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This glossary defines words and phrases used in this web site. To learn about additional terms related to radiation, please click on http://www.bt.cdc.gov/radiation/glossary.asp.


A dirty bomb is a mix of explosives, such as dynamite, with radioactive powder or pellets. When the dynamite or other explosives are set off, the blast spreads radioactive material into the surrounding area, mostly as dust and smoke.

A “dirty bomb” is not like an atomic bomb because the power of an atomic bomb comes from splitting atoms, which releases the energy and radiation that produce an atomic mushroom cloud. A dirty bomb cannot create an atomic blast. Instead, a dirty bomb uses dynamite or other explosives to scatter radioactive dust, smoke, or other material in order to cause radioactive contamination.

A nucleic acid that carries the genetic information in the cell and is capable of self-replication and synthesis of RNA. DNA consists of two long chains of nucleotides twisted into a double helix and joined by hydrogen bonds between the complementary bases adenine and thymine or cytosine and guanine. The sequence of nucleotides determines individual hereditary characteristics.

The slow descent of minute particles of radioactive debris in the atmosphere following a nuclear explosion.

The power of an atomic bomb comes from splitting atoms, which releases the energy and radiation that produce an atomic mushroom cloud. An extensive weapons-effects testing program and studies of the 1945 bombings of Hiroshima and Nagasaki provide what we know about the biological and environmental effects of nuclear explosions.

Radiation is energy moving in the form of particles or waves. Familiar radiations are heat, light, radio waves, and microwaves. Ionizing radiation is a very high-energy form of electromagnetic radiation.

A naturally occurring radioactive gas found in soils, rock, and water throughout the United States. Radon causes lung cancer and is a threat to health because it tends to collect in homes, sometimes to very high concentrations. As a result, radon is the largest source of exposure to people from naturally occurring radiation.

Dirty bombs are also known as Radiological Dispersal Devices or RDDs.

A unit of equivalent dose. Not all radiation has the same biological effect, even for the same amount of absorbed dose. Rem relates the absorbed dose in human tissue to the effective biological damage of the radiation.

When you are told to “shelter-in-place” it means to find a small, interior room, with no or few windows, and turning off ventilation systems. It does not require sealing off the entire home or office building.


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