1. Sources of exposure

Ionizing radiation is radiation which, when it interacts with matter, is likely to impart energy to atoms, causing the ejection of at least one electron from their atomic chain.

Particles include :

• charged, directly ionizing particles (alpha particles: helium nuclei; beta particles: positively or negatively charged electrons; protons, heavy ions);

• uncharged, indirectly ionizing particles (neutrons, gamma photons from a radioactive nucleus, X photons from transitions in an atom's electron chain). In this case, the particles ionize the medium by setting directly ionizing particles into motion.

Atoms with unstable nuclei are radioactive, and transform into stable nuclei by emitting radiation (alpha, beta or gamma). Radioactivity is either natural (due...