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Sample records for absorption spectra x-ray

  1. 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.

  2. Chemical Sensitivity of the Sulfur K-Edge X-ray Absorption Spectra of Organic Disulfides.

    PubMed

    Pickering, Ingrid J; Barney, Monica; Cotelesage, Julien J H; Vogt, Linda; Pushie, M Jake; Nissan, Andrew; Prince, Roger C; George, Graham N

    2016-09-22

    Sulfur K-edge X-ray absorption spectroscopy increasingly is used as a tool to provide speciation information about the sulfur chemical form in complex samples, with applications ranging from fossil fuels to soil science to health research. As part of an ongoing program of systematic investigations of the factors that affect the variability of sulfur K near-edge spectra, we have examined the X-ray absorption spectra of a series of organic symmetric disulfide compounds. We have used polarized sulfur K-edge spectra of single crystals of dibenzyl disulfide to confirm the assignments of the major transitions in the spectrum as 1s → (S-S)σ* and 1s → (S-C)σ*. We also have examined the solution spectra of an extended series of disulfides and show that the spectra change in a systematic and predictable manner with the nature of the external group. PMID:27571342

  3. 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.

  4. 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

  5. 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.

  6. Soft X-ray absorption excess in gamma-ray burst afterglow spectra: Absorption by turbulent ISM

    NASA Astrophysics Data System (ADS)

    Tanga, M.; Schady, P.; Gatto, A.; Greiner, J.; Krause, M. G. H.; Diehl, R.; Savaglio, S.; Walch, S.

    2016-10-01

    Two-thirds of long duration gamma-ray bursts (GRBs) show soft X-ray absorption in excess of the Milky Way. The column densities of metals inferred from UV and optical spectra differ from those derived from soft X-ray spectra, at times by an order of magnitude, with the latter being higher. The origin of the soft X-ray absorption excess observed in GRB X-ray afterglow spectra remains a heavily debated issue, which has resulted in numerous investigations on the effect of hot material both internal and external to the GRB host galaxy on our X-ray afterglow observations. Nevertheless, all models proposed so far have either only been able to account for a subset of our observations (i.e. at z> 2), or they have required fairly extreme conditions to be present within the absorbing material. In this paper, we investigate the absorption of the GRB afterglow by a collisionally ionised and turbulent interstellar medium (ISM). We find that a dense (3 cm-3) collisionally ionised ISM could produce UV/optical and soft X-ray absorbing column densities that differ by a factor of 10. However the UV/optical and soft X-ray absorbing column densities for such sightlines are 2-3 orders of magnitude lower in comparison to the GRB afterglow spectra. For those GRBs with a larger soft X-ray excess by up to an order of magnitude, the contribution in absorption from a turbulent ISM as considered here would ease the required conditions of additional absorbing components, such as the GRB circumburst medium and intergalactic medium.

  7. Calibration and analysis of spatially resolved x-ray absorption spectra from a nonuniform plasma

    SciTech Connect

    Knapp, P. F.; Hansen, S. B.; Pikuz, S. A.; Shelkovenko, T. A.; Hammer, D. A.

    2012-07-15

    We report here the calibration and analysis techniques used to obtain spatially resolved density and temperature measurements of a pair of imploding aluminum wires from x-ray absorption spectra. A step wedge is used to measure backlighter fluence at the film, allowing transmission through the sample to be measured with an accuracy of {+-}14% or better. A genetic algorithm is used to search the allowed plasma parameter space and fit synthetic spectra with 20 {mu}m spatial resolution to the measured spectra, taking into account that the object plasma nonuniformity must be physically reasonable. The inferred plasma conditions must be allowed to vary along the absorption path in order to obtain a fit to the spectral data. The temperature is estimated to be accurate to within {+-}25% and the density to within a factor of two. This information is used to construct two-dimensional maps of the density and temperature of the object plasma.

  8. 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.

  9. 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

  10. A wavelet analysis for the X-ray absorption spectra of molecules

    SciTech Connect

    Penfold, T. J.; Tavernelli, I.; Rothlisberger, U.; Milne, C. J.; Abela, R.; Reinhard, M.; Nahhas, A. El; Chergui, M.

    2013-01-07

    We present a Wavelet transform analysis for the X-ray absorption spectra of molecules. In contrast to the traditionally used Fourier transform approach, this analysis yields a 2D correlation plot in both R- and k-space. As a consequence, it is possible to distinguish between different scattering pathways at the same distance from the absorbing atom and between the contributions of single and multiple scattering events, making an unambiguous assignment of the fine structure oscillations for complex systems possible. We apply this to two previously studied transition metal complexes, namely iron hexacyanide in both its ferric and ferrous form, and a rhenium diimine complex, [ReX(CO){sub 3}(bpy)], where X = Br, Cl, or ethyl pyridine (Etpy). Our results demonstrate the potential advantages of using this approach and they highlight the importance of multiple scattering, and specifically the focusing phenomenon to the extended X-ray absorption fine structure (EXAFS) spectra of these complexes. We also shed light on the low sensitivity of the EXAFS spectrum to the Re-X scattering pathway.

  11. Galactic Soft X-ray Emission Revealed with Spectroscopic Study of Absorption and Emission Spectra

    NASA Astrophysics Data System (ADS)

    Yamasaki, Noriko Y.; Mitsuda, K.; Takei, Y.; Hagihara, T.; Yoshino, T.; Wang, Q. D.; Yao, Y.; McCammon, D.

    2010-03-01

    Spectroscopic study of Oxygen emission/absorption lines is a new tool to investigate the nature of the soft X-ray background. We investigated the emission spectra of 14 fields obtained by Suzaku, and detected OVII and OVIII lines separately. There is an almost isotropic OVII line emission with 2 LU intensity. As the attenuation length in the Galactic plane for that energy is short, that OVII emission should arise within 300 pc of our neighborhood. In comparison with the estimated emission measure for the local bubble, the most plausible origin of this component is the solar wind charge exchange with local interstellar materials. Another component presented from the correlation between the OVII and OVIII line intensity is a thermal emission with an apparent temperature of 0.2 keV with a field-to-field fluctuation of 10% in temperature, while the intensity varies about a factor of 4. By the combination analysis of the emission and the absorption spectra, we can investigate the density and the scale length of intervening plasma separately. We analyzed the Chanrdra grating spectra of LMC X-3 and PKS 2155-304, and emission spectra toward the line of sight by Suzaku. In both cases, the combined analysis showed that the hot plasma is not iso-thermal nor uniform. Assuming an exponential disk distribution, the thickness of the disk is as large as a few kpc. It suggests that there is a thick hot disk or hot halo surrounding our Galaxy, which is similar to X-ray hot haloes around several spiral galaxies.

  12. Simulation of X-ray absorption spectra with orthogonality constrained density functional theory†

    PubMed Central

    Derricotte, Wallace D.; Evangelista, Francesco A.

    2015-01-01

    Orthogonality constrained density functional theory (OCDFT) is a variational time-independent approach for the computation of electronic excited states. In this work we extend OCDFT to compute core-excited states and generalize the original formalism to determine multiple excited states. Benchmark computations on a set of 13 small molecules and 40 excited states show that unshifted OCDFT/B3LYP excitation energies have a mean absolute error of 1.0 eV. Contrary to time-dependent DFT, OCDFT excitation energies for first- and second-row elements are computed with near-uniform accuracy. OCDFT core excitation energies are insensitive to the choice of the functional and the amount of Hartree–Fock exchange. We show that OCDFT is a powerful tool for the assignment of X-ray absorption spectra of large molecules by simulating the gas-phase near-edge spectrum of adenine and thymine. PMID:25690350

  13. Effects of domain size on x-ray absorption spectra of boron nitride doped graphenes

    NASA Astrophysics Data System (ADS)

    Li, Xin; Hua, Weijie; Wang, Bo-Yao; Pong, Way-Faung; Glans, Per-Anders; Guo, Jinghua; Luo, Yi

    2016-08-01

    Doping is an efficient way to open the zero band gap of graphene. The control of the dopant domain size allows us to tailor the electronic structure and the properties of the graphene. We have studied the electronic structure of boron nitride doped graphenes with different domain sizes by simulating their near-edge X-ray absorption fine structure (NEXAFS) spectra at the N K-edge. Six different doping configurations (five quantum dot type and one phase-separated zigzag-edged type) were chosen, and N K-edge NEXAFS spectra were calculated with large truncated cluster models by using the density functional theory with hybrid functional and the equivalent core hole approximation. The opening of the band gap as a function of the domain size is revealed. We found that nitrogens in the dopant boundary contribute a weaker, red-shifted π* peak in the spectra as compared to those in the dopant domain center. The shift is related to the fact that these interfacial nitrogens dominate the lowest conduction band of the system. Upon increasing the domain size, the ratio of interfacial atom decreases, which leads to a blue shift of the π* peak in the total NEXAFS spectra. The spectral evolution agrees well with experiments measured at different BN-dopant concentrations and approaches to that of a pristine h-BN sheet.

  14. On Different Absorption Components in the X-ray Spectra of the Intermediate Polar Systems

    NASA Astrophysics Data System (ADS)

    Balman, S.; Okcu, B.

    2014-07-01

    We present orbital phase-resolved spectroscopy of the Intermediate polars (IP) AO Psc, HT Cam, V1223 Sgr and XSS J0056+4548 using the XMM-Newton EPIC pn data. We detect increase of absorption by neutral hydrogen column density N_{H} during the phases corresponding to the orbital minima in a range ˜ (1.0-2.0)× 10^{22} cm^{-2}. AO Psc indicates spectral hardening in the soft plasma emission component. HT Cam, reveals an increase of N_{H} at the orbital minimum from 0.05× 10^{22} cm^{-2} to 0.13× 10^{22} cm^{-2}. These high N_{H} values are most likely a result of absorption by the bulge material at the accretion impact zone. We discuss implications of this interms of warmabsorbers in IPs and bulge temperatures. The four IPs reveal a second high absorption component that is constant over the orbital phase in a range (5.0-11.0)× 10^{22} cm^{-2}. We attribute this component to the accretion column/curtain. These results are in accordance with the orbital phase-resolved analysis presented in Pekon & Balman (2011) for EX Hya and (2012) for FO Aqr. We strongly suggest that absorption by the bulge at the accretion impact zone is a distinct component in the IP X-ray spectra.

  15. Double photoexcitation involving 2p and 4f electrons in L3 -edge x-ray absorption spectra of protactinium

    NASA Astrophysics Data System (ADS)

    Hennig, Christoph; Le Naour, Claire; Auwer, Christophe Den

    2008-06-01

    The L3 -edge x-ray absorption spectrum of Pa(V) fluoride in aqueous solution show clear evidence for the double photoexcitation involving 2p and 4f electrons. A comparison with the [2p4f] double-electron excitations observed in the L3 -edge x-ray absorption spectra of other actinides (thorium, uranium, neptunium, plutonium, and americium) indicates a monotonic increase in the excitation energy. The sharp edgelike structure of the multielectron excitation reveals the origin of a shake-up channel.

  16. Gravitationally redshifted absorption lines in the X-ray burst spectra of a neutron star.

    PubMed

    Cottam, J; Paerels, F; Mendez, M

    2002-11-01

    The fundamental properties of neutron stars provide a direct test of the equation of state of cold nuclear matter, a relationship between pressure and density that is determined by the physics of the strong interactions between the particles that constitute the star. The most straightforward method of determining these properties is by measuring the gravitational redshift of spectral lines produced in the neutron star photosphere. The equation of state implies a mass-radius relation, while a measurement of the gravitational redshift at the surface of a neutron star provides a direct constraint on the mass-to-radius ratio. Here we report the discovery of significant absorption lines in the spectra of 28 bursts of the low-mass X-ray binary EXO0748-676. We identify the most significant features with the Fe XXVI and XXV n = 2-3 and O VIII n = 1-2 transitions, all with a redshift of z = 0.35, identical within small uncertainties for the respective transitions. For an astrophysically plausible range of masses (M approximately 1.3-2.0 solar masses; refs 2-5), this value is completely consistent with models of neutron stars composed of normal nuclear matter, while it excludes some models in which the neutron stars are made of more exotic matter. PMID:12422210

  17. Interpretation of X-ray absorption spectra of As(III) in solution using Monte Carlo simulations.

    PubMed

    Canche-Tello, Jesus; Vargas, M Cristina; Hérnandez-Cobos, Jorge; Ortega-Blake, Iván; Leclercq, Amelie; Solari, Pierre Lorenzo; Den Auwer, Christophe; Mustre de Leon, José

    2014-11-20

    We performed X-ray absorption spectroscopy measurements on the arsenic K-edge of As(III) in solution under acidic conditions. Extended X-ray absorption fine structure (EXAFS) and X-ray near edge structure (XANES) spectra were compared with theoretical calculations which use local atomic structure configurations, either derived from density functional theory (DFT) energy minimization (EM) calculations or based on classical Monte Carlo (MC) simulations, for a As(OH)3 cluster surrounded by water molecules. The nearest arsenic-oxygen distances obtained from the fit of the XAFS spectra are consistent with the distances present in configurations derived from Monte Carlo simulations but not with those obtained from DFT-EM calculations. Calculations of XANES using either DFT-EM or the average configuration obtained from MC simulations do not reproduce the XANES spectra in the vicinity of the absorption edge. However, specific local atomic structural configurations of the As(OH)3 and water molecules, obtained from MC simulations, which show some ordering of water molecules up to 5 Å from the arsenic, reproduce qualitatively the experimental spectra. These results highlight the capability of XANES to yield information about hydration of ions in solution.

  18. First-principles calculation of principal Hugoniot and K-shell X-ray absorption spectra for warm dense KCl

    SciTech Connect

    Zhao, Shijun; Zhang, Shen; Kang, Wei; Li, Zi; Zhang, Ping; He, Xian-Tu

    2015-06-15

    Principal Hugoniot and K-shell X-ray absorption spectra of warm dense KCl are calculated using the first-principles molecular dynamics (FPMD) method. Evolution of electronic structures as well as the influence of the approximate description of ionization on pressure (caused by the underestimation of the energy gap between conduction bands and valence bands) in the first-principles method are illustrated by the calculation. It is shown that approximate description of ionization in FPMD has small influence on Hugoniot pressure due to mutual compensation of electronic kinetic pressure and virial pressure. The calculation of X-ray absorption spectra shows that the band gap of KCl persists after the pressure ionization of the 3p electrons of Cl and K taking place at lower energy, which provides a detailed understanding to the evolution of electronic structures of warm dense matter.

  19. Soft X-ray absorption spectra of aqueous salt solutions with highly charged cations in liquid microjets

    SciTech Connect

    Schwartz, Craig P.; Uejio, Janel S.; Duffin, Andrew M.; Drisdell, Walter S.; Smith, Jared D.; Saykally, Richard J.

    2010-03-11

    X-ray absorption spectra of 1M aqueous solutions of indium (III) chloride, yttrium (III) bromide, lanthanum (III) chloride, tin (IV) chloride and chromium (III) chloride have been measured at the oxygen K-edge. Relatively minor changes are observed in the spectra compared to that of pure water. SnCl{sub 4} and CrCl{sub 3} exhibit a new onset feature which is attributed to formation of hydroxide or other complex molecules in the solution. At higher energy, only relatively minor, but salt-specific changes in the spectra occur. The small magnitude of the observed spectral changes is ascribed to offsetting perturbations by the cations and anions.

  20. Predicting X-ray absorption spectra of semiconducting polymers for electronic structure and morphology characterization

    NASA Astrophysics Data System (ADS)

    Su, Gregory; Patel, Shrayesh; Pemmaraju, C. Das; Kramer, Edward; Prendergast, David; Chabinyc, Michael

    2015-03-01

    Core-level X-ray absorption spectroscopy (XAS) reveals important information on the electronic structure of materials and plays a key role in morphology characterization. Semiconducting polymers are the active component in many organic electronics. Their electronic properties are critically linked to device performance, and a proper understanding of semiconducting polymer XAS is crucial. Techniques such as resonant X-ray scattering rely on core-level transitions to gain materials contrast and probe orientational order. However, it is difficult to identify these transitions based on experiments alone, and complementary simulations are required. We show that first-principles calculations can capture the essential features of experimental XAS of semiconducting polymers, and provide insight into which molecular model, such as oligomers or periodic boundary conditions, are best suited for XAS calculations. Simulated XAS can reveal contributions from individual atoms and be used to visualize molecular orbitals. This allows for improved characterization of molecular orientation and scattering analysis. These predictions lay the groundwork for understanding how chemical makeup is linked to electronic structure, and to properly utilize experiments to characterize semiconducting polymers.

  1. Restricted active space calculations of L-edge X-ray absorption spectra: from molecular orbitals to multiplet states.

    PubMed

    Pinjari, Rahul V; Delcey, Mickaël G; Guo, Meiyuan; Odelius, Michael; Lundberg, Marcus

    2014-09-28

    The metal L-edge (2p → 3d) X-ray absorption spectra are affected by a number of different interactions: electron-electron repulsion, spin-orbit coupling, and charge transfer between metal and ligands, which makes the simulation of spectra challenging. The core restricted active space (RAS) method is an accurate and flexible approach that can be used to calculate X-ray spectra of a wide range of medium-sized systems without any symmetry constraints. Here, the applicability of the method is tested in detail by simulating three ferric (3d(5)) model systems with well-known electronic structure, viz., atomic Fe(3+), high-spin [FeCl6](3-) with ligand donor bonding, and low-spin [Fe(CN)6](3-) that also has metal backbonding. For these systems, the performance of the core RAS method, which does not require any system-dependent parameters, is comparable to that of the commonly used semi-empirical charge-transfer multiplet model. It handles orbitally degenerate ground states, accurately describes metal-ligand interactions, and includes both single and multiple excitations. The results are sensitive to the choice of orbitals in the active space and this sensitivity can be used to assign spectral features. A method has also been developed to analyze the calculated X-ray spectra using a chemically intuitive molecular orbital picture.

  2. Finite temperature effects on the X-ray absorption spectra of lithium compounds: first-principles interpretation of X-ray Raman measurements.

    PubMed

    Pascal, Tod A; Boesenberg, Ulrike; Kostecki, Robert; Richardson, Thomas J; Weng, Tsu-Chien; Sokaras, Dimosthenis; Nordlund, Dennis; McDermott, Eamon; Moewes, Alexander; Cabana, Jordi; Prendergast, David

    2014-01-21

    We elucidate the role of room-temperature-induced instantaneous structural distortions in the Li K-edge X-ray absorption spectra (XAS) of crystalline LiF, Li2SO4, Li2O, Li3N, and Li2CO3 using high resolution X-ray Raman spectroscopy (XRS) measurements and first-principles density functional theory calculations within the eXcited electron and Core Hole approach. Based on thermodynamic sampling via ab initio molecular dynamics simulations, we find calculated XAS in much better agreement with experiment than those computed using the rigid crystal structure alone. We show that local instantaneous distortion of the atomic lattice perturbs the symmetry of the Li 1s core-excited-state electronic structure, broadening spectral line-shapes and, in some cases, producing additional spectral features. The excellent agreement with high-resolution XRS measurements validates the accuracy of our first-principles approach to simulating XAS, and provides both accurate benchmarks for model compounds and a predictive theoretical capability for identification and characterization of multi-component systems, such as lithium-ion batteries, under working conditions.

  3. First-principles calculations of K-shell X-ray absorption spectra for warm dense nitrogen

    NASA Astrophysics Data System (ADS)

    Li, Zi; Zhang, Shen; Wang, Cong; Kang, Wei; Zhang, Ping

    2016-05-01

    X-ray absorption spectrum is a powerful tool for atomic structure detection on warm dense matter. Here, we perform first-principles molecular dynamics and X-ray absorption spectrum calculations on warm dense nitrogen along a Hugoniot curve. From the molecular dynamics trajectory, the detailed atomic structures are examined for each thermodynamical condition. The K-shell X-ray absorption spectrum is calculated, and its changes with temperature and pressure along the Hugoniot curve are discussed. The warm dense nitrogen systems may contain isolated nitrogen atoms, N2 molecules, and nitrogen clusters, which show quite different contributions to the total X-ray spectrum due to their different electron density of states. The changes of X-ray spectrum along the Hugoniot curve are caused by the different nitrogen structures induced by the temperature and the pressure. Some clear signatures on X-ray spectrum for different thermodynamical conditions are pointed out, which may provide useful data for future X-ray experiments.

  4. Theoretical characterization of X-ray absorption, emission, and photoelectron spectra of nitrogen doped along graphene edges.

    PubMed

    Wang, Xianlong; Hou, Zhufeng; Ikeda, Takashi; Oshima, Masaharu; Kakimoto, Masa-aki; Terakura, Kiyoyuki

    2013-01-24

    K-edge X-ray absorption (XAS), emission (XES), and photoelectron (XPS) spectra of nitrogen doped along graphene edges are systematically investigated by using first-principles methods. In this study we considered pyridinium-like, pyridine-like, cyanide-like, and amine-like nitrogens at armchair and zigzag edges and pyrrole-like nitrogen at armchair edge as well as graphite-like nitrogen at graphene interior site. Our results indicate that nitrogen configuration and its location (armchair or zigzag edge) in nitrogen-doped graphene can be identified via the spectral analysis. Furthermore, some controversial spectral features observed in experiment for N-doped graphene-like materials are unambiguously assigned. The present analysis gives an explanation to the reason why the peak assignment is usually made differently between XPS and XAS.

  5. Vibronic fine structure in high-resolution x-ray absorption spectra from ion-bombarded boron nitride nanotubes

    SciTech Connect

    Petravic, Mladen; Peter, Robert; Varasanec, Marijana; Li Luhua; Chen Ying; Cowie, Bruce C. C.

    2013-05-15

    The authors have applied high-resolution near-edge x-ray absorption fine structure measurements around the nitrogen K-edge to study the effects of ion-bombardment on near-surface properties of boron nitride nanotubes. A notable difference has been observed between surface sensitive partial electron yield (PEY) and bulk sensitive total electron yield (TEY) fine-structure measurements. The authors assign the PEY fine structure to the coupling of excited molecular vibrational modes to electronic transitions in NO molecules trapped just below the surface. Oxidation resistance of the boron nitride nanotubes is significantly reduced by low energy ion bombardment, as broken B-N bonds are replaced by N-O bonds involving oxygen present in the surface region. In contrast to the PEY spectra, the bulk sensitive TEY measurements on as-grown samples do not exhibit any fine structure while the ion-bombarded samples show a clear vibronic signature of molecular nitrogen.

  6. Cost and sensitivity of restricted active-space calculations of metal L-edge X-ray absorption spectra.

    PubMed

    Pinjari, Rahul V; Delcey, Mickaël G; Guo, Meiyuan; Odelius, Michael; Lundberg, Marcus

    2016-02-15

    The restricted active-space (RAS) approach can accurately simulate metal L-edge X-ray absorption spectra of first-row transition metal complexes without the use of any fitting parameters. These characteristics provide a unique capability to identify unknown chemical species and to analyze their electronic structure. To find the best balance between cost and accuracy, the sensitivity of the simulated spectra with respect to the method variables has been tested for two models, [FeCl6 ](3-) and [Fe(CN)6 ](3-) . For these systems, the reference calculations give deviations, when compared with experiment, of ≤1 eV in peak positions, ≤30% for the relative intensity of major peaks, and ≤50% for minor peaks. When compared with these deviations, the simulated spectra are sensitive to the number of final states, the inclusion of dynamical correlation, and the ionization potential electron affinity shift, in addition to the selection of the active space. The spectra are less sensitive to the quality of the basis set and even a double-ζ basis gives reasonable results. The inclusion of dynamical correlation through second-order perturbation theory can be done efficiently using the state-specific formalism without correlating the core orbitals. Although these observations are not directly transferable to other systems, they can, together with a cost analysis, aid in the design of RAS models and help to extend the use of this powerful approach to a wider range of transition metal systems.

  7. X-ray absorption spectra of water within a plane-wave Car-Parrinello molecular dynamics framework

    NASA Astrophysics Data System (ADS)

    Cavalleri, Matteo; Odelius, Michael; Nilsson, Anders; Pettersson, Lars G. M.

    2004-11-01

    We describe the implementation of a simple technique to simulate core-level spectra within the Car-Parrinello plane-waves molecular dynamics framework. The x-ray absorption (XA) spectra are generated using the transition potential technique with the effect of the core hole included through a specifically developed pseudopotential for the core-excited atom. Despite the lack of 1s core orbitals in the pseudopotential treatment, the required transition moments are accurately calculated without reconstruction of the all-electron orbitals. The method is applied to the oxygen XA spectra of water in its various aggregation states, but it is transferable to any first-row element. The computed spectra are compared favorably with the results from all-electron cluster calculations, as well as with experimental data. The periodicity of the plane-wave technique improves the description of condensed phases. The molecular dynamics simulation enables in principle a proper treatment of thermal effects and dynamical averaging in complex systems.

  8. X-ray Absorption Spectra of Dissolved Polysulfides in Lithium-Sulfur Batteries from First-Principles.

    PubMed

    Pascal, Tod A; Wujcik, Kevin H; Velasco-Velez, Juan; Wu, Chenghao; Teran, Alexander A; Kapilashrami, Mukes; Cabana, Jordi; Guo, Jinghua; Salmeron, Miquel; Balsara, Nitash; Prendergast, David

    2014-05-01

    The X-ray absorption spectra (XAS) of lithium polysulfides (Li2Sx) of various chain lengths (x) dissolved in a model solvent are obtained from first-principles calculations. The spectra exhibit two main absorption features near the sulfur K-edge, which are unambiguously interpreted as a pre-edge near 2471 eV due to the terminal sulfur atoms at either end of the linear polysulfide dianions and a main-edge near 2473 eV due to the (x - 2) internal atoms in the chain, except in the case of Li2S2, which only has a low-energy feature. We find an almost linear dependence between the ratio of the peaks and chain length, although the linear dependence is modified by the delocalized, molecular nature of the core-excited states that can span up to six neighboring sulfur atoms. Thus, our results indicate that the ratio of the peak area, and not the peak intensities, should be used when attempting to differentiate the polysulfides from XAS.

  9. Accounting for nanometer-thick adventitious carbon contamination in X-ray absorption spectra of carbon-based materials.

    PubMed

    Mangolini, Filippo; McClimon, J Brandon; Rose, Franck; Carpick, Robert W

    2014-12-16

    Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy is a powerful technique for characterizing the composition and bonding state of nanoscale materials and the top few nanometers of bulk and thin film specimens. When coupled with imaging methods like photoemission electron microscopy, it enables chemical imaging of materials with nanometer-scale lateral spatial resolution. However, analysis of NEXAFS spectra is often performed under the assumption of structural and compositional homogeneity within the nanometer-scale depth probed by this technique. This assumption can introduce large errors when analyzing the vast majority of solid surfaces due to the presence of complex surface and near-surface structures such as oxides and contamination layers. An analytical methodology is presented for removing the contribution of these nanoscale overlayers from NEXAFS spectra of two-layered systems to provide a corrected photoabsorption spectrum of the substrate. This method relies on the subtraction of the NEXAFS spectrum of the overlayer adsorbed on a reference surface from the spectrum of the two-layer system under investigation, where the thickness of the overlayer is independently determined by X-ray photoelectron spectroscopy (XPS). This approach is applied to NEXAFS data acquired for one of the most challenging cases: air-exposed hard carbon-based materials with adventitious carbon contamination from ambient exposure. The contribution of the adventitious carbon was removed from the as-acquired spectra of ultrananocrystalline diamond (UNCD) and hydrogenated amorphous carbon (a-C:H) to determine the intrinsic photoabsorption NEXAFS spectra of these materials. The method alters the calculated fraction of sp(2)-hybridized carbon from 5 to 20% and reveals that the adventitious contamination can be described as a layer containing carbon and oxygen ([O]/[C] = 0.11 ± 0.02) with a thickness of 0.6 ± 0.2 nm and a fraction of sp(2)-bonded carbon of 0.19 ± 0.03. This

  10. Theoretical calculations of X-ray absorption spectra of a copper mixed ligand complex using computer code FEFF9

    NASA Astrophysics Data System (ADS)

    Gaur, A.; Shrivastava, B. D.

    2014-09-01

    The terms X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) refer, respectively, to the structure in the X-ray absorption spectrum at low and high energies relative to the absorption edge. Routine analysis of EXAFS experiments generally makes use of simplified models and several many-body parameters, e.g. mean free paths, many-body amplitude factors, and Debye-Waller factors, as incorporated in EXAFS analysis software packages like IFEFFIT which includes Artemis. Similar considerations apply to XANES, where the agreement between theory and experiment is often less satisfactory. The recently available computer code FEFF9 uses the real-space Green's function (RSGF) approach to calculate dielectric response over a broad spectrum including the dominant low-energy region. This code includes improved treatments of many-body effects such as inelastic losses, core-hole effects, vibrational amplitudes, and the extension to full spectrum calculations of optical constants including solid state effects. In the present work, using FEFF9, we have calculated the X-ray absorption spectrum at the K-edge of copper in a complex, viz., aqua (diethylenetriamine) (isonicotinato) copper(II), the crystal structure of which is unknown. The theoretical spectrum has been compared with the experimental spectrum, recorded by us at the XAFS beamline 11.1 at ELETTRA synchrotron source, Italy, in both XANES and EXAFS regions.

  11. Comparison of x-ray absorption spectra between water and ice: new ice data with low pre-edge absorption cross-section.

    PubMed

    Sellberg, Jonas A; Kaya, Sarp; Segtnan, Vegard H; Chen, Chen; Tyliszczak, Tolek; Ogasawara, Hirohito; Nordlund, Dennis; Pettersson, Lars G M; Nilsson, Anders

    2014-07-21

    The effect of crystal growth conditions on the O K-edge x-ray absorption spectra of ice is investigated through detailed analysis of the spectral features. The amount of ice defects is found to be minimized on hydrophobic surfaces, such as BaF2(111), with low concentration of nucleation centers. This is manifested through a reduction of the absorption cross-section at 535 eV, which is associated with distorted hydrogen bonds. Furthermore, a connection is made between the observed increase in spectral intensity between 544 and 548 eV and high-symmetry points in the electronic band structure, suggesting a more extended hydrogen-bond network as compared to ices prepared differently. The spectral differences for various ice preparations are compared to the temperature dependence of spectra of liquid water upon supercooling. A double-peak feature in the absorption cross-section between 540 and 543 eV is identified as a characteristic of the crystalline phase. The connection to the interpretation of the liquid phase O K-edge x-ray absorption spectrum is extensively discussed.

  12. Comparison of x-ray absorption spectra between water and ice: New ice data with low pre-edge absorption cross-section

    SciTech Connect

    Sellberg, Jonas A.; Nilsson, Anders; Kaya, Sarp; Segtnan, Vegard H.; Chen, Chen; Tyliszczak, Tolek; Ogasawara, Hirohito; Nordlund, Dennis; Pettersson, Lars G. M.

    2014-07-21

    The effect of crystal growth conditions on the O K-edge x-ray absorption spectra of ice is investigated through detailed analysis of the spectral features. The amount of ice defects is found to be minimized on hydrophobic surfaces, such as BaF{sub 2}(111), with low concentration of nucleation centers. This is manifested through a reduction of the absorption cross-section at 535 eV, which is associated with distorted hydrogen bonds. Furthermore, a connection is made between the observed increase in spectral intensity between 544 and 548 eV and high-symmetry points in the electronic band structure, suggesting a more extended hydrogen-bond network as compared to ices prepared differently. The spectral differences for various ice preparations are compared to the temperature dependence of spectra of liquid water upon supercooling. A double-peak feature in the absorption cross-section between 540 and 543 eV is identified as a characteristic of the crystalline phase. The connection to the interpretation of the liquid phase O K-edge x-ray absorption spectrum is extensively discussed.

  13. Quantum mechanics-molecular dynamics approach to the interpretation of x-ray absorption spectra.

    PubMed

    Kuzmin, A; Evarestov, R A

    2009-02-01

    The quantum mechanics-molecular dynamics approach to the simulation of configuration-averaged EXAFS spectra is proposed, and its application is discussed for the example of the Ti K-edge EXAFS spectrum in cubic perovskite SrTiO(3). Proper use of ab initio quantum mechanics allows a number of empirical parameters, used in the molecular dynamics simulation, to be reduced, whereas the molecular dynamics allows us to account for temperature effects. All together, the approach provides a way of accounting for static and dynamic disorder in EXAFS signals from the coordination shells above the first one, where many-atom (multiple-scattering) effects are often important.

  14. Theoretical modeling and interpretation of X-ray absorption spectra of liquid water.

    PubMed

    Wang, R L C; Kreuzer, H J; Grunze, M

    2006-11-01

    We report extensive calculations to examine the capability of theory to explain the XAS spectra of liquid water. Several aspects that enter the theoretical model are addressed, such as the quantum mechanical methods, the statistics and the XAS model. As input into our quantum mechanical calculations we will use structural information on liquid water obtained from first principles and from classical molecular dynamics simulations. As XAS models, we will examine the full core hole and the half core hole approximations to transition state theory. The quantum mechanics is performed on the basis of density functional theory. We conclude from this study that recent experimental results are fully consistent with, and can be completely explained by, present day theory, in particular, the pre-edge peak is reproduced. We also find that the average bond coordination in liquid water is 3.1 and that the assertion in a recent paper that the hydrogen bond number is much less than that cannot be substantiated. Our calculations emphasize that further advances in our understanding of water can only be made by more sophisticated spectroscopy with significantly increased resolution.

  15. X-ray absorption and infrared spectra of water and ice: A first-principles electronic structure study

    NASA Astrophysics Data System (ADS)

    Chen, Wei

    Water is of essential importance for chemistry and biology, yet the physics concerning many of its distinctive properties is not well known. In this thesis we present a theoretical study of the x-ray absorption (XA) and infrared (IR) spectra of water in liquid and solid phase. Our theoretical tools are the density functional theory (DFT), Car-Parrinello (CP) molecular dynamics (MD), and the so-called GW method. Since a systematic review of these ab initio methods is not the task of this thesis, we only briefly recall the main concepts of these methods as needed in the course of our exposition. The focus is, instead, an investigation of what is the important physics necessary for a better description of these excitation processes, in particular, core electron excitations (in XA) that reveal the local electronic structure, and vibrational excitations (in IR) associated to the molecular dynamics. The most interesting question we are trying to answer is: as we include better approximations and more complete physical descriptions of these processes, how do the aforementioned spectra reflect the underlying hydrogen-bonding network of water? The first part of this thesis consists of the first four chapters, which focus on the study of core level excitation of water and ice. The x-ray absorption spectra of water and ice are calculated with a many-body approach for electron-hole excitations. The experimental features, even the small effects of a temperature change in the liquid, are reproduced with quantitative detail using molecular configurations generated by ab initio molecular dynamics. We find that the spectral shape is controlled by two major modifications of the short range order that mark the transition from ice to water. One is associated to dynamic breaking of the hydrogen bonds which leads to a strong enhancement of the pre-edge intensity in the liquid. The other is due to densification, which follows the partial collapse of the hydrogen bond network and is

  16. X ray spectra of cataclysmic variables

    NASA Technical Reports Server (NTRS)

    Patterson, Joseph; Halpern, Jules

    1990-01-01

    X ray spectral parameters of cataclysmic variables observed with the 'Einstein' imaging proportional counter were determined by fitting an optically thin, thermal bremsstrahlung spectrum to the raw data. Most of the sources show temperatures of order a few keV, while a few sources exhibit harder spectra with temperatures in excess of 10 keV. Estimated 0.1 to 3.5 keV luminosities are generally in the range from 10(exp 30) to 10(exp 32) erg/sec. The results are consistent with the x rays originating in a disk/white dwarf boundary layer of non-magnetic systems, or in a hot, post-shock region in the accretion column of DQ Her stars, with a negligible contribution from the corona of the companion. In a few objects column densities were found that are unusually high for interstellar material. It was suggested that the absorption occurs in the system itself.

  17. 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

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

    DOE PAGES

    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

  19. 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.

  20. 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.

  1. 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

  2. Calibration of scalar relativistic density functional theory for the calculation of sulfur K-edge X-ray absorption spectra.

    PubMed

    Debeer George, Serena; Neese, Frank

    2010-02-15

    Sulfur K-edge X-ray absorption spectroscopy has been proven to be a powerful tool for investigating the electronic structures of sulfur-containing coordination complexes. The full information content of the spectra can be developed through a combination of experiment and time-dependent density functional theory (TD-DFT). In this work, the necessary calibration is carried out for a range of contemporary functionals (BP86, PBE, OLYP, OPBE, B3LYP, PBE0, TPSSh) in a scalar relativistic (0(th) order regular approximation, ZORA) DFT framework. It is shown that with recently developed segmented all-electron scalar relativistic (SARC) basis sets one obtains results that are as good as with large, uncontracted basis sets. The errors in the calibrated transition energies are on the order of 0.1 eV. The error in calibrated intensities is slightly larger, but the calculations are still in excellent agreement with experiment. The behavior of full TD-DFT linear response versus the Tamm-Dancoff approximation has been evaluated with the result that two methods are almost indistinguishable. The inclusion of relativistic effects barely changes the results for first row transition metal complexes, however, the contributions become visible for second-row transition metals and reach a maximum (of an approximately 10% change in the calibration parameters) for third row transition metal species. The protocol developed here is approximately 10 times more efficient than the previously employed protocol, which was based on large, uncontracted basis sets. The calibration strategy followed here may be readily extended to other edges. PMID:20092349

  3. X-ray spectra of galactic X-ray sources

    NASA Technical Reports Server (NTRS)

    Holt, S. S.

    1980-01-01

    The spectroscopic properties of the various classes of Galactic X-ray sources are discussed, with particular emphasis on binary sources containing an accreting compact object, where post-emission scattering in an accretion disk often prevents the initially produced X-radiation from being observed directly. Theoretical interpretations and X-ray observations are considered for the cataclysmic variables, binary systems with a white dwarf as the compact object and which suffer relatively less from Thomson scattering, and the similar phenomenological spectral characteristics of the bulge sources, including soft transients, bursters and steady X-ray sources with thermal spectra, thought to represent an accreting neutron star, are pointed out. The spectral characteristics of X-ray pulsars in accreting binary systems (rather than the Crab pulsar, which is losing rotational kinetic energy with time) are then presented and interpreted in terms of accretion in the polar regions, and mechanisms for the newly discovered X-ray emission from late-type RS CVn stars are considered.

  4. Separating Peaks in X-Ray Spectra

    NASA Technical Reports Server (NTRS)

    Nicolas, David; Taylor, Clayborne; Wade, Thomas

    1987-01-01

    Deconvolution algorithm assists in analysis of x-ray spectra from scanning electron microscopes, electron microprobe analyzers, x-ray fluorescence spectrometers, and like. New algorithm automatically deconvolves x-ray spectrum, identifies locations of spectral peaks, and selects chemical elements most likely producing peaks. Technique based on similarities between zero- and second-order terms of Taylor-series expansions of Gaussian distribution and of damped sinusoid. Principal advantage of algorithm: no requirement to adjust weighting factors or other parameters when analyzing general x-ray spectra.

  5. Soft X-Ray Absorption Spectroscopy at an X-ray Free Electron Laser

    NASA Astrophysics Data System (ADS)

    Higley, Daniel; Schlotter, William; Turner, Joshua; Moeller, Stefan; Mitra, Ankush; Tsukamoto, Arata; Marvel, Robert; Haglund, Richard; Durr, Hermann; Stohr, Joachim; Dakovski, Georgi

    2015-03-01

    X-ray free electron lasers, providing coherent, ultrafast, high intensity x-ray pulses, have enabled groundbreaking scattering experiments to probe the atomic structure of materials on femtosecond timescales. Nonetheless, x-ray absorption spectroscopy (XAS), one of the most fundamental and common x-ray techniques practiced at synchrotron light sources, has proven challenging to conduct with satisfactory signal-to-noise levels at soft x-ray energies using free electron laser sources. The ability to routinely collect high quality XAS spectra, especially in a time-resolved manner, will open many new scientific possibilities in the areas of ultrafast demagnetization, phase transitions and chemical dynamics to highlight a few. Here, we report how XAS using total fluorescence yield detection yields high signal-to-noise x-ray absorption spectra at an x-ray free electron laser source. Data were collected over multiple absorption edges on technologically relevant materials. These measurements were recorded on the Soft X-Ray Materials Science instrument at the Linac Coherent Light Source. The results are easily extendable to time-resolved measurements.

  6. Experimental and Theoretical Comparison of the O K-Edge Non-Resonant Inelastic X-ray Scattering and X-ray Absorption Spectra of NaReO4

    SciTech Connect

    Bradley, Joseph A.; Yang, Ping; Batista, Enrique R.; Boland, Kevin S.; Burns, Carol J.; Clark, David L.; Conradson, Steven D.; Kozimor, Stosh A.; Martin, Richard L.; Seidler, Gerald T.; Scott, Brian L.; Shuh, David K.; Tyliszczak, T.; Wilkerson, Marianne P.; Wolfsberg, Laura E.

    2010-09-14

    Accurate X-ray absorption spectra (XAS) of first row atoms, e.g. O, are notoriously difficult to obtain due to the extreme sensitivity of the measurement to surface contamination, self-absorption, and saturation effects. Herein, we describe a comprehensive approach for determining reliable O K-edge XAS data for ReO41- and provide methodology for obtaining trustworthy and quantitative data on non-conducting molecular systems, even in the presence of surface contamination. This involves comparing spectra measured by non-resonant inelastic X-ray scattering (NRIXS), a bulk-sensitive technique that is not prone to X-ray self-absorption and provides exact peak intensities, with XAS spectra obtained by three different detection modes, namely total electron yield (TEY), fluorescence yield (FY), and scanning transmission X-ray microscopy (STXM). For ReO41-, TEY measurements were heavily influenced by surface contamination, while the FY and STXM data agree well with the bulk NRIXS analysis. These spectra all showed two intense pre-edge features indicative of the covalent interaction between the Re 5d and O 2p orbitals. Time dependent density functional theory calculations were used to assign these two peaks as O 1s excitations to the e and t2 molecular orbitals that result from Re 5d and O 2p covalent mixing in Td symmetry. Electronic structure calculations were used to determine the amount of O 2p character (%) in these molecular orbitals. Time-dependent density functional theory (TD-DFT) was also used to calculate the energies and intensities of the pre-edge transitions. Overall, under these experimental conditions, this analysis suggests that NRIXS, STXM, and FY operate cooperatively, providing a sound basis for validation of bulk-like excitation spectra and, in combination with electronic structure calculations, suggest that NaReO4 may serve as a well-defined O K-edge energy and intensity standard for future O K edge XAS studies.

  7. Experimental and Theoretical Comparison of the O K-Edge Nonresonant Inelastic X-ray Scattering and X-ray Absorption Spectra of NaReO[subscript 4

    SciTech Connect

    Bradley, Joseph A.; Yang, Ping; Batista, Enrique R.; Boland, Kevin S.; Burns, Carol J.; Clark, David L.; Conradson, Steven D.; Kozimor, Stosh A.; Martin, Richard L.; Seidler, Gerald T.; Scott, Brian L.; Shuh, David K.; Tyliszczak, Tolek; Wilkerson, Marianne P.; Wolfsberg, Laura E.

    2010-12-07

    Accurate X-ray absorption spectra (XAS) of first row atoms, e.g., O, are notoriously difficult to obtain due to the extreme sensitivity of the measurement to surface contamination, self-absorption, and saturation affects. Herein, we describe a comprehensive approach for determining reliable O K-edge XAS data for ReO{sub 4}{sup 1-} and provide methodology for obtaining trustworthy and quantitative data on nonconducting molecular systems, even in the presence of surface contamination. This involves comparing spectra measured by nonresonant inelastic X-ray scattering (NRIXS), a bulk-sensitive technique that is not prone to X-ray self-absorption and provides exact peak intensities, with XAS spectra obtained by three different detection modes, namely total electron yield (TEY), fluorescence yield (FY), and scanning transmission X-ray microscopy (STXM). For ReO{sub 4}{sup 1-}, TEY measurements were heavily influenced by surface contamination, while the FY and STXM data agree well with the bulk NRIXS analysis. These spectra all showed two intense pre-edge features indicative of the covalent interaction between the Re 5d and O 2p orbitals. Density functional theory calculations were used to assign these two peaks as O 1s excitations to the e and t{sub 2} molecular orbitals that result from Re 5d and O 2p covalent mixing in T{sub d} symmetry. Electronic structure calculations were used to determine the amount of O 2p character (%) in these molecular orbitals. Time dependent-density functional theory (TD-DFT) was also used to calculate the energies and intensities of the pre-edge transitions. Overall, under these experimental conditions, this analysis suggests that NRIXS, STXM, and FY operate cooperatively, providing a sound basis for validation of bulk-like excitation spectra and, in combination with electronic structure calculations, suggest that NaReO{sub 4} may serve as a well-defined O K-edge energy and intensity standard for future O K-edge XAS studies.

  8. Nitrogen K-edge X-ray absorption near edge structure (XANES) spectra of purine-containing nucleotides in aqueous solution

    NASA Astrophysics Data System (ADS)

    Shimada, Hiroyuki; Fukao, Taishi; Minami, Hirotake; Ukai, Masatoshi; Fujii, Kentaro; Yokoya, Akinari; Fukuda, Yoshihiro; Saitoh, Yuji

    2014-08-01

    The N K-edge X-ray absorption near edge structure (XANES) spectra of the purine-containing nucleotide, guanosine 5'-monophosphate (GMP), in aqueous solution are measured under various pH conditions. The spectra show characteristic peaks, which originate from resonant excitations of N 1s electrons to π* orbitals inside the guanine moiety of GMP. The relative intensities of these peaks depend on the pH values of the solution. The pH dependence is explained by the core-level shift of N atoms at specific sites caused by protonation and deprotonation. The experimental spectra are compared with theoretical spectra calculated by using density functional theory for GMP and the other purine-containing nucleotides, adenosine 5'-monophosphate, and adenosine 5'-triphosphate. The N K-edge XANES spectra for all of these nucleotides are classified by the numbers of N atoms with particular chemical bonding characteristics in the purine moiety.

  9. General Method for Determination of the Surface Composition in Bimetallic Nanoparticle Catalysts from the L Edge X-ray Absorption Near-Edge Spectra

    SciTech Connect

    Wu, Tiapin; Childers, David; Gomez, Carolina; Karim, Ayman M.; Schweitzer, Neil; Kropf, Arthur; Wang, Hui; Bolin, Trudy B.; Hu, Yongfeng; Kovarik, Libor; Meyer, Randall; Miller, Jeffrey T.

    2012-10-08

    Bimetallic PtPd on silica nano-particle catalysts have been synthesized and their average structure determined by Pt L3 and Pd K-edge extended X-ray absorption finestructure (EXAFS) spectroscopy. The bimetallic structure is confirmed from elemental line scans by STEM for the individual 1-2 nm sized particles. A general method is described to determine the surface composition in bimetallic nanoparticles even when both metals adsorb, for example, CO. By measuring the change in the L3 X-ray absorption near-edge structure (XANES) spectra with and without CO in bimetallic particles and comparing these changes to those in monometallic particles of known size the fraction of surface atoms can be determined. The turnover rates (TOR) and neopentane hydrogenolysis and isomerization selectivities based on the surface composition suggest that the catalytic and spectroscopic properties are different from those in monometallic nano-particle catalysts. At the same neo-pentane conversion, the isomerization selectivity is higher for the PtPd catalyst while the TOR is lower than that of both Pt and Pd. As with the catalytic performance, the infrared spectra of adsorbed CO are not a linear combination of the spectra on monometallic catalysts. Density functional theory calculations indicate that the Pt-CO adsorption enthalpy increases while the Pd-CO bond energy decreases. The ability to determine the surface composition allows for a better understanding of the spectroscopic and catalytic properties of bimetallic nanoparticle catalysts.

  10. Simulations of iron K pre-edge X-ray absorption spectra using the restricted active space method.

    PubMed

    Guo, Meiyuan; Sørensen, Lasse Kragh; Delcey, Mickaël G; Pinjari, Rahul V; Lundberg, Marcus

    2016-01-28

    The intensities and relative energies of metal K pre-edge features are sensitive to both geometric and electronic structures. With the possibility to collect high-resolution spectral data it is important to find theoretical methods that include all important spectral effects: ligand-field splitting, multiplet structures, 3d-4p orbital hybridization, and charge-transfer excitations. Here the restricted active space (RAS) method is used for the first time to calculate metal K pre-edge spectra of open-shell systems, and its performance is tested against on six iron complexes: [FeCl6](n-), [FeCl4](n-), and [Fe(CN)6](n-) in ferrous and ferric oxidation states. The method gives good descriptions of the spectral shapes for all six systems. The mean absolute deviation for the relative energies of different peaks is only 0.1 eV. For the two systems that lack centrosymmetry [FeCl4](2-/1-), the ratios between dipole and quadrupole intensity contributions are reproduced with an error of 10%, which leads to good descriptions of the integrated pre-edge intensities. To gain further chemical insight, the origins of the pre-edge features have been analyzed with a chemically intuitive molecular orbital picture that serves as a bridge between the spectra and the electronic structures. The pre-edges contain information about both ligand-field strengths and orbital covalencies, which can be understood by analyzing the RAS wavefunction. The RAS method can thus be used to predict and rationalize the effects of changes in both the oxidation state and ligand environment in a number of hard X-ray studies of small and medium-sized molecular systems.

  11. X-ray spectra of supernova remnants

    NASA Technical Reports Server (NTRS)

    Szymkowiak, A. E.

    1985-01-01

    X-ray spectra were obtained from fields in three supernova remnants with the solid state spectrometer of the HEAO 2 satellite. These spectra, which contain lines from K-shell transitions of several abundant elements with atomic numbers between 10 and 22, were compared with various models, including some of spectra that would be produced by adiabatic phase remnants when the time-dependence of the ionization is considered.

  12. Vibrational, X-ray absorption, and Mössbauer spectra of sulfate minerals from the weathered massive sulfide deposit at Iron Mountain, California

    USGS Publications Warehouse

    Majzlan, Juraj; Alpers, Charles N.; Bender Koch, Christian; McCleskey, R. Blaine; Myneni, Satish B.C.; Neil, John M.

    2011-01-01

    The Iron Mountain Mine Superfund site in California is a prime example of an acid mine drainage (AMD) system with well developed assemblages of sulfate minerals typical for such settings. Here we present and discuss the vibrational (infrared), X-ray absorption, and M??ssbauer spectra of a number of these phases, augmented by spectra of a few synthetic sulfates related to the AMD phases. The minerals and related phases studied in this work are (in order of increasing Fe2O3/FeO): szomolnokite, rozenite, siderotil, halotrichite, r??merite, voltaite, copiapite, monoclinic Fe2(SO4)3, Fe2(SO4)3??5H2O, kornelite, coquimbite, Fe(SO4)(OH), jarosite and rhomboclase. Fourier transform infrared spectra in the region 750-4000cm-1 are presented for all studied phases. Position of the FTIR bands is discussed in terms of the vibrations of sulfate ions, hydroxyl groups, and water molecules. Sulfur K-edge X-ray absorption near-edge structure (XANES) spectra were collected for selected samples. The feature of greatest interest is a series of weak pre-edge peaks whose position is determined by the number of bridging oxygen atoms between Fe3+ octahedra and sulfate tetrahedra. M??ssbauer spectra of selected samples were obtained at room temperature and 80K for ferric minerals jarosite and rhomboclase and mixed ferric-ferrous minerals r??merite, voltaite, and copiapite. Values of Fe2+/[Fe2++Fe3+] determined by M??ssbauer spectroscopy agree well with those determined by wet chemical analysis. The data presented here can be used as standards in spectroscopic work where spectra of well-characterized compounds are required to identify complex mixtures of minerals and related phases. ?? 2011 Elsevier B.V.

  13. Vibrational, X-ray absorption, and Mössbauer spectra of sulfate minerals from the weathered massive sulfide deposit at Iron Mountain, California

    USGS Publications Warehouse

    Majzlan, Juraj; Alpers, Charles N.; Bender Koch, Christian; McCleskey, R. Blaine; Myneni, Satish B.C.; Neil, John M.

    2014-01-01

    The Iron Mountain Mine Superfund site in California is a prime example of an acid mine drainage (AMD) system with well developed assemblages of sulfate minerals typical for such settings. Here we present and discuss the vibrational (infrared), X-ray absorption, and Mössbauer spectra of a number of these phases, augmented by spectra of a few synthetic sulfates related to the AMD phases. The minerals and related phases studied in this work are (in order of increasing Fe2O3/FeO): szomolnokite, rozenite, siderotil, halotrichite, römerite, voltaite, copiapite, monoclinic Fe2(SO4)3, Fe2(SO4)3·5H2O, kornelite, coquimbite, Fe(SO4)(OH), jarosite and rhomboclase. Fourier transform infrared spectra in the region 750–4000 cm−1 are presented for all studied phases. Position of the FTIR bands is discussed in terms of the vibrations of sulfate ions, hydroxyl groups, and water molecules. Sulfur K-edge X-ray absorption near-edge structure (XANES) spectra were collected for selected samples. The feature of greatest interest is a series of weak pre-edge peaks whose position is determined by the number of bridging oxygen atoms between Fe3+ octahedra and sulfate tetrahedra. Mössbauer spectra of selected samples were obtained at room temperature and 80 K for ferric minerals jarosite and rhomboclase and mixed ferric–ferrous minerals römerite, voltaite, and copiapite. Values of Fe2+/[Fe2+ + Fe3+] determined by Mössbauer spectroscopy agree well with those determined by wet chemical analysis. The data presented here can be used as standards in spectroscopic work where spectra of well-characterized compounds are required to identify complex mixtures of minerals and related phases.

  14. X-ray absorption spectra of hexagonal ice and liquid water by all-electron Gaussian and augmented plane wave calculations.

    PubMed

    Iannuzzi, Marcella

    2008-05-28

    Full potential x-ray spectroscopy simulations of hexagonal ice and liquid water are performed by means of the newly implemented methodology based on the Gaussian augmented plane waves formalism. The computed spectra obtained within the supercell approach are compared to experimental data. The variations of the spectral distribution determined by the quality of the basis set, the size of the sample, and the choice of the core-hole potential are extensively discussed. The second part of this work is focused on the understanding of the connections between specific configurations of the hydrogen bond network and the corresponding contributions to the x-ray absorption spectrum in liquid water. Our results confirm that asymmetrically coordinated molecules, in particular, those donating only one or no hydrogen bond, are associated with well identified spectral signatures that differ significantly from the ice spectral profile. However, transient local structures, with half formed hydrogen bonds, may still give rise to spectra with dominant postedge contributions and relatively weaker oscillator strengths at lower energy. This explains why by averaging the spectra over all the O atoms of liquid instantaneous configurations extracted from ab initio molecular dynamics trajectories, the spectral features indicating the presence of weak or broken hydrogen bonds turn out to be attenuated and sometimes not clearly distinguishable.

  15. X-ray absorption spectra of hexagonal ice and liquid water by all-electron Gaussian and augmented plane wave calculations

    NASA Astrophysics Data System (ADS)

    Iannuzzi, Marcella

    2008-05-01

    Full potential x-ray spectroscopy simulations of hexagonal ice and liquid water are performed by means of the newly implemented methodology based on the Gaussian augmented plane waves formalism. The computed spectra obtained within the supercell approach are compared to experimental data. The variations of the spectral distribution determined by the quality of the basis set, the size of the sample, and the choice of the core-hole potential are extensively discussed. The second part of this work is focused on the understanding of the connections between specific configurations of the hydrogen bond network and the corresponding contributions to the x-ray absorption spectrum in liquid water. Our results confirm that asymmetrically coordinated molecules, in particular, those donating only one or no hydrogen bond, are associated with well identified spectral signatures that differ significantly from the ice spectral profile. However, transient local structures, with half formed hydrogen bonds, may still give rise to spectra with dominant postedge contributions and relatively weaker oscillator strengths at lower energy. This explains why by averaging the spectra over all the O atoms of liquid instantaneous configurations extracted from ab initio molecular dynamics trajectories, the spectral features indicating the presence of weak or broken hydrogen bonds turn out to be attenuated and sometimes not clearly distinguishable.

  16. The Be K-edge in beryllium oxide and chalcogenides: soft x-ray absorption spectra from first-principles theory and experiment.

