INTAKE	Quantity of material introduced into the body by inhalation, ingestion or through the skin, ie., absortion, puncture, etc.
INTERLOCK	A device, usually electrical and/or mechanical that is used to prevent activation of a control until a preliminary condition has been met. Its purpose usually is for safety reasons.
INTERNAL RADIATION	Radiation from a source within the body as a result of deposition of radionuclides in body tissues.
INVERSE SQUARE LAW	The intensity of radiation at any distance from a point source varies inversely as the square of that distance. For example, if the radiation exposure is 100 R/hr at 10 centimeters from an unshielded source, the exposure rate at 100 centimeters will be 1 R/hr.
ION	An atom that has too many or too few electrons, causing it to be chemically active; such as an electron that is not associated (in orbit) with a nucleus. Ions may be positively or negatively charged and vary in size.
IONIZATION	The process by which a neutral atom or molecule acquires either a positive or negative charge.
IONIZING RADIATION	Any radiation capable of displacing electrons from atoms or molecules, thereby producing ions. Examples are alpha, beta, gamma, x-rays, neutrons and ultraviolet light. High doses of ionizing radiation may produce severe skin or tissue damage.
IRRADIATION	The exposure to radiation.
ISOBARS	Nuclides having the same mass number (A) but different atomic numbers (Z).
ISOTONES	Nuclides having the same number of neutrons (N) in their nuclei.
ISOTOPES	Nuclides having the same number of protons in their nuclei, therefore having the same atomic number (Z), but differing in the number of neutrons (N) and in the mass number (A).