Ionising radiation carries enough energy per photon or particle to strip electrons from atoms and break molecules such as DNA, which is why it causes radiation sickness and cancer. Radio waves, visible light and infrared heat do not ionise, so they are not radiation hazards in this sense, though non-ionising energy can still burn or blind.
Part of Radiation Safety
The word radiation covers a very wide range of energies. Ionisation is the dividing line between energy that mostly heats tissue and energy that changes its chemistry.
The Dividing Line Is Energy Per Photon
The parent article, Nuclear Safety, says some radiation is harmless (visible light, radio waves) and some carries enough energy to knock electrons off atoms in your body. The difference is energy per photon or per particle, not total power. A weak source of high-energy gamma rays can ionise where a powerful radio transmitter cannot, because each radio photon is too low in energy to detach an electron from an atom.
Alpha, beta, gamma and neutron radiation are all ionising; so are X-rays. At the far end of the ultraviolet range the boundary becomes gradual. This guide gives no photon-energy figure for the boundary, since none is sourced in the corpus.
Non-Ionising Does Not Mean Harmless
The dividing line describes a mechanism, not a safety rating:
- Ultraviolet light burns skin and damages eyes by other chemical routes. The corpus uses the same ultraviolet to disinfect water; see Solar Disinfection. The parent article notes that UV purification kills bacteria and does nothing to radioactive contamination.
- Intense infrared and microwave energy heats tissue and can burn.
- A radio or a solar panel is not a source of ionising radiation, so neither adds to a radiation dose.
What Ionisation Does To A Cell
When ionising radiation passes through tissue it breaks chemical bonds along its path. Damage to DNA is the part that matters most: a cell may die, repair itself, or survive with a changed genetic code. Many cells killed in a short time produce acute radiation syndrome; a few cells altered by damage may later become a cancer. See Health Effects. The energy involved is tiny as heat: 1 gray, the unit of absorbed dose, is one joule per kilogram, which warms tissue by only about 0.0002 degrees; see Units of Measurement. The harm is chemical, not thermal.
Common Mistakes
- Fearing every transmitter. Radio equipment, lamps and stoves do not produce ionising radiation.
- Trusting sunscreen logic for gamma. Protection from UV does not carry over; skin cover blocks UV and does almost nothing to gamma.
- Thinking low power means safe. For ionising radiation the energy per photon is what counts, together with the time spent exposed.
Safety
"It's only light" is not protection against an unknown source
A glowing object or a blue-white light in a dark room is not proof of radiation, and the absence of a glow is not proof of safety. Radioactive material was reported glowing in at least one real accident (Goiania, Brazil, 1987), but most ionising sources show nothing to the eye. Do not use brightness or colour as a detector.
What’s Next
- Learn next: Types of Radiation — the four ionising kinds
- Combine with: Health Effects — what ionisation does to people