    PubMed

    Olovsson, W; Weinhardt, L; Fuchs, O; Tanaka, I; Puschnig, P; Umbach, E; Heske, C; Draxl, C

    2013-08-01

    We have carried out a theoretical and experimental investigation of the beryllium K-edge soft x-ray absorption fine structure of beryllium compounds in the oxygen group, considering BeO, BeS, BeSe, and BeTe. Theoretical spectra are obtained ab initio, through many-body perturbation theory, by solving the Bethe-Salpeter equation (BSE), and by supercell calculations using the core-hole approximation. All calculations are performed with the full-potential linearized augmented plane-wave method. It is found that the two different theoretical approaches produce a similar fine structure, in good agreement with the experimental data. Using the BSE results, we interpret the spectra, distinguishing between bound core-excitons and higher energy excitations.

  17. X-ray absorption spectroscopy of metalloproteins.

    PubMed

    Ward, Jesse; Ollmann, Emily; Maxey, Evan; Finney, Lydia A

    2014-01-01

    Metalloproteins are enormously important in biology. While a variety of techniques exist for studying metals in biology, X-ray absorption spectroscopy is particularly useful in that it can determine the local electronic and physical structure around the metal center, and is one of the few avenues for studying "spectroscopically silent" metal ions like Zn(II) and Cu(I) that have completely filled valence bands. While X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) are useful for studying metalloprotein structure, they suffer the limitation that the detected signal is an average of all the various metal centers in the sample, which limits its usefulness for studying metal centers in situ or in cell lysates. It would be desirable to be able to separate the various proteins in a mixture prior to performing X-ray absorption studies, so that the derived signal is from one species only. Here we describe a method for performing X-ray absorption spectroscopy on protein bands following electrophoretic separation and western blotting.

  18. Carbon X-ray absorption spectra of fluoroethenes and acetone: A study at the coupled cluster, density functional, and static-exchange levels of theory

    SciTech Connect

    Fransson, Thomas; Norman, Patrick; Coriani, Sonia; Christiansen, Ove

    2013-03-28

    Near carbon K-edge X-ray absorption fine structure spectra of a series of fluorine-substituted ethenes and acetone have been studied using coupled cluster and density functional theory (DFT) polarization propagator methods, as well as the static-exchange (STEX) approach. With the complex polarization propagator (CPP) implemented in coupled cluster theory, relaxation effects following the excitation of core electrons are accounted for in terms of electron correlation, enabling a systematic convergence of these effects with respect to electron excitations in the cluster operator. Coupled cluster results have been used as benchmarks for the assessment of propagator methods in DFT as well as the state-specific static-exchange approach. Calculations on ethene and 1,1-difluoroethene illustrate the possibility of using nonrelativistic coupled cluster singles and doubles (CCSD) with additional effects of electron correlation and relativity added as scalar shifts in energetics. It has been demonstrated that CPP spectra obtained with coupled cluster singles and approximate doubles (CC2), CCSD, and DFT (with a Coulomb attenuated exchange-correlation functional) yield excellent predictions of chemical shifts for vinylfluoride, 1,1-difluoroethene, trifluoroethene, as well as good spectral features for acetone in the case of CCSD and DFT. Following this, CPP-DFT is considered to be a viable option for the calculation of X-ray absorption spectra of larger {pi}-conjugated systems, and CC2 is deemed applicable for chemical shifts but not for studies of fine structure features. The CCSD method as well as the more approximate CC2 method are shown to yield spectral features relating to {pi}*-resonances in good agreement with experiment, not only for the aforementioned molecules but also for ethene, cis-1,2-difluoroethene, and tetrafluoroethene. The STEX approach is shown to underestimate {pi}*-peak separations due to spectral compressions, a characteristic which is inherent to this

  19. Carbon X-ray absorption spectra of fluoroethenes and acetone: a study at the coupled cluster, density functional, and static-exchange levels of theory.

    PubMed

    Fransson, Thomas; Coriani, Sonia; Christiansen, Ove; Norman, Patrick

    2013-03-28

    Near carbon K-edge X-ray absorption fine structure spectra of a series of fluorine-substituted ethenes and acetone have been studied using coupled cluster and density functional theory (DFT) polarization propagator methods, as well as the static-exchange (STEX) approach. With the complex polarization propagator (CPP) implemented in coupled cluster theory, relaxation effects following the excitation of core electrons are accounted for in terms of electron correlation, enabling a systematic convergence of these effects with respect to electron excitations in the cluster operator. Coupled cluster results have been used as benchmarks for the assessment of propagator methods in DFT as well as the state-specific static-exchange approach. Calculations on ethene and 1,1-difluoroethene illustrate the possibility of using nonrelativistic coupled cluster singles and doubles (CCSD) with additional effects of electron correlation and relativity added as scalar shifts in energetics. It has been demonstrated that CPP spectra obtained with coupled cluster singles and approximate doubles (CC2), CCSD, and DFT (with a Coulomb attenuated exchange-correlation functional) yield excellent predictions of chemical shifts for vinylfluoride, 1,1-difluoroethene, trifluoroethene, as well as good spectral features for acetone in the case of CCSD and DFT. Following this, CPP-DFT is considered to be a viable option for the calculation of X-ray absorption spectra of larger π-conjugated systems, and CC2 is deemed applicable for chemical shifts but not for studies of fine structure features. The CCSD method as well as the more approximate CC2 method are shown to yield spectral features relating to π∗-resonances in good agreement with experiment, not only for the aforementioned molecules but also for ethene, cis-1,2-difluoroethene, and tetrafluoroethene. The STEX approach is shown to underestimate π∗-peak separations due to spectral compressions, a characteristic which is inherent to this

  20. X-ray absorption microscopy of aqueous samples

    NASA Astrophysics Data System (ADS)

    Frazer, Brad; Gilbert, Benjamin; De Stasio, Gelsomina

    2002-03-01

    X-ray photoelectron emission microscopy (X-PEEM) is used for numerous applications in surface microchemical analysis of material science and biological specimens. We have reconfigured the MEPHISTO X-PEEM instrument that is installed at the University of Wisconsin Synchrotron Radiation Center to measure true x-ray transmission spectra by converting transmitted photons to photoelectrons via a thin photocathode layer of gold. We have also developed a method by which to introduce aqueous samples into ultrahigh vacuum. Hence x-ray spectroscopy can be performed on biologically relevant elements (such as K, Ca, etc.) in a physiological environment, i.e., in solution. More important, when coupled with X-PEEM imaging this technique may offer the unique and exciting possibility of studying living cells. We present initial x-ray absorption spectra of solutions of aqueous ionic and chelated Ca, with the aim of distinguishing bound and free ionic calcium in vivo.

  1. Nitrogen K-edge X-ray absorption near edge structure (XANES) spectra of purine-containing nucleotides in aqueous solution

    SciTech Connect

    Shimada, Hiroyuki; Fukao, Taishi; Minami, Hirotake; Ukai, Masatoshi; Fujii, Kentaro; Yokoya, Akinari; Fukuda, Yoshihiro; Saitoh, Yuji

    2014-08-07

    The N K-edge X-ray absorption near edge structure (XANES) spectra of the purine-containing nucleotide, guanosine 5{sup ′}-monophosphate (GMP), in aqueous solution are measured under various pH conditions. The spectra show characteristic peaks, which originate from resonant excitations of N 1s electrons to π* orbitals inside the guanine moiety of GMP. The relative intensities of these peaks depend on the pH values of the solution. The pH dependence is explained by the core-level shift of N atoms at specific sites caused by protonation and deprotonation. The experimental spectra are compared with theoretical spectra calculated by using density functional theory for GMP and the other purine-containing nucleotides, adenosine 5{sup ′}-monophosphate, and adenosine 5{sup ′}-triphosphate. The N K-edge XANES spectra for all of these nucleotides are classified by the numbers of N atoms with particular chemical bonding characteristics in the purine moiety.

  2. Gravitationally Redshifted Absorption Lines in the Burst Spectra of the Neutron Star in the X-Ray Binary EXO 0748-676

    NASA Technical Reports Server (NTRS)

    Cottoam, J.; Paerels, F.; Mendez, M.; White, Nicholas E. (Technical Monitor)

    2002-01-01

    The most straightforward manner of determining masses and radii of neutron stars is by measuring the gravitational redshift of spectral lines produced in the neutron star photosphere; such a measurement would provide direct constraints on the mass-to-radius ratio of the neutron star, and therefore on the equation of state for neutron star matter. Using data taken with the Reflection Grating Spectrometer on board the XMM-Newton observatory we identify, for the first time, significant absorption lines in the spectra of 28 bursts of the low-mass X-ray binary EXO 0748-676. The most significant features are consistent with the Fe XXVI and XXV n=2-3 and O VIII n=1-2 transitions, with a redshift of z=0.35, identical within small uncertainties for the different transitions. This constitutes the first direct and unambiguous measurement of the gravitational redshift in a neutron star.

  3. Structures of Plutonium(IV) and Uranium(VI) with N,N-Dialkyl Amides from Crystallography, X-ray Absorption Spectra, and Theoretical Calculations.

    PubMed

    Acher, Eléonor; Hacene Cherkaski, Yanis; Dumas, Thomas; Tamain, Christelle; Guillaumont, Dominique; Boubals, Nathalie; Javierre, Guilhem; Hennig, Christoph; Solari, Pier Lorenzo; Charbonnel, Marie-Christine

    2016-06-01

    The structures of plutonium(IV) and uranium(VI) ions with a series of N,N-dialkyl amides ligands with linear and branched alkyl chains were elucidated from single-crystal X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS), and theoretical calculations. In the field of nuclear fuel reprocessing, N,N-dialkyl amides are alternative organic ligands to achieve the separation of uranium(VI) and plutonium(IV) from highly concentrated nitric acid solution. EXAFS analysis combined with XRD shows that the coordination structure of U(VI) is identical in the solution and in the solid state and is independent of the alkyl chain: two amide ligands and four bidentate nitrate ions coordinate the uranyl ion. With linear alkyl chain amides, Pu(IV) also adopt identical structures in the solid state and in solution with two amides and four bidentate nitrate ions. With branched alkyl chain amides, the coordination structure of Pu(IV) was more difficult to establish unambiguously from EXAFS. Density functional theory (DFT) calculations were consequently performed on a series of structures with different coordination modes. Structural parameters and Debye-Waller factors derived from the DFT calculations were used to compute EXAFS spectra without using fitting parameters. By using this methodology, it was possible to show that the branched alkyl chain amides form partly outer-sphere complexes with protonated ligands hydrogen bonded to nitrate ions. PMID:27171842

  4. 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.

  5. Polarization-dependent nickel 2p x-ray-absorption spectra of La{sub 2}NiO{sub 4+{delta}}

    SciTech Connect

    Kuiper, P.; van Elp, J.; Rice, D.E.; Buttrey, D.J.; Lin, H.; Chen, C.T.

    1998-01-01

    We present polarization dependent x-ray-absorption spectra at nickel L edges of well-characterized La{sub 2}NiO{sub 4+{delta}} single crystals. In the stoichiometric compound the splitting between the x{sup 2}{minus}y{sup 2} and the 3z{sup 2}{minus}r{sup 2} orbitals is 0.7 eV, according to a fit of the 2p{sup 5}3d{sup 9} multiplet to the spectra. This value is in agreement with an assignment of dd excitations of the optical spectrum. The Ni L edges of the doped compound are consistent with the isotropic prepeak observed at the oxygen 1s edge. Theory does not predict holes on the apex oxygens, but we argue that doping causes a polaronic deformation which reduces the tetragonal distortion of the NiO{sub 6} octahedra, and delocalizes the hole over all six ligands. {copyright} {ital 1998} {ital The American Physical Society}

  6. Predicting Near Edge X-ray Absorption Spectra with the Spin-Free Exact-Two-Component Hamiltonian and Orthogonality Constrained Density Functional Theory.

    PubMed

    Verma, Prakash; Derricotte, Wallace D; Evangelista, Francesco A

    2016-01-12

    Orthogonality constrained density functional theory (OCDFT) provides near-edge X-ray absorption (NEXAS) spectra of first-row elements within one electronvolt from experimental values. However, with increasing atomic number, scalar relativistic effects become the dominant source of error in a nonrelativistic OCDFT treatment of core-valence excitations. In this work we report a novel implementation of the spin-free exact-two-component (X2C) one-electron treatment of scalar relativistic effects and its combination with a recently developed OCDFT approach to compute a manifold of core-valence excited states. The inclusion of scalar relativistic effects in OCDFT reduces the mean absolute error of second-row elements core-valence excitations from 10.3 to 2.3 eV. For all the excitations considered, the results from X2C calculations are also found to be in excellent agreement with those from low-order spin-free Douglas-Kroll-Hess relativistic Hamiltonians. The X2C-OCDFT NEXAS spectra of three organotitanium complexes (TiCl4, TiCpCl3, TiCp2Cl2) are in very good agreement with unshifted experimental results and show a maximum absolute error of 5-6 eV. In addition, a decomposition of the total transition dipole moment into partial atomic contributions is proposed and applied to analyze the nature of the Ti pre-edge transitions in the three organotitanium complexes.

  7. 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.

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

    NASA Astrophysics Data System (ADS)

    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.

  9. 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.

  10. Relativistic Effects on Reflection X-ray Spectra of AGN

    SciTech Connect

    Lee, Khee-Gan; Fuerst, Steven V.; Brandwardi-Raymond, Graziella; Wu, Kinwah; Crowley, Oliver; /University Coll. London

    2007-01-05

    We have calculated the reflection component of the X-ray spectra of active galactic nuclei (AGN) and shown that they can be significantly modified by the relativistic motion of the accretion flow and various gravitational effects of the central black hole. The absorption edges in the reflection spectra suffer severe energy shifts and smearing. The degree of distortion depends on the system parameters, and the dependence is stronger for some parameters such as the inner radius of the accretion disk and the disk viewing inclination angles. The relativistic effects are significant and are observable. Improper treatment of the reflection component of the X-ray continuum in spectral fittings will give rise to spurious line-like features, which will mimic the fluorescent emission lines and mask the relativistic signatures of the lines.

  11. Decomposition of Wavelength Dispersive X-Ray Spectra

    PubMed Central

    Rémond, Guy; Myklebust, Robert; Fialin, Michel; Nockolds, Clive; Phillips, Matthew; Roques-Carmes, Claude

    2002-01-01

    Line shapes of atomic lines and soft x-ray emission bands measured with a wavelength dispersive spectrometer (WDS) with the Electron Probe Micro Analyzer (EPMA) are reviewed. Least square fitting to pseudo-Voigt profiles of the digitally measured spectra are used to account for the presence of non-diagram features (high and low energy satellites) and instrumental induced distortions. The effect of line width and relative intensities on the quality of fits is illustrated. Spectral distortions resulting from the presence of absorption edges within the analyzed wavelength region are illustrated for the case of FeLα,β emission bands for pure Fe and iron oxides. For quantitative analysis, an analytical approach is presented where the measured soft x-ray emission bands are corrected for self absorption before extracting the intensities from the experimental data. PMID:27446750

  12. Experimental and theoretical correlations between vanadium K-edge X-ray absorption and K[Formula: see text] emission spectra.

    PubMed

    Rees, Julian A; Wandzilak, Aleksandra; Maganas, Dimitrios; Wurster, Nicole I C; Hugenbruch, Stefan; Kowalska, Joanna K; Pollock, Christopher J; Lima, Frederico A; Finkelstein, Kenneth D; DeBeer, Serena

    2016-09-01

    A series of vanadium compounds was studied by K-edge X-ray absorption (XAS) and K[Formula: see text] X-ray emission spectroscopies (XES). Qualitative trends within the datasets, as well as comparisons between the XAS and XES data, illustrate the information content of both methods. The complementary nature of the chemical insight highlights the success of this dual-technique approach in characterizing both the structural and electronic properties of vanadium sites. In particular, and in contrast to XAS or extended X-ray absorption fine structure (EXAFS), we demonstrate that valence-to-core XES is capable of differentiating between ligating atoms with the same identity but different bonding character. Finally, density functional theory (DFT) and time-dependent DFT calculations enable a more detailed, quantitative interpretation of the data. We also establish correction factors for the computational protocols through calibration to experiment. These hard X-ray methods can probe vanadium ions in any oxidation or spin state, and can readily be applied to sample environments ranging from solid-phase catalysts to biological samples in frozen solution. Thus, the combined XAS and XES approach, coupled with DFT calculations, provides a robust tool for the study of vanadium atoms in bioinorganic chemistry. PMID:27251139

  13. Complex polarization propagator approach in the restricted open-shell, self-consistent field approximation: the near K-edge X-ray absorption fine structure spectra of allyl and copper phthalocyanine.

    PubMed

    Linares, Mathieu; Stafström, Sven; Rinkevicius, Zilvinas; Ågren, Hans; Norman, Patrick

    2011-05-12

    A presentation of the complex polarization propagator in the restricted open-shell self-consistent field approximation is given. It rests on a formulation of a resonant-convergent, first-order polarization propagator approach that makes it possible to directly calculate the X-ray absorption cross section at a particular frequency without explicitly addressing the excited states. The quality of the predicted X-ray spectra relates only to the type of density functional applied without any separate treatment of dynamical relaxation effects. The method is applied to the calculation of the near K-edge X-ray absorption fine structure spectra of allyl and copper phthalocyanine. Comparison is made between the spectra of the radicals and those of the corresponding cations and anions to assess the effect of the increase of electron charge in the frontier orbital. The method offers the possibility for unique assignment of symmetry-independent atoms. The overall excellent spectral agreement motivates the application of the method as a routine precise tool for analyzing X-ray absorption of large systems of technological interest.

  14. X-ray absorption and high redshift quasars

    NASA Technical Reports Server (NTRS)

    Elvis, Martin

    1996-01-01

    The low energy cut-offs toward radio-loud quasars with z greater than 2, red quasars, and broad absorption line quasars are discussed. The X-ray absorption seems to be common among different types of red shift quasar. The Rosat position sensitive proportional counter (PSPC) spectra of z = 3 quasars and of a red quasar are presented. Broad absorption lines show outflow velocities of up to 0.1 c to 0.2 c. The advantages and the disadvantages of high red shift observations are underlined.

  15. X-ray absorption spectra of nucleotides (AMP, GMP, and CMP) in liquid water solutions near the nitrogen K-edge

    NASA Astrophysics Data System (ADS)

    Ukai, Masatoshi; Yokoya, Akinari; Fujii, Kentaro; Saitoh, Yuji

    2010-07-01

    The X-ray absorption of nucleotides (adenosine-5'-monophosphate, guanosine 5'-monophosphate, and cytidine 5'-monophosphate) are measured in both water solutions and thin solid films at X-ray energies near the nitrogen K-edge in the 'water-window' region. Each spectrum corresponds to the selective excitation of a nucleobase site in a nucleotide, and thus has features similar to the spectrum of the corresponding nucleobase. An additional new peak in the energy region of the nitrogen 1s → π* resonance is observed for each nucleotide. No significant difference between the water solutions and thin solid films is found, which might be attributable to the hydrophobic properties of a nucleobase in a nucleotide.

  16. Quasar x-ray spectra revisited

    NASA Technical Reports Server (NTRS)

    Shastri, P.; Wilkes, B. J.; Elvis, M.; Mcdowell, J.

    1992-01-01

    A sample of 45 quasars observed by the Imaging Proportional Counter (IPC) on the Einstein satellite is used to re-examine the relationship between the soft (0.2-3.5 keV) X-ray energy index and radio-loudness. We found the following: (1) the tendency for radio-loud quasars to have systematically flatter X-ray slopes than radio-quiet quasars (RQQ's) is confirmed with the soft X-ray excess having negligible effect; (2) there is a tendency for the flatness of the X-ray slope to correlate with radio core-dominance for radio-loud quasars, suggesting that a component of the X-ray emission is relativistically beamed; (3) for the RQQ's the soft X-ray slopes, with a mean of approximately 1.0, are consistent with the slopes found at higher energies (2-10 keV) although steeper than those observed for Seyfert 1 galaxies (also 2-10 keV) where the reflection model gives a good fit to the data; (4) the correlation of FeII emission line strength with X-ray energy index is confirmed for radio-quiet quasars using a subset of 18 quasars. The radio-loud quasars show no evidence for a correlation. This relation suggests a connection between the ionizing continuum and the line emission from the broad emission line region (BELR) of radio-quiet quasars, but in the opposite sense to that predicted by current photoionization models; and (5) the correlations of X-ray slope with radio core dominance and FeII equivalent width within the radio-loud and radio-quiet sub-classes respectively imply that the observed wide range of X-ray spectral slopes is real rather than due to the large measuring uncertainties for individual objects.

  17. Spectra of cosmic x-ray sources

    SciTech Connect

    Holt, S.S.; Mccray, R.

    1982-02-01

    X-ray measurements provide the most direct probes of astrophysical environments with temperatures exceeding one million K. Progress in experimental research utilizing dispersive techniques (e.g., Bragg and grating spectroscopy) is considerably slower than that in areas utilizing photometric techniques, because of the relative inefficiency of the former for the weak X-ray signals from celestial sources. As a result, the term spectroscopy as applied to X-ray astronomy has traditionally satisfied a much less restrictive definition (in terms of resolving power) than it has in other wavebands. Until quite recently, resolving powers of order unity were perfectly respectable, and still provide (in most cases) the most useful spectroscopic data. In the broadest sense, X-ray photometric measurements are spectroscopic, insofar as they represent samples of the overall electromagnetic continua of celestial objects.

  18. Spectra of cosmic X-ray sources

    NASA Technical Reports Server (NTRS)

    Holt, S. S.; Mccray, R.

    1982-01-01

    X-ray measurements provide the most direct probes of astrophysical environments with temperatures exceeding one million K. Progress in experimental research utilizing dispersive techniques (e.g., Bragg and grating spectroscopy) is considerably slower than that in areas utilizing photometric techniques, because of the relative inefficiency of the former for the weak X-ray signals from celestial sources. As a result, the term "spectroscopy" as applied to X-ray astronomy has traditionally satisfied a much less restrictive definition (in terms of resolving power) than it has in other wavebands. Until quite recently, resolving powers of order unity were perfectly respectable, and still provide (in most cases) the most useful spectroscopic data. In the broadest sense, X-ray photometric measurements are spectroscopic, insofar as they represent samples of the overall electromagnetic continua of celestial objects.

  19. 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.

  20. X-ray microprobe for micro x-ray fluorescence and absorption spectroscopies at GSECARS

    NASA Astrophysics Data System (ADS)

    Newville, M.; Sutton, S.; Rivers, M.

    2002-12-01

    The hard x-ray microprobe for x-ray fluorescence and absorption spectroscopy at GeoSoilEnviroCARS is presented. Using focused synchrotron radiation from an undulator beamline at the Advanced Photon Source at Argonne National Lab, the x-ray microprobe provides bright, monochromatic x-rays with typical spot sizes down to 1x1 μm for x-ray fluorescence and absorption spectroscopies. Quantitative x-ray fluorescence (XRF) analysis gives precise elemental composition and correlations, while x-ray absorption spectroscopy (XAS) gives the chemical state and local atomic coordination for a selected atomic species. These two techniques can be used in conjunction with one another on a wide range of samples, including minerals, glasses, fluid inclusions, soils, sediments, and plant tissue. This x-ray microprobe is part of the GeoSoilEnviroCARS user facility, available for use in all areas geological, soil, and environmental sciences, and selected examples from these fields will be given.

  1. X-ray Attenuation and Absorption Calculations.

    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.

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

    SciTech Connect

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

    2010-06-15

    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.

  3. Resonant X-Ray Scattering and Absorption

    NASA Astrophysics Data System (ADS)

    Collins, S. P.; Bombardi, A.

    This chapter outlines some of the basic ideas behind nonresonant and resonant X-ray scattering, using classical or semiclassical pictures wherever possible; specifically, we highlight symmetry arguments governing the observation of X-ray optical effects, such as X-ray magnetic circular dichroism and resonant "forbidden" diffraction. Without dwelling on the microscopic physics that underlies resonant scattering, we outline some key steps required for calculating its rotation and polarization dependence, based on Cartesian and spherical tensor frameworks. Several examples of resonant scattering, involving electronic anisotropy and magnetism, are given as illustrations. Our goal is not to develop or defend theoretical concepts in X-ray scattering, but to bring together existing ideas in a pragmatic and utilitarian manner.

  4. Increasing the applicability of density functional theory. V. X-ray absorption spectra with ionization potential corrected exchange and correlation potentials

    NASA Astrophysics Data System (ADS)

    Verma, Prakash; Bartlett, Rodney J.

    2016-07-01

    Core excitation energies are computed with time-dependent density functional theory (TD-DFT) using the ionization energy corrected exchange and correlation potential QTP(0,0). QTP(0,0) provides C, N, and O K-edge spectra to about an electron volt. A mean absolute error (MAE) of 0.77 and a maximum error of 2.6 eV is observed for QTP(0,0) for many small molecules. TD-DFT based on QTP (0,0) is then used to describe the core-excitation spectra of the 22 amino acids. TD-DFT with conventional functionals greatly underestimates core excitation energies, largely due to the significant error in the Kohn-Sham occupied eigenvalues. To the contrary, the ionization energy corrected potential, QTP(0,0), provides excellent approximations (MAE of 0.53 eV) for core ionization energies as eigenvalues of the Kohn-Sham equations. As a consequence, core excitation energies are accurately described with QTP(0,0), as are the core ionization energies important in X-ray photoionization spectra or electron spectroscopy for chemical analysis.

  5. Summarizing X-ray Stellar Spectra

    NASA Astrophysics Data System (ADS)

    Lee, Hyunsook; Kashyap, V.; XAtlas Collaboration

    2008-05-01

    XAtlas is a spectrum database made with the High Resolution Transmission Grating on the Chandra X-ray Observatory, after painstaking detailed emission measure analysis to extract quantified information. Here, we explore the possibility of summarizing this spectral information into relatively convenient measurable quantities via dimension reduction methods. Principal component analysis, simple component analysis, projection pursuit, independent component analysis, and parallel coordinates are employed to enhance any patterned structures embedded in the high dimensional space. We discuss pros and cons of each dimension reduction method as a part of developing clustering algorithms for XAtlas. The biggest challenge from analyzing XAtlas was handling missing values that pertain astrophysical importance. This research was supported by NASA/AISRP grant NNG06GF17G and NASA contract NAS8-39073.

  6. Synchrotron x-ray fluorescence and extended x-ray absorption fine structure analysis

    SciTech Connect

    Chen, J.R.; Gordon, B.M.; Hanson, A.L.; Jones, K.W.; Kraner, H.W.; Chao, E.C.T.; Minkin, J.A.

    1984-01-01

    The advent of dedicated synchrotron radiation sources has led to a significant increase in activity in many areas of science dealing with the interaction of x-rays with matter. Synchrotron radiation provides intense, linearly polarized, naturally collimated, continuously tunable photon beams, which are used to determine not only the elemental composition of a complex, polyatomic, dilute material but also the chemical form of the elements with improved accuracy. Examples of the application of synchrotron radiation include experiments in synchrotron x-ray fluorescence (SXRF) analysis and extended x-ray absorption fine structure (EXAFS) analysis. New synchrotron radiation x-ray microprobes for elemental analysis in the parts per billion range are under construction at several laboratories. 76 references, 24 figures.

  7. The peculiar optical-UV X-ray spectra of the X-ray weak quasar PG 0043+039

    NASA Astrophysics Data System (ADS)

    Kollatschny, W.; Schartel, N.; Zetzl, M.; Santos-Lleó, M.; Rodríguez-Pascual, P. M.; Ballo, L.; Talavera, A.

    2016-01-01

    Context. The object PG 0043+039 has been identified as a broad absorption line (BAL) quasar based on its UV spectra. However, this optical luminous quasar has not been detected before in deep X-ray observations, making it the most extreme X-ray weak quasar known today. Aims: This study aims to detect PG 0043+039 in a deep X-ray exposure. The question is what causes the extreme X-ray weakness of PG 0043+039? Does PG 0043+039 show other spectral or continuum peculiarities? Methods: We took simultaneous deep X-ray spectra with XMM-Newton, far-ultraviolet (FUV) spectra with the Hubble Space Telescope (HST), and optical spectra of PG 0043+039 with the Hobby-Eberly Telescope (HET) and Southern African Large Telescope (SALT) in July, 2013. Results: We have detected PG 0043+039 in our X-ray exposure taken in 2013. We presented our first results in a separate paper (Kollatschny et al. 2015). PG 0043+039 shows an extreme αox gradient (αox = -2.37). Furthermore, we were able to verify an X-ray flux of this source in a reanalysis of the X-ray data taken in 2005. At that time, it was fainter by a factor of 3.8 ±0.9 with αox = -2.55. The X-ray spectrum is compatible with a normal quasar power-law spectrum (Γ = 1.70-0.45+0.57) with moderate intrinsic absorption (NH = 5.5-3.9+6.9 × 1021 cm-2) and reflection. The UV/optical flux of PG 0043+039 has increased by a factor of 1.8 compared to spectra taken in the years 1990-1991. The FUV spectrum is highly peculiar and dominated by broad bumps besides Lyα. There is no detectable Lyman edge associated with the BAL absorbing gas seen in the CIV line. PG 0043+039 shows a maximum in the overall continuum flux at around λ ≈ 2500 Å in contrast to most other AGN where the maximum is found at shorter wavelengths. All the above is compatible with an intrinsically X-ray weak quasar, rather than an absorbed X-ray emission. Besides strong FeII multiplets and broad Balmer and HeI lines in the optical band we only detect a narrow [O ii

  8. Thomson Thick X-Ray Absorption in a Broad Absorption Line Quasar, PG 0946+301.

    PubMed

    Mathur; Green; Arav; Brotherton; Crenshaw; deKool; Elvis; Goodrich; Hamann; Hines; Kashyap; Korista; Peterson; Shields; Shlosman; van Breugel W; Voit

    2000-04-20

    We present a deep ASCA observation of a broad absorption line quasar (BALQSO) PG 0946+301. The source was clearly detected in one of the gas imaging spectrometers, but not in any other detector. If BALQSOs have intrinsic X-ray spectra similar to normal radio-quiet quasars, our observations imply that there is Thomson thick X-ray absorption (NH greater, similar1024 cm-2) toward PG 0946+301. This is the largest column density estimated so far toward a BALQSO. The absorber must be at least partially ionized and may be responsible for attenuation in the optical and UV. If the Thomson optical depth toward BALQSOs is close to 1, as inferred here, then spectroscopy in hard X-rays with large telescopes like XMM would be feasible.

  9. Measuring x-ray spectra of flash radiographic sources

    SciTech Connect

    Gehring, Amanda Elizabeth; Espy, Michelle A.; Haines, Todd Joseph; Mendez, Jacob; Moir, David C.; Sedillo, Robert; Shurter, Roger P.; Volegov, Petr Lvovich; Webb, Timothy J

    2015-11-02

    The x-ray spectra of flash radiographic sources is difficult to measure. The sources measured were Radiographic Integrated Test Stand-6 (370 rad at 1 m; 50 ns pulse) and Dual Axis Radiographic Hydrodynamic Test Facility (DARHT) (550 rad at 1 m; 50 ns pulse). Features of the Compton spectrometer are described, and spectra are shown. Additional slides present data on instrumental calibration.

  10. X-Ray Absorption Spectroscopy of Strontium(II) Coordination.

    PubMed

    Sahai; Carroll; Roberts; O'Day

    2000-02-15

    Sorption of dissolved strontium on kaolinite, amorphous silica, and goethite was studied as a function of pH, aqueous strontium concentration, the presence or absence of atmospheric CO(2) or dissolved phosphate, and aging over a 57-day period. Selected sorption samples ([Sr(aq)](i) approximately 0.5-1x10(-3) m) were examined with synchrotron X-ray absorption spectroscopy (XAS) at low (13-23 K) and room temperatures to determine the local molecular coordination around strontium. Quantitative analyses of the extended X-ray absorption fine structure (EXAFS) of kaolinite, amorphous silica, and most goethite sorption samples showed a single first shell of 9-10 (+/-1) oxygen atoms around strontium at an average Sr-O bond-distance of 2.61 (+/-0.02) Å, indicating hydrated surface complexes. The EXAFS spectra were unchanged after reaction for up to 57 days. Likewise, in kaolinite sorption samples prepared in 100% nitrogen atmosphere, the presence of dissolved phosphate (0.5x10(-3) m) in addition to strontium did not change the local coordination around strontium. In two goethite sorption samples reacted in air at pH approximately 8.5, the EXAFS spectra (collected at low and room temperature) clearly showed that the local structure around strontium is that of strontianite (SrCO(3)(s)). We also noted an increase in strontium uptake on goethite in the presence of atmospheric CO(2) in batch experiments, relative to CO(2)-free experiments. These observations suggest that sorption of carbonate may nucleate the precipitation of SrCO(3) in the pH range in which carbonate sorption on goethite is near a maximum. At higher pH, carbonate surface sorption decreases as dissolved CO(2) decreases. For goethite sorption samples above pH 8.6, hydrated surface complexes, rather than a precipitate, were observed in the EXAFS spectra. Copyright 2000 Academic Press.

  11. Absorption and phase X-ray imaging using reflected beam

    NASA Astrophysics Data System (ADS)

    Jakubek, Jan

    2011-05-01

    The X-ray structure imaging of the soft thin biological samples is particularly difficult as they are often attached to the solid carrier, which has much higher absorption of X-rays. The highly absorbing carrier forces the use of higher energies of X-rays decreasing the achievable contrast of the sample structure. The proposed method uses a flat sample carrier (metallic, glass or even plastic) acting as a mirror. The carrier with the sample is irradiated at grazing angle and the X-ray beam is reflected from the interface between the sample and carrier. That way the beam penetrates through the sample only without entering into the carrier. The energy of the X-ray beam can be low (e.g. nanofocus X-ray tube with Cr, Fe or Cu cathode) providing good contrast for soft sample imaging. The beam path in the sample is prolonged giving more chance for absorption in very thin samples. The reflectivity of X-ray depends on the beam properties and on the refractive index of the sample (for a given carrier material). Then, it is possible to make imaging of the refractive index distribution across the sample. Sufficient spatial resolution and good sensitivity can be achieved using nanofocus X-ray tube together with a highly sensitive pixelated detector Timepix. Several experimental results obtained with such a system verifying the principles described above are presented.

  12. Simulation of mammographic x-ray spectra.

    PubMed

    Johnson, G A; O'Foghludha, F

    1980-01-01

    Attempts to simulate Mo-anode spectra for film mammography by using Mo filters with W-anode tubes have been reported by several workers, and others have generated W-like continua for xeromammographic purposes by heavy Al filtration of Mo-anode tubes. In the present work the success of these simulations was tested by Si(Li) spectrometric methods that measured the spectral shapes and the exposure levels. Comparisons of Mo-anode/Al-filter with W-anode/Al-filter combinations were made, and also of W-anode/M-filter with Mo-anode/Mo-folter combinations. In certain circumstance the spectral shape is moderately well simulated but in all cases the useful output is less in the simulations than in the original spectra. The general conclusion is that simulation is always less attractive than direct use of the desired anode. PMID:7393143

  13. Simulation of mammographic x-ray spectra

    SciTech Connect

    Johnson, G.A.; O'Foghludha, F.

    1980-05-01

    Attempts to simulate Mo-anode spectra for film mammography by using Mo filters with W-anode tubes have been reported by several workers, and others have generated W-like continua for xeromammographic purposes by heavy A1 filtration of Mo-anode tubes. In the present work the success of these simulations was tested by Si(Li) spectrometric methods that measured the spectral shapes and the exposure levels. Comparisons of Mo-anode/A1-filter with W-anode/A1-filter combinations were made, and also of W-anode/M-filter with Mo-anode/Mo-folter combinations. In certain circumstance the spectral shape is moderately well simulated but in all cases the useful output is less in the simulations than in the original spectra. The general conclusion is that simulation is always less attractive than direct use of the desired anode.

  14. The X-ray spectra of galaxies. I - Spectral fits of individual galaxies and X-ray colors

    NASA Technical Reports Server (NTRS)

    Kim, D.-W.; Fabbiano, G.; Trinchieri, G.

    1992-01-01

    The X-ray spectra of normal galaxies is investigated systematically by using the Imaging Proportional Counter (IPC) data in the Einstein data bank. In addition to the standard model fitting technique, X-ray colors are introduced in order to extract spectral information from the fainter X-ray sources. Spectral parameters for 43 galaxies and X-ray colors for 127 galaxies are presented.

  15. Ab initio X-Ray Absorption Fine Structure Cumulants

    NASA Astrophysics Data System (ADS)

    Vila, F.; Rehr, J. J.; Rossner, H. H.; Krappe, H. J.

    2006-03-01

    Theoretical calculations of vibrational effects in x-ray absorption spectra typically employ semi-phenomenological models, e.g. empirical force constants or correlated Debye or Einstein models. Instead we introduce an efficient and generally applicable ab initio approach based on electronic structure calculations of the dynamical matrix together with the Lanczos recursion algorithm [1] and relations between the cumulants. The approach yields 1) the thermal expansion coefficients (first cumulant of the vibrational distribution function); 2) correlated Debye-Waller factors (second cumulants) and 3) anharmonic contributions (third cumulants). Results are presented for crystalline (Cu, Au, Ge, GaAs) and molecular (GeCl4, C6H6) systems. Our results for the Debye-Waller factors agree well with experiment. [1]H.J. Krappe and H.H. Rossner, Phys. Rev. B70, 104102 (2004).

  16. X-ray-binary spectra in the lamp post model

    NASA Astrophysics Data System (ADS)

    Vincent, F. H.; Różańska, A.; Zdziarski, A. A.; Madej, J.

    2016-05-01

    Context. The high-energy radiation from black-hole binaries may be due to the reprocessing of a lamp located on the black hole rotation axis and emitting X-rays. The observed spectrum is made of three major components: the direct spectrum traveling from the lamp directly to the observer; the thermal bump at the equilibrium temperature of the accretion disk heated by the lamp; and the reflected spectrum essentially made of the Compton hump and the iron-line complex. Aims: We aim to accurately compute the complete reprocessed spectrum (thermal bump + reflected) of black-hole binaries over the entire X-ray band. We also determine the strength of the direct component. Our choice of parameters is adapted to a source showing an important thermal component. We are particularly interested in investigating the possibility to use the iron-line complex as a probe to constrain the black hole spin. Methods: We computed in full general relativity the illumination of a thin accretion disk by a fixed X-ray lamp along the rotation axis. We used the ATM21 radiative transfer code to compute the local, energy-dependent spectrum emitted along the disk as a function of radius, emission angle and black hole spin. We then ray traced this local spectrum to determine the final reprocessed spectrum as received by a distant observer. We consider two extreme values of the black hole spin (a = 0 and a = 0.98) and discuss the dependence of the local and ray-traced spectra on the emission angle and black hole spin. Results: We show the importance of the angle dependence of the total disk specific intensity spectrum emitted by the illuminated atmosphere when the thermal disk emission is fully taken into account. The disk flux, together with the X-ray flux from the lamp, determines the temperature and ionization structure of the atmosphere. High black hole spin implies high temperature in the inner disk regions, therefore, the emitted thermal disk spectrum fully covers the iron-line complex. As a

  17. X-ray absorption fine structure measurement with a 9 V electric battery x-ray emitter

    SciTech Connect

    Mitsuya, Shota; Ishii, Hideshi; Kawai, Jun; Tanaka, Keiichi

    2006-09-25

    X-ray absorption spectral analysis is a well known technique for analyzing the chemical environment of an element in a specimen. It has been believed that high intensity and monochromatized x rays such as the synchrotron radiation are required for an x-ray absorption experiment. In the present study, however, we demonstrate that the x-ray absorption spectral measurement of transition metal foils with an energy resolution of 10 eV is possible with a combination of a 9 V dry electric battery pyroelectric x-ray generator and a superconducting microcalorimeter.

  18. Measuring Flash X-Ray Spectra with a Compton Spectrometer

    NASA Astrophysics Data System (ADS)

    Gehring, Amanda; Espy, Michelle; Haines, Todd; Hunter, James; King, Nick; Merrill, Frank; Sedillo, Robert; Urbaitis, Algis; Volegov, Petr

    2014-09-01

    The determination of the x-ray energy spectra of flash radiographic sources is difficult due to the short nature of the pulses (~50 ns). Recently, a Compton spectrometer has been refurbished and investigated as a potential device for conducting these measurements. The spectrometer was originally designed and characterized by Morgan et al.. The spectrometer consists of a 300 kg neodymium-iron magnet and measures spectra in the <1 MeV to 20 MeV energy range. In this apparatus, the incoming x-rays are collimated into a narrow beam before encountering a converter foil. Compton electrons are ejected and collimated so that the forward-directed electrons enter the magnetic field region of the device. The position of the electrons on the magnet focal plane is a function of their energy, allowing the x-ray spectrum to be reconstructed. Recent energy calibration measurements and the spectrum reconstruction of a Bremsstrahlung source will be presented. The determination of the x-ray energy spectra of flash radiographic sources is difficult due to the short nature of the pulses (~50 ns). Recently, a Compton spectrometer has been refurbished and investigated as a potential device for conducting these measurements. The spectrometer was originally designed and characterized by Morgan et al.. The spectrometer consists of a 300 kg neodymium-iron magnet and measures spectra in the <1 MeV to 20 MeV energy range. In this apparatus, the incoming x-rays are collimated into a narrow beam before encountering a converter foil. Compton electrons are ejected and collimated so that the forward-directed electrons enter the magnetic field region of the device. The position of the electrons on the magnet focal plane is a function of their energy, allowing the x-ray spectrum to be reconstructed. Recent energy calibration measurements and the spectrum reconstruction of a Bremsstrahlung source will be presented. LA-UR-14-23602.

  19. 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

  20. Oxygen binding by Helix pomatia alpha-haemocyanin studied by X-ray-absorption spectroscopy.

    PubMed Central

    Torensma, R; Phillips, J C

    1983-01-01

    The X-ray absorption spectra of haemocyanin from Helix pomatia were obtained by using X-rays from synchrotron radiation. Cu K-edges were recorded at four conditions, namely fully oxygenated, 85% oxygenated, 12% oxygenated and fully deoxygenated. The percentage oxygenation calculated from the edge-shift of the partially oxygenated samples did not agree with the percentage oxygenation as determined by u.v. measurements. Two intermediates in the oxygenation process are presented to explain the observed dissimilarities. PMID:6847624

  1. Analyzing the Spectra of Accreting X-Ray Pulsars

    NASA Astrophysics Data System (ADS)

    Wolff, Michael

    This proposal seeks funding for the analysis of accretion-powered X-ray pulsar spectra from NASA/ HEASARC archived X-ray data. Spectral modeling of accreting X-ray pulsars can tell us a great deal about the physical conditions in and near high mass X-ray binary systems. Such systems have accretion flows where plasma is initially channeled from an accretion disk by the strong neutron star magnetic field, eventually falling onto the magnetic polar cap of the neutron star compact object. Many of these accreting X-ray pulsars have X-ray spectra that consist of broad power-law continua with superposed cyclotron resonant scattering features indicating magnetic field strengths above 10^12 G. The energies of these cyclotron line features have recently been shown to vary with X-ray luminosity in a number of sources such as Her X-1 and V 0332+53, a phenomenon not well understood. Another recent development is the relatively new analytic model for the spectral continuum formation in accretion-powered pulsar systems developed by Becker & Wolff. In their formalism the accretion flows are assumed to go through radiation- dominated radiative shocks and settle onto the neutron star surface. The radiation field consists of strongly Comptonized bremsstrahlung emission from the entire plasma, Comptonized cyclotron emission from the de-excitations of Landau-excited electrons in the neutron star magnetic field, and Comptonized black-body emission from a thermal mound near the neutron star surface. We seek to develop the data analysis tools to apply this model framework to the X-ray data from a wide set of sources to make progress characterizing the basic accretion properties (e.g., magnetic field strength, plasma temperatures, polar cap size, accretion rate per unit area, dominance of bulk vs. thermal Comptonization) as well as understanding the variations of the cyclotron line energies with X-ray luminosity. The three major goals of our proposed work are as follows: In the first year

  2. Near Edge X-ray Absorption Spectroscopy of Polymers

    NASA Astrophysics Data System (ADS)

    Dhez, Olivier; Ade, Harald; Urquhart, Stephen

    2001-03-01

    Synthetic and natural polymers exhibit a rich carbon, nitrogen and oxygen K-edge Near Edge X-ray Absorption Fine Structure (NEXAFS). The spectroscopic variations with chemical structure and composition are interesting in their own right. In addition, the large spectroscopic variability can be utilized for the compositional analysis of materials. This is particularly useful for high spatial resolution NEXAFS microanalysis at lateral spatial resolutions exceeding that achievable with more traditional compositional analysis tools such as Infrared and NMR spectroscopy. To increase our understanding of NEXAFS spectra and to start a database for microanalysis, we acquired carbon NEXAFS spectra of the following polymers: polycarbonate, poly(oxybenzoate-co-2,6oxynaphthoate), poly (p-phenylene terephtalamide), toluene diisocyanate polyurethane, toluene diisocyanate polyurea, 4,4'-methylene di-p-phenylene isocyanate polyurethane, 4,4'-methylene di-p-phenylene isocyanate polyurea, poly(ether ether ketone), poly(alpha-methylstyrene), poly-styrene, poly bromostyrene, poly(2-vinyl styrene), polyethylene, poly(ethylene oxide), polypropylene, poly(propylene oxide), polyisobutylene, ethylene propylene rubber, poly(methyl -metacrylate). These spectra were obtained in transmission with an energy resolution of 150 meV. The energy scale was carefully calibrated in-situ utilizing C02 gas as a reference. Spectral assignments are made based on model compounds and theoretical calculations.

  3. 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.

  4. 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.

  5. 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.

  6. Accretion Shocks in Young Stars: the Role of Local Absorption on the X-ray Emission

    NASA Astrophysics Data System (ADS)

    Bonito, R.; Argiroffi, C.; Orlando, S.; Miceli, M.; Peres, G.; Matsakos, T.; Stehle, C.; Ibgui, L.

    2015-01-01

    We investigate the X-ray emission from accretion shocks in classical T Tauri stars, due to the infalling material impacting the stellar surface. Several aspects in both observations and models of the accretion process are still unclear: the observed X-ray luminosity of the post-shock plasma is below the predicted value, the density vs temperature structure of the shocked plasma, with increasing densities at higher temperature, is opposite of what expected from simple accretion shock models. To address these issues we performed numerical magnetohydrodynamic simulations describing the impact of an accretion stream onto the stellar surface and considered the local absorption due to the surrounding medium. We explored the effects of absorption for different viewing angles and for the He-like line triplets commonly used for density diagnostic. From the model results we synthesize the X-ray emission from the accretion shock, producing maps and spectra. We perform density and temperature diagnostics on the synthetic spectra, and we directly compare our results with the observations. Our model shows that the X-ray fluxes detected are lower than expected because of the local absorption. The emerging spectra suggest a complex density vs temperature distribution proving that a detailed model accounting for a realistic treatment of the local absorption is needed to interpret the observations of X-ray emitting accretion shocks.

  7. 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

  8. High-energy X-ray spectra of five sources.

    NASA Technical Reports Server (NTRS)

    Ricker, G. R.; Mcclintock, J. E.; Gerassimenko, M.; Lewin , W. H. G.

    1973-01-01

    On October 15-16, 1970, we carried out balloon X-ray observations from Australia at energies above 15 keV. We present the high-energy X-ray spectra of three sources discovered by us, GX 301-2, GX 304-1, and GX 1 + 4. The data suggest that these high-energy sources correspond to the sources 2U 1223-62, 2U 1258-61, and 2U 1728-24 respectively. We also present the spectra for two additional sources, GX 5-1 (2U 1757-25) and GX 3 + 1 (2U 1744-26). The average intensity of the highly variable source GX 301-2 was observed to be as great as Tau X-1 in the energy range 15-50 keV.

  9. 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.

  10. Biological X-ray absorption spectroscopy and metalloproteomics.

    PubMed

    Ascone, Isabella; Strange, Richard

    2009-05-01

    In the past seven years the size of the known protein sequence universe has been rapidly expanding. At present, more then five million entries are included in the UniProtKB/TrEMBL protein database. In this context, a retrospective evaluation of recent X-ray absorption studies is undertaken to assess its potential role in metalloproteomics. Metalloproteomics is the structural and functional characterization of metal-binding proteins. This is a new area of active research which has particular relevance to biology and for which X-ray absorption spectroscopy is ideally suited. In the last three years, biological X-ray absorption spectroscopy (BioXAS) has been included among the techniques used in post-genomics initiatives for metalloprotein characterization. The emphasis of this review is on the progress in BioXAS that has emerged from recent meetings in 2007-2008. Developments required to enable BioXAS studies to better contribute to metalloproteomics throughput are also discussed. Overall, this paper suggests that X-ray absorption spectroscopy could have a higher impact on metalloproteomics, contributing significantly to the understanding of metal site structures and of reaction mechanisms for metalloproteins. PMID:19395808

  11. Calculation of x-ray spectra emerging from an x-ray tube. Part II. X-ray production and filtration in x-ray targets

    SciTech Connect

    Poludniowski, Gavin G.

    2007-06-15

    A new approach to the calculation of the x-ray spectrum emerging from an x-ray tube is proposed. Theoretical results for the bremsstrahlung cross section appearing in the literature are summarized. Four different treatments of electron penetration, based on the work presented in Part I, are then used to generate bremsstrahlung spectra. These spectra are compared to experimental data at 50, 80 and 100 kVp tube potentials. The most sophisticated treatment of electron penetration was required to obtain good agreement. With this treatment both the National Institute of Standards and Technology bremsstrahlung cross sections, based on accurate partial wave calculations, and the Bethe-Heitler cross section [H. A. Bethe and W. Heitler, Proc R. Soc. London, Ser. A. 146, 83-112 (1934)] corrected by a modified Elwert factor [G. Elwert, Ann. Phys. (Leipzig) 426, 178-208 (1939)], provided good agreement to measured data. An approximate treatment of the characteristic spectrum is suggested. The dependencies of the bremsstrahlung and characteristic outputs of an x-ray tube on tube potential are compared to experimentally derived data for 70-140 kVp potentials. Agreement is to within a few percent of the total output over the entire range. The spectral predictions of the semiempirical models of Birch and Marshall [R. Birch and M. Marshall, Phys. Med. Biol. 24, 505-513 (1979)] (IPEM Report 78) and of Tucker et al. [D. M. Tucker, G. T. Barnes, and D. P. Chakraborty, Med. Phys. 18, 211-218 (1991).] are also assessed. The predictions of Tucker et al. are very close to the model developed here. The predictions of IPEM Report 78 are similar, but consistently harder for the range of tube potentials examined (50-100 kV). Unlike the semiempirical models, the model proposed here requires the introduction of no empirical and unphysical parameters in the differential bremsstrahlung cross section, bar an overall normalization factor which is close to unity.

  12. 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

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

    SciTech Connect

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

    2007-02-02

    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 {pi}* and {sigma}* 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 {pi}* peak. The lower-energy peak, denoted as the 'pre-peak', in the subtracted spectra and the {pi}*/{sigma}* 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 {pi}*/{sigma}* ratio reflect the local graphitic structure of carbon black.

  14. 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.

  15. Measuring X-ray Spectra of Flash Radiographic Sources

    NASA Astrophysics Data System (ADS)

    Gehring, Amanda; Espy, Michelle; Haines, Todd; Mendez, Jacob; Moir, David; Sedillo, Robert; Volegov, Petr; Webb, Tim

    2015-10-01

    A Compton spectrometer has been re-commissioned for measurements of flash radiographic sources. The determination of the energy spectrum provides information about the x-ray production mechanisms of these sources (ie. reaction history of plasmas, electron-target interactions) and benefits the analysis of images obtained at radiographic facilities. However, the measurements of the spectra are difficult due to the high count rates and short nature of the pulses (~ 50 ns). The spectrometer is a 300 kg neodymium-iron magnet which measures spectra in the <1 MeV to 20 MeV energy range. Incoming x-rays are collimated into a narrow beam incident on a converter foil. The ejected Compton electrons are collimated so that the forward-directed electrons enter the magnetic field region of the spectrometer. The position of the electrons at the focal plane of the magnet is a function of their momentum, allowing the x-ray spectrum to be reconstructed. Recent measurements of both flash and continuous radiographic sources will be presented.

  16. Measuring x-ray spectra of flash radiographic sources

    NASA Astrophysics Data System (ADS)

    Gehring, Amanda E.; Espy, Michelle A.; Haines, Todd J.; Mendez, Jacob; Moir, David C.; Sedillo, Robert; Shurter, Roger P.; Volegov, Petr; Webb, Timothy J.

    2015-08-01

    A Compton spectrometer has been re-commissioned for measurements of flash radiographic sources. The determination of the energy spectrum of these sources is difficult due to the high count rates and short nature of the pulses (~50 ns). The spectrometer is a 300 kg neodymium-iron magnet which measures spectra in the <1 MeV to 20 MeV energy range. Incoming x-rays are collimated into a narrow beam incident on a converter foil. The ejected Compton electrons are collimated so that the forward-directed electrons enter the magnetic field region of the spectrometer. The position of the electrons at the magnet's focal plane is a function of their momentum, allowing the x-ray spectrum to be reconstructed. Recent measurements of flash sources are presented.

  17. Vanadium K-edge X-ray absorption spectroscopy of bromoperoxidase from Ascophyllum nodosum

    SciTech Connect

    Arber, J.M.; de Boer, E.; Garner, C.D.; Hasnain, S.S.; Wever, R. )

    1989-09-19

    Bromoperoxidase from Ascophyllum nodusum was the first vanadium-containing enzyme to be isolated. X-ray absorption spectra have now been collected in order to investigate the coordination of vanadium in the native, native plus bromide, native plus hydrogen peroxide, and dithionite-reduced forms of the enzyme. The edge and X-ray absorption near-edge structures show that, in the four samples studied, it is only on reduction of the native enzyme that the metal site is substantially altered. In addition, these data are consistent with the presence of vanadium(IV) in the reduced enzyme and vanadium(V) in the other samples. Extended X-ray absorption fine structure data confirm that there are structural changes at the metal site on reduction of the native enzyme, notably a lengthening of the average inner-shell distance, and the presence of terminal oxygen together with histidine and oxygen-donating residues.

  18. The hard X-ray emission spectra from accretion columns in intermediate polars

    NASA Technical Reports Server (NTRS)

    Yi, Insu; Vishniac, Ethan T.

    1994-01-01

    We consider the hard (greater than 2 keV) X-ray emission from accretion columns in an intermediate polar system, GK Per, using a simple settling solution. The rate of photon emission per logarithmic energy interval can be fitted with a power law, E(exp -gamma), with gamma approximately 2.0, in agreement with observations. This index is only weakly dependent on the mass accretion rate, dot-M, for dot-M in the range of a few times 10(exp 16-18) g/s. The peak energy of the photon spectra (after photoelectric absorption) is expected to be E(sub p) approximately (5 keV) gamma(exp -1/3) (N(sub H)/10(exp 23)/sq cm)(exp 1/3) where N(sub H) is the hydrogen column density along the line of sight. The observed spectra of GK Per and possibly of V1223 Sgr suggest N(sub H) approximately 10(exp 23)/sq cm. This large N(sub H) may be due to partially ionized preshock column material. Alternatively, we also consider absorption by the cool outer parts of an accretion disk. In this case the photoelectric absorption depth in the disk is a sensitive function of inclination. For GK Per the required inclination is approximately 83 deg. For mass accretion rates larger than a critical rate of approximately 10(exp 18) g/s, X-ray emission from the column accretion is significantly affected by radiation drag. Although the mass accretion rate increases dramatically during outbursts, the observed hard (greater than 2 keV) X-ray luminosity will not rise proportionately. The slope and peak energy of the outburst spectra are only weakly affected. We conclude that the observed X-ray spectra can be explained by this simple analytic solution and that the production of hard X-rays from the accretion shock at the magnetic poles in the intermediate polars is in general agreement with the observations. However, since the X-ray emission and absorption depend on the mass accretion rate in a complicated manner, observed hard X-ray luminosities (greater than 2 keV) are not a good indicator of the mass

  19. 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.

  20. High Resolution X-Ray Spectra of WR 6

    NASA Astrophysics Data System (ADS)

    Huenemoerder, D.; Gayley, K.; Hamann, W.-R.; Ignace, R.; Nichols, J.; Oskinova, L. M.; Pollock, A. M. T.; Schulz, N.

