    PubMed

    Wang, Hongchang; Kashyap, Yogesh; Cai, Biao; Sawhney, Kawal

    2016-01-01

    High energy X-ray imaging has unique advantage over conventional X-ray imaging, since it enables higher penetration into materials with significantly reduced radiation damage. However, the absorption contrast in high energy region is considerably low due to the reduced X-ray absorption cross section for most materials. Even though the X-ray phase and dark-field imaging techniques can provide substantially increased contrast and complementary information, fabricating dedicated optics for high energies still remain a challenge. To address this issue, we present an alternative X-ray imaging approach to produce transmission, phase and scattering signals at high X-ray energies by using a random absorption mask. Importantly, in addition to the synchrotron radiation source, this approach has been demonstrated for practical imaging application with a laboratory-based microfocus X-ray source. This new imaging method could be potentially useful for studying thick samples or heavy materials for advanced research in materials science. PMID:27466217

  18. ON NEUTRAL ABSORPTION AND SPECTRAL EVOLUTION IN X-RAY BINARIES

    SciTech Connect

    Miller, J. M.; Cackett, E. M.; Reis, R. C.

    2009-12-10

    Current X-ray observatories make it possible to follow the evolution of transient and variable X-ray binaries across a broad range in luminosity and source behavior. In such studies, it can be unclear whether evolution in the low-energy portion of the spectrum should be attributed to evolution in the source, or instead to evolution in neutral photoelectric absorption. Dispersive spectrometers make it possible to address this problem. We have analyzed a small but diverse set of X-ray binaries observed with the Chandra High Energy Transmission Grating Spectrometer across a range in luminosity and different spectral states. The column density in individual photoelectric absorption edges remains constant with luminosity, both within and across source spectral states. This finding suggests that absorption in the interstellar medium strongly dominates the neutral column density observed in spectra of X-ray binaries. Consequently, evolution in the low-energy spectrum of X-ray binaries should properly be attributed to evolution in the source spectrum. We discuss our results in the context of X-ray binary spectroscopy with current and future X-ray missions.

  19. Interstellar dust grain composition from high-resolution X-ray absorption edge structure

    NASA Astrophysics Data System (ADS)

    Corrales, Lia

    2016-06-01

    X-ray light is sufficient to excite electrons from n=1 (K-shell) and n=2 (L-shell) energy levels of neutral interstellar metals, causing a sharp increase in the absorption cross-section. Near the ionization energy, the shape of the photoelectric absorption edge depends strongly on whether the atom is isolated or bound in molecules or minerals (dust). With high resolution X-ray spectroscopy, we can directly measure the state of metals and the mineral composition of dust in the interstellar medium. In addition, the scattering contribution to the X-ray extinction cross-section can be used to gauge grain size, shape, and filling factor. In order to fully take advantage of major advances in high resolution X-ray spectroscopy, lab measurements of X-ray absorption fine structure (XAFS) from suspected interstellar minerals are required. Optical constants derived from the absorption measurements can be used with Mie scattering or anomalous diffraction theory in order to model the full extinction cross-sections from the interstellar medium. Much like quasar spectra are used to probe other intergalactic gas, absorption spectroscopy of Galactic X-ray binaries and bright stars will yield key insights to the mineralogy and evolution of dust grains in the Milky Way.

  20. X-ray absorption Studies of Zinc species in Centella asiatica

    NASA Astrophysics Data System (ADS)

    Dehipawala, Sunil; Cheung, Tak; Hogan, Clayton; Agoudavi, Yao; Dehipawala, Sumudu

    2013-03-01

    Zinc is a very important mineral present in a variety of vegetables. It is an essential element in cellular metabolism and several bodily functions. We used X-ray fluorescence, and X-ray Absorption near Edge structure(XANES) to study the amount of zinc present in several leafy vegetables as well as its chemical environment within the plant. Main absorption edge position of XANES is sensitive to the oxidation state of zinc and is useful when comparing the type of zinc present in different vegetables to the standard zinc present in supplements. Normalized main edge height is proportional to the amount of zinc present in the sample. Several leafy greens were used in this study, such as Spinacia oleracea, Basella alba, Brassica oleracea, Cardiospermum halicacabumand Centella asiatica. All of these plant leaves contained approximately the same amount of zinc in the leaf portion of the plant and a slightly lower amount in the stems, except Centella asiatica. Both leaves and stems of the plant Centella asiatica contained nearly two times the zinc compared to other plants. Further investigation of zinc's chemical environment within Centella asiatica could lead to a much more efficient dietary consumption of zinc. Use of the National Synchrotron Light Source, Brookhaven National Laboratory, was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886

  1. Modelling of the X-ray broad absorption features in Narrow-Line Seyfert 1s

    NASA Astrophysics Data System (ADS)

    Porquet, Delphine; Mouchet, Martine; Dumont Anne-Marie

    2000-09-01

    We investigate the origin of the broad absorption features detected near 1-1.4 keV in several Narrow-Line Seyfert 1 galaxies, by modelling the absorbing medium with various physical parameters, using the ionization code PEGAS. The observed properties of the X-ray absorption features can be reproduced by taking into account the peculiar soft X-ray excess which is well fitted by a blackbody plus an underlying power law. We equally stress that the emission coming from the absorbing medium (related to the covering factor) has a strong influence on the resulting X-ray spectrum, in particular on the apparent position and depth of the absorption features. A non-solar iron abundance may be required to explain the observed deep absorption. We also investigate the influence of an additional collisional ionization process ("hybrid case") on the predicted absorption features.

  2. Lead foil in dental X-ray film: Backscattering rejection or image intensifier?

    NASA Astrophysics Data System (ADS)

    Hönnicke, M. G.; Delben, G. J.; Godoi, W. C.; Swinka-Filho, V.

    2014-11-01

    Dental X-ray films are still largely used due to sterilization issues, simplicity and, mainly, economic reasons. These films almost always are double coated (double emulsion) and have a lead foil in contact with the film for X-ray backscattering rejection. Herein we explore the use of the lead foil as an image intensifier. In these studies, spatial resolution was investigated when images were acquired on the dental X-ray films with and without the lead foil. Also, the lead foil was subjected to atomic analysis (fluorescent measurements) and structure analysis (X-ray diffraction). We determined that the use of the lead foil reduces the exposure time, however, does not affect the spatial resolution on the acquired images. This suggests that the fluorescent radiation spread is smaller than the grain sizes of the dental X-ray films.

  3. High-Energy X-ray Absorption Diagnostics as an Experimental Combustion Technique

    NASA Astrophysics Data System (ADS)

    Dunnmon, Jared; Sobhani, Sadaf; Hinshaw, Waldo; Fahrig, Rebecca; Ihme, Matthias

    2015-11-01

    X-ray diagnostics such as X-ray Computed Tomography (XCT) have recently been utilized for measurement of scalar concentration fields in gas-phase flow phenomena. In this study, we apply high-energy X-ray absorption techniques to visualize a laboratory-scale flame via fluoroscopic measurements by using krypton as a radiodense tracer media. Advantages of X-ray absorption diagnostics in a combustion context, including application to optically inaccessible environments and lack of ambient photon interference, are demonstrated. Analysis methods and metrics for extracting physical insights from these data are presented. The accuracy of the diagnostic is assessed via comparison to known results from canonical flame configurations, and the potential for further applications is discussed. Support from the NDSEG fellowship, Bosch, and NASA are gratefully acknolwedged.

  4. X-ray scattering and absorption studies of MnAs/GaAs heterostructures

    NASA Astrophysics Data System (ADS)

    Huang, S.; Ming, Z. H.; Soo, Y. L.; Kao, Y. H.; Tanaka, M.; Munekata, H.

    1996-02-01

    Ferromagnetic MnAs thin films grown on GaAs (001) substrates by molecular-beam epitaxy have been studied by the methods of grazing incidence x-ray scattering, x-ray diffraction, and extended x-ray-absorption fine structure. Microstructures in two films prepared with different first-layer growth conditions (template effects) are compared in terms of the interfacial roughness in the layer structure, lattice constants, epilayer thickness, local environment surrounding the Mn atoms, coordination number, and local disorder. Our results indicate that the template effects can cause significant differences in the local structures and crystallinity of the MnAs epitaxial layers.

  5. Refraction and absorption of x rays by laser-dressed atoms.

    SciTech Connect

    Buth, C.; Santra, R.; Young, L.

    2010-06-01

    X-ray refraction and absorption by neon atoms under the influence of an 800 nm laser with an intensity of 10{sup 13} W/cm{sup 2} is investigated. For this purpose, we use an ab initio theory suitable for optical strong-field problems. Its results are interpreted in terms of a three-level model. On the Ne 1s {yields} 3p resonance, we find electromagnetically induced transparency (EIT) for x rays. Our work opens novel perspectives for ultrafast x-ray pulse shaping.

  6. Short term X-ray spectral variability of the strong iron-k absorption feature in PDS 456

    NASA Astrophysics Data System (ADS)

    Matzeu, G.; Reeves, J.; Gofford, J.; Nardini, E.; Costa, M.; Braito, V.; O'Brien, P.; Ward, M.; Turner, J.; Miller, L.

    2014-07-01

    We present a recent 500 ks Suzaku and a simultaneous 500 ks XMM-Newton & NuSTAR observations, carried out in 2013, of the nearby (z=0.184) luminous (L_{bol}˜10^{47} erg s^{-1}) quasar PDS 456. Short term X-ray spectral variability, including the presence of a strong and rapidly variable iron-K absorption feature, is observed and subsequently investigated. Here, our attention is focused on the physical interpretation of the short term variability where two models are adopted in the spectral analysis (partial covering vs coronal changes), leading to two valid interpretations. In the partial covering scenario, rapidly varying absorption is due to inhomogeneous dense material and such short timescale changes also entail that that the absorption is due to gas located in the vicinity of the black hole possibly shielding part of the outflow. In the second scenario, the complex spectral variability is due to variations in the intrinsic continuum observed as changes in the soft X-ray spectrum leading subsequent changes in the hard X-ray power-law, possibly induced by Comptonisation in the disc corona. Furthermore it was possible to extrapolate the size and the location of the absorber, its outflowing velocity and a direct estimation of the size of the X-ray emitting region ˜20 R_{g}.

  7. The 16th International Conference on X-ray Absorption Fine Structure (XAFS16)

    NASA Astrophysics Data System (ADS)

    Grunwaldt, J.-D.; Hagelstein, M.; Rothe, J.

    2016-05-01

    This preface of the proceedings volume of the 16th International Conference on X- ray Absorption Fine Structure (XAFS16) gives a glance on the five days of cutting-edge X-ray science which were held in Karlsruhe, Germany, August 23 - 28, 2015. In addition, several satellite meetings took place in Hamburg, Berlin and Stuttgart, a Sino-German workshop, three data analysis tutorials as well as special symposia on industrial catalysis and XFELs were held at the conference venue.

  8. Ultraintense X-Ray Induced Ionization, Dissociation, and Frustrated Absorption in Molecular Nitrogen

    SciTech Connect

    Hoener, M.; Fang, L.; Murphy, B.; Berrah, N.; Kornilov, O.; Gessner, O.; Pratt, S. T.; Kanter, E. P.; Guehr, M.; Bucksbaum, P. H.; Cryan, J.; Glownia, M.; McFarland, B.; Petrovic, V.; Blaga, C.; DiMauro, L.; Bostedt, C.; Bozek, J. D.; Coffee, R.; Messerschmidt, M.

    2010-06-25

    Sequential multiple photoionization of the prototypical molecule N{sub 2} is studied with femtosecond time resolution using the Linac Coherent Light Source (LCLS). A detailed picture of intense x-ray induced ionization and dissociation dynamics is revealed, including a molecular mechanism of frustrated absorption that suppresses the formation of high charge states at short pulse durations. The inverse scaling of the average target charge state with x-ray peak brightness has possible implications for single-pulse imaging applications.

  9. Ultraintense x-ray induced ionization, dissociation and frustrated absorption in molecular nitrogen.

    SciTech Connect

    Hoener, M.; Fang, L.; Kornilov, O.; Gessner, O.; Pratt, S. T.; Guhr, M.; Kanter, E. P.; Blaga, C.; Bostedt, C.; Bozek, J. D.; Bucksbaum, P. H.; Buth, C.; Chen, M.; Coffee, R.; Cryan, J.; DiMauro, L.; Glownia, M.; Hosler, E.; Kukk, E.; Leone, S. R.; McFarland, B.; Messerschmidt, M.; Murphy, B.; Petrovic, V.; Rolles, D.; Berrah, N.; Chemical Sciences and Engineering Division; Western Michigan Univ.; LBNL; Ohio State Univ.; Louisiana State Univ.; LLNL; Univ. of Turku; Univ. of California at Berkeley; Max Planck Advanced Study Group, CFEL; LCLS

    2010-06-23

    Sequential multiple photoionization of the prototypical molecule N2 is studied with femtosecond time resolution using the Linac Coherent Light Source (LCLS). A detailed picture of intense x-ray induced ionization and dissociation dynamics is revealed, including a molecular mechanism of frustrated absorption that suppresses the formation of high charge states at short pulse durations. The inverse scaling of the average target charge state with x-ray peak brightness has possible implications for single-pulse imaging applications.

  10. Capturing Transient Electronic and Molecular Structures in Liquids by Picosecond X-Ray Absorption Spectroscopy

    SciTech Connect

    Gawelda, W.; Pham, V. T.; El Nahhas, A.; Kaiser, M.; Zaushitsyn, Y.; Bressler, C.; Chergui, M.; Johnson, S. L.; Grolimund, D.; Abela, R.; Hauser, A.

    2007-02-02

    We describe an advanced setup for time-resolved x-ray absorption fine structure (XAFS) Spectroscopy with picosecond temporal resolution. It combines an intense femtosecond laser source synchronized to the x-ray pulses delivered into the microXAS beamline of the Swiss Light Source (SLS). The setup is applied to measure the short-lived high-spin geometric structure of photoexcited aqueous Fe(bpy)3 at room temperature.

  11. Differentiation of biological hydroxyapatite compounds by infrared spectroscopy, x-ray diffraction and extended x-ray absorption fine structure

    NASA Astrophysics Data System (ADS)

    Chassot, E.; Oudadesse, H.; Irigaray, J.; Curis, E.; Bénazeth, S.; Nicolis, I.

    2001-12-01

    Pure hydroxyapatite (HAP) and HAP doped with 800 ppm of zinc were implanted in cortical bone of femur diaphysis of ovines [J. L. Irigaray et al., Mater. Clin. Appl. 28, 399 (1999)]. We observed that the doped HAP was better resorbed than pure HAP. The first hypothesis is that zinc acts as a stimulator on macrophage cells and improves quantity and quality of osteoblast cells. The second hypothesis is that zinc yields HAP structure that is better resorbed in biological field. For our experiment we used HAP doped with 3000 ppm of zinc in order to have a good sensitivity. In the present work, chemical studies by inductively coupled plasma absorption emission spectrometry, x ray diffraction, and infrared were carried out to determine the composition of major and trace elements in the doped hydroxyapatite, and the crystallographic structure. These studies can indicate possible modifications induced by the insertion of zinc. We used the extended x-ray absorption fine structure experimental station of LURE (Orsay, France) to try to clarify the atomic surroundings of zinc in doped HAP structure and transformations induced in initial lattice. Despite the low zinc concentration, we got good quality fluorescence mode spectra. These spectra showed medium range order of the material that is consistent with its crystalline form. To perform the analysis, we compared the result obtained with another models like β tricalcium phosphate and we created theoretical models of zinc in substitution of calcium in order to reproduce as well as possible the experimental spectrum. After this study, only two models are coherent with experimental spectrum, zinc in substitution of calcium in site I and zinc in the interstice between the two hydroxydes.

  12. Note: Application of a pixel-array area detector to simultaneous single crystal x-ray diffraction and x-ray absorption spectroscopy measurements

    SciTech Connect

    Sun, Cheng-Jun Brewe, Dale L.; Heald, Steve M.; Zhang, Bangmin; Chen, Jing-Sheng; Chow, G. M.; Venkatesan, T.

    2014-04-15

    X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) are two main x-ray techniques in synchrotron radiation facilities. In this Note, we present an experimental setup capable of performing simultaneous XRD and XAS measurements by the application of a pixel-array area detector. For XRD, the momentum transfer in specular diffraction was measured by scanning the X-ray energy with fixed incoming and outgoing x-ray angles. By selecting a small fixed region of the detector to collect the XRD signal, the rest of the area was available for collecting the x-ray fluorescence for XAS measurements. The simultaneous measurement of XRD and X-ray absorption near edge structure for Pr{sub 0.67}Sr{sub 0.33}MnO{sub 3} film was demonstrated as a proof of principle for future time-resolved pump-probe measurements. A static sample makes it easy to maintain an accurate overlap of the X-ray spot and laser pump beam.

  13. Femtosecond X-ray magnetic circular dichroism absorption spectroscopy at an X-ray free electron laser.

    PubMed

    Higley, Daniel J; Hirsch, Konstantin; Dakovski, Georgi L; Jal, Emmanuelle; Yuan, Edwin; Liu, Tianmin; Lutman, Alberto A; MacArthur, James P; Arenholz, Elke; Chen, Zhao; Coslovich, Giacomo; Denes, Peter; Granitzka, Patrick W; Hart, Philip; Hoffmann, Matthias C; Joseph, John; Le Guyader, Loïc; Mitra, Ankush; Moeller, Stefan; Ohldag, Hendrik; Seaberg, Matthew; Shafer, Padraic; Stöhr, Joachim; Tsukamoto, Arata; Nuhn, Heinz-Dieter; Reid, Alex H; Dürr, Hermann A; Schlotter, William F

    2016-03-01

    X-ray magnetic circular dichroism spectroscopy using an X-ray free electron laser is demonstrated with spectra over the Fe L(3,2)-edges. The high brightness of the X-ray free electron laser combined with high accuracy detection of incident and transmitted X-rays enables ultrafast X-ray magnetic circular dichroism studies of unprecedented sensitivity. This new capability is applied to a study of all-optical magnetic switching dynamics of Fe and Gd magnetic sublattices in a GdFeCo thin film above its magnetization compensation temperature. PMID:27036761

  14. Femtosecond X-ray magnetic circular dichroism absorption spectroscopy at an X-ray free electron laser

    NASA Astrophysics Data System (ADS)

    Higley, Daniel J.; Hirsch, Konstantin; Dakovski, Georgi L.; Jal, Emmanuelle; Yuan, Edwin; Liu, Tianmin; Lutman, Alberto A.; MacArthur, James P.; Arenholz, Elke; Chen, Zhao; Coslovich, Giacomo; Denes, Peter; Granitzka, Patrick W.; Hart, Philip; Hoffmann, Matthias C.; Joseph, John; Le Guyader, Loïc; Mitra, Ankush; Moeller, Stefan; Ohldag, Hendrik; Seaberg, Matthew; Shafer, Padraic; Stöhr, Joachim; Tsukamoto, Arata; Nuhn, Heinz-Dieter; Reid, Alex H.; Dürr, Hermann A.; Schlotter, William F.

    2016-03-01

    X-ray magnetic circular dichroism spectroscopy using an X-ray free electron laser is demonstrated with spectra over the Fe L3,2-edges. The high brightness of the X-ray free electron laser combined with high accuracy detection of incident and transmitted X-rays enables ultrafast X-ray magnetic circular dichroism studies of unprecedented sensitivity. This new capability is applied to a study of all-optical magnetic switching dynamics of Fe and Gd magnetic sublattices in a GdFeCo thin film above its magnetization compensation temperature.

  15. Is selective absorption of ultrasoft x-rays biologically important in mammalian cells?

    PubMed

    Goodhead, D T; Thacker, J; Cox, R

    1981-11-01

    This paper tests whether photon absorption processes in particular atomic element(s) may be responsible for the observed high relative biological effectiveness (RBE) of ultrasoft X-rays. The effectiveness of titanium K characteristic X-rays (4.55 keV) is compared with previous observations for aluminium (1.5 keV) and carbon (0.28 keV) K ultrasoft X-rays. For a given absorbed dose, five times more Ti K than Al K photons are absorbed in phosphorus; since Al K X-rays are observed to be more effective in killing human and hamster cells it is concluded that absorption in phosphorus does not play a dominant lethal role. This is supported by the observation that the absolute number of Al K photons absorbed in phosphorus of DNA of human fibroblasts is less than 1 per lethal event. For no element is the relative number of absorbed photons of the three X-ray energies even approximately proportional to their observed RBEs. The effectiveness of ultrasoft X-rays is apparently not due to selective absorption but rather to the secondary electrons; consequently the mechanism of action should be common to the large numbers of low energy secondary electrons produced by most other ionising radiations, including gamma-rays. PMID:7323149

  16. Near edge X-ray absorption mass spectrometry on coronene

    SciTech Connect

    Reitsma, G.; Deuzeman, M. J.; Hoekstra, R.; Schlathölter, T.; Boschman, L.; Hoekstra, S.

    2015-01-14

    We have investigated the photoionization and photodissociation of free coronene cations C{sub 24}H{sub 12}{sup +} upon soft X-ray photoabsorption in the carbon K-edge region by means of a time-of-flight mass spectrometry approach. Core excitation into an unoccupied molecular orbital (below threshold) and core ionization into the continuum both leave a C 1s vacancy, that is subsequently filled in an Auger-type process. The resulting coronene dications and trications are internally excited and cool down predominantly by means of hydrogen emission. Density functional theory was employed to determine the dissociation energies for subsequent neutral hydrogen loss. A statistical cascade model incorporating these dissociation energies agrees well with the experimentally observed dehydrogenation. For double ionization, i.e., formation of intermediate C{sub 24}H{sub 12}{sup 3+⋆}trications, the experimental data hint at loss of H{sup +} ions. This asymmetric fission channel is associated with hot intermediates, whereas colder intermediates predominantly decay via neutral H loss.

  17. 3D Imaging of Nickel Oxidation States using Full Field X-ray Absorption Near Edge Structure Nanotomography

    SciTech Connect

    Nelson, George; Harris, William; Izzo, John; Grew, Kyle N.

    2012-01-20

    Reduction-oxidation (redox) cycling of the nickel electrocatalyst phase in the solid oxide fuel cell (SOFC) anode can lead to performance degradation and cell failure. A greater understanding of nickel redox mechanisms at the microstructural level is vital to future SOFC development. Transmission x-ray microscopy (TXM) provides several key techniques for exploring oxidation states within SOFC electrode microstructure. Specifically, x-ray nanotomography and x-ray absorption near edge structure (XANES) spectroscopy have been applied to study samples of varying nickel (Ni) and nickel oxide (NiO) compositions. The imaged samples are treated as mock SOFC anodes containing distinct regions of the materials in question. XANES spectra presented for the individual materials provide a basis for the further processing and analysis of mixed samples. Images of composite samples obtained are segmented, and the distinct nickel and nickel oxide phases are uniquely identified using full field XANES spectroscopy. Applications to SOFC analysis are discussed.

