Concept:Industrial radiography uses penetrating gamma radiation from a suitable radioisotope to detect internal flaws in metal welds and castings.Explanation:Cobalt-60, written as 60Co, is a strong gamma emitter.Its gamma rays can penetrate thick metal sections and reveal cracks, voids, or faults on radiographic film.It is widely used in industrial radiography for checking welds and castings.Answer:C. cobalt-60