Fe K (fe + k)

Distribution by Scientific Domains

Selected Abstracts

Iron K -edge anomalous small-angle X-ray scattering at 15-ID-D at the Advanced Photon Source

Nigel Kirby
Small-angle X-ray scattering (SAXS) is an ideal technique for characterizing inorganic nanoparticles in biological specimens large enough to be representative of tissues. As tissues consist of complex mixtures of structures, identifying particular structural features from single-wavelength scattering data can be problematic. Synchrotron SAXS can supply element-specific structural information in complex samples, using anomalous scattering close to absorption edges. Anomalous dispersion is a secondary effect that produces relatively subtle changes in scattering patterns. In order to utilize this effect for anomalous SAXS analysis, stringent control of instrument performance is required. This work outlines the development of high-quality data collection and processing strategies for Fe K -edge anomalous SAXS on the ChemMatCARS beamline at the Advanced Photon Source (APS), Chicago, with an emphasis on intensity normalization. The methods reported here were developed during a study of iron-loaded mammal tissues, but could equally well be applied to other complex specimens. [source]

Analysing metals in bottle-grade poly(ethylene terephthalate) by X-ray fluorescence spectrometry

Wanderson Romăo
Abstract After a rigorous cleaning process, recycled food-grade poly(ethylene terephthalate) (PET), can be mixed with virgin PET resin in different concentrations and used for packaging of soft drinks. Therefore, it is important to have an experimental method to distinguish the presence of recycled polymer in a batch and to check its "true quality." One of the issues to be verified is the presence of inorganic contaminants due to the recycling process. X-ray fluorescence technique is one alternative for this kind of analysis. The results obtained in this work show that bottle-grade PET samples (PET-btg) are made either via direct esterification or by a transesterification process. Samples that were subjected to thermo-mechanical processings (superclean® processing, PET-btg blends processed in our laboratory and soft drink PET packaging) present Fe K, emission lines with higher intensities than those presented by virgin bottle-grade PET. After applying principal component analysis, it can be concluded that Fe is an intrinsic contaminant after the recycling process, furnishing a way to indicate class separations of PET-btg. A calibration and validation partial least squares model was constructed to predict the weight percent of post-consumption bottle-grade PET in commercial PET samples. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

Polycapillary-optics-based micro-XANES and micro-EXAFS at a third-generation bending-magnet beamline

Geert Silversmit
A focusing system based on a polycapillary half-lens optic has been successfully tested for transmission and fluorescence µ-X-ray absorption spectroscopy at a third-generation bending-magnet beamline equipped with a non-fixed-exit Si(111) monochromator. The vertical positional variations of the X-ray beam owing to the use of a non-fixed-exit monochromator were shown to pose only a limited problem by using the polycapillary optic. The expected height variation for an EXAFS scan around the Fe K -edge is approximately 200,µm on the lens input side and this was reduced to ,1,µm for the focused beam. Beam sizes (FWHM) of 12,16,µm, transmission efficiencies of 25,45% and intensity gain factors, compared with the non-focused beam, of about 2000 were obtained in the 7,14,keV energy range for an incoming beam of 0.5 × 2,mm (vertical × horizontal). As a practical application, an As K -edge µ-XANES study of cucumber root and hypocotyl was performed to determine the As oxidation state in the different plant parts and to identify a possible metabolic conversion by the plant. [source]

Compton scattering of Fe K, lines in magnetic cataclysmic variables

A. L. McNamara
ABSTRACT Compton scattering of X-rays in the bulk flow of the accretion column in magnetic cataclysmic variables (mCVs) can significantly shift photon energies. We present Monte Carlo simulations based on a non-linear algorithm demonstrating the effects of Compton scattering on the H-, He-like and neutral Fe K, lines produced in the post-shock region of the accretion column. The peak line emissivities of the photons in the post-shock flow are taken into consideration and frequency shifts due to Doppler effects are also included. We find that line profiles are most distorted by Compton scattering effects in strongly magnetized mCVs with a low white dwarf mass and high mass accretion rate and which are viewed at an oblique angle with respect to the accretion column. The resulting line profiles are most sensitive to the inclination angle. We have also explored the effects of modifying the accretion column width and using a realistic emissivity profile. We find that these do not have a significant overall effect on the resulting line profiles. A comparison of our simulated line spectra with high-resolution Chandra/HETGS observations of the mCV GK Per indicates that a wing feature redward of the 6.4-keV line may result from Compton recoil near the base of the accretion column. [source]

