Which gamma-ray source would be most suitable for radiographing a 7-inch thick steel product?

Cobalt-60 is the most suitable gamma-ray source for radiographing a 7-inch thick steel product due to its properties that make it effective for penetrating dense materials. Cobalt-60 emits gamma rays with a maximum energy of about 1.33 MeV, which provides significant penetrating power essential for effectively imaging thick steel sections.

In radiographic testing, the ability of the radiation source to penetrate the material is crucial for producing high-quality images and detecting potential defects within the material effectively. Cobalt-60's energy allows it to produce clear radiographs of thicker materials compared to the other options.

In contrast, Iridium-192, while also used in radiography, has a lower maximum energy of about 0.37 MeV. Although it can penetrate materials, it may not provide adequate penetration for a 7-inch thick steel product in comparison to Cobalt-60.

Cesium-137, with a maximum energy just above 0.6 MeV, and Technetium-99m, which has even lower energy (around 0.14 MeV), are neither as effective as Cobalt-60 for this thickness. Their gamma-ray energies limit their effectiveness for radiographing materials as thick as 7