Non-destructive method and apparatus for wall of tank housing radioactive liquid

PURPOSE: To obtain a method and an apparatus for non-destructive inspection of the wall of a tank for housing a liquid in which at least one radioactive element radiating gamma rays is distributed almost evenly. CONSTITUTION: A tank houses a liquid in which radioactive elements releasing gamma rays are distributed substantially evenly. A photon detector 15 is arranged near the external surface in a measuring band of a wall 12 and a counting is performed pertaining to photons which are released by the radioactive elements distributed in the liquid 7 and passes through the measuring band of he wall 12. The number of the photons determined by the counting is compared with a reference number thereof passing through a reference band of the wall. Thus, it is estimated whether a defect in the measuring band of the wall 12 exists or not. An inspecting instrument is provided with the photon- detector 15 arranged at one end of a collimator 16 made of heavy metal piercing a channel or a window 17.