(IUCr) The precession method

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The precession method

The precession camera was invented by Buerger in about 1940. This technique uses a flat film holder linked to the crystal oscillation axis. With the instrument set at zero, the X-ray beam must strike the crystal parallel to a real axis and perpendicular to the film. The crystal (and film) is tilted by an angle $\bar \mu$ of up to 30 $^\circ$ , and allowed to `precess' so that the real crystallographic axis traces a cone about the X-ray beam. See Fig. 28.

**Figure 28:** Buerger precession instrument.
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The motion is complex but results in a photograph that gives an undistorted picture of the `reciprocal lattice'.

This is the second most common single crystal camera in current use. It is very popular for studies of crystalline proteins.

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