Radiation

In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium.[65]
Radiation, flow of atomic and subatomic particles and of waves, such as those that characterize heat rays, light rays, and X rays. All matter is constantly bombarded with radiation of both types from cosmic and terrestrial sources.[66]

Radiation comes in different forms of energy in motion. Doses of radiation and the area of interest are important considerations when imaging patients, particularly during percutaneous procedures. Radiation is energy in movement. Electromagnetic radiation (EMR) refers to energy that travels in the form of waves. Another way of thinking about EMR is as a matterless bundle of energy called a photon. The photon is the “package” of energy that carries the energy through space. The other type of radiation is particulate, in which small particles (electrons, alpha particles) carry the energy. Particulate radiation can emanate from radioactive materials and linear accelerators. Particulate radiation is not effective for imaging due to low penetration of matter.[67]

Sources:

Weisstein, Eric W. "Radiation". Eric Weisstein's World of Physics. Wolfram Research. Retrieved 11 January 2014.

Coeditor of Radiation Processing of Polymers.