Ionising radiation refers to any particle or electromagnetic radiation that is capable of removing electrons from atoms or molecules (usually by impact processes). This leaves behind positively charged ions or molecular residues (ionisation).
A well-known example of ionising radiation is X-rays. Radioactive substances also emit ionising radiation. Since radioactive atoms are unstable, they decay after a certain time. In the process, they release energy in the form of ionising radiation. Colloquially, ionising radiation is sometimes also called radioactive radiation. However, radioactivity is the property of radioactive atoms to decay and thereby emit ionising radiation.
A distinction is made in radioactive decay between the following types of ionising radiation:
- alpha radiation (e.g. polonium-210 or radon-222)
- beta radiation (e.g. strontium-90 or iodine-131)
- gamma radiation (e.g. cobalt-60 or technetium-99)
- neutron radiation.
In most decays, a combination of different types of radiation occurs. All types of radiation can occur with both naturally occurring and artificially produced radioactive nuclides.