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X-Ray Diffraction from Atomic Planes

This applet was written as an extension to our applet showing interference from a set of diffracting sources. All atoms in a plane re-radiate in phase when the angle of the emitted waves to the plane is the same as the angle of the incident waves. This condition is always satisfied in the applet, which shows how the intensity of the waves diffracted from a set of planes depends on the phase relationship between diffraction from successive planes of atoms. This is embodied in Bragg's law, that gives the angles theta when the intensity is a maximum through the condition 2dsin theta = n lambda, where n is an integer. You can see in the applet that n represents the number of wavelengths in the path difference between the radiation from successive planes and that this must be an integer at the maxima of intensities.

  1. Left click on the University Logo to increase the number of planes from 10 to 50. This illustrates how the Bragg intensities are very sensitive to the number of planes illuminated.
  2. Right click on the graph at the bottom to change the scaling criteria. The lighter the colour green the more intense the signal.
  3. Right click on the University Logo to display the wave amplitude within the crystal that arises from the presence of both incident and diffracted waves. Note that the resulting standing wave pattern perpendicular to the planes just matches the interplanar spacing when the Bragg condition is satisfied.

This applet was produced and written by Gary Skinner.

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