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Bragg Xray Spectrometer

Bragg’s spectrometer is similar to an ordinary prism spectrometer. Two lead slits S₁ and S₂ define a narrow beam of X-rays coming from the target T.

This narrow beam of X-rays is then incident on the crystal C, mounted on the table of the spectrometer. The reflected beam after passing through the slit S₂ enters the ionization chamber D filled with methyl bromide. The ionization current is detected by the electrometer E. Instead of an ionization chamber, photography plate or scintillation counter can be used. The ionization current is recorded as the glancing angle θ is varied by rotating the crystal table. The chamber is rotated through double the angle through which the crystal is rotated so that the angle of incidence is equal to the angle of reflection.

A graph is plotted between the intensity of ionization and the glancing angle. In the case of sodium chloride crystal, the curve is as shown in fig. A₁ and B₁ correspond to two characteristic radiations in the incident beam. The maxima A₂, B₂ and A₃, B₃ are produced by second and third order reflections. The maxima A₁, A₂ and A₃ occur when θ is equal to 5.9˚, 11.75˚ and 18˚ respectively. The peak intensities occur whenever the Bragg equation nλ = 2d sin θ is satisfied.