It consists o a source of x ray, with a number of collimated slits. Crystal under investigation is mounted on a table, and the position of this table can be recorded on vernier scale. The x ray beam from source is incident on collimated slit S1 and S2 and then collimated beam is made to fall on crystal surface. The beam reflected from crystal surface enters in ionization chamber, mounted on an arm which can be rotated about the same axis at the crystal, its position can be read by vernier V2.
When this reflected beam enters in ionization chamber, it ionizes the gas and the resulting ionization current is measured by galvanometer. This ionization current is a measure of intensity of x ray reflected by crystal. The ionization current is plotted against glancing angle q.