Title Synchrotron light English 46.0 MB 86
##### Document Text Contents
Page 43

Thomson Elastic scattering

Elastic or coherent scattering :
Thomson diffusion (elastic) if E < Ebinding

X-ray diffraction is based on elastic scattering and results from the coherent sum of all EM waves that are
diffused from each atom of a periodic structure constituting the matter (the same that occurs with visible light
interaction with a grating). The scattering of x-rays by crystal atoms, produces diffraction patterns (peaks are

formed when scattered X-rays constructively interfere) that yields information about the structure of the
crystal but also to monochomatize X-ray white beams .

Incoming
X-rays

Diffracted
X-rays

X-rays incident upon samples will either be transmitted, in
which case they will continue along their original direction, or will
be scattered by the electrons of the atoms in the material.

All the atoms in the path of the X-ray beam scatter X-rays.

With visible light we can
use a prism and light
refraction to separate
different wavelengths with
X-ray we use crystals and
diffraction.

Incoming
polychromatic

X-rays

Diffracted
monochromatic

X-rays

Page 44

Elastic scattering and diffraction

Bragg’s Law: nλ = 2d sinθ

X-ray diffraction is an important tool used to identify phases by comparison with data from known
structures, quantify changes in the cell parameters, orientation, crystallite size and other structural

parameters. It is also used to determine the (crystallographic) structure (i.e. cell parameters, space group
and atomic coordinates) of novel or unknown crystalline materials.

Incoming
X-rays

Diffracted
X-rays

The interference pattern of X-rays scattered by crystals (XRD or X Ray Diffraction pattern) can be
used study the atomic structure of interest. Bragg’s law explains the relation between: d, the

distance between atomic layers in a crystal, λ is the wavelength of the incident X-ray beam and θ the
angle of incidence at which the faces of crystals appear to reflect X-ray beams.