Gamma Radiography (Metrology)

22.9.
Principle of detecting defects is the same as X-ray radiography.
Gamma rays are emitted during the disintegration of radioactive material and like X-rays are electromagnetic radiation. Gamma-rays are of shorter wavelength and consequently are more penetrating. The chief merits of Gamma sources are (1) small size, (2) high penetration, (3) relatively low cost compared with X-ray units, (4) independence from supply of electricity and water. The major disadvantages of such sources are :
(1) They are of low intensity requiring long explosure.
(2) Some sources have a short half-life which necessitates decay correction or replacement.
(3) Since they cannot be ‘shut off protection is always necessary.