Ionising and Non-Ionising Radiation

Electromagnetic radiation can be described as ionising or non-ionising depending on whether individual photons have enough energy to remove electrons from atoms or molecules.

Lower-frequency electromagnetic waves are generally non-ionising. Examples include: radio; microwaves; infrared; visible light. Their photons generally do not have enough energy to ionise ordinary atoms directly.

Higher-frequency radiation can be ionising. Examples include: higher-energy ultraviolet; X-rays; * gamma rays. Ionising radiation can remove electrons and form ions.

Ionisation can damage important biological molecules such as DNA. This makes exposure control important.

The exact dividing line is not simply a named colour boundary. Photon energy matters: **E = hf**