Three modes of exposition to radiation
Exposure to ionising rays, whether from a radioactive source or not, can occur internally, externally, or through direct contact. For external sources, the important factors are the duration of the exposure, the strength and distance of the source as well as the location of any potential screens. Exposure through contact is rare, and normally involves the handling of contaminated material. By far the most dangerous of the three, however, is internal irradiation, whose consequences depend on the absorption mode (ingestion or inhalation), the organs affected and how long the radioactive atoms will remain in the body.