Ionizing radiation may consist of streams of high-energy particles or high-frequency (short-wavelength) electromagnetic radiation, including:
· alpha particles (high-speed helium nuclei)
· beta particles (high-speed electrons)
· other fast-moving particles, such as neutrons and protons
· X-rays and gamma rays (high frequency electromagnetic waves)
Neutrons are not themselves ionizing but their collisions with nuclei lead to the ejection of other charged particles that do cause ionization.
Ionizing radiation can have a particularly serious effect on biological tissues, although this depends much on the type of radiation and the extent of exposure.