  18. Fabrication of 200 nanometer period centimeter area hard x-ray absorption gratings by multilayer deposition.

    PubMed

    Lynch, S K; Liu, C; Morgan, N Y; Xiao, X; Gomella, A A; Mazilu, D; Bennett, E E; Assoufid, L; de Carlo, F; Wen, H

    2012-10-01

    We describe the design and fabrication trials of x-ray absorption gratings of 200 nm period and up to 100:1 depth-to-period ratios for full-field hard x-ray imaging applications. Hard x-ray phase-contrast imaging relies on gratings of ultra-small periods and sufficient depth to achieve high sensitivity. Current grating designs utilize lithographic processes to produce periodic vertical structures, where grating periods below 2.0 μm are difficult due to the extreme aspect ratios of the structures. In our design, multiple bilayers of x-ray transparent and opaque materials are deposited on a staircase substrate, and mostly on the floor surfaces of the steps only. When illuminated by an x-ray beam horizontally, the multilayer stack on each step functions as a micro-grating whose grating period is the thickness of a bilayer. The array of micro-gratings over the length of the staircase works as a single grating over a large area when continuity conditions are met. Since the layers can be nanometers thick and many microns wide, this design allows sub-micron grating periods and sufficient grating depth to modulate hard x-rays. We present the details of the fabrication process and diffraction profiles and contact radiography images showing successful intensity modulation of a 25 keV x-ray beam. PMID:23066175

  19. Fabrication of 200 nanometer period centimeter area hard x-ray absorption gratings by multilayer deposition

    PubMed Central

    Lynch, S K; Liu, C; Morgan, N Y; Xiao, X; Gomella, A A; Mazilu, D; Bennett, E E; Assoufid, L; de Carlo, F; Wen, H

    2012-01-01

    We describe the design and fabrication trials of x-ray absorption gratings of 200 nm period and up to 100:1 depth-to-period ratios for full-field hard x-ray imaging applications. Hard x-ray phase-contrast imaging relies on gratings of ultra-small periods and sufficient depth to achieve high sensitivity. Current grating designs utilize lithographic processes to produce periodic vertical structures, where grating periods below 2.0 μm are difficult due to the extreme aspect ratios of the structures. In our design, multiple bilayers of x-ray transparent and opaque materials are deposited on a staircase substrate, and mostly on the floor surfaces of the steps only. When illuminated by an x-ray beam horizontally, the multilayer stack on each step functions as a micro-grating whose grating period is the thickness of a bilayer. The array of micro-gratings over the length of the staircase works as a single grating over a large area when continuity conditions are met. Since the layers can be nanometers thick and many microns wide, this design allows sub-micron grating periods and sufficient grating depth to modulate hard x-rays. We present the details of the fabrication process and diffraction profiles and contact radiography images showing successful intensity modulation of a 25 keV x-ray beam. PMID:23066175

  20. Time-resolved near-edge x-ray absorption fine structure spectroscopy on photo-induced phase transitions using a tabletop soft-x-ray spectrometer

    NASA Astrophysics Data System (ADS)

    Grossmann, P.; Rajkovic, I.; Moré, R.; Norpoth, J.; Techert, S.; Jooss, C.; Mann, Klaus

    2012-05-01

    We present a table-top soft-x-ray spectrometer for the wavelength range λ = 1-5 nm based on a stable laser-driven x-ray source, making use of a gas-puff target. With this setup, optical light-pump/soft-x-ray probe near-edge x-ray absorption fine structure (NEXAFS) experiments with a temporal resolution of about 230 ps are feasible. Pump-probe NEXAFS measurements were carried out in the "water-window" region (2.28 nm-4.36 nm) on the manganite Pr0.7Ca0.3MnO3, investigating diminutive changes of the oxygen K edge that derive from an optically induced phase transition. The results show the practicability of the table-top soft-x-ray spectrometer on demanding investigations so far exclusively conducted at synchrotron radiation sources.

  1. Laser-driven hard-x-ray generation based on ultrafast selected energy x-ray absorption spectroscopy measurements of Ni compounds

    SciTech Connect

    Shan Fang; Carter, Josh D.; Ng, Vicky; Guo Ting

    2005-02-01

    Three Ni compounds were studied by ultrafast selected energy x-ray absorption spectroscopy using a laser-driven electron x-ray source with a tungsten target. The measured K edges of these Ni compounds using this self-referencing method were made identical to those measured with synchrotron x-ray sources. This enabled us to determine the absolute peak positions of tungsten L{alpha}{sub 1} and L{alpha}{sub 2} emitted from this source to be within 1 eV of those from the neutral tungsten atoms, which strongly suggested that the x rays were emitted from high energy electrons interacting with tungsten atoms in the solid target. This is the best evidence to date that directly supports the cold atom x-ray generation theory.

  2. Determination of uranyl incorporation into biogenic manganese oxides using X-ray absorption spectroscopy and scattering

    USGS Publications Warehouse

    Webb, S.M.; Fuller, C.C.; Tebo, B.M.; Bargar, J.R.

    2006-01-01

    Biogenic manganese oxides are common and an important source of reactive mineral surfaces in the environment that may be potentially enhanced in bioremediation cases to improve natural attenuation. Experiments were performed in which the uranyl ion, UO22+ (U(VI)), at various concentrations was present during manganese oxide biogenesis. At all concentrations, there was strong uptake of U onto the oxides. Synchrotron-based extended X-ray absorption fine structure (EXAFS) spectroscopy and X-ray diffraction (XRD) studies were carried out to determine the molecular-scale mechanism by which uranyl is incorporated into the oxide and how this incorporation affects the resulting manganese oxide structure and mineralogy. The EXAFS experiments show that at low concentrations (2 mol % U, >4 ??M U(VI) in solution), the presence of U(VI) affects the stability and structure of the Mn oxide to form poorly ordered Mn oxide tunnel structures, similar to todorokite. EXAFS modeling shows that uranyl is present in these oxides predominantly in the tunnels of the Mn oxide structure in a tridentate complex. Observations by XRD corroborate these results. Structural incorporation may lead to more stable U(VI) sequestration that may be suitable for remediation uses. These observations, combined with the very high uptake capacity of the Mn oxides, imply that Mn-oxidizing bacteria may significantly influence dissolved U(VI) concentrations in impacted waters via sorption and incorporation into Mn oxide biominerals. ?? 2006 American Chemical Society.

  3. A table-top femtosecond time-resolved soft x-ray transient absorption spectrometer

    SciTech Connect

    Leone, Stephen; Loh, Zhi-Heng; Khalil, Munira; Correa, Raoul E.; Leone, Stephen R.

    2008-05-21

    A laser-based, table-top instrument is constructed to perform femtosecond soft x-ray transient absorption spectroscopy. Ultrashort soft x-ray pulses produced via high-order harmonic generation of the amplified output of a femtosecond Ti:sapphire laser system are used to probe atomic core-level transient absorptions in atoms and molecules. The results provide chemically specific, time-resolved dynamics with sub-50-fs time resolution. In this setup, high-order harmonics generated in a Ne-filled capillary waveguide are refocused by a gold-coated toroidal mirror into the sample gas cell, where the soft x-ray light intersects with an optical pump pulse. The transmitted high-order harmonics are spectrally dispersed with a home-built soft x-ray spectrometer, which consists of a gold-coated toroidal mirror, a uniform-line spaced plane grating, and a soft x-ray CCD camera. The optical layout of the instrument, design of the soft x-ray spectrometer, and spatial and temporal characterization of the high-order harmonics are described. Examples of static and time-resolved photoabsorption spectra collected on this apparatus are presented.

  4. The irradiation of ammonia ice studied by near edge x-ray absorption spectroscopy

    SciTech Connect

    Parent, Ph.; Bournel, F.; Lasne, J.; Laffon, C.; Carniato, S.; Lacombe, S.; Strazzulla, G.; Gardonio, S.; Lizzit, S.; Kappler, J.-P.; Joly, L.

    2009-10-21

    A vapor-deposited NH{sub 3} ice film irradiated at 20 K with 150 eV photons has been studied with near-edge x-ray absorption fine structure (NEXAFS) spectroscopy at the nitrogen K-edge. Irradiation leads to the formation of high amounts (12%) of molecular nitrogen N{sub 2}, whose concentration as a function of the absorbed energy has been quantified to 0.13 molecule/eV. The stability of N{sub 2} in solid NH{sub 3} has been also studied, showing that N{sub 2} continuously desorbs between 20 and 95 K from the irradiated ammonia ice film. Weak concentrations (<1%) of other photoproducts are also detected. Our NEXAFS simulations show that these features own to NH{sub 2}, N{sub 2}H{sub 2}, and N{sub 3}{sup -}.

  5. Elemental biological imaging by differential absorption with a laser-produced x-ray source

    NASA Astrophysics Data System (ADS)

    Tillman, C.; Mercer, I.; Svanberg, S.; Herrlin, K.

    1996-01-01

    We demonstrate the novel application of hard x rays emitted by a laser-produced plasma for differential imaging of elements. An x-ray-emitting laser-produced plasma, obtained by the focusing of radiation from a 10-Hz terawatt laser, is used for biological imaging. The x-ray source can be arranged to yield characteristic x-ray emission lines with photon energies that bridge the K absorption edge of a chosen atomic species. One can obtain element-specific radiographs by recording transillumination images for different target materials on digital image plates and by subsequently subtracting or dividing the images. Successful phantom and experimental animal imaging are performed utilizing tantalum and gadolinium as target materials for the terawatt laser and gadolinium as the imaged contrast agent.

  6. Weak Hard X-ray Emission from Broad Absorption Line Quasars Observed with NuSTAR: Evidence for Intrinsic X-ray Weakness

    NASA Astrophysics Data System (ADS)

    Luo, Bin; Brandt, W. Niel; Alexander, David M; Stern, Daniel; Teng, Stacy H.; Arevalo, Patricia; Bauer, Franz E.; Boggs, Steven E.; Christensen, Finn; Comastri, Andrea; Craig, William W.; Farrah, Duncan; Gandhi, Poshak; Hailey, Charles James; Harrison, Fiona; Koss, Michael; Ogle, Patrick M.; Puccetti, Simonetta; Saez, Cristian; Scott, Amy; Walton, Dom; Zhang, William

    2014-08-01

    We report NuSTAR observations of a sample of six X-ray weak broad absorption line (BAL) quasars. These targets, at z=0.148-1.223, are among the optically brightest and most luminous BAL quasars known at z<1.3. However, their rest-frame 2 keV luminosities are 14 to >330 times weaker than expected for typical quasars. Our results from a pilot NuSTAR study of two low-redshift BAL quasars, a Chandra stacking analysis of a sample of high-redshift BAL quasars, and a NuSTAR spectral analysis of the local BAL quasar Mrk 231 have already suggested the existence of intrinsically X-ray weak BAL quasars, i.e., quasars not emitting X-rays at the level expected from their optical/UV emission. The aim of the current program is to extend the search for such extraordinary objects. Three of the six new targets are weakly detected by NuSTAR with <45 counts in the 3-24 keV band, and the other three are not detected. The hard X-ray (8-24 keV) weakness observed by NuSTAR requires Compton-thick absorption if these objects have nominal underlying X-ray emission. However, a soft stacked effective photon index (Γ 1.8) for this sample disfavors Compton-thick absorption in general. The uniform hard X-ray weakness observed by NuSTAR for this and the pilot samples selected with <10 keV weakness also suggests that the X-ray weakness is intrinsic in at least some of the targets. We conclude that the NuSTAR observations have likely discovered a significant population (>33%) of intrinsically X-ray weak objects among the BAL quasars with significantly weak <10 keV emission. We suggest that intrinsically X-ray weak quasars might be preferentially observed as BAL quasars.

  7. Undistorted X-ray Absorption Spectroscopy Using s-Core-Orbital Emissions.

    PubMed

    Golnak, Ronny; Xiao, Jie; Atak, Kaan; Unger, Isaak; Seidel, Robert; Winter, Bernd; Aziz, Emad F

    2016-05-12

    Detection of secondary emissions, fluorescence yield (FY), or electron yield (EY), originating from the relaxation processes upon X-ray resonant absorption has been widely adopted for X-ray absorption spectroscopy (XAS) measurements when the primary absorption process cannot be probed directly in transmission mode. Various spectral distortion effects inherent in the relaxation processes and in the subsequent transportation of emitted particles (electron or photon) through the sample, however, undermine the proportionality of the emission signals to the X-ray absorption coefficient. In the present study, multiple radiative (FY) and nonradiative (EY) decay channels have been experimentally investigated on a model system, FeCl3 aqueous solution, at the excitation energy of the Fe L-edge. The systematic comparisons between the experimental spectra taken from various decay channels, as well as the comparison with the theoretically simulated Fe L-edge XA spectrum that involves only the absorption process, indicate that the detection of the Fe 3s → 2p partial fluorescence yield (PFY) gives rise to the true Fe L-edge XA spectrum. The two key characteristics generalized from this particular decay channel-zero orbital angular momentum (i.e., s orbital) and core-level emission-set a guideline for obtaining undistorted X-ray absorption spectra in the future. PMID:27101344

  8. Testing interaction models by using x-ray absorption spectroscopy: solid Pb

    NASA Astrophysics Data System (ADS)

    Di Cicco, Andrea; Minicucci, Marco; Principi, Emiliano; Witkowska, Agnieszka; Rybicki, Jaroslaw; Laskowski, Robert

    2002-04-01

    Structural models obtained using classical molecular dynamics (MD) simulations and realistic interatomic potentials for solid metals are tested using experimental results obtained by x-ray absorption spectroscopy (XAS). Accurate L-edge extended x-ray absorption fine-structure (EXAFS) measurements of Pb grains dispersed in BN and graphite matrices have been collected for temperatures up to the melting point. The thermal expansion of the grains was measured by energy-dispersive x-ray diffraction techniques and found to be coincident with that of pure Pb up to the limit of the present measurements. L3-edge EXAFS measurements of solid Pb at various temperatures have been analysed using advanced data-analysis techniques (GNXAS) based on exact spherical-wave multiple-scattering simulation of the absorption cross-section. Realistic structural models for solid Pb were obtained from MD simulations using an empirical pair potential (Dzugutov, Larsson and Ebbsjo (DLE)), a tight-binding (TB) square-root functional, and an embedded-atom (EA) model potential parametrized by us. The short-range pair distribution function g(r) reconstructed by means of EXAFS is compared with those obtained by MD simulations. The empirical DLE potential, originally designed for the liquid state, is too soft, showing too-large values for the average distance R, variance σ2, and skewness β. The TB and EA potentials are both compatible with XAS data as regards the average distance and skewness of the first neighbours. The distance variance, associated with the thermal vibration amplitudes, is underestimated for the TB potential, while the EA model is found to be in agreement with XAS data. The present results are also compared with those from a previous EXAFS study on solid lead, where the cumulant expansion and a simple one-dimensional anharmonic oscillator model were used. The need for realistic interaction models and appropriate simulation schemes for reliable XAS data analysis is emphasized

  9. Application of X-ray Absorption Spectroscopy to the study of nuclear structural materials

    NASA Astrophysics Data System (ADS)

    Liu, Shanshan

    One of key technologies for the next generation nuclear systems are advanced materials, including high temperature structural materials, fast neutron resistance core materials and so on. Local structure determination in these systems, which often are crystallographically intractable, is critical to gaining an understanding of their properties. In this thesis, X-ray Absorption Spectroscopy (XAS), including Extended X-ray Absorption Fine Structure (EXAFS) and X-ray Absorption Near Edge Structure (XANES), is used to examine the geometric and electronic structure of nuclear structural materials under varying conditions. The thesis is divided into two main sections. The first examines the structural analysis of nanostructured ferritic alloys (NFA) which are dispersion strengthened by an ultra high density of Y-Ti-O enriched nano-features, resulting in remarkable high temperature creep strength and radiation damage resistance. Titanium and Yttrium K-edge XAS shows commercial alloys MA957 and J12YWT more closely resemble the as received Fe-14Cr-3W-0.4Ti (wt. %) powders, and mechanically alloyed (MA) powders with 0.25Y2O3 (wt. %). It shows that a significant fraction of substitutional Ti remains dissolved in the (BCC) ferrite matrix. In contrast, annealed powders and hot isostatic press (HIP) consolidated alloys show high temperature heat treatments shift the Y and Ti to more oxidized states that are consistent with combinations of Y2Ti2O7 and, especially, TiO. The second section describes corrosion studies of Pb with 316L stainless steel, molybdenum and spinet (MgAl2O4) at high temperature by XAS. The corrosion of fuel cladding and structural materials by liquid lead at elevated temperatures is an issue that must be considered when designing advanced nuclear systems and high-power spallation neutron targets. The results of ex-situ studies show that a Mo substrate retained a smooth and less corroded surface than 316L stainless steel sample at elevated temperature. In

  10. Intracellular nanoparticles mass quantification by near-edge absorption soft X-ray nanotomography

    NASA Astrophysics Data System (ADS)

    Conesa, Jose Javier; Otón, Joaquín; Chiappi, Michele; Carazo, Jose María; Pereiro, Eva; Chichón, Francisco Javier; Carrascosa, José L.

    2016-03-01

    We used soft X-ray three-dimensional imaging to quantify the mass of superparamagnetic iron oxide nanoparticles (SPION) within whole cells, by exploiting the iron oxide differential absorption contrast. Near-edge absorption soft X-ray nanotomography (NEASXT) combines whole-cell 3D structure determination at 50 nm resolution, with 3D elemental mapping and high throughput. We detected three-dimensional distribution of SPIONs within cells with 0.3 g/cm3 sensitivity, sufficient for detecting the density corresponding to a single nanoparticle.

  11. Intracellular nanoparticles mass quantification by near-edge absorption soft X-ray nanotomography

    PubMed Central

    Conesa, Jose Javier; Otón, Joaquín; Chiappi, Michele; Carazo, Jose María; Pereiro, Eva; Chichón, Francisco Javier; Carrascosa, José L.

    2016-01-01

    We used soft X-ray three-dimensional imaging to quantify the mass of superparamagnetic iron oxide nanoparticles (SPION) within whole cells, by exploiting the iron oxide differential absorption contrast. Near-edge absorption soft X-ray nanotomography (NEASXT) combines whole-cell 3D structure determination at 50 nm resolution, with 3D elemental mapping and high throughput. We detected three-dimensional distribution of SPIONs within cells with 0.3 g/cm3 sensitivity, sufficient for detecting the density corresponding to a single nanoparticle. PMID:26960695

  12. X ray absorption by dark nebulae (HEAO-2 guest investigator program)

    NASA Technical Reports Server (NTRS)

    Sanders, W. T.

    1991-01-01

    A study is described of data obtained from the Imaging Proportional Counter (IPC) x ray detector aboard the HEAO-2 satellite (Einstein Observatory). The research project involved a search for absorption of diffuse low energy x ray background emission by galactic dark nebulae. The commonly accepted picture that the bulk of the C band emission originates locally, closer that a few hundred parsec, and the bulk of the M band emission originates farther away than a few hundred parsec, was tested. The idea was to look for evidence of absorption of the diffuse background radiation by nearby interstellar clouds.

  13. Intracellular nanoparticles mass quantification by near-edge absorption soft X-ray nanotomography.

    PubMed

    Conesa, Jose Javier; Otón, Joaquín; Chiappi, Michele; Carazo, Jose María; Pereiro, Eva; Chichón, Francisco Javier; Carrascosa, José L

    2016-01-01

    We used soft X-ray three-dimensional imaging to quantify the mass of superparamagnetic iron oxide nanoparticles (SPION) within whole cells, by exploiting the iron oxide differential absorption contrast. Near-edge absorption soft X-ray nanotomography (NEASXT) combines whole-cell 3D structure determination at 50 nm resolution, with 3D elemental mapping and high throughput. We detected three-dimensional distribution of SPIONs within cells with 0.3 g/cm(3) sensitivity, sufficient for detecting the density corresponding to a single nanoparticle. PMID:26960695

  14. Comparison of Synchrotron X-Ray Fluorescence Mapping and Micro-XANES to Bulk X-Ray Absorption Spectra in Metal-Contaminated Sediments

    SciTech Connect

    O'Day, P; Carroll, S A; Bajt, S

    2003-01-16

    Synchrotron X-ray absorption spectroscopy (XAS) is one of the few techniques that can supply molecular-scale information for a variety of elements at concentrations relevant to natural systems in non-vacuum conditions. Bulk XAS analysis supplies the dominant chemical bonding mode(s) for a specific element. In complex materials such as natural soils and sediments, however, the dominant mode may not necessarily be the most reactive because changes in speciation at surfaces may results in changes in reactivity. Our previous work at Naval Air Station (NAS) Alameda (CA) focused on in situ metal chemistry in surface and deep sediments, and the impact of metal mobility by sediment oxidation. Estuary sediments at the Alameda Naval Station Air in California have elevated metal concentrations that increase with increasing depth. The metal concentrations in these sediments are: Cd (10-350 ppm), Cr (200-1000 ppm), Cu (100-230 ppm), Pb (200-1200 ppm) and Zn (250-600 ppm). We have extensively characterized these sediments using bulk XAS and other non-synchrotron supporting methods [ 1]. In this experiment, we collected fluorescence element maps using synchrotron X-ray microprobe of unreacted and seawater-oxidized sediment samples from Alameda NAS to determine the spatial distribution and correlation of lead, zinc, and iron. We then compared micro-XANES spectra for lead and zinc collected with the X-ray microprobe to previously collected bulk XANES spectra. The results from our bulk XAS characterization of the sediments showed both oxide and sulfide components for the trace metals. However, the bulk XAS data were not able to identify the composition of the oxide component (i.e. carbonate or hydroxide), nor could absorbed species or solid solutions be definitively identified. Our objective in using micro-XANES and fluorescence element maps was to attempt a more precise identification of metal speciation in or on individual particles.

  15. PKS 0483-436 - A high-redshift quasar with strong X-ray absorption

    NASA Technical Reports Server (NTRS)

    Wilkes, Belinda J.; Elvis, Martin; Fiore, Fabrizio; Mcdowell, Jonathan C.; Tananbaum, Harvey; Lawrence, Andrew

    1992-01-01

    The first X-ray spectrum of a high-redshift (z = 2.85) quasar is reported. The Rosat PSPC spectrum of PKS 0438-436, covering 0.3-9 keV in the quasar's rest frame, reveals unexpected absorption of about 1 x 10 exp 22/sq cm, assuming it occurs at the source. Only one other high-luminosity quasar (of greater than about 50 observed by Einstein) shows significant absorption in its X-ray spectrum. Of the common line-of-sight absorbers, only highly ionized Ly-alpha forest clouds may be able to explain this amount of absorption. Candidates for an intrinsic absorber are discussed. Absorption at about 1 keV (rest frame) is due primarily to heavy elements. (O, Ne, Mg, Si, S) raising the possibility of measuring early universe abundances via X-ray absorption in this and like quasars. PKS 0438-436 may be a high-redshift member of a population of quasars which can contribute to the X-ray background above 2 keV, without being detectable by previous imaging missions.

  16. Oxygen, neon, and iron X-ray absorption in the local interstellar medium

    NASA Astrophysics Data System (ADS)

    Gatuzz, Efraín; García, Javier A.; Kallman, Timothy R.; Mendoza, Claudio

    2016-04-01

    Aims: We present a detailed study of X-ray absorption in the local interstellar medium by analyzing the X-ray spectra of 24 galactic sources obtained with the Chandra High Energy Transmission Grating Spectrometer and the XMM-Newton Reflection Grating Spectrometer. Methods: By modeling the continuum with a simple broken power-law and by implementing the new ISMabs X-ray absorption model, we have estimated the total H, O, Ne, and Fe column densities towards the observed sources. Results: We have determined the absorbing material distribution as a function of source distance and galactic latitude-longitude. Conclusions: Direct estimates of the fractions of neutrally, singly, and doubly ionized species of O, Ne, and Fe reveal the dominance of the cold component, thus indicating an overall low degree of ionization. Our results are expected to be sensitive to the model used to describe the continuum in all sources.

