Interactive Tutorial about Diffraction
Interactive example: Phase angles

Phase problem
Shift in real space
Centrosymmetric vs. Acentric

Interactive examples
Single atom
Pair of atoms
One atom in unit cell
Two atoms in unit cell


In this interactive example you should investigate the effect of the atom position on the intensity and phase angle of the X-ray diffraction pattern.

The controls of the simulator window allow you to create a single electron a single Si or a single Pb atom located on the x-axis. The position of the atom/electron is given in A. You can also select whether to calculate X-ray or neutron intensities. The calculated range for the scattering intensity h is fixed to -2.0A**-1 to 2.0A**-1 parallel to the x-axis.

Start exploring and try to answer the questions below:

  • What is the effect of the position on the intensity, the real part, the imaginary part and the phase angle of the diffraction pattern ?
  • What is the difference between a shift in the positive and the negative x-direction ?
  • What is the influence of the electron/atom type on the X-ray diffraction pattern ?
  • Describe the difference between X-ray and neutron diffraction results.
  • Try to work out the relationship between the magnitude of the shift and the phase angle ?
  • Why does the phase angle change periodically, although the other features of the diffraction pattern do not ?

Once you are done, click here to verify your answers.
© Th. Proffen and R.B. Neder, 2003