Ionizing radiation

[Rennhack]

Ionizing radiation is radiation with enough energy so that during an interaction with an atom, it can remove tightly bound electrons from their orbits, causing the atom to become charged or ionized. Examples are gamma rays and neutrons. Radiation is measured in many ways, and commonly expressed in units of RAD.

[Rennhack]

Alpha particles, beta particles, gamma rays, x-rays, neutrons, high-speed electrons, high-speed protons, and other particles capable of producing ions. Radiation, as used in 10 CFR Part 20, does not include non-ionizing radiation, such as radio- or microwaves, or visible, infrared, or ultraviolet light (see also 10 CFR 20.1003).

[Rennhack]

Any radiation capable of displacing electrons from atoms or molecules, thereby producing ions. Some examples are alpha, beta, gamma, and X-rays. High doses of ionizing radiation may produce severe skin or tissue damage.

http://www.epa.gov/radiation/understand/ionize_nonionize.htm