  17. Ultra-soft x-ray absorption spectroscopy: A bulk and surface probe of materials

    SciTech Connect

    Fischer, D.A. ); Mitchell, G.E.; Dekoven, B.M. ); Yeh, A.T.; Gland, J.L. ); Moodenbaugh, A.R. )

    1993-01-01

    Direct comparisons between surface and bulk of diverse materials can be made by simultaneous electron yield (5 nm depth sensitivity) and fluorescence yield (200 nm) ultra soft x-ray absorption spectroscopy measurements utilizing a rapid sample interchange apparatus. For example the orientations of functional groups have been characterized at and near the surface of a series of model polymeric materials highlighting the chemical and molecular sensitivity of ultra soft x-ray absorption spectroscopy. In addition we discuss a bulk sensitive use of fluorescence yield to non destructively study a buried metal polymer interface. A second bulk sensitive example is the use of fluorescence yield oxygen K near edge x-ray spectroscopy as a method to determine the hole state density of high Tc materials.

  18. Ultra-soft x-ray absorption spectroscopy: A bulk and surface probe of materials

    SciTech Connect

    Fischer, D.A.; Mitchell, G.E.; Dekoven, B.M.; Yeh, A.T.; Gland, J.L.; Moodenbaugh, A.R.

    1993-06-01

    Direct comparisons between surface and bulk of diverse materials can be made by simultaneous electron yield (5 nm depth sensitivity) and fluorescence yield (200 nm) ultra soft x-ray absorption spectroscopy measurements utilizing a rapid sample interchange apparatus. For example the orientations of functional groups have been characterized at and near the surface of a series of model polymeric materials highlighting the chemical and molecular sensitivity of ultra soft x-ray absorption spectroscopy. In addition we discuss a bulk sensitive use of fluorescence yield to non destructively study a buried metal polymer interface. A second bulk sensitive example is the use of fluorescence yield oxygen K near edge x-ray spectroscopy as a method to determine the hole state density of high Tc materials.

  19. Search for correlated UV and x ray absorption of NGC 3516

    NASA Technical Reports Server (NTRS)

    Martin, Christopher; Halpern, Jules P.; Kolman, Michiel

    1991-01-01

    NGC 3516, a low-luminosity Seyfert galaxy, is one of a small fraction of Seyfert galaxies that exhibit broad absorption in a resonance line. In order to determine whether the UV and x ray absorption in NGC 3516 are related, 5 IUE observations were obtained, quasi-simultaneously with 4 Ginga observations. The results are presented and discussed. The following subject areas are covered: short-term UV variability; emission lines; galactic absorption lines; the C IV, N V, and Si IV absorption features; lower limit on the carbon column density; estimate of the distance from the absorber to the continuum source; variability in the continuum and absorption; a comparison with BAL QSO's; and the x ray-UV connection.

  20. THE LONG-TERM X-RAY VARIABILITY OF BROAD ABSORPTION LINE QUASARS

    SciTech Connect

    Saez, C.; Brandt, W. N.; Garmire, G. P.; Gallagher, S. C.; Bauer, F. E.

    2012-11-01

    We analyze the long-term (rest-frame 3-30 yr) X-ray variability of 11 broad absorption line (BAL) quasars, mainly to constrain the variation properties of the X-ray absorbing shielding gas that is thought to play a critical role in BAL wind launching. Our BAL quasar sample has coverage with multiple X-ray observatories including Chandra, XMM-Newton, BeppoSAX, ASCA, ROSAT, and Einstein; 3-11 observations are available for each source. For seven of the eleven sources we have obtained and analyzed new Chandra observations suitable for searching for any strong X-ray variability. We find highly significant X-ray variability in three sources (PG 1001+054, PG 1004+130, and PG 2112+059). The maximum observed amplitude of the 2-8 keV variability is a factor of 3.8 {+-} 1.3, 1.5 {+-} 0.2, and 9.9 {+-} 2.3 for PG 1001+054, PG 1004+130, and PG 2112+059, respectively, and these sources show detectable variability on rest-frame timescales down to 5.8, 1.4, and 0.5 yr. For PG 1004+130 and PG 2112+059 we also find significant X-ray spectral variability associated with the flux variability. Considering our sample as a whole, we do not find that BAL quasars exhibit exceptional long-term X-ray variability when compared to the quasar population in general. We do not find evidence for common strong changes in the shielding gas owing to physical rearrangement or accretion-disk rotation, although some changes are found; this has implications for modeling observed ultraviolet BAL variability. Finally, we report for the first time an X-ray detection of the highly polarized and well-studied BAL quasar IRAS 14026+4341 in its new Chandra observation.

  1. Microsecond X-ray Absorption Spectroscopy Identification of Co(I) Intermediates in Cobaloxime-Catalyzed Hydrogen Evolution.

    PubMed

    Smolentsev, Grigory; Cecconi, Bianca; Guda, Alexander; Chavarot-Kerlidou, Murielle; van Bokhoven, Jeroen A; Nachtegaal, Maarten; Artero, Vincent

    2015-10-19

    Rational development of efficient photocatalytic systems for hydrogen production requires understanding the catalytic mechanism and detailed information about the structure of intermediates in the catalytic cycle. We demonstrate how time-resolved X-ray absorption spectroscopy in the microsecond time range can be used to identify such intermediates and to determine their local geometric structure. This method was used to obtain the solution structure of the Co(I) intermediate of cobaloxime, which is a non-noble metal catalyst for solar hydrogen production from water. Distances between cobalt and the nearest ligands including two solvent molecules and displacement of the cobalt atom out of plane formed by the planar ligands have been determined. Combining in situ X-ray absorption and UV/Vis data, we demonstrate how slight modification of the catalyst structure can lead to the formation of a catalytically inactive Co(I) state under similar conditions. Possible deactivation mechanisms are discussed. PMID:26388205

  2. Insights into the mechanism of X-ray-induced disulfide-bond cleavage in lysozyme crystals based on EPR, optical absorption and X-ray diffraction studies

    PubMed Central

    Sutton, Kristin A.; Black, Paul J.; Mercer, Kermit R.; Garman, Elspeth F.; Owen, Robin L.; Snell, Edward H.; Bernhard, William A.

    2013-01-01

    Electron paramagnetic resonance (EPR) and online UV–visible absorption microspectrophotometry with X-ray crystallography have been used in a complementary manner to follow X-ray-induced disulfide-bond cleavage. Online UV–visible spectroscopy showed that upon X-irradiation, disulfide radicalization appeared to saturate at an absorbed dose of approximately 0.5–0.8 MGy, in contrast to the saturating dose of ∼0.2 MGy observed using EPR at much lower dose rates. The observations suggest that a multi-track model involving product formation owing to the interaction of two separate tracks is a valid model for radiation damage in protein crystals. The saturation levels are remarkably consistent given the widely different experimental parameters and the range of total absorbed doses studied. The results indicate that even at the lowest doses used for structural investigations disulfide bonds are already radicalized. Multi-track considerations offer the first step in a comprehensive model of radiation damage that could potentially lead to a combined computational and experimental approach to identifying when damage is likely to be present, to quantitate it and to provide the ability to recover the native unperturbed structure. PMID:24311579

  3. LISA: the Italian CRG beamline for x-ray Absorption Spectroscopy at ESRF

    NASA Astrophysics Data System (ADS)

    d'Acapito, F.; Trapananti, A.; Puri, A.

    2016-05-01

    LISA is the acronym of Linea Italiana per la Spettroscopia di Assorbimento di raggi X (Italian beamline for X-ray Absorption Spectroscopy) and is the upgrade of the former GILDA beamline installed on the BM08 bending magnet port of European Synchrotron Radiation Facility (ESRF). Within this contribution a full description of the project is provided.

  4. Application of x-ray absorption spectroscopy to the study of corrosion and inhibition

    SciTech Connect

    Davenport, A.J.; Isaacs, H.S.

    1991-01-01

    X-ray absorption spectroscopy is a powerful technique for determination of valency and coordination. Measurements can be made in air or in situ under electrochemical control. The technique will be described and its application to the analysis of passive oxide films, corrosion products, and inhibitors will be reviewed.

  5. X-ray absorption spectroscopic characterization of a cytochrome P450 compound II derivative

    PubMed Central

    Newcomb, Martin; Halgrimson, James A.; Horner, John H.; Wasinger, Erik C.; Chen, Lin X.; Sligar, Stephen G.

    2008-01-01

    The cytochrome P450 enzyme CYP119, its compound II derivative, and its nitrosyl complex were studied by iron K-edge x-ray absorption spectroscopy. The compound II derivative was prepared by reaction of the resting enzyme with peroxynitrite and had a lifetime of ≈10 s at 23°C. The CYP119 nitrosyl complex was prepared by reaction of the enzyme with nitrogen monoxide gas or with a nitrosyl donor and was stable at 23°C for hours. Samples of CYP119 and its derivatives were studied by x-ray absorption spectroscopy at temperatures below 140 (K) at the Advanced Photon Source of Argonne National Laboratory. The x-ray absorption near-edge structure spectra displayed shifts in edge and pre-edge energies consistent with increasing effective positive charge on iron in the series native CYP119 < CYP119 nitrosyl complex < CYP119 compound II derivative. Extended x-ray absorption fine structure spectra were simulated with good fits for k = 12 Å−1 for native CYP119 and k = 13 Å−1 for both the nitrosyl complex and the compound II derivative. The important structural features for the compound II derivative were an iron-oxygen bond length of 1.82 Å and an iron-sulfur bond length of 2.24 Å, both of which indicate an iron-oxygen single bond in a ferryl-hydroxide, FeIVOH, moiety. PMID:18174331

  6. Characterization of the X-ray absorption in the Galactic ISM

    NASA Astrophysics Data System (ADS)

    Gatuzz, E.; García, J.; Kallman, T.; Mendoza, C.

    2016-06-01

    The physical conditions of the Galactic interstellar medium (ISM) can be studied in detail through the high-resolution X-ray spectroscopy provided by the grating instruments in both Chandra and XMM-Newton. Using an X-ray source, which acts as a lamp, one can analyze the absorption features that are imprinted in the spectra by the gas located between the observer and the X-ray source, which offers the opportunity to study physical properties of the ISM such as ionization degree, column densities, and elemental abundances. We present a detailed analysis of the H, O, Ne, and Fe absorption in the X-ray spectra of 24 bright galactic sources obtained with the Chandra and XMM-Newton observatories. Implementing our new absorption model ISMabs, we have measured column densities, ionization fractions, and abundances for H, O, Ne, and Fe in the direction of each source. We find that the column densities tend to increase with source distance and decrease with galactic latitude, while the ionization fractions and abundances are mostly constant along every line of sight. Finally, we found that molecules and grains are not a major contributor to the absorption features in the O K-edge wavelength region.

  7. Discovery of Broad Soft X-ray Absorption Lines from the Quasar Wind in PDS 456

    NASA Astrophysics Data System (ADS)

    Reeves, J. N.; Braito, V.; Nardini, E.; Behar, E.; O’Brien, P. T.; Tombesi, F.; Turner, T. J.; Costa, M. T.

    2016-06-01

    High-resolution soft X-ray spectroscopy of the prototype accretion disk wind quasar, PDS 456, is presented. Here, the XMM-Newton reflection grating spectrometer spectra are analyzed from the large 2013–2014 XMM-Newton campaign, consisting of five observations of approximately 100 ks in length. During the last observation (OBS. E), the quasar is at a minimum flux level, and broad absorption line (BAL) profiles are revealed in the soft X-ray band, with typical velocity widths of {σ }{{v}}˜ {{10,000}} km s‑1. During a period of higher flux in the third and fourth observations (OBS. C and D, respectively), a very broad absorption trough is also present above 1 keV. From fitting the absorption lines with models of photoionized absorption spectra, the inferred outflow velocities lie in the range ˜ 0.1{--}0.2c. The absorption lines likely originate from He and H-like neon and L-shell iron at these energies. A comparison with earlier archival data of PDS 456 also reveals a similar absorption structure near 1 keV in a 40 ks observation in 2001, and generally the absorption lines appear most apparent when the spectrum is more absorbed overall. The presence of the soft X-ray BALs is also independently confirmed by an analysis of the XMM-Newton EPIC spectra below 2 keV. We suggest that the soft X-ray absorption profiles could be associated with a lower ionization and possibly clumpy phase of the accretion disk wind, where the latter is known to be present in this quasar from its well-studied iron K absorption profile and where the wind velocity reaches a typical value of 0.3c.

  8. High Resolution Spectroscopy of X-ray Quasars: Searching for the X-ray Absorption from the Warm-Hot Intergalactic Medium

    NASA Technical Reports Server (NTRS)

    Fang, Taotao; Canizares, Claude R.; Marshall, Herman L.

    2004-01-01

    We present a survey of six low to moderate redshift quasars with Chandra and XMM-Newton. The primary goal is to search for the narrow X-ray absorption lines produced by highly ionized metals in the Warm-Hot Intergalactic Medium. All the X-ray spectra can be well fitted by a power law with neutral hydrogen absorption. Only one feature is detected at above 3-sigma level in all the spectra, which is consistent with statistic fluctuation. We discuss the implications in our understanding of the baryon content of the universe. We also discuss the implication of the non-detection of the local (z approx. 0) X-ray absorption.

  9. X-ray absorption spectroscopy study of prototype chemical systems: Theory vs. experiment

    NASA Astrophysics Data System (ADS)

    Schwartz, Craig Philip

    Understanding the details of the intensities and spectral shapes of x-ray absorption spectra is a long-standing problem in chemistry and physics. Here, I present detailed studies of x-ray absorption for prototypical liquids, solids and gases with the goal of enhancing our general understanding of core-level spectroscopy via comparisons of modern theory and experiment. In Chapter 2, I investigate the importance of quantum motions in the x-ray absorption spectra of simple gases. It is found that rare fluctuations in atomic positions can be a cause of features in the spectra of gaseous molecules. In Chapter 3, I explore a novel quantization scheme for the excited and ground state potential surfaces for an isolated nitrogen molecule. This allows for the explicit calculation of the "correct" transition energies and peak widths (i.e. without any adjustable parameters). In Chapter 4, the importance of nuclear motion in molecular solids is investigated for glycine. We find that the inclusion of these motions permits the spectrum to be accurately calculated without any additional adjustable parameters. In Chapter 5, I provide a detailed study of the hydroxide ion solvated in water. There has been recent controversy as to how hydroxide is solvated, with two principal models invoked. I show that some of the computational evidence favoring one model of solvation over the other has been either previously obtained with inadequate precision or via a method that is systematically biased. In Chapter 6, the measured and computed x-ray absorption spectra of pyrrole in both the gas phase and when solvated by water are compared. We are able to accurately predict the spectra in both cases. In Chapter 7, the measured x-ray absorption of a series of highly charged cationic salts (YBr3, CrCl3, SnCl4 , LaCl3 and InCl3) solvated in water are presented and explained. In Chapter 8, the measured x-ray absorption spectrum at the nitrogen K-edge of aqueous triglycine is presented, including

  10. Ultraviolet/X-ray Variability and the Extended X-ray Emission of the Radio-loud Broad Absorption Line Quasar PG 1004+130

    NASA Astrophysics Data System (ADS)

    Scott, A. E.; Brandt, W. N.; Miller, B. P.; Luo, B.; Gallagher, S. C.

    2015-06-01

    We present the results of recent Chandra, XMM-Newton, and Hubble Space Telescope observations of the radio-loud (RL), broad absorption line (BAL) quasar PG 1004+130. We compare our new observations to archival X-ray and UV data, creating the most comprehensive, high signal-to-noise, multi-epoch, spectral monitoring campaign of a RL BAL quasar to date. We probe for variability of the X-ray absorption, the UV BAL, and the X-ray jet, on month-year timescales. The X-ray absorber has a low column density of {N}H=8× {10}20-4× {10}21 {{cm}}-2 when it is assumed to be fully covering the X-ray emitting region, and its properties do not vary significantly between the four observations. This suggests that the observed absorption is not related to the typical “shielding gas” commonly invoked in BAL quasar models, but is likely due to material further from the central black hole. In contrast, the C iv BAL shows strong variability. The equivalent width (EW) in 2014 is {EW}=11.24+/- 0.56 \\AA, showing a fractional increase of Δ {EW}/< {EW}> =1.16+/- 0.11 from the 2003 observation, 3183 days earlier in the rest-frame. This places PG 1004+130 among the most highly variable BAL quasars. By combining Chandra observations we create an exposure that is 2.5 times deeper than studied previously, with which to investigate the nature of the X-ray jet and extended diffuse X-ray emission. An X-ray knot, likely with a synchrotron origin, is detected in the radio jet ˜ 8\\prime\\prime (30 kpc) from the central X-ray source with a spatial extent of ˜ 4\\prime\\prime (15 kpc). No similar X-ray counterpart to the counterjet is detected. Asymmetric, non-thermal diffuse X-ray emission, likely due to inverse Compton scattering of Cosmic Microwave Background photons, is also detected.

  11. Experimental investigation of X-ray spectral absorption coefficients in heated Al and Ge on the Iskra-5 laser facility

    SciTech Connect

    Bondarenko, S V; Garanin, Sergey G; Zhidkov, N V; Pinegin, A V; Suslov, N A

    2012-01-31

    We set forth the data of experimental investigation of X-ray spectral absorption coefficients in the 1.1 - 1.6 keV photon energy range for Al and Ge specimens bulk heated by soft X-ray radiation. Two experimental techniques are described: with the use of one facility channel and the heating of specimens by the X-ray radiation from a plane burnthrough target, as well as with the use of four channels and the heating by the radiation from two cylindrical targets with internal input of laser radiation. The X-ray radiation absorption coefficients were studied by way of transmission absorption spectroscopy using backlighting X-ray radiation from a point source. The results of investigation of X-ray spectral absorption coefficients on the 1s - 2p transitions in Al atoms and the 2p - 3d transitions in Ge atoms are presented.

  12. X-RAY EMISSION AND ABSORPTION FEATURES DURING AN ENERGETIC THERMONUCLEAR X-RAY BURST FROM IGR J17062-6143

    SciTech Connect

    Degenaar, N.; Miller, J. M.; Wijnands, R.; Altamirano, D.; Fabian, A. C.

    2013-04-20

    Type-I X-ray bursts are thermonuclear explosions occurring in the surface layers of accreting neutron stars. These events are powerful probes of the physics of neutron stars and their surrounding accretion flow. We analyze a very energetic type-I X-ray burst from the neutron star low-mass X-ray binary IGR J17062-6143 that was detected with Swift on 2012 June 25. The light curve of the {approx_equal}18 minute long X-ray burst tail shows an episode of {approx_equal}10 minutes during which the intensity is strongly fluctuating by a factor of {approx_equal}3 above and below the underlying decay trend on a timescale of seconds. The X-ray spectrum reveals a highly significant emission line around {approx_equal}1 keV, which can be interpreted as an Fe-L shell line caused by the irradiation of cold gas. We also detect significant absorption lines and edges in the Fe-K band, which are strongly suggestive of the presence of hot, highly ionized gas along the line of sight. None of these features are present in the persistent X-ray spectrum of the source. The timescale of the strong intensity variations, the velocity width of the Fe-L emission line (assuming Keplerian motion), and photoionization modeling of the Fe-K absorption features each independently point to gas at a radius of {approx_equal} 10{sup 3} km as the source of these features. The unusual X-ray light curve and spectral properties could have plausibly been caused by a disruption of the accretion disk due to the super-Eddington fluxes reached during the X-ray burst.

  13. Surface extended x-ray absorption fine structure of low-Z absorbates using fluorescence detection

    SciTech Connect

    Stoehr, J.; Kollin, E.B.; Fischer, D.A.; Hastings, J.B.; Zaera, F.; Sette, F.

    1985-05-01

    Comparison of x-ray fluorescence yield (FY) and electron yield surface extended x-ray absorption fine structure spectra above the S K-edge for c(2 x 2) S on Ni(100) reveals an order of magnitude higher sensitivity of the FY technique. Using FY detection, thiophene (C/sub 4/H/sub 4/S) chemisorption on Ni(100) is studied with S coverages down to 0.08 monolayer. The molecule dissociates at temperatures as low as 100K by interaction with fourfold hollow Ni sites. Blocking of these sites by oxygen leaves the molecule intact.

  14. Thermal Expansion Behaviour of Silver Examined by Extended X-Ray Absorption Fine Structure Spectroscopy

    SciTech Connect

    Dubiel, M.; Chasse, A.; Haug, J.; Schneider, R.; Kruth, H.

    2007-02-02

    EXAFS (extended X-ray absorption fine structure) investigations are reported concerning the thermal expansion behaviour of silver in an extended range of temperature from 10 K to about 950 K measured in transmission mode. Both the ratio method and an EXAFS fitting procedure were applied to reveal the temperature dependence of EXAFS parameters. Models based on quantum and classical thermodynamic perturbation theory have been used to interpret experimental data and compared to XRD (X-ray diffraction) results of bulk silver material. The description of thermodynamic data of thermal expansion of silver in the complete range of temperature by EXAFS Spectroscopy was successful by first calculations using third order quantum perturbation theory.

  15. Observing heme doming in myoglobin with femtosecond X-ray absorption spectroscopy

    DOE PAGESBeta

    Levantino, M.; Lemke, H. T.; Schirò, G.; Glownia, M.; Cupane, A.; Cammarata, M.

    2015-07-01

    We report time-resolved X-ray absorption measurements after photolysis of carbonmonoxy myoglobin performed at the LCLS X-ray free electron laser with nearly 100 fs (FWHM) time resolution. Data at the Fe K-edge reveal that the photoinduced structural changes at the heme occur in two steps, with a faster (~70 fs) relaxation preceding a slower (~400 fs) one. We tentatively attribute the first relaxation to a structural rearrangement induced by photolysis involving essentially only the heme chromophore and the second relaxation to a residual Fe motion out of the heme plane that is coupled to the displacement of myoglobin F-helix.

  16. Picosecond-resolved X-ray absorption spectroscopy at low signal contrast using a hard X-ray streak camera

    SciTech Connect

    Adams, Bernhard W.; Rose-Petruck, Christoph; Jiao, Yishuo

    2015-06-24

    A picosecond-resolving hard-X-ray streak camera has been in operation for several years at Sector 7 of the Advanced Photon Source (APS). Several upgrades have been implemented over the past few years to optimize integration into the beamline, reduce the timing jitter, and improve the signal-to-noise ratio. These include the development of X-ray optics for focusing the X-rays into the sample and the entrance slit of the streak camera, and measures to minimize the amount of laser light needed to generate the deflection-voltage ramp. For the latter, the photoconductive switch generating the deflection ramp was replaced with microwave power electronics. With these, the streak camera operates routinely at 88 MHz repetition rate, thus making it compatible with all of the APS fill patterns including use of all the X-rays in the 324-bunch mode. Sample data are shown to demonstrate the performance.

  17. Phase-dependent absorption features in X-ray spectra of XDINSs

    NASA Astrophysics Data System (ADS)

    Borghese, A.; Rea, N.

