Cobalt 60 is normally used for radiography of steel within which thickness range?

Cobalt-60 is commonly used in industrial radiography because of its ability to produce gamma rays that can penetrate materials at considerable thicknesses. The range of 1.5 inches to 7 inches of steel is well-suited for Cobalt-60 as it provides adequate penetration for detecting flaws such as cracks, voids, or inclusions within the material.

In this thickness range, Cobalt-60 provides a balance between sufficient radiation exposure for imaging and the ability to maintain safety standards required during radiographic inspections. The effective penetration capability of Cobalt-60 in this range allows for high-quality images to be obtained without excessively increasing the radiation dose to personnel or the environment.

The other options fall outside of the typical application of Cobalt-60 for steel. For instance, thinner materials may not require the use of Cobalt-60, as other isotopes or methods could provide sufficient imaging quality without the same level of hazard. Conversely, thicker materials may require different radiographic methods or isotopes, as the limitations of gamma ray intensity and exposure times influence the effectiveness of radiography for significantly thick steel sections.