Development of a one-sided gamma ray tomography system

GA Technologies has constructed an experimental device which has determined the location and size of macroscopic features such as voids and steel bars in concrete structures. The device measures relative density variations along a plane perpendicular to the structure surface using the intensity of gamma radiation scattered back from the concrete. Collimation and energy discrimination are used to detect gamma rays from a Co 60 source which have undergone a single Compton scatter through a prescribed angle. Since the source and detector are mounted side by side the system can readily locate and discriminate between voids, cracks, and inclusions. Detection limits for flaw size and depth are given. The system was also used to locate holes in a steel block.