    2016-06-01

    A detailed pulse phase spectroscopy using all the available XMM-Newton observations of X-ray dim isolated neutron stars (XDINSs) have revealed the presence of narrow and strongly phase-dependent absorption X-ray features. The first discovered was in the X-ray spectrum of the nearby XDINS RX J0720.4-3125. The line seems to be stable in time over a timespan of 12 years and is present in 20% of the pulsar rotation. Because of its narrow width and its strong dependency on the rotational phase, the spectral line is probably due to proton cyclotron absorption in a ˜10^{14} G confined magnetic structure (with a field strength about 7 times the dipolar field of this pulsar). Performing the same analysis to all archival XDINS data, a new possible candidate was found in the X-ray spectrum of RX J1308.6+2127. This absorption feature shows the same phase dependency and energy as the first one, revealing the presence of a high-B structure close to the stellar surface. This result supports the proposed scenario of XDINSs being aged magnetars, having still a strong non-dipolar crustal B-field component.

  18. X-RAY ABSORPTION SPECTROSCOPY OF YB3+-DOPED OPTICAL FIBERS

    SciTech Connect

    Citron, Robert; Kropf, A.J.

    2008-01-01

    Optical fibers doped with Ytterbium-3+ have become increasingly common in fiber lasers and amplifiers. Yb-doped fibers provide the capability to produce high power and short pulses at specific wavelengths, resulting in highly effective gain media. However, little is known about the local structure, distribution, and chemical coordination of Yb3+ in the fibers. This information is necessary to improve the manufacturing process and optical qualities of the fibers. Five fibers doped with Yb3+ were studied using Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy and X-ray Absorption Near Edge Spectroscopy (XANES), in addition to Yb3+ mapping. The Yb3+ distribution in each fiber core was mapped with 2D and 1D intensity scans, which measured X-ray fluorescence over the scan areas. Two of the five fibers examined showed highly irregular Yb3+ distributions in the core center. In four of the five fibers Yb3+ was detected outside of the given fiber core dimensions, suggesting possible Yb3+ diffusion from the core, manufacturing error, or both. X-ray absorption spectroscopy (XAS) analysis has so far proven inconclusive, but did show that the fibers had differing EXAFS spectra. The Yb3+ distribution mapping proved highly useful, but additional modeling and examination of fiber preforms must be conducted to improve XAS analysis, which has been shown to have great potential for the study of similar optical fi bers.

  19. New Approaches for Correction of Interlayer Absorption Effects in X-ray Fluorescence Imaging of Paintings.

    PubMed

    Wróbel, Paweł M; Frączek, Piotr; Lankosz, Marek

    2016-02-01

    The X-ray fluorescence imaging technique allows not only the imaging itself but also the identification of the hidden paint layers what makes it much more versatile as compared with X-ray radiography. One of the main disadvantages of the former method is the fact that the characteristic X-rays from the deeper paint layers are absorbed in the covering layers. This effect is manifested by some artifacts that impede a proper interpretation of the acquired images. In this work, it is shown that the methodology for correction of the interlayer absorption effects can be extended to the case of polychromatic excitation. Additionally, a new approach for determination of the optimal correction parameters has also been presented. The methodology was verified using either the test painting or the mock-up painting both measured with a table-top micro-XRF setup. PMID:26708500

  20. The effects of dust scattering on high-resolution X-ray absorption edge structure

    NASA Astrophysics Data System (ADS)

    Corrales, Lia; Garcia, Javier; Wilms, Joern; Baganoff, Frederick K.

    2016-04-01

    In high resolution X-ray spectroscopy, dust scattering significantly enhances the total extinction optical depth and alters the shape of photoelectric absorption edges. This effect is modulated by the dust grain size distribution, spatial location along the line of sight, and the imaging resolution of the X-ray telescope. We focus in particular on the Fe L-edge at 0.7 keV, fitting a template for the total extinction to the high resolution spectrum of three X-ray binaries from the Chandra archive: GX 9+9, XTE J1817-330, and Cyg X-1. In cases where dust is intrinsic to the source, a covering factor based on the angular extent of the dusty material must be applied to the extinction curve, regardless of imaging resolution. We discuss the various astrophysical cases in which scattering effects need to be taken into account.

  1. Capturing molecular structural dynamics by 100 ps time-resolved X-ray absorption spectroscopy.

    PubMed

    Sato, Tokushi; Nozawa, Shunsuke; Ichiyanagi, Kohei; Tomita, Ayana; Chollet, Matthieu; Ichikawa, Hirohiko; Fujii, Hiroshi; Adachi, Shin Ichi; Koshihara, Shin Ya

    2009-01-01

    An experimental set-up for time-resolved X-ray absorption spectroscopy with 100 ps time resolution at beamline NW14A at the Photon Factory Advanced Ring is presented. The X-ray positional active feedback to crystals in a monochromator combined with a figure-of-merit scan of the laser beam position has been utilized as an essential tool to stabilize the spatial overlap of the X-ray and laser beams at the sample position. As a typical example, a time-resolved XAFS measurement of a photo-induced spin crossover reaction of the tris(1,10-phenanthrorine)iron(II) complex in water is presented. PMID:19096182

  2. Gas cell for in situ soft X-ray transmission-absorption spectroscopy of materials

    SciTech Connect

    Drisdell, W. S.; Kortright, J. B.

    2014-07-15

    A simple gas cell design, constructed primarily from commercially available components, enables in situ soft X-ray transmission-absorption spectroscopy of materials in contact with gas at ambient temperature. The cell has a minimum X-ray path length of 1 mm and can hold gas pressures up to ∼300 Torr, and could support higher pressures with simple modifications. The design enables cycling between vacuum and gas environments without interrupting the X-ray beam, and can be fully sealed to allow for measurements of air-sensitive samples. The cell can attach to the downstream port of any appropriate synchrotron beamline, and offers a robust and versatile method for in situ measurements of certain materials. The construction and operation of the cell are discussed, as well as sample preparation and proper spectral analysis, illustrated by examples of spectral measurements. Potential areas for improvement and modification for specialized applications are also mentioned.

  3. Density of BCR-2 basalt glass at high pressure by X-ray Absorption Microtomography

    NASA Astrophysics Data System (ADS)

    Clark, A. N.; Lesher, C. E.; Gaudio, S. J.; Yamada, A.; Wang, Y.

    2009-12-01

    Improved understanding of compressibility and thermal expansion and their integral properties, density and volume, of basaltic liquids are important for modeling the thermodynamics of partial melting and crystallization, and melt migration in the Earth’s crust and mantle. We are using X-ray absorption in conjunction with microtomography to determine density of basalt glass/melt at high pressures from the linear attenuation coefficient of voxels calibrated using internal calibration standards at monochromatic energy. Experiments are conducted with the rotating anvil apparatus on the 13-BM-D beamline at the Advanced Photon Source, Argonne National Laboratory in an opposing anvil (Drickamer) assembly with 4 mm truncations and 20o taper. The sample and standards are contained within a single crystal diamond sleeve capped with Mo lids inserted into a graphite box-type heater with Mo leads and surrounded by pyrophillite, zirconia and a composite boron epoxy-diamond epoxy--pyrophillite gasket. Pressure is determined by using energy dispersive X-ray diffraction of MgO and Au contained within the capsule. Temperature is controlled to within ±25 oC by regulating power to the heater based on prior calibration. The density of USGS standard BCR-2 (Columbia River Basalt) glass is determined by this technique up to 3 GPa at room temperature giving a compressibility (Ko) for the glass of 70 ±5 GPa, assuming K’= 4. The cell was successfully heated to 900 oC at 1 GPa with tomographic data sets collected at 200 oC temperature intervals. The variation in density with temperature gives a thermal expansion for BCR-2 glass of 3x10-5 K-1. Success in performing microtomography under simultaneous high pressure-temperature conditions will enable this technique to be extended to the melting interval for basalt at elevated pressures in the near future.

  4. X-Ray Absorption Toward the Einstein Ring Source PKS 1830-211

    NASA Technical Reports Server (NTRS)

    Mathur, Smita; Nair, Sunita

    1997-01-01

    PKS 1830-211 is an unusually radio-loud gravitationally lensed quasar. In the radio spectrum, the system appears as two compact, dominant features surrounded by relatively extended radio emission that forms an Einstein ring. As the line of sight to it passes close to our Galactic center, PKS 1830-211 has not been detected in wave bands other than the radio and X-ray so far. Here we present X-ray data of PKS 1830-211 observed with ROSAT Position Sensitive Proportional Counter. The X-ray spectrum shows that absorption in excess of the Galactic contribution is highly likely, which at the redshift of the lensing galaxy (z(sub t)=0.886) corresponds to N(sub H)=3.5((sup 0.6)(sub -0.5))x10(exp 22) atoms sq cm. The effective optical extinction is large, A(sub V)(observed) is greater than or approximately 5.8. When corrected for this additional extinction, the two-point optical to X-ray slope alpha(sub ox) of PKS 1830-211 lies just within the observed range of quasars. It is argued here that both compact images must be covered by the X-ray absorber(s) that we infer to be the lensing galaxy (galaxies). The dust-to-gas ratio along the line of sight within the lensing galaxy is likely to be somewhat larger than for our Galaxy.

  5. Analytic model of energy-absorption response functions in compound X-ray detector materials.

    PubMed

    Yun, Seungman; Kim, Ho Kyung; Youn, Hanbean; Tanguay, Jesse; Cunningham, Ian A

    2013-10-01

    The absorbed energy distribution (AED) in X-ray imaging detectors is an important factor that affects both energy resolution and image quality through the Swank factor and detective quantum efficiency. In the diagnostic energy range (20-140 keV), escape of characteristic photons following photoelectric absorption and Compton scatter photons are primary sources of absorbed-energy dispersion in X-ray detectors. In this paper, we describe the development of an analytic model of the AED in compound X-ray detector materials, based on the cascaded-systems approach, that includes the effects of escape and reabsorption of characteristic and Compton-scatter photons. We derive analytic expressions for both semi-infinite slab and pixel geometries and validate our approach by Monte Carlo simulations. The analytic model provides the energy-dependent X-ray response function of arbitrary compound materials without time-consuming Monte Carlo simulations. We believe this model will be useful for correcting spectral distortion artifacts commonly observed in photon-counting applications and optimal design and development of novel X-ray detectors. PMID:23744671

  6. Determination of the texture of arrays of aligned carbon nanotubes from the angular dependence of the X-ray emission and X-ray absorption spectra

    SciTech Connect

    Okotrub, A. V. Belavin, V. V.; Bulusheva, L. G.; Gusel'nikov, A. V.; Kudashov, A. G.; Vyalikh, D. V.; Molodtsov, S. L.

    2008-09-15

    The properties of materials containing carbon nanotubes depend on the degree of alignment and the internal structure of nanotubes. It is shown that the degree of misorientation of carbon nanotubes in samples can be evaluated from the measurements of the angular dependences of the carbon X-ray emission and carbon X-ray absorption spectra. The CK{sub {alpha}} emission and CK X-ray absorption spectra of the array of multiwalled carbon nanotubes synthesized by catalytic thermolysis of a mixture of fullerene and ferrocene are measured. A comparison of the calculated model dependences of the relative intensities of the {pi} and {sigma} bands in the spectra with the experimental results makes it possible to evaluate the degree of misorientation of nanotubes in the sample and their internal texture.

  7. X-ray absorption spectroscopy on the basis of hybrid X-pinch radiation

    NASA Astrophysics Data System (ADS)

    Tilikin, I. N.; Shelkovenko, T. A.; Pikuz, S. A.; Knapp, P. F.; Hammer, D. A.

    2015-07-01

    Results of experiments on X-ray absorption spectroscopy carried out at the BIN (270 kA, 100 ns) and XP (450 kA, 45 ns) facilities are presented. Continuum radiation of a Mo hybrid X-pinch was used as probing radiation, against which absorption lines of the plasma of exploded Al wires placed in the return current circuit of a hybrid X-pinch, as well as in a two- and four-wire array, were observed. The experiments have demonstrated that the radiation of a hybrid X-pinch hot spot can be used as probing radiation for X-ray absorption spectroscopy and that, in many parameters, such a source surpasses those on the basis of laser-produced plasma. The plasma parameters in arrays made of two and four Al wires were studied experimentally.

  8. Soft X-Ray Absorption Spectroscopy of High-Abrasion-Furnace Carbon Black

    NASA Astrophysics Data System (ADS)

    Muramatsu, Yasuji; Harada, Ryusuke; Gullikson, Eric M.

    2007-02-01

    The soft x-ray absorption spectra of high-abrasion-furnace carbon black were measured to obtain local-structure/chemical-states information of the primary particles and/or crystallites. The soft x-ray absorption spectral features of carbon black represent broader π* and σ* peak structures compared to highly oriented pyrolytic graphite (HOPG). The subtracted spectra between the carbon black and HOPG, (carbon black) — (HOPG), show double-peak structures on both sides of the π* peak. The lower-energy peak, denoted as the "pre-peak", in the subtracted spectra and the π*/σ* peak intensity ratio in the absorption spectra clearly depend on the specific surface area by nitrogen adsorption (NSA). Therefore, it is concluded that the pre-peak intensity and the π*/σ* ratio reflect the local graphitic structure of carbon black.

  9. X-ray absorption spectroscopy on the basis of hybrid X-pinch radiation

    SciTech Connect

    Tilikin, I. N. Shelkovenko, T. A.; Pikuz, S. A.; Knapp, P. F.; Hammer, D. A.

    2015-07-15

    Results of experiments on X-ray absorption spectroscopy carried out at the BIN (270 kA, 100 ns) and XP (450 kA, 45 ns) facilities are presented. Continuum radiation of a Mo hybrid X-pinch was used as probing radiation, against which absorption lines of the plasma of exploded Al wires placed in the return current circuit of a hybrid X-pinch, as well as in a two- and four-wire array, were observed. The experiments have demonstrated that the radiation of a hybrid X-pinch hot spot can be used as probing radiation for X-ray absorption spectroscopy and that, in many parameters, such a source surpasses those on the basis of laser-produced plasma. The plasma parameters in arrays made of two and four Al wires were studied experimentally.

  10. X-ray absorption study of the electronic structure of Mn-doped amorphous Si

    SciTech Connect

    Arenholz, Elke; Zeng, Li; Huegel, A.; Helgren, E.; Hellman, F.; Piamonteze, C.; Arenholz, E.

    2008-03-08

    The electronic structure of Mn in amorphous Si (a-Mn{sub x}Si{sub 1?x}) is studied by X-ray absorption spectroscopy at the Mn L{sub 3,2} edges for x = 0.005-0.18. Except the x = 0.005 sample, which shows a slight signature of Mn{sup 2+} atomic multiplets associated with a local Mn moment, all samples have broad and featureless L{sub 3,2} absorption peaks, corresponding to an itinerant state for all 3d electrons. The broad X-ray absorption spectra exclude the possibility of a localized 3d moment and explain the unexpectedly quenched Mn moment in this magnetically-doped amorphous semiconductor. Such a fully delocalized d state of Mn dopant in Si has not been previously suggested.

  11. Complex X-ray Absorption and the Fe K(alpha) Profile in NGC 3516

    NASA Technical Reports Server (NTRS)

    Turner, T. J.; Kraemer, S. B.; George, I. M.; Reeves, J. N.; Botorff, M. C.

    2004-01-01

    We present data from simultaneous Chandra, XMM-Newton and BeppoSAX observations of the Seyfert 1 galaxy NGC 3516, taken during 2001 April and November. We have investigated the nature of the very flat observed X-ray spectrum. Chandra grating data show the presence of X-ray absorption lines, revealing two distinct components of the absorbing gas, one which is consistent with our previous model of the UV/X-ray absorber while the other, which is outflowing at a velocity of approximately 1100 kilometers per second, has a larger column density and is much more highly ionized. The broad-band spectral characteristics of the X-ray continuum observed with XMM during 2001 April, reveal the presence of a third layer of absorption consisting of a very large column (approximately 2.5 x 10(exp 23) per square centimeter) of highly ionized gas with a covering fraction approximately 50%. This low covering fraction suggests that the absorber lies within a few 1t-days of the X-ray source and/or is filamentary in structure. Interestingly, these absorbers are not in thermal equilibrium with one another. The two new components are too highly ionized to be radiatively accelerated, which we suggest is evidence for a hydromagnetic origin for the outflow. Applying our model to the November dataset, we can account for the spectral variability primarily by a drop in the ionization states of the absorbers, as expected by the change in the continuum flux. When this complex absorption is accounted for we find the underlying continuum to be typical of Seyfert 1 galaxies. The spectral curvature attributed to the high column absorber, in turn, reduces estimates of the flux and extent of any broad Fe emission line from the accretion disk.

  12. Tracking ink composition on Herculaneum papyrus scrolls: quantification and speciation of lead by X-ray based techniques and Monte Carlo simulations.

    PubMed

    Tack, Pieter; Cotte, Marine; Bauters, Stephen; Brun, Emmanuel; Banerjee, Dipanjan; Bras, Wim; Ferrero, Claudio; Delattre, Daniel; Mocella, Vito; Vincze, Laszlo

    2016-01-01

    The writing in carbonized Herculaneum scrolls, covered and preserved by the pyroclastic events of the Vesuvius in 79 AD, was recently revealed using X-ray phase-contrast tomography, without the need of unrolling the sensitive scrolls. Unfortunately, some of the text is difficult to read due to the interference of the papyrus fibers crossing the written text vertically and horizontally. Recently, lead was found as an elemental constituent in the writing, rendering the text more clearly readable when monitoring the lead X-ray fluorescence signal. Here, several hypotheses are postulated for the origin and state of lead in the papyrus writing. Multi-scale X-ray fluorescence micro-imaging, Monte Carlo quantification and X-ray absorption microspectroscopy experiments are used to provide additional information on the ink composition, in an attempt to determine the origin of the lead in the Herculaneum scrolls and validate the postulated hypotheses. PMID:26854067

  13. Tracking ink composition on Herculaneum papyrus scrolls: quantification and speciation of lead by X-ray based techniques and Monte Carlo simulations

    NASA Astrophysics Data System (ADS)

    Tack, Pieter; Cotte, Marine; Bauters, Stephen; Brun, Emmanuel; Banerjee, Dipanjan; Bras, Wim; Ferrero, Claudio; Delattre, Daniel; Mocella, Vito; Vincze, Laszlo

    2016-02-01

    The writing in carbonized Herculaneum scrolls, covered and preserved by the pyroclastic events of the Vesuvius in 79 AD, was recently revealed using X-ray phase-contrast tomography, without the need of unrolling the sensitive scrolls. Unfortunately, some of the text is difficult to read due to the interference of the papyrus fibers crossing the written text vertically and horizontally. Recently, lead was found as an elemental constituent in the writing, rendering the text more clearly readable when monitoring the lead X-ray fluorescence signal. Here, several hypotheses are postulated for the origin and state of lead in the papyrus writing. Multi-scale X-ray fluorescence micro-imaging, Monte Carlo quantification and X-ray absorption microspectroscopy experiments are used to provide additional information on the ink composition, in an attempt to determine the origin of the lead in the Herculaneum scrolls and validate the postulated hypotheses.

  14. Tracking ink composition on Herculaneum papyrus scrolls: quantification and speciation of lead by X-ray based techniques and Monte Carlo simulations

    PubMed Central

    Tack, Pieter; Cotte, Marine; Bauters, Stephen; Brun, Emmanuel; Banerjee, Dipanjan; Bras, Wim; Ferrero, Claudio; Delattre, Daniel; Mocella, Vito; Vincze, Laszlo

    2016-01-01

    The writing in carbonized Herculaneum scrolls, covered and preserved by the pyroclastic events of the Vesuvius in 79 AD, was recently revealed using X-ray phase-contrast tomography, without the need of unrolling the sensitive scrolls. Unfortunately, some of the text is difficult to read due to the interference of the papyrus fibers crossing the written text vertically and horizontally. Recently, lead was found as an elemental constituent in the writing, rendering the text more clearly readable when monitoring the lead X-ray fluorescence signal. Here, several hypotheses are postulated for the origin and state of lead in the papyrus writing. Multi-scale X-ray fluorescence micro-imaging, Monte Carlo quantification and X-ray absorption microspectroscopy experiments are used to provide additional information on the ink composition, in an attempt to determine the origin of the lead in the Herculaneum scrolls and validate the postulated hypotheses. PMID:26854067

  15. An investigation of dose changes for therapeutic kilovoltage x-ray beams with underlying lead shielding

    SciTech Connect

    Hill, Robin; Healy, Brendan; Holloway, Lois; Baldock, Clive

    2007-07-15

    Kilovoltage x-ray beams are used to treat cancer on or close to the skin surface. Many clinical cases use high atomic number materials as shielding to reduce dose to underlying healthy tissues. In this work, we have investigated the effect on both the surface dose and depth doses in a water phantom with lead shielding at depth in the phantom. The EGSnrc Monte Carlo code was used to simulate the water phantom and to calculate the surface doses and depth doses using primary x-ray beam spectra derived from an analytical model. The x-ray beams were in the energy range of 75-135 kVp with field sizes of 2, 5 and 8 cm diameter. The lead sheet was located beneath the water surface at depths ranging from 0.5-7.5 cm. The surface dose decreased as the lead was positioned closer to the water surface and as the field size was increased. The variation in surface dose as a function of x-ray beam energy was only small but the maximum reduction occurred for the 100 kVp x-ray beam. For the 8 cm diameter field with the lead at 1 cm depth and using the 100 kVp x-ray beam, the surface dose was reduced to 0.898 of the surface dose in the water phantom only. Measured surface dose changes, using a Farmer-type ionization chamber, agreed with the Monte Carlo calculated doses. Calculated depth doses in water with a lead sheet positioned below the surface showed that the dose fall-off increased as the lead was positioned closer to the water surface as compared to the depth dose in the water phantom only. Monte Carlo calculations of the total x-ray beam spectrum at the water surface showed that the total fluence decreased due to a reduction in backscatter from within the water and very little backscatter from the lead. The mean energy of the x-ray spectrum varied less than 1 keV, with the lead at 1 cm beneath the water phantom surface. As the Monte Carlo calculations showed good agreement with the measured results, this method can be used to verify surface dose changes in clinical situations

  16. High energy neutrino absorption and its effects on stars in close X-ray binaries

    NASA Technical Reports Server (NTRS)

    Gaisser, T. K.; Stecker, F. W.

    1986-01-01

    The physics and astrophysics of high energy neutrino production and interactions in close X-ray binary systems are studied. These studies were stimulated by recent observations of ultrahigh energy gamma-rays and possibly other ultrahigh energy particles coming from the directions of Cygnus X-3 and other binary systems and possessing the periodicity characteristics of these systems. Systems in which a compact object, such as a neutron star, is a strong source of high energy particles which, in turn, produce photons, neutronos and other secondary particles by interactions in the atmosphere of the companion star were considered. The highest energy neutrinos are absorbed deep in the companion and the associated energy deposition may be large enough to effect its structure or lead to its ultimate disruption. This neutrino heating was evaluated, starting with a detailed numerical calculation of the hadronic cascade induced in the atmosphere of the companion star. For some theoretical models, the resulting energy deposition from neutrino absorption may be so great as to disrupt the companion star over an astronomically small timescale of the order of 10,000 years. Even if the energy deposition is smaller, it may still be high enough to alter the system substantially, perhaps leading to quenching of high energy signals from the source. Given the cosmic ray luminosities required to produce the observed gamma rays from cygnus X-3 and LMX X-4, such a situation may occur in these sources.

