Debye Scherrer camera:

A very small amount of powdered material is sealed into a fine capillary tube made from glass that does not diffract x-rays. The specimen is placed in the Debye Scherrer camera and is accurately aligned to be in the centre of the camera. X-rays enter the camera through a collimator.

The powder diffracts the x-rays in accordance with Braggs law to produce cones of diffracted beams. These cones intersect a strip of photographic film located in the cylindrical camera to produce a characteristic set of arcs on the film.

Investigate the powder diffraction method using the simulation here, by clicking on the start button repeatedly.

When the film is removed from the camera, flattened and processed, it shows the diffraction lines and the holes for the incident and transmitted beams.

There are always two arcs in the x-ray beams Ka and Kb, this causes the highest angle back-reflected arcs to be doubled. From noting this, it is always clear which hole is for the transmitted beam and which is for the incident beam in the film.