Terms

Alpha Particle: A positively charged particle by certain radioactive materials. Alpha particles can be stopped by a sheet of paper.

Alpha Radiation: The least penetrating type of radiation. Alpha radiation can be stopped by a sheet of paper.

Ambient Radiation Levels: Surrounding radiation levels.

Atom: The basic component of all matter; the smallest part of an element that has all the chemical properties of that element. Atoms in turn are made up of protons, neutrons and electrons.

Background Radiation: The radioactivity in the environment including cosmic rays from space and radiation that exists everywhere  in the air, in the earth, and in man-made materials that surround us. In the United States most people receive 100 to 250 millirems of background radiation per year.

Beta Particle: A negatively charged particle emitted from an atom during radioactive decay. A beta particle is an electron that has a mass equal to 1/1837 that of a proton. A beta particle can be stopped by an inch of wood or a thin sheet of aluminum.

Beta Radiation: Emitted from a nucleus during fission. Beta radiation can be stopped by an inch of wood or a thin sheet of aluminum.

Boiling Water Reactor: A nuclear reactor in which water is boiled in the reactor vessel; the resulting steam drives a turbine to generate electricity.

Chain Reaction: A self-sustaining series of events occurring when a neutron splits a heavy atom releasing sufficient neutrons to cause many other atoms to split in the same way.

Control Room: The operation center of a nuclear power plant from which the plant can be monitored and controlled.

Coolant: A fluid, usually water, used to cool a nuclear reactor and transfer heat energy. The water also moderates, or slows down, the fissioning of neutrons.

Criticality: The point at which a nuclear reactor is just capable of sustaining a chain reaction.

Deposition Footprint: The entire area in which radioactive material has deposited on the ground.

Dosimeter: A device, such as a film badge, which can be worn and used to measure the radiation dosage a person receives over a period of time.

Fission: The splitting or breaking apart of a heavy atom into two or more new atoms. When a heavy atom, such as uranium, is split, large amounts of energy and on or more neutrons are released.

Fission Products: The atoms formed when uranium is split in a nuclear reactor. Fission products are usually radioactive.

Gamma Radiation: A form of electromagnetic, high-energy radiation emitted from a nucleus. Gamma rays are essentially the same as X-rays and require heavy shielding, such as lead brick, to stop them.

Geiger Counter: An instrument for detecting and measuring beta and gamma radiation.

Millirem: A unit of radiation dosage equal to one-thousandth of a rem. An individual member of the public can receive up to 500 millirems per year according to federal standards. This limit does not include radiation received for medical treatment nor does the limit include the 100 to 250 millirems people receive annually from background radiation.

Neutron: An uncharged particle with a mass nearly equal to the mass of a proton. Neutrons are the particles that sustain a chain reaction in a nuclear reactor.

Noble Gases: Gases which do not combine chemically with other materials. The noble gases are helium, neon, argon, krypton, xenon and radon.

Nuclear Power Plant: A facility designed to convert nuclear energy into electricity.

PAD - Protective Action Decision: Decision made by decision-makers after a PAR has been made.

PAR - Protective Action Recommendation: Recommendation made to decision-makers based on Radiological Conditions Assessment.

Pressurized Water Reactor: A reactor in which water, heated by nuclear energy, is kept at high pressure to prevent the water from boiling. Steam is then generated in a secondary loop.

Radiation: Refers to the process of emitting energy in the form of rays or particles which are thrown off by disintegrating atoms; may consist of alpha, beta, or gamma radiation.

Radioactivity: The property possessed by some elements, such as uranium, of spontaneously emitting alpha, beta or gamma rays.

Radiological Deposition: Radioactive material that has deposited on the ground from a release.

REM: An acronym for Roentgen Equivalent Man, a measure of radiation exposure that indicates the potential impact on human cells.

Shielding: Material, such as lead or concrete, around a nuclear reactor used to prevent the escape of radiation and to protect workers and equipment.

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