Glossary D - F

Decay, Radioactive

The decrease in the amount of any radioactive isotope with the passage of time due to the spontaneous emission of radiation from the atomic nuclei (either alpha or beta particles, often accompanied by gamma radiation), and consequent transformation to a different chemical form.

Decay Chain

The series of decays that certain radioisotopes go through before reaching a stable form. For example, the decay chain that begins with Uranium-238 culminates in Lead-206, after forming intermediates such as Uranium-234, Thorium-230, Radium-226, and Radon-222. Also called the "decay series."

Decay Products

The isotopes or elements that form and the particles and high-energy electromagnetic radiation emitted by the nuclei of radionuclides during radioactive decay. Also known as "decay chain products," "daughter products," or "progeny" (the isotopes and elements).

Dirty Bomb

Commonly refers to a device that spreads radioactive material by exploding a conventional (non-nuclear) explosive, such as dynamite. Because they do not involve the sophisticated technology required to create a nuclear explosion, dirty bombs are much simpler to make than a true nuclear bomb.

Dose (Radiation)

Denotes the quantity of radiation or energy absorbed. Dose may refer to the following:

• Absorbed dose - the amount of energy deposited per unit mass
• Equivalent dose - the absorbed dose adjusted for the relative biological effect of the type of radiation being measured
• Committed dose - a dose that accounts for continuing exposures over long periods of time (such as 30, 50, or 70 years)

To learn more about dose Health Effects.

Electron

Exposure (Radiation)

A term relating to the amount of ionizing radiation that strikes a living or inanimate material. (This is a general definition. In health physics, exposure is specifically defined as a measure of ionization in air caused by x-ray or gamma radiation only.)

Fission (Fissioning)

The splitting of a nucleus into at least two other nuclei and the release of a relatively large amount of energy. Two or three neutrons are usually released during this type of transformation. Fissioning is also referred to as 'burning'.

Fissioning that occurs without any outside cause, such as bombardment with a neutron, is called 'spontaneous fission.'