    As WR 6 is a putatively single WN4 star, and is relatively bright (V = 6.9), it is an ideal case for studying the wind mechanisms in these extremely luminous stars. To obtain higher resolution spectra at higher energy (above 1 keV) than previously obtained with the XMM/Newton RGS, we have observed WR 6 with the Chandra High Energy Transmission Grating Spectrometer for 450 ks. We have resolved emission lines of S, Si, Mg, Ne, and Fe, which all show a “fin"-shaped prole, characteristic of a self-absorbed uniformly expanding shell. Steep blue edges gives robust maximal expansion velocities of about 2000 km/s, somewhat larger than the 1700km/s derived from UV lines. The He-like lines all indicate that X-ray emitting plasmas are far from the photosphere - even at the higher energies where opacity is lowest { as was also the case for the longer wavelength lines observed with XMM-Newton/RGS. Abundances determined from X-ray spectral modeling indicate enhancements consistent with nucleosynthesis. The star was also variable in X-rays and in simultaneous optical photometry obtained with Chandra aspect camera, but not coherently with the optically known period of 3.765 days.

  1. 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.

  2. 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.

  3. X-ray spectra from convective photospheres of neutron stars

    SciTech Connect

    Zavlin, V.E.; Pavlov, G.G. |; Shibanov, Yu.A.; Rogers, F.J.; Iglesias, C.A.

    1996-01-17

    We present first results of modeling convective photospheres of neutron stars. We show that in photospheres composed of the light elements convection arises only at relatively low effective temperatures ({le}3 - 5 x 10{sup 4} K), whereas in the case of iron composition it arises at T{sub eff}{le} 3 x 10{sup 5}K. Convection changes the depth dependence of the photosphere temperature and the shapes of the emergent spectra. Thus, it should be taken into account for the proper interpretation of EUV/soft-X-ray observations of the thermal radiation from neutron stars.

  4. The soft X-ray excess in Einstein quasar spectra

    NASA Technical Reports Server (NTRS)

    Masnou, J. L.; Wilkes, B. J.; Elvis, M.; Mcdowell, J. C.; Arnaud, K. A.

    1992-01-01

    An SNR-limited subsample of 14 quasars from the Wilkes and Elvis (1987) sample is presently investigated for low-energy excess above a high-energy power law in the X-ray spectra obtained by the Einstein Imaging Proportional Counter. A significant excess that is 1-6 times as strong as the high-energy component at 0.2 keV is noted in eight of the 14 objects. In the case of 3C273, multiple observations show the excess to be variable.

  5. Diagnostic of dense plasmas using X-ray spectra

    NASA Astrophysics Data System (ADS)

    Yu, Q. Z.; Zhang, J.; Li, Y. T.; Zhang, Z.; Jin, Z.; Lu, X.; Li, J.; Yu, Y. N.; Jiang, X. H.; Li, W. H.; Liu, S. Y.

    2005-12-01

    The spectrally and spatially resolved X-ray spectra emitted from a dense aluminum plasma produced by 500 J, 1 ns Nd:glass laser pulses are presented. Six primary hydrogen-like and helium-like lines are identified and simulated with the atomic physics code FLY. We find that the plasma is almost completely ionized under the experimental conditions. The highest electron density we measured reaches up to 1023 cm-3. The spatial variations of the electron temperature and density are compared with the simulations of MEDUSA hydrocode for different geometry targets. The results indicate that lateral expansion of the plasma produced with this laser beam plays an important role.

  6. Bethe-Salpeter Equation Approach for Calculations of X-ray Spectra

    NASA Astrophysics Data System (ADS)

    Vinson, John

    X-ray spectroscopy is a powerful and widely used tool for the investigation of the electronic structure of a large variety of solid state materials, including crystals materials, liquids, amorphous solids, molecules, and extended states such as clusters or interfaces. The local nature of x-ray mediated electronic excitations, involving transitions to or from localized, atomic-like, core levels, makes them ideal probes of local electronic properties: bonding character, charge transfer, and local geometry. The interpretation of spectra relies on modeling the excitations accurately to provide a concrete connection between specific properties of a system and the resulting x-ray spectrum. As experimental techniques and facilities have improved, including third generation synchrotron sources and the advent of x-ray free electron lasers, measurements have been taken on wider ranges of systems, exploring the effects of temperature and pressure, and at higher resolutions than before, but theoretical techniques have lagged. Our goal is to develop a first-principles theoretical framework capable of achieving quantitative agreement with x-ray absorption near-edge structure (XANES) experiments. This thesis aims to develop the Bethe-Salpeter equation (BSE), a particle-hole Green's function method, for describing the excited electronic state produced in core-level x-ray absorption and related spectroscopies. Building upon density functional theory along with self-energy corrections, our approach provides connection to experiment with minimal adjustable parameters, to both aid in interpretation and highlight unaccounted for physical processes. While a fully parameter-free method for calculating x-ray spectroscopy remains elusive, our method presented here allows for quantitative comparison to experiment without system-dependent fits. This method has been implemented in the OCEAN software package, and results are presented for both insulating and metallic materials, including 3d

  7. K{beta} resonant x-ray emission spectra in MnF{sub 2}

    SciTech Connect

    Taguchi, M.; Parlebas, J. C.; Uozumi, T.; Kotani, A.; Kao, C.-C.

    2000-01-15

    We report experimental and theoretical results on Mn K{beta} resonant x-ray emission spectra (K{beta} RXES) at the pre-edge region of K-edge x-ray absorption spectroscopy in a powdered MnF{sub 2} sample. The experimental results are studied theoretically in terms of coherent second-order optical process, using a MnF{sub 6}{sup -4} cluster model with the effects of intra-atomic multiplet coupling and interatomic hybridization in the space of three configurations and taking into account both the Mn 1s-3d quadrupole excitation and the Mn 1s-4p dipole excitation. The agreement between theory and experiment is good. Moreover, we show that if the sample is a single crystal the resonant x-ray emission spectroscopy caused by the quadrupole excitation has a strong sensitivity to the angle of the incident photon. (c) 2000 The American Physical Society.

  8. 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.

  9. Excited state X-ray absorption spectroscopy: Probing both electronic and structural dynamics

    NASA Astrophysics Data System (ADS)

    Neville, Simon P.; Averbukh, Vitali; Ruberti, Marco; Yun, Renjie; Patchkovskii, Serguei; Chergui, Majed; Stolow, Albert; Schuurman, Michael S.

    2016-10-01

    We investigate the sensitivity of X-ray absorption spectra, simulated using a general method, to properties of molecular excited states. Recently, Averbukh and co-workers [M. Ruberti et al., J. Chem. Phys. 140, 184107 (2014)] introduced an efficient and accurate L 2 method for the calculation of excited state valence photoionization cross-sections based on the application of Stieltjes imaging to the Lanczos pseudo-spectrum of the algebraic diagrammatic construction (ADC) representation of the electronic Hamiltonian. In this paper, we report an extension of this method to the calculation of excited state core photoionization cross-sections. We demonstrate that, at the ADC(2)x level of theory, ground state X-ray absorption spectra may be accurately reproduced, validating the method. Significantly, the calculated X-ray absorption spectra of the excited states are found to be sensitive to both geometric distortions (structural dynamics) and the electronic character (electronic dynamics) of the initial state, suggesting that core excitation spectroscopies will be useful probes of excited state non-adiabatic dynamics. We anticipate that the method presented here can be combined with ab initio molecular dynamics calculations to simulate the time-resolved X-ray spectroscopy of excited state molecular wavepacket dynamics.

  10. 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.

  11. Opacity of iron, nickel, and copper plasmas in the x-ray wavelength range: Theoretical interpretation of 2p-3d absorption spectra

    SciTech Connect

    Blenski, T.; Loisel, G.; Poirier, M.; Thais, F.; Arnault, P.; Caillaud, T.; Fariaut, J.; Gilleron, F.; Pain, J.-C.; Porcherot, Q.; Reverdin, C.; Silvert, V.; Villette, B.; Bastiani-Ceccotti, S.; Turck-Chieze, S.; Foelsner, W.; Gaufridy de Dortan, F. de

    2011-09-15

    This paper deals with theoretical studies on the 2p-3d absorption in iron, nickel, and copper plasmas related to LULI2000 (Laboratoire pour l'Utilisation des Lasers Intenses, 2000J facility) measurements in which target temperatures were of the order of 20 eV and plasma densities were in the range 0.004-0.01 g/cm{sup 3}. The radiatively heated targets were close to local thermodynamic equilibrium (LTE). The structure of 2p-3d transitions has been studied with the help of the statistical superconfiguration opacity code sco and with the fine-structure atomic physics codes hullac and fac. A new mixed version of the sco code allowing one to treat part of the configurations by detailed calculation based on the Cowan's code rcg has been also used in these comparisons. Special attention was paid to comparisons between theory and experiment concerning the term features which cannot be reproduced by sco. The differences in the spin-orbit splitting and the statistical (thermal) broadening of the 2p-3d transitions have been investigated as a function of the atomic number Z. It appears that at the conditions of the experiment the role of the term and configuration broadening was different in the three analyzed elements, this broadening being sensitive to the atomic number. Some effects of the temperature gradients and possible non-LTE effects have been studied with the help of the radiative-collisional code scric. The sensitivity of the 2p-3d structures with respect to temperature and density in medium-Z plasmas may be helpful for diagnostics of LTE plasmas especially in future experiments on the {Delta}n=0 absorption in medium-Z plasmas for astrophysical applications.

  12. 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.

  13. Femtosecond time-resolved X-ray absorption spectroscopy of liquid using a hard X-ray free electron laser in a dual-beam dispersive detection method.

    PubMed

    Obara, Yuki; Katayama, Tetsuo; Ogi, Yoshihiro; Suzuki, Takayuki; Kurahashi, Naoya; Karashima, Shutaro; Chiba, Yuhei; Isokawa, Yusuke; Togashi, Tadashi; Inubushi, Yuichi; Yabashi, Makina; Suzuki, Toshinori; Misawa, Kazuhiko

    2014-01-13

    We present femtosecond time-resolved X-ray absorption spectroscopy of aqueous solution using a hard x-ray free electron laser (SACLA) and a synchronized Ti:sapphire laser. The instrumental response time is 200 fs, and the repetition rate of measurement is 10 Hz. A cylindrical liquid beam 100 μm in diameter of aqueous ammonium iron(III) oxalate solution is photoexcited at 400 nm, and the transient X-ray absorption spectra are measured in the K-edge region of iron, 7.10 - 7.26 keV, using a dual X-ray beam dispersive detection method. Each of the dual beams has the pulse energy of 1.4 μJ, and pump-induced absorbance change on the order of 10(-3) is successfully detected. The photoexcited iron complex exhibits a red shifted iron K-edge with the appearance time constant of 260 fs. The X-ray absorption difference spectra, with and without the pump pulses, are independent of time delay after 1.5 ps up to 100 ps, indicating that the photoexcited species is long-lived.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

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

    NASA Astrophysics Data System (ADS)

    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 106-107 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.

  19. 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.

  20. 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.

  1. X-ray structure analysis of a metalloprotein with enhanced active-site resolution using in situ x-ray absorption near edge structure spectroscopy.

    PubMed

    Arcovito, Alessandro; Benfatto, Maurizio; Cianci, Michele; Hasnain, S Samar; Nienhaus, Karin; Nienhaus, G Ulrich; Savino, Carmelinda; Strange, Richard W; Vallone, Beatrice; Della Longa, Stefano

    2007-04-10

    X-ray absorption spectroscopy is exquisitely sensitive to the coordination geometry of an absorbing atom and therefore allows bond distances and angles of the surrounding atomic cluster to be measured with atomic resolution. By contrast, the accuracy and resolution of metalloprotein active sites obtainable from x-ray crystallography are often insufficient to analyze the electronic properties of the metals that are essential for their biological functions. Here, we demonstrate that the combination of both methods on the same metalloprotein single crystal yields a structural model of the protein with exceptional active-site resolution. To this end, we have collected an x-ray diffraction data set to 1.4-A resolution and Fe K-edge polarized x-ray absorption near edge structure (XANES) spectra on the same cyanomet sperm whale myoglobin crystal. The XANES spectra were quantitatively analyzed by using a method based on the multiple scattering approach, which yielded Fe-heme structural parameters with +/-(0.02-0.07)-A accuracy on the atomic distances and +/-7 degrees on the Fe-CN angle. These XANES-derived parameters were subsequently used as restraints in the crystal structure refinement. By combining XANES and x-ray diffraction, we have obtained an cyanomet sperm whale myoglobin structural model with a higher precision of the bond lengths and angles at the active site than would have been possible with crystallographic analysis alone.

  2. 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}.

  3. Effect of Viewing Angle on Super-Soft-Source X-Ray Spectra

    NASA Astrophysics Data System (ADS)

    Ness, Jan-Uwe

    2012-09-01

    The advent of the X-ray grating spectrometers has given new momentum to the studies of Super-Soft-Source (SSS) X-ray spectra in high resolution. Earlier CCD-type spectra only allow determinations of effective temperatures while in the grating spectra, lines and continuum can be resolved. I have studied the X-ray grating spectra of eight classical novae during their SSS phase, two of them candidates for recurrent novae, two established recurrent novae, and four permanent SSSs including the prototypes Cal 83 and Cal 87. I discovered two categories of SSSs: those dominated by emission lines (SSSe) and by absorption line (SSSa). All spectra contain photospheric continuum emission, indicated by the shape of a blackbody. For the majority of SSSe, the inclination angle is known, which are all greater than 75 degrees. I argue that the SSSe are high-inclination systems in which photospheric X-ray emission from the central source is partially blocked and scattered via Thompson scattering, which preserves the spectral shape of the continuum. Since the electrons in the scattering medium move at high velocities, photospheric absorption lines are smeared out and are therefore not seen. Additional emission lines are produced by resonant line scattering. The fact that only high inclination systems show these effects of scattering, the scattering material must be concentrated to the ecliptic plane. While in permanent SSSs, the accretion disk can explain this behavior, this result implies that in novae, the reformation of the accretion disk has already progressed to an advanced stage during their SSS phase. I argue that also the novae in low-inclination angle systems possess a reformed accretion disk. The viewing angle dependence requires non-symmetrical modeling approaches. Early disk reformation can also explain high-amplitude variations that have frequently been observed during the early SSS phase.

  4. Diagnostics of imploded core plasma dynamics using time-resolved x-ray spectra and x-ray monochromatic images

    NASA Astrophysics Data System (ADS)

    Ochi, Y.; Fujita, K.; Fukao, M.; Niki, I.; Nishimura, H.; Sunahara, A.; Shiraga, H.; Miyanaga, N.; Azechi, H.; Takabe, H.; Mima, K.; Yamanaka, T.; Butzbach, R.; Uschmann, I.; Foerster, E.; Golovkin, I.; Mancini, R. C.; Lee, R. W.; Klein, L.

    2000-10-01

    Direct-drive implosion of fusion pellets has been investigated using time- and space-resolved x-ray spectroscopic measurements. The experiments were conducted at ILE, Osaka University, and were designed to explore the influence of the low-modal irradiation non-uniformity on the imploded core plasma dynamics. The time-resolved spectra covered the range from Ar^16+Heα (1s^2-1s2p) to Ar^17+Lyβ (1s-3p) were recorded using an x-ray streak spectrograph (XSS). Time- and space-resolved monochromatic x-ray images of Heβ (1s^2-1s3p) and Lyβ were observed with a monochromatic x-ray framing camera (MXFC). The XSS's spectra were absolutely calibrated with the aid of spectra recorded by an x-ray spectrometer coupled to a calibrated CCD camera. Spatial gradients of the electron temperature and electron density in the imploded core are being investigated by means of a self-consistent analysis of the spectra from the XSS data and emissivities obtained by Abel inversion for the MXFC data. The results will be discussed.

  5. 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.

  6. 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.

  7. X-ray spectra from convective photospheres of neutron stars

    NASA Technical Reports Server (NTRS)

    Zavlin, V. E.; Pavlov, G. G.; Shibanov, Yu. A.; Rogers, F. J.; Iglesias, C. A.

    1996-01-01

    The preliminary results from the simulation of convective photospheres of neutron stars are presented. It is shown that in photospheres composed of light elements, convection arises at relatively low effective temperatures of between 3 x 10(exp 4) and 5 x 10(exp 4) K, whereas, in the case of iron composition, it arises at temperatures of less than or equal to 3 x 10(exp 5) K. Convection changes the depth dependence of the photosphere temperature and the shapes of the emergent spectra. It is concluded that depth should be taken into account for the correct interpretation of extreme ultraviolet/soft X-ray observations of the thermal radiation from neutron stars.

  8. Development of achromatic full-field hard x-ray microscopy and its application to x-ray absorption near edge structure spectromicroscopy

    NASA Astrophysics Data System (ADS)

    Matsuyama, S.; Emi, Y.; Kino, H.; Kohmura, Y.; Yabashi, M.; Ishikawa, T.; Yamauchi, K.

    2014-09-01

    An achromatic and high-resolution hard X-ray microscope was developed, in which advanced Kirkpatrick-Baez mirror optics with four total-reflection mirrors was employed as an objective. A fine test pattern with a 100 nm feature size could successfully be resolved. Full-field imaging, in combination with X-ray absorption near edge structure (XANES) spectroscopy, was used to characterize tungsten particles. XANES spectra were obtained over the entire observation area, showing good agreement with the XANES spectrum of pure tungsten.

  9. 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.

  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. Silicon 1s near edge X-ray absorption fine structure spectroscopy of functionalized silicon nanocrystals

    NASA Astrophysics Data System (ADS)

    Ritchie, A.; Cao, W.; Dasog, M.; Purkait, T. K.; Senger, C.; Hu, Y. F.; Xiao, Q. F.; Veinot, J. G. C.; Urquhart, S. G.

    2016-10-01

    Silicon 1s Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra of silicon nanocrystals have been examined as a function of nanocrystal size (3-100 nm), varying surface functionalization (hydrogen or 1-pentyl termination), or embedded in oxide. The NEXAFS spectra are characterized as a function of nanocrystal size and surface functionalization. Clear spectroscopic evidence for long range order is observed silicon nanocrystals that are 5-8 nm in diameter or larger. Energy shifts in the silicon 1s NEXAFS spectra of covalently functionalized silicon nanocrystals with changing size are attributed to surface chemical shifts and not to quantum confinement effects.

  12. 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.

  13. Spectra and Luminosities of X-Ray Active Galactic Nuclei

    NASA Astrophysics Data System (ADS)

    Morgan, Windsor Anthony, Jr.

    1995-01-01

    I present results of the analysis of 112 X-ray -selected and fully optically-identified quasars in four sky fields in the southern hemisphere, detected by the Rosat Position Sensitive Proportional Counters. These fields were originally studied (Boyle et al. 1990) for the ultraviolet-excess properties of objects in the fields. This is one of the largest sets of fully-identified Rosat-observed quasars. The quasars were optically identified during observing runs with the AUTOFIB multi-fiber spectrograph on the Anglo-Australian Telescope in Australia. I determine the quasars' power-law spectral index alphaE with three different methods: spectral "stacking", hardness ratios, and direct fitting, and discuss the differences between each of these methods. Both spectral stacking and the hardness ratio methods are used because several of the quasars were too dim to reliably calculate spectral indices individually. The spectral stacking method, which involves co-adding quasar spectra energy bins (after first binning the quasars themselves in redshift bins) shows that a definite change in quasar spectral index with redshift, which I have attributed to thermal bremsstrahlung emission (Morgan et al. 1992). The hardness ratio method, taken from a suggestion by Zamorani et al. (1988), uses the hardness ratios, using energy bins of 0.15-0.8 keV and 0.8-2.0 keV, and the known galactic column density N_{H } to determine the quasar power-law spectral index. I find that the hardness-ratio method yields spectral indices which do not change appreciably with redshift. I derive monochromatic X-ray and optical luminosities L_{rm x} and L opt, by using the spectral indices I found and the optical observations of the quasars. I discuss the relationship between L_{x } and Lopt, examine the optical-X-ray spectral slope alpha ox and the related L x/L_{opt } ratio and their relationship to the redshift. I finally present a model which could explain the observations.

  14. 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.}

  15. 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.

  16. 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.

  17. Particle-hole cumulant approach for inelastic losses in x-ray spectra

    NASA Astrophysics Data System (ADS)

    Kas, J. J.; Rehr, J. J.; Curtis, J. B.

    2016-07-01

    Inelastic losses in core level x-ray spectra arise from many-body excitations, leading to broadening and damping as well as satellite peaks in x-ray photoemission (XPS) and x-ray absorption (XAS) spectra. Here we present a practical approach for calculating these losses based on a cumulant representation of the particle-hole Green's function, a quasiboson approximation, and a partition of the cumulant into extrinsic, intrinsic, and interference terms. The intrinsic losses are calculated using real-time time-dependent density functional theory while the extrinsic losses are obtained from the G W approximation of the photoelectron self-energy and the interference terms are approximated. These effects are included in the spectra using a convolution with an energy dependent particle-hole spectral function. The approach elucidates the nature of the spectral functions in XPS and XAS and explains the significant cancellation between extrinsic and intrinsic losses. Edge-singularity effects in metals are also accounted for. Illustrative results are presented for the XPS and XAS of both weakly and more correlated systems.

  18. STRONG EVOLUTION OF X-RAY ABSORPTION IN THE TYPE IIn SUPERNOVA SN 2010jl

    SciTech Connect

    Chandra, Poonam; Chevalier, Roger A.; Irwin, Christopher M.; Chugai, Nikolai; Fransson, Claes; Soderberg, Alicia M.

    2012-05-01

    We report two epochs of Chandra-ACIS X-ray imaging spectroscopy of the nearby bright Type IIn supernova SN 2010jl, taken around two months and then a year after the explosion. The majority of the X-ray emission in both spectra is characterized by a high temperature ({approx}> 10 keV) and is likely to be from the forward shocked region resulting from circumstellar interaction. The absorption column density in the first spectrum is high ({approx}10{sup 24} cm{sup -2}), more than three orders of magnitude higher than the Galactic absorption column, and we attribute it to absorption by circumstellar matter. In the second epoch observation, the column density has decreased by a factor of three, as expected for shock propagation in the circumstellar medium. The unabsorbed 0.2-10 keV luminosity at both epochs is {approx}7 Multiplication-Sign 10{sup 41} erg s{sup -1}. The 6.4 keV Fe line clearly present in the first spectrum is not detected in the second spectrum. The strength of the fluorescent line is roughly that expected for the column density of circumstellar gas, provided the Fe is not highly ionized. There is also evidence for an absorbed power-law component in both spectra, which we attribute to a background ultraluminous X-ray source.

  19. Diagnosis of a two wire X-pinch by X-ray absorption spectroscopy utilizing a doubly curved ellipsoidal crystal

    SciTech Connect

    Cahill, A. D. Hoyt, C. L. Shelkovenko, T. A. Pikuz, S. A. Hammer, D. A.

    2014-12-15

    X-ray absorption spectroscopy is a powerful tool for the diagnosis of plasmas over a wide range of both temperature and density. However, such a measurement is often limited to probing plasmas with temperatures well below that of the x-ray source in order to avoid object plasma emission lines from obscuring important features of the absorption spectrum. This has excluded many plasmas from being investigated by this technique. We have developed an x-ray spectrometer that provides the ability to record absorption spectra from higher temperature plasmas than the usual approach allows without the risk of data contamination by line radiation emitted by the plasma under study. This is accomplished using a doubly curved mica crystal which is bent both elliptically and cylindrically. We present here initial absorption spectra obtained from an aluminum x-pinch plasma.

  20. Ab initio self-consistent x-ray absorption fine structure analysis for metalloproteins.

    PubMed

    Dimakis, Nicholas; Bunker, Grant

    2006-12-01

    X-ray absorption fine structure is a powerful tool for probing the structures of metals in proteins in both crystalline and noncrystalline environments. Until recently, a fundamental problem in biological XAFS has been that ad hoc assumptions must be made concerning the vibrational properties of the amino acid residues that are coordinated to the metal to fit the data. Here, an automatic procedure for accurate structural determination of active sites of metalloproteins is presented. It is based on direct multiple-scattering simulation of experimental X-ray absorption fine structure spectra combining electron multiple scattering calculations with density functional theory calculations of vibrational modes of amino acid residues and the genetic algorithm differential evolution to determine a global minimum in the space of fitting parameters. Structure determination of the metalloprotein active site is obtained through a self-consistent iterative procedure with only minimal initial information.

  1. 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

  2. Metalloprotein active site structure determination: synergy between X-ray absorption spectroscopy and X-ray crystallography.

    PubMed

    Cotelesage, Julien J H; Pushie, M Jake; Grochulski, Pawel; Pickering, Ingrid J; George, Graham N

    2012-10-01

    Structures of metalloprotein active sites derived from X-ray crystallography frequently contain chemical anomalies such as unexpected atomic geometries or elongated bond-lengths. Such anomalies are expected from the known errors inherent in macromolecular crystallography (ca. 0.1-0.2Å) and from the lack of appropriate restraints for metal sites which are often without precedent in the small molecule structure literature. Here we review the potential of X-ray absorption spectroscopy to provide information and perspective which could aid in improving the accuracy of metalloprotein crystal structure solutions. We also review the potential problem areas in analysis of the extended X-ray absorption fine structure (EXAFS) and discuss the use of density functional theory as another possible source of geometrical restraints for crystal structure analysis of metalloprotein active sites.

  3. X-ray absorption study of pulsed laser deposited boron nitride films

    SciTech Connect

    Chaiken, A.; Terminello, L.J.; Wong, J.; Doll, G.L.; Sato, T.

    1994-02-02

    B and N K-edge x-ray absorption spectroscopy measurements have been performed on three BN thin films grown on Si substrates using ion- assisted pulsed laser deposition. Comparison of the films` spectra to those of several single-phase BN powder standards shows that the films consist primarily of sp{sup 2} bonds. Other features in the films`s spectra suggest the presence of secondary phases, possibly cubic or rhombohedral BN. Films grown at higher deposition rates and higher ion-beam voltages are found to be more disordered, in agreement with previous work.

  4. Quasar X-Ray Spectra At z=1.5

    NASA Technical Reports Server (NTRS)

    Siemiginowska, Aneta

    2001-01-01

    The predicted counts for ASCA observation was much higher than actually observed counts in the quasar. However, there are three weak hard x-ray sources in the GIS field. We are adding them to the source counts in modeling of hard x-ray background. The work is in progress. We have published a paper in Ap.J. on the luminosity function and the quasar evolution. Based on the theory described in this paper we are predicting a number of sources and their contribution to the x-ray background at different redshifts. These model predictions will be compared to the observed data in the final paper.

  5. Towards simultaneous measurements of electronic and structural properties in ultra-fast x-ray free electron laser absorption spectroscopy experiments

    SciTech Connect

    Gaudin, J.; Fourment, C.; Cho, B. I.; Engelhorn, K.; Galtier, E.; Harmand, M.; Leguay, P. M.; Lee, H. J.; Nagler, B.; Nakatsutsumi, M.; Ozkan, C.; Störmer, M.; Toleikis, S.; Tschentscher, Th.; Heimann, P. A.; Dorchies, F.

    2014-04-17

    The rapidly growing ultrafast science with X-ray lasers unveils atomic scale processes with unprecedented time resolution bringing the so called “molecular movie” within reach. X-ray absorption spectroscopy is one of the most powerful x-ray techniques providing both local atomic order and electronic structure when coupled with ad-hoc theory. Collecting absorption spectra within few x-ray pulses is possible only in a dispersive setup. We demonstrate ultrafast time-resolved measurements of the LIII-edge x-ray absorption near-edge spectra of irreversibly laser excited Molybdenum using an average of only few x-ray pulses with a signal to noise ratio limited only by the saturation level of the detector. The simplicity of the experimental set-up makes this technique versatile and applicable for a wide range of pump-probe experiments, particularly in the case of non-reversible processes.

  6. Towards simultaneous measurements of electronic and structural properties in ultra-fast x-ray free electron laser absorption spectroscopy experiments

    DOE PAGES

    Gaudin, J.; Fourment, C.; Cho, B. I.; Engelhorn, K.; Galtier, E.; Harmand, M.; Leguay, P. M.; Lee, H. J.; Nagler, B.; Nakatsutsumi, M.; et al

    2014-04-17

    The rapidly growing ultrafast science with X-ray lasers unveils atomic scale processes with unprecedented time resolution bringing the so called “molecular movie” within reach. X-ray absorption spectroscopy is one of the most powerful x-ray techniques providing both local atomic order and electronic structure when coupled with ad-hoc theory. Collecting absorption spectra within few x-ray pulses is possible only in a dispersive setup. We demonstrate ultrafast time-resolved measurements of the LIII-edge x-ray absorption near-edge spectra of irreversibly laser excited Molybdenum using an average of only few x-ray pulses with a signal to noise ratio limited only by the saturation level ofmore » the detector. The simplicity of the experimental set-up makes this technique versatile and applicable for a wide range of pump-probe experiments, particularly in the case of non-reversible processes.« less

  7. Towards simultaneous measurements of electronic and structural properties in ultra-fast x-ray free electron laser absorption spectroscopy experiments

    NASA Astrophysics Data System (ADS)

    Gaudin, J.; Fourment, C.; Cho, B. I.; Engelhorn, K.; Galtier, E.; Harmand, M.; Leguay, P. M.; Lee, H. J.; Nagler, B.; Nakatsutsumi, M.; Ozkan, C.; Störmer, M.; Toleikis, S.; Tschentscher, Th; Heimann, P. A.; Dorchies, F.

    2014-04-01

    The rapidly growing ultrafast science with X-ray lasers unveils atomic scale processes with unprecedented time resolution bringing the so called ``molecular movie'' within reach. X-ray absorption spectroscopy is one of the most powerful x-ray techniques providing both local atomic order and electronic structure when coupled with ad-hoc theory. Collecting absorption spectra within few x-ray pulses is possible only in a dispersive setup. We demonstrate ultrafast time-resolved measurements of the LIII-edge x-ray absorption near-edge spectra of irreversibly laser excited Molybdenum using an average of only few x-ray pulses with a signal to noise ratio limited only by the saturation level of the detector. The simplicity of the experimental set-up makes this technique versatile and applicable for a wide range of pump-probe experiments, particularly in the case of non-reversible processes.

  8. Towards simultaneous measurements of electronic and structural properties in ultra-fast x-ray free electron laser absorption spectroscopy experiments.

    PubMed

    Gaudin, J; Fourment, C; Cho, B I; Engelhorn, K; Galtier, E; Harmand, M; Leguay, P M; Lee, H J; Nagler, B; Nakatsutsumi, M; Ozkan, C; Störmer, M; Toleikis, S; Tschentscher, Th; Heimann, P A; Dorchies, F

    2014-04-17

    The rapidly growing ultrafast science with X-ray lasers unveils atomic scale processes with unprecedented time resolution bringing the so called "molecular movie" within reach. X-ray absorption spectroscopy is one of the most powerful x-ray techniques providing both local atomic order and electronic structure when coupled with ad-hoc theory. Collecting absorption spectra within few x-ray pulses is possible only in a dispersive setup. We demonstrate ultrafast time-resolved measurements of the LIII-edge x-ray absorption near-edge spectra of irreversibly laser excited Molybdenum using an average of only few x-ray pulses with a signal to noise ratio limited only by the saturation level of the detector. The simplicity of the experimental set-up makes this technique versatile and applicable for a wide range of pump-probe experiments, particularly in the case of non-reversible processes.

  9. EUV/soft x-ray spectra for low B neutron stars

    NASA Technical Reports Server (NTRS)

    Romani, Roger W.; Rajagopal, Mohan; Rogers, Forrest J.; Iglesias, Carlos A.

    1995-01-01

    Recent ROSAT and EUVE detections of spin-powered neutron stars suggest that many emit 'thermal' radiation, peaking in the EUV/soft X-ray band. These data constrain the neutron stars' thermal history, but interpretation requires comparison with model atmosphere computations, since emergent spectra depend strongly on the surface composition and magnetic field. As recent opacity computations show substantial change to absorption cross sections at neutron star photospheric conditions, we report here on new model atmosphere computations employing such data. The results are compared with magnetic atmosphere models and applied to PSR J0437-4715, a low field neutron star.

  10. A disc-reflected component in the spectra of X-ray bursters

    NASA Technical Reports Server (NTRS)

    Day, C. S. R.; Done, C.

    1991-01-01

    An argument is presented to the effect that a disk-reflected component should be present in the spectra of X-ray bursts and is best seen just after the burst peak when the reflected photons, delayed by their passage to the site of reflection, appear in stronger contrast to the fast-declining primary emission from the cooling neutron star. It is shown that disk reflection has an observable effect on the spectrum of the burst tail. The possible use of the concomitant absorption edge as a diagnostic of the accretion disk is discussed.

  11. 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.

  12. 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.

  13. Galaxy cluster thermal x-ray spectra constrain axionlike particles

    NASA Astrophysics Data System (ADS)

    Conlon, Joseph P.; Powell, Andrew J.; Marsh, M. C. David

    2016-06-01

    Axionlike particles (ALPs) and photons interconvert in the presence of a magnetic field. At keV energies in the environment of galaxy clusters, the conversion probability can become unsuppressed for light ALPs. Conversion of thermal x-ray photons into ALPs can introduce a steplike feature into the cluster thermal bremsstrahlung spectrum, and we argue that existing x-ray data on galaxy clusters should be sufficient to extend bounds on ALPs in the low-mass region ma≲1 ×10-12 eV down to M ˜7 ×1011 GeV , and that for 1011 GeV x-ray (and potentially x-ray polarization) observations of galaxy clusters.

  14. Chandra X-ray grating spectra of V959 Mon

    NASA Astrophysics Data System (ADS)

    Orio, Marina; Zemko, Polina; Peretz, Uria; Behar, Ehud

    2016-07-01

    V959 Mon (Nova Mon 2012) was discovered in X-rays and gamma rays in the Summer of 2012, before it could be observed optically. It was observed twice with the Chandra gratings, by us in December of 2012 with the Low Energy Transmission Grating (LETG) and previously, in September of 2012, by another team with the Chandra High Energy Transmission Gratings. Although it seems very likely that only a small fraction of the ejecta emitted X-rays in small, dense clumps, the X-ray emission of the ejecta are very important for what the teach us about the kinematics, the chemical composition and nucleosynthesis of the nova. By December, the central source had shrunk almost to pre-outburst size and was visible in X-rays, revealing a massive, hot oxygen-neon white dwarf.

  15. The associated X-ray spectra of Amersham caesium-137 afterloading sources.

    PubMed

    Bradley, D A; Chong, C S

    1987-02-01

    Low-energy X rays are clearly observed in the energy spectra of Amersham 137Cs afterloading sources. Examination is made of the effects of encapsulation and source train attenuation on the source spectra. Estimates of the resulting X-ray intensities are also made.

  16. X-ray spectra of clusters of galaxies

    NASA Technical Reports Server (NTRS)

    Mushotzky, R. F.

    1984-01-01

    The X-ray emission from luminous clusters of galaxies is dominated by thermal bremsstrahlung from an intergalactic medium. The central density of the gas is strongly correlated with the X-ray surface brightness. The X-ray surface brightness S(sigma) of many clusters is well modeled by a law of the form S(sigma) alpha S(o) 1 + R(2)/A(2) to the minus 3 beta + 1/2 power with beta approximately equal to 0.66. However, this model does not fit the X-ray spectral or optical galaxy counts well. In clusters with cooling flows in their center there is a strong correlation between the cooling rates of X-ray emitting material and optical H alpha emission. It is not clear, at present, what percentage of the virial mass of the cluster is in hot gas but if beta = 0.66, it is possible for the values to be of the order of 1/2. Spatially resoled X-ray spectroscopy is necessary to determine this value with any accuracy.

  17. Correlated single-crystal electronic absorption spectroscopy and X-ray crystallography at NSLS beamline X26-C

    SciTech Connect

    Orville, A.M.; Buono, R.; Cowan, M.; Heroux, A.; Shea-McCarthy, G.; Schneider, D. K.; Skinner, J. M.; Skinner, M. J.; Stoner-Ma, D.; Sweet, R. M.

    2011-05-01

    The research philosophy and new capabilities installed at NSLS beamline X26-C to support electronic absorption and Raman spectroscopies coupled with X-ray diffraction are reviewed. This beamline is dedicated full time to multidisciplinary studies with goals that include revealing the relationship between the electronic and atomic structures in macromolecules. The beamline instrumentation has been fully integrated such that optical absorption spectra and X-ray diffraction images are interlaced. Therefore, optical changes induced by X-ray exposure can be correlated with X-ray diffraction data collection. The installation of Raman spectroscopy into the beamline is also briefly reviewed. Data are now routinely generated almost simultaneously from three complementary types of experiments from the same sample. The beamline is available now to the NSLS general user population.

  18. Correlated Single-Crystal Electronic Absorption Spectroscopy and X-ray Crystallography at NSLS Beamline X26-C

    SciTech Connect

    A Orville; R Buono; M Cowan; A Heroux; G Shea-McCarthy; D Schneider; J Skinner; M Skinner; D Stoner-Ma; R Sweet

    2011-12-31

    The research philosophy and new capabilities installed at NSLS beamline X26-C to support electronic absorption and Raman spectroscopies coupled with X-ray diffraction are reviewed. This beamline is dedicated full time to multidisciplinary studies with goals that include revealing the relationship between the electronic and atomic structures in macromolecules. The beamline instrumentation has been fully integrated such that optical absorption spectra and X-ray diffraction images are interlaced. Therefore, optical changes induced by X-ray exposure can be correlated with X-ray diffraction data collection. The installation of Raman spectroscopy into the beamline is also briefly reviewed. Data are now routinely generated almost simultaneously from three complementary types of experiments from the same sample. The beamline is available now to the NSLS general user population.

  19. 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.

  20. 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.

  1. Redox Chemisty of Tantalum Clusters on Silica Characterized by X-ray Absorption Spectroscopy

    SciTech Connect

    Nemana,S.; Gates, B.

    2006-01-01

    SiO{sub 2}-supported clusters of tantalum were synthesized from adsorbed Ta(CH{sub 2}Ph){sub 5} by treatment in H{sub 2} at 523 K. The surface species were characterized by X-ray absorption spectroscopy (extended X-ray absorption fine structure (EXAFS) spectroscopy and X-ray absorption near edge spectroscopy (XANES)) and ultraviolet-visible spectroscopy. The EXAFS data show that SiOO{sub 2}-supported tantalum clusters were characterized by a Ta-Ta coordination number of approximately 2, consistent with the presence of tritantalum clusters, on average. When these were reduced in H{sub 2} and reoxidized in O{sub 2}, the cluster nuclearity remained essentially unchanged, although reduction and oxidation occurred, respectively, as shown by XANES and UV-vis spectra; in the reoxidation, the tantalum oxidation state change was approximately two electronic charges per tritantalum cluster. The data demonstrate an analogy between the chemistry of group 5 metals on the SiO{sub 2} support and their chemistry in solution, as determined by the group of Cotton.

  2. X-ray absorption spectroscopy by full-field X-ray microscopy of a thin graphite flake: Imaging and electronic structure via the carbon K-edge

    PubMed Central

    Hitchock, Adam P; Ke, Xiaoxing; Van Tendeloo, Gustaaf; Ewels, Chris P; Guttmann, Peter

    2012-01-01

    Summary We demonstrate that near-edge X-ray-absorption fine-structure spectra combined with full-field transmission X-ray microscopy can be used to study the electronic structure of graphite flakes consisting of a few graphene layers. The flake was produced by exfoliation using sodium cholate and then isolated by means of density-gradient ultracentrifugation. An image sequence around the carbon K-edge, analyzed by using reference spectra for the in-plane and out-of-plane regions of the sample, is used to map and spectrally characterize the flat and folded regions of the flake. Additional spectral features in both π and σ regions are observed, which may be related to the presence of topological defects. Doping by metal impurities that were present in the original exfoliated graphite is indicated by the presence of a pre-edge signal at 284.2 eV. PMID:23016137

  3. 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.

  4. 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.

  5. Obscuration effects in super-soft-source X-ray spectra

    NASA Astrophysics Data System (ADS)

    Ness, J.-U.; Osborne, J. P.; Henze, M.; Dobrotka, A.; Drake, J. J.; Ribeiro, V. A. R. M.; Starrfield, S.; Kuulkers, E.; Behar, E.; Hernanz, M.; Schwarz, G.; Page, K. L.; Beardmore, A. P.; Bode, M. F.

    2013-11-01

    Context. Super-soft-source (SSS) X-ray spectra are blackbody-like spectra with effective temperatures ~3-7 × 105 K and luminosities of 1035-38 erg s-1. Grating spectra of SSS and novae in outburst that show SSS type spectra display atmospheric absorption lines. Radiation transport atmosphere models can be used to derive physical parameters. Blue-shifted absorption lines suggest that hydrostatic equilibrium is an insufficient assumption, and more sophisticated models are required. Aims: In this paper, we bypass the complications of spectral models and concentrate on the data in a comparative, qualitative study. We inspect all available X-ray grating SSS spectra to determine systematic, model-independent trends. Methods: We collected all grating spectra of conventional SSS like Cal 83 and Cal 87 plus observations of novae during their SSS phase. We used comparative plots of spectra of different systems to find common and different features. The results were interpreted in the context of system parameters obtained from the literature. Results: We find two distinct types of SSS spectra that we name SSa and SSe. Their main observational characteristics are either clearly visible absorption lines or emission lines, respectively, while both types contain atmospheric continuum emission. SSa spectra are highly structured with no spectral model currently able to reproduce all details. The emission lines clearly seen in SSe may also be present in SSa, hidden within the forest of complex atmospheric absorption and emission features. This suggests that SSe are in fact obscured SSa systems. Similarities between SSe and SSa with obscured and unobscured AGN, respectively, support this interpretation. We find all known or suspected high-inclination systems to emit permanently in an SSe state. Some sources are found to transition between SSa and SSe states, becoming SSe when fainter. Conclusions: SSS spectra are subject to various occultation processes. In persistent SSS spectra

  6. 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.

  7. A Simulation Study on the Flash X-Ray Spectra Spatial Distribution

    NASA Astrophysics Data System (ADS)

    Xu, Xiufeng; Li, Shiping; Cao, Hongrui; Xiao, Rui; Chen, Nan; Zhang, Linwen; Yin, Zejie

    2013-11-01

    Accurate measurement of flash X-ray energy spectra plays an important role in high-energy flash radiography. In this paper, by virtue of Geant4 toolkit, we simulated the generation and transport of X-ray photons resulting from the interaction of a high-energy electron beam with a solid thin target. We obtained the flash X-ray energy spectral distribution in the plane perpendicular to the electron beam incident direction. Our results indicate that the flash X-ray spectrum is almost uniform in the azimuthal direction but is quite different in the radius direction. Specifically, as the radius increases, the incident X-ray dose decreases significantly. Our work paves a theoretical basis for selecting appropriate structures and layout of the spectrometer and facilitates the measurements of flash X-ray energy spectra.

  8. 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.

  9. An in situ cell for characterization of solids by soft x-ray absorption

    NASA Astrophysics Data System (ADS)

    Drake, Ian J.; Liu, Teris C. N.; Gilles, Mary; Tyliszczak, Tolek; Kilcoyne, A. L. David; Shuh, David K.; Mathies, Richard A.; Bell, Alexis T.

    2004-10-01

    A cell has been designed and fabricated for in situ characterization of catalysts and environmental materials using soft x-ray absorption spectroscopy and spectromicroscopy at photon energies above 250 eV. "Lab-on-a-chip" technologies were used to fabricate the cell on a glass wafer. The sample compartment is 1.0 mm in diameter and has a gas path length of 0.8 mm to minimize x-ray absorption in the gas phase. The sample compartment can be heated to 533 K by an Al resistive heater and gas flows up to 5.0 cm3 min-1 can be supplied to the sample compartment through microchannels. The performance of the cell was tested by acquiring Cu L3-edge x-ray appearance near-edge structure (XANES) data during the reduction and oxidation of a silica-supported Cu catalyst using the beam line 11.0.2 scanning transmission x-ray microscope (STXM) at the Advanced Light Source of Lawrence Berkeley National Laboratory (Berkeley, CA). Two-dimensional images of individual catalyst particles were recorded at photon energies between 926 and 937 eV, the energy range in which the Cu(II) and Cu(I) L3 absorption edges are observed. Oxidation state specific images of the catalyst clearly show the disappearance of Cu(II) species during the exposure of the oxidized sample to 4% CO in He while increasing the temperature from 308 to 473 K. Reoxidation restores the intensity of the image associated with Cu(II). Cu L3-edge XANES spectra obtained from stacks of STXM images show that with increasing temperature the Cu(II) peak intensity decreases as the Cu(I) peak intensity increases.

  10. 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

  11. X-ray absorption spectroscopy for wire-array Z-pinches at the non-radiative stage

    NASA Astrophysics Data System (ADS)

    Ivanov, V. V.; Hakel, P.; Mancini, R. C.; Chittenden, J. P.; Anderson, A.; Shevelko, A. P.; Wiewior, P.; Durmaz, T.; Altemara, S. D.; Papp, D.; Astanovitskiy, A. L.; Nalajala, V.; Chalyy, O.; Dmitriev, O.

    2011-12-01

    Absorption spectroscopy was applied to wire-array Z-pinches on the 1 MA pulsed-power Zebra generator at the Nevada Terawatt Facility (NTF). The 50 TW Leopard laser was coupled with the Zebra generator for X-ray backlighting of wire arrays at the ablation stage. Broadband X-ray emission from a laser-produced Sm plasma was used to backlight Al star wire arrays in the range of 7-9 Å. Two time-integrated X-ray conical spectrometers recorded reference and absorption spectra. The spectrometers were shielded from the bright Z-pinch X-ray burst by collimators. The comparison of plasma-transmitted spectra with reference spectra indicates absorption lines in the range of 8.1-8.4 Å. Analysis of Al K-shell absorption spectra with detailed atomic kinetics models shows a distribution of electron temperature in the range of 10-30 eV that was fitted with an effective two-temperature model. Temperature and density distributions in wire-array plasma were simulated with a three-dimension magneto-hydrodynamic code. Post-processing of this code's output yields synthetic transmission spectrum which is in general agreement with the data.

  12. Probing Cu(I) in homogeneous catalysis using high-energy-resolution fluorescence-detected X-ray absorption spectroscopy.

    PubMed

    Walroth, Richard C; Uebler, Jacob W H; Lancaster, Kyle M

    2015-06-18

    Metal-to-ligand charge transfer excitations in Cu(I) X-ray absorption spectra are introduced as spectroscopic handles for the characterization of species in homogeneous catalytic reaction mixtures. Analysis is supported by correlation of a spectral library to calculations and to complementary spectroscopic parameters.

  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. Cometary Spectra Induced by Scattering and Florescence of Hard Solar X-Rays

    NASA Astrophysics Data System (ADS)

    Snios, B. T.; Lewkow, N.; Kharchenko, V. A.

    2013-12-01

    Accurate calculations of X-ray emissions from cometary atmospheres due to Scattering and Florescence (SF) of solar X-rays are carried out over the photon energy range 0.4-3.0 keV. Computations of the X-ray SF spectra are performed for different distributions of the cometary neutral gas, dust, and ice grains, including nano-size particles. The SF spectra of cometary X-rays above 1 keV are determined for different solar conditions, incorporating X-ray spectra induced by solar flares. Theoretical X-ray SF spectra are compared with the results of recent observations of several comets with the Chandra X-ray Observatory [1]. A correlation between the spectral shapes of the observed cometary and solar X-ray emissions above 1 keV has been found and analyzed. The strong similarity between the cometary SF spectra and the X-ray spectra observed from the Jupiter atmosphere with XMM-Newton [2] is analyzed in detail. Upper limits on the density of cometary nano-particles are determined through comparison of the theoretical and observational data. The X-ray SF spectra with photon energies above 1 keV are predicted for a model history of solar activity and compositions of cometary gas, dust, and ice particles, which could reflect evolutionary transformations of cometary environment. [1] Ewing, I., Christina, D. J., & Bodewits, D. et al. 2013, ApJ, 763, 66 [2] Branduardi-Raymont, G., Bhardwaj, A., & Elsner, R. F. et al. 2007, Planet. Space Sci., 55, 1126

  15. Unveiling the X-ray/UV properties of AGN winds using Broad and mini-Broad Absorption Line Quasars

    NASA Astrophysics Data System (ADS)

    Giustini, M.

    2015-07-01

    BAL/mini-BALs are observed in the UV spectra of ˜ 20-30% of optically selected AGN as broad absorption troughs blueshifted by several thousands km/s, indicative of powerful nuclear winds. They could be representative of the average AGN if their winds cover only 20-30% of the continuum source, and/or represent an evolutionary state analogous to the high-soft state of BHB, when the jet emission is quenched and strong X-ray absorbing equatorial disk winds are virtually ubiquitous. High-quality, possibly time-resolved X-ray/UV studies are crucial to assess the global amount and 'character' of absorption in BAL/mini-BAL QSOs and to constrain the physical mechanism responsible for the launch and acceleration of their winds, therefore placing them in the broader context of AGN geometry and evolution. I will review here the known X-ray properties of BAL/mini-BAL QSOs, and present new results from a comprehensive X-ray spectral analysis of all the Palomar-Green BAL/mini-BAL QSOs with available XMM-Newton observations, for a total of 51 pointings of 14 different sources. These will include the most recent results from a high-quality simultaneous XMM/HST observational campaign on the mini-BAL QSO PG 1126-041, that unveiled with stunning details the X-ray/UV connection in action in an AGN disk wind through correlated X-ray/UV absorption variability.

  16. Unwrapping the X-ray spectra of active galactic nuclei

    NASA Astrophysics Data System (ADS)

    Reynolds, C. S.

    2016-05-01

    Active galactic nuclei (AGN) are complex phenomena. At the heart of an AGN is a relativistic accretion disk around a spinning supermassive black hole (SMBH) with an X-ray emitting corona and, sometimes, a relativistic jet. On larger scales, the outer accretion disk and molecular torus act as the reservoirs of gas for the continuing AGN activity. And on all scales from the black hole outwards, powerful winds are seen that probably affect the evolution of the host galaxy as well as regulate the feeding of the AGN itself. In this review article, we discuss how X-ray spectroscopy can be used to study each of these components. We highlight how recent measurements of the high-energy cutoff in the X-ray continuum by NuSTAR are pushing us to conclude that X-ray coronae are radiatively-compact and have electron temperatures regulated by electron-positron pair production. We show that the predominance of rapidly-rotating objects in current surveys of SMBH spin is entirely unsurprising once one accounts for the observational selection bias resulting from the spin-dependence of the radiative efficiency. We review recent progress in our understanding of fast (v˜ (0.1-0.3)c, highly-ionized (mainly visible in Fe XXV and Fe XXVI lines), high-column density winds that may dominate quasar-mode galactic feedback. Finally, we end with a brief look forward to the promise of Astro-H and future X-ray spectropolarimeters.

  17. Electronic structure measurements of metal-organic solar cell dyes using x-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Johnson, Phillip S.

    The focus of this thesis is twofold: to report the results of X-ray absorption studies of metal-organic dye molecules for dye-sensitized solar cells and to provide a basic training manual on X-ray absorption spectroscopy techniques and data analysis. The purpose of our research on solar cell dyes is to work toward an understanding of the factors influencing the electronic structure of the dye: the choice of the metal, its oxidation state, ligands, and cage structure. First we study the effect of replacing Ru in several common dye structures by Fe. First-principles calculations and X-ray absorption spectroscopy at the C 1s and N 1s edges are combined to investigate transition metal dyes in octahedral and square planar N cages. Octahedral molecules are found to have a downward shift in the N 1s-to-pi* transition energy and an upward shift in C 1s-to-pi* transition energy when Ru is replaced by Fe, explained by an extra transfer of negative charge from Fe to the N ligands compared to Ru. For the square planar molecules, the behavior is more complex because of the influence of axial ligands and oxidation state. Next the crystal field parameters for a series of phthalocyanine and porphyrins dyes are systematically determined using density functional calculations and atomic multiplet calculations with polarization-dependent X-ray absorption spectra. The polarization dependence of the spectra provides information on orbital symmetries which ensures the determination of the crystal field parameters is unique. A uniform downward scaling of the calculated crystal field parameters by 5-30% is found to be necessary to best fit the spectra. This work is a part of the ongoing effort to design and test new solar cell dyes. Replacing the rare metal Ru with abundant metals like Fe would be a significant advance for dye-sensitized solar cells. Understanding the effects of changing the metal centers in these dyes in terms of optical absorption, charge transfer, and electronic

  18. Sulfur 1s near-edge x-ray absorption fine structure (NEXAFS) of thiol and thioether compounds

    SciTech Connect

    Beyhan, Shirin; Urquhart, Stephen G.; Hu Yongfeng

    2011-06-28

    The speciation and quantification of sulfur species based on sulfur K-edge x-ray absorption spectroscopy is of wide interest, particularly for biological and petroleum science. These tasks require a firm understanding of the sulfur 1s near-edge x-ray absorption fine structure (NEXAFS) spectra of relevant species. To this end, we have examined the gas phase sulfur 1s NEXAFS spectra of a group of simple thiol and thioether compounds. These high-resolution gas phase spectra are free of solid-state broadening, charging, and saturation effects common in the NEXAFS spectra of solids. These experimental data have been further analyzed with the aid of improved virtual orbital Hartree-Fock ab initio calculations. The experimental sulfur 1s NEXAFS spectra show fine features predicted by calculation, and the combination of experiment and calculation has been used to improve assignment of spectroscopic features relevant for the speciation and quantification of the sulfur compounds.

  19. Modeling Spectra of the North and South Jovian X-ray Auroras

    SciTech Connect

    Kharchenko, Vasili A; Bhardwaj, Anil; Dalgarno, A.; Schultz, David Robert; Stancil, Phillip C.

    2008-08-01

    Spectra of Jovian X-ray auroras observed from the North and South poles with the Chandra X-ray telescope are analyzed and compared with predicted spectra of the charge-exchange mechanism. To determine the theoretical spectra of Jovian X-ray auroras, we model numerically the collisionally induced evolution of energy and charge distributions of Oq+ and Sq+ ions, precipitating into the Jovian atmosphere. Monte Carlo simulations of the energy and charge relaxation of the precipitating ions are carried out with updated cross-sections of the ion stripping, electron capture, and gas-ionization collisions. X-ray and Extreme Ultraviolet (EUV) spectra of cascading radiation induced by individual energetic sulfur and oxygen ions are calculated, and relative intensities of X-ray emission lines are determined. Synthetic spectra of X-ray and EUV photons are computed at different initial kinetic energies and compositions of ion-precipitating fluxes. Theoretical spectra with adjustable initial energies and relative fraction of sulfur and oxygen ions are shown to be in good agreement with the spectra of X rays detected from the South and North polar regions. The abundances and initial energies of the precipitating ions are inferred by comparing synthetic and observed X-ray spectra. Comparisons are performed independently for the North and South pole emissions. Abundances of the precipitating sulfur ions are found to be four to five times smaller than those of oxygen ions, and averaged ion energies are determined to lie between 1 and 2 MeV/amu. Slightly different ion flux compositions are found to describe the observed spectra of X-ray emission from the North and South poles.

  20. A doubly curved elliptical crystal spectrometer for the study of localized x-ray absorption in hot plasmas

    SciTech Connect

    Cahill, Adam D. Hoyt, Cad L.; Pikuz, Sergei A.; Shelkovenko, Tania; Hammer, David A.

    2014-10-15

    X-ray absorption spectroscopy is a powerful tool for the diagnosis of plasmas over a wide range of both temperature and density. However, such a measurement is often limited to probing plasmas with temperatures well below that of the x-ray source in order to avoid object plasma emission lines from obscuring important features of the absorption spectrum. This has excluded many plasmas from being investigated by this technique. We have developed an x-ray spectrometer that provides the ability to record absorption spectra from higher temperature plasmas than the usual approach allows without the risk of data contamination by line radiation emitted by the plasma under study. This is accomplished using a doubly curved mica crystal which is bent both elliptically and cylindrically. We present here the foundational work in the design and development of this spectrometer along with initial results obtained with an aluminum x-pinch as the object plasma.

  1. 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.

  2. The spectra of ten galactic X-ray sources in the southern sky

    NASA Technical Reports Server (NTRS)

    Cruddace, R.; Bowyer, S.; Lampton, M.; Mack, J. E., Jr.; Margon, B.

