Anomalous X-ray scattering
- Anomalous X-ray scattering
Anomalous X-ray scattering AXRS or XRAS is a technique within X-ray diffraction that makes use of the anomalous dispersion that occurs when a wavelength is selected that is in the vicinity of an absorption edge of one of the constituent elements of the sample.
Atomic scattering factors
In X-ray diffraction the scattering factor "f" for an atom is roughly proportional to the number of electrons that it possesses. However for wavelengths that approximate those for which the atom strongly absorbs radiation the scattering factor undergoes a change due to anomalous dispersion. The dispersion not only affects the magnitude of the factor but also imparts a phase shift in the elastic collision of the photon. The scattering factor can therefore best be described as a complex number [ X-ray diffraction in crystals, imperfect crystals and amorphous bodies. A. Guinier. Dover 1994 ISBN 0-486-68011-8 original publication 1963] : f= fo + Δf' + i.Δf"
Contrast variation
The anomalous aspects of X-ray scattering have become the focus of considerable interest in the scientific community because of the availability of synchrotron radiation. In contrast to desktop X-ray sources that work at a limited set of fixed wavelength, synchrotron radiation has a continuous spectrum from which one can select a single wavelength by means of a monochromator. This allows scientists to "vary" the wavelength, which in turn makes it possible to vary the scattering factor for one particular element in the sample under investigation. Thus a particular element can be 'high-lighted'. This is known as "contrast variation". In addition to this effect the anomalous scatter is more sensitive to any deviation from sphericity of the electron cloud around the atom. This can lead to resonant effects involving transitions in the outer shell of the atom: Resonant anomalous X-ray scattering.
Wikimedia Foundation.
2010.
Look at other dictionaries:
Small-angle X-ray scattering — (SAXS) is a small angle scattering (SAS) technique where the elastic scattering of X rays (wavelength 0.1 ... 0.2 nm) by a sample which has inhomogeneities in the nm range, is recorded at very low angles (typically 0.1 10°). This angular range… … Wikipedia
X-ray crystallography — can locate every atom in a zeolite, an aluminosilicate with many important applications, such as water purification. X ray crystallography is a method of determining the arrangement of atoms within a crystal, in which a beam of X rays strikes a… … Wikipedia
Cosmic ray — For the film, see Cosmic Ray (film). Cosmic radiation redirects here. For some background types of cosmic radiation, see cosmic background radiation and cosmic background. The energy spectrum for cosmic rays Cosmic rays are energetic charged… … Wikipedia
Multi-wavelength anomalous dispersion — Multi wavelength anomalous diffraction (sometimes Multi wavelength anomalous dispersion; abbreviated MAD) is a technique used in X ray crystallography that facilitates the determination of the three dimensional structure of biological… … Wikipedia
Compton scattering — Light–matter interaction Low energy phenomena … Wikipedia
List of materials analysis methods — List of materials analysis methods: Contents: Top · 0–9 · A B C D E F G H I J K L M N O P Q R S T U V W X Y Z μSR see Muon spin spectroscopy … Wikipedia
Diffusion anomale — En diffraction de rayons X, la diffusion anomale ou diffusion résonante est un phénomène qui apparaît lorsque l énergie des rayons X incidents est proche d une arête d absorption d un atome du cristal. Les photons incidents sont alors absorbés et … Wikipédia en Français
Powder diffraction — is a scientific technique using X ray, neutron, or electron diffraction on powder or microcrystalline samples for structural characterization of materials. [B.D. Cullity Elements of X ray Diffraction Addison Wesley Mass. 1978] Explanation Ideally … Wikipedia
Magnetic structure — The term magnetic structure of a material pertains to the ordered arrangement of magnetic spins, typically within an ordered crystallographic lattice. Its study is a branch of solid state chemistry. A very simple antiferromagnetic structure… … Wikipedia
atom — /at euhm/, n. 1. Physics. a. the smallest component of an element having the chemical properties of the element, consisting of a nucleus containing combinations of neutrons and protons and one or more electrons bound to the nucleus by electrical… … Universalium