Gamma Radiography has been used for NDT Inspection of remote locations. The method makes use of Ir-192, Co-60 & similar sources were used for applications such as weld inspections, plants. The method requires the use of compact, robust, high activity sources with small focal dimensions. Earlier the source of Se-75 was too large and the projectors used for the technique failed to optimize the focal geometry
Gamma Radiography using Se- 75 has been established recently for industrial radiography .The Selenium-75 isotope provides radiation energies considerably lower than the Ir-192 spectrum, which results in largely improved quality of weld radiographs. The range of application of Se-75 lies between that of Ir-192 and Yb-169. The application and use of Se 75 is applicable for steel Thickness over 5mm.
Advantages of Se-75 over Ir-192
Ensuring product integrity, and hence its reliability.
Longer Half Life
Half life of Se75 reduces source change out frequency compared with Iridium 192
The use of this method of Gamma Radiography is not allowed in some countries due to the issues concerning human safety because of its high reactivity & volatility.