    1971-01-01

    Data on ten galactic X-ray sources were obtained during a rocket flight from Brazil in June 1969. Detailed spectra of these sources have been compared with bremsstrahlung, black body, and power law models, each including interstellar absorption. Six of the sources were fitted well by one or more of these models. In only one case were the data sufficient to distinguish the best model. Three of the sources were not fitted by any of the models, which suggests that more complex emission mechanisms are applicable. A comparison of our results with those of previous investigations provides evidence that five of the sources vary in intensity by a factor of 2 or more, and that three have variable spectra. New or substantially improved positions have been derived for four of the sources observed.

  3. The spectra of ten galactic X-ray sources in the southern sky.

    NASA Technical Reports Server (NTRS)

    Cruddace, R.; Bowyer, S.; Lampton, M.; Mack, J.; Margon, B.

    1972-01-01

    Data on 10 galactic X-ray sources located between 320 and 20 deg galactic longitude were obtained during a rocket flight from Brazil in June 1969. Detailed spectra of these sources have been compared with bremsstrahlung, blackbody, and power-law models, each including interstellar absorption. Six of the sources were fitted well by one or more of these models. In only one case were the data sufficient to distinguish the best model. Three of the sources were not fitted by any of the models, which suggests that more complex emission mechanisms are applicable. A comparison of our results with those of previous investigations provides evidence that five of the sources vary in intensity by a factor of two or more, and that three have variable spectra.

  4. X-ray absorption in matter. Reengineering XCOM

    NASA Astrophysics Data System (ADS)

    Gerward, L.; Guilbert, N.; Bjørn Jensen, K.; Levring, H.

    2001-01-01

    A Windows version of XCOM, the well-known program for calculating X-ray and gamma-ray attenuation coefficients and interaction cross sections, has been developed. The new program, called WinXCom, has an improved user interface.

  5. Calculation of the Kramers-Kronig transform of X-ray spectra by a piecewise Laurent polynomial method.

    PubMed

    Watts, Benjamin

    2014-09-22

    An algorithm is presented for the calculation of the Kramers-Kronig transform of a spectrum via a piecewise Laurent polynomial method. This algorithm is demonstrated to be highly accurate, while also being computationally efficient. The algorithm places no requirements on data point spacing and is capable of integrating across the full spectrum (i.e. from zero to infinity). Further, we present a computer application designed to aid in calculating the Kramers-Kronig transform on near-edge experimental X-ray absorption spectra (extended with atomic scattering factor data) in order to produce the dispersive part of the X-ray refractive index, including near-edge features.

  6. Calculation of the Kramers-Kronig transform of X-ray spectra by a piecewise Laurent polynomial method.

    PubMed

    Watts, Benjamin

    2014-09-22

    An algorithm is presented for the calculation of the Kramers-Kronig transform of a spectrum via a piecewise Laurent polynomial method. This algorithm is demonstrated to be highly accurate, while also being computationally efficient. The algorithm places no requirements on data point spacing and is capable of integrating across the full spectrum (i.e. from zero to infinity). Further, we present a computer application designed to aid in calculating the Kramers-Kronig transform on near-edge experimental X-ray absorption spectra (extended with atomic scattering factor data) in order to produce the dispersive part of the X-ray refractive index, including near-edge features. PMID:25321829

  7. ATOMIC AND MOLECULAR PHYSICS: X-ray absorption near the edge structure and X-ray photoelectron spectroscopy studies on pyrite prepared by thermally sulfurizing iron films

    NASA Astrophysics Data System (ADS)

    Zhang, Hui; Liu, Ying-Shu; Wang, Bao-Yi; Wei, Long; Kui, Re-Xi; Qian, Hai-Jie

    2009-07-01

    This paper reports how pyrite films were prepared by thermal sulfurization of magnetron sputtered iron films and characterized by x-ray absorption near edge structure spectra and x-ray photoelectron spectroscopy on a 4B9B beam line at the Beijing Synchrotron Radiation Facility. The band gap of the pyrite agrees well with the optical band gap obtained by a spectrophotometer. The octahedral symmetry of pyrite leads to the splitting of the d orbit into t2g and eg levels. The high spin and low spin states were analysed through the difference of electron exchange interaction and the orbital crystal field. Only when the crystal field splitting is higher than 1.5 eV, the two weak peaks above the white lines can appear, and this was approved by experiments in the present work.

  8. The soft X ray excess in Einstein quasar spectra

    NASA Technical Reports Server (NTRS)

    Wilkes, Belinda J.; Masnou, Jean-Louis; Elvis, Martin; Mcdowell, Jonathan; Arnaud, Keith

    1989-01-01

    The soft X-ray excess component is studied for a signal to noise limited subsample of 14 quasars from the WE87 sample observed with the Einstein Imaging Proportional Counter (IPC). Detailed analysis of the IPC data, combined with Einstein Monitor Proportional Counter (MPC) data where possible, and use of accurate galactic N sub H values allows estimation of the strength of any excess and improvement of constraints on the spectral slope at higher X-ray energies. A significant excess in 9 of the 14 objects is found. It is confined in all but one case to below 0.6 keV and variable in the two cases where there are multiple observations. The relation of the soft excess to other continuum properties of the quasars is investigated.

  9. 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.

  10. Measurements of photon interference X-ray absorption fine structure (piXAFS).

    PubMed

    Tröger, L; Kappen, P; Nishino, Y; Haack, N; Materlik, G

    2001-03-01

    Experimental data are presented which demonstrate the existence of a fine structure in extended X-ray absorption spectra due to interference effects in the initial photon state (piXAFS). Interference occurs between the incident electromagnetic wave and its coherently scattered waves from neighboring atoms. Using fine platinum and tungsten powders as well as polycrystalline platinum foil, piXAFS was measured in high-precision absorption experiments at beamline X1 at HASYLAB/DESY over a wide energy range. piXAFS is observed below and above absorption-edge positions in both transmission and total-electron-yield detection. Based on experimental data it is shown that piXAFS is sensitive to geometric atomic structure. Fourier-transformed piXAFS data carry information, comparable with that of EXAFS, about the short-range-order structure of the sample. Sharp structures occur in piXAFS when a Bragg backscattering condition of the incident X-rays is fulfilled. They allow precise measurement of long-range-order structural information. Measured data are compared with simulations based on piXAFS theory. Although piXAFS structures are similarly observed in two detection techniques, the importance of scattering off the sample for the measurements needs to be investigated further. Disentangling piXAFS, multielectron photoexcitations and atomic XAFS in high-precision measurements close to absorption edges poses a challenge for future studies.

  11. Absorption features in the x-ray spectrum of an ordinary radio pulsar.

    PubMed

    Kargaltsev, Oleg; Durant, Martin; Misanovic, Zdenka; Pavlov, George G

    2012-08-24

    The vast majority of known nonaccreting neutron stars (NSs) are rotation-powered radio and/or γ-ray pulsars. So far, their multiwavelength spectra have all been described satisfactorily by thermal and nonthermal continuum models, with no spectral lines. Spectral features have, however, been found in a handful of exotic NSs and were thought to be a manifestation of their unique traits. Here, we report the detection of absorption features in the x-ray spectrum of an ordinary rotation-powered radio pulsar, J1740+1000. Our findings bridge the gap between the spectra of pulsars and other, more exotic, NSs, suggesting that the features are more common in the NS spectra than they have been thought so far.

  12. Auto-oligomerization and hydration of pyrrole revealed by x-ray absorption spectroscopy

    SciTech Connect

    Advanced Light Source; Schwartz, Craig P.; Uejio, Janel S.; Duffin, Andrew M.; England, Alice H.; Prendergast, David; Saykally, Richard J

    2009-05-29

    Near edge x-ray absorption fine structure (NEXAFS) spectra have been measured at the carbon and nitrogen K-edges of the prototypical aromatic molecule, pyrrole, both in the gas phase and when solvated in water, and compared with spectra simulated using a combination of classical molecular dynamics and first principles density functional theory in the excited state core hole approximation. The excellent agreement enabled detailed assignments. Pyrrole is highly reactive, particularly in water, and reaction products formed by the auto-oligomerization of pyrrole are identified. The solvated spectra have been measured at two different temperatures, indicating that the final states remain largely unaffected by both hydration and temperature. This is somewhat unexpected, since the nitrogen in pyrrole can donate a hydrogen bond to water.

  13. X-ray absorption and resonant inelastic x-ray scattering (RIXS) show the presence of Cr{sup +} at the surface and in the bulk of CrF{sub 2}

    SciTech Connect

    Jiménez-Mier, J.; Olalde-Velasco, P.; Yang, W.-L.; Denlinger, J.

    2015-07-23

    X-Ray absorption and resonant inelastic x-ray scattering (RIXS) spectra of CrF{sub 2} recorded at the chromium L{sub 2,3} are presented. An atomic multiplet crystal field calculation is compared with the experimental data. Experiment and theory are in agreement once the calculation includes three chromium oxidation states, namely Cr{sup +}, Cr{sup 2+}, and Cr{sup 3+}. X-Ray absorption allows a direct determination of the surface oxidation, while the RIXS spectra shows the presence of these three oxidation states in the sample bulk. To give a quantitative interpretation of the RIXS data the effect of the incomming and outgoing photon penetration depth and self-absorption must be considered. For the much simpler case of MnF{sub 2}, with only one metal oxidation state, the measured RIXS spectra relative intensities are found to be proportional to the square of the sample attenuation length.

  14. X-ray spectra and atmospheric structures of bursting neutron stars

    NASA Technical Reports Server (NTRS)

    Ebisuzaki, Toshikazu

    1987-01-01

    Atmospheric structures and emitted X-ray spectra of bursting neutron stars are investigated. Theoretical curves are fitted to observational ones on the color temperature vs. luminosity diagram and two relations among mass, radius, and distance of the bursters are obtained. The fit of the theoretical curve to observations is statistically acceptable. Two possible sets of mass, radius, and distance to the X-ray bursts source MXB 1636-536 are derived, taking into account absorption lines at 4.1 keV, theoretical mass-radius relations of neutron star models, and the distance to the Galactic center. If the absorption line is due to Cr XX III, then M = 1.7-2.0 solar masses, R = 11-12 km, and d = 6.3-6.7 kpc, and if it is due to Fe XXV, then M = 1.8-2.1 solar masses, R = 8-10 km, and d = 5.8-6,4 kpc. The distance to the Galactic center is almost the same as that to MXB 1636-536.

  15. XAP, a program for deconvolution and analysis of complex X-ray spectra

    USGS Publications Warehouse

    Quick, James E.; Haleby, Abdul Malik

    1989-01-01

    The X-ray analysis program (XAP) is a spectral-deconvolution program written in BASIC and specifically designed to analyze complex spectra produced by energy-dispersive X-ray analytical systems (EDS). XAP compensates for spectrometer drift, utilizes digital filtering to remove background from spectra, and solves for element abundances by least-squares, multiple-regression analysis. Rather than base analyses on only a few channels, broad spectral regions of a sample are reconstructed from standard reference spectra. The effects of this approach are (1) elimination of tedious spectrometer adjustments, (2) removal of background independent of sample composition, and (3) automatic correction for peak overlaps. Although the program was written specifically to operate a KEVEX 7000 X-ray fluorescence analytical system, it could be adapted (with minor modifications) to analyze spectra produced by scanning electron microscopes, electron microprobes, and probes, and X-ray defractometer patterns obtained from whole-rock powders.

  16. Electronic structure of individual hybrid colloid particles studied by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy in the X-ray microscope.

    PubMed

    Henzler, Katja; Guttmann, Peter; Lu, Yan; Polzer, Frank; Schneider, Gerd; Ballauff, Matthias

    2013-02-13

    The electronic structure of individual hybrid particles was studied by nanoscale near-edge X-ray absorption spectromicroscopy. The colloidal particles consist of a solid polystyrene core and a cross-linked poly-N-(isopropylacrylamide) shell with embedded crystalline titanium dioxide (TiO(2)) nanoparticles (d = 6 ± 3 nm). The TiO(2) particles are generated in the carrier network by a sol-gel process at room temperature. The hybrid particles were imaged with photon energy steps of 0.1 eV in their hydrated environment with a cryo transmission X-ray microscope (TXM) at the Ti L(2,3)-edge. By analyzing the image stacks, the obtained near-edge X-ray absorption fine structure (NEXAFS) spectra of our individual hybrid particles show clearly that our synthesis generates TiO(2) in the anastase phase. Additionally, our spectromicroscopy method permits the determination of the density distribution of TiO(2) in single carrier particles. Therefore, NEXAFS spectroscopy combined with TXM presents a unique method to get in-depth insight into the electronic structure of hybrid materials. PMID:23360082

  17. Simultaneous X-ray and Far-Ultraviolet Spectra of AGN with ASCA and HUT

    NASA Technical Reports Server (NTRS)

    Kriss, Gerard A.

    1997-01-01

    We obtained ASCA spectra of the Seyfert 1 galaxy NGC 3516 in March 1995. Simultaneous far-UV observations were obtained with the Hopkins Ultraviolet Telescope on the Astro-2 shuttle mission. The ASCA spectrum shows a lightly absorbed power law of energy index 0.78. The low energy absorbing column is significantly less than previously seen. Prominent 0 VII and 0 VIII absorption edges are visible, but, consistent with the much lower total absorbing column, no Fe K absorption edge is detectable. A weak, narrow Fe K(alpha) emission line from cold material is present as well as a broad Fe K(alpha) line. These features are similar to those reported in other Seyfert 1 galaxies. A single warm absorber model provides only an imperfect description of the low energy absorption. In addition to a highly ionized absorber with ionization parameter U = 1.66 and a total column density of 1.4 x 10(exp 22)/sq cm, adding a lower ionization absorber with U = 0.32 and a total column of 6.9 x 10(exp 21)/sq cm significantly improves the fit. The contribution of resonant line scattering to our warm absorber models limits the Doppler parameter to less than 160 km/s at 90% confidence. Turbulence at the sound speed of the photoionized gas provides the best fit. None of the warm absorber models fit to the X-ray spectrum can match the observed equivalent widths of all the UV absorption lines. Accounting for the X-ray and UV absorption simultaneously requires an absorbing region with a broad range of ionization parameters and column densities.

  18. 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.

  19. Ionised Iron Lines in X-ray Reflection Spectra

    NASA Astrophysics Data System (ADS)

    Ballantyne, D. R.; Ross, R. R.; Fabian, A. C.

    2000-10-01

    We present results from new calculations of the reflected X-ray spectrum from ionised accretion disks in Active Galactic Nuclei (AGN). These calculations improve on our previous models by including the condition of hydrostatic balance in the vertical direction, following the work of Nayakshin, Kazanas & Kallman (2000). Our results show that, for gas pressure dominated accretion discs, ionised iron features are found in the reflection spectrum over a range of conditions. We also explore extending our results into radiation pressure dominated discs, and discuss the limitations of the current models.

  20. Characterization and speciation of mercury-bearing mine wastes using X-ray absorption spectroscopy

    USGS Publications Warehouse

    Kim, C.S.; Brown, Gordon E.; Rytuba, J.J.

    2000-01-01

    Mining of mercury deposits located in the California Coast Range has resulted in the release of mercury to the local environment and water supplies. The solubility, transport, and potential bioavailability of mercury are controlled by its chemical speciation, which can be directly determined for samples with total mercury concentrations greater than 100 mg kg-1 (ppm) using X-ray absorption spectroscopy (XAS). This technique has the additional benefits of being non-destructive to the sample, element-specific, relatively sensitive at low concentrations, and requiring minimal sample preparation. In this study, Hg L(III)-edge extended X-ray absorption fine structure (EXAFS) spectra were collected for several mercury mine tailings (calcines) in the California Coast Range. Total mercury concentrations of samples analyzed ranged from 230 to 1060 ppm. Speciation data (mercury phases present and relative abundances) were obtained by comparing the spectra from heterogeneous, roasted (calcined) mine tailings samples with a spectral database of mercury minerals and sorbed mercury complexes. Speciation analyses were also conducted on known mixtures of pure mercury minerals in order to assess the quantitative accuracy of the technique. While some calcine samples were found to consist exclusively of mercuric sulfide, others contain additional, more soluble mercury phases, indicating a greater potential for the release of mercury into solution. Also, a correlation was observed between samples from hot-spring mercury deposits, in which chloride levels are elevated, and the presence of mercury-chloride species as detected by the speciation analysis. The speciation results demonstrate the ability of XAS to identify multiple mercury phases in a heterogeneous sample, with a quantitative accuracy of ??25% for the mercury-containing phases considered. Use of this technique, in conjunction with standard microanalytical techniques such as X-ray diffraction and electron probe microanalysis

  1. Unveiling the intrinsic X-ray properties of broad absorption line quasars with a relatively unbiased sample

    SciTech Connect

    Morabito, Leah K.; Dai, Xinyu; Leighly, Karen M.; Sivakoff, Gregory R.; Shankar, Francesco

    2014-05-01

    There is growing evidence of a higher intrinsic fraction of broad absorption line quasars (BALQSOs) than that obtained in optical surveys, on which most previous X-ray studies of BALQSOs have focused. Here we present Chandra observations of 18 BALQSOs at z ∼ 2, selected from a near-infrared (Two Micron All Sky Survey) sample, where the BALQSO fraction is likely to be close to the intrinsic fraction. We measure photon indices using the stacked spectra of the optically faint (i – K{sub s} ≥ 2.3 mag) and optically bright (i – K{sub s} < 2.3 mag) samples to be Γ ≅ 1.5-2.1. We constrain their intrinsic column density by modeling the X-ray fractional hardness ratio, finding a mean column density of 3.5 × 10{sup 22} cm{sup –2} assuming neutral absorption. We incorporate Sloan Digital Sky Survey optical measurements (rest frame UV) to study the broadband spectral index between the X-ray and UV bands, and compare this to a large sample of normal quasars. We estimate that the optically faint BALQSOs are X-ray weaker than the optically bright ones, and the entire sample of BALQSOs are intrinsically X-ray weak when compared to normal active galactic nuclei (AGNs). Correcting for magnification of X-ray emission via gravitational lensing by the central black hole viewed at large inclination angles makes these BALQSOs even more intrinsically X-ray weak. Finally, we estimate AGN kinetic feedback efficiencies of a few percent for an X-ray wind of 0.3c in high-ionization BALQSOs. Combined with energy carried by low-ionization BALQSOs and UV winds, the total kinetic energy in BALQSOs can be sufficient to provide AGN kinetic feedback required to explain the co-evolution between black holes and host galaxies.

  2. Determination of copper binding in Pseudomonas putida CZ1 by chemical modifications and X-ray absorption spectroscopy.

    PubMed

    Chen, XinCai; Shi, JiYan; Chen, YingXu; Xu, XiangHua; Chen, LiTao; Wang, Hui; Hu, TianDou

    2007-03-01

    Previously performed studies have shown that Pseudomonas putida CZ1 biomass can bind an appreciable amount of Cu(II) and Zn(II) ions from aqueous solutions. The mechanisms of Cu- and Zn-binding by P. putida CZ1 were ascertained by chemical modifications of the biomass followed by Fourier transform infrared and X-ray absorption spectroscopic analyses of the living or nonliving cells. A dramatic decrease in Cu(II)- and Zn(II)-binding resulted after acidic methanol esterification of the nonliving cells, indicating that carboxyl functional groups play an important role in the binding of metal to the biomaterial. X-ray absorption spectroscopy was used to determine the speciation of Cu ions bound by living and nonliving cells, as well as to elucidate which functional groups were involved in binding of the Cu ions. The X-ray absorption near-edge structure spectra analysis showed that the majority of the Cu was bound in both samples as Cu(II). The fitting results of Cu K-edge extended X-ray absorption fine structure spectra showed that N/O ligands dominated in living and nonliving cells. Therefore, by combining different techniques, our results indicate that carboxyl functional groups are the major ligands responsible for the metal binding in P. putida CZ1. PMID:17021877

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

    PubMed

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

    2016-07-28

    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. PMID:27475372

  4. 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.

  5. Model Atmospheres and X-Ray Spectra of Bursting Neutron Stars: Hydrogen-Helium Comptonized Spectra

    NASA Astrophysics Data System (ADS)

    Madej, J.; Joss, P. C.; Różańska, A.

    2004-02-01

    Compton scattering plays a crucial role in determining the structure of the atmosphere of an X-ray burster and its theoretical spectrum. Our paper presents a description of the plane-parallel model atmosphere of a very hot neutron star and its theoretical flux spectrum of outgoing radiation. Our model equations take into account all bound-free and free-free monochromatic opacities relevant to hydrogen-helium chemical composition and take into account the effects of Compton scattering of radiation in thermal plasma with fully relativistic thermal velocities. We use Compton scattering terms in the equation of transfer, which precisely describe photon-electron energy and momentum exchange for photons with initial energies exceeding the electron rest mass of 511 keV. Model atmosphere equations are solved with the variable Eddington factors technique. The grid of H-He model atmospheres and flux spectra is computed on a dense mesh of 107K<=Teff<=3×107K and a surface gravity of logg. In many cases, the assumed logg approached the critical gravity loggcr, i.e., the Eddington limit. We confirm that H-He spectra of X-ray bursters deviate from blackbody spectra and discuss their shapes. The table of color to effective temperature ratios shows that theoretical values of Tc/Teff do not exceed 1.9 in H-He atmospheres in hydrostatic and radiative equilibrium.

  6. The Broadband XMM-Newton and NuSTAR X-Ray Spectra of Two Ultraluminous X-Ray Sources in the Galaxy IC 342

    NASA Astrophysics Data System (ADS)

    Rana, Vikram; Harrison, Fiona A.; Bachetti, Matteo; Walton, Dominic J.; Furst, Felix; Barret, Didier; Miller, Jon M.; Fabian, Andrew C.; Boggs, Steven E.; Christensen, Finn C.; Craig, William W.; Grefenstette, Brian W.; Hailey, Charles J.; Madsen, Kristin K.; Ptak, Andrew F.; Stern, Daniel; Webb, Natalie A.; Zhang, William W.

    2015-02-01

    We present results for two ultraluminous X-ray sources (ULXs), IC 342 X-1 and IC 342 X-2, using two epochs of XMM-Newton and NuSTAR observations separated by ~7 days. We observe little spectral or flux variability above 1 keV between epochs, with unabsorbed 0.3-30 keV luminosities being 1.04+0.08-0.06 × 1040 erg s-1 for IC 342 X-1 and 7.40 ± 0.20 × 1039 erg s-1 for IC 342 X-2, so that both were observed in a similar, luminous state. Both sources have a high absorbing column in excess of the Galactic value. Neither source has a spectrum consistent with a black hole binary in low/hard state, and both ULXs exhibit strong curvature in their broadband X-ray spectra. This curvature rules out models that invoke a simple reflection-dominated spectrum with a broadened iron line and no cutoff in the illuminating power-law continuum. X-ray spectrum of IC 342 X-1 can be characterized by a soft disk-like blackbody component at low energies and a cool, optically thick Comptonization continuum at high energies, but unique physical interpretation of the spectral components remains challenging. The broadband spectrum of IC 342 X-2 can be fit by either a hot (3.8 keV) accretion disk or a Comptonized continuum with no indication of a seed photon population. Although the seed photon component may be masked by soft excess emission unlikely to be associated with the binary system, combined with the high absorption column, it is more plausible that the broadband X-ray emission arises from a simple thin blackbody disk component. Secure identification of the origin of the spectral components in these sources will likely require broadband spectral variability studies.

  7. The x ray variability of NGC6814: Power spectra

    NASA Technical Reports Server (NTRS)

    Done, C.; Madejski, G. M.; Mushotsky, R. F.; Turner, T. J.; Koyama, K.; Kunieda, H.

    1992-01-01

    Simulation techniques are used to obtain the X-ray variability power spectrum of unevenly sampled GINGA data from NGC6814. A simple power law is not an adequate description of the power spectrum, with the residuals showing excess power on timescales consistent with the periodicity seen in EXOSAT observations of this object. However the shape of the folded lightcurve is very different, with 3 main peaks, two of which are separated by an extremely sharp dip instead of the single peak and small harmonic structure observed by EXOSAT. Using the dip as a fiducial mark, a second GINGA observation of this source taken one year later is found to be consistent with being completely periodic and phase coherent with this first GINGA observation. Thus the period is consistent with being constant over a period of 6 years, but phase coherence is only maintained on timescales of approximately 1 year. Over 75 percent of the total source variability is due to the periodic component (r.m.s. amplitude of 36 percent). The residual variability can be described as the more usual 'flicker noise' f(exp -1.1) powerlaw. This shows no apparent high frequency break on timescales greater than 300 seconds. Subtle differences in the shape of the folded light curve with energy, and the very large amount of power in the periodic component suggest occultation as its origin, though amplification of variability from an X-ray emitting 'hot spot' at the disk inner radius through gravitational lensing is also possible. The former suffers from the very arbitrary nature of the periodic timescale, while the latter is unattractive as it cannot simply explain the lack of high frequency break in the residual power. That these models probably fail to provide an adequate explanation may be due to the added complexity of anisotropy of the X-ray emission, suggested by the discrepancy between the lack of soft photons implied by the flat spectrum and the copious source of soft photons available from reprocessing in

  8. Time- and space-resolved X-ray absorption spectroscopy of aluminum irradiated by a subpicosecond high-power laser

    NASA Astrophysics Data System (ADS)

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

    2006-05-01

    The ionization and recombination dynamics of transient aluminum plasmas was measured using point projection K-shell absorption spectroscopy. An aluminum plasma was produced with a subpicosecond beam of the 100-TW laser at the LULI facility and probed at different times with a picosecond X-ray backlighter created with a synchronized subpicosecond laser beam. Fourier-Domain-Interferometry (FDI) was used to measure the electron temperature at the peak of the heating laser pulse. Absorption X-ray spectra at early times are characteristic of a dense and rather homogeneous plasma, with limited longitudinal gradients as shown by hydrodynamic simulations. The shift of the Al K-edge was measured in the cold dense plasma located at the edge of the heated plasma. From the 1s 2p absorption spectra, the average ionization was measured as a function of time and was also modeled with a collisional-radiative atomic physics code coupled with hydrodynamic simulations.

  9. X-ray absorption spectroscopy of aluminum z-pinch plasma with tungsten backlighter planar wire array source.

    PubMed

    Osborne, G C; Kantsyrev, V L; Safronova, A S; Esaulov, A A; Weller, M E; Shrestha, I; Shlyaptseva, V V; Ouart, N D

    2012-10-01

    Absorption features from K-shell aluminum z-pinch plasmas have recently been studied on Zebra, the 1.7 MA pulse power generator at the Nevada Terawatt Facility. In particular, tungsten plasma has been used as a semi-backlighter source in the generation of aluminum K-shell absorption spectra by placing a single Al wire at or near the end of a single planar W array. All spectroscopic experimental results were recorded using a time-integrated, spatially resolved convex potassium hydrogen phthalate (KAP) crystal spectrometer. Other diagnostics used to study these plasmas included x-ray detectors, optical imaging, laser shadowgraphy, and time-gated and time-integrated x-ray pinhole imagers. Through comparisons with previous publications, Al K-shell absorption lines are shown to be from much lower electron temperature (∼10-40 eV) plasmas than emission spectra (∼350-500 eV).

  10. Melting of iron determined by X-ray absorption spectroscopy to 100 GPa

    PubMed Central

    Aquilanti, Giuliana; Trapananti, Angela; Karandikar, Amol; Kantor, Innokenty; Marini, Carlo; Mathon, Olivier; Pascarelli, Sakura; Boehler, Reinhard

    2015-01-01

    Temperature, thermal history, and dynamics of Earth rely critically on the knowledge of the melting temperature of iron at the pressure conditions of the inner core boundary (ICB) where the geotherm crosses the melting curve. The literature on this subject is overwhelming, and no consensus has been reached, with a very large disagreement of the order of 2,000 K for the ICB temperature. Here we report new data on the melting temperature of iron in a laser-heated diamond anvil cell to 103 GPa obtained by X-ray absorption spectroscopy, a technique rarely used at such conditions. The modifications of the onset of the absorption spectra are used as a reliable melting criterion regardless of the solid phase from which the solid to liquid transition takes place. Our results show a melting temperature of iron in agreement with most previous studies up to 100 GPa, namely of 3,090 K at 103 GPa. PMID:26371317

  11. Melting of iron determined by X-ray absorption spectroscopy to 100 GPa.

    PubMed

    Aquilanti, Giuliana; Trapananti, Angela; Karandikar, Amol; Kantor, Innokenty; Marini, Carlo; Mathon, Olivier; Pascarelli, Sakura; Boehler, Reinhard

    2015-09-29

    Temperature, thermal history, and dynamics of Earth rely critically on the knowledge of the melting temperature of iron at the pressure conditions of the inner core boundary (ICB) where the geotherm crosses the melting curve. The literature on this subject is overwhelming, and no consensus has been reached, with a very large disagreement of the order of 2,000 K for the ICB temperature. Here we report new data on the melting temperature of iron in a laser-heated diamond anvil cell to 103 GPa obtained by X-ray absorption spectroscopy, a technique rarely used at such conditions. The modifications of the onset of the absorption spectra are used as a reliable melting criterion regardless of the solid phase from which the solid to liquid transition takes place. Our results show a melting temperature of iron in agreement with most previous studies up to 100 GPa, namely of 3,090 K at 103 GPa.

  12. Real-time cumulant approach for inelastic losses in x-ray spectra

    NASA Astrophysics Data System (ADS)

    Kas, J. J.; Rehr, J. J.; Curtis, J. B.

    Intrinsic inelastic losses in core level x-ray absorption (XAS), emission (XES), and x-ray photo-emission spectra (XPS), arise from excitations of the system due to the sudden creation or annihilation of a deep core hole. Additional extrinsic losses arise during the propagation of the photoelectron, and interference processes are also important. These excitations are reflected in the satellite peaks observed in XPS. Formally the distribution of these excitations are described in terms of the core-hole spectral function, which can be calculated in terms of the core-hole Green's function represented in exponential form. Here we discuss an approach for calculating the exponent, or cumulant in terms of local density fluctuations via real-space, real-time time-dependent density functional theory. The role of extrinsic and interference terms is also discussed. Our method is illustrated in calculations of XAS and XPS for number of systems, including weakly correlated as well as d- and f-electron materials. Supported by DOE BES Grant DE-FG03-97ER45623.

  13. Medieval glass from the Cathedral in Paderborn: a comparative study using X-ray absorption spectroscopy, X-ray fluorescence, and inductively coupled laser ablation mass spectrometry

    NASA Astrophysics Data System (ADS)

    Hormes, J.; Roy, A.; Bovenkamp, G.-L.; Simon, K.; Kim, C.-Y.; Börste, N.; Gai, S.

    2013-04-01

    We have investigated four stained glass samples recovered from an archaeological excavation at the Cathedral in Paderborn (Germany) between 1978 and 1980. On two of the samples there are parts of paintings. Concentrations of major elements were determined using two independent techniques: LA-ICP-MS (a UV laser ablation microsampler combined with an inductively coupled plasma mass spectrometer) and synchrotron radiation X-ray excited X-ray fluorescence (SR-XRF). The SR-XRF data were quantified by using the program package PyMCA developed by the software group of the ESRF in Grenoble. Significant differences were found between the concentrations determined by the two techniques that can be explained by concentration gradients near the surface of the glasses caused, for example, by corrosion/leaching processes and the different surface sensitivities of the applied techniques. For several of the elements that were detected in the glass and in the colour pigments used for the paintings X-ray absorption near edge structure (XANES) spectra were recorded in order to determine the chemical speciation of the elements of interest. As was expected, most elements in the glass were found as oxides in their most stable form. Two notable exceptions were observed: titanium was not found as rutile—the most stable form of TiO2—but in the form of anatase, and lead was not found in one defined chemical state but as a complex mixture of oxide, sulphate, and other compounds.

  14. GSFC Contributions to the NATO X-ray Astronomy Institute, Erice, July 1979. [X-ray spectra of supernova remants, galactic X-ray sources, active galactic nuclei, and clusters of galaxies

    NASA Technical Reports Server (NTRS)

    Holt, S. S.; Mushotzky, R. F.

    1979-01-01

    An overview of X-ray astronomical spectroscopy in general is presented and results obtained by HEAO 1 and 2 as well as earlier spacecraft are examined. Particular emphasis is given to the spectra of supernova remnants; galactic binary X-ray sources, cataclysmic variables, bulges, pulsars, and stars; the active nuclei of Seyfert 1 galaxy, BL Lac, and quasars; the diffuse X-ray background; and galactic clusters.

  15. X-ray absorption spectroscopy of lithium sulfur battery reaction intermediates

    NASA Astrophysics Data System (ADS)

    Wujcik, Kevin; Pascal, Tod; Prendergast, David; Balsara, Nitash

    2015-03-01

    Lithium sulfur batteries have a theoretical energy density nearly five times greater than current lithium ion battery standards, but questions still remain regarding the reaction pathways through which soluble lithium polysulfide (Li2Sx, ``x'' ranging from 2 to 8) reaction intermediates are formed. Complicating spectroelectrochemical approaches to elucidate redox pathways is the challenge of obtaining spectral standards for individual Li2Sx species. Lithium polysulfides cannot be isolated as individual component and exist only in solution as a distribution of different Li2Sx molecules formed via disproportionation reactions (e.g. 2Li2S4 goes to Li2S3 + Li2S5). X-ray absorption spectroscopy (XAS) at the sulfur K-edge has recently been employed as a technique to study Li-S chemistry. We have recently obtained XAS standards for individual Li2Sx species via first principles DFT simulations and the excited electron and core hole approach. Here, experimental sulfur K-edge XAS of Li2Sx species dissolved in poly(ethylene oxide) are compared to spectra obtained from analogous theoretical calculations. The impact that polysulfide solution concentration and the presence of other lithium salts (e.g. LiNO3) have on X-ray spectra of Li2Sx species is explored via experiment and theory.

  16. Structural changes of nucleic acid base in aqueous solution as observed in X-ray absorption near edge structure (XANES)

    NASA Astrophysics Data System (ADS)

    Shimada, Hiroyuki; Fukao, Taishi; Minami, Hirotake; Ukai, Masatoshi; Fujii, Kentaro; Yokoya, Akinari; Fukuda, Yoshihiro; Saitoh, Yuji

    2014-01-01

    X-ray absorption near edge structure (XANES) spectra for adenine-containing nucleotides, adenosine 5‧-monophosphate (AMP) and adenosine 5‧-triphosphate (ATP) in aqueous solutions at the nitrogen K-edge region were measured. The two intense peaks in XANES spectra are assigned to transitions of 1s electrons to the π∗ orbitals of different types of N atoms with particular bonding characteristics. The difference between their spectra is ascribed to protonation of a particular N atom. Similarity observed in XANES spectra of guanosine 5‧-monophosphate (GMP) and ATP is also interpreted as similar bonding characters of the N atoms in the nucleobase moiety.

  17. Titanium local structure in tektite probed by X-ray absorption fine structure spectroscopy.

    PubMed

    Wang, Ling; Yoshiasa, Akira; Okube, Maki; Takeda, Takashi

    2011-11-01

    The local structure of titanium in tektites from six strewn fields was studied by Ti K-edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) in order to provide quantitative data on Ti-O distance and Ti coordination number. The titanium in tektites possessed different coordination environment types. XANES spectra patterns revealed resemblance to high-temperature TiO(2)-SiO(2) glass and TiO(2) anatase. All samples showed that the valence of Ti is 4+. Based on the Ti-O distances, coordination numbers and radial distribution function determined by EXAFS analyses, the tektites were classified into three types: type I, Ti occupies a four-coordinated tetrahedral site with Ti-O distances of 1.84-1.79 Å; type II, Ti occupies a five-coordinated trigonal bipyramidal or tetragonal pyramidal site with Ti-O distances of 1.92-1.89 Å; type III, Ti occupies a six-coordinated octahedral site with Ti-O distances of 2.00-1.96 Å. Although Ti occupies the TiO(6) octahedral site in most titanium minerals under ambient conditions, some tektites have four- and five-coordinated Ti. This study indicated that the local structure of Ti might change in impact events and the following stages.

  18. Evaluation of iron-containing carbon nanotubes by near edge X-ray absorption technique

    NASA Astrophysics Data System (ADS)

    Osorio, A. G.; Bergmann, C. P.

    2015-10-01

    The synthesis of carbon nanotubes (CNTs) via Chemical Vapor Deposition method with ferrocene results in CNTs filled with Fe-containing nanoparticles. The present work proposes a novel route to characterize the Fe phases in CNTs inherent to the synthesis process. CNTs were synthesized and, afterwards, the CNTs were heat treated at 1000 °C for 20 min in an inert atmosphere during a thermogravimetric experiment. X-Ray Absorption Spectroscopy (XAS) experiments were performed on the CNTs before and after the heat treatment and, also, during the heat treatment, e.g., in situ tests were performed while several Near-Edge X-Ray Absorption (XANES) spectra were collected during the heating of the samples. The XAS technique was successfully applied to evaluate the phases encapsulated by CNTs. Phase transformations of the Fe-based nanoparticles were also observed from iron carbide to metallic iron when the in situ experiments were performed. Results also indicated that the applied synthesis method guarantees that Fe phases are not oxidize. In addition, the results show that heat treatment under inert atmosphere can control which phase remains encapsulated by the CNTs.

  19. Strontium localization in bone tissue studied by X-ray absorption spectroscopy.

    PubMed

    Frankær, Christian Grundahl; Raffalt, Anders Christer; Stahl, Kenny

    2014-02-01

    Strontium has recently been introduced as a pharmacological agent for the treatment and prevention of osteoporosis. We determined the localization of strontium incorporated into bone matrix from dogs treated with Sr malonate by X-ray absorption spectroscopy. A new approach for analyzing the X-ray absorption spectra resulted in a compositional model and allowed the relative distribution of strontium in the different bone components to be estimated. Approximately 35-45% of the strontium present is incorporated into calcium hydroxyapatite (CaHA) by substitution of some of the calcium ions occupying highly ordered sites, and at least 30% is located at less ordered sites where only the first solvation shell is resolved, suggesting that strontium is surrounded by only oxygen atoms similar to Sr(2+) in solution. Strontium was furthermore shown to be absorbed in collagen in which it obtains a higher structural order than when present in serum but less order than when it is incorporated into CaHA. The total amount of strontium in the samples was determined by inductively coupled plasma mass spectrometry, and the amount of Sr was found to increase with increasing dose levels and treatment periods, whereas the relative distribution of strontium among the different components appears to be independent of treatment period and dose level.

  20. Millisecond Kinetics of Nanocrystal Cation Exchange UsingMicrofluidic X-ray Absorption Spectroscopy

    SciTech Connect

    Chan, Emory M.; Marcus, Matthew A.; Fakra, Sirine; Elnaggar,Mariam S.; Mathies, Richard A.; Alivisatos, A. Paul

    2007-05-07

    We describe the use of a flow-focusing microfluidic reactorto measure the kinetics of theCdSe-to-Ag2Se nanocrystal cation exchangereaction using micro-X-ray absorption spectroscopy (mu XAS). The smallmicroreactor dimensions facilitate the millisecond mixing of CdSenanocrystal and Ag+ reactant solutions, and the transposition of thereaction time onto spatial coordinates enables the in situ observation ofthe millisecond reaction with mu XAS. XAS spectra show the progression ofCdSe nanocrystals to Ag2Se over the course of 100 ms without the presenceof long-lived intermediates. These results, along with supporting stoppedflow absorption experiments, suggest that this nanocrystal cationexchange reaction is highly efficient and provide insight into how thereaction progresses in individual particles. This experiment illustratesthe value and potential of in situ microfluidic X-ray synchrotrontechniques for detailed studies of the millisecond structuraltransformations of nanoparticles and other solution-phase reactions inwhich diffusive mixing initiates changes in local bond structures oroxidation states.

  1. Strontium localization in bone tissue studied by X-ray absorption spectroscopy.

    PubMed

    Frankær, Christian Grundahl; Raffalt, Anders Christer; Stahl, Kenny

    2014-02-01

    Strontium has recently been introduced as a pharmacological agent for the treatment and prevention of osteoporosis. We determined the localization of strontium incorporated into bone matrix from dogs treated with Sr malonate by X-ray absorption spectroscopy. A new approach for analyzing the X-ray absorption spectra resulted in a compositional model and allowed the relative distribution of strontium in the different bone components to be estimated. Approximately 35-45% of the strontium present is incorporated into calcium hydroxyapatite (CaHA) by substitution of some of the calcium ions occupying highly ordered sites, and at least 30% is located at less ordered sites where only the first solvation shell is resolved, suggesting that strontium is surrounded by only oxygen atoms similar to Sr(2+) in solution. Strontium was furthermore shown to be absorbed in collagen in which it obtains a higher structural order than when present in serum but less order than when it is incorporated into CaHA. The total amount of strontium in the samples was determined by inductively coupled plasma mass spectrometry, and the amount of Sr was found to increase with increasing dose levels and treatment periods, whereas the relative distribution of strontium among the different components appears to be independent of treatment period and dose level. PMID:24101232

  2. Titanium local structure in tektite probed by X-ray absorption fine structure spectroscopy.

    PubMed

    Wang, Ling; Yoshiasa, Akira; Okube, Maki; Takeda, Takashi

    2011-11-01

    The local structure of titanium in tektites from six strewn fields was studied by Ti K-edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) in order to provide quantitative data on Ti-O distance and Ti coordination number. The titanium in tektites possessed different coordination environment types. XANES spectra patterns revealed resemblance to high-temperature TiO(2)-SiO(2) glass and TiO(2) anatase. All samples showed that the valence of Ti is 4+. Based on the Ti-O distances, coordination numbers and radial distribution function determined by EXAFS analyses, the tektites were classified into three types: type I, Ti occupies a four-coordinated tetrahedral site with Ti-O distances of 1.84-1.79 Å; type II, Ti occupies a five-coordinated trigonal bipyramidal or tetragonal pyramidal site with Ti-O distances of 1.92-1.89 Å; type III, Ti occupies a six-coordinated octahedral site with Ti-O distances of 2.00-1.96 Å. Although Ti occupies the TiO(6) octahedral site in most titanium minerals under ambient conditions, some tektites have four- and five-coordinated Ti. This study indicated that the local structure of Ti might change in impact events and the following stages. PMID:21997913

  3. 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.

  4. First Principles Calculations for X-ray Resonant Spectra and Elastic Properties

    SciTech Connect

    Lee, Yongbin

    2004-01-01

    In this thesis, we discuss applications of first principles methods to x-ray resonant spectra and elastic properties calculation. We start with brief reviews about theoretical background of first principles methods, such as density functional theory, local density approximation (LDA), LDA+U, and the linear augmented plane wave (LAPW) method to solve Kohn-Sham equations. After that we discuss x-ray resonant scattering (XRMS), x-ray magnetic circular dichroism (XMCD) and the branching problem in the heavy rare earths Ledges. In the last chapter we discuss the elastic properties of the second hardest material AlMgB14.

  5. Measuring the angular dependence of betatron x-ray spectra in a laser-wakefield accelerator

    SciTech Connect

    Albert, F.; Pollock, B. B.; Shaw, J. L.; Marsh, K. A.; Ralph, J. E.; Chen, Y. -H.; Alessi, D.; Pak, A.; Clayton, C. E.; Glenzer, S. H.; Joshi, C.

    2014-07-22

    This paper presents a new technique to measure the angular dependence of betatron x-ray spectra in a laser-wakefield accelerator. Measurements are performed with a stacked image plates spectrometer, capable of detecting broadband x-ray radiation up to 1 MeV. It can provide measurements of the betatron x-ray spectrum at any angle of observation (within a 40 mrad cone) and of the beam profile. A detailed description of our data analysis is given, along with comparison for several shots. As a result, these measurements provide useful information on the dynamics of the electrons are they are accelerated and wiggled by the wakefield.

  6. 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.

  7. Impact of rare earth element added filters on the X-ray beam spectra: a Monte Carlo approach.

    PubMed

    Eskandarlou, Amir; Jafari, Amir Abbas; Mohammadi, Mohammad; Zehtabian, Mehdi; Faghihi, Reza; Shokri, Abbas; Pourolajal, Jalal

    2014-01-01

    The effectiveness of added filters including conventional and rare earth materials for dental radiography tasks was investigated using a simulation approach. Current study focuses on the combination of a range of various filters to investigate the reduction of radiation absorbed dose and improving the quality of a radiography image. To simulate the X-ray beam spectrum, a MCNP5 code was applied. Relative intensity, beam quality, and mean energy were investigated for a typical dental radiography machine. The impact of different rare-earth materials with different thicknesses and tube voltages on the X-ray spectrum was investigated. For Aluminum as a conventional filter, the modeled X-ray spectra and HVL values were in a good agreement with those reported by IPEM. The results showed that for a 70 kVp voltage, with an increase of the thickness and atomic number of a given added filters, an increase of HVL values were observed. However, with the increase of the attenuator thickness, X-ray beam intensity decreases. For mean energy, different results were observed. It was also found that rare earth made filters reduce high energy X-ray radiation due to k-edge absorption. This leads to an ideal beam for intra-oral radiography tasks. However, as a disadvantage of rare earth added filters, the reduction of the tube output levels should also be considered.

  8. Correcting x ray spectra obtained from the AXAF VETA-I mirror calibration for pileup, continuum, background and deadtime

    NASA Technical Reports Server (NTRS)

    Chartas, G.; Flanagan, Kathy; Hughes, John P.; Kellogg, Edwin M.; Nguyen, D.; Zombeck, M.; Joy, M.; Kolodziejezak, J.

    1992-01-01

    The VETA-I mirror was calibrated with the use of a collimated soft X-ray source produced by electron bombardment of various anode materials. The FWHM, effective area and encircled energy were measured with the use of proportional counters that were scanned with a set of circular apertures. The pulsers from the proportional counters were sent through a multichannel analyzer that produced a pulse height spectrum. In order to characterize the properties of the mirror at different discrete photon energies one desires to extract from the pulse height distribution only those photons that originated from the characteristic line emission of the X-ray target source. We have developed a code that fits a modeled spectrum to the observed X-ray data, extracts the counts that originated from the line emission, and estimates the error in these counts. The function that is fitted to the X-ray spectra includes a Prescott function for the resolution of the detector a second Prescott function for a pileup peak and a X-ray continuum function. The continuum component is determined by calculating the absorption of the target Bremsstrahlung through various filters correcting for the reflectivity of the mirror and convolving with the detector response.

  9. Correcting X-ray spectra obtained from the AXAF VETA-I mirror calibration for pileup, continuum, background and deadtime

    NASA Technical Reports Server (NTRS)

    Chartas, G.; Flanagan, K.; Hughes, J. P.; Kellogg, E. M.; Nguyen, D.; Zombek, M.; Joy, M.; Kolodziejezak, J.

    1993-01-01

    The VETA-I mirror was calibrated with the use of a collimated soft X-ray source produced by electron bombardment of various anode materials. The FWHM, effective area and encircled energy were measured with the use of proportional counters that were scanned with a set of circular apertures. The pulsers from the proportional counters were sent through a multichannel analyzer that produced a pulse height spectrum. In order to characterize the properties of the mirror at different discrete photon energies one desires to extract from the pulse height distribution only those photons that originated from the characteristic line emission of the X-ray target source. We have developed a code that fits a modeled spectrum to the observed X-ray data, extracts the counts that originated from the line emission, and estimates the error in these counts. The function that is fitted to the X-ray spectra includes a Prescott function for the resolution of the detector a second Prescott function for a pileup peak and a X-ray continuum function. The continuum component is determined by calculating the absorption of the target Bremsstrahlung through various filters, correcting for the reflectivity of the mirror and convolving with the detector response.

  10. Photoluminescence and radioluminescence spectra of x-ray phosphors

    NASA Astrophysics Data System (ADS)

    Ignatovych, M.; Kelemen, A.; Peto, A.; Chuiko, O.

    2003-04-01

    In the present paper a comparative spectral study -- steady state and time-resolved photoluminescence (PhL) and radioluminescence (RL) -- of Eu-doped phosphors in different host lattices: BaFCl;Sr3(PO4)2; Y2O2S;Y2O3 is reported. Steady state and time-resolved (induced by X-Ray tube, N2-laser and high-energy accelerated electrons respectively) PhL and RL measurements were performed. Bright mono-band and fine-structure line emissions in the blue-green and orange-red region were recorded in PhL and RL for all phosphors. The spectroscopic investigation permits the following conclusions: (i) The spectral patterns, decay curves and life-times observed in both PhL and RL are basically the same for all phosphors. On these observations it was assumed that similar luminescent species are involved in the both PhL and RL processes namely: mono-species Eu2+ and Eu3+ and their clusters (ii) Strong host-lattice influence on the status of Eu in the samples under consideration reflected in the spectral pattern, life-time and quantum efficiency was revealed.

  11. 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.

  12. Local electronic states of Fe{sub 4}N films revealed by x-ray absorption spectroscopy and x-ray magnetic circular dichroism

    SciTech Connect

    Ito, Keita; Toko, Kaoru; Suemasu, Takashi; Takeda, Yukiharu; Saitoh, Yuji; Oguchi, Tamio; Kimura, Akio

    2015-05-21

    We performed x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) measurements at Fe L{sub 2,3} and N K-edges for Fe{sub 4}N epitaxial films grown by molecular beam epitaxy. In order to clarify the element specific local electronic structure of Fe{sub 4}N, we compared experimentally obtained XAS and XMCD spectra with those simulated by a combination of a first-principles calculation and Fermi's golden rule. We revealed that the shoulders observed at Fe L{sub 2,3}-edges in the XAS and XMCD spectra were due to the electric dipole transition from the Fe 2p core-level to the hybridization state generated by σ* anti-bonding between the orbitals of N 2p at the body-centered site and Fe 3d on the face-centered (II) sites. Thus, the observed shoulders were attributed to the local electronic structure of Fe atoms at II sites. As to the N K-edge, the line shape of the obtained spectra was explained by the dipole transition from the N 1s core-level to the hybridization state formed by π* and σ* anti-bondings between the Fe 3d and N 2p orbitals. This hybridization plays an important role in featuring the electronic structures and physical properties of Fe{sub 4}N.

  13. 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%.

  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. 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.

  16. Properties of Liquid Silicon Observed by Time-Resolved X-Ray Absorption Spectroscopy

    NASA Astrophysics Data System (ADS)

    Johnson, S. L.; Heimann, P. A.; Lindenberg, A. M.; Jeschke, H. O.; Garcia, M. E.; Chang, Z.; Lee, R. W.; Rehr, J. J.; Falcone, R. W.

    2003-10-01

    Time-resolved x-ray spectroscopy at the Si L edges is used to probe the electronic structure of an amorphous Si foil as it melts following absorption of an ultrafast laser pulse. Picosecond temporal resolution allows observation of the transient liquid phase before vaporization and before the liquid breaks up into droplets. The melting causes changes in the spectrum that match predictions of molecular dynamics and ab initio x-ray absorption codes.

  17. Diamond solid state ionization chambers for x-ray absorption spectroscopy applications

    SciTech Connect

    De Sio, A.; Bocci, A.; Pace, E.; Castellano, C.; Cinque, G.; Tartoni, N.; D'Acapito, F.

    2008-08-25

    The photoresponse of a diamond detector has been compared with a standard ionization chamber in x-ray absorption spectroscopy applications. A photoconductive device based on a nitrogen-doped single crystal diamond has been tested by synchrotron radiation. Time stability and linearity have been studied by x rays at 10 keV to assess its performances. Finally, extended x-ray absorption fine structure at the Fe K-edge was carried on a standard iron target using both the diamond device and the IC. Spectroscopical results have been compared including references to literature.

  18. Absorption of the x ray background by the large magellanic cloud

    NASA Technical Reports Server (NTRS)

    Hamilton, Thomas T.

    1991-01-01

    Soft x ray flux of extragalactic origin should be partially absorbed during passage through the Large Magellanic Cloud. Past attempts to measure this absorption have been frustrated by the LMC's intrinsic x ray emission. New calibration techniques were developed to enable precise (within 5 pct.) measurement of the flux and spectrum of diffuse x rays detected by the Einstein Observatory IPC. These techniques were used to measure the absorption of extragalactic flux by neutral gas in the LMC, and to determine that at least 50 pct. of the observed flux in the 0.16 to 2 keV band is of extragalactic origin.

  19. Experimental station for laser-based picosecond time-resolved x-ray absorption near-edge spectroscopy

    SciTech Connect

    Dorchies, F. Fedorov, N.; Lecherbourg, L.

    2015-07-15

    We present an experimental station designed for time-resolved X-ray Absorption Near-Edge Spectroscopy (XANES). It is based on ultrashort laser-plasma x-ray pulses generated from a table-top 100 mJ-class laser at 10 Hz repetition rate. A high transmission (10%–20%) x-ray beam line transport using polycapillary optics allows us to set the sample in an independent vacuum chamber, providing high flexibility over a wide spectral range from 0.5 up to 4 keV. Some XANES spectra are presented, demonstrating 1% noise level in only ∼1 mn and ∼100 cumulated laser shots. Time-resolved measurements are reported, indicating that the time resolution of the entire experimental station is 3.3 ± 0.6 ps rms.

  20. 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.

  1. Experimental station for laser-based picosecond time-resolved x-ray absorption near-edge spectroscopy.

    PubMed

    Dorchies, F; Fedorov, N; Lecherbourg, L

    2015-07-01

    We present an experimental station designed for time-resolved X-ray Absorption Near-Edge Spectroscopy (XANES). It is based on ultrashort laser-plasma x-ray pulses generated from a table-top 100 mJ-class laser at 10 Hz repetition rate. A high transmission (10%-20%) x-ray beam line transport using polycapillary optics allows us to set the sample in an independent vacuum chamber, providing high flexibility over a wide spectral range from 0.5 up to 4 keV. Some XANES spectra are presented, demonstrating 1% noise level in only ∼1 mn and ∼100 cumulated laser shots. Time-resolved measurements are reported, indicating that the time resolution of the entire experimental station is 3.3 ± 0.6 ps rms.

  2. K-edge x-ray-absorption spectroscopy of laser-generated Kr{sup +} and Kr{sup 2+}

    SciTech Connect

    Southworth, S. H.; Arms, D. A.; Dufresne, E. M.; Dunford, R. W.; Ederer, D. L.; Hoehr, C.; Kanter, E. P.; Kraessig, B.; Landahl, E. C.; Peterson, E. R.; Rudati, J.; Santra, R.; Walko, D. A.; Young, L.

    2007-10-15

    Tunable, polarized, microfocused x-ray pulses were used to record x-ray absorption spectra across the K edges of Kr{sup +} and Kr{sup 2+} produced by laser ionization of Kr. Prominent 1s{yields}4p and 5p excitations are observed below the 1s ionization thresholds in accord with calculated transition energies and probabilities. Due to alignment of 4p hole states in the laser-ionization process, the Kr{sup +} 1s{yields}4p cross section varies with respect to the angle between the laser and x-ray polarization vectors. This effect is used to determine the Kr{sup +} 4p{sub 3/2} and 4p{sub 1/2} quantum state populations, and these are compared with results of an adiabatic strong-field ionization theory that includes spin-orbit coupling.

  3. K-edge x-ray absorption spectroscopy of laser-generated Kr{sup +} and Kr{sup 2+}.

    SciTech Connect

    Southworth, S. H.; Arms, D. A.; Dufresne, E. M.; Dunford, R. W.; Ederer, D. L.; Hoehr, C.; Kanter, E. P.; Krassig, B.; Landahl, E. C.; Peterson, E. R.; Rudati, J.; Santra, R.; Walko, D. A.; Young, L.

    2007-10-01

    Tunable, polarized, microfocused x-ray pulses were used to record x-ray absorption spectra across the K edges of Kr{sup +} and Kr{sup 2+} produced by laser ionization of Kr. Prominent 1s {yields} 4p and 5p excitations are observed below the 1s ionization thresholds in accord with calculated transition energies and probabilities. Due to alignment of 4p hole states in the laser-ionization process, the Kr{sup +} 1s {yields} 4p cross section varies with respect to the angle between the laser and x-ray polarization vectors. This effect is used to determine the Kr{sup +} 4p{sub 3/2} and 4p{sub 1/2} quantum state populations, and these are compared with results of an adiabatic strong-field ionization theory that includes spin-orbit coupling.

  4. 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.

