Dose: The amount of energy absorbed by matter received from ionizing radiation per unit mass of matter; expressed in rads.

Exposure: A measure of the ionization produced in air by X- or gamma radiation; expressed in roentgens (R).

Although "dose" and "exposure" often are used interchangeably, the former (dose) is a measurement of energy absorbed in body tissue, the latter (exposure) is a measurement of ionizations in the air due to the presence of radiation.

Rad: Unit of radiation dose.

Roentgen (R): Unit of exposure, applicable only to X- and gamma radiations.

Rem: (Roentgen Equivalent Man) A unit used to express all types of ionizing radiations on a common scale to indicate relative biological effects. For beta and gamma radiations: Exposure to 1 Roentgen delivers a dose of 1 Rad, which is equivalent to 1 Rem.

Curie (Ci): Amount of radioactive material in which 3.7 x 10 atoms decay per second. The rate at which radioactive material is released to the environment may be expressed in units of curies per second (Ci/sec.).

Milli - (m): One-thousandth of a unit (10 ), i.e., millirem (mRem) XX r milliroentgen (mR).

Micro - z)u): One-millionth of a unit (10).

Pico - (p) : One-trillionth of a unit (10 ).


Airborne Radioactive Material:
Any radioactive material dispersed in the air in the form of dust, fumes, mist, vapor or gas.

Background Radiation: Cosmic rays and natural radioactivity are always present in the environment. In addition, man-made sources also may contribute to the background radiation level. The average New Yorker receives approximately 360 millirem per year from radon and background radiation.

Decontamination: The reduction or removal of contaminating radioactive material from a structure, area, object or person.

Dosimeter: A personnel monitoring instrument that measures the radiation dose received by an individual using the device.


Exposure Pathways: The ways in which the presence of radioactive materials in the environment lead to potential exposure to humans, i.e., inhalation of airborne radioactive material; ingestion of contaminated food or drink; and whole body exposure to a passing plume or ground contamination.

Exposure Rate: Amount of exposure received per unit of time, i.e., roentgens per second or roentgens per hour. The exposure rate is measured by a radiation detection instrument such as a Geiger counter or an ionization chamber.

Film Badge: Film encased in a badge-like holder that records radiation exposure for personnel monitoring purposes. The film usually is processed monthly for calculation of the absorbed dose. Results are reported in millirems (mRems).

Half-life: The time required for radioactive material to lose 50% of its activity by radioactive decay.

Monitoring: Periodic or continuous measuring of radiation by means of survey instruments that can detect and measure ionizing radiation.

Area Monitoring: Measurement of radiation level or contamination present in a specific area, building, room, etc.

Personnel Monitoring: Measurement of radiation levels that may have been received by an individual to the whole body or specific organs or body parts. The most common devices used for measuring exposure from external sources are film badges, thermoluminescent dosimeters (TLDs) and pocket dosimeters. Whole body counting or bioassay measurements of breath or excretions may be taken to determine internal intake of radioactive materials.

Nuclear Reactor: A device in which a fission chain reaction can be initiated, maintained and controlled. Its essential component is a core with fissionable fuel.

Radiation: The emission of energy through a material medium in the form of electromagnetic waves or particles that may impart their energy to the medium through the creation of electrically charged ion pairs. X- and gamma rays and alpha and beta particles are examples of ionizing radiation.

Radioactive Decay: The process by which an unstable nucleus of an atom spontaneously releases energy through the emission of radiation.

Radioactive Release: Introduction of radioactive materials into an uncontrolled environment.

Thyroid Blocking Agent: A substance taken as a protective measure to reduce the uptake by the thyroid of radioiodine, e.g., potassium iodine (KI).

Thyroid Exposure: Exposure of the thyroid gland to radiation from radioactive isotopes of iodine which have either been inhaled, absorbed or ingested. Accumulation of iodine is rapid in the thyroid gland.

Thermoluminescent Dosimeter (TLD): A dosimeter made of material that when heated emits light in amounts proportional to the amount of the radiation dose it received. Placed in a badge-type holder, it can be worn by an individual to measure his/her possible exposure to ionizing radiation.

Transportation Emergency: A radiological emergency that occurs during the transportation of radioactive materials.

Whole Body Exposure: Exposure of a major portion of the body to an external radiation field or resulting from the presence of radioactive material distributed throughout the body. Exposure of blood forming organs, gonads, head, trunk and lenses of the eyes is also considered exposure to the whole body.