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Measurement of Diffraction Angle

Measurement of Diffraction Angle

Measurement of Diffraction Angle: Rotating crystal method (Braggs, 1913)

Powder method (Debye and Scherrer, 1916)

The measurement of diffraction angle, θ, required for Bragg equation can be done in two ways.
1. Rotating Crystal Method (Braggs, 1913)
2. Powder Method (Debye and Scherrer, 1916)

Rotating Crystal Method

The apparatus used by Bragg is shown in figure below. A beam of X-rays of known wave length falls on a face of the crystal mounted on a graduated turn table. The diffracted rays pass into the ionisation chamber of the recorder. Here they ionise the air and a current flows between the chamber wall and an electrode inserted in it which is connected to an electrometer. The electrometer reading is proportional to the intensity of X-rays. As the recorder along with the crystal is rotated, the angles of maximum intensity are noted on the scale. Thus values of θ for n = 1, 2, 3, etc. are used to calculate the distance d between the lattice planes parallel to the face of the crystal.

Rotating Crystal Method
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