  5. Foqus: a FORTRAN program for the quantitative analysis of x-ray spectra from thin biological specimens.

    PubMed

    Fuchs, H; Fuchs, W

    1981-01-01

    An online FORTRAN program for the quantitative analysis of energy dispersive X-ray spectra from thin biological specimens is presented. The methods of background suppression by digital filtering and peak deconvolution by linear least-squares fitting with measured peak profiles are used. The continuum quantitation method for spectra from thin biological sections as proposed by Hall is applied. The performance of the computer program, utilizing the facilities of a disk operating system, is demonstrated. The routines were optimized for speed, resulting in a run-time of less than 5 seconds on a 16 bit minicomputer for a full quantitation for 7 elements of an energy dispersive thin section X-ray spectrum, including an optional absorption correction. Since no assembly language subroutines are implemented, the restrictions for the use of the program with different computer systems are minimized.

  6. 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

  7. 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

  8. Scintillating screen CCD camera using fast analog on-chip storage for time-resolved x-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Koch, Andreas; Hagelstein, Michael; San Miguel, Alfonso; Fontaine, Alain; Ressler, Thorsten

    1995-03-01

    Serial readout of cooled, linear Si-photodiode arrays or CCDs offer a high dynamic range but only at moderate pixel readout rates. Recording spectroscopic information, i.e. 1D images, requires only a few sensitive lines of a 2D CCD array. A camera is presented where the unexposed part of the CCD is used as a buffer to store successive spectra with high frame rates. In this 'streak mode' the time resolution for data acquisition depends only on the line shift time of the CCD and no longer on the slow pixel readout time. A frame rate of 10 kHz for X-ray absorption spectra has been achieved. The CCD is part of an X-ray camera consisting of a scintillating screen lens-coupled to the CCD. The camera provides a high dynamic range of 17 bit, a spatial resolution of 60 micrometers (FWHM) and a high detective quantum efficiency of > 40% for x- ray energies between 4 keV and 25 keV. The camera is used for time- resolved energy-dispersive XAFS (X-ray Absorption Fine Structure) experiments. This technique permits the study of time-dependent variations of electronic properties and the local environment of atoms under induced external perturbation.

  9. Preliminary optical design of a varied line-space spectrograph for the multi-channel detection of near-edge X-ray absorption fine structure (NEXAFS) spectra in the 280-550 eV energy range

    SciTech Connect

    Wheeler, B.S.; McKinney, W.R.; Hussain, Z.; Padmore, H.

    1996-07-01

    The optical design of a varied line-space spectrograph for the multi-channel recording of NEXAFS spectra in a single {open_quotes}snapshot{close_quotes} is proposed. The spectrograph is to be used with a bending magnet source on beamline 7.3.2 at the Advanced Light Source (ALS). Approximately 20 volts of spectra are simultaneously imaged across a small square of material sample at each respective K absorption edge of carbon, nitrogen, and oxygen. Photoelectrons emitted from the material sample will be collected by an electron imaging microscope, the view field of which determines the sampling size. The sample also forms the exit slit of the optical system. This dispersive method of NEXAFS data acquisition is three to four orders of magnitude faster than the conventional method of taking data point-to-point using scanning of the grating. The proposed design is presented along with the design method and supporting SHADOW raytrace analysis.

  10. Low-potential iron-sulfur centers in photosystem I: an X-ray absorption spectroscopy study.

    PubMed

    McDermott, A E; Yachandra, V K; Guiles, R D; Britt, R D; Dexheimer, S L; Sauer, K; Klein, M P

    1988-05-31

    We have measured the X-ray absorption spectra of Fe in photosystem I (PS I) preparations from spinach and a thermophilic cyanobacterium, Synechococcus sp., to characterize structures of the Fe complexes that function as electron acceptors in PS I. These acceptors include centers A and B, which are probably typical [4Fe-4S] ferredoxins, and X. The structure of X is not known, but its electron paramagnetic resonance (EPR) spectrum has generated the suggestions that it is either a [2Fe-2S] or [4Fe-4S] ferredoxin or an Fe-quinone species. The iron X-ray absorption K-edge and iron extended X-ray absorption fine structure (EXAFS) spectra reveal that essentially all of the 11-14 Fe atoms present in the reaction center are present in the form of Fe-S centers and that not more than 1 atom out of 12 could be octahedral or oxygen-coordinated Fe. This suggests that, besides A and B, additional Fe-S clusters are present which are likely to be X. Our EXAFS spectra cannot be simulated adequately by a mixture of [4Fe-4S] ferredoxins with typical bond lengths and disorder parameters because the amplitude of Fe backscattering is small; however, excellent simulations of the data are consistent with a mixture of [2Fe-2S] ferredoxins and [4Fe-4S] ferredoxins, or with unusually distorted [4Fe-4S] clusters. We presume that the [2Fe-2S] or distorted [4Fe-4S] centers are X. The X-ray absorption spectra of PS I preparations from Synechococcus and spinach are essentially indistinguishable.

  11. X-ray Absorption Spectroscopy Systematics at the Tungsten L-Edge

    PubMed Central

    2015-01-01

    A series of mononuclear six-coordinate tungsten compounds spanning formal oxidation states from 0 to +VI, largely in a ligand environment of inert chloride and/or phosphine, was interrogated by tungsten L-edge X-ray absorption spectroscopy. The L-edge spectra of this compound set, comprised of [W0(PMe3)6], [WIICl2(PMePh2)4], [WIIICl2(dppe)2][PF6] (dppe = 1,2-bis(diphenylphosphino)ethane), [WIVCl4(PMePh2)2], [WV(NPh)Cl3(PMe3)2], and [WVICl6], correlate with formal oxidation state and have usefulness as references for the interpretation of the L-edge spectra of tungsten compounds with redox-active ligands and ambiguous electronic structure descriptions. The utility of these spectra arises from the combined correlation of the estimated branching ratio of the L3,2-edges and the L1 rising-edge energy with metal Zeff, thereby permitting an assessment of effective metal oxidation state. An application of these reference spectra is illustrated by their use as backdrop for the L-edge X-ray absorption spectra of [WIV(mdt)2(CO)2] and [WIV(mdt)2(CN)2]2– (mdt2– = 1,2-dimethylethene-1,2-dithiolate), which shows that both compounds are effectively WIV species even though the mdt ligands exist at different redox levels in the two compounds. Use of metal L-edge XAS to assess a compound of uncertain formulation requires: (1) Placement of that data within the context of spectra offered by unambiguous calibrant compounds, preferably with the same coordination number and similar metal ligand distances. Such spectra assist in defining upper and/or lower limits for metal Zeff in the species of interest. (2) Evaluation of that data in conjunction with information from other physical methods, especially ligand K-edge XAS. (3) Increased care in interpretation if strong π-acceptor ligands, particularly CO, or π-donor ligands are present. The electron-withdrawing/donating nature of these ligand types, combined with relatively short metal–ligand distances, exaggerate the difference

  12. X-ray absorption spectroscopy systematics at the tungsten L-edge.

    PubMed

    Jayarathne, Upul; Chandrasekaran, Perumalreddy; Greene, Angelique F; Mague, Joel T; DeBeer, Serena; Lancaster, Kyle M; Sproules, Stephen; Donahue, James P

    2014-08-18

    A series of mononuclear six-coordinate tungsten compounds spanning formal oxidation states from 0 to +VI, largely in a ligand environment of inert chloride and/or phosphine, was interrogated by tungsten L-edge X-ray absorption spectroscopy. The L-edge spectra of this compound set, comprised of [W(0)(PMe3)6], [W(II)Cl2(PMePh2)4], [W(III)Cl2(dppe)2][PF6] (dppe = 1,2-bis(diphenylphosphino)ethane), [W(IV)Cl4(PMePh2)2], [W(V)(NPh)Cl3(PMe3)2], and [W(VI)Cl6], correlate with formal oxidation state and have usefulness as references for the interpretation of the L-edge spectra of tungsten compounds with redox-active ligands and ambiguous electronic structure descriptions. The utility of these spectra arises from the combined correlation of the estimated branching ratio of the L3,2-edges and the L1 rising-edge energy with metal Zeff, thereby permitting an assessment of effective metal oxidation state. An application of these reference spectra is illustrated by their use as backdrop for the L-edge X-ray absorption spectra of [W(IV)(mdt)2(CO)2] and [W(IV)(mdt)2(CN)2](2-) (mdt(2-) = 1,2-dimethylethene-1,2-dithiolate), which shows that both compounds are effectively W(IV) species even though the mdt ligands exist at different redox levels in the two compounds. Use of metal L-edge XAS to assess a compound of uncertain formulation requires: (1) Placement of that data within the context of spectra offered by unambiguous calibrant compounds, preferably with the same coordination number and similar metal ligand distances. Such spectra assist in defining upper and/or lower limits for metal Zeff in the species of interest. (2) Evaluation of that data in conjunction with information from other physical methods, especially ligand K-edge XAS. (3) Increased care in interpretation if strong π-acceptor ligands, particularly CO, or π-donor ligands are present. The electron-withdrawing/donating nature of these ligand types, combined with relatively short metal-ligand distances, exaggerate

  13. (HP)Ge Measurement of spectra for diagnostic X-ray beams.

    PubMed

    Nogueira, M S; Mota, H C; Campos, L L

    2004-01-01

    The X-ray spectra applied in diagnostic radiology to the energy range between 50 and 125 kVp, were experimentally determined using a high-purity germanium detector, (HP)Ge, coupled to a multichannel analyser. A simple stripping procedure was implemented, according to that described by Seelentag and Panzer, to correct the pulse height distribution and then to determine the photon spectra. The measurements were performed for those conditions where the X-ray beam is transmitted through Pb filters 0.2-0.7 mm thick. It was necessary to estimate the effective dose in the same way that it is done for radiology diagnosis room shielding projects. The spectra were also determined to the X-ray qualities recommended by the IEC for primary diagnostic X-ray and for X-ray beams attenuated by aluminium filters 2.5-42.5 mm thick. The spectra obtained were compared with data derived from the literature presenting good agreement. PMID:15367779

  14. X-ray Absorption Improvement of Single Wall Carbon Nanotube through Gadolinium Encapsulation

    NASA Astrophysics Data System (ADS)

    Alimin; Narsito, I.; Kartini; Santosa, S. J.

    2016-02-01

    X-ray absorption improvement of single-wall carbon nanotube (SWCNT) through gadolinium (Gd) encapsulation has been studied. The liquid phase adsorption using ethanol has been performed for the doping treatment. The Gd-doped SWCNT (Gd@SWCNT) was characterized by nitrogen adsorption isotherms, Raman spectroscopy, Transmission electron microscopy (TEM), and thermal gravimetric analysis (TGA) techniques. A relatively high residual weight of Gd@SWCNT compared to non-doped SWCNT (n-SWCNT) indicated that Gd has been doped in the nanotube. Even though Gd nanoparticles could not be observed clearly by TEM image, however, a significant decrease of nitrogen uptakes at low pressure and RBM (Radial Breathing Mode) upshift of Raman spectra of Gd@SWCNT specimen suggest that the metal nanoparticles might be encapsulated in the internal tube spaces of the nanotube. It was found that Gd-doped in the SWCNT increased significantly mass attenuation coefficient of the nanotube.

  15. Electronic topological transition in zinc under pressure: An x-ray absorption spectroscopy study

    NASA Astrophysics Data System (ADS)

    Aquilanti, G.; Trapananti, A.; Minicucci, M.; Liscio, F.; Twaróg, A.; Principi, E.; Pascarelli, S.

    2007-10-01

    Zinc metal has been studied at high pressure using x-ray absorption spectroscopy. In order to investigate the role of the different degrees of hydrostaticity on the occurrence of structural anomalies following the electronic topological transition, two pressure transmitting media have been used. Results show that the electronic topological transition, if it exists, does not induce an anomaly in the local environment of compressed Zn as a function of hydrostatic pressure and any anomaly must be related to a loss of hydrostaticity of the pressure transmitting medium. The near-edge structures of the spectra, sensitive to variations in the electronic density of states above the Fermi level, do not show any evidence of electronic transition whatever pressure transmitting medium is used.

  16. X-ray absorption studies of gamma irradiated Nd doped phosphate glass

    SciTech Connect

    Rai, V. N.; Rajput, Parasmani; Jha, S. N.; Bhattacharyya, D.

    2015-06-24

    This paper presents the X-ray absorption near edge structure (XANES) studies of Nd doped phosphate glasses before and after gamma irradiation. The intensity and location of L{sub III} edge white line peak of Nd changes depending on its concentration as well as on the ratio of O/Nd in the glass matrix. The decrease in the peak intensity of white line after gamma irradiation indicates towards reduction of Nd{sup 3+} to Nd{sup 2+} in the glass matrix, which increases with an increase in the doses of gamma irradiation. Similarity in the XANES spectra of Nd doped phosphate glasses and Nd{sub 2}O{sub 3} suggests that coordination geometry around Nd{sup 3+} in glass samples may be identical to that of Nd{sub 2}O{sub 3}.

  17. X-Ray absorption spectroscopy investigation of 1-alkyl-3-methylimidazolium bromide salts

    SciTech Connect

    D'Angelo, Paola; Zitolo, Andrea; Migliorati, Valentina; Bodo, Enrico; Caminiti, Ruggero; Aquilanti, Giuliana; Hazemann, Jean Louis; Testemale, Denis; Mancini, Giordano

    2011-08-21

    X-ray absorption spectroscopy (XAS) has been used to unveil the bromide ion local coordination structure in 1-alkyl-3-methylimidazolium bromide [C{sub n}mim]Br ionic liquids (ILs) with different alkyl chains. The XAS spectrum of 1-ethyl-3-methylimidazolium bromide has been found to be different from those of the other members of the series, from the butyl to the decyl derivatives, that have all identical XAS spectra. This result indicates that starting from 1-buthyl-3-methylimidazolium bromide the local molecular arrangement around the bromide anion is the same independently from the length of the alkyl chain, and that the imidazolium head groups in the liquid ILs with long alkyl chains assume locally the same orientation as in the [C{sub 4}mim]Br crystal. With this study we show that the XAS technique is an effective direct tool for unveiling the local structural arrangements around selected atoms in ILs.

  18. Structural analysis of sulfur in natural rubber using X-ray absorption near-edge spectroscopy.

    PubMed

    Pattanasiriwisawa, Wanwisa; Siritapetawee, Jaruwan; Patarapaiboolchai, Orasa; Klysubun, Wantana

    2008-09-01

    X-ray absorption near-edge spectroscopy (XANES) has been applied to natural rubber in order to study the local environment of sulfur atoms in sulfur crosslinking structures introduced in the vulcanization process. Different types of chemical accelerators in conventional, semi-efficient and efficient vulcanization systems were investigated. The experimental results show the good sensitivity and reproducibility of XANES to characterize the local geometry and electronic environment of the sulfur K-shell under various conditions of vulcanization and non-vulcanization of natural rubber. Several applications of XANES in this study demonstrate an alternative way of identifying sulfur crosslinks in treated natural rubber based on differences in their spectra and oxidation states. PMID:18728323

  19. Bremsstrahlung X-ray spectra of Jupiter and Saturn - Predictions for future planetary spacecraft

    NASA Astrophysics Data System (ADS)

    Barbosa, D. D.

    1990-07-01

    Calculations of X-ray spectra due to bremsstrahlung from precipitating auroral electrons of Jupiter and Saturn are presented. The model assumes that a field-aligned potential drop accelerates a primary beam of electrons into the atmosphere where a population of secondary electrons having a power law energy dependence is generated. The spectrum at Jupiter is normalized to the soft X-ray observations of Metzger et al. (1983) at the low-energy end and constrained at the high-energy end by UV auroral energy requirements. The spectrum at Saturn is constructed by analogy to the Jovian case allowing for variation of the beam energy, energy flux, and scale size of the Saturnian aurora. The results indicate that a significant flux of X-rays is emanating from both planets which may serve as a basis for conducting planetary X-ray astronomy as a part of future spacecraft missions to the planets.

  20. X-Ray Spectra of Quasars from the ROSAT Public Archive

    NASA Technical Reports Server (NTRS)

    Elvis, Martin S.; West, Donald (Technical Monitor)

    2000-01-01

    This has been a most productive proposal. We have: (1) Found many new X-ray absorbed quasars at z>2; (2) Determined that all of these are radio-loud, favoring an intrinsic origin for the absorption; (3) Found that the one radio-quiet exception lay close to a nearby galaxy, so initiating the X-ray study of the ISM of normal galaxies via X-ray spectroscopy; (4) Discovered a class of 'red quasars', probably the tip of a large obscured population; and (5) Discovered a class of 'blank field X-ray sources'. These are a heterogeneous collection but probably include several peculiar types of active galactic nuclei (AGN). Follow-up of the 'blanks' is being undertaken under a separate ADP program. Chandra and XMM-Newton observing time for these objects has been approved. This program has produced six refereed papers and six published conference proceedings.

  1. X-ray absorption spectroscopy of iron at multimegabar pressures in laser shock experiments

    NASA Astrophysics Data System (ADS)

    Harmand, M.; Ravasio, A.; Mazevet, S.; Bouchet, J.; Denoeud, A.; Dorchies, F.; Feng, Y.; Fourment, C.; Galtier, E.; Gaudin, J.; Guyot, F.; Kodama, R.; Koenig, M.; Lee, H. J.; Miyanishi, K.; Morard, G.; Musella, R.; Nagler, B.; Nakatsutsumi, M.; Ozaki, N.; Recoules, V.; Toleikis, S.; Vinci, T.; Zastrau, U.; Zhu, D.; Benuzzi-Mounaix, A.

    2015-07-01

    Taking advantage of the new opportunities provided by x-ray free electron laser (FEL) sources when coupled to a long laser pulse as available at the Linear Coherent Light Source (LCLS), we have performed x-ray absorption near-edge spectroscopy (XANES) of laser shock compressed iron up to 420 GPa (±50 ) and 10 800 K (±1390 ). Visible diagnostics coupled with hydrodynamic simulations were used to infer the thermodynamical conditions along the Hugoniot and the release adiabat. A modification of the pre-edge feature at 7.12 keV in the XANES spectra is observed above pressures of 260 GPa along the Hugoniot. Comparing with ab initio calculations and with previous laser-heated diamond cell data, we propose that such changes in the XANES pre-edge could be a signature of molten iron. This interpretation then suggests that iron is molten at pressures and temperatures higher than 260 GPa (±29 ) and 5680 K (±700 ) along the principal Fe Hugoniot.

  2. X-ray absorption and X-ray photoelectron spectroscopic study of arsenic mobilization during mackinawite (FeS) oxidation.

    PubMed

    Jeong, Hoon Y; Han, Young-Soo; Hayes, Kim F

    2010-02-01

    In this study we investigated the speciation of the solid-phase As formed by reacting 2 x 10(-4) M As(III) with 1.0 g/L mackinawite and the potential for these sorbed species to be mobilized (released into the aqueous phase) upon exposure to atmospheric oxygen at pH 4.9, 7.1, and 9.1. Before oxygen exposure, X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) analyses indicated that As(III) was removed from the aqueous phase by forming As(0), AsS, and surface precipitates as thioarsenites at pH 4.9 and As(0) and thioarsenite surface precipitates at pH 7.1 and 9.1. When oxygen was introduced, XAS analysis indicated that As(0) and the surface precipitates were quickly transformed, whereas AsS was persistent. During intermediate oxygen exposure times, dissolved As increased at pH 4.9 and 7.1 due to the rapid oxidation of As(0) and the slow precipitation of iron (oxyhydr)oxides, the oxidation products of mackinawite. This indicates that oxidative mobilization is a potential pathway for arsenic contamination of water at acidic to neutral pH. The mobilized As was eventually resorbed by forming edge-sharing and double-corner-sharing surface complexes with iron (oxyhydr)oxides.

  3. Incorporation of arsenic in mammal bone: X-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Kretschmer, X.; Pingitore, N. E.; Cruz-Jimenez, G.

    2002-12-01

    X-ray absorption spectroscopy (XAS) of the distal tibia of a modern deer, Odocoileus virginianus, revealed that the energy position of the As K edge matched that of a reference arsenic(V) model compound. Comparison of the x-ray absorption near edge structure (XANES) of the deer spectrum to the spectra of model As compounds indicated a close match to arsenate(V), e.g., zinc orthoarsenate(5). This indicates that the nearest-neighbor shell of the arsenic in the bone consists of four oxygens in the tetrahedral arrangement typical of arsenic(V) oxysalts. The XANES analysis demonstrates that the arsenic in the deer bone is not associated with an organic compound as a result of methylation. This suggests that the arsenic is associated with the mineral fraction of the bone, most likely with As substituting for P at the latter's structural site in the hydroxyapatite. The XAS data for the deer bone were very noisy due to the low level of arsenic present, just over 1 ppm.. A total of 18 scans, taking nearly a full 8-hour beam shift, were averaged to obtain the spectrum studied. It is not clear that the second neighbor shell can be characterized sufficiently from these data to confirm that As substitutes for P in hydroxyapatite. We conducted our XAS experiments on beam line 4-3 at the Stanford Synchrotron Radiation Laboratory. Data were collected in the fluorescence mode, using a solid state, 13-element Ge-detector. The energy reference was As(0) metal foil run parasitically in transmission mode during collection of the bone spectra. The edge shift seen in the experimental and As(V) model compound relative to the energy position of the arsenic(0) foil is consistent with the additional energy required to photoeject the 1-s electron of As(V), relative to that required for As(0). Arsenic content of the deer bone was determined by inductively coupled plasma mass spectrometry.

  4. Distribution and speciation of bromine in mammalian tissue and fluids by X-ray fluorescence imaging and X-ray absorption spectroscopy.

    PubMed

    Ceko, Melanie J; Hummitzsch, Katja; Hatzirodos, Nicholas; Bonner, Wendy; James, Simon A; Kirby, Jason K; Rodgers, Raymond J; Harris, Hugh H

    2015-05-01

    Bromine is one of the most abundant and ubiquitous trace elements in the biosphere and until recently had not been shown to perform any essential biological function in animals. A recent study demonstrated that bromine is required as a cofactor for peroxidasin-catalysed formation of sulfilimine crosslinks in Drosophila. In addition, bromine dietary deficiency is lethal in Drosophila, whereas bromine replenishment restores viability. The aim of this study was to examine the distribution and speciation of bromine in mammalian tissues and fluids to provide further insights into the role and function of this element in biological systems. In this study we used X-ray fluorescence (XRF) imaging and inductively coupled plasma-mass spectrometry (ICP-MS) to examine the distribution of bromine in bovine ovarian tissue samples, follicular fluid and aortic serum, as well as human whole blood and serum and X-ray absorption spectroscopy (XAS) to identify the chemical species of bromine in a range of mammalian tissue (bovine, ovine, porcine and murine), whole blood and serum samples (bovine, ovine, porcine, murine and human), and marine samples (salmon (Salmo salar), kingfish (Seriola lalandi) and Scleractinian coral). Bromine was found to be widely distributed across all tissues and fluids examined. In the bovine ovary in particular it was more concentrated in the sub-endothelial regions of arterioles. Statistical comparison of the near-edge region of the X-ray absorption spectra with a library of bromine standards led to the conclusion that the major form of bromine in all samples analysed was bromide.

  5. Distribution and speciation of bromine in mammalian tissue and fluids by X-ray fluorescence imaging and X-ray absorption spectroscopy.

    PubMed

    Ceko, Melanie J; Hummitzsch, Katja; Hatzirodos, Nicholas; Bonner, Wendy; James, Simon A; Kirby, Jason K; Rodgers, Raymond J; Harris, Hugh H

    2015-05-01

    Bromine is one of the most abundant and ubiquitous trace elements in the biosphere and until recently had not been shown to perform any essential biological function in animals. A recent study demonstrated that bromine is required as a cofactor for peroxidasin-catalysed formation of sulfilimine crosslinks in Drosophila. In addition, bromine dietary deficiency is lethal in Drosophila, whereas bromine replenishment restores viability. The aim of this study was to examine the distribution and speciation of bromine in mammalian tissues and fluids to provide further insights into the role and function of this element in biological systems. In this study we used X-ray fluorescence (XRF) imaging and inductively coupled plasma-mass spectrometry (ICP-MS) to examine the distribution of bromine in bovine ovarian tissue samples, follicular fluid and aortic serum, as well as human whole blood and serum and X-ray absorption spectroscopy (XAS) to identify the chemical species of bromine in a range of mammalian tissue (bovine, ovine, porcine and murine), whole blood and serum samples (bovine, ovine, porcine, murine and human), and marine samples (salmon (Salmo salar), kingfish (Seriola lalandi) and Scleractinian coral). Bromine was found to be widely distributed across all tissues and fluids examined. In the bovine ovary in particular it was more concentrated in the sub-endothelial regions of arterioles. Statistical comparison of the near-edge region of the X-ray absorption spectra with a library of bromine standards led to the conclusion that the major form of bromine in all samples analysed was bromide. PMID:25675086

  6. X-ray Signature of Charge Exchange in the Spectra of L-shell Iron Ions

    SciTech Connect

    Beiersdorfer, P; Schweikhard, L; Liebisch, P; Brown, G V

    2007-01-05

    The X-ray signature of charge exchange between highly charged L-shell iron ions and neutral gas atoms was studied in the laboratory in order to assess its diagnostic utility. Significant differences with spectra formed by electron-impact excitation were observed. In particular, a strong enhancement was found of the emission corresponding to n {le} 4 {yields} n = 2 transitions relative to the n = 3 {yields} n = 2 emission. This enhancement was detectable even with relatively low-resolution X-ray instrumentation (E/{Delta}E {approx} 10) and may enable future identification of charge exchange as a line-formation mechanism in astrophysical spectra.

  7. 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.

  8. X-Ray Absorption Studies of Silica-Supported Platinum Catalysts.

    NASA Astrophysics Data System (ADS)

    Mansour, Azzam Nouman

    X-ray absorption spectroscopy (near-edge structure and EXAFS) was used to characterize Pt/SiO(,2) catalysts both electronically and structurally. Two major developments have been made to characterize this system. A technique to quantitatively extract the number of d-band holes in a material utilizing measurements of the L(,2) and L(,3) x-ray absorption edge spectra is presented. The quantity determined is called "the d-electron character" and is defined as the fractional change in the number of d-band holes relative to a reference material. Next, EXAFS analysis procedures were extended to the higher shells (second, third, and fourth) by using the appropriate model shells from EXAFS data of a 2.5-(mu)m-thick platinum foil taken at liquid nitrogen temperature. Four samples were prepared: three by the ion-exchange technique with Pt loadings of 2 wt.%, 1 wt.%, and 0.5 wt.%, and one by the impregnation (incipient wetness) technique with Pt loading of 2 wt.%. The samples were subjected to different pretreatment conditions and were characterized by atomic absorption spectroscopy, electron microscopy, and hydrogen chemisorption. The conclusions made by x-ray absorption spectroscopy were as follows. All samples consist of highly dispersed spherical Pt particles with an average size in the range of 8-28 (ANGSTROM) and are electron deficient relative to bulk Pt. No significant changes on the structural and electronic properties are observed for Pt loadings in the range 1-2 wt.% and H('2)-reduction temperatures in the range 473-723 K for samples prepared by the ion-exchange technique. Slightly smaller Pt particles, which are more electron deficient, are formed when the Pt loading is decreased to 0.5 wt.%. The ion-exchange technique produces smaller Pt particles, which are more electron deficient relative to the impregnation technique. Samples prepared without the O('2)-calcination consist of smaller Pt particles, which are more electron deficient relative to samples prepared

  9. Direct analysis of molybdenum target generated x-ray spectra with a portable device.

    PubMed

    Stumbo, S; Bottigli, U; Golosio, B; Oliva, P; Tangaro, S

    2004-10-01

    In routine applications, information about the photon flux of x-ray tubes is obtained from exposure measurements and cataloged spectra. This approach relies mainly on the assumption that the real spectrum is correctly approximated by the cataloged one, once the main characteristics of the tube such as voltage, target material, anode angle, and filters are taken account of. In practice, all this information is not always available. Moreover, x-ray tubes with the same characteristics may have different spectra. We describe an apparatus that should be useful for quality control in hospitals and for characterizing new radiographic systems. The apparatus analyzes the spectrum generated by an x-ray mammographic unit. It is based on a commercial CZT produced by AMPTEK Inc. and a set of tungsten collimator disks. The electronics of the CZT are modified so as to obtain a faster response. The signal is digitized using an analog to digital converter with a sampling frequency of up to 20 MHz. The whole signal produced by the x-ray tube is acquired and analyzed off-line in order to accurately recognize pile-up events and reconstruct the emitted spectrum. The energy resolution has been determined using a calibrated x-ray source. Spectra were validated by comparison of the HVL measured using an ionization chamber.

  10. Lifetime-vibrational interference effects in resonantly excited x-ray emission spectra of CO

    SciTech Connect

    Skytt, P.; Glans, P.; Gunnelin, K.

    1997-04-01

    The parity selection rule for resonant X-ray emission as demonstrated for O{sub 2} and N{sub 2} can be seen as an effect of interference between coherently excited degenerate localized core states. One system where the core state degeneracy is not exact but somewhat lifted was previously studied at ALS, namely the resonant X-ray emission of amino-substituted benzene (aniline). It was shown that the X-ray fluorescence spectrum resulting from excitation of the C1s at the site of the {open_quotes}aminocarbon{close_quotes} could be described in a picture separating the excitation and the emission processes, whereas the spectrum corresponding to the quasi-degenerate carbons could not. Thus, in this case it was necessary to take interference effects between the quasi-degenerate intermediate core excited states into account in order to obtain agreement between calculations and experiment. The different vibrational levels of core excited states in molecules have energy splittings which are of the same order of magnitude as the natural lifetime broadening of core excitations in the soft X-ray range. Therefore, lifetime-vibrational interference effects are likely to appear and influence the band shapes in resonant X-ray emission spectra. Lifetime-vibrational interference has been studied in non-resonant X-ray emission, and in Auger spectra. In this report the authors discuss results of selectively excited soft X-ray fluorescence spectra of molecules, where they focus on lifetime-interference effects appearing in the band shapes.

  11. Spectroscopic analysis of solar and cosmic X-ray spectra. 1: The nature of cosmic X-ray spectra and proposed analytical techniques

    NASA Technical Reports Server (NTRS)

    Walker, A. B. C., Jr.

    1975-01-01

    Techniques for the study of the solar corona are reviewed as an introduction to a discussion of modifications required for the study of cosmic sources. Spectroscopic analysis of individual sources and the interstellar medium is considered. The latter was studied via analysis of its effect on the spectra of selected individual sources. The effects of various characteristics of the ISM, including the presence of grains, molecules, and ionization, are first discussed, and the development of ISM models is described. The expected spectral structure of individual cosmic sources is then reviewed with emphasis on supernovae remnants and binary X-ray sources. The observational and analytical requirements imposed by the characteristics of these sources are identified, and prospects for the analysis of abundances and the study of physical parameters within them are assessed. Prospects for the spectroscopic study of other classes of X-ray sources are also discussed.

  12. Properties of aqueous nitrate and nitrite from x-ray absorption spectroscopy

    SciTech Connect

    Smith, Jacob W.; Lam, Royce K.; Saykally, Richard J.; Shih, Orion; Rizzuto, Anthony M.; Prendergast, David

    2015-08-28

    Nitrate and nitrite ions are of considerable interest, both for their widespread use in commercial and research contexts and because of their central role in the global nitrogen cycle. The chemistry of atmospheric aerosols, wherein nitrate is abundant, has been found to depend on the interfacial behavior of ionic species. The interfacial behavior of ions is determined largely by their hydration properties; consequently, the study of the hydration and interfacial behavior of nitrate and nitrite comprises a significant field of study. In this work, we describe the study of aqueous solutions of sodium nitrate and nitrite via X-ray absorption spectroscopy (XAS), interpreted in light of first-principles density functional theory electronic structure calculations. Experimental and calculated spectra of the nitrogen K-edge XA spectra of bulk solutions exhibit a large 3.7 eV shift between the XA spectra of nitrate and nitrite resulting from greater stabilization of the nitrogen 1s energy level in nitrate. A similar shift is not observed in the oxygen K-edge XA spectra of NO{sub 3}{sup −} and NO{sub 2}{sup −}. The hydration properties of nitrate and nitrite are found to be similar, with both anions exhibiting a similar propensity towards ion pairing.

  13. Investigation of protein conformation and interactions with salts via X-ray absorption spectroscopy

    PubMed Central

    Schwartz, Craig P.; Uejio, Janel S.; Duffin, Andrew M.; England, Alice H.; Kelly, Daniel N.; Prendergast, David; Saykally, Richard J.

    2010-01-01

    Nitrogen K-edge spectra of aqueous triglycine were measured using liquid microjets, and the effects of Hofmeister-active salts on the spectra were observed. Spectra simulated using density functional theory, sampled from room temperature classical molecular dynamics trajectories, capture all major features in the measured spectra. The spectrum of triglycine in water is quite similar to that in the presence of chaotropic sodium bromide (and other halides), which raises the solubility of proteins. However, a new feature is found when kosmotropic Na2SO3, which lowers solubility, is present; this feature results from excitations of the nitrogen atom in the terminal amino group of triglycine. Both direct interactions between this salt and the protonated amino terminus, as well as corresponding changes in the conformational dynamics of the system, contribute to this new feature. These molecular measurements support a different mechanism for the Hofmeister effect than has previously been suggested based on thermodynamic measurements. It is also shown that near edge X-ray absorption fine structure (NEXAFS) is sensitive to strong direct interaction between certain salts and charged peptides. However, by investigating the sensitivity of NEXAFS to the extreme structural differences between model β-sheets and α-helices, we conclude that this technique is relatively insensitive to secondary structure of peptides and proteins. PMID:20660784

  14. 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.

  15. 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.

  16. X-ray absorption spectroscopy and X-ray photoelectron spectroscopy studies of CaSO 4:Dy thermoluminescent phosphors

    NASA Astrophysics Data System (ADS)

    Bakshi, A. K.; Jha, S. N.; Olivi, L.; Phase, D. M.; Kher, R. K.; Bhattacharyya, D.

    2007-11-01

    Extended X-ray absorption fine structure (EXAFS) measurements have been carried out on CaSO4:Dy phosphor samples at the Dy L3 edge with synchrotron radiation. Measurements were carried out on a set of samples which were subjected to post-preparation annealing at different temperatures and for different cycles. The EXAFS data have been analysed to find the Dy-S and Dy-O bond lengths in the neighbourhood of the Dy atoms in a CaSO4 matrix. The observations from EXAFS measurements were verified with XANES and XPS techniques. On the basis of these measurements, efforts were made to explain the loss of thermoluminescence sensitivity of CaSO4:Dy phosphors after repeated cycles of annealing at 400 °C in air for 1 h.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. Line intensity enhancements in stellar coronal X-ray spectra due to opacity effects

    NASA Astrophysics Data System (ADS)

    Rose, S. J.; Matranga, M.; Mathioudakis, M.; Keenan, F. P.; Wark, J. S.

    2008-06-01

    Context: The I(15.01 Å)/I(16.78 Å) emission line intensity ratio in Fe xvii has been reported to deviate from its theoretical value in solar and stellar X-ray spectra. This is attributed to opacity in the 15.01 Å line, leading to a reduction in its intensity, and was interpreted in terms of a geometry in which the emitters and absorbers are spatially distinct. Aims: We study the I(15.01 Å)/I(16.78 Å) intensity ratio for the active cool dwarf EV Lac, in both flare and quiescent spectra. Methods: The observations were obtained with the Reflection Grating Spectrometer on the XMM-Newton satellite. The emission measure distribution versus temperature reconstruction technique is used for our analysis. Results: We find that the 15.01 Å line exhibits a significant enhancement in intensity over the optically thin value. To our knowledge, this is the first time that such an enhancement has been detected on such a sound statistical basis. We interpret this enhancement in terms of a geometry in which the emitters and absorbers are not spatially distinct, and where the geometry is such that resonant pumping of the upper level has a greater effect on the observed line intensity than resonant absorption in the line-of-sight.

  2. X-Ray Spectra of VY Scl Stars Are Not Blackbodies

    NASA Technical Reports Server (NTRS)

    Mauche, C. W.; Mukai, K.

    2001-01-01

    Using ASCA data, we find, contrary to other researchers using ROSAT data, that the X, ray spectra of the VY Scl stars TT Ari and KR Aur are poorly fit by an absorbed blackbody model but are well fit by an absorbed thermal plasma model. The different conclusions about the nature of the X-ray spectrum of KR Aur may be due to differences in the accretion rate, since this star was in a high optical state during the ROSAT observation, but in an intermediate optical state during the ASCA observation. TT Ari, on the other hand, was in a high optical state during both observations, so directly contradicts the hypothesis that the X-ray spectra of VY Sol stars in their high optical states are blackbodies. Instead, based on theoretical expectations and the ASCA, Chandra, and XMM spectra of other nonmagnetic cataclysmic variables, we believe that the X-ray spectra of VY Sol stars in their low and high optical states are due to hot thermal plasma in the boundary layer between the accretion disk and the surface of the white dwarf, and appeal to the acquisition of Chandra and XMM grating spectra to test this prediction.

  3. XMM-Newton Spectroscopy of the X-ray Detected Broad Absorption Line QSO CSO 755

    NASA Technical Reports Server (NTRS)

    Brandt, Niel

    2005-01-01

    We present the results from XMM-Newton observations of the highly optically polarized broad absorption line quasar (BALQSO) CSO 755. By analyzing its X-ray spectrum with a total of approximately 3000 photons we find that this source has an X-ray continuum of "typical" radio-quiet quasars, with a photon index of Gamma=1.83, and a rather flat (X-ray bright) intrinsic optical-to-X-ray spectral slope of alpha_ox=- 1.51. The source shows evidence for intrinsic absorption, and fitting the spectrum with a neutral-absorption model gives a column density of N_H approximately 1.2x10^22 cm^{-2}; this is among the lowest X-ray columns measured for BALQSOs. We do not detect, with high significance, any other absorption features in the X-ray spectrum. Upper limits we place on the rest-frame equivalent width of a neutral (ionized) Fe K-alpha line, less than =180 eV (less than =120 eV), and on the Compton-reflection component parameter, R less than =0.2, suggest that most of the X-rays from the source are directly observed rather than being scattered or reflected; this is also supported by the relatively flat intrinsic alpha ox we measure. The possibility that most of the X-ray flux is scattered due to the high level of UV-optical polarization is ruled out. Considering data for 46 BALQSOs from the literature, including CSO 755, we have found that the UV-optical continuum polarization level of BALQSOs is not correlated with any of their X-ray properties. A lack of significant short-term and long-term X-ray flux variations in the source may be attributed to a large black-hole mass in CSO 755. We note that another luminous BALQSO, PG 2112+059, has both similar shallow C IV BALs and moderate X-ray absorption.

  4. Time-resolved soft x-ray spectra from laser-produced Cu plasma

    SciTech Connect

    Cone, K. V.; Baldis, H. A.; Dunn, J.; May, M. J.; Schneider, M. B.; Scott, H. A.; Purvis, M. A.

    2012-10-15

    The volumetric heating of a thin copper target has been studied with time resolved x-ray spectroscopy. The copper target was heated by a plasma produced using the Lawrence Livermore National Laboratory's Compact Multipulse Terawatt (COMET) laser. A variable spaced grating spectrometer coupled to an x-ray streak camera measured soft x-ray emission (800-1550 eV) from the back of the copper target to characterize the bulk heating of the target. Radiation hydrodynamic simulations were modeled in two-dimensions using the HYDRA code. The target conditions calculated by HYDRA were post-processed with the atomic kinetics code CRETIN to generate synthetic emission spectra. A comparison between the experimental and simulated spectra indicates the presence of specific ionization states of copper and the corresponding electron temperatures and ion densities throughout the laser-heated copper target.

  5. Time-resolved soft x-ray spectra from laser-produced Cu plasma.

    PubMed

    Cone, K V; Baldis, H A; Dunn, J; May, M J; Purvis, M A; Schneider, M B; Scott, H A

    2012-10-01

    The volumetric heating of a thin copper target has been studied with time resolved x-ray spectroscopy. The copper target was heated by a plasma produced using the Lawrence Livermore National Laboratory's Compact Multipulse Terawatt (COMET) laser. A variable spaced grating spectrometer coupled to an x-ray streak camera measured soft x-ray emission (800-1550 eV) from the back of the copper target to characterize the bulk heating of the target. Radiation hydrodynamic simulations were modeled in two-dimensions using the HYDRA code. The target conditions calculated by HYDRA were post-processed with the atomic kinetics code CRETIN to generate synthetic emission spectra. A comparison between the experimental and simulated spectra indicates the presence of specific ionization states of copper and the corresponding electron temperatures and ion densities throughout the laser-heated copper target.

  6. Electron-positron pairs, Compton reflection, and the X-ray spectra of active galactic nuclei

    NASA Technical Reports Server (NTRS)

    Zdziarski, Andrzej A.; Ghisellini, Gabriele; George, Ian M.; Fabian, A. C.; Svensson, Roland; Done, Chris

    1990-01-01

    It is shown here that reprocessing of radiation fron nonthermal pair cascades by cold material in the central parts of active galactic nuclei (AGN) gives rise to X-ray and gamma-ray spectra that satisfy current observational constraints. An average 1-30 keV X-ray spectral index alpha(x) of about 0.7 in the compact range 30-300 is obtained for a wide range of Lorentz factors of the injected electrons. The gamma-ray spectra are steep, with alpha(gamma) about two, and satisfy the observational constraints. Radiation from pair cascades exhibits steep power law decreases in soft X-rays similar to those observed in AGN. The overall picture is consistent with AGN having an accretion disk which intercepts and reprocesses a substantial fraction of the nonthermal continuum incident upon it from above and below.

  7. Time-resolved soft x-ray spectra from laser-produced Cu plasma

    SciTech Connect

    Cone, K V; Dunn, J; Baldis, H A; May, M J; Purvis, M A; Scott, H A; Schneider, M B

    2012-05-02

    The volumetric heating of a thin copper target has been studied with time resolved x-ray spectroscopy. The copper target was heated from a plasma produced using the Lawrence Livermore National Laboratory's Compact Multipulse Terrawatt (COMET) laser. A variable spaced grating spectrometer coupled to an x-ray streak camera measured soft x-ray emission (800-1550 eV) from the back of the copper target to characterize the bulk heating of the target. Radiation hydrodynamic simulations were modeled in 2-dimensions using the HYDRA code. The target conditions calculated by HYDRA were post-processed with the atomic kinetics code CRETIN to generate synthetic emission spectra. A comparison between the experimental and simulated spectra indicates the presence of specific ionization states of copper and the corresponding electron temperatures and ion densities throughout the laser-heated copper target.

  8. Sensitivity Analysis of X-ray Spectra from Scanning Electron Microscopes

    SciTech Connect

    Miller, Thomas Martin; Patton, Bruce W.; Weber, Charles F.; Bekar, Kursat B.

    2014-10-01

    The primary goal of this project is to evaluate x-ray spectra generated within a scanning electron microscope (SEM) to determine elemental composition of small samples. This will be accomplished by performing Monte Carlo simulations of the electron and photon interactions in the sample and in the x-ray detector. The elemental inventories will be determined by an inverse process that progressively reduces the difference between the measured and simulated x-ray spectra by iteratively adjusting composition and geometric variables in the computational model. The intended benefit of this work will be to develop a method to perform quantitative analysis on substandard samples (heterogeneous phases, rough surfaces, small sizes, etc.) without involving standard elemental samples or empirical matrix corrections (i.e., true standardless quantitative analysis).

  9. Characterizing Quasar Outflows IV: Regulating Outflows Through X-ray and EUV Absorption

    NASA Astrophysics Data System (ADS)

    Derseweh, Jeffrey; Ganguly, R.; Richmond, J. M.; Stark, M. A.; Christenson, D. H.; Robbins, J. M.; Townsend, S. L.

    2012-05-01

    Galaxy evolution models have shown that quasars are a crucial ingredient in the evolution of massive galaxies. Outflows play a key role in the story of quasars and their host galaxies, by helping regulate the accretion process, the star-formation rate and mass of the host galaxy (i.e., feedback). The prescription for modeling outflows as a contributor to feedback requires knowledge of the outflow velocity, geometry, and column density. In particular, we need to understand how these depend on physical parameters and how much is determined stochastically (and with what distribution). For this purpose, we are examining a sample of 11000 z=1.7-2.0 quasars from the Sloan Digital Sky Survey. This redshift range permits the following from the SDSS spectra: (1) separation of objects that do and do not exhibit outflows; (2) classification/measurement of outflow properties (ionization, velocity, velocity width); and (3) measurements of UV emission line and continuum parameters. In this poster, we add photometry from the GALEX All-sky imaging survey, as well as the Chandra and ROSAT archives. These provide coverage of the rest-frame extreme ultraviolet, and soft X-ray bands. In an accompanying poster, we have subjectively divided these quasars into four categories: broad absorption-line quasars (2700 objects), associated absorption-line quasars (1700 objects), reddened quasars (160 objects), and unabsorbed/unreddened quasars (6300 objects). We are interested in testing the radiative-driving hypothesis that requires a suppression of X-ray flux in order to transfer momentum efficiently to the UV-absorbing gas. Hence, we explore how absorption in both the extreme ultraviolet and the soft X-ray bands correlate with properties of the UV outflows, quasar property, and changes in SED shape. This material is based upon work supported by the National Aeronautics and Space Administration under Grant No. 09-ADP09-0016 issued through the Astrophysics Data Analysis Program and by Chandra

  10. Probing symmetry and symmetry breaking in resonant soft-x-ray fluorescence spectra of molecules

    SciTech Connect

    Glans, P.; Gunnelin, K.; Guo, J.

    1997-04-01

    Conventional non-resonant soft X-ray emission brings about information about electronic structure through its symmetry and polarization selectivity, the character of which is governed by simple dipole rules. For centro-symmetric molecules with the emitting atom at the inversion center these rules lead to selective emission through the required parity change. For the more common classes of molecules which have lower symmetry or for systems with degenerate core orbitals (delocalized over identical sites), it is merely the local symmetry selectivity that provides a probe of the local atomic orbital contribution to the molecular orbital. For instance, in X-ray spectra of first row species the intensities essentially map the p-density at each particular atomic site, and, in a molecular orbital picture, the contribution of the local p-type atomic orbitals in the LCAO description of the molecular orbitals. The situation is different for resonant X-ray fluorescence spectra. Here strict parity and symmetry selectivity gives rise to a strong frequency dependence for all molecules with an element of symmetry. In addition to symmetry selectivity the strong frequency dependence of resonant X-ray emission is caused by the interplay between the shape of a narrow X-ray excitation energy function and the lifetime and vibrational broadenings of the resonantly excited core states. This interplay leads to various observable effects, such as linear dispersion, resonance narrowing and emission line (Stokes) doubling. Also from the point of view of polarization selectivity, the resonantly excited X-ray spectra are much more informative than the corresponding non-resonant spectra. Examples are presented for nitrogen, oxygen, and carbon dioxide molecules.

  11. Arsenic speciation in solids using X-ray absorption spectroscopy

    USGS Publications Warehouse

    Foster, Andrea L.; Kim, Chris S.

    2014-01-01

    One of the most important aims of this review is to clarify the different types of analysis that are performed on As-XAS spectra, and to describe the benefits, drawbacks, and limitations of each. Arsenic XAS spectra are analyzed to obtain one or more of the following types of information (in increasing order of sophistication):

  12. THE BROADBAND XMM-NEWTON AND NuSTAR X-RAY SPECTRA OF TWO ULTRALUMINOUS X-RAY SOURCES IN THE GALAXY IC 342

    SciTech Connect

    Rana, Vikram; Harrison, Fiona A.; Walton, Dominic J.; Furst, Felix; Grefenstette, Brian W.; Madsen, Kristin K.; Bachetti, Matteo; Barret, Didier; Webb, Natalie A.; Miller, Jon M.; Fabian, Andrew C.; Boggs, Steven E.; Craig, William W.; Christensen, Finn C.; Hailey, Charles J.; Ptak, Andrew F.; Zhang, William W.; Stern, Daniel

    2015-02-01

    We present results for two ultraluminous X-ray sources (ULXs), IC 342 X-1 and IC 342 X-2, using two epochs of XMM-Newton and NuSTAR observations separated by ∼7 days. We observe little spectral or flux variability above 1 keV between epochs, with unabsorbed 0.3-30 keV luminosities being 1.04{sub −0.06}{sup +0.08}×10{sup 40} erg s{sup –1} for IC 342 X-1 and 7.40 ± 0.20 × 10{sup 39} erg s{sup –1} for IC 342 X-2, so that both were observed in a similar, luminous state. Both sources have a high absorbing column in excess of the Galactic value. Neither source has a spectrum consistent with a black hole binary in low/hard state, and both ULXs exhibit strong curvature in their broadband X-ray spectra. This curvature rules out models that invoke a simple reflection-dominated spectrum with a broadened iron line and no cutoff in the illuminating power-law continuum. X-ray spectrum of IC 342 X-1 can be characterized by a soft disk-like blackbody component at low energies and a cool, optically thick Comptonization continuum at high energies, but unique physical interpretation of the spectral components remains challenging. The broadband spectrum of IC 342 X-2 can be fit by either a hot (3.8 keV) accretion disk or a Comptonized continuum with no indication of a seed photon population. Although the seed photon component may be masked by soft excess emission unlikely to be associated with the binary system, combined with the high absorption column, it is more plausible that the broadband X-ray emission arises from a simple thin blackbody disk component. Secure identification of the origin of the spectral components in these sources will likely require broadband spectral variability studies.

  13. 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.

  14. High quality x-ray absorption spectroscopy measurements with long energy range at high pressure using diamond anvil cell

    SciTech Connect

    Hong, X.; Newville, M.; Prakapenka, V.B.; Rivers, M.L.; Sutton, S.R.

    2009-07-31

    We describe an approach for acquiring high quality x-ray absorption fine structure (XAFS) spectroscopy spectra with wide energy range at high pressure using diamond anvil cell (DAC). Overcoming the serious interference of diamond Bragg peaks is essential for combining XAFS and DAC techniques in high pressure research, yet an effective method to obtain accurate XAFS spectrum free from DAC induced glitches has been lacking. It was found that these glitches, whose energy positions are very sensitive to the relative orientation between DAC and incident x-ray beam, can be effectively eliminated using an iterative algorithm based on repeated measurements over a small angular range of DAC orientation, e.g., within {+-}3{sup o} relative to the x-ray beam direction. Demonstration XAFS spectra are reported for rutile-type GeO{sub 2} recorded by traditional ambient pressure and high pressure DAC methods, showing similar quality at 440 eV above the absorption edge. Accurate XAFS spectra of GeO{sub 2} glass were obtained at high pressure up to 53 GPa, providing important insight into the structural polymorphism of GeO{sub 2} glass at high pressure. This method is expected be applicable for in situ XAFS measurements using a diamond anvil cell up to ultrahigh pressures.

  15. High quality x-ray absorption spectroscopy measurements with long energy range at high pressure using diamond anvil cell

    PubMed Central

    Hong, Xinguo; Newville, Matthew; Prakapenka, Vitali B.; Rivers, Mark L.; Sutton, Stephen R.

    2009-01-01

    We describe an approach for acquiring high quality x-ray absorption fine structure (XAFS) spectroscopy spectra with wide energy range at high pressure using diamond anvil cell (DAC). Overcoming the serious interference of diamond Bragg peaks is essential for combining XAFS and DAC techniques in high pressure research, yet an effective method to obtain accurate XAFS spectrum free from DAC induced glitches has been lacking. It was found that these glitches, whose energy positions are very sensitive to the relative orientation between DAC and incident x-ray beam, can be effectively eliminated using an iterative algorithm based on repeated measurements over a small angular range of DAC orientation, e.g., within ±3° relative to the x-ray beam direction. Demonstration XAFS spectra are reported for rutile-type GeO2 recorded by traditional ambient pressure and high pressure DAC methods, showing similar quality at 440 eV above the absorption edge. Accurate XAFS spectra of GeO2 glass were obtained at high pressure up to 53 GPa, providing important insight into the structural polymorphism of GeO2 glass at high pressure. This method is expected be applicable for in situ XAFS measurements using a diamond anvil cell up to ultrahigh pressures. PMID:19655966

  16. X-ray ionization yields and energy spectra in liquid argon

    NASA Astrophysics Data System (ADS)

    Bondar, A.; Buzulutskov, A.; Dolgov, A.; Shekhtman, L.; Sokolov, A.

    2016-04-01

    The main purpose of this work is to provide reference data on X-ray ionization yields and energy spectra in liquid Ar to the studies in the field of Cryogenic Avalanche Detectors (CRADs) for rare-event and other experiments, based on liquid Ar detectors. We present the results of two related researches. First, the X-ray recombination coefficients in the energy range of 10-1000 keV and ionization yields at different electric fields, between 0.6 and 2.3 kV/cm, are determined in liquid Ar based on the results of a dedicated experiment. Second, the energy spectra of pulsed X-rays in liquid Ar in the energy range of 15-40 keV, obtained in given experiments including that with the two-phase CRAD, are interpreted and compared to those calculated using a computer program, to correctly determine the absorbed X-ray energy. The X-ray recombination coefficients and ionization yields have for the first time been presented for liquid Ar in systematic way.

  17. Voltage-controlled magnetic anisotropy in Fe|MgO tunnel junctions studied by x-ray absorption spectroscopy

    SciTech Connect

    Miwa, Shinji Matsuda, Kensho; Tanaka, Kazuhito; Goto, Minori; Suzuki, Yoshishige; Kotani, Yoshinori; Nakamura, Tetsuya

    2015-10-19

    In this study, voltage-controlled magnetic anisotropy (VCMA) in Fe|MgO tunnel junctions was investigated via the magneto-optical Kerr effect, soft x-ray absorption spectroscopy, and magnetic circular dichroism spectroscopy. The Fe|MgO tunnel junctions showed enhanced perpendicular magnetic anisotropy under external negative voltage, which induced charge depletion at the Fe|MgO interface. Despite the application of voltages of opposite polarity, no trace of chemical reaction such as a redox reaction attributed to O{sup 2−} migration was detected in the x-ray absorption spectra of the Fe. The VCMA reported in the Fe|MgO-based magnetic tunnel junctions must therefore originate from phenomena associated with the purely electric effect, that is, surface electron doping and/or redistribution induced by an external electric field.

  18. Design of a continuous-flow reactor for in situ x-ray absorption spectroscopy of solids in supercritical fluids.

    PubMed

    Dreher, M; De Boni, E; Nachtegaal, M; Wambach, J; Vogel, F

    2012-05-01

    This paper presents the design and performance of a novel high-temperature and high-pressure continuous-flow reactor, which allows for x-ray absorption spectroscopy or diffraction in supercritical water and other fluids under high pressure and temperature. The in situ cell consists of a tube of sintered, polycrystalline aluminum nitride, which is tolerant to corrosive chemical media, and was designed to be stable at temperatures up to 500 °C and pressures up to 30 MPa. The performance of the reactor is demonstrated by the measurement of extended x-ray absorption fine structure spectra of a carbon-supported ruthenium catalyst during the continuous hydrothermal gasification of ethanol in supercritical water at 400 °C and 24 MPa.

  19. Molecular conformation changes in alkylthiol ligands as a function of size in gold nanoparticles: X-ray absorption studies

    SciTech Connect

    Ramallo-Lopez, J. M.; Giovanetti, L. J.; Requejo, F. G.; Isaacs, S. R.; Shon, Y. S.; Salmeron, M.

    2006-08-15

    The bonding of hexanethiols to gold nanoparticles of 1.5, 2.0, and 3 nm was studied using x-ray absorption near-edge spectroscopy (XANES) and extended x-ray absorption fine structure (EXAFS). The XANES spectra revealed that a substantial fraction of weakly bound hexanethiol molecules are present in addition to those forming covalent bonds with Au atoms. The weakly bound molecules can be removed by washing in dichloromethane. After removal of the weakly bound molecules the S K-edge XANES reveals peaks due to S-Au and S-C bonds with intensities that change as a function of particle size. Au L{sub 3}-edge EXAFS results indicate that these changes follow the changes in coordination number of Au to the S atoms at the surface of the particles.

  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. X-ray spectra from the Cornell Electron-Beam Ion Source (CEBIS I)

    SciTech Connect

    Johnson, B.M.; Jones, K.W.; Kostroun, V.O.; Ghanbari, E.; Janson, S.W.