  17. Study of exploding Al wire plasmas using X-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Pikuz, Sergey A.; Shelkovenko, Tatiana A.; Hoyt, Cad L.; Cahill, Adam D.; Hammer, David A.

    2012-10-01

    X-ray absorption spectroscopy is a powerful diagnostic technique useful for determining the charge state, temperature and density of plasmas under a wide range of conditions and situations. Our particular interest was the study of the core-corona system generated in electrically exploded wires and wire array Z-pinches. Two wide-bandwidth spectrographs with flat and concave cylindrically bent KAP crystals, and high-resolution spectrographs with spherically bent quartz crystals have been used on the XP and COBRA pulsers at Cornell University. The hybrid X-pinch was used as the continuum x-ray source in the photon energy range of interest for absorption spectroscopy with exploding Al wire experiments. This source is capable of producing broadband continuum x-ray pulses with micron source size and 100 ps duration. Absorption spectra of single exploded Al wires and 2 - 4 wire arrays were recorded with high spatial resolution. The parameters of the dense wire core plasmas and the ablating plasma streams were estimated under different experimental conditions. New spectral features in absorption spectra were observed.

  18. Extended x-ray absorption fine structure of NaBr and Ge at high pressure

    SciTech Connect

    Ingalls, R.; Crozier, E.D.; Whitmore, J.E.; Seary, A.J.; Tranquada, J.M.

    1980-06-01

    The x-ray absorption spectra of Ge and of Br in NaBr have been measured to pressures of 52 and 21 kbars, respectively, in a boron carbide and diamond anvil cell in which pressure was measured via the ruby-fluorescence technique. Although Bragg peaks from the diamond anvil reduced the accuracy, atomic spacings in both materials could be determined by extended x-ray absorption fine-structure (EXAFS) analysis. Changes in the nearest-neighbor separations in NaBr, and Ge to at least 40 kbars, agreed with literature values, indicating that the EXAFS phase shifts are quite insensitive to such pressures. In addition the near-edge peak positions in the NaBr spectra appeared to readily shift with pressure, which suggests that NaBr may be quite suitable as a pressure standard in future work of this type.

  19. Electrochemical flowcell for in-situ investigations by soft x-ray absorption and emission spectroscopy

    SciTech Connect

    Schwanke, C.; Lange, K. M.; Golnak, R.; Xiao, J.

    2014-10-15

    A new liquid flow-cell designed for electronic structure investigations at the liquid-solid interface by soft X-ray absorption and emission spectroscopy is presented. A thin membrane serves simultaneously as a substrate for the working electrode and solid state samples as well as for separating the liquid from the surrounding vacuum conditions. In combination with counter and reference electrodes this approach allows in-situ studies of electrochemical deposition processes and catalytic reactions at the liquid-solid interface in combination with potentiostatic measurements. As model system in-situ monitoring of the deposition process of Co metal from a 10 mM CoCl{sub 2} aqueous solution by X-ray absorption and emission spectroscopy is presented.

  20. X-ray absorption spectroscopic studies of mononuclear non-heme iron enzymes

    SciTech Connect

    Westre, T.E.

    1996-01-01

    Fe-K-edge X-ray absorption spectroscopy (XAS) has been used to investigate the electronic and geometric structure of the iron active site in non-heme iron enzymes. A new theoretical extended X-ray absorption fine structure (EXAFS) analysis approach, called GNXAS, has been tested on data for iron model complexes to evaluate the utility and reliability of this new technique, especially with respect to the effects of multiple-scattering. In addition, a detailed analysis of the 1s{yields}3d pre-edge feature has been developed as a tool for investigating the oxidation state, spin state, and geometry of iron sites. Edge and EXAFS analyses have then been applied to the study of non-heme iron enzyme active sites.

  1. Local environment of metal ions in phthalocyanines: K-edge X-ray absorption spectra.

    PubMed

    Rossi, G; d'Acapito, F; Amidani, L; Boscherini, F; Pedio, M

    2016-09-14

    We report a detailed study of the K-edge X-ray absorption spectra of four transition metal phthalocyanines (MPc, M = Fe, Co, Cu and Zn). We identify the important single and multiple scattering contributions to the spectra in the extended energy range and provide a robust treatment of thermal damping; thus, a generally applicable model for the interpretation of X-ray absorption fine structure spectra is proposed. Consistent variations of bond lengths and Debye Waller factors are found as a function of atomic number of the metal ion, indicating a variation of the metal-ligand bond strength which correlates with the spatial arrangement and occupation of molecular orbitals. We also provide an interpretation of the near edge spectral features in the framework of a full potential real space multiple scattering approach and provide a connection to the local electronic structure. PMID:27510989

  2. Picosecond time-resolved X-ray absorption spectroscopy of ultrafast aluminum plasmas.

    PubMed

    Audebert, P; Renaudin, P; Bastiani-Ceccotti, S; Geindre, J-P; Chenais-Popovics, C; Tzortzakis, S; Nagels-Silvert, V; Shepherd, R; Matsushima, I; Gary, S; Girard, F; Peyrusse, O; Gauthier, J-C

    2005-01-21

    We have used point-projection K-shell absorption spectroscopy to infer the ionization and recombination dynamics of transient aluminum plasmas. Two femtosecond beams of the 100 TW laser at the LULI facility were used to produce an aluminum plasma on a thin aluminum foil (83 or 50 nm), and a picosecond x-ray backlighter source. The short-pulse backlighter probed the aluminum plasma at different times by adjusting the delay between the two femtosecond driving beams. Absorption x-ray spectra at early times are characteristic of a dense and rather homogeneous plasma. Collisional-radiative atomic physics coupled with hydrodynamic simulations reproduce fairly well the measured average ionization as a function of time. PMID:15698184

  3. Single shot near edge x-ray absorption fine structure spectroscopy in the laboratory

    NASA Astrophysics Data System (ADS)

    Mantouvalou, I.; Witte, K.; Martyanov, W.; Jonas, A.; Grötzsch, D.; Streeck, C.; Löchel, H.; Rudolph, I.; Erko, A.; Stiel, H.; Kanngießer, B.

    2016-05-01

    With the help of adapted off-axis reflection zone plates, near edge X-ray absorption fine structure spectra at the C and N K-absorption edge have been recorded using a single 1.2 ns long soft X-ray pulse. The transmission experiments were performed with a laser-produced plasma source in the laboratory rendering time resolved measurements feasible independent on large scale facilities. A resolving power of E/ΔE ˜ 950 at the respective edges could be demonstrated. A comparison of single shot spectra with those collected with longer measuring time proves that all features of the used reference samples (silicon nitrate and polyimide) can be resolved in 1.2 ns. Hence, investigations of radiation sensitive biological specimen become possible due to the high efficiency of the optical elements enabling low dose experiments.

  4. Solution spectroelectrochemical cell for in situ X-ray absorption fine structure

    SciTech Connect

    Antonio, M.R.; Soderholm, L.; Song, I.

    1995-06-12

    A purpose-built spectroelectrochemical cell for in situ fluorescence XAFS (X-ray Absorption Fine Structure) measurements of bulk solution species during constant-potential electrolysis is described. The cell performance was demonstrated by the collection of europium L{sub 3}-edge XANES (X-ray Absorption Near Edge Structure) throughout the course of electrolysis of an aqueous solution of EuCl{sub 3}{center_dot}6H{sub 2}O in 1 M H{sub 2}SO{sub 4}. The europium L{sub 3}-edge resonances reported here for the Eu{sup III} and Eu{sup II} ions demonstrate that their 2p{sub 3/2} {yields} 5d electronic transition probabilities are not the same.

  5. Polarized x-ray-absorption spectroscopy of the uranyl ion: Comparison of experiment and theory

    SciTech Connect

    Hudson, E.A.; Allen, P.G.; Terminello, L.J.; Denecke, M.A.; Reich, T.

    1996-07-01

    The x-ray linear dichroism of the uranyl ion (UO{sub 2}{sup 2+}) in uranium {ital L}{sub 3}-edge extended x-ray-absorption fine structure (EXAFS), and {ital L}{sub 1}- and {ital L}{sub 3}-edge x-ray-absorption near-edge structure (XANES), has been investigated both by experiment and theory. A striking polarization dependence is observed in the experimental XANES and EXAFS for an oriented single crystal of uranyl acetate dihydrate [UO{sub 2}(CH{sub 3}CO{sub 2}){sub 2}{center_dot}2H{sub 2}O], with the x-ray polarization vector aligned either parallel or perpendicular to the bond axis of the linear uranyl cation (O-U-O). Single-crystal results are compared to experimental spectra for a polycrystalline uranyl acetate sample and to calculations using the {ital ab} {ital initio} multiple-scattering (MS) code FEFF 6. Theoretical XANES spectra for uranyl fluoride (UO{sub 2}F{sub 2}) reproduce all the features of the measured uranyl acetate spectra. By identifying scattering paths which contribute to individual features in the calculated spectrum, a detailed understanding of the {ital L}{sub 1}-edge XANES is obtained. MS paths within the uranyl cation have a notable influence upon the XANES. The measured {ital L}{sub 3}-edge EXAFS is also influenced by MS, especially when the x-ray polarization is parallel to the uranyl species. These MS contributions are extracted from the total EXAFS and compared to calculations. The best agreement with the isolated MS signal is obtained by using nonoverlapped muffin-tin spheres in the FEFF 6 calculation. This contrasts the {ital L}{sub 1}-edge XANES calculations, in which overlapping was required for the best agreement with experiment. {copyright} {ital 1996 The American Physical Society.}

  6. Polarized x-ray-absorption spectroscopy of the uranyl ion: Comparison of experiment and theory

    NASA Astrophysics Data System (ADS)

    Hudson, E. A.; Allen, P. G.; Terminello, L. J.; Denecke, M. A.; Reich, T.

    1996-07-01

    The x-ray linear dichroism of the uranyl ion (UO2+2) in uranium L3-edge extended x-ray-absorption fine structure (EXAFS), and L1- and L3-edge x-ray-absorption near-edge structure (XANES), has been investigated both by experiment and theory. A striking polarization dependence is observed in the experimental XANES and EXAFS for an oriented single crystal of uranyl acetate dihydrate [UO2(CH3CO2)2.2H2O], with the x-ray polarization vector aligned either parallel or perpendicular to the bond axis of the linear uranyl cation (O-U-O). Single-crystal results are compared to experimental spectra for a polycrystalline uranyl acetate sample and to calculations using the ab initio multiple-scattering (MS) code FEFF 6. Theoretical XANES spectra for uranyl fluoride (UO2F2) reproduce all the features of the measured uranyl acetate spectra. By identifying scattering paths which contribute to individual features in the calculated spectrum, a detailed understanding of the L1-edge XANES is obtained. MS paths within the uranyl cation have a notable influence upon the XANES. The measured L3-edge EXAFS is also influenced by MS, especially when the x-ray polarization is parallel to the uranyl species. These MS contributions are extracted from the total EXAFS and compared to calculations. The best agreement with the isolated MS signal is obtained by using nonoverlapped muffin-tin spheres in the FEFF 6 calculation. This contrasts the L1-edge XANES calculations, in which overlapping was required for the best agreement with experiment.

  7. X-ray absorption lines - Signature for preheat level in non-explosive laser implosions

    NASA Astrophysics Data System (ADS)

    Yaakobi, B.; McCrory, R. L.; Skupsky, S.; Delettrez, J. A.; Bourke, P.; Soures, J. M.; Hooper, C. F.; Deckman, H.

    1980-08-01

    The measured X-ray spectrum from thick glass shells imploded with two TW six-beam laser pulses displayed absorption by transitions of Si ions. This indicates the existence around the time of peak compression of a cooler (less than approximately 200 eV) layer surrounding the hot innermost glass layer, of density times thickness approximately 0.0006 g/sq cm. This temperature is indicative of the preheat level ealier in the implosion.

  8. Atomic structure of machined semiconducting chips: An x-ray absorption spectroscopy study

    SciTech Connect

    Paesler, M.; Sayers, D.

    1988-12-01

    X-ray absorption spectroscopy (XAS) has been used to examine the atomic structure of chips of germanium that were produced by single point diamond machining. It is demonstrated that although the local (nearest neighbor) atomic structure is experimentally quite similar to that of single crystal specimens information from more distant atoms indicates the presence of considerable stress. An outline of the technique is given and the strength of XAS in studying the machining process is demonstrated.

  9. X-Ray Absorption Spectroscopy Of Thin Foils Irradiated By An Ultra-short Laser Pulse

    SciTech Connect

    Renaudin, P.; Blancard, C.; Cosse, P.; Faussurier, G.; Lecherbourg, L.; Audebert, P.; Bastiani-Ceccotti, S.; Geindre, J.-P.; Shepherd, R.

    2007-08-02

    Point-projection K-shell absorption spectroscopy has been used to measure absorption spectra of transient plasma created by an ultra-short laser pulse. The 1s-2p and 1s-3p absorption lines of weakly ionized aluminum and the 2p-3d absorption lines of bromine were measured over an extended range of densities in a low-temperature regime. Independent plasma characterization was obtained using frequency domain interferometry diagnostic (FDI) that allows the interpretation of the absorption spectra in terms of spectral opacities. Assuming local thermodynamic equilibrium, spectral opacity calculations have been performed using the density and temperature inferred from the FDI diagnostic to compare to the measured absorption spectra. A good agreement is obtained when non-equilibrium effects due to non-stationary atomic physics are negligible at the x-ray probe time.

  10. X-Ray Absorption Spectroscopy Of Thin Foils Irradiated By An Ultra-short Laser Pulse

    NASA Astrophysics Data System (ADS)

    Renaudin, P.; Lecherbourg, L.; Blancard, C.; Cossé, P.; Faussurier, G.; Audebert, P.; Bastiani-Ceccotti, S.; Geindre, J.-P.; Shepherd, R.

    2007-08-01

    Point-projection K-shell absorption spectroscopy has been used to measure absorption spectra of transient plasma created by an ultra-short laser pulse. The 1s-2p and 1s-3p absorption lines of weakly ionized aluminum and the 2p-3d absorption lines of bromine were measured over an extended range of densities in a low-temperature regime. Independent plasma characterization was obtained using frequency domain interferometry diagnostic (FDI) that allows the interpretation of the absorption spectra in terms of spectral opacities. Assuming local thermodynamic equilibrium, spectral opacity calculations have been performed using the density and temperature inferred from the FDI diagnostic to compare to the measured absorption spectra. A good agreement is obtained when non-equilibrium effects due to non-stationary atomic physics are negligible at the x-ray probe time.

  11. Lead adsorption at the calcite-water interface: Synchrotron x-ray standing wave and x-ray reflectivity studies

    SciTech Connect

    Sturchio, N.C.; Chiarello, R.P.; You, Hoydoo

    1997-01-01

    By combining synchrotron X-ray standing wave (XSW) measurements with synchrotron X-ray reflectivity measurements, we have determined: (1) the precise three-dimensional location within the calcite unit cell of submonolayer Pb ions adsorbed at the calcite (104) surface from dilute aqueous solutions, and (2) the precise one-dimensional location of these unit cells relative to the calcite surface. Our XSW measurements, using three separate calcite Bragg reflections for triangulation, show that most adsorbed Pb ions occupy Ca sites in the calcite lattice with an ordered coverage of 0.05 equivalent monolayers, while the remaining Pb ions are disordered with a coverage of 0.03 equivalent monolayers. Our X-ray reflectivity measurements show that the ordered Ph ions occur primarily (>70%) in the surface atomic layer of calcite. Atomic force microscopy (AFM) was used to characterize the topography of the calcite (104) surface under conditions similar to the X-ray experiments. The quantitative morphological information obtained by AFM was used to develop realistic models of the calcite surface. The calculated X-ray reflectivities for these model surfaces were compared with the measured X-ray reflectivities. The new combined X-ray method that we have developed can be used to determine the atomic-scale structure of other metals adsorbed at mineral-water interfaces. Such high-resolution structural determinations are essential before detailed conceptual and theoretical models can be further developed to understand and predict the behavior of dissolved metals in mineral-water systems. 60 refs., 8 figs., 3 tabs.

  12. ODS steel raw material local structure analysis using X-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Cintins, A.; Anspoks, A.; Purans, J.; Kuzmin, A.; Timoshenko, J.; Vladimirov, P.; Gräning, T.; Hoffmann, J.

    2015-03-01

    Oxide dispersion strengthened (ODS) steels are promising materials for fusion power reactors, concentrated solar power plants, jet engines, chemical reactors as well as for hydrogen production from thermolysis of water. In this study we used X-ray absorption spectroscopy at the Fe and Cr K-edges as a tool to get insight into the local structure of ferritic and austenitic ODS steels around Fe and Cr atoms and its transformation during mechanical alloying process. Using the analysis of X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) we found that for austenitic samples a transformation of ferritic steel to austenitic steel is detectable after 10 hours of milling and proceeds till 40 hours of milling; only small amount of a-phase remains after 80 hours of milling. We found that the Cr K-edge EXAFS can be used to observe distortions inside the material and to get an impression on the formation of chromium clusters. In-situ EXAFS experiments offer a reliable method to investigate the ferritic to austenitic transformation.

  13. The effects of dust scattering on high-resolution X-ray absorption edge structure

    NASA Astrophysics Data System (ADS)

    Corrales, L.; García, J.; Wilms, J.; Baganoff, F.

    2016-06-01

    High energy studies of astrophysical dust complement observations of dusty interstellar gas at other wavelengths. With high resolution X-ray spectroscopy, dust scattering significantly enhances the total extinction optical depth and alters the shape of photoelectric absorption edges. This effect is modulated by the dust grain size distribution, spatial location along the line of sight, and the imaging resolution of the X-ray telescope. At soft energies, the spectrum of scattered light is likely to have significant features at the 0.3 keV (C-K), 0.5 keV (O-K), and 0.7 keV (Fe-L) photoelectric absorption edges. This direct probe of ISM dust grain elements will be important for (i) understanding the relative abundances of graphitic grains or PAHs versus silicates, and (ii) measuring the depletion of gas phase elements into solid form. We focus in particular on the Fe-L edge, fitting a template for the total extinction to the high resolution spectrum of three X-ray binaries from the Chandra archive: GX 9+9, XTE J1817-330, and Cyg X-1. We discuss ways in which spectroscopy with XMM can yield insight into dust obscured objects such as stars, binaries, AGN, and foreground quasar absorption line systems.

  14. Quick scanning monochromator for millisecond in situ and in operando X-ray absorption spectroscopy.

    PubMed

    Müller, O; Lützenkirchen-Hecht, D; Frahm, R

    2015-09-01

    The design and capabilities of a novel Quick scanning Extended X-ray Absorption Fine Structure (QEXAFS) monochromator are presented. The oscillatory movement of the crystal stage is realized by means of a unique open-loop driving scheme operating a direct drive torque motor. The entire drive mechanics are installed inside of a goniometer located on the atmospheric side of the vacuum chamber. This design allows remote adjustment of the oscillation frequency and spectral range, giving complete control of QEXAFS measurements. It also features a real step-scanning mode, which operates without a control loop to prevent induced vibrations. Equipped with Si(111) and Si(311) crystals on a single stage, it facilitates an energy range from 4.0 keV to 43 keV. Extended X-ray absorption fine structure spectra up to k = 14.4 Å(-1) have been acquired within 17 ms and X-ray absorption near edge structure spectra covering more than 200 eV within 10 ms. The achieved data quality is excellent as shown by the presented measurements. PMID:26429455

  15. Quick scanning monochromator for millisecond in situ and in operando X-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Müller, O.; Lützenkirchen-Hecht, D.; Frahm, R.

    2015-09-01

    The design and capabilities of a novel Quick scanning Extended X-ray Absorption Fine Structure (QEXAFS) monochromator are presented. The oscillatory movement of the crystal stage is realized by means of a unique open-loop driving scheme operating a direct drive torque motor. The entire drive mechanics are installed inside of a goniometer located on the atmospheric side of the vacuum chamber. This design allows remote adjustment of the oscillation frequency and spectral range, giving complete control of QEXAFS measurements. It also features a real step-scanning mode, which operates without a control loop to prevent induced vibrations. Equipped with Si(111) and Si(311) crystals on a single stage, it facilitates an energy range from 4.0 keV to 43 keV. Extended X-ray absorption fine structure spectra up to k = 14.4 Å-1 have been acquired within 17 ms and X-ray absorption near edge structure spectra covering more than 200 eV within 10 ms. The achieved data quality is excellent as shown by the presented measurements.

  16. Surface Arsenic Speciation of a Drinking-Water Treatment Residual Using X-Ray Absorption Spectroscopy

    SciTech Connect

    Makris, K.C.; Sarkar, D.; Parsons, J.G.; Datta, R.; Gardea-Torresdey, J.L.

    2009-06-03

    Drinking-water treatment residuals (WTRs) present a low-cost geosorbent for As-contaminated waters and soils. Previous work has demonstrated the high affinity of WTRs for As, but data pertaining to the stability of sorbed As is missing. Sorption/desorption and X-ray absorption spectroscopy (XAS), both XANES (X-ray absorption near edge structure) and EXAFS (extended X-ray absorption fine structure) studies, were combined to determine the stability of As sorbed by an Fe-based WTR. Arsenic(V) and As(III) sorption kinetics were biphasic in nature, sorbing <90% of the initial added As (15,000 mg kg{sup -1}) after 48 h of reaction. Subsequent desorption experiments with a high P load (7500 mg kg{sup -1}) showed negligible As desorption for both As species, approximately <3.5% of sorbed As; the small amount of desorbed As was attributed to the abundance of sorption sites. XANES data showed that sorption kinetics for either As(III) or As(V) initially added to solution had no effect on the sorbed As oxidation state. EXAFS spectroscopy suggested that As added either as As(III) or as As(V) formed inner-sphere mononuclear, bidentate complexes, suggesting the stability of the sorbed As, which was further corroborated by the minimum As desorption from the Fe-WTR.

  17. Quantitative investigation of two metallohydrolases by X-ray absorption spectroscopy near-edge spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhao, W.; Chu, W. S.; Yang, F. F.; Yu, M. J.; Chen, D. L.; Guo, X. Y.; Zhou, D. W.; Shi, N.; Marcelli, A.; Niu, L. W.; Teng, M. K.; Gong, W. M.; Benfatto, M.; Wu, Z. Y.

    2007-09-01

    The last several years have witnessed a tremendous increase in biological applications using X-ray absorption spectroscopy (BioXAS), thanks to continuous advancements in synchrotron radiation (SR) sources and detector technology. However, XAS applications in many biological systems have been limited by the intrinsic limitations of the Extended X-ray Absorption Fine Structure (EXAFS) technique e.g., the lack of sensitivity to bond angles. As a consequence, the application of the X-ray absorption near-edge structure (XANES) spectroscopy changed this scenario that is now continuously changing with the introduction of the first quantitative XANES packages such as Minut XANES (MXAN). Here we present and discuss the XANES code MXAN, a novel XANES-fitting package that allows a quantitative analysis of experimental data applied to Zn K-edge spectra of two metalloproteins: Leptospira interrogans Peptide deformylase ( LiPDF) and acutolysin-C, a representative of snake venom metalloproteinases (SVMPs) from Agkistrodon acutus venom. The analysis on these two metallohydrolases reveals that proteolytic activities are correlated to subtle conformation changes around the zinc ion. In particular, this quantitative study clarifies the occurrence of the LiPDF catalytic mechanism via a two-water-molecules model, whereas in the acutolysin-C we have observed a different proteolytic activity correlated to structural changes around the zinc ion induced by pH variations.

