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Science Terms Definitions - B

Background Level - In air pollution, the level of pollutants present in ambient air from natural sources. More generally, the level of pollution present in any environmental medium attributable to natural or ubiquitous sources.

Background Radiation - Radiation from cosmic sources, naturally occurring radioactive materials, including radon (except as a decay product of source or special nuclear material) and global fallout as it exists in the environment from the testing of nuclear explosive devices. It does not include radiation from source, byproduct, or special nuclear materials regulated by the Nuclear Regulatory Commission. The typically quoted average individual exposure from background radiation is 360 millirems per year.

Becquerel - A unit of radioactivity equal to one disintegration per second. [37 billion (3.7x1010) becquerels = 1 curie (Ci)].

Benign - Not malignant; remaining localized.

Best Available Control Measures (BACM) - A term used to refer to the most effective measures (according to EPA guidance) for controlling small or dispersed particulates from sources such as roadway dust, soot and ash from woodstoves and open burning of brush, timber, grasslands, or trash.

Best Available Control Technology - An emission limitation (including a visible emission standard) based on the maximum degree of reduction for each pollutant subject to regulation under the [Clean Air] Act which would be emitted from any proposed major stationary source or major modification which the Administrator, on a case-by-case basis, taking into account energy, environmental, and economic impacts and other costs, determines is achievable for such source or modification through application of production processes or available methods, systems, and techniques, including fuel cleaning or treatment or innovative fuel combustion techniques for control of such pollutant.

Best Demonstrated Available Technology (BDAT) - As identified by EPA, the most effective commercially available means of treating specific types of hazardous waste. The BDATs may change with advances in treatment technologies.

Best Management Practice (BMP) - Methods that have been determined to be the most effective, practical means of preventing or reducing pollution from nonpoint sources.

Beta Decay - The emission of electrons or positrons (particles identical to electrons, but with a positive electrical charge) from the nucleus of an element in the process of radioactive decay of the element.

Beta Particle - A charged particle emitted from a nucleus during radioactive decay, with a mass equal to 1/1837 that of a proton. A negatively charged beta particle is identical to an electron. A positively charged beta particle is called a positron. Large amounts of beta radiation may cause skin burns, and beta emitters are harmful if they enter the body. Beta particles may be stopped by thin sheets of metal or plastic.

Beta Radiation - Radiation consisting of electrons or positrons emitted in many radioactive disintegrations, at speeds approaching the speed of light.

Bias - Any difference between the true value and that actually obtained due to all causes other than sampling variability.

Binding Energy - The energy that is required to separate the nucleons in a nucleus into separate, free particles.

Bioaccumulation - The process whereby certain toxic substances collect in living tissues, thus posing a substantial hazard to human health or the environment.

Biological Half-life - The time required for a biological system (such as a human or animal) to eliminate, by natural processes, half the amount of a substance (such as a radioactive material) that has been absorbed into that system.

Biological Magnification - Refers to the process whereby certain substances such as pesticides or heavy metals move up the food chain, work their way into rivers or lakes, and are eaten by aquatic organisms such as fish, which in turn are eaten by large birds, animals or humans. The substances become concentrated in tissues or internal organs as they move up the chain.

Bioremediation - Use of living organisms to clean up oil spills or remove other pollutants from soil, water, or wastewater; use of organisms such as non-harmful insects to remove agricultural pests or counteract diseases of trees, plants, and garden soil.

Biota - The sum total of the living organisms of any designated area.

Body Burden - The total amount of a specific substance (for example, lead) in an organism, including the amount stored, the amount that is mobile, and the amount absorbed.

Bone Seeker - A radioisotope that tends to accumulate in the bones when it is introduced into the body. An example is strontium-90, which behaves chemically like calcium.

Breeder Reactor - A reactor that is designed to produce more fissile material than it consumes; also sometimes called "fast reactor" since most breeder reactors use fast neutrons for sustaining the nuclear chain reaction.

BTU - British thermal unit. The amount of energy gained by a pound of water when its temperature is increased by one degree Fahrenheit.

Burial Ground (Graveyard) - A disposal site for radioactive waste materials that uses earth or water as a shield.

Burn-up - The amount of energy that has been generated from a unit of nuclear fuel; usually measured in megawatt-days per metric ton of initial heavy metal.

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