Irradiation corresponds to the exposure of an individual to a radioactive source situated outside of the body. The body absorbs either all or part of the energy of the ionizing radiation emitted by this source. This exposure is dependent on the type of radiation, the distance between the source and the person, the duration of exposure, and the protective shields. It will stop as soon as one leaves the radiation field.
In contrast, internal contamination corresponds to the penetration of radioactive material by incorporation into the body. This can occur by ingestion, inhalation, diffusion through the skin, or directly by absorption through a contaminated wound.
Depositing of a radioactive compound on someone’s skin or hair is called external contamination.