Ionizing radiation
![Ionizing radiation hazard symbol](/Images/godic/202502/05/Radioactive.svg2242.png")
![Alpha (α) radiation consists of a fast-moving helium-4 (4He) nucleus and is stopped by a sheet of paper. Beta (β) radiation, consisting of electrons, is halted by an aluminium plate. Gamma (γ) radiation, consisting of energetic photons, is eventually absorbed as it penetrates a dense material. Neutron (n) radiation consists of free neutrons that are blocked by light elements, like hydrogen, which slow and/or capture them. Not shown: galactic cosmic rays that consist of energetic charged nuclei such as protons, helium nuclei, and high-charged nuclei called HZE ions.](/Images/godic/202502/05/Alfa_beta_gamma_neutron_radiation.svg2242.png")
![Different types of electromagnetic radiation](/Images/godic/202502/05/EM-spectrum.svg2242.png")
![The total absorption coefficient of lead (atomic number 82) for gamma rays, plotted versus gamma energy, and the contributions by the three effects. Here, the photoelectric effect dominates at low energy. Above 5 MeV, pair production starts to dominate.](/Images/godic/202502/05/Pb-gamma-xs.svg2242.png")
Ionizing (or ionising in British English) radiation is radiation that carries enough energy to free electrons from atoms or molecules, thereby ionizing them. Ionizing radiation is made up of energetic subatomic particles, ions or atoms moving at high speeds (usually greater than 1% of the speed of light), and electromagnetic waves on the high-energy end of the electromagnetic spectrum.