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Frequently Asked Questions:

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What is X-ray Diffraction?
X-rays scatter from electrons. Diffraction is the accumulative result of the x-ray scattering of a group of electrons. For an incident X-ray photon of monochromatic wavelength ?, coherent waves are produced at an angle of theta (2-theta with respect to the incident x-ray) if the electron groups interact with the x-ray and are spaced at a distance d. The interaction is described by Bragg's law : nlamda =2dsin(theta). The intensity of the scattered x-ray is proportional to the number of electrons that the x-ray is scattered from.

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Why do you use X-rays?
Normally one would use a microscope to view small objects. For a microscope, light is scattered by an object and collected using lenses, which in turn magnifies the image of the object. The limit of the microscope is intrinsic to the nature of the electromagnetic radiation that is used to probe the object. If we use light we cannot look at objects smaller than the wavelength of light which is about 10-6 m. Since the atom has dimensions of about 10-10 m we cannot image an atom with a photon of light. X-rays, on the other hand, have a wavelength of about 10-10 m and are suitable for imaging objects at the atomic scale.

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What are crystal lattices and the unit cell?
A single-crystal is described as an order set of atoms (electrons) in a fixed orientation. The smallest non-reproducible volume of the crystal is called the unit cell. By application of symmetry the unit cell can be repeated, in three dimensions, to describe the entire crystal. The unit cell in turn can be described by three non-coplanar axis a, b and c and the inter axis angles alpha ,beta and gamma which are called the Lattice Parameters. Seven crystal systems are described in terms of the lattice parameters.

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What should I know before submitting my samples?
You should know exactly your needs from XRD analysis; for example, in case of powder diffraction, you should know if you just need an XRD Pattern, Phase identification or full quantitative analysis and you must also know the required diffraction angle range (2Θ).

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What are the acceptable forms of the sample?
We can accept only fine powder materials (at least 500 mg), thin film samples, also metals and alloys with homogenous surface. Good crystals in case of single crystal analysis.

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How I get the results?
By E-mail (if requested) or you can bring a blank CD in which you can get everything inside. also we will give you printed copy of the XRD chart.

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What the most important contents in the CD?
You will find a report as a *.rtf file and your raw data as (ascii) text file formatted as two columns (2theta, intensity), which can be easily drawn using excel, origin, etc.

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Extra Resources
Physics Division, National Research Center (NRC), Egypt.
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