What is the approximate practical thickness limit for a cobalt-60 gamma ray source?

The practical thickness limit for a cobalt-60 gamma ray source is typically around 9 inches of steel. Cobalt-60 is a commonly used gamma ray source in radiographic testing due to its high energy and penetrating power. When assessing the depth of penetration into steel, it is important to recognize that very dense materials, like steel, significantly attenuate gamma radiation.

The thickness of steel that cobalt-60 can effectively penetrate is influenced by several factors, including the energy of the emitted gamma rays (which is approximately 1.17 and 1.33 MeV for cobalt-60) and the material composition. With adequate shielding, approximately up to 9 inches of steel is achievable in practical applications without excessive loss of resolution or quality in the radiographic imagery. Beyond this thickness, the ability to obtain clear and usable radiographs diminishes because the radiation becomes increasingly absorbed, leading to reduced image contrast and definition.

Thus, 9 inches of steel represents a balance between effective penetration for quality radiographic inspection and the limitations imposed by material attenuation.