American Society for Nondestructive Testing (ASNT) Radiographic Testing Practice Test

The isotopes predominantly used in gamma radiography are Iridium-192 (Ir-192) and Cobalt-60 (Co-60) due to their favorable properties that make them ideal for imaging applications.

Ir-192 is favored for its relatively high activity and gamma energy output, enabling a good contrast in imaging while maintaining a reasonable exposure time. It emits gamma rays with energies around 470 keV, which is effective for penetrating materials like steel, making it suitable for a variety of industrial applications, including pipeline inspections and weld evaluations.

Cobalt-60 is another commonly used isotope in gamma radiography. It emits gamma radiation at energies of about 1.17 MeV and 1.33 MeV, allowing it to penetrate thicker materials effectively. The half-life of Co-60 is approximately 5.27 years, providing a long-lasting source that is also reasonably safe to handle with proper shielding.

While the other isotopes listed in the other choices may have applications in various types of radiographic testing or other fields, they are not as widely used in gamma radiography due to either lower energy emissions, shorter half-lives, or safety concerns that limit their utility for this specific purpose. Ir-192 and Co-60