  18. Dimerization of single selenium chains confined in nanochannels of cancrinite: An x-ray absorption study

    NASA Astrophysics Data System (ADS)

    Kolobov, A. V.; Oyanagi, H.; Poborchii, V. V.; Tanaka, K.

    1999-04-01

    Local structure of selenium confined in nanochannels of cancrinite (Can-Se) single crystal and powder samples have been studied by polarized x-ray absorption. The spectra for a single crystal are strongly anisotropic implying linear arrangement of Se species. Polarization dependence of extended x-ray absorption fine structure (EXAFS) data provides direct evidence that dimers with the bond length of 2.40+/-0.01 Å are formed. Polarized x-ray absorption near-edge structure (XANES) spectra demonstrate that they are aligned along the channel of cancrinite. Deconvolution of XANES spectra into Lorentzians (localized states) and the remaining steplike function (continuous states) shows that two localized state peaks are present. While the one polarized parallel to the cancrinite axis is strongly polarized, the other one is essentially isotropic. Comparison of XANES peak positions for Can-Se with that for bulk selenium provides evidence for negative charge on dimers. Despite strong temperature dependence of Raman-scattering spectra found earlier, EXAFS data do not exhibit any noticeable temperature dependence. Possible mechanisms for dimer stabilization are discussed.

  19. Communication: Hydrogen bonding interactions in water-alcohol mixtures from X-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Lam, Royce K.; Smith, Jacob W.; Saykally, Richard J.

    2016-05-01

    While methanol and ethanol are macroscopically miscible with water, their mixtures exhibit negative excess entropies of mixing. Despite considerable effort in both experiment and theory, there remains significant disagreement regarding the origin of this effect. Different models for the liquid mixture structure have been proposed to address this behavior, including the enhancement of the water hydrogen bonding network around the alcohol hydrophobic groups and microscopic immiscibility or clustering. We have investigated mixtures of methanol, ethanol, and isopropanol with water by liquid microjet X-ray absorption spectroscopy on the oxygen K-edge, an atom-specific probe providing details of both inter- and intra-molecular structure. The measured spectra evidence a significant enhancement of hydrogen bonding originating from the methanol and ethanol hydroxyl groups upon the addition of water. These additional hydrogen bonding interactions would strengthen the liquid-liquid interactions, resulting in additional ordering in the liquid structures and leading to a reduction in entropy and a negative enthalpy of mixing, consistent with existing thermodynamic data. In contrast, the spectra of the isopropanol-water mixtures exhibit an increase in the number of broken alcohol hydrogen bonds for mixtures containing up to 0.5 water mole fraction, an observation consistent with existing enthalpy of mixing data, suggesting that the measured negative excess entropy is a result of clustering or micro-immiscibility.

  20. Communication: Hydrogen bonding interactions in water-alcohol mixtures from X-ray absorption spectroscopy.

    PubMed

    Lam, Royce K; Smith, Jacob W; Saykally, Richard J

    2016-05-21

    While methanol and ethanol are macroscopically miscible with water, their mixtures exhibit negative excess entropies of mixing. Despite considerable effort in both experiment and theory, there remains significant disagreement regarding the origin of this effect. Different models for the liquid mixture structure have been proposed to address this behavior, including the enhancement of the water hydrogen bonding network around the alcohol hydrophobic groups and microscopic immiscibility or clustering. We have investigated mixtures of methanol, ethanol, and isopropanol with water by liquid microjet X-ray absorption spectroscopy on the oxygen K-edge, an atom-specific probe providing details of both inter- and intra-molecular structure. The measured spectra evidence a significant enhancement of hydrogen bonding originating from the methanol and ethanol hydroxyl groups upon the addition of water. These additional hydrogen bonding interactions would strengthen the liquid-liquid interactions, resulting in additional ordering in the liquid structures and leading to a reduction in entropy and a negative enthalpy of mixing, consistent with existing thermodynamic data. In contrast, the spectra of the isopropanol-water mixtures exhibit an increase in the number of broken alcohol hydrogen bonds for mixtures containing up to 0.5 water mole fraction, an observation consistent with existing enthalpy of mixing data, suggesting that the measured negative excess entropy is a result of clustering or micro-immiscibility. PMID:27208929

  1. Coupling MD Simulations and X-ray Absorption Spectroscopy to Study Ions in Solution

    SciTech Connect

    Marcos, E. Sanchez; Beret, E. C.; Martinez, J. M.; Pappalardo, R. R.; Ayala, R.; Munoz-Paez, A.

    2007-11-29

    The structure of ionic solutions is a key-point in understanding physicochemical properties of electrolyte solutions. Among the reduced number of experimental techniques which can supply direct information on the ion environment, X-ray Absorption techniques (XAS) have gained importance during the last decades although they are not free of difficulties associated to the data analysis leading to provide reliable structures. Computer simulations of ions in solution is a theoretical alternative to provide information on the solvation structure. Thus, the use of computational chemistry can increase the understanding of these systems although an accurate description of ionic solvation phenomena represents nowadays a significant challenge to theoretical chemistry. We present: (a) the assignment of features in the XANES spectrum to well defined structural motif in the ion environment, (b) MD-based evaluation of EXAFS parameters used in the fitting procedure to make easier the structural resolution, and (c) the use of the agreement between experimental and simulated XANES spectra to help in the choice of a given intermolecular potential for Computer Simulations. Chemical problems examined are: (a) the identification of the second hydration shell in dilute aqueous solutions of highly-charged cations, such as Cr{sup 3+}, Rh{sup 3+}, Ir{sup 3+}, (b) the invisibility by XAS of certain structures characterized by Computer Simulations but exhibiting high dynamical behavior and (c) the solvation of Br{sup -} in acetonitrile.

  2. Toward picosecond time-resolved X-ray absorption studies of interfacial photochemistry

    NASA Astrophysics Data System (ADS)

    Gessner, Oliver; Mahl, Johannes; Neppl, Stefan

    2016-05-01

    We report on the progress toward developing a novel picosecond time-resolved transient X-ray absorption spectroscopy (TRXAS) capability for time-domain studies of interfacial photochemistry. The technique is based on the combination of a high repetition rate picosecond laser system with a time-resolved X-ray fluorescent yield setup that may be used for the study of radiation sensitive materials and X-ray spectroscopy compatible photoelectrochemical (PEC) cells. The mobile system is currently deployed at the Advanced Light Source (ALS) and may be used in all operating modes (two-bunch and multi-bunch) of the synchrotron. The use of a time-stamping technique enables the simultaneous recording of TRXAS spectra with delays between the exciting laser pulses and the probing X-ray pulses spanning picosecond to nanosecond temporal scales. First results are discussed that demonstrate the viability of the method to study photoinduced dynamics in transition metal-oxide semiconductor (SC) samples under high vacuum conditions and at SC-liquid electrolyte interfaces during photoelectrochemical water splitting. Opportunities and challenges are outlined to capture crucial short-lived intermediates of photochemical processes with the technique. This work was supported by the Department of Energy Office of Science Early Career Research Program.

  3. A new endstation at the Swiss Light Source for ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy measurements of liquid solutions

    SciTech Connect

    Brown, Matthew A.; Redondo, Amaia Beloqui; Duyckaerts, Nicolas; Mächler, Jean-Pierre; Jordan, Inga; Wörner, Hans Jakob; Lee, Ming-Tao; Ammann, Markus; Nolting, Frithjof; Kleibert, Armin; Huthwelker, Thomas; Birrer, Mario; Honegger, Juri; Wetter, Reto; Bokhoven, Jeroen A. van

    2013-07-15

    A new liquid microjet endstation designed for ultraviolet (UPS) and X-ray (XPS) photoelectron, and partial electron yield X-ray absorption (XAS) spectroscopies at the Swiss Light Source is presented. The new endstation, which is based on a Scienta HiPP-2 R4000 electron spectrometer, is the first liquid microjet endstation capable of operating in vacuum and in ambient pressures up to the equilibrium vapor pressure of liquid water at room temperature. In addition, the Scienta HiPP-2 R4000 energy analyzer of this new endstation allows for XPS measurements up to 7000 eV electron kinetic energy that will enable electronic structure measurements of bulk solutions and buried interfaces from liquid microjet samples. The endstation is designed to operate at the soft X-ray SIM beamline and at the tender X-ray Phoenix beamline. The endstation can also be operated using a Scienta 5 K ultraviolet helium lamp for dedicated UPS measurements at the vapor-liquid interface using either He I or He II α lines. The design concept, first results from UPS, soft X-ray XPS, and partial electron yield XAS measurements, and an outlook to the potential of this endstation are presented.

  4. The INTEGRAL/IBIS AGN catalogue - I. X-ray absorption properties versus optical classification

    NASA Astrophysics Data System (ADS)

    Malizia, A.; Bassani, L.; Bazzano, A.; Bird, A. J.; Masetti, N.; Panessa, F.; Stephen, J. B.; Ubertini, P.

    2012-11-01

    In this work we present the most comprehensive INTEGRAL active galactic nucleus (AGN) sample. It lists 272 AGN for which we have secure optical identifications, precise optical spectroscopy and measured redshift values plus X-ray spectral information, i.e. 2-10 and 20-100 keV fluxes plus column density. Here we mainly use this sample to study the absorption properties of active galaxies, to probe new AGN classes and to test the AGN unification scheme. We find that half (48 per cent) of the sample is absorbed, while the fraction of Compton-thick AGN is small (˜7 per cent). In line with our previous analysis, we have however shown that when the bias towards heavily absorbed objects which are lost if weak and at large distance is removed, as it is possible in the local Universe, the above fractions increase to become 80 and 17 per cent. We also find that absorption is a function of source luminosity, which implies some evolution in the obscuration properties of AGN. A few peculiar classes, so far poorly studied in the hard X-ray band, have been detected and studied for the first time such as 5 X-ray bright optically normal galaxies, 5 type 2 QSOs and 11 low-ionization nuclear emission regions. In terms of optical classification, our sample contains 57 per cent of type 1 and 43 per cent of type 2 AGN; this subdivision is similar to that found in X-rays if unabsorbed versus absorbed objects are considered, suggesting that the match between optical and X-ray classifications is overall good. Only a small percentage of sources (12 per cent) does not fulfil the expectation of the unified theory as we find 22 type 1 AGN which are absorbed and 10 type 2 AGN which are unabsorbed. Studying in depth these outliers we found that most of the absorbed type 1 AGN have X-ray spectra characterized by either complex or warm/ionized absorption more likely due to ionized gas located in an accretion disc wind or in the biconical structure associated with the central nucleus, therefore

  5. X-ray absorption spectroscopy measurements of thin foil heating by Z-pinch radiation.

    PubMed

    MacFarlane, J J; Bailey, J E; Chandler, G A; Deeney, C; Douglas, M R; Jobe, D; Lake, P; Nash, T J; Nielsen, D S; Spielman, R B; Wang, P; Woodruff, P

    2002-10-01

    Absorption spectroscopy measurements of the time-dependent heating of thin foils exposed to intense z-pinch radiation sources are presented. These measurements and their analysis provide valuable benchmarks for, and insights into, the radiative heating of matter by x-ray sources. Z-pinch radiation sources with peak powers of up to 160 TW radiatively heated thin plastic-tamped aluminum foils to temperatures approximately 60 eV. The foils were located in open slots at the boundary of z-pinch hohlraums surrounding the pinch. Time-resolved Kalpha satellite absorption spectroscopy was used to measure the evolution of the Al ionization distribution, using a geometry in which the pinch served as the backlighter. The time-dependent pinch radius and x-ray power were monitored using framing camera, x-ray diode array, and bolometer measurements. A three-dimensional view factor code, within which one-dimensional (1D) radiation-hydrodynamics calculations were performed for each surface element in the view factor grid, was used to compute the incident and reemitted radiation flux distribution throughout the hohlraum and across the foil surface. Simulated absorption spectra were then generated by postprocessing radiation-hydrodynamics results for the foil heating using a 1D collisional-radiative code. Our simulated results were found to be in good general agreement with experimental x-ray spectra, indicating that the spectral measurements are consistent with independent measurements of the pinch power. We also discuss the sensitivity of our results to the spectrum of the radiation field incident on the foil, and the role of nonlocal thermodynamic equilibrium atomic kinetics in affecting the spectra. PMID:12443339

  6. Simultaneous determination of thorium, niobium, lead, and zinc by photon-induced x-ray fluorescence of lateritic material

    SciTech Connect

    LaBrecque, J.J.; Adames, D.; Parker, W.C.

    1981-01-01

    A rapid method is presented for the simultaneous determinations of thorium, niobium, lead, and zinc in lateritic material from Cerro Impacto, Estado Bolivar, Venezuela. This technique uses a PDP - 11/05 processor - based photon induced x-ray fluorescence system. The total variations of approximately 5% for concentrations of approximately 1 and 10% for concentrations of approximately 0.1% were obtained with only 500 s of fluorescent time. The values obtained by this method were in agreement with values measured by conventional flame atomic absorption spectroscopy for lead and zinc. The values for thorium measured were in agreement with the reported values for the reference materials supplied by NBL.

  7. A high resolution x-ray fluorescence spectrometer for near edge absorption studies

    SciTech Connect

    Stojanoff, V.; Hamalainen, K.; Siddons, D.P.; Hastings, J.B.; Berman, L.E.; Cramer, S.; Smith, G.

    1991-01-01

    A high resolution fluorescence spectrometer using a Johann geometry in a back scattering arrangement was developed. The spectrometer, with a resolution of 0.3 eV at 6.5 keV, combined with an incident beam, with a resolution of 0.7 eV, form the basis of a high resolution instrument for measuring x-ray absorption spectra. The advantages of the instrument are illustrated with the near edge absorption spectrum of dysprosium nitrate. 10 refs., 4 figs.

  8. A high resolution x-ray fluorescence spectrometer for near edge absorption studies

    SciTech Connect

    Stojanoff, V.; Hamalainen, K.; Siddons, D.P.; Hastings, J.B.; Berman, L.E.; Cramer, S.; Smith, G.

    1991-12-31

    A high resolution fluorescence spectrometer using a Johann geometry in a back scattering arrangement was developed. The spectrometer, with a resolution of 0.3 eV at 6.5 keV, combined with an incident beam, with a resolution of 0.7 eV, form the basis of a high resolution instrument for measuring x-ray absorption spectra. The advantages of the instrument are illustrated with the near edge absorption spectrum of dysprosium nitrate. 10 refs., 4 figs.

  9. Oscillator strength of the peptide bond {pi}* resonances at all relevant x-ray absorption edges

    SciTech Connect

    Kummer, K.; Vyalikh, D. V.; Molodtsov, S. L.; Sivkov, V. N.; Nekipelov, S. V.; Maslyuk, V. V.; Mertig, I.; Blueher, A.; Mertig, M.; Bredow, T.

    2009-10-15

    Absolute x-ray absorption cross sections of a regular bacterial surface-layer protein deposited on a naturally oxidized silicon substrate were determined experimentally. Upon separation of the partial cross sections of the three relevant 1s absorption edges, the oscillator strengths of the 1s{yields}{pi}* excitations within the peptide-backbone unit were extracted. Comparison with results of first-principles calculations revealed their close correlation to the topology of {pi}{sub peptide}* orbitals of the peptide backbone.

  10. X-ray Absorption Studies in Spinel-Type LiMn 2O 4

    NASA Astrophysics Data System (ADS)

    Liu, R. S.; Jang, L. Y.; Chen, J. M.; Tsai, Y. C.; Hwang, Y. D.; Liu, R. G.

    1997-02-01

    The electronic structure of the spinel-type LiMn2O4as the cathode material for the application in secondary batteries was probed using both MnK- andL23-edge X-ray absorption near edge structure (XANES) spectra. Based on the energy shifts of the absorption peaks in the XANES spectrum correlated to the effective charge, the valence of Mn in LiMn2O4was determined to be ∼4+. This suggests that the chemical substitution of low valent Li+ions into the Mn sites is possible to result in high valence of Mn.

  11. X-ray Emission and Absorption Lines During the SSS Phase of RS Ophiuchi

    NASA Astrophysics Data System (ADS)

    Schönrich, R. A.; Ness, J.-U.

    2008-12-01

    The high-resolution X-ray spectra of the sixth outburst of RS Ophiuchi revealed P Cygni-like line profiles. We use the column densities of selected isolated absorption lines to derive the nitrogen-to-oxygen abundance ratio. We next discuss the origin of the emission lines, which may originate from the shock, and the absorption and emission lines may thus have a different formation history. Finally, we discuss the correlation of high-amplitude variability detected during the early SSS phase with variability in the hardness ratio that follows the same pattern but is shifted by 1000~sec.

  12. Microscopic nonlinear relativistic quantum theory of absorption of powerful x-ray radiation in plasma.

    PubMed

    Avetissian, H K; Ghazaryan, A G; Matevosyan, H H; Mkrtchian, G F

    2015-10-01

    The microscopic quantum theory of plasma nonlinear interaction with the coherent shortwave electromagnetic radiation of arbitrary intensity is developed. The Liouville-von Neumann equation for the density matrix is solved analytically considering a wave field exactly and a scattering potential of plasma ions as a perturbation. With the help of this solution we calculate the nonlinear inverse-bremsstrahlung absorption rate for a grand canonical ensemble of electrons. The latter is studied in Maxwellian, as well as in degenerate quantum plasma for x-ray lasers at superhigh intensities and it is shown that one can achieve the efficient absorption coefficient in these cases. PMID:26565352

  13. Enhanced X-ray absorption for micro-CT analysis of low density polymers.

    PubMed

    Crica, Livia Elena; Wengenroth, Jonas; Tiainen, Hanna; Ionita, Mariana; Haugen, Håvard Jostein

    2016-06-01

    X-ray microtomography (micro-CT), one of the most resourceful instruments for high resolution 3D analysis, can provide qualitative and quantitative accurate structural and compositional information for a broad range of materials. Yet its contribution to the field of biopolymeric materials science is often limited by low imaging contrast due to scarce X-ray attenuation features, particularly for sponges and foam-like structures. This limitation can be overcome to some extent by adjusting the working parameters of micro-CT equipment. However, such approach also facilitates noise and artefacts, and solving the signal-to-noise trade-off has been always problematic. Searching for alternatives turns one's attention towards the improvement of X-ray attenuation features. While several studies report the use of contrast agents for biological materials, studies to integrate multiple micro-CT approaches for biopolymers were not conducted so far. This method paper is thus aimed to serve as a platform for micro-CT analysis of low X-ray absorptive polymers. Here, several contrast enhancing artifices were developed and trialled on gelatin and poly(vinyl alcohol) biopolymer composites (GP). Accordingly, GP were modified with iodine, barium, silver-based chemicals and hexa(methyl disilazane) by two different methods, i.e. addition of high atomic number chemicals during materials synthesis and post-synthesis staining, respectively. Consequently, cross-sectional scanning electron microscopy emerged as complementary characterization, aimed to confirm the reproducibility of samples morphological features. The most versatile methods were barium chloride additive incorporation and iodine staining coupled with hexa(methyl disilazane) chemical drying. Both methods significantly improved the X-ray absorbance of our polymeric samples, providing better contrast of micro-CT tomograms. PMID:26863157

  14. Effect of iron oxide reductive dissolution on the transformation and immobilization of arsenic in soils: New insights from X-ray photoelectron and X-ray absorption spectroscopy.

    PubMed

    Fan, Jian-Xin; Wang, Yu-Jun; Liu, Cun; Wang, Li-Hua; Yang, Ke; Zhou, Dong-Mei; Li, Wei; Sparks, Donald L

    2014-08-30

    The geochemical behavior and speciation of arsenic (As) in paddy soils is strongly controlled by soil redox conditions and the sequestration by soil iron oxyhydroxides. Hence, the effects of iron oxide reductive dissolution on the adsorption, transformation and precipitation of As(III) and As(V) in soils were investigated using batch experiments and synchrotron based techniques to gain a deeper understanding at both macroscopic and microscopic scales. The results of batch sorption experiments revealed that the sorption capacity of As(V) on anoxic soil was much higher than that on control soil. Synchrotron based X-ray fluorescence (μ-XRF) mapping studies indicated that As was heterogeneously distributed and was mainly associated with iron in the soil. X-ray absorption near edge structure (XANES), micro-X-ray absorption near edge structure (μ-XANES) and X-ray photoelectron spectroscopy (XPS) analyses revealed that the primary speciation of As in the soil is As(V). These results further suggested that, when As(V) was introduced into the anoxic soil, the rapid coprecipitation of As(V) with ferric/ferrous ion prevented its reduction to As(III), and was the main mechanism controlling the immobilization of As. This research could improve the current understanding of soil As chemistry in paddy and wetland soils. PMID:25064258

  15. Absorption and Phase Contrast X-Ray Imaging in Paleontology Using Laboratory and Synchrotron Sources.

    PubMed

    Bidola, Pidassa; Stockmar, Marco; Achterhold, Klaus; Pfeiffer, Franz; Pacheco, Mírian L A F; Soriano, Carmen; Beckmann, Felix; Herzen, Julia

    2015-10-01

    X-ray micro-computed tomography (μCT) is commonly used for imaging of samples in biomedical or materials science research. Owing to the ability to visualize a sample in a nondestructive way, X-ray μCT is perfectly suited to inspect fossilized specimens, which are mostly unique or rare. In certain regions of the world where important sedimentation events occurred in the Precambrian geological time, several fossilized animals are studied to understand questions related to their origin, environment, and life evolution. This article demonstrates the advantages of applying absorption and phase-contrast CT on the enigmatic fossil Corumbella werneri, one of the oldest known animals capable of building hard parts, originally discovered in Corumbá (Brazil). Different tomographic setups were tested to visualize the fossilized inner structures: a commercial laboratory-based μCT device, two synchrotron-based imaging setups using conventional absorption and propagation-based phase contrast, and a commercial X-ray microscope with a lens-coupled detector system, dedicated for radiography and tomography. Based on our results we discuss the strengths and weaknesses of the different imaging setups for paleontological studies. PMID:26306692

  16. Time-resolved X-ray Absorption Spectroscopy for Electron Transport Study in Warm Dense Gold

    NASA Astrophysics Data System (ADS)

    Lee, Jong-Won; Bae, Leejin; Engelhorn, Kyle; Heimann, Philip; Ping, Yuan; Barbrel, Ben; Fernandez, Amalia; Beckwith, Martha Anne; Cho, Byoung-Ick; GIST Team; IBS Team; LBNL Collaboration; SLAC Collaboration; LLNL Collaboration

    2015-11-01

    The warm dense Matter represents states of which the temperature is comparable to Fermi energy and ions are strongly coupled. One of the experimental techniques to create such state in the laboratory condition is the isochoric heating of thin metal foil with femtosecond laser pulses. This concept largely relies on the ballistic transport of electrons near the Fermi-level, which were mainly studied for the metals in ambient conditions. However, they were barely investigated in warm dense conditions. We present a time-resolved x-ray absorption spectroscopy measured for the Au/Cu dual layered sample. The front Au layer was isochorically heated with a femtosecond laser pulse, and the x-ray absorption changes around L-edge of Cu, which was attached on the backside of Au, was measured with a picosecond resolution. Time delays between the heating of the `front surface' of Au layer and the alternation of x-ray spectrum of Cu attached on the `rear surface' of Au indicate the energetic electron transport mechanism through Au in the warm dense conditions. IBS (IBS-R012-D1) and the NRF (No. 2013R1A1A1007084) of Korea.

