The two principal modes of exposure to ionising rays
Exposure to radiations comes from internal and external sources. Internal exposure results from the ingestion of radioactive atoms present in food and drink as well as the inhalation of radioactive isotopes carried by air-borne particles. If these radioactive atoms attach themselves to our organs, glands or bones, then their subsequent decay may damage our cells and affect our health. External exposure results from the exposure to the rays emitted by a radioactive source, a source of X-rays or can be natural (for example cosmic rays, radioactivity of rocks).