RT involves the use of penetrating X or gamma radiation to examine parts and products for imperfections.
An X-ray machine or radioactive isotope is used as source of radiation. Radiation is directed through a part and onto film. When the film is developed, a shadowgraph is obtained that shows the internal soundness of a part.
Possible imperfections show up as density changes in the film, in much the same manner as a medical radiograph can show broken bones.
The radiation used in radiography testing is a higher energy (shorter wavelength) version of the electromagnetic waves that we see as visible light. The radiation comes from an X-ray generator.
The part is placed between the radiation source and a piece of film. The part will stop some of the radiation. Thicker and more dense area will stop more of radiation.
The film darkness (density) will vary with the amount of radiation reaching the film through the test object.