Ionising radiation in the form of a particle includes very small (sub-atomic) particles such as electrons, protons and neutrons. When radioactive material (see below) transforms by decay, it can emit ‘beta particles’ (electrons), ‘alpha particles’ (two protons and two neutrons) and/or single neutrons. The radionuclide uranium-238, found in all rocks, soil, and the food we eat, emits (predominantly) alpha particles.