See Help on X-Ray Diffraction.
Powder X-ray Diffraction (XRD) is one of the primary techniques used by mineralogists and solid state chemists to examine the physico-chemical make-up of unknown materials. This data is represented in a collection of single-phase X-ray powder diffraction patterns for the three most intense D values in the form of tables of interplanar spacings (D), relative intensities (I/Io), mineral name and chemical formulae
The XRD technique takes a sample of the material and places a powdered sample in a holder, then the sample is illuminated with x-rays of a fixed wave-length and the intensity of the reflected radiation is recorded using a goniometer. This data is then analyzed for the reflection angle to calculate the inter-atomic spacing (D value in Angstrom units - 10-8 cm). The intensity(I) is measured to discriminate (using I ratios) the various D spacings and the results are compared to this table to identify possible matches. Note: 2 theta (Θ) angle calculated from the Bragg Equation, 2 Θ = 2(arcsin(n λ/(2d)) where n=1
For more information about this technique, see X-Ray Analysis of a Solid or take an internet course at Birkbeck College On-line Courses. Many thanks to Frederic Biret for these data.
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