Measurements of anomalous dispersion made with X-ray interferometers

1981 ◽  
Vol 376 (1766) ◽  
pp. 465-482 ◽  
Keyword(s):  
Satisfactory Agreement ◽  
Absorption Edge ◽  
Anomalous Dispersion ◽  
Wavelength Band ◽  
Systematic Comparison ◽  
X Ray ◽  
Computational Errors ◽  
Computer Controlled ◽  
Absolute Measurements ◽  
Theory And Experiment

Absolute measurements of the anomalous dispersion constants f ' for zirconium, niobium and molybdenum made with a computer controlled X-ray interferometer have achieved a precision that permits systematic comparison with the available theories. Measurements were made at about 80 wavelengths within ± 3 keV of the elements’ K-absorption edge. After modification, to minimize computational errors, the theory of Cromer and Liberman is in satisfactory agreement with the results obtained so far, but small systematic differences between theory and experiment are apparent. Further work on a wide variety of elements and over a wide wavelength band is in progress.

Anomalous Dispersion with Edges in the Soft X-ray Region: First Results of Diffraction from Single Crystals of Trypsin Near the K-Absorption Edge of Sulfur

1997 ◽  
Vol 4 (5) ◽  
pp. 298-310 ◽  
Author(s):  
S. Stuhrmann ◽  
K. S. Bartels ◽  
W. Braunwarth ◽  
R. Doose ◽  
F. Dauvergne ◽  
...  
Keyword(s):  
Single Crystals ◽  
Absorption Edge ◽  
Anomalous Dispersion ◽  
X Ray ◽  
First Results

Layered structure analysis of GMR multilayers by X-ray reflectometry using the anomalous dispersion effect

1998 ◽  
Vol 5 (3) ◽  
pp. 969-971 ◽  
Author(s):  
Tatsumi Hirano ◽  
Katsuhisa Usami ◽  
Kazuhiro Ueda ◽  
Hiroyuki Hoshiya
Keyword(s):  
Absorption Edge ◽  
Layered Structure ◽  
Anomalous Dispersion ◽  
X Rays ◽  
Dispersion Effect ◽  
Accurate Analysis ◽  
Final Thickness ◽  
X Ray ◽  
Interface Width ◽  
Good Agreement

As a basic layered structure for giant magnetoresistive (GMR) heads, NiFe/Cu/NiFe/Ta/Si substrate was measured by X-ray reflectometry at Cu Kα, Cu Kβ and Cu K-absorption-edge energies. The accuracy of both the Cu thickness and the interface width between the upper NiFe and the Cu layers was found to improve in the order Cu Kα < Cu Kβ < Cu K-edge. The final thickness and interface width values obtained from Cu Kβ reflectivity are in good agreement with those from the Cu K-edge. The anomalous-dispersion effect is useful in the more accurate analysis of the layered structure of transition metal multilayers because it causes a large difference in the refractive indices of specific elements near the absorption edge. The Kβ X-rays, which can be produced from conventional X-ray sources, are also available for the accurate analysis of reflectivity measurements.

X-Ray absorption edge elemental imaging of B. thuringienis

1989 ◽  
Vol 47 ◽  
pp. 212-213
Author(s):  
R. L. Stears
Keyword(s):  
Absorption Edge ◽  
Elemental Distribution ◽  
X Rays ◽  
Differential Absorption ◽  
Synchrotron Source ◽  
High Brightness ◽  
X Ray ◽  
Elemental Imaging ◽  
Cellular Integrity ◽  
X Ray Absorption

Because of the nature of the bacterial endospore, little work has been done on analyzing their elemental distribution and composition in the intact, living, hydrated state. The majority of the qualitative analysis entailed intensive disruption and processing of the endospores, which effects their cellular integrity and composition.Absorption edge imaging permits elemental analysis of hydrated, unstained specimens at high resolution. By taking advantage of differential absorption of x-ray photons in regions of varying elemental composition, and using a high brightness, tuneable synchrotron source to obtain monochromatic x-rays, contact x-ray micrographs can be made of unfixed, intact endospores that reveal sites of elemental localization. This study presents new data demonstrating the application of x-ray absorption edge imaging to produce elemental information about nitrogen (N) and calcium (Ca) localization using Bacillus thuringiensis as the test specimen.

scholarly journals Modeling of the Resonant X-ray Response of a Chiral Cubic Phase

Crystals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 214
Author(s):  
Timon Grabovac ◽  
Ewa Gorecka ◽  
Damian Pociecha ◽  
Nataša Vaupotič
Keyword(s):  
Absorption Edge ◽  
Unit Cell ◽  
Resonant Peak ◽  
Cubic Phase ◽  
Tensor Form ◽  
Resonant Enhancement ◽  
X Ray ◽  
X Ray Scattering ◽  
Thermotropic Liquid Crystals ◽  
Carbon Absorption

The structure of a continuous-grid chiral cubic phase made of achiral constituent molecules is a hot topic in the field of thermotropic liquid crystals. Several structural models have been proposed so far. Resonant X-ray scattering (RXS), which gives information on the molecular orientation in the unit cell, could be applied to select the most appropriate model. We modeled the RXS response for the recently proposed chiral cubic phase structure with an all-hexagon chiral continuous grid. A tensor form factor of a unit cell is constructed, which enables calculation of intensities of peaks for all Miller indices. We find that all the symmetry allowed peaks are resonantly enhanced, and their intensity is much stronger than the intensity of the symmetry forbidden (resonant) peaks. In particular, we predict that a strong resonant enhancement of the symmetry allowed peaks (011) and (002), not observed in a nonresonant scattering, could be observed by RXS at the carbon absorption edge. By RXS at the sulfur absorption edge, one might observe a resonant peak (113) and resonantly enhanced peak (233), and resonant enhancement of all the peaks that are observed in a nonresonant scattering, which probably hide the rest of the predicted resonant peaks.

CHOOCH: a program for deriving anomalous-scattering factors from X-ray fluorescence spectra

2001 ◽  
Vol 34 (1) ◽  
pp. 82-86 ◽  
Author(s):  
Gwyndaf Evans ◽  
Robert F. Pettifer
Keyword(s):  
Absorption Edge ◽  
Fluorescence Spectra ◽  
Heavy Atom ◽  
Fortran Program ◽  
Anomalous Scattering ◽  
Tabular Data ◽  
X Ray ◽  
Scattering Factor ◽  
Experimental Values ◽  
Kronig Relation

A Fortran programCHOOCH, which derives experimental values of the anomalous-scattering factorsf′′ andf′ from X-ray fluorescence spectra, is described. The program assumes knowledge of theoretical values for the imaginary term,f′′, of the anomalous-scattering factor away from the absorption edge to scale the experimental fluorescence spectrum and thus derive values off′′ near the absorption edge, where tabular data are inappropriate. The Kramers–Kronig relation is used to calculate the real part,f′, of the anomalous-scattering factor. The program aids the decision-making process in macromolecular crystallographic experiments where optimal wavelength selection is required. Magnitudes off′ andf′′ at selected wavelengths can later be used as starting values for heavy-atom refinement with crystallographic phasing programs.

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