    1985-01-01

    Radiation emitted from the Cornell electron beam ion source (CEBIS I) has been surveyed with a Si(Li) x-ray detector. These spectra can be used to estimate backgrounds from electron bremsstrahlung and to evaluate the feasibility of atomic physics experiments using the CEBIS I source in this configuration. 1 ref., 2 figs.

  2. Filter-fluorescer measurement of low-voltage simulator x-ray energy spectra

    SciTech Connect

    Baldwin, G.T.; Craven, R.E.

    1986-01-01

    X-ray energy spectra of the Maxwell Laboratories MBS and Physics International Pulserad 737 were measured using an eight-channel filter-fluorescer array. The PHOSCAT computer code was used to calculate channel response functions, and the UFO code to unfold spectrum.

  3. X-Ray Reflected Spectra from Accretion Disk Models. II. Diagnostic Tools for X-Ray Observations

    NASA Technical Reports Server (NTRS)

    Garcia, J.; Kallman, T. R.; Mushotzky, R. F.

    2011-01-01

    We present a comprehensive study of the emission spectra from accreting sources. We use our new reflection code to compute the reflected spectra from an accretion disk illuminated by X-rays. This set of models covers different values of ionization parameter, solar iron abundance and photon index for the illuminating spectrum. These models also include the most complete and recent atomic data for the inner-shell of the iron and oxygen isonuclear sequences. We concentrate our analysis to the 2 - 10 keV energy region, and in particular to the iron K-shell emission lines. We show the dependency of the equivalent width (EW) of the Fe Ka with the ionization parameter. The maximum value of the EW is approx. 800 eV for models with log Epsilon approx. 1.5, and decreases monotonically as Epsilon increases. For lower values of Epsilon the Fe K(alpha) EW decreases to a minimum near log Epsilon approx. 0.8. We produce simulated CCD observations based on our reflection models. For low ionized, reflection dominated cases, the 2 -10 keV energy region shows a very broad, curving continuum that cannot be represented by a simple power-law. We show that in addition to the Fe K-shell emission, there are other prominent features such as the Si and S L(alpha) lines, a blend of Ar VIII-XI lines, and the Ca x K(alpha) line. In some cases the S xv blends with the He-like Si RRC producing a broad feature that cannot be reproduced by a simple Gaussian profile. This could be used as a signature of reflection.

  4. X-ray Absorption Spectroscopy and Coherent X-ray Diffraction Imaging for Time-Resolved Investigation of the Biological Complexes: Computer Modelling towards the XFEL Experiment

    NASA Astrophysics Data System (ADS)

    Bugaev, A. L.; Guda, A. A.; Yefanov, O. M.; Lorenz, U.; Soldatov, A. V.; Vartanyants, I. A.

    2016-05-01

    The development of the next generation synchrotron radiation sources - free electron lasers - is approaching to become an effective tool for the time-resolved experiments aimed to solve actual problems in various fields such as chemistry’ biology’ medicine’ etc. In order to demonstrate’ how these experiments may be performed for the real systems to obtain information at the atomic and macromolecular levels’ we have performed a molecular dynamics computer simulation combined with quantum chemistry calculations for the human phosphoglycerate kinase enzyme with Mg containing substrate. The simulated structures were used to calculate coherent X-ray diffraction patterns’ reflecting the conformational state of the enzyme, and Mg K-edge X-ray absorption spectra, which depend on the local structure of the substrate. These two techniques give complementary information making such an approach highly effective for time-resolved investigation of various biological complexes, such as metalloproteins or enzymes with metal-containing substrate, to obtain information about both metal-containing active site or substrate and the atomic structure of each conformation.

  5. Isotope effects in liquid water probed by transmission mode x-ray absorption spectroscopy at the oxygen K-edge.

    PubMed

    Schreck, Simon; Wernet, Philippe

    2016-09-14

    The effects of isotope substitution in liquid water are probed by x-ray absorption spectroscopy at the O K-edge as measured in transmission mode. Confirming earlier x-ray Raman scattering experiments, the D2O spectrum is found to be blue shifted with respect to H2O, and the D2O spectrum to be less broadened. Following the earlier interpretations of UV and x-ray Raman spectra, the shift is related to the difference in ground-state zero-point energies between D2O and H2O, while the difference in broadening is related to the difference in ground-state vibrational zero-point distributions. We demonstrate that the transmission-mode measurements allow for determining the spectral shapes with unprecedented accuracy. Owing in addition to the increased spectral resolution and signal to noise ratio compared to the earlier measurements, the new data enable the stringent determination of blue shift and broadening in the O K-edge x-ray absorption spectrum of liquid water upon isotope substitution. The results are compared to UV absorption data, and it is discussed to which extent they reflect the differences in zero-point energies and vibrational zero-point distributions in the ground-states of the liquids. The influence of the shape of the final-state potential, inclusion of the Franck-Condon structure, and differences between liquid H2O and D2O resulting from different hydrogen-bond environments in the liquids are addressed. The differences between the O K-edge absorption spectra of water from our transmission-mode measurements and from the state-of-the-art x-ray Raman scattering experiments are discussed in addition. The experimentally extracted values of blue shift and broadening are proposed to serve as a test for calculations of ground-state zero-point energies and vibrational zero-point distributions in liquid H2O and D2O. This clearly motivates the need for new calculations of the O K-edge x-ray absorption spectrum of liquid water. PMID:27634266

  6. Isotope effects in liquid water probed by transmission mode x-ray absorption spectroscopy at the oxygen K-edge

    NASA Astrophysics Data System (ADS)

    Schreck, Simon; Wernet, Philippe

    2016-09-01

    The effects of isotope substitution in liquid water are probed by x-ray absorption spectroscopy at the O K-edge as measured in transmission mode. Confirming earlier x-ray Raman scattering experiments, the D2O spectrum is found to be blue shifted with respect to H2O, and the D2O spectrum to be less broadened. Following the earlier interpretations of UV and x-ray Raman spectra, the shift is related to the difference in ground-state zero-point energies between D2O and H2O, while the difference in broadening is related to the difference in ground-state vibrational zero-point distributions. We demonstrate that the transmission-mode measurements allow for determining the spectral shapes with unprecedented accuracy. Owing in addition to the increased spectral resolution and signal to noise ratio compared to the earlier measurements, the new data enable the stringent determination of blue shift and broadening in the O K-edge x-ray absorption spectrum of liquid water upon isotope substitution. The results are compared to UV absorption data, and it is discussed to which extent they reflect the differences in zero-point energies and vibrational zero-point distributions in the ground-states of the liquids. The influence of the shape of the final-state potential, inclusion of the Franck-Condon structure, and differences between liquid H2O and D2O resulting from different hydrogen-bond environments in the liquids are addressed. The differences between the O K-edge absorption spectra of water from our transmission-mode measurements and from the state-of-the-art x-ray Raman scattering experiments are discussed in addition. The experimentally extracted values of blue shift and broadening are proposed to serve as a test for calculations of ground-state zero-point energies and vibrational zero-point distributions in liquid H2O and D2O. This clearly motivates the need for new calculations of the O K-edge x-ray absorption spectrum of liquid water.

  7. 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.

  8. Near-infrared photoluminescence and ligand K-edge x-ray absorption spectroscopies of AnO2Cl42-(An:u, NP, Pu)

    SciTech Connect

    Wilkerson, Marianne P; Berg, John M; Clark, David L; Conradson, Steven D; Hobart, David E; Kozimor, Stosh A; Scott, Brian L

    2008-01-01

    We have used photoluminescence and X-ray absorption spectroscopies to investigate electronic structures and metal-ligand bonding of a series of An02CI/ ' (An = U, Np, Pu) compounds. Specifically, we will discuss time-resolved near-infrared emission spectra of crystalline Cs2U(An)02C14 (An = Np and Pu) both at 23 K and 75 K, as well as chlorine Kedge X-ray absorption spectra ofCs2An02CI4 (An = U, Np).

  9. Spectra Transmitted by Mortar Barite in x-ray Qualities Applied in Diagnostic Radiology as Shielding

    NASA Astrophysics Data System (ADS)

    Almeida, A. T., Jr.; Araújo, F. G. S.; Nogueira, M. S.; Santos, M. A. P.

    2016-07-01

    Concrete which contains water, cement and aggregate, is widely used in building construction such as medical hospitals. The CdZnTe spectrometry system was used to acquire the transmitted spectra in the RQR qualities and the stripping procedure was performed by taking into account both the contributions of efficiency and x-ray escape fraction, experimentally determined. The samples were prepared in rectangular plate format with dimensions of (5 x 5) cm with thicknesses varying from 0.2cm to 2cm and exposed to x-ray beams generated. The HVL and the mean energy in this energy range was determined.

  10. KEMP: A program script for automated biological x-ray absorption spectroscopy data reduction

    SciTech Connect

    Korbas, Malgorzata; Fulla Marsa, Daniel; Meyer-Klaucke, Wolfram

    2006-06-15

    Automation of x-ray absorption spectroscopic (XAS) data reduction is essential to cope with high-throughput data collection becoming available at an increasing number of synchrotron radiation centers. A flexible script called KEMP has been developed and implemented at the XAS beamline at EMBL Hamburg. It automatically processes fluorescence XAS data. The pipeline includes dead time correction, energy calibration, selection of fluorescence detector channels, as well as the extraction of x-ray absorption near-edge structure and extended x-ray-absorption fine structure. The output is quickly available and thus can be included in the design of further experiments, which results in a more efficient use of the beam time.

  11. Normal incidence X-ray telescope power spectra of X-ray emission from solar active regions. I - Observations. II - Theory

    NASA Technical Reports Server (NTRS)

    Gomez, Daniel O.; Martens, Petrus C. H.; Golub, Leon

    1993-01-01

    Fourier analysis is applied to very high resolution image of coronal active regions obtained by the Normal Incidence X-Ray Telescope is used to find a broad isotropic power-law spectrum of the spatial distribution of soft X-ray intensities. Magnetic structures of all sizes are present down to the resolution limit of the instrument. Power spectra for the X-ray intensities of a sample of topologically different active regions are found which fall off with increasing wavenumber as 1/k-cubed. A model is presented that relates the basic features of coronal magnetic fluctuations to the subphotospheric hydrodynamic turbulence that generates them. The model is used to find a theoretical power spectrum for the X-ray intensity which falls off with increasing wavenumber as 1/k-cubed. The implications of a turbulent regime in active regions are discussed.

  12. Americium characterization by X-ray fluorescence and absorption spectroscopy in plutonium uranium mixed oxide

    SciTech Connect

    Degueldre, Claude Cozzo, Cedric; Martin, Matthias; Grolimund, Daniel; Mieszczynski, Cyprian

    2013-06-01

    Plutonium uranium mixed oxide (MOX) fuels are currently used in nuclear reactors. The actinides in these fuels need to be analyzed after irradiation for assessing their behaviour with regard to their environment and the coolant. In this work the study of the atomic structure and next-neighbour environment of Am in the (Pu,U)O₂ lattice in an irradiated (60 MW d kg⁻¹) MOX sample was performed employing micro-X-ray fluorescence (µ-XRF) and micro-X-ray absorption fine structure (µ-XAFS) spectroscopy. The chemical bonds, valences and stoichiometry of Am (~0.66 wt%) are determined from the experimental data gained for the irradiated fuel material examined in its peripheral zone (rim) of the fuel. In the irradiated sample Am builds up as Am³⁺ species within an [AmO₈]¹³⁻ coordination environment (e.g. >90%) and no (<10%) Am(IV) or (V) can be detected in the rim zone. The occurrence of americium dioxide is avoided by the redox buffering activity of the uranium dioxide matrix. - Graphical abstract: Americium LIII XAFS spectra recorded for the irradiated MOX sub-sample in the rim zone for a 300 μm×300 μm beam size area investigated over six scans of 4 h. The records remain constant during multi-scan. The analysis of the XAFS signal shows that Am is found as trivalent in the UO₂ matrix. This analytical work shall open the door of very challenging analysis (speciation of fission product and actinides) in irradiated nuclear fuels. - Highlights: • Americium was characterized by microX-ray absorption spectroscopy in irradiated MOX fuel. • The americium redox state as determined from XAS data of irradiated fuel material was Am(III). • In the sample, the Am³⁺ face an AmO₈¹³⁻coordination environment in the (Pu,U)O₂ matrix. • The americium dioxide is reduced by the uranium dioxide matrix.

  13. Ab Initio Calculations of X-ray Spectra: Atomic Multiplet and Molecular Orbital Effects in a Multiconfigurational SCF Approach to the L-Edge Spectra of Transition Metal Complexes.

    PubMed

    Josefsson, Ida; Kunnus, Kristjan; Schreck, Simon; Föhlisch, Alexander; de Groot, Frank; Wernet, Philippe; Odelius, Michael

    2012-12-01

    A new ab initio approach to the calculation of X-ray spectra is demonstrated. It combines a high-level quantum chemical description of the chemical interactions and local atomic multiplet effects. We show here calculated L-edge X-ray absorption (XA) and resonant inelastic X-ray scattering spectra for aqueous Ni(2+) and XA spectra for a polypyridyl iron complex. Our quantum chemical calculations on a high level of accuracy in a post-Hartree-Fock framework give excellent agreement with experiment. This opens the door to reliable and detailed information on chemical interactions and the valence electronic structure in 3d transition-metal complexes also in transient excited electronic states. As we combine a molecular-orbital description with a proper treatment of local atomic electron correlation effects, our calculations uniquely allow, in particular, identifying the influence of interatomic chemical interactions versus intra-atomic correlations in the L-edge X-ray spectra.

  14. Characterization of neutron yield and x-ray spectra of a High Flux Neutron Generator (HFNG)

    NASA Astrophysics Data System (ADS)

    Nnamani, Nnaemeka; HFNG Collaboration

    2015-04-01

    The High Flux Neutron Generator (HFNG) is a DD plasma-based source, with a self-loading target intended for fundamental science and engineering applications, including 40 Ar/39 Ar geochronology, neutron cross section measurements, and radiation hardness testing of electronics. Our first estimate of the neutron yield, based on the population of the 4.486 hour 115 In isomer gave a neutron yield of the order 108 n/sec; optimization is ongoing to achieve the design target of 1011 n/sec. Preliminary x-ray spectra showed prominent energy peaks which are likely due to atomic line-emission from back-streaming electrons accelerated up to 100 keV impinging on various components of the HFNG chamber. Our x-ray and neutron diagnostics will aid us as we continue to evolve the design to suppress back-streaming electrons, necessary to achieve higher plasma beam currents, and thus higher neutron flux. This talk will focus on the characterization of the neutron yield and x-ray spectra during our tests. A collimation system is being installed near one of the chamber ports for improved observation of the x-ray spectra. This work is supported by NSF Grant No. EAR-0960138, U.S. DOE LBNL Contract No. DE-AC02-05CH11231, U.S. DOE LLNL Contract No. DE-AC52-07NA27344, and the UC Office of the President Award 12-LR-238745.

  15. Analysis of neon soft x-ray spectra from short-pulse laser-produced plasmas

    SciTech Connect

    Abare, A.C.; Keane, C.J.; Crane, J.K.; DaSilva, L.B.; Lee, R.W.; Perry, M.D.; Falcone, R.W.

    1993-04-01

    We report preliminary results from the analysis of streaked soft x-ray neon spectra obtained from the interaction of a picosecond Nd:glass laser with a gas jet target. In these experiments streaked spectra show prompt harmonic emission followed by longer time duration soft x-ray line emission. The majority of the line emission observed was found to originate from Li- and Be-like Ne and the major transitions in the observed spectra have been identified. Li-like emission lines were observed to decay faster in time than Be-like transitions, suggesting that recombination is taking place. Line ratios of n=4-2 and n=3-2 transitions supported the view that these lines were optically thin and thick, respectively. The time history of Li-like Ne 2p-4d and 2p-3d lines is in good agreement with a simple adiabatic expansion model coupled to a time dependent collisional-radiative code. Further x-ray spectroscopic analysis is underway which is aimed at diagnosing plasma conditions and assessing the potential of this recombining neon plasma as a quasi-steady-state recombination x-ray laser medium.

  16. Analysis of neon soft x-ray spectra from short-pulse laser-produced plasmas

    NASA Astrophysics Data System (ADS)

    Abare, Amber C.; Keane, Christopher J.; Crane, John K.; Da Silva, Luiz B.; Lee, Richard W.; Perry, Michael D.; Falcone, Roger W.

    1993-07-01

    We report preliminary results from the analysis of streaked soft x-ray neon spectra obtained from the interaction of a picosecond Nd:glass laser with a gas jet target. In these experiments streaked spectra show prompt harmonic emission followed by longer time duration soft x-ray line emission. The majority of the line emission observed was found to originate from Li- and Be-like Ne and the major transitions in the observed spectra have been identified. Li-like emission lines were observed to decay faster in time than Be-like transitions, suggesting that recombination is taking place. Line ratios of n equals 4 - 2 and n equals 3 - 2 transitions supported the view that these lines were optically thin and thick, respectively. The time history of Li-like Ne 2p-4d and 2p-3d lines is in good agreement with a simple adiabatic expansion model coupled to a time dependent collisional-radiative code. Further x-ray spectroscopic analysis is underway which is aimed at diagnosing plasma conditions and assessing the potential of this recombining neon plasma as a quasi-steady-state recombination x-ray laser medium.

  17. Determination of X-ray excitation spectra in micro X-ray fluorescence spectrometry with capillary optics

    NASA Astrophysics Data System (ADS)

    Perez, R. D.; Sosa, C.; Sbarato, V.; Leani, J.; Sánchez, H. J.

    2016-03-01

    The quantitative X-ray fluorescence microanalysis by fundamental parameters requires the knowledge of the energy distribution of the excitation beam. When this beam is produced by capillary optics, its high intensity and anisotropy complicate a direct determination. An alternative is an indirect determination based on measurement of induced X-ray fluorescence in a set of targets. In this work the X-ray excitation spectrum is determined by an iterative deconvolution process of the fundamental parameter expression for the X-ray fluorescence intensities. The method has the advantage that it does not require any assumption about the energy distribution of the X-ray source or the energy dependence of the lens transmission. Numerous XRF targets of pure elements with emission lines covering the full energy range of the X-ray source are employed. The only requirement on the targets is a high homogeneity in its composition. In fact, it does not impose any condition on the sample thickness. The accuracy observed in the validation process implemented with reference materials is similar to that reported with alternative approaches: 5% for main components, 10% for minor elements and 15% for trace elements.

  18. X-Ray Spectra from MHD Simulations of Accreting Black Holes

    NASA Technical Reports Server (NTRS)

    Schnittman, Jeremy D.; Noble, Scott C.; Krolik, Julian H.

    2011-01-01

    We present new global calculations of X-ray spectra from fully relativistic magneto-hydrodynamic (MHO) simulations of black hole (BH) accretion disks. With a self consistent radiative transfer code including Compton scattering and returning radiation, we can reproduce the predominant spectral features seen in decades of X-ray observations of stellar-mass BHs: a broad thermal peak around 1 keV, power-law continuum up to >100 keV, and a relativistically broadened iron fluorescent line. By varying the mass accretion rate, different spectral states naturally emerge: thermal-dominant, steep power-law, and low/hard. In addition to the spectral features, we briefly discuss applications to X-ray timing and polarization.

  19. Data management and visualization of x-ray diffraction spectra from thin film ternary composition spreads

    SciTech Connect

    Takeuchi, I.; Long, C.J.; Famodu, O.O.; Murakami, M.; Hattrick-Simpers, J.; Rubloff, G.W.; Stukowski, M.; Rajan, K.

    2005-06-15

    We discuss techniques for managing and visualizing x-ray diffraction spectrum data for thin film composition spreads which map large fractions of ternary compositional phase diagrams. An in-house x-ray microdiffractometer is used to obtain spectra from over 500 different compositions on an individual spread. The MATLAB software is used to quickly organize the data and create various plots from which one can quickly grasp different information regarding structural and phase changes across the composition spreads. Such exercises are valuable in rapidly assessing the 'overall' picture of the structural evolution across phase diagrams before focusing in on specific composition regions for detailed structural analysis. We have also shown that simple linear correlation analysis of the x-ray diffraction peak information (position, intensity and full width at half maximum) and physical properties such as magnetization can be used to obtain insight about the physical properties.

  20. 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

  1. Direct measurement of mammographic x-ray spectra using a CdZnTe detector.

    PubMed

    Matsumoto, M; Yamamoto, A; Honda, I; Taniguchi, A; Kanamori, H

    2000-07-01

    Our purpose is to directly measure mammographic x-ray spectra with collimators and a low-efficiency CdZnTe detector developed recently and to find out the best fit response function of CdZnTe detector to correct the measured spectra. Photon spectra (target Mo or Rh) produced by a mammographic x-ray unit at 25-32 kV and 240 mAs (= 3 times of 80 mAs) and transmitted through 0.03 mm Mo or 0.025 mm Rh filter and object (0.1 mm Al to 0.8 mm Al phantoms) have been analyzed. Since detected spectra were distorted by the response of CdZnTe detector and did not present the true photon spectra, the correction was applied by the stripping procedure. The response function of detector used in this procedure has been determined by the evaluation of interactions (K-escape, coherent scattering, and Compton scattering processes) and incomplete charge collection calculated using the Monte Carlo method. We have used Kalpha1, Kalpha2, Kbeta1, Kbeta2 radiations of Cd, Zn, and Te, respectively and have used the weight function for the incomplete charge collection and have considered Compton scattering. The Monte Carlo simulations were continued by changing the important factors (mean path length of hole lambda(h), dead layer of the CZT crystal and weight factor Wq) of incomplete charge collection until the best fit response function was found out. Corrected photon spectra were compared with the mammographic x-ray spectral data of Bureau of Radiological Health (BRH) measured using a Ge detector. Attenuation curves of aluminum for 25-32 kV were calculated from the corrected photon spectra and compared with the attenuation curves measured using an ionization chamber. These results obtained using the CdZnTe detector agreed with the mammographic x-ray spectral data of BRH and attenuation curves obtained by the ionization chamber.

  2. Comparison of hard and soft x-ray photoelectron spectra of silicon

    NASA Astrophysics Data System (ADS)

    Offi, F.; Werner, W. S. M.; Sacchi, M.; Torelli, P.; Cautero, M.; Cautero, G.; Fondacaro, A.; Huotari, S.; Monaco, G.; Paolicelli, G.; Smekal, W.; Stefani, G.; Panaccione, G.

    2007-08-01

    A detailed comparison of the surface sensitivity of x-ray photoemission spectroscopy for hard and soft x rays is presented and discussed. Electron scattering parameters and their energy dependence are given for Si and two Si spectra are analyzed: a MgKα (hν=1253.6eV) excited spectrum of the Si2p and 2s lines and a hard x-ray excited spectrum (hν=5925eV) of the Si1s line. The differential inelastic scattering characteristics for Si are extracted from reflection electron energy loss spectra taken at energies of 1500 and 4000eV . Using these scattering characteristics and electron mean free paths from the literature, simulated spectra are compared with experiment. The experimental spectra are deconvoluted to give the true intrinsic line shape corresponding to the theoretical collision statistics when interference effects between intrinsic and extrinsic scattering are neglected. The magnitude of interference effects cannot be assessed by our analysis. Within the (unknown) uncertainty introduced by neglecting interference effects, it is possible to determine the relative intensity of intrinsic and extrinsic excitations. In this way, it is found that in the case of the soft x-ray excited photoelectron spectrum of the shallower electronic shells ( 2p and 2s ), intrinsic plasmon creation is rather weak, and the apparent asymmetric line shape of the spectrum might be interpreted as the fact that electron-hole pair creation dominates the intrinsic loss spectrum, while an alternative explanation in terms of surface core level shifted components is also proposed. For the deeper core electronic shell, probed with hard x rays, the opposite situation is observed: while intrinsic electron-hole pair creation was not observed, a strong contribution of intrinsic plasmon losses of about 30% was seen.

  3. Modeling of the EUV and X-Ray Emission Spectra Induced by the Solar Winds Ions in the Heliosphere

    NASA Technical Reports Server (NTRS)

    Kharchenko, Vasili

    2005-01-01

    We have carried out investigation of the EUV and X-ray emission spectra induced in interaction between the Solar Wind (SW) and interstellar neutral gas. The spectra of most important SW ions have been computed for the charge-exchange mechanism of X-ray emission using new accurate spectroscopic data from recent laboratory measurements and theoretical calculations. Total spectra have been constructed as a sum of spectra induced in the charge-exchange collisions by individual O(exp q+), C(exp q+), N(exp q+), Ne(exp q+), Mg (exp q+) and Fe(exp q+) ions. Calculations have been performed for X-ray emission from the heliospheric hydrogen and helium gas. X-ray maps of the heliosphere have been computed. The power density of X-ray sources in the heliospheric ecliptic plane is shown for the H gas and for the He gas. Distances from the Sun (0,0) are given in AU. The helium cone is clear seen in the X-ray map of the charge-exchange emission induced by the solar wind. X-ray emission spectra detected by the Chandra X-ray telescope from the "dark" side of Moon has been identified as a X-ray background emission induced by the solar wind from the geocorona. Spectra and intensities of this charge-exchange X-rays have been compared with the heliospheric component of the X-ray background. Observations and modeling of the SW spectra induced from the geocorona indicate a strong presence of emission lines of highly charged oxygen ions. Anisotropy in distribution of heliospheric X-rays has been predicted and calculated for the regions of the fast and slow solar winds.

  4. 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.

  5. 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

  6. Electronic Structure of Manganites Determined by Spin-Polarized X-Ray Absorption Spectroscopy

    NASA Astrophysics Data System (ADS)

    Qian, Qing; Tyson, Trevor; Savrassov, S.; Kao, C.-C.; Croft, M.

    2003-03-01

    A systematic study of spin dependent Mn K-edge x-ray absorption spectra was performed on La_1-xCa_xMnO3 and other Mn oxide systems. A model was developed to predict the temperature dependent changes in the local magnetic ordering based on changes in spin-polarized Mn K-Edge measurements. With this model, one can ascertain the change of local ordering that occurs on transiting the magnetic ordering temperature. Parallel LDA and LDA+U computations are used to label the symmetries of the unoccupied bands, determine the degree of electron correlation and to provide a direct comparison with the band ordering predicted by the temperature dependent spin-polarized measurements. The spin magnetic moment and ordering of the t_2g and eg states are also determined. We find that the occupied t_2g orbitals are always ordered with lobes near 45° to the local Mn-O directions. The Mn K-Edge main line splitting is discussed in terms of the effective spin-polarized charge density. Comparison with bandstructure computations are made. The oxygen hole contribution to the net magnetic moment is seen to be important. We survey the spin-polarized XANES spectra of a large group of manganese oxides showing the general trends in the main line spin splitting as a function of valence. This work is supported by NSF Career Grant DMR-9733862 and DMR-0216858.

  7. 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.

  8. X-ray atomic absorption of cesium and xenon in the L-edge region

    SciTech Connect

    Kodre, A.; Padeznik Gomilsek, J.; Arcon, I.; Aquilanti, G.

    2010-08-15

    X-ray absorption of atomic cesium is measured in the L-edge region, using a beryllium-window cell for cesium vapor. For comparison, absorption in Xe gas in the same energy region is remeasured with improved signal-to-noise ratio. By combining deconvolution and modeling, the edge profiles are studied to determine the threshold energies and the shape of the edge apex with exponential slope of the high-energy flank. In both elements, multielectron excitations show the same basic ordering in compact groups, largely independent of the core-hole subshell, following the energy sequence of coexcited valence and subvalence orbitals. The main effect of 6s electron in Cs, apart from 2(s,p)6s excitation, is the enhancement of single- as well as some multielectron resonant channels. The spectra of both elements show the ''polarization effect'': a convex basic curvature of the L{sub 2} and L{sub 3} segments, a concave L{sub 1} segment. Previously, Kutzner demonstrated a convincing theoretical explanation of the effect on Xe in a relativistic random-phase approximation with relaxation involving overlap integrals with continuum [Rad. Phys. Chem. 70, 95 (2004)].

  9. Study on the Coordination Structure of Pt Sorbed on Bacterial Cells Using X-Ray Absorption Fine Structure Spectroscopy

    PubMed Central

    Tanaka, Kazuya; Watanabe, Naoko

    2015-01-01

    Biosorption has been intensively investigated as a promising technology for the recovery of precious metals from solution. However, the detailed mechanism responsible for the biosorption of Pt on a biomass is not fully understood because of a lack of spectroscopic studies. We applied X-ray absorption fine structure spectroscopy to elucidate the coordination structure of Pt sorbed on bacterial cells. We examined the sorption of Pt(II) and Pt(IV) species on bacterial cells of Bacillus subtilis and Shewanella putrefaciens in NaCl solutions. X-ray absorption near-edge structure and extended X-ray absorption fine structure (EXAFS) of Pt-sorbed bacteria suggested that Pt(IV) was reduced to Pt(II) on the cell’s surface, even in the absence of an organic material as an exogenous electron donor. EXAFS spectra demonstrated that Pt sorbed on bacterial cells has a fourfold coordination of chlorine ions, similar to PtCl42-, which indicated that sorption on the protonated amine groups of the bacterial cells. This work clearly demonstrated the coordination structure of Pt sorbed on bacterial cells. The findings of this study will contribute to the understanding of Pt biosorption on biomass, and facilitate the development of recovery methods for rare metals using biosorbent materials. PMID:25996945

  10. 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.

  11. 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.

  12. Hard X-ray photoelectron and X-ray absorption spectroscopy characterization of oxidized surfaces of iron sulfides

    NASA Astrophysics Data System (ADS)

    Mikhlin, Yuri; Tomashevich, Yevgeny; Vorobyev, Sergey; Saikova, Svetlana; Romanchenko, Alexander; Félix, Roberto

    2016-11-01

    Hard X-ray photoelectron spectroscopy (HAXPES) using an excitation energy range of 2 keV to 6 keV in combination with Fe K- and S K-edge XANES, measured simultaneously in total electron (TEY) and partial fluorescence yield (PFY) modes, have been applied to study near-surface regions of natural polycrystalline pyrite FeS2 and pyrrhotite Fe1-xS before and after etching treatments in an acidic ferric chloride solution. It was found that the following near-surface regions are formed owing to the preferential release of iron from oxidized metal sulfide lattices: (i) a thin, no more than 1-4 nm in depth, outer layer containing polysulfide species, (ii) a layer exhibiting less pronounced stoichiometry deviations and low, if any, concentrations of polysulfide, the composition and dimensions of which vary for pyrite and pyrrhotite and depend on the chemical treatment, and (iii) an extended almost stoichiometric underlayer yielding modified TEY XANES spectra, probably, due to a higher content of defects. We suggest that the extended layered structure should heavily affect the near-surface electronic properties, and processes involving the surface and interfacial charge transfer.

  13. Direct Measurement of Mammographic X-Ray Spectra with a Digital CdTe Detection System

    PubMed Central

    Abbene, Leonardo; Gerardi, Gaetano; Principato, Fabio; Sordo, Stefano Del; Raso, Giuseppe

    2012-01-01

    In this work we present a detection system, based on a CdTe detector and an innovative digital pulse processing (DPP) system, for high-rate X-ray spectroscopy in mammography (1–30 keV). The DPP system performs a height and shape analysis of the detector pulses, sampled and digitized by a 14-bit, 100 MHz ADC. We show the results of the characterization of the detection system both at low and high photon counting rates by using monoenergetic X-ray sources and a nonclinical X-ray tube. The detection system exhibits excellent performance up to 830 kcps with an energy resolution of 4.5% FWHM at 22.1 keV. Direct measurements of clinical molybdenum X-ray spectra were carried out by using a pinhole collimator and a custom alignment device. A comparison with the attenuation curves and the half value layer values, obtained from the measured and simulated spectra, from an ionization chamber and from a solid state dosimeter, also shows the accuracy of the measurements. These results make the proposed detection system a very attractive tool for both laboratory research, calibration of dosimeters and advanced quality controls in mammography. PMID:22969406

  14. 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.

  15. Comprehensive X-Ray Absorption Models for Oxygen and Neon

    NASA Astrophysics Data System (ADS)

    Gorczyca, Thomas

    2013-09-01

    We propose to perform state-of-the-art R-matrix calculations for the oxygen and neon photoabsorption cross sections to improve upon earlier, incomplete data. Several important higher-order effects will be addressed: orbital relaxation, Auger line broadening, two-electron shake, and elimination of pseudoresonances. The computed atomic cross sections will first be fit by a recently-developed analytical fitting formula, and then benchmarked further to experimental and Chandra observed absorption lines. The resulting data will be uploaded into the AtomDB, XSPEC, and ISIS databases for spectral modeling use. These definitive cross sections will resolve an outstanding discrepancy between XSTAR and SPEX spectral modeling predictions of molecular (dust and/or ice) abundances in the ISM.

  16. The Galactic plane at faint X-ray fluxes - II. Stacked X-ray spectra of a sample of serendipitous XMM-Newton sources

    NASA Astrophysics Data System (ADS)

    Warwick, R. S.; Byckling, K.; Pérez-Ramírez, D.

    2014-03-01

    We have investigated the X-ray spectral properties of a sample of 138 X-ray sources detected serendipitously in XMM-Newton observations of the Galactic plane, at an intermediate to faint flux level. We divide our sample into five subgroups according to the spectral hardness of the sources, and stack (i.e. co-add) the individual source spectra within each subgroup. As expected these stacked spectra show a softening trend from the hardest to the softest subgroups, which is reflected in the inferred line-of-sight column density. The spectra of the three hardest subgroups are characterized by a hard continuum plus superimposed Fe-line emission in the 6-7 keV bandpass. The average equivalent width (EW) of the 6.7-keV He-like Fe Kα line is 170^{+35}_{-32} eV, whereas the 6.4-keV Fe K fluorescence line from neutral iron and the 6.9-keV H-like Fe Lyα line have EWs of 89^{+26}_{-25} and 81^{+30}_{-29} eV, respectively, i.e. roughly half that of the 6.7-keV line. The remaining subgroups exhibit soft thermal spectra. Virtually all of the spectrally soft X-ray sources can be associated with relatively nearby coronally active late-type stars, which are evident as bright near-infrared (NIR) objects within the X-ray error circles. On a similar basis only a minority of the spectrally hard X-ray sources have likely NIR identifications. The average continuum and Fe-line properties of the spectrally hard sources are consistent with those of magnetic cataclysmic variables but the direct identification of large numbers of such systems in Galactic X-ray surveys, probing intermediate to faint flux levels, remains challenging.

  17. WITS-HEX: A renovated code for analysis of PIXE X-ray spectra

    NASA Astrophysics Data System (ADS)

    Lipworth, A. D.; Annegarn, H. J.; Bauman, S.; Molokomme, T.; Walker, A. J.

    1990-04-01

    The code REX [H.C. Kaufmann and K.R. Akselsson, Adv. X-ray Anal. 18 (1975) 353] and its successor, HEX were developed at Florida State University and University of Lund in the early seventies for quantitative reduction of PIXE spectra. HEX modelled many of the physical processes, including target self-absorption. Lack of adequate documentation and several inherent software related problems hampered widespread adoption and further development. HEX was designed using a hierarchical functional design approach, coded in FORTRAN IV. Its element library and request list are tightly constrained. ANSI standard FORTRAN provides few structured constructs, nor does it support dynamic data structures. HEX has a batch mode of interaction which affords minimal (interim) user interactions. To overcome these limitations we have modernised the program to run on IBM PC compatible computers by using object-oriented design techniques, documented in Program Description Language (pseudo-code) and implemented in a modern programming language, Pascal. Turbo Pascal 5.5 provides an integrated program development environment, a high resolution graphics library, an operating system interface and many software development tools to improve programmer productivity. A menu-based highly interactive screen management library is used for the user interface. A demonstration version is available for user evaluation. Further rigorous testing and the development of user acquired spectra interfacing code will be developed before the first release. The renovated code, WITS-HEX, has extracted the intellectual value embodied in HEX. It will be inherently more stable, reliable, versatile, maintainable and easy to use to facilitate future process modifications.

  18. Recovery of x-ray absorption spectral profile in etched TiO{sub 2} thin films

    SciTech Connect

    Sano, Keiji; Niibe, Masahito; Kawakami, Retsuo; Nakano, Yoshitaka

    2015-05-15

    Near edge x-ray absorption fine structure (NEXAFS) spectra of plasma-etched TiO{sub 2} thin films were observed using the total fluorescence yield method involving visible emission. The disrupted spectrum recovered its as-grown (nonetched) profile, upon soft x-ray (SX) irradiation. This recovery was investigated by ultraviolet (UV) irradiation, spatial distribution measurements, exposing recovered samples to air, and NEXAFS measurements of ultrafine TiO{sub 2} particles. The spectral profile recovered upon UV irradiation, and at sample positions outside of the SX irradiation site. The recovered spectral profiles were disrupted again, upon exposure to air. Nonetched ultrafine TiO{sub 2} particles also exhibited a disrupted spectral profile, which was recovered upon SX irradiation. The spectral recovery is explained by a model involving electrons trapped in oxygen vacancies generated by etching.

  19. Exploration of Heterogeneous Chemistry in Model Atmospheric Particles Using Extended X-ray Absorption Fine Structure Analysis

    SciTech Connect

    Bramante,J.; Hinrichs, R.; Brown, E.; Calvin, S.

    2007-01-01

    As models of the composition and heterogeneous chemical reactions of the troposphere undergo refinement, novel application of state-of-the-art analytical techniques will be necessary to propound realistic characterizations of mineral dust chemistry. In this study, strontium carbonate particles treated with gaseous nitric acid and nitrogen dioxide were examined with X-ray absorption fine structure analysis (EXAFS). The X-ray spectra of carbonate and nitrate standards were fitted to ab initio calculations, which were used to determine the structure and consistency of strontium nitrate formed on strontium carbonate. By examining differences in mean square radial displacement and lattice spacing values obtained for bulk Sr(NO3)2 as compared to Sr(NO3)2 formed on SrCO3, EXAFS proves effective as a tool for investigating the local structure and composition of heterogeneous aerosol particles. The implications of findings on reacted strontium carbonate for atmospheric models of calcium carbonate aerosol are discussed.

  20. Theoretical study of Raman chirped adiabatic passage by X-ray absorption spectroscopy: Highly excited electronic states and rotational effects

    SciTech Connect

    Engin, Selma; Sisourat, Nicolas Selles, Patricia; Taïeb, Richard; Carniato, Stéphane

    2014-06-21

    Raman Chirped Adiabatic Passage (RCAP) is an efficient method to climb the vibrational ladder of molecules. It was shown on the example of fixed-in-space HCl molecule that selective vibrational excitation can thus be achieved by RCAP and that population transfer can be followed by X-ray Photoelectron spectroscopy [S. Engin, N. Sisourat, P. Selles, R. Taïeb, and S. Carniato, Chem. Phys. Lett. 535, 192–195 (2012)]. Here, in a more detailed analysis of the process, we investigate the effects of highly excited electronic states and of molecular rotation on the efficiency of RCAP. Furthermore, we propose an alternative spectroscopic way to monitor the transfer by means of X-ray absorption spectra.

  1. New Chandra observations of the jet in 3C273. 1. Softer X-ray than radio spectra and the X-ray emission mechanism

    SciTech Connect

    Jester, Sebastian; Harris, D.E.; Marshall, H.L.; Meisenheimer, K.; /Heidelberg, Max Planck Inst. Astron.

    2006-05-01

    The jet in 3C273 is a high-power quasar jet with radio, optical and X-ray emission whose size and brightness allow a detailed study of the emission processes acting in it. We present deep Chandra observations of this jet and analyze the spectral properties of the jet emission from radio through X-rays. We find that the X-ray spectra are significantly softer than the radio spectra in all regions of the bright part of the jet except for the first bright ''knot A'', ruling out a model in which the X-ray emission from the entire jet arises from beamed inverse-Compton scattering of cosmic microwave background photons in a single-zone jet flow. Within two-zone jet models, we find that a synchrotron origin for the jet's X-rays requires fewer additional assumptions than an inverse-Compton model, especially if velocity shear leads to efficient particle acceleration in jet flows.

  2. Comptonization in a radiation-dominated shock, and the spectra of X-ray pulsars

    NASA Astrophysics Data System (ADS)

    Lyubarskij, Y. E.; Syunyaev, R. A.

    1982-10-01

    If a neutron star is accreting material at a high rate, much of the accretion energy will be released in a radiation-dominated shock. The radiation will arrest the plasma flow and withdraw energy. As the flow is braked, its electrons will multiply scatter the photons, forming distinctive radiation spectra and causing the electrons to become heated. The hard-photon tail in X-ray pulsar spectra is presumably formed by such a mechanism. These spectra have a small spectral index (alpha in the range between 0 and 1) and an exponential cutoff for (h) x (nu) approximately equal to or greater than 100 keV.

  3. 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.

  4. MAGNETOHYDRODYNAMIC MODELING OF THE ACCRETION SHOCKS IN CLASSICAL T TAURI STARS: THE ROLE OF LOCAL ABSORPTION IN THE X-RAY EMISSION

    SciTech Connect

    Bonito, R.; Argiroffi, C.; Peres, G.; Orlando, S.; Miceli, M.; Ibgui, L.; Matsakos, T.; Stehle, C.

    2014-11-10

    We investigate the properties of X-ray emission from accretion shocks in classical T Tauri stars (CTTSs), generated where the infalling material impacts the stellar surface. Both observations and models of the accretion process reveal several aspects that are still unclear: the observed X-ray luminosity in accretion shocks is below the predicted value, and the density versus temperature structure of the shocked plasma, with increasing densities at higher temperature, deduced from the observations, is at odds with that proposed in the current picture of accretion shocks. To address these open issues, we investigate whether a correct treatment of the local absorption by the surrounding medium is crucial to explain the observations. To this end, we describe the impact of an accretion stream on a CTTS by considering a magnetohydrodynamic model. From the model results, we synthesize the X-ray emission from the accretion shock by producing maps and spectra. We perform density and temperature diagnostics on the synthetic spectra, and we directly compare the results with observations. Our model shows that the X-ray fluxes inferred from the emerging spectra are lower than expected because of the complex local absorption by the optically thick material of the chromosphere and of the unperturbed stream. Moreover, our model, including the effects of local absorption, explains in a natural way the apparently puzzling pattern of density versus temperature observed in the X-ray emission from accretion shocks.

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

    NASA Astrophysics Data System (ADS)

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

    2012-01-01

    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.

  6. 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.

  7. Use of X-ray absorption spectroscopy in the search for the best LIGO mirror coatings

    NASA Astrophysics Data System (ADS)

    McGuire, Stephen C.

    2008-03-01

    The Laser Interferometer Gravitational-wave Observatory (LIGO) seeks to improve its sensitivity for gravity-wave detection by a factor of ten during its next phase of operation, Advanced LIGO. In order to achieve this goal it is necessary to design and fabricate test mass mirrors that help minimize the noise in the interferometers and in doing so maximize gravity-wave detection capability. In this talk we will present recent results from our program of X-ray absorption spectroscopy measurements to obtain detailed chemical composition and structure of titania (TiO2)-doped tantala (Ta2O5) multilayers fabricated via ion beam sputtering on SiO2 substrates. Our investigations focus on how the microscopic features of the coatings influence their macroscopic mechanical loss properties. Our goal is to obtain correlations between chemical impurities and/or dopants and the optical absorption and mechanical loss characteristics of these multilayer coatings. To examine our samples we use synchrotron-based X-ray absorption Spectroscopy (XAS) techniques including Extended X-ray Absorption Fine Structure (EXAFS), X-ray Absorption Near Edge Structure (XANES) and X-ray Fluorescence (XRF). We present chemical and structural data obtained at the titanium K-edge and tantalum LIII-edge as well as relative elemental distribution information (Ti/Ta, Fe/Ta, and Cr/Ta) obtained via XRF. Following a brief description of the LIGO experiment, our program of research in optical materials for use in advanced versions of the interferometer will be described.

  8. WAVELENGTH MEASUREMENTS OF K TRANSITIONS OF OXYGEN, NEON, AND MAGNESIUM WITH X-RAY ABSORPTION LINES

    SciTech Connect

    Liao Jinyuan; Zhang Shuangnan; Yao Yangsen

    2013-09-10

    Accurate atomic transition data are important in many astronomical research areas, especially for studies of line spectroscopy. Whereas transition data of He-like and H-like ions (i.e., ions in high-charge states) have been accurately calculated, the corresponding data of K transitions of neutral or low-ionized metal elements are still very uncertain. Spectroscopy of absorption lines produced in the interstellar medium (ISM) has been proven to be an effective way to measure the central wavelengths of these atomic transitions. In this work, we analyze 36 Chandra High Energy Transmission Grating observations to search for and measure the ISM absorption lines along sight lines to 11 low-mass X-ray binaries. We correct the Galactic rotation velocity to the rest frame for every observation and then use two different methods to merge all the corrected spectra to a co-added spectrum. However, the co-added spectra obtained by this method exhibit biases, toward to either observations with high counts or lines with high signal-to-noise ratios. We do a Bayesian analysis of several significantly detected lines to obtain the systematic uncertainty and the bias correction for other lines. Compared to previous studies, our results improve the wavelength accuracy by a factor of two to five and significantly reduce the systematic uncertainties and biases. Several weak transitions (e.g., 1s-2p of Mg IV and Mg V; 1s-3p of Mg III and Mg V) are also detected for the first time, albeit with low significance; future observations with improved accuracy are required to confirm these detections.

  9. X-Ray Absorption Spectroscopy Study of Copper Doped ZnO Thin Films

    SciTech Connect

    Ma Qing

    2007-02-02

    X-ray absorption spectroscopy technique is used to study copper-doped ZnO thin films, prepared by pulsed-laser deposition. The samples with various doping levels are examined. It is found that the samples contain metallic clusters with the sizes {<=} 2 nm as well as Cu1+ and Cu2+ states. The Cu1+ states exist as stable oxide clusters, while the Cu2+ ones participate in the ZnO lattice some of which may be pertaining to the surfaces of the Cu clusters as well. The copper clusters of {approx}1 nm are unstable and fragment under monochromatic x-ray beam illumination.

  10. 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.

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

    DOE PAGES

    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.

  12. X-ray absorption fine structure spectroscopic determination of plutonium speciation at the Rocky Flats environmental technology

    SciTech Connect

    Lezama-pacheco, Juan S; Conradson, Steven D; Clark, David L

    2008-01-01

    X-ray Absorption Fine Structure spectroscopy was used to probe the speciation of the ppm level Pu in thirteen soil and concrete samples from the Rocky Flats Environmental Technology Site in support of the site remediation effort that has been successfully completed since these measurements. In addition to X-ray Absorption Near Edge Spectra, two of the samples yielded Extended X-ray Absorption Fine Structure spectra that could be analyzed by curve-fits. Most of these spectra exhibited features consistent with PU(IV), and more specificaJly, PuO{sub 2+x}-type speciation. Two were ambiguous, possibly indicating that Pu that was originally present in a different form was transforming into PuO{sub 2+x}, and one was interpreted as demonstrating the presence of an unusual Pu(VI) compound, consistent with its source being spills from a PUREX purification line onto a concrete floor and the resultant extreme conditions. These experimental results therefore validated models that predicted that insoluble PuO{sub 2+x} would be the most stable form of Pu in equilibrium with air and water even when the source terms were most likely Pu metal with organic compounds or a Pu fire. A corollary of these models' predictions and other in situ observations is therefore that the minimal transport of Pu that occurred on the site was via the resuspension and mobilization of colloidal particles. Under these conditions, the small amounts of diffusely distributed Pu that were left on the site after its remediation pose only a negligible hazard.

  13. Characterization of selective binding of alkali cations with carboxylate by x-ray absorption spectroscopy of liquid microjets

    SciTech Connect

    Saykally, Richard J; Uejio, Janel S.; Schwartz, Craig P.; Duffin, Andrew M.; Drisdell, Walter S.; Cohen, Ronald C.; Saykally, Richard J.

    2008-01-08

    We describe an approach for characterizing selective binding between oppositely charged ionic functional groups under biologically relevant conditions. Relative shifts in K-shell x-ray absorption spectra of aqueous cations and carboxylate anions indicate the corresponding binding strengths via perturbations of carbonyl antibonding orbitals. XAS spectra measured for aqueous formate and acetate solutions containing lithium, sodium, and potassium cations reveal monotonically stronger binding of the lighter metals, supporting recent results from simulations and other experiments. The carbon K-edge spectra of the acetate carbonyl feature centered near 290 eV clearly indicate a preferential interaction of sodium versus potassium, which was less apparent with formate. These results are in accord with the Law of Matching Water Affinities, relating relative hydration strengths of ions to their respective tendencies to form contact ion pairs. Density functional theory calculations of K-shell spectra support the experimental findings.

  14. Determining x-ray spectra of radiographic sources with a Compton spectrometer

    NASA Astrophysics Data System (ADS)

    Gehring, Amanda E.; Espy, Michelle A.; Haines, Todd J.; Hunter, James F.; King, Nick S. P.; Manard, Manuel J.; Merrill, Frank E.; Morgan, George L.; Sedillo, Robert; Trainham, Rusty; Urbaitis, Algis V.; Volegov, Petr

    2014-09-01

    Flash radiography is a diagnostic with many physics applications, and the characterization of the energy spectra of such sources is of interest. A Compton spectrometer has been proposed to conduct these measurements. Our Compton spectrometer is a 300 kg neodymium-iron magnet constructed by Morgan et al1, and it is designed to measure spectra in the <1 MeV to 20 MeV range. In this device, the x-rays from a radiographic source are collimated into a narrow beam directed on a converter foil. The forward-selected Compton electrons that are ejected from the foil enter the magnetic field region of the spectrometer. The electrons are imaged on a focal plane, with their position determined as a function of their energy. The x-ray spectrum is then reconstructed. Challenges in obtaining these measurements include limited dose of x-rays and the short pulse duration (about 50 ns) for time-resolved measurements. Here we present energy calibration measurements of the spectrometer using a negative ion source. The resolution of the spectrometer was measured in previous calibration experiments to be the greater of 1% or 0.1 MeV/c1. The reconstruction of spectra from a bremsstrahlung source and Co-60 source are also presented.

  15. Mechanisms of mercury removal by biochars produced from different feedstocks determined using X-ray absorption spectroscopy.

    PubMed

    Liu, Peng; Ptacek, Carol J; Blowes, David W; Landis, Richard C

    2016-05-01

    Thirty-six biochars produced from distinct feedstocks at different temperatures were evaluated for their potential to remove mercury (Hg) from aqueous solution at environmentally relevant concentrations. Concentrations of total Hg (THg) decreased by >90% in batch systems containing biochars produced at 600 and 700 °C and by 40-90% for biochars produced at 300 °C. Elevated concentrations of SO4(2-) (up to 1000 mg L(-1)) were observed in solutions mixed with manure-based biochars. Sulfur X-ray absorption near edge structure (XANES) analyses indicate the presence of both reduced and oxidized S species in both unwashed and washed biochars. Sulfur XANES spectra obtained from biochars with adsorbed Hg were similar to those of washed biochars. Micro-X-ray fluorescence mapping results indicate that Hg was heterogeneously distributed across biochar particles. Extended X-ray absorption fine structure modeling indicates Hg was bound to S in biochars with high S content and to O and Cl in biochars with low S content. The predominant mechanisms of Hg removal are likely the formation of chemical bonds between Hg and various functional groups on the biochar. This investigation provides information on the effectiveness and mechanisms of Hg removal that is critical for evaluating biochar applications for stabilization of Hg in surface water, groundwater, soils, and sediments. PMID:26844404

  16. Non-equilibrium-state x-ray absorption spectroscopy: a local structure study of photo-induced phase transition

    NASA Astrophysics Data System (ADS)

    Oyanagi, H.; Tayagaki, T.; Tanaka, K.

    2003-01-01

    We describe non-equilibrium-state x-ray absorption spectroscopy focusing on local structure of photo-excited states trapped at low temperature. For this purpose, a novel Ge 100 pixel array detector with a packing density of 88% was developed. The local structure of photo-induced phase of Fe(II) spin crossover complex, [Fe(2-pic)3]Cl2EtOH (2-pic=2-aminomethyl pyridine), was investigated at low temperature (T <150 K). The use of pixel array detector and high-flux synchrotron x-ray source (multipole wiggler) successfully provided x-ray absorption spectra with high quality, in-situ, during the photo-excitation. It was found that the photo-induced phase under optical pumping at low temperature (T < 50 K) has an octahedral geometry with the elongated Fe-N distance (2.16 ± 0.01 Å), stabilizing the high spin state (S=2) configuration. No indication of symmetry breaking of FeN6 clusters upon LS↔HS spin-state switching was observed. It was demonstrated that the technique is a promising means to probe the local structure of non-equilibrium state such as trapped excited states or metastable states.

  17. X-ray magnetic circular dichroism and x-ray absorption spectroscopy of novel magnetic thin films

    SciTech Connect

    Brewer, M.A.; Ju, H.L.; Krishnan, K.M.

    1997-04-01

    The optimization of the magnetic properties of materials for a wide range of applications requires a dynamic iteration between synthesis, property measurements and characterization at appropriate length scales. The authors interest arises both from the increased appreciation of the degree to which magnetic properties can be influenced by tailored microstructures and the ability to characterize them by x-ray scattering/dichroism techniques. Preliminary results of this work at the ALS on `giant` moment in {alpha}{double_prime}-Fe{sub 16}N{sub 2} and `colossal` magnetoresistance in manganite perovskites is presented here. It has recently been claimed that {alpha}{double_prime}-Fe{sub 16}N{sub 2} possesses a giant magnetization of 2.9 T ({approximately}2300 emu/cc) when grown on lattice-matched In{sub 0.2}Ga{sub 0.8}As(001) and Fe/GaAs(001). However, attempts at growth on simpler substrates have resulted in only a modest enhancement in moment and often in multiphase mixtures. Theoretical calculations based on the band structure of Fe{sub 16}N{sub 2} predict values for the magnetization around 2.3 T ({approximately}1780 emu/cc), well below Sugita`s claims, but consistent with the magnetization reported by several other workers. Using appropriate sum rules applied to the integrated MCD spectrum, they hope to determine the magnetic moment of the iron species in the {alpha}{double_prime}-Fe{sub 16}N{sub 2} films and other phases and resolve the orbital and spin contributions to the moment. There is also rapidly growing interest in the `colossal magnetoresistance` effect observed in manganese oxides for both fundamental and commercial applications. To address some of these issues the authors have measured the electron energy loss spectra (EELS) of manganese perovskites at room temperature.

  18. Site partitioning of Cr3+ in the trichroic alexandrite BeAl2O4:Cr3+ crystal: contribution from x-ray absorption spectroscopy.

    PubMed

    Bordage, Amélie; Rossano, Stéphanie; Horn, Adolf Heinrich; Fuchs, Yves

    2012-06-01

    X-ray absorption spectroscopy measurements at the Cr K-edge of a trichroic crystal of alexandrite BeAl(2)O(4):Cr(3+) for different orientations of the crystal with respect to the polarization and direction of the x-ray incident beam have been performed. Analysis of the experimental spectra with the help of first-principles calculations of x-ray absorption spectra allowed us to estimate the proportion of chromium Cr(3+) cations among the two different octahedral sites of the alexandrite structure (70% in the C(s) site-30% in the C(i) site). The methodology presented in this work opens up new possibilities in the field of mineralogy for the study of complex minerals containing several sites potentially occupied by several transition elements or for solid solutions.

  19. Site partitioning of Cr3+ in the trichroic alexandrite BeAl2O4:Cr3+ crystal: contribution from x-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Bordage, Amélie; Rossano, Stéphanie; Horn, Adolf Heinrich; Fuchs, Yves

    2012-06-01

    X-ray absorption spectroscopy measurements at the Cr K-edge of a trichroic crystal of alexandrite BeAl2O4:Cr3+ for different orientations of the crystal with respect to the polarization and direction of the x-ray incident beam have been performed. Analysis of the experimental spectra with the help of first-principles calculations of x-ray absorption spectra allowed us to estimate the proportion of chromium Cr3+ cations among the two different octahedral sites of the alexandrite structure (70% in the Cs site-30% in the Ci site). The methodology presented in this work opens up new possibilities in the field of mineralogy for the study of complex minerals containing several sites potentially occupied by several transition elements or for solid solutions.

  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. 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.

