Ionizing radiation carries enough energy to remove electrons from atoms or molecules, creating ions. It includes high-energy photons — X-rays and gamma rays — and particle radiation such as alpha particles, beta particles and neutrons. Radio waves, microwaves and visible light are non-ionizing.
Reviewed 2026-09-24
What “ionization” means
When radiation transfers energy to an electron that exceeds its binding energy, the electron leaves the atom and an ion pair is formed. In living tissue this can damage DNA directly, or indirectly through free radicals produced from water.
Two families: photons and particles
| Family | Radiation | Nature |
|---|---|---|
| Electromagnetic (photon) | X | Photons from electron processes outside the nucleus |
| Electromagnetic (photon) | γ | Photons emitted by nuclear transitions |
| Particle | α | Helium nucleus: two protons and two neutrons |
| Particle | β | Electron or positron |
| Particle | Neutron | Uncharged nuclear particle |
X-rays and gamma rays are both photons
They are physically the same kind of radiation and are distinguished by origin, not by energy: X-rays come from electrons (bremsstrahlung and characteristic emission), gamma rays from the nucleus. Their energies overlap, so shielding is chosen from the actual spectrum and geometry, not from the name.
Ionizing and non-ionizing radiation
| Type | Examples | Ionizing? |
|---|---|---|
| Static and extremely-low-frequency fields (0–300 Hz) | Power lines, household wiring | No |
| Intermediate frequency and radio frequency (300 Hz–300 GHz) | Induction cookers, radio, mobile phones, microwaves | No |
| Infrared, visible light | Heat lamps, sunlight | No |
| Ultraviolet | Sunlight, UV lamps | Only the highest-energy part; usually treated separately |
| X-rays, gamma rays | Medical imaging, security scanners, radionuclides | Yes |
Frequency bands follow the WHO classification of electromagnetic fields.
References
- IAEA — Radiation, People and the Environment (2004)
- WHO — Ionizing radiation and health effects (fact sheet)
- WHO — Electromagnetic fields
- 新莱福防辐射产品手册（2024-09 V1）科普章节
This encyclopedia is for general and engineering reference and is not medical advice. Consult radiation protection or medical professionals for individual exposure assessment.