The warm absorber of the type 1 Seyfert galaxy H1419+480

X. Barcons
ABSTRACT The bright type 1 Seyfert galaxy H1419+480 (z, 0.072), whose X-ray colours from earlier HEAO-1 and ROSAT missions suggested a complex X-ray spectrum, has been observed with XMM,Newton. The EPIC spectrum above 2 keV is well fitted by a power law with photon index ,= 1.84 ± 0.01 and an Fe K, line of equivalent width ,250 eV. At softer energies, a decrement with respect to this model extending from 0.5 to 1 keV is clearly detected. After trying a number of models, we find that the best fit corresponds to O vii absorption at the emission redshift, plus a 2, detection of O viii absorption. A photoionized gas model fit yields log ,, 1.15,1.30 (, in erg cm s,1) with NH, 5 × 1021 cm,2 for solar abundances. We find that the ionized absorber was weaker or absent in an earlier ROSAT observation. An International Ultraviolet Explorer spectrum of this source obtained two decades before shows a variable (within a year) C iv absorber outflowing with a velocity ,1800 km s,1. We show that both X-ray and ultraviolet absorptions are consistent with arising in the same gas, with varying ionization. [source]

Iron K, line profiles and the inner boundary condition of accretion flows

A. Merloni
ABSTRACT Recent X-ray observations have shown evidence for exceptionally broad and skewed iron K, emission lines from several accreting black hole systems. The lines are assumed to be due to fluorescence of the accretion disc illuminated by a surrounding corona and require a steep emissivity profile increasing into the innermost radius. This appears to question both standard accretion disc theory and the zero-torque assumption for the inner boundary condition, both of which predict a much less extreme profile. Instead it argues that a torque may be present due to magnetic coupling with matter in the plunging region or even to the spinning black hole itself. Discussion so far has centred on the torque acting on the disc. However, the crucial determinant of the iron line profile is the radial variation of the power radiated in the corona. Here we study the effects of different inner boundary conditions on the coronal emissivity and on the profiles of the observable Fe K, lines. We argue that in the extreme case where a prominent highly redshifted component of the iron line is detected, requiring a steep emissivity profile in the innermost part and a flatter one outside, energy from the gas plunging into the black hole is being fed directly to the corona. [source]

Relativistic ionized accretion disc models of MCG,6-30-15

D.R. Ballantyne
We present results from fitting of ionized accretion disc models to three long ASCA observations of the Seyfert 1 galaxy MCG,6-30-15. All three data sets can be fitted by a model consisting of ionized reflection from the inner region of the accretion disc (with twice solar Fe abundance) and a separate disc-line component from farther out on the disc. The disc-line is required to fit the height of the observed Fe K, line profile. However, we show that a much simpler model of reflection from a very weakly ionized constant-density disc also fits the data. In this case only a single cold Fe K, line at 6.4 keV is required to fit the observed line. The ionized disc models predict that O viii K,, C vi K,, Fe xvii L, and Fe xviii L, lines will appear in the soft X-ray region of the reflection spectrum, but are greatly blurred as a result of Compton scattering. The equivalent width (EW) of O viii K, is estimated to be about 10 eV and seems to be as strong as the blend of the Fe L lines. This result creates difficulty for the claim of a strong relativistic O viii line in the XMM - Newton grating spectrum of MCG,6-30-15, although we cannot strictly rule it out since MCG,6-30-15 was in an anomalously low state during that observation. We find that increasing the O abundance or breaking the continuum below 2 keV will not significantly strengthen the line. The second Fe K, line component in the ionized disc model may arise from neutral reflection from a flared disc, or from a second illumination event. The data cannot distinguish between the two cases, and we conclude that single-zone ionized disc models have difficulty fitting these hard X-ray data of MCG,6-30-15. [source]