  2. Study on Coloration Mechanism of Chinese Ancient Ceramics by X-ray Absorption Near-edge Structure

    NASA Astrophysics Data System (ADS)

    Peng, Y. H.; Xie, Z.; He, J. F.; Liu, Q. H.; Pan, Z. Y.; Cheng, W. R.; Wei, S. Q.

    2013-04-01

    The Fe K-edge X-ray absorption near-edge structure (XANES) spectra of a series of ceramic shards were measured by fluorescence mode to reveal the color-generating techniques of Chinese porcelain. The analysis disclosed relationships among the chemical form of the iron, the firing conditions and the colors of the ceramics. The results indicate that the coloration for different ceramics depend on the valence states of iron as the main color element in glaze and the proportion of Fe2+ and Fe3+ was attributed to the baking technology. The findings provide important information for archaeologist on the coloration researches.

  3. Solving local structure around dopants in metal nanoparticles with ab initio modeling of X-ray absorption near edge structure

    DOE PAGES

    Timoshenko, J.; Shivhare, A.; Scott, R. W.; Lu, D.; Frenkel, A. I.

    2016-06-30

    We adopted ab-initio X-ray Absorption Near Edge Structure (XANES) modelling for structural refinement of local environments around metal impurities in a large variety of materials. Our method enables both direct modelling, where the candidate structures are known, and the inverse modelling, where the unknown structural motifs are deciphered from the experimental spectra. We present also estimates of systematic errors, and their influence on the stability and accuracy of the obtained results. We illustrate our approach by following the evolution of local environment of palladium atoms in palladium-doped gold thiolate clusters upon chemical and thermal treatments.

  4. Using Synchrotron-based X-ray Absorption Spectrometry to Identify the Arsenic Chemical Forms in Mine Waste Materials

    SciTech Connect

    Matanitobua, Vitukawalu P.; Noller, Barry N.; Chiswell, Barry; Ng, Jack C.; Bruce, Scott L.; Huang, Daphne; Riley, Mark; Harris, Hugh H.

    2007-01-19

    X-ray Absorption Near Edge Spectroscopy (XANES) gives arsenic form directly in the solid phase and has lower detection limits than extraction techniques. An important and common application of XANES is to use the shift of the edge position to determine the valence state. XANES speciation analysis is based on fitting linear combinations of known spectra from model compounds to determine the ratios of valence states and/or phases present. As(V)/As(III) ratios were determined for various Australian mine waste samples and dispersed mine waste samples from river/creek sediments in Vatukoula, Fiji.

  5. 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.

  6. X-ray absorption near edge structure and extended X-ray absorption fine structure analysis of standards and biological samples containing mixed oxidation states of chromium(III) and chromium(VI).

    PubMed

    Parsons, J G; Dokken, K; Peralta-Videa, J R; Romero-Gonzalez, J; Gardea-Torresdey, J L

    2007-03-01

    For the first time a method has been developed for the extended X-ray absorption fine structure (EXAFS) data analyses of biological samples containing multiple oxidation states of chromium. In this study, the first shell coordination and interatomic distances based on the data analysis of known standards of potassium chromate (Cr(VI)) and chromium nitrate hexahydrate (Cr(III)) were investigated. The standards examined were mixtures of the following molar ratios of Cr(VI):Cr(III), 0:1, 0.25:0.75, 0.5:0.5, 0.75:0.25, and 1:0. It was determined from the calibration data that the fitting error associated with linear combination X-ray absorption near edge structure (LC-XANES) fittings was approximately +/-10% of the total fitting. The peak height of the Cr(VI) pre-edge feature after normalization of the X-ray absorption (XAS) spectra was used to prepare a calibration curve. The EXAFS fittings of the standards were also investigated and fittings to lechuguilla biomass samples laden with different ratios of Cr(III) and Cr(VI) were performed as well. An excellent agreement between the XANES data and the data presented in the EXAFS spectra was observed. The EXFAS data also presented mean coordination numbers directly related to the ratios of the different chromium oxidation states in the sample. The chromium oxygen interactions had two different bond lengths at approximately 1.68 and 1.98 A for the Cr(VI) and Cr(III) in the sample, respectively. PMID:17389076

  7. X-Ray Absorption Near Edge Structure And Extended X-Ray Absorption Fine Structure Analysis of Standards And Biological Samples Containing Mixed Oxidation States of Chromium(III) And Chromium(VI)

    SciTech Connect

    Parsons, J.G.; Dokken, K.; Peralta-Videa, J.R.; Romero-Gonzalez, J.; Gardea-Torresdey, J.L.

    2009-06-02

    For the first time a method has been developed for the extended X-ray absorption fine structure (EXAFS) data analyses of biological samples containing multiple oxidation states of chromium. In this study, the first shell coordination and interatomic distances based on the data analysis of known standards of potassium chromate (Cr(VI)) and chromium nitrate hexahydrate (Cr(III)) were investigated. The standards examined were mixtures of the following molar ratios of Cr(VI):Cr(III), 0:1, 0.25:0.75, 0.5:0.5, 0.75:0.25, and 1:0. It was determined from the calibration data that the fitting error associated with linear combination X-ray absorption near edge structure (LC-XANES) fittings was approximately {+-}10% of the total fitting. The peak height of the Cr(VI) pre-edge feature after normalization of the X-ray absorption (XAS) spectra was used to prepare a calibration curve. The EXAFS fittings of the standards were also investigated and fittings to lechuguilla biomass samples laden with different ratios of Cr(III) and Cr(VI) were performed as well. An excellent agreement between the XANES data and the data presented in the EXAFS spectra was observed. The EXFAS data also presented mean coordination numbers directly related to the ratios of the different chromium oxidation states in the sample. The chromium oxygen interactions had two different bond lengths at approximately 1.68 and 1.98 {angstrom} for the Cr(VI) and Cr(III) in the sample, respectively.

  8. Iron near absorption edge X-ray spectroscopy at aqueous-membrane interfaces

    SciTech Connect

    Wang, Wenjie; Kuzmenko, Ivan; Vaknin, David

    2014-01-01

    Employing synchrotron X-ray scattering, we systematically determine the absorption near-edge spectra (XANES) of iron in its ferrous (Fe2+) and ferric (Fe3+) states both as ions in aqueous solutions and as they bind to form a single layer to anionic templates that consist of carboxyl or phosphate groups at aqueous/vapor interfaces. While the XANES of bulk iron ions show that the electronic state and coordination of iron complexes in the bulk are isotropic, the interfacial bound ions show a signature of a broken inversion-symmetry environment. The XANES of Fe2+ and Fe3+ in the bulk possess distinct profiles however, upon binding they practically exhibit similar patterns. This indicates that both bound ions settle into a stable electronic and coordination configuration with an effective fractional valence (for example, Fe[2+nu]+, 0 < nu < 1) at charged organic templates. Such two dimensional properties may render interfacial iron, abundant in living organisms, a more efficient and versatile catalytic behavior.

  9. Speciation of selenium in stream insects using X-ray absorption spectroscopy

    SciTech Connect

    Ruwandi Andrahennadi; Mark Wayland; Ingrid J. Pickering

    2007-11-15

    Selenium contamination in the environment is a widespread problem affecting insects and other wildlife. Insects occupy a critical middle link and aid in trophic transfer of selenium in many terrestrial and freshwater food chains, but the mechanisms of selenium uptake through the food chain are poorly understood. In particular, biotransformation of selenium by insects into different chemical forms will greatly influence how toxic or benign the selenium is to that organism or to its predators. We have used X-ray absorption spectroscopy (XAS) to identify the chemical form of selenium in insects inhabiting selenium contaminated streams near Hinton, Alberta (Canada). Selenium K near-edge spectra indicate a variability of selenium speciation among the insects that included mayflies (Ephemeroptera), stoneflies (Plecoptera), caddisflies (Trichoptera), and craneflies (Diptera). Higher percentages of inorganic selenium were observed in primary consumers, detritivores, and filter feeders than in predatory insects. Among the organic forms of selenium, organic selenides constituted a major fraction in most organisms. A species modeled as trimethylselenonium was observed during the pupal stage of caddisflies. These results provide insights into how the insects cope with their toxic cargo, including how the selenium is biotransformed into less toxic forms and how it can be eliminated from the insects. More broadly, this study demonstrates the strengths of XAS to probe the effects of heavy elements at trace levels in insects from the field.

  10. Neutron induced damage in reactor pressure vessel steel: An X-ray absorption fine structure study

    NASA Astrophysics Data System (ADS)

    Kuri, G.; Cammelli, S.; Degueldre, C.; Bertsch, J.; Gavillet, D.

    2009-03-01

    The radiation damage produced in reactor pressure vessel (RPV) steels during neutron irradiation is a long-standing problem of considerable practical interest. In this study, an extended X-ray absorption fine structure (EXAFS) spectroscopy has been applied at Cu, Ni and Mn K-edges to systematically investigate neutron induced radiation damage to the metal-site bcc structure of RPV steels, irradiated with neutrons in the fluence range from 0.85 to 5.0 × 1019 cm-2. An overall similarity of Cu, Ni and Mn atomic environment in the iron matrix is observed. The radial distribution functions (RDFs), derived from EXAFS data have been found to evolve continuously as a function of neutron fluence describing the atomic-scale structural modifications in RPVs by neutron irradiations. From the pristine data, long range order beyond the first- and second-shell is apparent in the RDF spectra. In the irradiated specimens, all near-neighbour peaks are greatly reduced in magnitude, typical of damaged material. Prolonged annealing leads annihilation of point defects to give rise to an increase in the coordination numbers of near-neighbour atomic shells approaching values close to that of non-irradiated material, but does not suppress the formation of nano-sized Cu and/or Ni-rich-precipitates. Total amount of radiation damage under a given irradiation condition has been determined. The average structural parameters estimated from the EXAFS data are presented and discussed.

  11. 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.

  12. 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.

  13. Speciation of Selenium in Stream Insects Using X-Ray Absorption Spectroscopy

    SciTech Connect

    Andrahennadi, R.; Wayland, M.; Pickering, I.J.

    2009-05-28

    Selenium contamination in the environment is a widespread problem affecting insects and other wildlife. Insects occupy a critical middle link and aid in trophic transfer of selenium in many terrestrial and freshwater food chains, but the mechanisms of selenium uptake through the food chain are poorly understood. In particular, biotransformation of selenium by insects into different chemical forms will greatly influence how toxic or benign the selenium is to that organism or to its predators. We have used X-ray absorption spectroscopy (XAS) to identify the chemical form of selenium in insects inhabiting selenium contaminated streams near Hinton, Alberta (Canada). Selenium K near-edge spectra indicate a variability of selenium speciation among the insects that included mayflies (Ephemeroptera), stoneflies (Plecoptera), caddisflies (Trichoptera), and craneflies (Diptera). Higher percentages of inorganic selenium were observed in primary consumers, detritivores, and filter feeders than in predatory insects. Among the organic forms of selenium, organic selenides constituted a major fraction in most organisms. A species modeled as trimethylselenonium was observed during the pupal stage of caddisflies. These results provide insights into how the insects cope with their toxic cargo, including how the selenium is biotransformed into less toxic forms and how it can be eliminated from the insects. More broadly, this study demonstrates the strengths of XAS to probe the effects of heavy elements at trace levels in insects from the field.

  14. Dynamics of Femtosecond Laser Ablation Plume Studied With Ultrafast X-ray Absorption Fine Structure Imaging

    SciTech Connect

    Oguri, Katsuya; Okano, Yasuaki; Nishikawa, Tadashi; Nakano, Hidetoshi

    2010-10-08

    We investigated the dynamic process of an expanding femtosecond laser ablation plume of aluminum generated in an irradiation intensity range of 10{sup 13}-10{sup 15} W/cm{sup 2} with the ultrafast x-ray absorption fine structure (XAFS) imaging technique. The XAFS spectra of the aluminum L{sub II,III} edge of the plume revealed that the plume consists of doubly and singly charged ions, neutral atoms, liquid particles, and possible atomic clusters. Scanning electron microscopy of deposited ablation particles confirmed that the liquid particles corresponds to the spherical nanoparticles with a size ranging from several tens nanometers to approximately 200 nm. The spatiotemporal evolution of the XAFS image of the plume shows the sequential appearance of each ablation particle from aluminum surface according to its ejection velocity. The result suggests that the photomechanical fragmentation process, which was theoretically proposed, is dominant mechanism for the nanoparticle ejection under the irradiation intensity far from the ablation threshold of aluminum. This study clearly demonstrates the potential of our technique for measuring the ultrafast dynamics of femtosecond laser ablation process.

  15. 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

  16. X-ray color analysis of the spectra of active galactic nuclei

    NASA Technical Reports Server (NTRS)

    Netzer, Hagai; Turner, T. J.; George, Ian M.

    1994-01-01

    The identification and detection of X-ray absorption and emission features depends on the resolution and the signal-to-noise ratio (S/N) of the observation, the understanding of the instrument response, and the Galactic line-of-sight absorption. Since many of the active galactic nucleus (AGN) data sets are limited in their S/N and full modeling of the physical conditions is rather complicated, we suggest a new analysis method based on 'X-ray colors.' The two sets of X-ray colors, defined for low (ROSAT Position Sensitive Proportional Counter (PSPC)) and medium (Broad Band X-Ray Telescope (BBXRT)) and ASCA Solid-State Imaging Spectrometers (SIS) resolution experiments, are used to separate regions of different physical conditions in a two-dimensional color-color plane. They are similar but superior to previous methods using the X-ray 'hardness ratio' in being able to reveal more of the physical properties of the source. We illustrate the use of such diagrams by studying a number of AGNs suspected of showing absorption features. A sample of 14 AGNs observed by the ROSAT PSPC is presented which includes several objects with suspected 'warm absorbers' along the line-of-sight to the nucleus, several others exhibiting intrinsic continuum variations, and a number of control objects thought to be featureless. Our new observations show, for the first time, the color variation as a function of time for three of the Seyfert 1 sources: NGC 4051, Mrk 335, and Mrk 766. The variations suggest that in two sources we are witnessing real changes in continuum shape, while one (NGC 4051) is consistent with having a warm absorber. Four of the objects observed by BBXRT are reanalyzed using our X-ray colors. Out of these, we discuss in detail the case of NGC 4151 and show that the color-color analysis agrees very well with previous, detailed spectral fitting methods. In particular, we confirm that the observed BBXRT observation of this source is not consistent with the warm absorber

  17. On the X-ray spectra of luminous, inhomogeneous accretion flows

    NASA Astrophysics Data System (ADS)

    Merloni, A.; Malzac, J.; Fabian, A. C.; Ross, R. R.

    2006-08-01

    We discuss the expected X-ray spectral and variability properties of black hole accretion discs at high luminosity, under the hypothesis that radiation-pressure-dominated discs are subject to violent clumping instabilities and, as a result, have a highly inhomogeneous two-phase structure. After deriving the full accretion disc solutions explicitly in terms of the parameters of the model, we study their radiative properties both with a simple two-zone model, treatable analytically, and with radiative transfer simulations which account simultaneously for energy balance and Comptonization in the hot phase, together with reflection, reprocessing, ionization and thermal balance in the cold phase. We show that, if not only the density, but also the heating rate within these flows is inhomogeneous, then complex reflection-dominated spectra can be obtained for a high enough covering fraction of the cold phase. In general, large reflection components in the observed X-ray spectra should be associated with strong soft excesses, resulting from the combined emission of ionized atomic emission lines. The variability properties of such systems are such that, even when contributing to a large fraction of the hard X-ray spectrum, the reflection component is less variable than the power-law-like emission originating from the hot Comptonizing phase, in agreement with what is observed in many Narrow Line Seyfert 1 galaxies and bright Seyfert 1. Our model falls within the family of those trying to explain the complex X-ray spectra of bright AGN with ionized reflection, but presents an alternative, specific, physically motivated, geometrical set-up for the complex multiphase structure of the inner regions of near-Eddington accretion flows.

  18. Structural characterisation of Ni clusters in AlN via X-ray absorption, X-ray diffraction and transmission electron microscopy

    NASA Astrophysics Data System (ADS)

    Zanghi, D.; Traverse, A.; Dallas, J.-P.; Snoeck, E.

    Ni ions were implanted in bulk AlN with the goal to form embedded metallic clusters. Combining several characterisation techniques such as X-ray absorption spectroscopy, X-ray diffraction and high resolution transmission electron microscopy, we determined the lattice parameter of the Ni clusters that display a fcc crystalline structure. The average size increases when the ion fluence is increased or after a thermal treatment. Thanks to moiré fringes observed by high resolution transmission electron microscopy and to satellite peaks seen on the diffraction patterns, we concluded that the annealed Ni clusters orientate their (002) planes on the (101) of AlN. Moreover, the satellite positions allowed us to calculate Ni cluster average diameters, that are in agreement with average sizes deduced by X-ray absorption spectroscopy.

  19. Measurement of the x-ray tube anodes' surface profile and its effects on the x-ray spectra

    SciTech Connect

    Erdelyi, M.; Lajko, M.; Kakonyi, R.; Szabo, G.

    2009-02-15

    An experimental study--involving measurements with an optical microscope, a profilometer, and a scanning electron microscope--for determination of the surface profile of x-ray tube anodes is presented. The islands on the ''mud-flatting'' surface are separated by approximately 8 {mu}m deep cracks. The surface roughness on the island is typically below 1 {mu}m, and the area ratio of cracks to the total surface is higher on the more extensively used regions (anode aging). A simple model was proposed to calculate the spectrum modification introduced by the rough surface. Loss of x-ray intensity of 4% was predicted using the roughest surface at a small emission angle.

  20. Monte Carlo analysis of energy dependent anisotropy of bremsstrahlung x-ray spectra

    SciTech Connect

    Kakonyi, Robert; Erdelyi, Miklos; Szabo, Gabor

    2009-09-15

    The energy resolved emission angle dependence of x-ray spectra was analyzed by MCNPX (Monte Carlo N particle Monte Carlo) simulator. It was shown that the spectral photon flux had a maximum at a well-defined emission angle due to the anisotropy of the bremsstrahlung process. The higher the relative photon energy, the smaller the emission angle belonging to the maximum was. The trends predicted by the Monte Carlo simulations were experimentally verified. The Monte Carlo results were compared to both the Institute of Physics and Engineering in Medicine spectra table and the SPEKCALCV1.0 code.

  1. Absorbed Dose Determination Using Experimental and Analytical Predictions of X-Ray Spectra

    NASA Technical Reports Server (NTRS)

    Edwards, D. L.; Carruth, Ralph (Technical Monitor)

    2001-01-01

    Electron beam welding in a vacuum is a technology that NASA is investigating as a joining technique for manufacture of space structures. This investigation characterizes the x-ray environment due to operation of an in-vacuum electron beam welding tool and provides recommendations for adequate shielding for astronauts performing the in-vacuum electron beam welding. NASA, in a joint venture with the Russian Space Agency, was scheduled to perform a series of welding in space experiments on board the U.S. Space Shuttle. This series of experiments was named the international space welding experiment (ISWE). The hardware associated with the ISWE was leased to NASA by the Paton Welding Institute (PWI) in Ukraine for ground-based welding experiments in preparation for flight. Two ground tests were scheduled, using the ISWE electron beam welding tool, to characterize the radiation exposure to an astronaut during the operation of the ISWE. These radiation exposure tests used thermoluminescence dosimeters (TLD's) shielded with material currently used by astronauts during extravehicular activities to measure the radiation dose. The TLD's were exposed to x-ray radiation generated by operation of the ISWE in-vacuum electron beam welding tool. This investigation was the first known application of TLD's to measure absorbed dose from x rays of energy less than 10 keV. The ISWE hardware was returned to Ukraine before the issue of adequate shielding for the astronauts was completely verified. Therefore, alternate experimental and analytical methods were developed to measure and predict the x-ray spectral and intensity distribution generated by ISWE electron beam impact with metal. These x-ray spectra were normalized to an equivalent ISWE exposure, then used to calculate the absorbed radiation dose to astronauts. These absorbed dose values were compared to TLD measurements obtained during actual operation of the ISWE in-vacuum electron beam welding tool. The calculated absorbed dose

  2. X-Ray Emitting GHz-Peaked Spectrum Galaxies: Testing a Dynamical-Radiative Model with Broad-Band Spectra

    SciTech Connect

    Ostorero, L.; Moderski, R.; Stawarz, L.; Diaferio, A.; Kowalska, I.; Cheung, C.C.; Kataoka, J.; Begelman, M.C.; Wagner, S.J.; /Heidelberg Observ.

    2010-06-07

    In a dynamical-radiative model we recently developed to describe the physics of compact, GHz-Peaked-Spectrum (GPS) sources, the relativistic jets propagate across the inner, kpc-sized region of the host galaxy, while the electron population of the expanding lobes evolves and emits synchrotron and inverse-Compton (IC) radiation. Interstellar-medium gas clouds engulfed by the expanding lobes, and photoionized by the active nucleus, are responsible for the radio spectral turnover through free-free absorption (FFA) of the synchrotron photons. The model provides a description of the evolution of the GPS spectral energy distribution (SED) with the source expansion, predicting significant and complex high-energy emission, from the X-ray to the {gamma}-ray frequency domain. Here, we test this model with the broad-band SEDs of a sample of eleven X-ray emitting GPS galaxies with Compact-Symmetric-Object (CSO) morphology, and show that: (i) the shape of the radio continuum at frequencies lower than the spectral turnover is indeed well accounted for by the FFA mechanism; (ii) the observed X-ray spectra can be interpreted as non-thermal radiation produced via IC scattering of the local radiation fields off the lobe particles, providing a viable alternative to the thermal, accretion-disk dominated scenario. We also show that the relation between the hydrogen column densities derived from the X-ray (N{sub H}) and radio (N{sub HI}) data of the sources is suggestive of a positive correlation, which, if confirmed by future observations, would provide further support to our scenario of high-energy emitting lobes.

  3. X-RAY-EMITTING GHz-PEAKED-SPECTRUM GALAXIES: TESTING A DYNAMICAL-RADIATIVE MODEL WITH BROADBAND SPECTRA

    SciTech Connect

    Ostorero, L.; Diaferio, A.; Moderski, R.; Stawarz, L.; Kowalska, I.; Cheung, C. C.; Kataoka, J.; Begelman, M. C.; Wagner, S. J.

    2010-06-01

    In a dynamical-radiative model we recently developed to describe the physics of compact, GHz-peaked-spectrum (GPS) sources, the relativistic jets propagate across the inner, kpc-sized region of the host galaxy, while the electron population of the expanding lobes evolves and emits synchrotron and inverse-Compton (IC) radiation. Interstellar-medium gas clouds engulfed by the expanding lobes, and photoionized by the active nucleus, are responsible for the radio spectral turnover through free-free absorption (FFA) of the synchrotron photons. The model provides a description of the evolution of the spectral energy distribution (SED) of GPS sources with their expansion, predicting significant and complex high-energy emission, from the X-ray to the {gamma}-ray frequency domain. Here, we test this model with the broadband SEDs of a sample of 11 X-ray-emitting GPS galaxies with compact-symmetric-object morphology, and show that (1) the shape of the radio continuum at frequencies lower than the spectral turnover is indeed well accounted for by the FFA mechanism and (2) the observed X-ray spectra can be interpreted as non-thermal radiation produced via IC scattering of the local radiation fields off the lobe particles, providing a viable alternative to the thermal, accretion-disk-dominated scenario. We also show that the relation between the hydrogen column densities derived from the X-ray (N {sub H}) and radio (N {sub HI}) data of the sources is suggestive of a positive correlation, which, if confirmed by future observations, would provide further support to our scenario of high-energy emitting lobes.

  4. Structural Characterization of Bimetallic Nanomaterials with Overlapping X-ray Absorption Edges

    SciTech Connect

    Menard, L.; Wang, Q; Kang, J; Sealey, A; Girolami, G; Teng, X; Frenkel, A; Nuzzo, R

    2009-01-01

    We describe a data analysis method for extended x-ray absorption fine structure spectroscopy suitable for use with compounds of diverse form that contain overlapping absorption edges. This method employs direct concurrent analysis of the data-demonstrated here for cases involving two interfering metal edges-and does not utilize subtractive or data filtering strategies that have been previously used to address this challenge. Its generality and precision are demonstrated in analyses made on two model nanoscale samples: (1) a Ir-Pt nanoparticle system supported on ?-Al2O3 and (2) a hybrid system of Pt nanowires on which Au nanoparticles have been nucleated and grown at the nanowire tips, stacking faults, and twinning boundaries. The results obtained demonstrate the unique compositional and structural qualities of these two systems as well as the broader utility of the new x-ray absorption spectroscopy based protocol used to characterize them.

  5. 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.

  6. 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.

  7. A MINI X-RAY SURVEY OF SUB-DAMPED LYMAN-ALPHA ABSORPTION SYSTEMS: SEARCHING FOR ACTIVE GALACTIC NUCLEI FORMED IN PROTOGALAXIES

    SciTech Connect

    Chartas, G.; Asper, A.; Kulkarni, V. P. E-mail: kulkarni@sc.edu

    2013-10-01

    A significant fraction of the sub-damped Lyman-alpha (sub-DLA) absorption systems in quasar spectra appear to be metal-rich, including many with even super-solar element abundances. This raises the question whether some sub-DLAs may harbor active galactic nuclei (AGNs), since supersolar metallicities are observed in AGNs. Here, we investigate this question based on a mini-survey of 21 quasars known to contain sub-DLAs in their spectra. The X-ray observations were performed with the Chandra X-ray Observatory. In cases of no detection, we estimated upper limits for the X-ray luminosities of possible AGNs at the redshifts of the sub-DLAs. In six cases, we find possible X-ray emission within ∼1'' of the background quasar, which is consistent with the presence of a nearby X-ray source. If these nearby X-ray sources are at the redshifts of the sub-DLAs, then their estimated 0.2-10 keV luminosities range between 0.8 × 10{sup 44} h {sup –2} and 4.2 × 10{sup 44} h {sup –2} erg s{sup –1}, thus ruling out a normal late-type galaxy origin, and suggesting that the emission originates in a galactic nucleus near the center of a protogalaxy. The projected distances of these possible nearby X-ray sources from the background quasars lie in the range of 3-7 h {sup –1} kpc, which is consistent with our hypothesis that they represent AGNs centered on the sub-DLAs. Deeper follow-up X-ray and optical observations are required to confirm the marginal detections of X-rays from these sub-DLA galaxies.

  8. Spatial power-spectra from Yohkoh soft X-ray images

    NASA Technical Reports Server (NTRS)

    Martens, Petrus C. H.; Gomez, Daniel O.

    1992-01-01

    We analyze three sequences of images from active regions, and a full disk image obtained by Yohkoh's Soft X-ray Telescope. Two sequences are from a region at center disk observed through different filters, and one sequence is from the limb. After Fourier-transforming the X-ray intensity of the images we find nearly isotropic power-spectra with an azimuthally integrated slope of -2.1 for the center disk, and -2.8 for the limb images. The full-disk picture yields a spectrum of -2.4. These results are different from the active region spectra obtained with the Normal Incidence X-ray Telescope which have a slope of the order of -3.0, and we ascribe this to the difference in temperature response between the instruments. However, both the SXT and NIXT results are consistent with coronal heating as the end result of a downward quasistatic cascade (in lengthscales) of free magnetic energy in the corona, driven by footpoint motions in the photosphere.

  9. High-resolution study of the x-ray resonant Raman scattering process around the 1s absorption edge for aluminium, silicon, and their oxides

    SciTech Connect

    Szlachetko, J.; Dousse, J.-Cl.; Berset, M.; Fennane, K.; Szlachetko, M.; Hoszowska, J.; Barrett, R.; Pajek, M.; Kubala-Kukus, A.

    2007-02-15

    X-ray resonant Raman scattering (RRS) spectra of Al, Al{sub 2}O{sub 3}, Si, and SiO{sub 2} were measured at the European Synchrotron Radiation Facility, using a high-resolution Bragg-type curved crystal spectrometer. The x-ray RRS spectra were collected at several beam energies tuned below the 1s absorption thresholds of Al and Si. Differences in the spectral features between the elemental samples and the oxide ones were clearly observed. The data were interpreted using the second-order perturbation theory within the Kramers-Heisenberg (KH) approach. It is shown that, using the KH formalism, oscillator strengths that are similar to the ones deduced from x-ray absorption measurements can be extracted from emission x-ray RRS spectra. The total cross sections for the x-ray RRS process were derived for the different photon beam energies and compared with theoretical predictions. For elemental silicon, the weak 1s-3p excitation was observed and found to be consistent with results of density of states calculations.

  10. Redox State of Iron in Lunar Glasses using X-ray Absorption Spectroscopy and Multivariate Analysis

    NASA Astrophysics Data System (ADS)

    Dyar, M. D.; McCanta, M. C.; Lanzirotti, A.; Sutton, S. R.; Carey, C. J.; Mahadevan, S.; Rutherford, M. J.

    2014-12-01

    The oxidation state of igneous materials on a planet is a critically-important variable in understanding magma evolution on bodies in our solar system. However, direct and indirect methods for quantifying redox states are challenging, especially across the broad spectrum of silicate glass compositions found on airless bodies. On the Moon, early Mössbauer studies of bulk samples suggested the presence of significant Fe3+ (>10%) in lunar glasses (green, orange, brown); lunar analog glasses synthesized at fO2 <10-11 have similar Fe3+. All these Mössbauer spectra are challenging to interpret due to the presence of multiple coordination environments in the glasses. X-ray absorption spectroscopy (XAS) allows pico- and nano-scale interrogation of primitive planetary materials using the pre-edge, main edge, and EXAFS regions of absorption edge spectra. Current uses of XAS require availability of standards with compositions similar to those of unknowns and complex procedures for curve-fitting of pre-edge features that produce results with poorly constrained accuracy. A new approach to accurate and quantitative redox measurements with XAS is to couple use of spectra from synthetic glass standards covering a broad compositional range with multivariate analysis (MVA) techniques. Mössbauer and XAS spectra from a suite of 33 synthetic glass standards covering a wide range of compositions and fO2(Dyar et al., this meeting) were used to develop a MVA model that utilizes valuable predictive information not only in the major spectral peaks/features, but in all channels of the XAS region. Algorithms for multivariate analysis t were used to "learn" the characteristics of a data set as a function of varying spectral characteristics. These models were applied to the study of lunar glasses, which provide a challenging test case for these newly-developed techniques due to their very low fO2. Application of the new XAS calibration model to Apollo 15 green (15426, 15427 and 15425

  11. Two Types of Soft X-ray Spectra in Cataclysmic Variables

    NASA Technical Reports Server (NTRS)

    White, Nicholas E. (Technical Monitor); Mukai, K.; Kinkhabwala, A.; Peterson, J. R.; Kahn, S. M.; Paerels, F.

    2002-01-01

    We present results of analyses of Chandra HETG soft X-ray spectra (Lambda = 1.5-25 A) of seven cataclysmic variables. We find that these spectra divide unambiguously into two distinct types. Spectra of the first type, consisting of EX Hya, V603 Aql, U Gem, and SS Cyg, are remarkably well fit by a simple cooling flow model, which assumes only steady-state isobaric radiative cooling. This model has only two free parameters, the maximum temperature, kT(sub max), which provides a rough measurement of the depth of the potential well, and the overall normalization, which provides a highly precise measurement of the total accretion rate. Spectra of the second type, consisting of V1223 Sgr, A Psc, and GK Per, are grossly inconsistent with a simple cooling flow model. They instead exhibit a hard continuum, and, in addition, show strong H-like and He-like ion emission but little Fe L-shell emission, which is consistent with expectations for line emission from a photoionized plasma. Using a simple photoionization model, we argue that the observed line emission for these sources can be driven entirely by the hard continuum. The physical significance of these two distinct types of X-ray spectra is also explored.

  12. 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.

  13. X-ray Reflected Spectra from Accretion Disk Models. I. Constant Density Atmospheres

    NASA Technical Reports Server (NTRS)

    Garcia, Javier; Kallman, Timothy R.

    2009-01-01

    We present new models for illuminated accretion disks, their structure and reprocessed emission. We consider the effects of incident X-rays on the surface of an accretion disk by solving simultaneously the equations of radiative transfer, energy balance and ionization equilibrium over a large range of column densities. We assume plane-parallel geometry and azimuthal symmetry, such that each calculation corresponds to a ring at a given distance from the central object. Our models include recent and complete atomic data for K-shell of the iron and oxygen isonuclear sequences. We examine the effect on the spectrum of fluorescent Ka line emission and absorption in the emitted spectrum. We also explore the dependence of the spectrum on the strength of the incident X-rays and other input parameters, and discuss the importance of Comptonization on the emitted spectrum.

  14. The ROSAT Deep Survey. 2; Optical Identification, Photometry and Spectra of X-Ray Sources in the Lockman Field

    NASA Technical Reports Server (NTRS)

    Schmidt, M.; Hasinger, G.; Gunn, J.; Schneider, D.; Burg, R.; Giacconi, R.; Lehmann, I.; MacKenty, J.; Truemper, J.; Zamorani, G.

    1998-01-01

    The ROSAT Deep Survey includes a complete sample of 50 X-ray sources with fluxes in the 0.5 - 2 keV band larger than 5.5 x 10(exp -15)erg/sq cm/s in the Lockman field (Hasinger et al., Paper 1). We have obtained deep broad-band CCD images of the field and spectra of many optical objects near the positions of the X-ray sources. We define systematically the process leading to the optical identifications of the X-ray sources. For this purpose, we introduce five identification (ID) classes that characterize the process in each case. Among the 50 X-ray sources, we identify 39 AGNs, 3 groups of galaxies, 1 galaxy and 3 galactic stars. Four X-ray sources remain unidentified so far; two of these objects may have an unusually large ratio of X-ray to optical flux.

  15. X-RAY SPECTRA FROM MAGNETOHYDRODYNAMIC SIMULATIONS OF ACCRETING BLACK HOLES

    SciTech Connect

    Schnittman, Jeremy D.; Krolik, Julian H.; Noble, Scott C. E-mail: jhk@pha.jhu.edu

    2013-06-01

    We present the results of a new global radiation transport code coupled to a general relativistic magnetohydrodynamic simulation of an accreting, non-rotating black hole. For the first time, we are able to explain from first principles in a self-consistent way all the components seen in the X-ray spectra of stellar-mass black holes, including a thermal peak and all the features associated with strong hard X-ray emission: a power law extending to high energies, a Compton reflection hump, and a broad iron line. Varying only the mass accretion rate, we are able to reproduce a wide range of X-ray states seen in most galactic black hole sources. The temperature in the corona is T{sub e} {approx} 10 keV in a boundary layer near the disk and rises smoothly to T{sub e} {approx}> 100 keV in low-density regions far above the disk. Even as the disk's reflection edge varies from the horizon out to Almost-Equal-To 6M as the accretion rate decreases, we find that the shape of the Fe K{alpha} line is remarkably constant. This is because photons emitted from the plunging region are strongly beamed into the horizon and never reach the observer. We have also carried out a basic timing analysis of the spectra and find that the fractional variability increases with photon energy and viewer inclination angle, consistent with the coronal hot spot model for X-ray fluctuations.

  16. Chemical-state analysis of organic semiconductors using soft X-ray absorption spectroscopy combined with first-principles calculation.

    PubMed

    Natsume, Yutaka; Kohno, Teiichiro; Minakata, Takashi; Konishi, Tokuzo; Gullikson, Eric M; Muramatsu, Yasuji

    2012-02-16

    The chemical states of organic semiconductors were investigated by total-electron-yield soft X-ray absorption spectroscopy (TEY-XAS) and first-principles calculations. The organic semiconductors, pentacene (C(22)H(14)) and pentacenequinone (C(22)H(12)O(2)), were subjected to TEY-XAS and the experimental spectra obtained were compared with the 1s core-level excited spectra of C and O atoms, calculated by a first-principles planewave pseudopotential method. Excellent agreement between the measured and the calculated spectra were obtained for both materials. Using this methodology, we examined the chemical states of the aged pentacene, and confirmed that both C-OH and C═O chemical bonds are generated by exposure to air. This result implies that not only oxygen but also humidity causes pentacene oxidation.

  17. Cadmium Chemical Form in Mine Waste Materials by X-ray Absorption Spectroscopy

    SciTech Connect

    Diacomanolis, V.; Ng, J. C.; Sadler, R.; Harris, H. H.; Nomura, M.; Noller, B. N.

    2010-06-23

    This study examines the molecular form of cadmium (Cd) present in mine wastes by X-ray Absorption Spectroscopy (XAS; Cd>20 mg/kg) using the K-edge of Cd at the Photon Factory Advanced Ring (PF-AR), NW10A beam line at KEK-Tsukuba-Japan. Mine waste materials and zinc concentrate were analyzed for Cd by ICPMS prior to undertaking XAS (range 21-452 mg/kg). Model compounds (CdO, Cd(OH){sub 2}, CdCO{sub 3}, Cdacetate, CdS, Cdstearate, CdDEDTC) and samples were examined in solid form at 20 K. The XANES spectra showed similar E max values for both model compounds and samples. The EXAFS showed that Cd-S in CdS, gives a flatter spectrum in the extended region compared to Cd-O found with CdCO{sub 3}, CdO and Cd Stearate. Linear combination fitting with model Cd compounds did not give clear assignments of composition, indicating that more detailed EXAFS spectra is required as mineral forms containing Cd were present rather than simple Cd compounds such as CdCO{sub 3}. The Cd bond for a single shell model in mine waste sample matrices appears to be either Cd-O or Cd-S, or a combination of both. Comparison of molecular data from the XAS studies with bioaccessibility data giving a prediction of bioavailability for mine waste materials provides useful information about the significance of the cadmium form as a contaminant for health risk assessment purposes.

  18. Intermediate Coupling For Core-Level Excited States: Consequences For X-Ray Absorption Spectroscopy

    SciTech Connect

    Bagus, Paul S.; Sassi, Michel JPC; Rosso, Kevin M.

    2015-04-15

    The origin of the complex NEXAFS features of X-Ray Absorption, XAS, spectra in transition metal complexes is analyzed and interpreted in terms of the angular momentum coupling of the open shell electrons. Especially for excited configurations where a core-electron is promoted to an open valence shell, the angular momentum coupling is intermediate between the two limits of Russell- Saunders, RS, coupling where spin-orbit splitting of the electron shells is neglected and j-j coupling where this splitting is taken as dominant. The XAS intensities can be understood in terms of two factors: (1) The dipole selection rules that give the allowed excited RS multiplets and (2) The contributions of these allowed multiplets to the wavefunctions of the intermediate coupled levels. It is shown that the origin of the complex XAS spectra is due to the distribution of the RS allowed multiplets over several different intermediate coupled excited levels. The specific case that is analyzed is the L2,3 edge XAS of an Fe3+ cation, because this cation allows a focus on the angular momentum coupling to the exclusion of other effects; e.g., chemical bonding. Arguments are made that the properties identified for this atomic case are relevant for more complex materials. The analysis is based on the properties of fully relativistic, ab initio, many-body wavefunctions for the initial and final states of the XAS process. The wavefunction properties considered include the composition of the wavefunctions in terms of RS multiplets and the occupations of the spin-orbit split open shells; the latter vividly show whether the coupling is j-j or not.

  19. Probing Warm Dense Matter electronic structure using X-ray absorption Near Edge Spectroscopy (XANES)

    NASA Astrophysics Data System (ADS)

    Benuzzi Mounaix, Alessandra

    2011-06-01

    The behavior and physical properties of warm dense matter, fundamental for various branches of physics including planetology and Inertial Confinement Fusion, are non trivial to simulate either theoretically, numerically or experimentally. Despite important progress obtained in the last decade on macroscopic characterization (e.g. equations of state), microscopic studies are today necessary to investigate finely the WDM structure changes, the phase transitions and to test physical hypothesis and approximations commonly used in calculations. In this work, highly compressed aluminum has been investigated with the aim of bringing information on the evolution of its electronic structure by using K-edge shift and XANES. The experiment was performed at LULI laboratory where we used one long pulse (500 ps, IL ~ 8 1013 W/cm2) to create a uniform shock and a second ps beam (IL ~ 1017 W/cm2) to generate an ultra-short broadband X-ray source near the Al K-edge. The spectra were registered by using two conical KAP Bragg crystals. The main target was designed to probe the Aluminum in reshocked conditions allowing us to probe and to test theories in an extreme regime up to now unexplored (ρ ~ 3 ρ0 and T ~ 8 eV). The hydrodynamical Al conditions were measured by using VISARs interferometers and self-emission diagnostics. By increasing the delay between the two beams, we have been able to observe the modification of absorption spectra for unloading Al conditions (ρ >= 0.5 g/cc), and to put in evidence the relocalization of the 3p valence electrons occurring in the metal-non metal transition. All data have been compared to ab initio and dense plasma calculations.

  20. Soft X-Ray Irradiation Effects of Li2O2, Li2CO3 and Li2O Revealed by Absorption Spectroscopy

    PubMed Central

    Qiao, Ruimin; Chuang, Yi-De; Yan, Shishen; Yang, Wanli

    2012-01-01

    Li2O2, Li2CO3, and Li2O are three critical compounds in lithium-air and lithium-ion energy storage systems. Extensive measurements have been carried out to study the chemical species and their evolutions at difference stages of the device operation. While x-ray spectroscopy has been demonstrated to be one of the most powerful tools for such purpose, no systematic study on the irradiation effects have been reported. Here we carry out extensive time, position, and irradiation dependent Li K-edge soft x-ray absorption spectroscopy on these compounds with so far the best energy resolution. The ultra-high resolution in the current study allows the features in the absorption spectra to be well-resolved. The spectral lineshape thus serves as the fingerprints of these compounds, enabling the tracking of their evolution under x-ray irradiation. We found that both Li2O2 and Li2CO3 evidently evolve towards Li2O under the soft x-ray irradiation with Li2CO3 exhibiting a surprisingly higher sensitivity to x-rays than Li2O2. On the other hand, Li2O remains the most stable compound despite experiencing substantial irradiation dose. We thus conclude that high resolution soft x-ray spectroscopy could unambiguously fingerprint different chemical species, but special cautions on irradiation effects would be needed in performing the experiments and interpreting the data properly. PMID:23145116

  1. Laboratory Studies of X-ray Spectra Formed by Charge Exchange

    NASA Astrophysics Data System (ADS)

    Beiersdorfer, Peter; Ali, R.; Brown, G. V.; Koutroumpa, D.; Kelley, R. L.; Kilbourne, C.; Leutenegger, M. A.; Porter, F.

    2013-04-01

    Charge exchange between ions and neutral atoms or molecules has been accepted at an important soft producing process in our solar system. By extension, charge exchange may contribute to the X-ray emission of circumstellar material. It may also produce X-ray emission at the boundaries of supernova ejecta and star burst galaxies, or whenever hot plasma collides with neutral matter. X-ray spectra of K-shell and L-shell ions formed by charge exchange have now been studied in a variety of laboratory settings. These experiments have shown several characteristic features of line formation by charge exchange when compared to the X-ray emission produced by electron-impact excitation, e.g., enhancement emission of forbidden lines and of lines from levels with high principal quantum number. They have also shown a dependence on the interaction gas and on the energy of the ion-neutral collision. Moreover, the transfer of multiple electrons is typically preferred, provided the donor molecules or atoms have multiple valence-shell electrons. The laboratory measurements are in qualitative agreement with theory. However, the details of the observed X-ray spectra, especially those recorded with high spectral resolution, can differ substantially from predictions, especially for spectra produced at collision velocities equal to or lower than those found in thermal plasmas or produced with neutral gases other than atomic hydrogen. Puzzling discrepancies can be noted, such as enhanced emission from an upper level with the 'wrong' principal quantum number. Even more puzzling is a recent experiment in which two, co-mixed bare ion species of similar atomic number produce very different Lyman series emission upon charge exchange with a given neutral gas, defying both theoretical predictions and empirical scaling. Laboratory measurements have also shown that some of the characteristic features of charge exchange can be reproduced by radiative electron capture, i.e., by capture of a continuum

  2. In situ micro X-ray absorption near edge structure study of microbiologically reduced selenite (SeO 32-)

    NASA Astrophysics Data System (ADS)

    Oger, Phil M.; Daniel, I.; Cournoyer, B.; Simionovici, A.

    2004-10-01

    The possibility exists that life originated from high-pressure, high-temperature environments fueled by the reduction of metal ions. These environments or their modern equivalent cannot be studied by standard microbiological techniques, but, metal reduction and oxidation kinetics may be accessible to X-ray analyses. We have evaluated the compatibility, the sensitivity and the efficiency of μX-ray absorption near edge structure (μXANES) and μX-ray fluorescence (μXRF) to study the kinetics of selenite reduction by prokaryotes under controlled pressure and temperature using a dedicated diamond anvil cell. These tests were performed in quartz capillaries, but the experimental set up was designed so as to accommodate the diamond anvil cell. Using μXRF coupled with μXANES, we show that we can detect and quantify Se species in solution from as low as 2 ppm. Lower quantification levels could be readily obtained by increasing counting time or incident flux and changing detectors. The chemical composition of mixtures of different selenium species has been directly determined by a combination of individual μXANES spectra made from standard solutions. The sensitivity of this method is sufficiently high to allow the study of the speciation of selenium in solution in situ and in vivo in the diamond anvil cell under controlled pressure and temperature.

  3. Protein dynamics in an intermediate state of myoglobin: optical absorption, resonance Raman spectroscopy, and x-ray structure analysis.

    PubMed Central

    Engler, N; Ostermann, A; Gassmann, A; Lamb, D C; Prusakov, V E; Schott, J; Schweitzer-Stenner, R; Parak, F G

    2000-01-01

    A metastable state of myoglobin is produced by reduction of metmyoglobin at low temperatures. This is done either by irradiation with x-rays at 80 K or by electron transfer from photoexcited tris(2, 2'-bipyridine)-ruthenium(II) at 20 K. At temperatures above 150 K, the conformational transition toward the equilibrium deoxymyoglobin is observed. X-ray crystallography, Raman spectroscopy, and temperature-dependent optical absorption spectroscopy show that the metastable state has a six-ligated iron low-spin center. The x-ray structure at 115K proves the similarity of the metastable state with metmyoglobin. The Raman spectra yield the high-frequency vibronic modes and give additional information about the distortion of the heme. Analysis of the temperature dependence of the line shape of the Soret band reveals that a relaxation within the metastable state starts at approximately 120 K. Parameters representative of static properties of the intermediate state are close to those of CO-ligated myoglobin, while parameters representative of dynamics are close to deoxymyoglobin. Thus within the metastable state the relaxation to the equilibrium is initiated by changes in the dynamic properties of the active site. PMID:10733986

  4. X-ray Diffraction Spectra in Cu-Implanted SiO{sub 2} Films on Si(100) Substrates

    SciTech Connect

    Shirokoff, J.; Lewis, J. Courtenay

    2010-10-29

    Cu-implanted SiO{sub 2} films on Si(100) have been studied using x-ray methods and x-ray diffraction pattern processing. The x-ray results indicate the presence of a preferred orientation for Cu {l_brace}111{r_brace} planes parallel to the substrate surface without directional orientation for Cu-implanted SiO{sub 2}/Si(100) and nano-crystalline-Cu/SiO{sub 2}/Si(100)(ie. after implanted and annealed Cu). The x-ray diffraction spectra of the Cu-implanted and nano-crystalline-Cu phases were analyzed (ie. in terms of peak search, profile fit, crystallite size) and compared to data from complimentary techniques (RBS, TEM). Results are discussed with respect to x-ray spectral lines shapes derived from XRD spectra processing and the nanostructure problem.

  5. Absorption lines from magnetically driven winds in X-ray binaries

    NASA Astrophysics Data System (ADS)

    Chakravorty, S.; Petrucci, P.-O.; Ferreira, J.; Henri, G.; Belmont, R.; Clavel, M.; Corbel, S.; Rodriguez, J.; Coriat, M.; Drappeau, S.; Malzac, J.

    2016-05-01

    Context. High resolution X-ray spectra of black hole X-ray binaries (BHBs) show blueshifted absorption lines suggesting the presence of outflowing winds. Furthermore, observations show that the disk winds are equatorial and they occur in the Softer (disk dominated) states of the outburst and are less prominent or absent in the Harder (power-law dominated) states. Aims: We want to test whether the self-similar magneto-hydrodynamic (MHD) accretion-ejection models can explain the observational results for accretion disk winds in BHBs. In our models, the density at the base of the outflow from the accretion disk is not a free parameter. This mass loading is determined by solving the full set of dynamical MHD equations without neglecting any physical term. Thus, the physical properties of the outflow depend on and are controlled by the global structure of the disk. Methods: We studied different MHD solutions characterized by different values of the disk aspect ratio (ɛ) and the ejection efficiency (p). We also generate two kinds of MHD solutions depending on the absence (cold solution) or presence (warm solution) of heating at the disk surface. Such heating could be either from dissipation of energy due to MHD turbulence in the disk or from illumination of the disk surface. Warm solutions can have large (>0.1) values of p, which would imply larger wind mass loading at the base of the outflow. We use each of these MHD solutions to predict the physical parameters (distance, density, velocity, magnetic field, etc.) of an outflow. Motivated by observational results, we have put limits on the ionization parameter (ξ), column density, and timescales. Further constraints were derived for the allowed values of ξ from thermodynamic instability considerations, particularly for the Hard SED. These physical constraints were imposed on each of these outflows to select regions within it, which are consistent with the observed winds. Results: The cold MHD solutions are found to be

  6. Electronic and chemical state of aluminum from the single- (K) and double-electron excitation (KLII&III, KLI) x-ray absorption near-edge spectra of α-alumina, sodium aluminate, aqueous Al³⁺•(H₂O)₆, and aqueous Al(OH)₄⁻

    SciTech Connect

    Fulton, John L.; Govind, Niranjan; Huthwelker, Thomas; Bylaska, Eric J.; Vjunov, Aleksei; Pin, Sonia; Smurthwaite, Tricia D.

    2015-07-02

    We probe, at high energy resolution, the double electron excitation (KLII&II) x-ray absorption region that lies approximately 115 eV above the main Al K-edge (1566 eV) of α-alumina and sodium aluminate. The two solid standards, α-alumina (octahedral) and sodium aluminate (tetrahedral) are compared to aqueous species that have the same Al coordination symmetries, Al³⁺•6H₂O (octahedral) and Al(OH)₄⁻ (tetrahedral). For the octahedral species, the edge height of the KLII&III-edge is approximately 10% of the main K-edge however the edge height is much weaker (3% of K-edge height) for Al species with tetrahedral symmetry. For the α-alumina and aqueous Al³⁺•6H₂O the KLII&III spectra contain white line features and extended absorption fine structure (EXAFS) that mimics the K-edge spectra. The KLII&III-edge feature interferes with an important region of the extended-XAFS region of the spectra for the K-edge of the crystalline and aqueous standards. The K-edge spectra and K-edge positions are predicted using time-dependent density functional theory (TDDFT). The TDDFT calculations for the K-edge XANES spectra reproduce the observed transitions in the experimental spectra of the four Al species. The KLII&III and KLI onsets and their corresponding chemical shifts for the four standards are estimated using the delta self-consistent field (ΔSCF) method. Research by JLF, NG, EJB, AV, TDS was supported by U.S. Department of Energy’s (DOE), Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. NG thanks Amity Andersen for help with the α-Al₂O₃ and tetrahedral sodium aluminate (NaAlO₂) clusters. All the calculations were performed using the Molecular Science Computing Capability at EMSL, a national scientific user facility sponsored by the U.S. Department of Energy’s Office of Biological and Environmental Research and located at

  7. Surface relaxation in liquid water and methanol studied by x-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Wilson, Kevin R.; Schaller, R. D.; Co, D. T.; Saykally, R. J.; Rude, Bruce S.; Catalano, T.; Bozek, J. D.

    2002-10-01

    X-ray absorption spectroscopy is a powerful probe of local electronic structure in disordered media. By employing extended x-ray absorption fine structure spectroscopy of liquid microjets, the intermolecular O-O distance has been observed to undergo a 5.9% expansion at the liquid water interface, in contrast to liquid methanol for which there is a 4.6% surface contraction. Despite the similar properties of liquid water and methanol (e.g., abnormal heats of vaporization, boiling points, dipole moments, etc.), this result implies dramatic differences in the surface hydrogen bond structure, which is evidenced by the difference in surface tension of these liquids. This result is consistent with surface vibrational spectroscopy, which indicates both stronger hydrogen bonding and polar ordering at the methanol surface as a consequence of "hydrophobic packing" of the methyl group.

  8. 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.

  9. 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.

  10. Absorbed dose determination using experimental and analytical predictions of x-ray spectra

    NASA Astrophysics Data System (ADS)

    Edwards, David Lee

    1999-10-01

    Electron beam welding in a vacuum is a technology that NASA is investigating as a joining technique for manufacture of space structures. The interaction of energetic electrons with metal produces x-rays. This investigation characterizes the x-ray environment due to operation of an in-vacuum electron beam welding tool and provides recommendations for adequate radiation shielding for astronauts performing the in-vacuum electron beam welding. NASA, in a joint venture with the Russian Space Agency, was scheduled to perform a series of welding in space experiments on board the United States Space Shuttle. This series of experiments was named the International Space Welding Experiment (ISWE). The hardware associated with the ISWE was leased to NASA, by the Paton Welding Institute (PWI) in Ukraine, for ground based welding experiments in preparation for flight. Two ground tests were scheduled, using the ISWE electron beam welding tool, to characterize the radiation exposure to an astronaut during the operation of the ISWE. These radiation exposure tests used Thermoluminescence Dosimeters (TLD's) shielded with material currently used by astronauts during Extra Vehicular Activities (EVA) to measure the radiation dose. The TLD's were exposed to x- ray radiation generated by operation of the ISWE in- vacuum electron beam welding tool. This investigation was the first known application of TLD's to measure absorbed dose from x-rays of energy less than 10 keV. The ISWE hardware was returned to Ukraine before the issue of adequate shielding for the astronauts was completely verified. Therefore alternate experimental and analytical methods were developed to measure and predict the x-ray spectral and intensity distribution generated by ISWE electron beam impact with metal. These x-ray spectra were normalized to an equivalent ISWE exposure then used to calculate the absorbed radiation dose to astronauts. These absorbed dose values were compared to TLD measurements obtained during

  11. In operando observation system for electrochemical reaction by soft X-ray absorption spectroscopy with potential modulation method

    SciTech Connect

    Nagasaka, Masanari Kosugi, Nobuhiro; Yuzawa, Hayato; Horigome, Toshio

    2014-10-15

    In order to investigate local structures of electrolytes in electrochemical reactions under the same scan rate as a typical value 100 mV/s in cyclic voltammetry (CV), we have developed an in operando observation system for electrochemical reactions by soft X-ray absorption spectroscopy (XAS) with a potential modulation method. XAS spectra of electrolytes are measured by using a transmission-type liquid flow cell with built-in electrodes. The electrode potential is swept with a scan rate of 100 mV/s at a fixed photon energy, and soft X-ray absorption coefficients at different potentials are measured at the same time. By repeating the potential modulation at each fixed photon energy, it is possible to measure XAS of electrochemical reaction at the same scan rate as in CV. We have demonstrated successful measurement of the Fe L-edge XAS spectra of aqueous iron sulfate solutions and of the change in valence of Fe ions at different potentials in the Fe redox reaction. The mechanism of these Fe redox processes is discussed by correlating the XAS results with those at different scan rates.

  12. 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.

  13. X-ray absorption spectroscopy beyond the core-hole lifetime

    SciTech Connect

    Haemaelaeinen, K.; Hastings, J.B.; Siddons, D.P.; Berman, L.

    1992-10-01

    A new technique to overcome the core-hole lifetime broadening in x-ray absorption spectroscopy is presented. It utilizes a high resolution fluorescence spectrometer which can be used to analyze the fluorescence photon energy with better resolution than the natural lifetime width. Furthermore, the high resolution spectrometer can also be used to select the final state in the fluorescence process which can offer spin selectivity even without long range magnetic order in the sample.

  14. X-ray absorption spectroscopy beyond the core-hole lifetime

    SciTech Connect

    Haemaelaeinen, K.; Hastings, J.B.; Siddons, D.P.; Berman, L.

    1992-01-01

    A new technique to overcome the core-hole lifetime broadening in x-ray absorption spectroscopy is presented. It utilizes a high resolution fluorescence spectrometer which can be used to analyze the fluorescence photon energy with better resolution than the natural lifetime width. Furthermore, the high resolution spectrometer can also be used to select the final state in the fluorescence process which can offer spin selectivity even without long range magnetic order in the sample.

