RT uses ionizing radiation to inspect materials and components with the objective of locating defects. Radiation that is used in industrial radiography is produced by either X-Ray or Gamma Rays.
X-Rays are produced in a vacuum tube where a filament is heated causing electrons to free and then attracted to a target. When the electrons hit the target the energy produced is called X-Rays. Because X-Rays tubes have a filament that is heated by electricity X-Rays Can be turned off and on easily.
Due to the effects that radiation can have on the human body safety is of the up most importance when performing RT. RT Technicians are required to take and pass a 40 hour RT Safety class before going onsite and assisting in radiographic operations. Some safety precautions include roping areas off and using signs to restricting access to areas where radiation is present. The Technician also is required to wear specific safety equipment such as a dosimeter, film badge, and alarm rate meter that can record the amount of radiation the Technician has been exposed to. Survey meters are also used and can detect the amount of radiation that is present in the air.
One of the major advantages of RT is that an image is created on film creating a permanent record. There have been many advancements in RT such as Computed and Digital Radiography which utilize flat panels to display the image. With these advancements, the Technician is able to adjust the contrast and other parameters which makes it easier for the technician to locate discontinuities
Gamma Rays are created by taking a stable element such as Cobalt-59 or Iridium-191 and bombarding it with neutrons to make them radioactive. The radioactive Cobalt-60 or Iridium-192 decays as Gamma Rays are produced. The decay rate is measured in half life. Cobalt-60 has a half life of 5.3 years and Iridium-192's half life is 74 days.