Iridium 192 in medical applications

Most radiography cameras use iridium-192, but a significant number of radiography devices use cobalt-60 or selenium-75. The chosen radioisotope depends on the material to be radiographed and its thickness. The higher-energy gamma rays of cobalt-60 are normally used for thicker sections of steel, from one to several inches. Iridium-192 is used for steel up to 2.5 cm in thickness, and selenium-75 is used for lighter and thinner metals. Radiography sources are typically Category 2 sources in the International Atomic Energy Agency (IAEA) system. Gamma radiography cameras are constructed of a steel casing, typically welded closed, that encases a depleted uranium, tungsten, or lead shield. Depleted uranium (DU) is normally used as shielding for iridium-192 due to DU’s high density and ability to safely shield the high-activity sources with the external dose rates meeting regulatory requirements. Tungsten is typically used for shielding selenium-75 sources. The source is attached to a short wire or a short flexible cable often called a “pig tail” that positions the source in the shielded position and allows for the source to be securely locked in the stored position.