  17. X-ray Absorption Study of Graphene Oxide and Transition Metal Oxide Nanocomposites

    PubMed Central

    2015-01-01

    The surface properties of the electrode materials play a crucial role in determining the performance and efficiency of energy storage devices. Graphene oxide and nanostructures of 3d transition metal oxides were synthesized for construction of electrodes in supercapacitors, and the electronic structure and oxidation states were probed using near-edge X-ray absorption fine structure. Understanding the chemistry of graphene oxide would provide valuable insight into its reactivity and properties as the graphene oxide transformation to reduced-graphene oxide is a key step in the synthesis of the electrode materials. Polarized behavior of the synchrotron X-rays and the angular dependency of the near-edge X-ray absorption fine structures (NEXAFS) have been utilized to study the orientation of the σ and π bonds of the graphene oxide and graphene oxide–metal oxide nanocomposites. The core-level transitions of individual metal oxides and that of the graphene oxide nanocomposite showed that the interaction of graphene oxide with the metal oxide nanostructures has not altered the electronic structure of either of them. As the restoration of the π network is important for good electrical conductivity, the C K edge NEXAFS spectra of reduced graphene oxide nanocomposites confirms the same through increased intensity of the sp2-derived unoccupied states π* band. A pronounced angular dependency of the reduced sample and the formation of excitonic peaks confirmed the formation of extended conjugated network. PMID:25152800

  18. Diamond sensors and polycapillary lenses for X-ray absorption spectroscopy

    SciTech Connect

    Ravel, B.; Attenkofer, K.; Bohon, J.; Muller, E.; Smedley, J.

    2013-10-15

    Diamond sensors are evaluated as incident beam monitors for X-ray absorption spectroscopy experiments. These single crystal devices pose a challenge for an energy-scanning experiment using hard X-rays due to the effect of diffraction from the crystalline sensor at energies which meet the Bragg condition. This problem is eliminated by combination with polycapillary lenses. The convergence angle of the beam exiting the lens is large compared to rocking curve widths of the diamond. A ray exiting one capillary from the lens meets the Bragg condition for any reflection at a different energy from the rays exiting adjacent capillaries. This serves to broaden each diffraction peak over a wide energy range, allowing linear measurement of incident intensity over the range of the energy scan. Extended X-ray absorption fine structure data are measured with a combination of a polycapillary lens and a diamond incident beam monitor. These data are of comparable quality to data measured without a lens and with an ionization chamber monitoring the incident beam intensity.

  19. In Situ X-Ray Absorption Spectroscopy Study of the LiNiO2 Electrode

    NASA Astrophysics Data System (ADS)

    Mansour, A. N.; McBreen, J.; Melendres, C. A.

    1997-03-01

    LiNiO2 is one of the most promising active material for the development of novel 4V rechargeable lithium batteries. Recent x-ray diffraction studies showed that the electrochemical reactivity of this electrode is sensitive to the structure of the starting material as well as the charged products. To further examine this material, we have conducted an x-ray absorption spectroscopy (XAS) study to determine the structure of this electrode as a function of its charge state. Specifically, the x-ray absorption Ni K-edge energy, the pre-edge structure, and local structure parameters such as bond lengths, coordination numbers and disorders were investigated at various states of charge corresponding to Li_(1-x)NiO2 for x values of 0.0, 0.11, 0.23, 0.34, 0.45, 0.82, and 0.99. The charging which proceeds via lithium de-intercalation was conducted using constant current anodization at 0.5 mA in a non aqueous electrolyte consisting of 1M LiPF6 in 1:1:3 propylene ! carbonate, ethylene carbonate and dimethyl carbonate. The XAS results for this electrode will be compared with those of γ-NiOOH and KNiIO_6, the latter being used as a reference for quadrivalent nickel.

  20. Absorption and Phase Contrast X-Ray Imaging in Paleontology Using Laboratory and Synchrotron Sources

    SciTech Connect

    Bidola, Pidassa; Stockmar, Marco; Achterhold, Klaus; Pfeiffer, Franz; Pacheco, Mirian L.A.F.; Soriano, Carmen; Beckmann, Felix; Herzen, Julia

    2015-10-01

    X-ray micro-computed tomography (CT) is commonly used for imaging of samples in biomedical or materials science research. Owing to the ability to visualize a sample in a nondestructive way, X-ray CT is perfectly suited to inspect fossilized specimens, which are mostly unique or rare. In certain regions of the world where important sedimentation events occurred in the Precambrian geological time, several fossilized animals are studied to understand questions related to their origin, environment, and life evolution. This article demonstrates the advantages of applying absorption and phase-contrast CT on the enigmatic fossil Corumbella werneri, one of the oldest known animals capable of building hard parts, originally discovered in Corumba (Brazil). Different tomographic setups were tested to visualize the fossilized inner structures: a commercial laboratory-based CT device, two synchrotron-based imaging setups using conventional absorption and propagation-based phase contrast, and a commercial X-ray microscope with a lens-coupled detector system, dedicated for radiography and tomography. Based on our results we discuss the strengths and weaknesses of the different imaging setups for paleontological studies.

  1. Hard x-ray phase contrast imaging using single absorption grating and hybrid semiconductor pixel detector.

    PubMed

    Krejci, Frantisek; Jakubek, Jan; Kroupa, Martin

    2010-11-01

    A method for x-ray phase contrast imaging is introduced in which only one absorption grating and a microfocus x-ray source in a tabletop setup are used. The method is based on precise subpixel position determination of the x-ray pattern projected by the grating directly from the pattern image. For retrieval of the phase gradient and absorption image (both images obtained from one exposure), it is necessary to measure only one projection of the investigated object. Thus, our method is greatly simplified compared with the phase-stepping method and our method can significantly reduce the time-consuming scanning and possibly the unnecessary dose. Furthermore, the technique works with a fully polychromatic spectrum and gives ample variability in object magnification. Consequently, the approach can open the way to further widespread application of phase contrast imaging, e.g., into clinical practice. The experimental results on a simple testing object as well as on complex biological samples are presented. PMID:21133473

  2. X-ray absorption spectroscopy of cuprous-thiolate clusters in proteins and model systems

    SciTech Connect

    Pickering, I.J.; George, G.N. ); Dameron, C.T.; Kurz, B.; Winge, D.R. ); Dance, I.G. )

    1993-10-20

    Cuprous-thiolate multimetallic clusters exist in a range of different biological molecules for which no structural information exists from X-ray crystallography. Spectroscopic tools such as X-ray absorption spectroscopy have provided the major structural insights into this family of biological molecules. Recent nuclear magnetic resonance data on silver-substituted metallothionein, thought to be analogous with the copper proteins, have suggested the presence of digonal coordination. In order to test this in the copper case, we have examined a series of structurally characterized cuprous-thiolate model compounds, containing different proportions of digonal and trigonal copper sites, using copper K-edge X-ray absorption spectroscopy. The edge spectra, which have been previously used as a probe for the average copper coordination environment in proteins, show little variation between the models, indicating that these are not useful as a probe of coordination environment in the case of cuprous-thiolate clusters (as opposed to isolated metal sites). We show that systematic trends in the average Cu-S bond length from EXAFS curve-fitting analysis can be used to obtain an estimate of the fraction of digonal and trigonal copper sites. This correlation is applied to a series of different proteins containing cuprous-thiolate clusters which are found to contain significant fractions of digonal copper. 41 refs., 7 figs., 3 tabs.

  3. Interstellar X-Ray Absorption Spectroscopy of the Crab Pulsar with the LETGS

    NASA Technical Reports Server (NTRS)

    Paerels, Frits; Weisskopf, Martin C.; Tennant, Allyn F.; ODell, Stephen L.; Swartz, Douglas A.; Kahn, Steven M.; Behar, Ehud; Becker, Werner; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    We study the interstellar X-ray absorption along the line of sight to the Crab Pulsar. The Crab was observed with the Low Energy Transmission Grating Spectrometer on the Chandra X-ray Observatory, and the pulsar, a point source, produces a full resolution spectrum. The continuum spectrum appears smooth, and we compare its parameters with other measurements of the pulsar spectrum. The spectrum clearly shows absorption edges due to interstellar Ne, Fe, and O. The O edge shows spectral structure that is probably due to O bound in molecules or dust. We search for near-edge structure (EXAFS) in the O absorption spectrum. The Fe L absorption spectrum is largely due to a set of unresolved discrete n=2-3 transitions in neutral or near-neutral Fe, and we analyze it using a new set of dedicated atomic structure calculations, which provide absolute cross sections. In addition to being interesting in its own right, the ISM absorption needs to be understood in quantitative detail in order to derive spectroscopic constraints on possible soft thermal radiation from the pulsar.

  4. X-ray absorption fine structure of aged, Pu-doped glass and ceramic waste forms

    NASA Astrophysics Data System (ADS)

    Hess, N. J.; Weber, W. J.; Conradson, S. D.

    1998-04-01

    X-ray absorption spectroscopic (XAS) studies were performed on three compositionally identical, Pu-doped, borosilicate glasses prepared 15 years ago at different α-activities by varying the 239Pu/ 238Pu isotopic ratio. The resulting α-activities ranged from 1.9×10 7 to 4.2×10 9 Bq/g and have current, accumulated doses between 8.8×10 15 to 1.9×10 18 α-decays/g. Two ceramic, polycrystalline zircon (ZrSiO 4) samples prepared 16 years ago with 10.0 wt% Pu was also investigated. Varying the 239Pu/ 238Pu isotopic ratio in these samples resulted in α-activities of 2.5×10 8 and 5.6×10 10 Bq/g and current, accumulated doses of 1.2×10 17 and 2.8×10 19 α-decays/g. The multicomponent composition of the waste forms permitted XAS investigations at six absorption edges for the borosilicate glass and at three absorption edges for the polycrystalline zircons. For both waste forms, analysis of extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectra indicates that the local environment around the cations exhibits different degrees of disorder as a result of the accumulated α-decay dose. In general, cations with short cation-oxygen bonds show little effect from self-radiation whereas cations with long cation-oxygen bonds show a greater degree of disorder with accumulated α-decay dose.

  5. Sensitive X-ray detectors made of methylammonium lead tribromide perovskite single crystals

    NASA Astrophysics Data System (ADS)

    Wei, Haotong; Fang, Yanjun; Mulligan, Padhraic; Chuirazzi, William; Fang, Hong-Hua; Wang, Congcong; Ecker, Benjamin R.; Gao, Yongli; Loi, Maria Antonietta; Cao, Lei; Huang, Jinsong

    2016-05-01

    The large mobilities and carrier lifetimes of hybrid perovskite single crystals and the high atomic numbers of Pb, I and Br make them ideal for X-ray and gamma-ray detection. Here, we report a sensitive X-ray detector made of methylammonium lead bromide perovskite single crystals. A record-high mobility–lifetime product of 1.2 × 10–2 cm2 V–1 and an extremely small surface charge recombination velocity of 64 cm s–1 are realized by reducing the bulk defects and passivating surface traps. Single-crystal devices with a thickness of 2–3 mm show 16.4% detection efficiency at near zero bias under irradiation with continuum X-ray energy up to 50 keV. The lowest detectable X-ray dose rate is 0.5 μGyair s–1 with a sensitivity of 80 μC Gy‑1air cm–2, which is four times higher than the sensitivity achieved with α-Se X-ray detectors. This allows the radiation dose applied to a human body to be reduced for many medical and security check applications.

  6. Instrument for x-ray absorption spectroscopy with in situ electrical control characterizations

    SciTech Connect

    Huang, Chun-Chao; Chang, Shu-Jui; Yang, Chao-Yao; Tseng, Yuan-Chieh; Chou, Hsiung

    2013-12-15

    We report a synchrotron-based setup capable of performing x-ray absorption spectroscopy and x-ray magnetic circular dichroism with simultaneous electrical control characterizations. The setup can enable research concerning electrical transport, element- and orbital-selective magnetization with an in situ fashion. It is a unique approach to the real-time change of spin-polarized electronic state of a material/device exhibiting magneto-electric responses. The performance of the setup was tested by probing the spin-polarized states of cobalt and oxygen of Zn{sub 1-x}Co{sub x}O dilute magnetic semiconductor under applied voltages, both at low (∼20 K) and room temperatures, and signal variations upon the change of applied voltage were clearly detected.

  7. X-ray absorption to determine the metal oxidation state of transition metal compounds

    NASA Astrophysics Data System (ADS)

    Jiménez-Mier, J.; Olalde-Velasco, P.; Carabalí-Sandoval, G.; Herrera-Pérez, G.; Chavira, E.; Yang, W.-L.; Denlinger, J.

    2013-07-01

    We present three examples where x-ray absorption at the transition metal L2,3 edges is used to investigate the valence states of various strongly correlated (SC) and technological relevant materials. Comparison with ligand field multiplet calculations is needed to determine the metal oxidation states. The examples are CrF2, the La1-xSrxCoO3 family and YVO3. For CrF2 the results indicate a disproportionation reaction that generates Cr+, Cr2+ and Cr3+ in different proportions that can be quantified directly from the x-ray spectra. Additionally, it is shown that Co2+ is present in the catalytic La1-xSrxCoO3 perovskite family. Finally, surface effects that change the vanadium valence are also found in YVO3 nanocrystals.

  8. Xe nanocrystals in Si studied by x-ray absorption fine structure spectroscopy

    SciTech Connect

    Faraci, Giuseppe; Pennisi, Agata R.; Zontone, Federico

    2007-07-15

    The structural configuration of Xe clusters, obtained by ion implantation in a Si matrix, has been investigated as a function of the temperature by x-ray absorption fine structure spectroscopy. In contrast with previous results, we demonstrate that an accurate analysis of the data, using high order cumulants, gives evidence of Xe fcc nanocrystals at low temperature, even in the as-implanted Si; expansion of the Xe lattice is always found as a function of the temperature, with no appreciable overpressure. We point out that a dramatic modification of these conclusions can be induced by an incorrect analysis using standard symmetrical pair distribution function G(r); for this reason, all the results were checked by x-ray diffraction measurements.

  9. Detection, identification and mapping of iron anomalies in brain tissue using X-ray absorption spectroscopy

    PubMed Central

    Mikhaylova, A; Davidson, M; Toastmann, H; Channell, J.E.T; Guyodo, Y; Batich, C; Dobson, J

    2005-01-01

    This work describes a novel method for the detection, identification and mapping of anomalous iron compounds in mammalian brain tissue using X-ray absorption spectroscopy. We have located and identified individual iron anomalies in an avian tissue model associated with ferritin, biogenic magnetite and haemoglobin with a pixel resolution of less than 5 μm. This technique represents a breakthrough in the study of both intra- and extra-cellular iron compounds in brain tissue. The potential for high-resolution iron mapping using microfocused X-ray beams has direct application to investigations of the location and structural form of iron compounds associated with human neurodegenerative disorders—a problem which has vexed researchers for 50 years. PMID:16849161

  10. Note: Sample chamber for in situ x-ray absorption spectroscopy studies of battery materials

    SciTech Connect

    Pelliccione, CJ; Timofeeva, EV; Katsoudas, JP; Segre, CU

    2014-12-01

    In situ x-ray absorption spectroscopy (XAS) provides element-specific characterization of both crystalline and amorphous phases and enables direct correlations between electrochemical performance and structural characteristics of cathode and anode materials. In situ XAS measurements are very demanding to the design of the experimental setup. We have developed a sample chamber that provides electrical connectivity and inert atmosphere for operating electrochemical cells and also accounts for x-ray interactions with the chamber and cell materials. The design of the sample chamber for in situ measurements is presented along with example XAS spectra from anode materials in operating pouch cells at the Zn and Sn K-edges measured in fluorescence and transmission modes, respectively. (C) 2014 AIP Publishing LLC.

  11. Observing heme doming in myoglobin with femtosecond X-ray absorption spectroscopya)

    PubMed Central

    Levantino, M.; Lemke, H. T.; Schirò, G.; Glownia, M.; Cupane, A.; Cammarata, M.

    2015-01-01

    We report time-resolved X-ray absorption measurements after photolysis of carbonmonoxy myoglobin performed at the LCLS X-ray free electron laser with nearly 100 fs (FWHM) time resolution. Data at the Fe K-edge reveal that the photoinduced structural changes at the heme occur in two steps, with a faster (∼70 fs) relaxation preceding a slower (∼400 fs) one. We tentatively attribute the first relaxation to a structural rearrangement induced by photolysis involving essentially only the heme chromophore and the second relaxation to a residual Fe motion out of the heme plane that is coupled to the displacement of myoglobin F-helix. PMID:26798812

  12. Detection, identification and mapping of iron anomalies in brain tissue using X-ray absorption spectroscopy

    SciTech Connect

    Mikhaylova, A.; Davidson, M.; Toastmann, H.; Channell, J.E.T.; Guyodo, Y.; Batich, C.; Dobson, J.

    2008-06-16

    This work describes a novel method for the detection, identification and mapping of anomalous iron compounds in mammalian brain tissue using X-ray absorption spectroscopy. We have located and identified individual iron anomalies in an avian tissue model associated with ferritin, biogenic magnetite and haemoglobin with a pixel resolution of less than 5 {micro}m. This technique represents a breakthrough in the study of both intra- and extra-cellular iron compounds in brain tissue. The potential for high-resolution iron mapping using microfocused X-ray beams has direct application to investigations of the location and structural form of iron compounds associated with human neurodegenerative disorders - a problem which has vexed researchers for 50 years.

  13. Pressure-induced structural distortion of TbMnO3 : A combined x-ray diffraction and x-ray absorption spectroscopy study

    NASA Astrophysics Data System (ADS)

    Chen, J. M.; Chou, T. L.; Lee, J. M.; Chen, S. A.; Chan, T. S.; Chen, T. H.; Lu, K. T.; Chuang, W. T.; Sheu, H.-S.; Chen, S. W.; Lin, C. M.; Hiraoka, N.; Ishii, H.; Tsuei, K. D.; Yang, T. J.

    2009-04-01

    The variation of electronic states and structural distortion in highly compressed multiferroic TbMnO3 was probed by x-ray diffraction (XRD) and x-ray absorption spectroscopy (XAS) using synchrotron radiation. Refined XRD data enabled observation of a reduced local Jahn-Teller (JT) distortion of Mn sites within MnO6 octahedra in TbMnO3 with increasing hydrostatic pressure. A progressively increasing intensity of the white line in MnK -edge x-ray absorption spectra of TbMnO3 was detected with increasing pressure. The absorption threshold of MnK -edge spectra of TbMnO3 is shifted toward higher energy, whereas the pre-edge peak is slightly shifted to lower energy with increasing hydrostatic pressure. We provide spectral evidence for pressure-induced bandwidth broadening for mangnites. The enhanced intensity of the white line and the shifted absorption threshold of MnK -edge spectra are explained in terms of a reduced JT distortion of MnO6 octahedra in compressed TbMnO3 . Comparison of XAS data with full-multiple-scattering calculations using code FDMNES shows satisfactory agreement between experimental and calculated MnK -edge spectra.

  14. A Spectral Variability Survey of X-ray Reflection and Absorption in Seyfert AGN using the Rossi X-ray Timing Explorer Database

    NASA Astrophysics Data System (ADS)

    Markowitz, Alex

    The Rossi X-ray Timing Explorer (RXTE) is the current longest-running X-ray mission. It has collected data on over 130 Active Galactic Nuclei (AGN) over its 15-year lifetime. We plan to systematically analyze the broad X-ray spectra of all AGN observed with RXTE to produce the ultimate and complete spectral sample with which to solidify the legacy of RXTE towards AGN science and towards understanding the nature of reprocessing and reflection processes in Seyferts. In many cases, RXTE conducted sustained monitoring spanning a baseline of many years, so our proposed time-averaged spectral analysis reduces the ambiguity inherent in individual snapshots due to source variability, thereby providing the community with long-term average X-ray spectral properties as well as identifying any state changes in sources. We will also perform time- and flux-resolved spectroscopy to search for variability in the Fe K alpha emission line in response to X-ray continuum flux variations to constrain its location via reverberation mapping, e.g., material commensurate with the optical Broad Line Region or a parsec- scale torus. Our proposed work will place important constraints on the location and homogeneity of the Compton-thick circumnuclear accreting gas. We will also search for variations in the line-of-sight column density of absorbing material in Seyferts to test classical Seyfert 1/2 unification schemes against newer models which rely on distributions of clumps of gas and for which X-ray absorption is a viewing-angle dependent probability, and provide observational constraints for these latter models. This research supports NASA Strategic Goal 2 by expanding scientific understanding of the universe in which we live, how the universe works, and how the observable universe came to be.

  15. Synchrotron X-ray Studies of the Keel of the Short-Spined Sea Urchin Lytechinus variegatus: Absorption Microtomography (microCT) and Small Beam Diffraction Mapping

    SciTech Connect

    Stock, S. R.; Barss, J.; Dahl, T.; Veis, A.; Almer, J. D.; De Carlo, F.

    2003-05-01

    In sea urchin teeth, the keel plays an important structural role, and this paper reports results of microstructural characterization of the keel of Lytechinus variegatus using two noninvasive synchrotron x-ray techniques: x-ray absorption microtomography (microCT) and x-ray diffraction mapping. MicroCT with 14 keV x-rays mapped the spatial distribution of mineral at the 1.3 microm level in a millimeter-sized fragment of a mature portion of the keel. Two rows of low absorption channels (i.e., primary channels) slightly less than 10 microm in diameter were found running linearly from the flange to the base of the keel and parallel to its sides. The primary channels paralleled the oral edge of the keel, and the microCT slices revealed a planar secondary channel leading from each primary channel to the side of the keel. The primary and secondary channels were more or less coplanar and may correspond to the soft tissue between plates of the carinar process. Transmission x-ray diffraction with 80.8 keV x-rays and a 0.1 mm beam mapped the distribution of calcite crystal orientations and the composition Ca(1-x)Mg(x)CO(3) of the calcite. Unlike the variable Mg concentration and highly curved prisms found in the keel of Paracentrotus lividus, a constant Mg content (x = 0.13) and relatively little prism curvature was found in the keel of Lytechinus variegatus.

  16. Development of a two-dimensional imaging system of X-ray absorption fine structure.

    PubMed

    Katayama, Misaki; Sumiwaka, Koichi; Hayashi, Kazuhiro; Ozutsumi, Kazuhiko; Ohta, Toshiaki; Inada, Yasuhiro

    2012-09-01

    A two-dimensional imaging system of X-ray absorption fine structure (XAFS) has been developed at beamline BL-4 of the Synchrotron Radiation Center of Ritsumeikan University. The system mainly consists of an ionization chamber for I(0) measurement, a sample stage, and a two-dimensional complementary metal oxide semiconductor (CMOS) image sensor for measuring the transmitted X-ray intensity. The X-ray energy shift in the vertical direction, which originates from the vertical divergence of the X-ray beam on the monochromator surface, is corrected by considering the geometrical configuration of the monochromator. This energy correction improves the energy resolution of the XAFS spectrum because each pixel in the CMOS detector has a very small vertical acceptance of ∼0.5 µrad. A data analysis system has also been developed to automatically determine the energy of the absorption edge. This allows the chemical species to be mapped based on the XANES feature over a wide area of 4.8 mm (H) × 3.6 mm (V) with a resolution of 10 µm × 10 µm. The system has been applied to the chemical state mapping of the Mn species in a LiMn(2)O(4) cathode. The heterogeneous distribution of the Mn oxidation state is demonstrated and is considered to relate to the slow delocalization of Li(+)-defect sites in the spinel crystal structure. The two-dimensional-imaging XAFS system is expected to be a powerful tool for analyzing the spatial distributions of chemical species in many heterogeneous materials such as battery electrodes. PMID:22898951

  17. Density Measurement for MORB Melts by X-ray Absorption Method

    NASA Astrophysics Data System (ADS)

    Sakamaki, T.; Urakawa, S.; Suzuki, A.; Ohtani, E.; Katayama, Y.

