Irradiation of an Organism

the exposure of a living organism to any form of radiation. Under natural conditions, organisms undergo thermal irradiation from infrared light as well as irradiation from visible and ultra-violet sunlight; organisms are also exposed to cosmic rays and to ionizing radiation of terrestrial origin.

Artificial irradiation is usually accomplished with ionizing, ultraviolet, or ultrahigh-frequency radiation. Several types of artificial irradiation are distinguished. In whole-body irradiation, as opposed to partial, or local, irradiation, the entire body is exposed to radiation; in short-term irradiation, as opposed to prolonged irradiation, the duration of the exposure time is short. The dose of radiation can be administered at once or in fractions. The source of radiation can be external or internal; the latter involves the introduction of radioactive substances into the body.

The biological effects of ionizing radiation depend on the dose, type, and energy of the radiation and on the physiological state of the body. Chemical substances can alter the radiosensitivity of the body, either protecting it from or making it more susceptible to radiation. All other factors being equal, a whole-body, short-term, single-dose irradiation produces the greatest biological effects. Humans are irradiated in radiotherapeutic and X-ray diagnostic procedures; irradiation of animals is performed in the course of various radiobiological investigations.