Mumbai university > FE > SEM 1 > Applied Physics 1

Marks: 8M

Year: May 2014

• In powder method, a specimen is finely powdered and taken in a thin walled capillary tube.

• The specimen consists of tiny crystals or crystallites which are oriented randomly.

• When a narrow beam of X-ray incidents on the specimen, it comes across few crystallites with planes at glancing angle θ so as to satisfy Bragg's Law.

• Since all the orientations are equally likely, the diffracted rays will form a cone with the line of incident beam as the axis and the semi cone angle θ.

• These diffracted beams are detected by placing a photographic film along the circumference of the circle with specimen at the center.

• If "L" is the circumferential distance from the two extreme edges of cone formed by the diffracted X-rays and "R" is the radius of the circle along which film was placed, then;

$$\frac{L}{2πR} = \frac{4θ}{360}$$

$$ ∴ θ = \frac{45 L}{πR}$$

• Using θ, we can find the inter-planar spacing using Bragg's Law.