Definitions for "ionizing radiation"
rays of rapidly moving subatomic particles, x-reys, or gamma rays, sufficiently energetic to cause ionization when absorbed by matter.
Radiation that produces ions as it passes through matter.
Radiation of sufficient energy to displace electrons from the atoms of cells and produce ions. Ionized cells are damaged and must repair themselves; otherwise, they will die. Generally, normal cells are better able to repair themselves than cancer cells.