    2006-12-01

    Density of silicate melts at high pressure is one of the most important properties to understand magma migration in the planetary interior and the differentiation of the terrestrial planets. The density measurements of silicate melts have been carried out by several methods (shock compression experiments and sink-float method in static experiments, etc.). However, since these methods have difficulties in acquisition of data at a desired pressure and temperature, the density of the silicate melt have been measured under only a few conditions. Recently a new density measurement was developed by the X-ray absorption method. Advantage of this method is to measure density of liquids at a desired pressure and temperature. In the present study we measured the density of MORB melt by X-ray absorption method. Experiments were carried out at the BL22XU beamline at SPring-8. A DIA-type cubic anvil apparatus was used for generation of high pressure and temperature. We used tungsten carbide anvils with the top anvil sizes of 6 mm and 4 mm. The energy of monochromateized X-ray beam was 23 keV. The intensities of incident and transmitted X-ray were measured by ion chambers. The density of the melt was calculated on the basis of Beer-Lambert law. The starting material was a glass with the MORB composition. Experiments were made from 1 atm to 5 GPa, from 300 to 2000 K. We compared the density of MORB melt with the compression curve of the melt in previous works. The density measured by this study is lower than that expected from the compression curve determined at higher pressures by the sink-float method. Structural change of the MORB melt with increasing pressure might be attributed to this discrepancy.

  18. Density Measurement for MORB Melts by X-ray Absorption Method

    NASA Astrophysics Data System (ADS)

    Sakamaki, T.; Urakawa, S.; Ohtani, E.; Suzuki, A.; Katayama, Y.

    2005-12-01

    Density of silicate melts at high pressure is one of the most important properties to understand magma migration in the planetary interior and the differentiation of the terrestrial planets. The density measurements of silicate melts have been carried out by several methods (shock compression experiments and sink-float method in static experiments, etc.). However, since these methods have difficulties in acquisition of data at a desired pressure and temperature, the density of the silicate melt have been measured under only a few conditions. Recently a new density measurement was developed by the X-ray absorption method. Advantage of this method is to measure density of liquids at a desired pressure and temperature. In the present study we measured the density of MORB melt by X-ray absorption method. Experiments were carried out at the BL22XU beamline at SPring-8. A DIA-type cubic anvil apparatus was used for generation of high pressure and temperature. We used tungsten carbide anvils with the edge-length of 6 mm. The energy of monochromateized X-ray beam was 23 keV. The intensities of incident and transmitted X-ray were measured by ion chambers. The density of the melt was calculated on the basis of Beer-Lambert law. The starting material was a glass with the MORB composition. Experiments were made from 1 atm to 4 GPa, from 300 to 2200 K. We compared the density of MORB melt with the compression curve of the melt in previous works. The density measured by this study is lower than that expected from the compression curve determined at higher pressures by the sink-float method. Structural change of the MORB melt with increasing pressure might be attributed to this discrepancy.

  19. Ultrafast Excited State Relaxation of a Metalloporphyrin Revealed by Femtosecond X-ray Absorption Spectroscopy.

    PubMed

    Shelby, Megan L; Lestrange, Patrick J; Jackson, Nicholas E; Haldrup, Kristoffer; Mara, Michael W; Stickrath, Andrew B; Zhu, Diling; Lemke, Henrik T; Chollet, Matthieu; Hoffman, Brian M; Li, Xiaosong; Chen, Lin X

    2016-07-20

    Photoexcited Nickel(II) tetramesitylporphyrin (NiTMP), like many open-shell metalloporphyrins, relaxes rapidly through multiple electronic states following an initial porphyrin-based excitation, some involving metal centered electronic configuration changes that could be harnessed catalytically before excited state relaxation. While a NiTMP excited state present at 100 ps was previously identified by X-ray transient absorption (XTA) spectroscopy at a synchrotron source as a relaxed (d,d) state, the lowest energy excited state (J. Am. Chem. Soc., 2007, 129, 9616 and Chem. Sci., 2010, 1, 642), structural dynamics before thermalization were not resolved due to the ∼100 ps duration of the available X-ray probe pulse. Using the femtosecond (fs) X-ray pulses of the Linac Coherent Light Source (LCLS), the Ni center electronic configuration from the initial excited state to the relaxed (d,d) state has been obtained via ultrafast Ni K-edge XANES (X-ray absorption near edge structure) on a time scale from hundreds of femtoseconds to 100 ps. This enabled the identification of a short-lived Ni(I) species aided by time-dependent density functional theory (TDDFT) methods. Computed electronic and nuclear structure for critical excited electronic states in the relaxation pathway characterize the dependence of the complex's geometry on the electron occupation of the 3d orbitals. Calculated XANES transitions for these excited states assign a short-lived transient signal to the spectroscopic signature of the Ni(I) species, resulting from intramolecular charge transfer on a time scale that has eluded previous synchrotron studies. These combined results enable us to examine the excited state structural dynamics of NiTMP prior to thermal relaxation and to capture intermediates of potential photocatalytic significance. PMID:27286410

  20. X-Ray Absorption, Nuclear Infrared Emission, and Dust Covering Factors of AGNs: Testing Unification Schemes

    NASA Astrophysics Data System (ADS)

    Mateos, S.; Carrera, F. J.; Alonso-Herrero, A.; Hernán-Caballero, A.; Barcons, X.; Asensio Ramos, A.; Watson, M. G.; Blain, A.; Caccianiga, A.; Ballo, L.; Braito, V.; Ramos Almeida, C.

    2016-03-01

    We present the distributions of the geometrical covering factors of the dusty tori (f2) of active galactic nuclei (AGNs) using an X-ray selected complete sample of 227 AGNs drawn from the Bright Ultra-hard XMM-Newton Survey. The AGNs have z from 0.05 to 1.7, 2-10 keV luminosities between 1042 and 1046 erg s-1, and Compton-thin X-ray absorption. Employing data from UKIDSS, 2MASS, and the Wide-field Infrared Survey Explorer in a previous work, we determined the rest-frame 1-20 μm continuum emission from the torus, which we model here with the clumpy torus models of Nenkova et al. Optically classified type 1 and type 2 AGNs are intrinsically different, with type 2 AGNs having, on average, tori with higher f2 than type 1 AGNs. Nevertheless, ˜20% of type 1 AGNs have tori with large covering factors, while ˜23%-28% of type 2 AGNs have tori with small covering factors. Low f2 are preferred at high AGN luminosities, as postulated by simple receding torus models, although for type 2 AGNs the effect is certainly small. f2 increases with the X-ray column density, which implies that dust extinction and X-ray absorption take place in material that share an overall geometry and most likely belong to the same structure, the putative torus. Based on our results, the viewing angle, AGN luminosity, and also f2 determine the optical appearance of an AGN and control the shape of the rest-frame ˜1-20 μm nuclear continuum emission. Thus, the torus geometrical covering factor is a key ingredient of unification schemes.

  1. Probing the Absorption Structures in Seyfert Galaxies with X-ray Spectroscopy

    NASA Astrophysics Data System (ADS)

    Gelbord, J.

    2001-12-01

    The paradigm of the unified model for Seyfert galaxies has had many successes in explaining the range of phenomena observed in active galaxies. However, the structures invoked in this scenario have been difficult to observe due to their limited sizes and due to contaminating flux from other regions. As a result, some of these structures, notably the putative obscuring torus, are poorly constrained. The difficulty in isolating the emission from the central regions can be mitigated (but not eliminated!) by focusing upon high-energy radiation, which is dominated by direct and reprocessed radiation from the nuclear region. We have drawn upon the large number of X-ray spectra available in the ASCA archive in order to study the distribution of properties in a large sample of high-energy observations. Furthermore, by uniformly processing the data ourselves, we minimize systematic effects. One asset of X-rays is that they provide a sensitive probe of absorbers in the line of sight toward the central region, because photoelectric absorption cuts off the continuum at low energies. In the ASCA bandpass column densities of ~1021-23 cm-2 can be measured. This is an interesting range of densities because it allows us to distinguish between absorption in a torus or possibly a warped accretion disk (where column densities are expected to be high) and absorption taking place at larger scales in the host galaxy (where column densities are expected to be closer to Galactic values of 1020-21 cm-2). This data is then compared to data from other wavebands. Published radio studies (e.g.: Nagar & Wilson 1999, Kinney et al. 2000) have put constraints on the orientations of the accretion systems in Seyfert galaxies. We combine these and the X-ray measurements for the ~50 sources in these studies which have ASCA data in order to constrain the various possible absorption structures and test the unification scenario.

  2. X-ray absorption toward the red quasar 3C 212

    NASA Technical Reports Server (NTRS)

    Elvis, Martin; Fiore, Fabrizio; Mathur, Smita; Wilkes, Belinda J.

    1994-01-01

    A Roentgen Satellite (ROSAT) X-ray spectrum of the z = 1.049 'red quasar' 3C 212 has a strong low-energy cutoff. The spectrum can be fitted with a power law (of energy index 1.4(+0.8, -0.6) with low-energy photoelectric absorption in excess of the Galactic value that, if at the redhsift of the quasar, would have a column density of (0.9(+0.8, -0.6)) x 10(exp 22) atoms/sq cm. Possible sites for the absorption are a nuclear torus, an intervening damped Lyman-alpha system, or intracluster material (e.g., a cooling flow) around the quasar. The implied absorbing column density is sufficient to redden a normal quasar spectrum to the observed steep optical slope. The observed continuum, if dereddened by this amount, can produce the observed emission line fluxes and ratios. The absence of the graphite lambda-2175 feature in 3C 212 however, requires dust different from the local Milky Way composition, or an intervening absorber with z less than 0.4. Alternative acceptable fits to the X-ray spectrum are (1) a blackbody with a temperature of 0.7 keV (in the quasar frame) modified only by Galactic absorption, and (2) an optically thin thermal plasma with excess absorption. Although a blackbody spectrum would be unprecedented, the model is consistent with all the available X-ray and optical data and cannot be ruled out. We discuss possible observations that can discriminate among the above models.

  3. X-ray absorption spectroscopy of hemes and hemeproteins in solution: multiple scattering analysis.

    PubMed

    D'Angelo, Paola; Lapi, Andrea; Migliorati, Valentina; Arcovito, Alessandro; Benfatto, Maurizio; Roscioni, Otello Maria; Meyer-Klaucke, Wolfram; Della-Longa, Stefano

    2008-11-01

    A full quantitative analysis of Fe K-edge X-ray absorption spectra has been performed for hemes in two porphynato complexes, that is, iron(III) tetraphenylporphyrin chloride (Fe(III)TPPCl) and iron(III) tetraphenylporphyrin bis(imidazole) (Fe(III)TPP(Imid)2), in two protein complexes whose X-ray structure is known at atomic resolution (1.0 A), that is, ferrous deoxy-myoglobin (Fe(II)Mb) and ferric aquo-myoglobin (Fe(III)MbH2O), and in ferric cyano-myoglobin (Fe(III)MbCN), whose X-ray structure is known at lower resolution (1.4 A). The analysis has been performed via the multiple scattering approach, starting from a muffin tin approximation of the molecular potential. The Fe-heme structure has been obtained by analyzing independently the Extended X-ray Absorption Fine Structure (EXAFS) region and the X-ray Absorption Near Edge Structure (XANES) region. The EXAFS structural results are in full agreement with the crystallographic values of the models, with an accuracy of +/- 0.02 A for Fe-ligand distances, and +/-6 degrees for angular parameters. All the XANES features above the theoretical zero energy (in the lower rising edge) are well accounted for by single-channel calculations, for both Fe(II) and Fe(III) hemes, and the Fe-N p distance is determined with the same accuracy as EXAFS. XANES evaluations of Fe-5th and Fe-6th ligand distances are determined with 0.04-0.07 A accuracy; a small discrepancy with EXAFS (0.01 to 0.05 A beyond the statistical error), is found for protein compounds. Concerns from statistical correlation among parameters and multiple minima in the parameter space are discussed. As expected, the XANES accuracy is slightly lower than what was found for polarized XANES on Fe(III)MbCN single crystal (0.03-0.04 A), and states the actual state-of-the-art of XANES analysis when used to extract heme-normal parameters in a solution spectrum dominated by heme-plane scattering. PMID:18837548

  4. Theory and interpretation of L-shell X-ray absorption spectra

    NASA Astrophysics Data System (ADS)

    Nesvizhskii, Alexey I.

    X-ray absorption near edge structure (XANES) directly reflects the electronic structure in a material. However, despite significant progress in XANES theory, the quantitative analysis of XANES is not fully developed and remains a challenge. In this work, a detailed analysis of the L2,3 edge XANES in transition metals was performed using relativistic, self-consistent real space Green's function code FEFFS. Several prescriptions for taking into account core hole in calculations of x-ray absorption spectra (XAS) were discussed. It was found that in most cases of L2,3 edge XANES in transition metals, the initial state (ground state) calculations were in the best agreement with experimental data. A procedure was developed for quantitative applications of the sum rules for XAS, e.g., for x-ray magnetic circular dichroism and for obtaining hole counts. The approach is based on theoretical atomic calculations of transformations relating various experimental spectra to corresponding operator-spectral densities. This approach overcomes the difficulties of background subtraction and hole-count normalization of other sum rule analysis methods and yields quantitative values for spin- and orbital-moments from experimental absorption spectra. The developed approach was theoretically tested and applied to experimental XAS data in Cu, Ni, Co, Fe, and other materials. Hole counts obtained from XAS are often interpreted in terms of free-atom occupation numbers or Mulliken counts. We demonstrated that renormalized-atom (RA) counts are a better choice to characterize the configuration of occupied electron states in molecules and condensed matter. A projection-operator approach was introduced to subtract delocalized states and to determine such hole counts from XAS quantitatively. Theoretical tests for the s- and d-electrons in transition metals showed that the approach works well. A formalism was developed based on time dependent local density approximation (TDLDA) theory that takes

  5. X-ray absorption spectral studies of copper (II) mixed ligand complexes

    NASA Astrophysics Data System (ADS)

    Soni, B.; Dar, Davood Ah; Shrivastava, B. D.; Prasad, J.; Srivastava, K.

    2014-09-01

    X-ray absorption spectra at the K-edge of copper have been studied in two copper mixed ligand complexes, one having tetramethyethylenediamine (tmen) and the other having tetraethyethylenediamine (teen) as one of the ligands. The spectra have been recorded at BL-8 dispersive extended X-ray absorption fine structure (EXAFS) beamline at the 2.5 GeV INDUS- 2 synchrotron, RRCAT, Indore, India. The data obtained has been processed using the data analysis program Athena. The energy of the K-absorption edge, chemical shift, edge-width and shift of the principal absorption maximum in the complexes have been determined and discussed. The values of these parameters have been found to be approximately the same in both the complexes indicating that the two complexes possess similar chemical environment around the copper metal atom. The chemical shift has been utilized to estimate effective nuclear charge on the absorbing atom. The normalized EXAFS spectra have been Fourier transformed. The position of the first peak in the Fourier transform gives the value of first shell bond length, which is shorter than the actual bond length because of energy dependence of the phase factors in the sine function of the EXAFS equation. This distance is thus the phase- uncorrected bond length. Bond length has also been determined by Levy's, Lytle's and Lytle, Sayers and Stern's (LSS) methods. The results obtained from LSS and the Fourier transformation methods are comparable with each other, since both are phase uncorrected bond lengths.

  6. In vivo X-ray fluorescence of lead in bone: review and current issues.

    PubMed Central

    Todd, A C; Chettle, D R

    1994-01-01

    Bone lead measurements can assess long-term lead dosimetry because the residence time of lead in bone is long. Bone lead measurements thus complement blood and plasma lead measurements, which reflect more short-term exposure. Although the noninvasive, in vivo measurement of lead in bone by X-ray fluorescence (XRF) has been under development since the 1970s, its use is still largely confined to research institutions. There are three principal methods used that vary both in the how lead X-rays are fluoresced and in which lead X-rays are fluoresced. Several groups have reported the independent development of in vivo measurement systems, the majority adopting the 109Cd K XRF method because of its advantages: a robust measurement, a lower detection limit (compared to 57Co K XRF), and a lower effective (radiation) dose (compared to L XRF) when calculated according to the most recent guidelines. These advantages, and the subsequent widespread adoption of the 109Cd method, are primarily consequences of the physics principles of the technique. This paper presents an explanation of the principles of XRF, a description of the practical measurement systems, a review of the human bone lead studies performed to date; and a discussion of some issues surrounding future application of the methods. Images p172-a PMID:8033846

  7. In Situ Density Measurement of Basaltic Melts at High Pressure by X-ray Absorption Method

    NASA Astrophysics Data System (ADS)

    Ando, R.; Ohtani, E.; Suzuki, A.; Urakawa, S.; Katayama, Y.

    2004-12-01

    Density of silicate melt at high pressure is one of the most important properties to understand magma migration in the planetary interior. However, because of experimental difficulties, the density of magma at high pressure is poorly known. Katayama et al. (1996) recently developed a new in situ density measurement method for metallic melts, based on the density dependency of X-ray absorption in the sample. In this study, we tried to measure the density of basaltic melt by this absorption method. When X-ray is transmitted to the sample, the intensity of the transmitted X-ray beam (I) is expressed as follows; I=I0exp(-μ ρ t), where I0 is the intensity of incident X-ray beam, μ is the mass absorption coefficient, ρ is the density of the sample, and t is the thickness of the sample. If t and μ are known, we can determine the density of the sample by measuring I and I0. This is the principle of the absorption method for density measurement. In this study, in order to determine t, we used a single crystalline diamond cylinder as a sample capsule, diamond is less compressive and less deformable so that even at high pressure t (thickness of the sample at the point x) is expressed as follows; t = 2*(R02-x2)1/2, R0 is the inner radius of cylinder at the ambient condition, and x is distance from a center of the capsule. And diamond also shows less absorption so that this make it possible to measure the density of silicate melt with smaller absorption coefficient than metallic melts. In order to know the μ of the sample, we measured both densities (ρ ) and absorptions (I/I0) for some glasses and crystals with same composition of the sample at the ambient condition, and calculated as fallows; μ =ln(I/I0)/ρ . Experiments were made at the beamline (BL22XU) of SPring-8. For generation of high pressure and high temperature, we used DIA-type cubic anvil apparatus (SMAP180) there. We used tungsten carbide anvils with the edge-length of 6 mm. The energy of monochromatic X-ray

  8. A variable absorption feature in the X-ray spectrum of a magnetar.

    PubMed

    Tiengo, Andrea; Esposito, Paolo; Mereghetti, Sandro; Turolla, Roberto; Nobili, Luciano; Gastaldello, Fabio; Götz, Diego; Israel, Gian Luca; Rea, Nanda; Stella, Luigi; Zane, Silvia; Bignami, Giovanni F

    2013-08-15

    Soft-γ-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs) are slowly rotating, isolated neutron stars that sporadically undergo episodes of long-term flux enhancement (outbursts) generally accompanied by the emission of short bursts of hard X-rays. This behaviour can be understood in the magnetar model, according to which these sources are mainly powered by their own magnetic energy. This is supported by the fact that the magnetic fields inferred from several observed properties of SGRs and AXPs are greater than-or at the high end of the range of-those of radio pulsars. In the peculiar case of SGR 0418+5729, a weak dipole magnetic moment is derived from its timing parameters, whereas a strong field has been proposed to reside in the stellar interior and in multipole components on the surface. Here we show that the X-ray spectrum of SGR 0418+5729 has an absorption line, the properties of which depend strongly on the star's rotational phase. This line is interpreted as a proton cyclotron feature and its energy implies a magnetic field ranging from 2 × 10(14) gauss to more than 10(15) gauss. PMID:23955229

  9. Plutonium-uranium mixed oxide characterization by coupling micro-X-ray diffraction and absorption investigations

    NASA Astrophysics Data System (ADS)

    Degueldre, C.; Martin, M.; Kuri, G.; Grolimund, D.; Borca, C.

    2011-09-01

    Plutonium-uranium mixed oxide (MOX) fuels are currently used in nuclear reactors. The potential differences of metal redox state and microstructural developments of the matrix before and after irradiation are commonly analysed by electron probe microanalysis. In this work the structure and next-neighbor atomic environments of Pu and U oxide features within unirradiated homogeneous MOX and irradiated (60 MW d kg -1) MOX samples was analysed by micro-X-ray fluorescence (μ-XRF), micro-X-ray diffraction (μ-XRD) and micro-X-ray absorption fine structure (μ-XAFS) spectroscopy. The grain properties, chemical bonding, valences and stoichiometry of Pu and U are determined from the experimental data gained for the unirradiated as well as for irradiated fuel material examined in the center of the fuel as well as in its peripheral zone (rim). The formation of sub-grains is observed as well as their development from the center to the rim (polygonization). In the irradiated sample Pu remains tetravalent (>95%) and no (<5%) Pu(V) or Pu(VI) can be detected while the fuel could undergo slight oxidation in the rim zone. Any slight potential plutonium oxidation is buffered by the uranium dioxide matrix while locally fuel cladding interaction could also affect the redox of the fuel.

  10. Solvation structure of the halides from x-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Antalek, Matthew; Pace, Elisabetta; Hedman, Britt; Hodgson, Keith O.; Chillemi, Giovanni; Benfatto, Maurizio; Sarangi, Ritimukta; Frank, Patrick

    2016-07-01

    Three-dimensional models for the aqueous solvation structures of chloride, bromide, and iodide are reported. K-edge extended X-ray absorption fine structure (EXAFS) and Minuit X-ray absorption near edge (MXAN) analyses found well-defined single shell solvation spheres for bromide and iodide. However, dissolved chloride proved structurally distinct, with two solvation shells needed to explain its strikingly different X-ray absorption near edge structure (XANES) spectrum. Final solvation models were as follows: iodide, 8 water molecules at 3.60 ± 0.13 Å and bromide, 8 water molecules at 3.40 ± 0.14 Å, while chloride solvation included 7 water molecules at 3.15 ± 0.10 Å, and a second shell of 7 water molecules at 4.14 ± 0.30 Å. Each of the three derived solvation shells is approximately uniformly disposed about the halides, with no global asymmetry. Time-dependent density functional theory calculations simulating the chloride XANES spectra following from alternative solvation spheres revealed surprising sensitivity of the electronic state to 6-, 7-, or 8-coordination, implying a strongly bounded phase space for the correct structure during an MXAN fit. MXAN analysis further showed that the asymmetric solvation predicted from molecular dynamics simulations using halide polarization can play no significant part in bulk solvation. Classical molecular dynamics used to explore chloride solvation found a 7-water solvation shell at 3.12 (-0.04/+0.3) Å, supporting the experimental result. These experiments provide the first fully three-dimensional structures presenting to atomic resolution the aqueous solvation spheres of the larger halide ions.