  15. X-ray spectra and time variability of active galactic nuclei

    NASA Technical Reports Server (NTRS)

    Mushotzky, R. F.

    1984-01-01

    The X-ray spectra of broad line active galactic nuclei (AGN) of all types (Seyfert I's, NELG's, broadline radio galaxies) are well fit by a power law in the .5 to 100 keV band of man energy slope alpha = .68 + or - .15. There is, as yet, no strong evidence for time variability of this slope in a given object. The constraints that this places on simple models of the central energy source are discussed. BL Lac objects have quite different X-ray spectral properties and show pronounced X-ray spectral variability. On time scales longer than 12 hours most radio quiet AGN do not show strong, delta I/I .5, variability. The probability of variability of these AGN seems to be inversely related to their luminosity. However characteristics timescales for variability have not been measured for many objects. This general lack of variability may imply that most AGN are well below the Eddington limit. Radio bright AGN tend to be more variable than radio quiet AGN on long, tau approx 6 month, timescales.

  16. X-ray Spectra from GRMHD Simulations of Accreting Black Holes

    NASA Astrophysics Data System (ADS)

    Schnittman, Jeremy; Noble, Scott; Krolik, Julian H.; Kinch, Brooks

    2016-04-01

    We present the results of a global radiation transport code coupled to general relativistic magnetohydrodynamic (GRMHD) simulations of accreting black holes. For the first time, we are able to explain from first principles in a self-consistent way all the components seen in the X-ray spectra of stellar-mass black holes, including a thermal peak and all the features associated with strong hard X-ray emission: a power law extending to high energies, a Compton reflection hump, and a broad iron line. Varying only the mass accretion rate, we are able to reproduce a wide range of X-ray states seen in most galactic black hole sources. The temperature in the corona is Te ~ 10 keV in a boundary layer near the disk and rises smoothly to Te >~ 100 keV in low-density regions far above the disk. We self-consistently solve for the ionization state of gas in each vertical column of the disk, in turn giving iron fluorescent emissivity profile.

  17. 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.

    PubMed

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

    2013-07-01

    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. PMID:23902081

  18. 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.

  19. Proton-induced x-ray emission, proton-induced gamma-ray emission, and x-ray absorption spectroscopy: applications to environmental analysis

    SciTech Connect

    Lytle, N.W.

    1986-01-01

    Two sample preparation techniques, the single-acid wet-oxidation and the lithium metaborate fusion-dissolution, have been applied to PIXE analysis with acceptable trace-element recoveries. A variety of samples have been prepared, including: white bass organs, deer and elk antlers. NRS standard reference materials, IAEA standard animal bone, USGS standard rock samples, and munitions disposal residues. PIGE analysis has been applied to light-element analysis of environment samples. Thin-and thick-target gamma-ray yields were determined for Li, B, O, F, Na, Mg, and Al. Light-elements in coal and oil fly ash were determined with parts per million sensitivity. Nickel and vanadium compounds have been identified in fly ash collected from vanadium compounds have been identified in fly ash collected from the flue lines of an oil-fired power plant using x-ray absorption spectroscopy. VOSO/sub 4/.3H/sub 2/O was the primary vanadium compound and NiO and NiSO/sub 4/ were the primary nickel compounds. NXRAY was written to control data acquisition on a Canberra Series 90 MCA-PDP 11/23PLUS computer system. This program provides for data to be transferred between individual collection regions of the MCA and the host computer, and spectra to be plotted on a HP 7475A graphics plotter.

  20. On the relation between X-ray absorption and optical extinction in AGN

    NASA Astrophysics Data System (ADS)

    Ordovás-Pascual, Ignacio; Mateos, Silvia; Carrera, Francisco J.; Wiersema, Klaas; Caccianiga, Alessandro; Severgnini, Paola; Della Ceca, Roberto; Ballo, Lucia; Moretti, Alberto

    2016-08-01

    According to the Unified Model of Active Galactic Nuclei (AGN), an X-ray unabsorbed AGN should appear as unobscured in the optical (Type-1) and viceversa (Type-2). However, there is an important fraction (10-30%) of AGN whose optical and X-ray classifications do not match. To provide insight into the origin of such apparent discrepancies, we have conducted two analyses: 1) a detailed study of the UV-to-near-IR emission of two X-ray unabsorbed Type-2 AGN drawn from the Bright Ultra-Hard XMM-Newton Survey (BUXS); 2) a statistical analysis of the optical obscuration and X-ray absorption properties of 159 Type-1 AGN drawn from BUXS to determine the distribution of dust-to-gas ratios in AGN over a broad range of luminosities and redshifts. In our works we have also determined the impact of contamination from the AGN hosts in the optical classification of AGNs. Our studies are already provided very exciting results such as the detection of objects with extreme dust-to-gas ratios, between 300-10000 times below the Galactic dust-to-gas ratio.

  1. Surface arsenic speciation of a drinking-water treatment residual using X-ray absorption spectroscopy.

    PubMed

    Makris, Konstantinos C; Sarkar, Dibyendu; Parsons, Jason G; Datta, Rupali; Gardea-Torresdey, Jorge L

    2007-07-15

    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(-1)) after 48 h of reaction. Subsequent desorption experiments with a high P load (7500 mg kg(-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.

  2. 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.

  3. 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.

  4. Solar flare composition and thermodynamics from RESIK X-ray spectra

    SciTech Connect

    Sylwester, B.; Sylwester, J.; Kępa, A.; Mrozek, T.; Phillips, K. J. H. E-mail: js@cbk.pan.wroc.pl E-mail: kennethjhphillips@yahoo.com

    2014-06-01

    Previous estimates of the solar flare abundances of Si, S, Cl, Ar, and K from the RESIK X-ray crystal spectrometer on board the CORONAS-F spacecraft were made on the assumption of isothermal X-ray emission. We investigate the effect on these estimates by relaxing this assumption and instead determining the differential emission measure (DEM) or thermal structure of the emitting plasma by re-analyzing RESIK data for a GOES class M1.0 flare on 2002 November 14 (SOL2002-11-14T22:26) for which there was good data coverage. The analysis method uses a maximum-likelihood (Withbroe-Sylwester) routine for evaluating the DEM. In a first step, called here AbuOpt, an optimized set of abundances of Si, S, Ar, and K is found that is consistent with the observed spectra. With these abundances, the DEM evolution during the flare is found. The abundance optimization leads to revised abundances of silicon and sulfur in the flare plasma: A(S) = 6.94 ± 0.06 and A(Si) = 7.56 ± 0.08 (on a logarithmic scale with A(H) = 12). Previously determined abundances of Ar, K, and Cl from an isothermal assumption are still the preferred values. During the flare's maximum phase, the X-ray-emitting plasma has a basically two-temperature structure, with the cooler plasma with approximately constant temperature (3-6 MK) and a hotter plasma with temperature 16-21 MK. Using imaging data from the RHESSI hard X-ray spacecraft, the emission volume of the hot plasma is deduced from which lower limits of the electron density N{sub e} and the thermal content of the plasma are given.

  5. New Observations of Soft X-ray (0.5-5 keV) Solar Spectra

    NASA Astrophysics Data System (ADS)

    Caspi, A.; Woods, T. N.; Mason, J. P.; Jones, A. R.; Warren, H. P.

    2013-12-01

    The solar corona is the brightest source of X-rays in the solar system, and the X-ray emission is highly variable on many time scales. However, the actual solar soft X-ray (SXR) (0.5-5 keV) spectrum is not well known, particularly during solar quiet periods, as, with few exceptions, this energy range has not been systematically studied in many years. Previous observations include high-resolution but very narrow-band spectra from crystal spectrometers (e.g., Yohkoh/BCS), or integrated broadband irradiances from photometers (e.g., GOES/XRS, TIMED/XPS, etc.) that lack detailed spectral information. In recent years, broadband measurements with moderate energy resolution (~0.5-0.7 keV FWHM) were made by SphinX on CORONAS-Photon and SAX on MESSENGER, although they did not extend to energies below ~1 keV. We present observations of solar SXR emission obtained using new instrumentation flown on recent SDO/EVE calibration rocket underflights. The photon-counting spectrometer, a commercial Amptek X123 with a silicon drift detector and an 8 μm Be window, measures the solar disk-integrated SXR emission from ~0.5 to >10 keV with ~0.15 keV FWHM resolution and 1 s cadence. A novel imager, a pinhole X-ray camera using a cooled frame-transfer CCD (15 μm pixel pitch), Ti/Al/C filter, and 5000 line/mm Au transmission grating, images the full Sun in multiple spectral orders from ~0.1 to ~5 nm with ~10 arcsec/pixel and ~0.01 nm/pixel spatial and spectral detector scales, respectively, and 10 s cadence. These instruments are prototypes for future CubeSat missions currently being developed. We present new results of solar observations on 04 October 2013 (NASA sounding rocket 36.290). We compare with previous results from 23 June 2012 (NASA sounding rocket 36.286), during which solar activity was low and no signal was observed above ~4 keV. We compare our spectral and imaging measurements with spectra and broadband irradiances from other instruments, including SDO/EVE, GOES/XRS, TIMED

  6. A model of the spectra and high-frequency quasi-periodic oscillations in black hole X-ray binaries

    NASA Astrophysics Data System (ADS)

    Dexter, Jason

    2016-07-01

    High-frequency quasi-periodic oscillations (HFQPOs) in black hole X-ray binaries have frequencies comparable to the orbital frequency at the innermost stable circular orbit, and therefore may encode information about strong field general relativity. However, the origin of the oscillations and the associated X-ray spectra remain uncertain. I will discuss a new model for these spectra, which also acts to filter coherent QPOs from local accretion disk oscillations. This model explains many puzzling aspects of HFQPOs, makes predictions which are testable with archival and future X-ray data, and can in principle be used as a new method to measure black hole spin.

  7. Structure of epitaxial (Fe,N) codoped rutile TiO2 thin films by x-ray absorption

    NASA Astrophysics Data System (ADS)

    Kaspar, T. C.; Ney, A.; Mangham, A. N.; Heald, S. M.; Joly, Y.; Ney, V.; Wilhelm, F.; Rogalev, A.; Yakou, F.; Chambers, S. A.

    2012-07-01

    Homoepitaxial thin films of Fe:TiO2 and (Fe,N):TiO2 were deposited on rutile(110) by molecular beam epitaxy. X-ray absorption near edge spectroscopy (XANES) spectra were collected at the Ti L-edge, Fe L-edge, Ti K-edge, O K-edge, and N K-edge. No evidence of structural disorder associated with a high concentration of oxygen vacancies is observed. Substitution of Fe for Ti could be inferred, and secondary phases such as Fe2O3, Fe3O4, and FeTiO3 can be ruled out. The similarity of the N K-edge spectra to O, and the presence of a strong x-ray linear dichroism signal for the N K-edge, indicates that N is substitutional for O in the rutile lattice and is not present as a secondary phase such as TiN. Simulations of the XANES spectra confirm substitution, although N appears to be present in more than one local environment. Neither Fe:TiO2 nor (Fe,N):TiO2 exhibit intrinsic room temperature ferromagnetism, despite the presence of mixed valent Fe(II)/Fe(III) in the reduced (Fe,N):TiO2 film.

  8. High-Pressure Evolution of Fe2O3 Electronic Structure Revealed by X-ray Absorption

    SciTech Connect

    Kao, Chi-Chang

    2011-08-12

    We report the first high pressure measurement of the Fe K-edge in hematite (Fe{sub 2}O{sub 3}) by X-ray absorption spectroscopy in partial fluorescence yield geometry. The pressure-induced evolution of the electronic structure as Fe{sub 2}O{sub 3} transforms from a high-spin insulator to a low-spin metal is reflected in the x-ray absorption pre-edge. The crystal field splitting energy was found to increase monotonically with pressure up to 48 GPa, above which a series of phase transitions occur. Atomic multiplet, cluster diagonalization, and density-functional calculations were performed to simulate the pre-edge absorption spectra, showing good qualitative agreement with the measurements. The mechanism for the pressure-induced phase transitions of Fe{sub 2}O{sub 3} is discussed and it is shown that ligand hybridization significantly reduces the critical high-spin/low-spin gap pressure.

  9. On the origin of X-ray spectra in luminous blazars

    SciTech Connect

    Sikora, Marek; Janiak, Mateusz; Moderski, Rafał; Nalewajko, Krzysztof; Madejski, Greg M. E-mail: mjaniak@camk.edu.pl

    2013-12-10

    Gamma-ray luminosities of some quasar-associated blazars imply jet powers reaching values comparable to the accretion power even if assuming very strong Doppler boosting and very high efficiency of gamma-ray production. With much lower radiative efficiencies of protons than of electrons, and the recent reports of very strong coupling of electrons with shock-heated protons indicated by particle-in-cell simulations, the leptonic models seem to be strongly favored over the hadronic ones. However, the electron-proton coupling combined with the external-radiation-Compton (ERC) models of gamma-ray production in leptonic models predict extremely hard X-ray spectra, with energy indices α {sub x} ∼ 0. This is inconsistent with the observed 2-10 keV slopes of blazars, which cluster around α {sub x} ∼ 0.6. This problem can be resolved by assuming that electrons can be efficiently cooled down radiatively to non-relativistic energies, or that blazar spectra are entirely dominated by the synchrotron self-Compton (SSC) component up to at least 10 keV. Here, we show that the required cooling can be sufficiently efficient only at distances r < 0.03 pc. SSC spectra, on the other hand, can be produced roughly co-spatially with the observed synchrotron and ERC components, which are most likely located roughly at a parsec scale. We show that the dominant SSC component can also be produced much further than the dominant synchrotron and ERC components, at distances of ≳ 10 pc. Hence, depending on the spatial distribution of the energy dissipation along the jet, one may expect to see γ-ray/optical events with either correlated or uncorrelated X-rays. In all cases the number of e{sup +}e{sup –} pairs per proton is predicted to be very low. The direct verification of the proposed SSC scenario, and particularly the question of the co-spatiality of the SSC component with other spectral components, requires sensitive observations in the hard X-ray band. This is now possible with the

  10. Measuring key X-ray parameters from simulated spectra of Seyfert galaxies

    NASA Astrophysics Data System (ADS)

    Bonson, K.; Gallo, L. C.

    2016-05-01

    Supermassive black hole (SMBH) accretion is an important topic of astrophysical research for a variety of fields. However, literature shows that precisely modelling the X-ray reflection component of an accretion disk around a SMBH is challenging. We test how reliably we can measure key active galactic nuclei (AGN) X-ray reflection parameters by simulating the spectra of average Seyfert 1 galaxies and then fitting those spectra using common modelling techniques. The AGN spectra were created from 0.01-300.0 keV using XMM-Newton pn responses and with (3.75±0.10)×106 counts in the 2-10 keV band. The model RELXILL was used to create all spectra with a reflection fraction (ratio of reflected flux over primary flux from 0.1-100 keV) of R = 1. The values of six key parameters were generated randomly within given ranges to simulate the spectra: photon index (Γ), inner emissivity index (q1), black hole spin (a), disk inclination angle (θ), ionization (ξ), and iron abundance in solar units (A_Fe). Once the simulated spectra were created, they were autonomously fit with RELXILL from 2.5-10.0 keV. All six key parameters were allowed to vary throughout the modelling process, with a gradual thawing of model parameters to mimic manual fitting procedure. We find that we can successfully measure key AGN spectral components in this scenario, but some conditions apply: Γ, θ, and A_Fe are well constrained, however they are also consistently overestimated. Only black hole spin (a) measurements that are in extrema, a > 0.9, can be considered reliable. Lastly, ξ and q1 cannot be measured and these parameters - along with intermediate spin values - should be verified using other techniques.

  11. Evidence for core–shell nanoclusters in oxygen dispersion strengthened steels measured using X-ray absorption spectroscopy

    SciTech Connect

    Liu, S.; Odette, G. R.; Segre, C. U.

    2014-02-01

    Nanostructured ferritic alloys (NFA) dispersion strengthened by an ultra high density of Y–Ti–O enriched nano-features (NF) exhibit superior creep strength and the potential for high resistance to radiation damage. However, the detailed character of the NF, that precipitate from solid solution during hot consolidation of metallic powders mechanically alloyed with Y₂O₃, are not well understood. In order to clarify the nature of the NF, X-ray absorption spectroscopy (XAS) technique, including X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) were used to characterize the local structure of the Ti and Y atoms in both NFA powders and consolidated alloys. The powders were characterized in the as-received, as-milled and after annealing milled powders at 850, 1000 and 1150 °C. The consolidated alloys included powders hot isostatic pressed (HIPed) at 1150 °C and commercial vendor alloys, MA957 and J12YWT. The NFA XAS data were compared various Ti and Y-oxide standards. The XANES and EXAFS spectra for the annealed and HIPed powders are similar and show high temperature heat treatments shift the Y and Ti to more oxidized states that are consistent with combinations of Y₂Ti₂O₇ and, especially, TiO. However, the MA957 and J12YWT and annealed–consolidated powder data differ. The commercial vendor alloys results more closely resemble the as-milled powder data and all show that a significant fraction of substitutional Ti remains dissolved in the (BCC) ferrite matrix.

  12. Ab initio calculations of X-ray magnetic circular dichroism spectra within the projector augmented wave method: An implementation into the VASP code

    NASA Astrophysics Data System (ADS)

    Dixit, Anant; Alouani, M.

    2016-10-01

    X-ray absorption and X-ray magnetic circular dichroism (XMCD) are very powerful tools for probing the orbital and spin moments of each atomic species orbital of magnetic materials. In this work, we present the implementation of a module for computing the X-ray absorption and XMCD spectra into the VASP code. We provide a derivation of the absorption cross-section in the electric dipole approximation. The matrix elements, which make up the X-ray absorption cross-section for a given polarization of light, are then computed using either the momentum operator p or the position operator r, within the projector augmented wave method. The core electrons are described using the relativistic basis-set whereas for the valence electrons, the spin-orbit coupling is added perturbatively to the semi-relativistic Hamiltonian. We show that both the p and the r implementations lead to the same results. The results for the K-edge and L23-edges of bcc-iron are then computed and compared to experiment.

  13. A Differential Absorption/Emission Analysis of the Galactic Central Diffuse X-ray Enhancement

    NASA Astrophysics Data System (ADS)

    Yao, Yangsen; Wang, Q.

    2007-05-01

    The soft X-ray background shows a general enhancement toward the inner region of the Galaxy. But whether this enhancement is a local feature (e.g., a superbubble within a distance of 200 pc or a phenomenon related to energetic outflows from the Galactic center/bulge remains unclear. Here we report a comparative X-ray emission and absorption study of diffuse hot gas along the sight lines toward 3C 273 and Mrk 421, on and off the enhancement, but at similar Galactic latitudes. The diffuse 3/4-keV emission intensity, as estimated from the ROSAT All Sky Survey, is about three times higher toward 3C 273 than toward Mrk 421. Based on archival Chandra grating observations of these two AGNs, we detect z 0 X-ray absorption lines (e.g., OVII Kalpha, Kbeta, and OVIII Kalpha transitions) and find that the mean hot gas thermal and kinematic properties along the two sight lines are significantly different. By subtracting the background contribution, as determined along the Mrk 421 sight line, we isolate the net X-ray absorption and emission produced by the hot gas associated with the enhancement in the direction of 3C 273. From a joint analysis of these differential data sets, we obtain the temperature, dispersion velocity, and hydrogen column density as 2.0E6 K, 200 km/s, and 2E19 cm^{-2}, respectively, assuming that the gas is approximately isothermal, solar in metal abundances, and in collisional ionization equilibrium. We also constrain the effective extent of the gas to be 3.4 kpc, strongly suggesting that the enhancement most likely represents a Galactic central phenomenon.

  14. The Galactic Central Diffuse X-Ray Enhancement: A Differential Absorption/Emission Analysis

    NASA Astrophysics Data System (ADS)

    Yao, Yangsen; Wang, Q. Daniel

    2007-09-01

    The soft X-ray background shows a general enhancement toward the inner region of the Galaxy. But whether this enhancement is a local feature (e.g., a superbubble within a distance of <~200 pc) and/or a phenomenon related to energetic outflows from the Galactic center/bulge remains unclear. Here we report a comparative X-ray emission and absorption study of diffuse hot gas along the sight lines toward 3C 273 and Mrk 421, on and off the enhancement, but at similar Galactic latitudes. The diffuse 3/4 keV emission intensity, as estimated from the ROSAT All Sky Survey, is about 3 times higher toward 3C 273 than toward Mrk 421. Based on archival Chandra grating observations of these two AGNs, we detect X-ray absorption lines (e.g., O VII Kα, Kβ, and O VIII Kα transitions at z~0) and find that the mean hot gas thermal and kinematic properties along the two sight lines are significantly different. By subtracting the foreground and background contribution, as determined along the Mrk 421 sight line, we isolate the net X-ray absorption and emission produced by the hot gas associated with the enhancement in the direction of 3C 273. From a joint analysis of these differential data sets, we obtain the temperature, dispersion velocity, and hydrogen column density as 2.0(1.6,2.3)×106 K, 216(104, 480) km s-1, and 2.2(1.4,4.1)×1019 cm-2, respectively (90% confidence intervals), assuming that the gas is approximately isothermal, solar in metal abundances, and equilibrium in collisional ionization. We also constrain the effective line-of-sight extent of the gas to be 3.4(1.0, 10.1) kpc, strongly suggesting that the enhancement most likely represents a Galactic central phenomenon.

  15. 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

  16. 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.

  17. Calculation of x-ray spectra emerging from an x-ray tube. Part I. Electron penetration characteristics in x-ray targets

    SciTech Connect

    Poludniowski, Gavin G.; Evans, Philip M.

    2007-06-15

    The penetration characteristics of electron beams into x-ray targets are investigated for incident electron kinetic energies in the range 50-150 keV. The frequency densities of electrons penetrating to a depth x in a target, with a fraction of initial kinetic energy, u, are calculated using Monte Carlo methods for beam energies of 50, 80, 100, 120 and 150 keV in a tungsten target. The frequency densities for 100 keV electrons in Al, Mo and Re targets are also calculated. A mixture of simple modeling with equations and interpolation from data is used to generalize the calculations in tungsten. Where possible, parameters derived from the Monte Carlo data are compared to experimental measurements. Previous electron transport approximations in the semiempirical models of other authors are discussed and related to this work. In particular, the crudity of the use of the Thomson-Whiddington law to describe electron penetration and energy loss is highlighted. The results presented here may be used towards calculating the target self-attenuation correction for bremsstrahlung photons emitted within a tungsten target.

  18. 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.

  19. 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.

  20. Synchrotron Radiation X-Ray Spectroscopy for Investigations of Intracellular Metallointercalators: X-Ray Fluorescence Imaging and X-Ray Absorption Spectroscopy

    NASA Astrophysics Data System (ADS)

    Dillon, Carolyn T.

    In an effort to determine the therapeutic feasibility of DNA metallointercalators as potential anticancer drugs it is important to confirm that they are capable of targeting DNA in cancer cells or tumours - as is the intended purpose of their design. Microprobe synchrotron radiation X-ray fluorescence (micro-SRXRF) spectroscopy is an ideal technique for investigating the cellular uptake and distribution of metallointercalators. The technique is capable of submicron elemental imaging so that samples as small as individual cells (~10 μm diameter), and the features within them, can be resolved. Consequently, the technique can ascertain whether intracellular metallointercalators colocalise with DNA; namely, in the nucleus during interphase or at the chromosomes during middle prophase to late anaphase. Metals, such as those commonly incorporated into metallointercalators (e.g., Cr, Ni, Co, Pd, Pt, Ru, Rh), are often naturally present in negligible quantities in cancer cells. This fact, together with their higher atomic number, Z, makes them ideal for direct probing using hard X-ray microprobes (as discussed in Sect. 11.2). There is no need for the incorporation of fluorescent tracker dyes or radioactive labels into their chemical structure. This is advantageous since it is unknown whether such chemical modifications alter the uptake kinetics of the metallointercalator [1, 2].

  1. Ab initio calculation of x-ray absorption of iron up to 3 Mbar and 8000 K

    NASA Astrophysics Data System (ADS)

    Mazevet, S.; Recoules, V.; Bouchet, J.; Guyot, F.; Harmand, M.; Ravasio, A.; Benuzzi-Mounaix, A.

    2014-03-01

    Using ab initio simulations within the generalized gradient approximation, we calculate x-ray absorption near edge spectra (XANES) at the iron K edge throughout the high-pressure phase diagram and up to extreme density and temperature conditions that are representative of the Earth's inner core (up to 3 Mbar and 8000 K). We show that XANES spectra near the Fe K edge exhibit clear signatures for the different high-temperature, high-pressure phases of iron. This suggests that XANES spectroscopy might be used to resolve ongoing controversies regarding both the high-pressure melting curve of iron and the nature of the solid phases undergoing melting up to several Mbar. In contrast to diffraction measurements, it also offers a severe constraint for density functional theory predictions of the transport properties of iron by providing direct information on the electronic structure of iron at these extreme conditions.

  2. X-ray absorption spectroscopy of GeO2 glass to 64 GPa.

    PubMed

    Hong, Xinguo; Newville, Matthew; Duffy, Thomas S; Sutton, Stephen R; Rivers, Mark L

    2014-01-22

    The structural behavior of GeO2 glass has been investigated up to 64 GPa using results from x-ray absorption spectroscopy in a diamond anvil cell combined with previously reported density measurements. The difference between the nearest Ge-O distances of glassy and rutile-type GeO2 disappears at the Ge-O distance maximum at 20 GPa, indicating completion of the tetrahedral-octahedral transition in GeO2 glass. The mean-square displacement σ(2) of the Ge-O distance in the first Ge-O shell increases progressively to a maximum at 10 GPa, followed by a substantial reduction at higher pressures. The octahedral glass is, as expected, less dense and has a higher compressibility than the corresponding crystalline phase, but the differences in Ge-O distance and density between the glass and the crystals are gradually eliminated over the 20-40 GPa pressure range. Above 40 GPa, GeO2 forms a dense octahedral glass with a compressibility similar to that of the corresponding crystalline phase (α-PbO2 type). The EXAFS and XANES spectra show evidence for subtle changes in the dense glass continuing to occur at these high pressures. The Ge-O bond distance shows little change between 45-64 GPa, and this may reflect a balance between bond shortening and a gradual coordination number increase with compression. The density of the glass is similar to that of the α-PbO2-type phase, but the Ge-O distance is longer and is close to that in the higher-coordination pyrite-type phase which is stable above ∼60 GPa. The density data provide evidence for a possible discontinuity and change in compressibility at 40-45 GPa, but there are no major changes in the corresponding EXAFS spectra. A pyrite-type local structural model for the glass can provide a reasonable fitting to the XAFS spectra at 64 GPa. PMID:24285424

  3. 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.

  4. Use of X-ray absorption imaging to examine heterogeneous diffusion in fractured crystalline rocks.

    PubMed

    Altman, Susan J; Uchida, Masahiro; Tidwell, Vincent C; Boney, Craig M; Chambers, Bryan P

    2004-03-01

    Heterogeneous diffusion in different regions of a fractured granodiorite from Japan has been observed and measured through the use of X-ray absorption imaging. These regions include gouge-filled fractures, recrystallized fracture-filling material and hydrothermally altered matrix. With the X-ray absorption imaging technique, porosity, relative concentration, and relative mass of an iodine tracer were imaged in two dimensions with a sub-millimeter pixel size. Because portions of the samples analyzed have relatively low porosity values, imaging errors can potentially impact the results. For this reason, efforts were made to better understand and quantify this error. Based on the X-ray data, pore diffusion coefficients (Dp) for the different regions were estimated assuming a single diffusion rate and a lognormal multirate distribution of Dp. Results show Dp for the gouge-filled fractures are over an order of magnitude greater than those of the recrystallized fracture-filling material, which in turn is approximately two times greater than those for the altered matrix. The recrystallized fracture-filling material was found to exhibit the greatest degree of variability. The results of these experiments also provide evidence that diffusion from advective zones in fractures through the gouge-filled fractures and recrystallized fracture-filling material could increase the pore space available for matrix diffusion. This evidence is important for understanding the performance of potential nuclear waste repositories in crystalline rocks as diffusion is thought to be an important retardation mechanism for radionuclides.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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

  10. EVOLUTION OF X-RAY SPECTRA AND LIGHT CURVES OF V1494 AQUILAE

    SciTech Connect

    Rohrbach, J. G.; Ness, J.-U.; Starrfield, S. E-mail: Jan-Uwe.Ness@asu.edu E-mail: juness@sciops.esa.int

    2009-06-15

    We present six Chandra X-ray spectra and light curves obtained for the nova V1494 Aql (1999 No. 2) in outburst. The first three observations were taken with the Advanced CCD Imaging Spectrometer (ACIS-I) on days 134, 187, and 248 after outburst. The count rates were 1.00, 0.69, and 0.53 counts s{sup -1}, respectively. We found no significant periodicity in the ACIS light curves. The X-ray spectra show continuum emission and lines originating from N and O. We found acceptable spectral fits using isothermal APEC models with significantly increased elemental abundances of O and N for all observations. On day 248 after outburst a bright soft component appeared in addition to the fading emission lines. The Chandra observations on days 300, 304, and 727 were carried out with the High Resolution Camera/Low Energy Transmission Grating Spectrometer (LETGS). The spectra consist of continuum emission plus strong emission lines of O and N, implying a high abundance of these elements. On day 300, a flare occurred and periodic oscillations were detected in the light curves taken on days 300 and 304. This flare must have originated deep in the outflowing material since it was variable on short timescales. The spectra extracted immediately before and after the flare are remarkably similar, implying that the flare was an extremely isolated event. Our attempts to fit blackbody, cloudy, or APEC models to the LETGS spectra failed, owing to the difficulty in disentangling continuum and emission-line components. The spectrum extracted during the flare shows a significant increase in the strengths of many of the lines and the appearance of several previously undetected lines. In addition, some of the lines seen before and after the flare are not present during the flare. On day 727 only the count rate from the zeroth order could be derived, and the source was too faint for the extraction of a light curve or spectrum.

  11. The origin of blueshifted absorption features in the X-ray spectrum of PG 1211+143: outflow or disc

    NASA Astrophysics Data System (ADS)

    Gallo, L. C.; Fabian, A. C.

    2013-07-01

    In some radio-quiet active galactic nuclei (AGN), high-energy absorption features in the X-ray spectra have been interpreted as ultrafast outflows (UFOs) - highly ionized material (e.g. Fe XXV and Fe XXVI) ejected at mildly relativistic velocities. In some cases, these outflows can carry energy in excess of the binding energy of the host galaxy. Needless to say, these features demand our attention as they are strong signatures of AGN feedback and will influence galaxy evolution. For the same reason, alternative models need to be discussed and refuted or confirmed. Gallo and Fabian proposed that some of these features could arise from resonance absorption of the reflected spectrum in a layer of ionized material located above and corotating with the accretion disc. Therefore, the absorbing medium would be subjected to similar blurring effects as seen in the disc. A priori, the existence of such plasma above the disc is as plausible as a fast wind. In this work, we highlight the ambiguity by demonstrating that the absorption model can describe the ˜7.6 keV absorption feature (and possibly other features) in the quasar PG 1211+143, an AGN that is often described as a classic example of a UFO. In this model, the 2-10 keV spectrum would be largely reflection dominated (as opposed to power law dominated in the wind models) and the resonance absorption would be originating in a layer between about 6 and 60 gravitational radii. The studies of such features constitute a cornerstone for future X-ray observatories like Astro-H and Athena+. Should our model prove correct, or at least important in some cases, then absorption will provide another diagnostic tool with which to probe the inner accretion flow with future missions.

  12. Manganese L-edge X-ray absorption spectroscopy of manganese catalase from Lactobacillus plantarum and mixed valence manganese complexes

    SciTech Connect

    Grush, M.M.; Chen, J.; George, S.J.

    1996-01-10

    The first Mn L-edge absorption spectra of a Mn metalloprotein are presented in this paper. Both reduced and superoxidized Mn catalase have been examined by fluorescence-detected soft X-ray absorption spectroscopy, and their Mn L-edge spectra are dramatically different. The spectrum of reduced Mn(II)Mn(II) catalase has been interpreted by ligand field atomic multiplet calculations and by comparison to model compound spectra. The analysis finds a 10 Dq value of nearly 1.1 eV, consistent with coordination by predominately nitrogen and oxygen donor ligands. For interpretation of mixed valence Mn spectra, an empirical simulation procedure based on the addition of homovalent model compound spectra has been developed and was tested on a variety of Mn complexes and superoxidized Mn catalase. This routine was also used to determine the oxidation state composition of the Mn in [Ba{sub 8}Na{sub 2}ClMn{sub 16}(OH){sub 8}(CO{sub 3}){sub 4}L{sub 8}] .53 H{sub 2}O (L=1,3-diamino-2-hydroxypropane-N,N,N`N`-tetraacetic acid). 27 refs., 6 figs.

  13. Inside and Outside: X-ray Absorption Spectroscopy Mapping of Chemical Domains in Graphene Oxide.

    PubMed

    De Jesus, Luis R; Dennis, Robert V; Depner, Sean W; Jaye, Cherno; Fischer, Daniel A; Banerjee, Sarbajit

    2013-09-19

    The oxidative chemistry of graphite has been investigated for over 150 years and has attracted renewed interest given the importance of exfoliated graphene oxide as a precursor to chemically derived graphene. However, the bond connectivities, steric orientations, and spatial distribution of functional groups remain to be unequivocally determined for this highly inhomogeneous nonstoichiometric material. Here, we demonstrate the application of principal component analysis to scanning transmission X-ray microscopy data for the construction of detailed real space chemical maps of graphene oxide. These chemical maps indicate very distinct functionalization motifs at the edges and interiors and, in conjunction with angle-resolved near-edge X-ray absorption fine structure spectroscopy, enable determination of the spatial location and orientations of functional groups. Chemical imaging of graphene oxide provides experimental validation of the modified Lerf-Klinowski structural model. Specifically, we note increased contributions from carboxylic acid moieties at edge sites with epoxide and hydroxyl species dominant within the interior domains.

  14. Elemental characterisation of melanin in feathers via synchrotron X-ray imaging and absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Edwards, Nicholas P.; van Veelen, Arjen; Anné, Jennifer; Manning, Phillip L.; Bergmann, Uwe; Sellers, William I.; Egerton, Victoria M.; Sokaras, Dimosthenis; Alonso-Mori, Roberto; Wakamatsu, Kazumasa; Ito, Shosuke; Wogelius, Roy A.

    2016-09-01

    Melanin is a critical component of biological systems, but the exact chemistry of melanin is still imprecisely known. This is partly due to melanin’s complex heterogeneous nature and partly because many studies use synthetic analogues and/or pigments extracted from their natural biological setting, which may display important differences from endogenous pigments. Here we demonstrate how synchrotron X-ray analyses can non-destructively characterise the elements associated with melanin pigment in situ within extant feathers. Elemental imaging shows that the distributions of Ca, Cu and Zn are almost exclusively controlled by melanin pigment distribution. X-ray absorption spectroscopy demonstrates that the atomic coordination of zinc and sulfur is different within eumelanised regions compared to pheomelanised regions. This not only impacts our fundamental understanding of pigmentation in extant organisms but also provides a significant contribution to the evidence-based colour palette available for reconstructing the appearance of fossil organisms.

  15. Elemental characterisation of melanin in feathers via synchrotron X-ray imaging and absorption spectroscopy

    PubMed Central

    Edwards, Nicholas P.; van Veelen, Arjen; Anné, Jennifer; Manning, Phillip L.; Bergmann, Uwe; Sellers, William I.; Egerton, Victoria M.; Sokaras, Dimosthenis; Alonso-Mori, Roberto; Wakamatsu, Kazumasa; Ito, Shosuke; Wogelius, Roy A.

    2016-01-01

    Melanin is a critical component of biological systems, but the exact chemistry of melanin is still imprecisely known. This is partly due to melanin’s complex heterogeneous nature and partly because many studies use synthetic analogues and/or pigments extracted from their natural biological setting, which may display important differences from endogenous pigments. Here we demonstrate how synchrotron X-ray analyses can non-destructively characterise the elements associated with melanin pigment in situ within extant feathers. Elemental imaging shows that the distributions of Ca, Cu and Zn are almost exclusively controlled by melanin pigment distribution. X-ray absorption spectroscopy demonstrates that the atomic coordination of zinc and sulfur is different within eumelanised regions compared to pheomelanised regions. This not only impacts our fundamental understanding of pigmentation in extant organisms but also provides a significant contribution to the evidence-based colour palette available for reconstructing the appearance of fossil organisms. PMID:27658854

  16. Saturable Absorption of an X-Ray Free-Electron-Laser Heated Solid-Density Plasma

    NASA Astrophysics Data System (ADS)

    Wark, J. S.; Rackstraw, D. S.; Ciricosta, O.; Vinko, S. M.; Burian, T.; Chalupsky, J.; Hajkova, V.; Juha, L.; Barbrel, B.; Engelhorn, K.; Cho, B.-I.; Chung, H.-K.; Dakovski, G.; Krzywinski, J.; Heimann, P.; Holmes, M.; Turner, J.; Lee, R. W.; Toleikis, S.; Zastrau, U.

    2015-11-01

    High-intensity ~1017 Wcm-2, short duration (100 fsec) x-ray pulses from the LCLS x-ray free-electron laser, with photon energies ranging from below to above the K-edge of cold Al (1560 eV), are used to generate and probe a solid-density aluminum plasma. The photon-energy-dependent transmission of the heating beam is studied through the use of a photodiode. Saturable absorption is observed, with the resulting transmission differing significantly from the cold case, with the increased transmission being due to the K-edge energy of the dominant ion species shifting in time as the solid-density target is heated, in good agreement with atomic-kinetics simulations.

  17. 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.

  18. 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

  19. 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.

  20. Pristine and reacted surfaces of pyrrhotite and arsenopyrite as studied by X-ray absorption near-edge structure spectroscopy

    NASA Astrophysics Data System (ADS)

    Mikhlin, Yu.; Tomashevich, Ye.

    2005-05-01

    Fe L-, S L-, and O K-edge X-ray absorption spectra of natural monoclinic and hexagonal pyrrhotites, Fe1-xS, and arsenopyrite, FeAsS, have been measured and compared with the spectra of minerals oxidized in air and treated in aqueous acidic solutions, as well as with the previous XPS studies. The Fe L-edge X-ray absorption near-edge structure (XANES) of vacuum-cleaved pyrrhotites showed the presence of, aside from high-spin Fe2+, small quantity of Fe3+, which was higher for a monoclinic mineral. The spectra of the essentially metal-depleted surfaces produced by the non-oxidative and oxidative acidic leaching of pyrrhotites exhibit substantially enhanced contributions of Fe3+ and a form of high-spin Fe2+ with the energy of the 3d orbitals increased by 0.3 0.8 eV; low-spin Fe2+ was not confidently distinguished, owing probably to its rapid oxidation. The changes in the S L-edge spectra reflect the emergence of Fe3+ and reduced density of S s Fe 4s antibonding states. The Fe L-edge XANES of arsenopyrite shows almost unsplit eg band of singlet Fe2+ along with minor contributions attributable to high-spin Fe2+ and Fe3+. Iron retains the low-spin state in the sulphur-excessive layer formed by the oxidative leaching in 0.4 M ferric chloride and ferric sulphate acidic solutions. The S L-edge XANES of arsenopyrite leached in the ferric chloride, but not ferric sulphate, solution has considerably decreased pre-edge maxima, indicating the lesser admixture of S s states to Fe 3d orbitals in the reacted surface layer. The ferric nitrate treatment produces Fe3+ species and sulphur in oxidation state between +2 and +4.

  1. X-Ray Spectra from MHD Simulations of Accreting Black Holes

    NASA Technical Reports Server (NTRS)

    Schnittman, Jeremy D.; Krolik, Julian H.; Noble, Scott C.

    2012-01-01

    We present the results of a new global radiation transport code coupled to a general relativistic magneto-hydrodynamic simulation of an accreting, nonrotating black hole. For the first time, we are able to explain from first principles in a self-consistent way the X-ray spectra observed from stellar-mass black holes, including a thermal peak, Compton reflection hump, power-law tail, and broad iron line. Varying only the mass accretion rate, we are able to reproduce the low/hard, steep power-law, and thermal-dominant states seen in most galactic black hole sources. The temperature in the corona is T(sub e) 10 keV in a boundary layer near the disk and rises smoothly to T(sub e) greater than or approximately 100 keV in low-density regions far above the disk. Even as the disk's reflection edge varies from the horizon out to approximately equal to 6M as the accretion rate decreases, we find that the shape of the Fe Ka line is remarkably constant. This is because photons emitted from the plunging region are strongly beamed into the horizon and never reach the observer. We have also carried out a basic timing analysis of the spectra and find that the fractional variability increases with photon energy and viewer inclination angle, consistent with the coronal hot spot model for X-ray fluctuations.

  2. EMISSION LINES BETWEEN 1 AND 2 keV IN COMETARY X-RAY SPECTRA

    SciTech Connect

    Ewing, Ian; Christian, Damian J.; Bodewits, Dennis; Dennerl, Konrad; Lisse, Carey M.; Wolk, Scott J. E-mail: daman.christian@csun.edu

    2013-01-20

    We present the detection of new cometary X-ray emission lines in the 1.0-2.0 keV range using a sample of comets observed with the Chandra X-Ray Observatory and ACIS spectrometer. We have selected five comets from the Chandra sample with good signal-to-noise spectra. The surveyed comets are C/1999 S4 (LINEAR), C/1999 T1 (McNaught-Hartley), 153P/2002 (Ikeya-Zhang), 2P/2003 (Encke), and C/2008 8P (Tuttle). We modeled the spectra with an extended version of our solar wind charge exchange (SWCX) emission model. Above 1 keV, we find Ikeya-Zhang to have strong emission lines at 1340 and 1850 eV which we identify as being created by SWCX lines of Mg XI and Si XIII, respectively, and weaker emission lines at 1470, 1600, and 1950 eV formed by SWCX of Mg XII, Mg XI, and Si XIV, respectively. The Mg XI and XII and Si XIII and XIV lines are detected at a significant level for the other comets in our sample (LS4, MH, Encke, 8P), and these lines promise additional diagnostics to be included in SWCX models. The silicon lines in the 1700-2000 eV range are detected for all comets, but with the rising background and decreasing cometary emission, we caution that these detections need further confirmation with higher resolution instruments.

  3. Monte Carlo simulation of the effects of anode surface roughness on x-ray spectra

    SciTech Connect

    Kakonyi, Robert; Erdelyi, Miklos; Szabo, Gabor

    2010-11-15

    Purpose: Spectral and angular distribution of the x-ray beam generated by medical x-ray tubes as a function of anode surface roughness was analyzed. Methods: Different sets of profiles such as ideal flat, regular profiles, and measured profiles adopted from the literature were analyzed by means of MCNPX Monte Carlo simulator. The geometry used was simplified to separate different physical effects. A sphere centered on the origin of the coordinate system was divided into two hemispheres filled with tungsten and a vacuum, respectively. The studied anode surfaces were placed at the center of the plane of the hemisphere. The profiles were realized by means of the general lattice structure of the MCNPX. The energy and angular distributions of the excited photons were recorded with energy and angular resolutions of 0.5 keV and 1 deg., respectively, by means of point detectors. The range of the studied anode surface roughness was 0-550 {mu}m R{sub a}. The emission angle dependencies of the following quantities were analyzed: Half value layer (HVL) value, intensity, and spectral photon flux. Results: The analysis of the HVL of the x-ray beam showed that around an emission angle of 5 deg., the hardness of the beam was practically independent of the surface roughness. The value of this emission angle depends on the filtration. Below this critical angle, the HVL value decreases, while at a higher emission angle, the beam becomes harder with increasing surface roughness. The intensity degradation saturates with increasing roughness. The position of the maximum spectral photon flux shifts to higher emission angles as the anode surface roughness increases. The surface roughness (R{sub a}) was found to be an inadequate quantity to describe the effect of anode surface roughness on x-ray spectra since no definite connection was found between the values of the intensity degradation and surface roughness. At 120 kVp tube voltage and at a 3.84 {mu}m R{sub a} roughness value, the

  4. Local structure of Fe in Fe-doped misfit-layered calcium cobaltite: An X-ray absorption spectroscopy study

    SciTech Connect

    Prasoetsopha, Natkrita; Pinitsoontorn, Supree; Bootchanont, Atipong; Kidkhunthod, Pinit; Srepusharawoot, Pornjuk; Kamwanna, Teerasak; Amornkitbamrung, Vittaya; Kurosaki, Ken; Yamanaka, Shinsuke

    2013-08-15

    Polycrystalline Ca{sub 3}Co{sub 4−x}Fe{sub x}O{sub 9+δ} ceramics (x=0, 0.01, 0.03, 0.05) were fabricated using a simple thermal hydro-decomposition method and a spark plasma sintering technique. Thermoelectric property measurements showed that increasing Fe concentration resulted in a decrease in electrical resistivity, thermopower and thermal conductivity, leading to an improvement in the dimensionless figure-of-merit, >35% for x=0.05 at 1073 K. An X-ray absorption spectroscopy technique was used to investigate the local structure of Fe ions in the Ca{sub 3}Co{sub 4−x}Fe{sub x}O{sub 9+δ} structure for the first time. By fitting data from the extended X-ray absorption fine structure (EXAFS) spectra and analyzing the X-ray absorption near-edge structure (XANES) spectra incorporated with first principle simulation, it was shown that Fe was substituted for Co in the the Ca{sub 2}CoO{sub 3} (rocksalt, RS) layer rather than in the CoO{sub 2} layer. Variation in the thermoelectric properties as a function of Fe concentration was attributed to charge transfer between the CoO{sub 2} and the RS layers. The origin of the preferential Fe substitution site was investigated considering the ionic radii of Co and Fe and the total energy of the system. - Graphical abstract: The Fe K-edge XANES spectra of: (a) experimental result in comparison to the simulated spectra when Fe atoms were substituted in the RS layer; (b) with magnetic moment; (c) without magnetic moment, and in the CoO{sub 2} layer; (d) with magnetic moment and (e) without magnetic moment. Highlights: • Synthesis, structural studies, and thermoelectric properties of Ca{sub 3}Co{sub 4−x}Fe{sub x}O{sub 9+δ}. • Direct evidence for the local structure of the Fe ions in the Ca{sub 3}Co{sub 4−x}Fe{sub x}O{sub 9+δ} using XAS analysis. • EXAFS and XANES analysis showed that Fe was likely to be situated in the RS layer structure. • Changes in TE property with Fe content was due to charge transfer between

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Unidentified line in x-ray spectra of the Andromeda galaxy and Perseus galaxy cluster.

    PubMed

    Boyarsky, A; Ruchayskiy, O; Iakubovskyi, D; Franse, J

    2014-12-19

    We report a weak line at 3.52±0.02  keV in x-ray spectra of the Andromeda galaxy and the Perseus galaxy cluster observed by the metal-oxide-silicon (MOS) and p-n (PN) CCD cameras of the XMM-Newton telescope. This line is not known as an atomic line in the spectra of galaxies or clusters. It becomes stronger towards the centers of the objects; is stronger for Perseus than for M31; is absent in the spectrum of a deep "blank sky" data set. Although for each object it is hard to exclude that the feature is due to an instrumental effect or an atomic line, it is consistent with the behavior of a dark matter decay line. Future (non-)detections of this line in multiple objects may help to reveal its nature.

  10. Unidentified line in x-ray spectra of the Andromeda galaxy and Perseus galaxy cluster.

    PubMed

    Boyarsky, A; Ruchayskiy, O; Iakubovskyi, D; Franse, J

    2014-12-19

    We report a weak line at 3.52±0.02  keV in x-ray spectra of the Andromeda galaxy and the Perseus galaxy cluster observed by the metal-oxide-silicon (MOS) and p-n (PN) CCD cameras of the XMM-Newton telescope. This line is not known as an atomic line in the spectra of galaxies or clusters. It becomes stronger towards the centers of the objects; is stronger for Perseus than for M31; is absent in the spectrum of a deep "blank sky" data set. Although for each object it is hard to exclude that the feature is due to an instrumental effect or an atomic line, it is consistent with the behavior of a dark matter decay line. Future (non-)detections of this line in multiple objects may help to reveal its nature. PMID:25554871

  11. Nuclear Magnetic Resonance and X-Ray Absorption Spectroscopic Studies of Lithium Insertion in Silver Vanadium Oxide Cathodes

    SciTech Connect

    Leifer,N.; Colon, A.; Martocci, k.; Greenbaum, S.; Alamgir, F.; Reddy, T.; Gleason, N.; Leising, R.; Takeuchi, E.

    2007-01-01

    Structural studies have been carried out on Ag{sub 2}V{sub 4}O{sub 11} (silver vanadium oxide, SVO) and Li{sub x}Ag{sub 2}V{sub 4}O{sub 11}, lithiated SVO with x=0.72, 2.13, and 5.59 using nuclear magnetic resonance (NMR) and X-ray absorption spectroscopy (XAS). Lithium-7 NMR indicates the formation of a solid electrolyte interphase layer on the x=0.72 sample and lithium intercalation into both octahedral and tetrahedral sites in the SVO lattice, and that most but not all of the Ag (I) is reduced prior to initiation of V(V) reduction. Vanadium-51 NMR studies of SVO and lithiated SVO show decreased crystallinity with increased lithiation, as previously reported. Silver XAS studies indicate the formation of metallic silver crystallites in all the lithiated samples. A comparison of X-ray absorption near edge spectroscopy spectra for vanadium in these samples with those of reference compounds shows that some reduction of vanadium (V) occurs in the lithiated SVO with x=0.72 and increases with further lithiation leading to the formation of V(IV) and V(III) species. The results of this study indicate that vanadium(V) reduction occurs in parallel with silver (I) reduction during the initial stages of SVO lithiation, leading ultimately to the formation of vanadium (IV) and (III) species with further lithiation.

  12. Electronic structure of d{sup 0} vanadates obtained by x-ray absorption and emission spectroscopies

    SciTech Connect

    Herrera, G.; Jimenez-Mier, J.; Chavira, E.; Moewes, A.; Wilks, R.

    2009-01-29

    We present experimental results for x-ray absorption at the L{sub 2,3}-edge of vanadium in V{sub 2}O{sub 5}, YVO{sub 4} and LaVO{sub 4} compounds and at the M{sub 4,5}-edge of lanthanum in LaVO{sub 4} compound. The data are interpreted in terms of the multiplet structure of the transition metal ion V{sup 5+} (d{sup 0}) and rare earth ion La{sup 3+} (d{sup 10}). The data are compared with calculations in the free-ion approximation for La and including the effects of the D{sub 4h} ligand field and charge transfer for V. These calculations allow a direct interpretation of the absorption spectra. Good overall agreement between experiment and theory is found. We also show resonant x-ray emission (XES) data for these compounds obtained at the top of the L{sub 2} excitation.

  13. X-ray absorption of cadmium in the L-edge region

    SciTech Connect

    Padeznik Gomilsek, J.; Kodre, A.; Arcon, I.; Bratina, G.

    2011-11-15

    Atomic x-ray absorption of cadmium in the energy region of L edges was measured on the vapor of the element, in parallel with the absorption of Cd metal foil. Ionization thresholds of the three subshells are determined from the edge profiles, through the energies of pre-edge resonances and indium optical levels in the Z + 1 approximation. A purely experimental result, without extraneous data and with an accuracy of 0.2 eV, is the energy difference between the pre-edge resonance and the threshold energy of the metallic state. Some multielectron-excitation resonances are identified within 30 eV above the edges. The metal foil absorption is used for absolute determination of Cd absorption coefficient.

  14. 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.

  15. Probing cation antisite disorder in Gd2 Ti2 O7 pyrochlore by site-specific near-edge x-ray-absorption fine structure and x-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Nachimuthu, P.; Thevuthasan, S.; Engelhard, M. H.; Weber, W. J.; Shuh, D. K.; Hamdan, N. M.; Mun, B. S.; Adams, E. M.; McCready, D. E.; Shutthanandan, V.; Lindle, D. W.; Balakrishnan, G.; Paul, D. M.; Gullikson, E. M.; Perera, R. C. C.; Lian, J.; Wang, L. M.; Ewing, R. C.

    2004-09-01

    Disorder in Gd2Ti2O7 is investigated by near-edge x-ray-absorption fine structure (NEXAFS) and x-ray photoelectron spectroscopy (XPS). NEXAFS shows Ti4+ ions occupy octahedral sites with a tetragonal distortion induced by vacant oxygen sites. O1s XPS spectra obtained with a charge neutralization system from Gd2Ti2O7(100) and the Gd2Ti2O7 pyrochlore used by Chen [Phys. Rev. Lett. 88, 105901 (2002)], both yielded a single peak, unlike the previous result on the latter that found two peaks. The current results give no evidence for an anisotropic distribution of Ti and O. The extra features reported in the aforementioned communication resulted from charging effects and incomplete surface cleaning. Thus, a result confirming the direct observation of simultaneous cation-anion antisite disordering and lending credence to the split vacancy model has been clarified.

  16. 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

  17. Implications of solar flare hard X-ray ``knee'' spectra observed by RHESSI

    NASA Astrophysics Data System (ADS)

    Conway, A. J.; Brown, J. C.; Eves, B. A. C.; Kontar, E.

    2003-08-01

    We analyse the RHESSI photon spectra of four flares that exhibit significant deviations from power laws - i.e. changes in the ``local'' Hard X-ray spectral index. These spectra are characterised by two regions of constant power law index connected by a region of changing spectral index - the ``knee''. We develop theoretical and numerical methods of describing such knees in terms of variable photon spectral indices and we study the results of their inversions for source mean thin target and collisional thick target injection electron spectra. We show that a particularly sharp knee can produce unphysical negative values in the electron spectra, and we derive inequalities that can be used to test for this without the need for an inversion to be performed. Such unphysical features would indicate that source model assumptions were being violated, particularly strongly for the collisional thick target model which assumes a specific form for electron energy loss. For all four flares considered here we find that the knees do not correspond to unphysical electron spectra. In the three flares that have downward knees we conclude that the knee can be explained in terms of transport effects through a region of non-uniform ionisation. In the other flare, which has an upward knee, we conclude that it is most likely a feature of the accelerated spectrum.

  18. In-situ X-ray absorption spectroscopy analysis of capacity fade in nanoscale-LiCoO{sub 2}

    SciTech Connect

    Patridge, Christopher J.; Swider-Lyons, Karen E.; Twigg, Mark E.; Ramaker, David E.

    2013-07-15

    The local structure of nanoscale (∼10–40 nm) LiCoO{sub 2} is monitored during electrochemical cycling utilizing in-situ X-ray absorption spectroscopy (XAS). The high surface area of the LiCoO{sub 2} nanoparticles not only enhances capacity fade, but also provides a large signal from the particle surface relative to the bulk. Changes in the nanoscale LiCoO{sub 2} metal-oxide bond lengths, structural disorder, and chemical state are tracked during cycling by adapting the delta mu (Δμ) technique in complement with comprehensive extended X-ray absorption fine structure (EXAFS) modeling. For the first time, we use a Δμ EXAFS method, and by comparison of the difference EXAFS spectra, extrapolate significant coordination changes and reduction of cobalt species with cycling. This combined approach suggests Li–Co site exchange at the surface of the nanoscale LiCoO{sub 2} as a likely factor in the capacity fade and irreversible losses in practical, microscale LiCoO{sub 2}. - Graphical abstract: Electrochemical cycling of Li-ion batteries has strong impact on the structure and integrity of the cathode active material particularly near the surface/electrolyte interface. In developing a new method, we have used in-situ X-ray absorption spectroscopy during electrochemical cycling of nanoscale LiCoO{sub 2} to track changes during charge and discharge and between subsequent cycles. Using difference spectra, several small changes in Co-O bond length, Co-O and Co-Co coordination, and site exchange between Co and Li sites can be tracked. These methods show promise as a new technique to better understand processes which lead to capacity fade and loss in Li-ion batteries. - Highlights: • A new method is developed to understand capacity fade in Li-ion battery cathodes. • Structural changes are tracked during Li intercalation/deintercalation of LiCoO{sub 2}. • Surface structural changes are emphasized using nanoscale-LiCoO{sub 2} and difference spectra. • Full multiple

  19. 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

  20. 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.