Unit of activity equal to one radioactive disintegration per second. Replaces the older unit, the Curie (Ci): 1 Ci = 3.7x1010Bq.

A single rod of fissionable material encased in cladding. Fuel rods are assembled into fuel elements.

Measure of biological effect of radiation (dose). Now superseded by the sievert (Sv): 1 Sv = 100 rems.

Nuclear fuel elements in which fission products have built up and the fissile material depleted to a level where a chain reaction does not operate efficiently. Also referred to as irradiated fuel.

 

Elements with 89 or more protons in their nucleus that behave chemically like actinium. All are radioactive and many are long- lived alpha-emitters.

The number of disintegrations per unit time taking place in a radioactive material. The unit of activity is the Becquerel (Bq), one disintegration per second.

A positively charged particle emitted from the nucleus of an atom during radioactive decay and consists of two protons and two neutrons (a helium-4 nucleus). Although alpha particles are normally highly energetic, they travel only a few centimetres in air and are stopped by a sheet of paper or the outer layer of dead skin.

A particle of matter that cannot be broken up by chemical means. Atoms have a nucleus consisting of positively charged protons and uncharged neutrons of about the same mass. In a neutral atom the positive charges of the protons in the nucleus are balanced by the same number of negatively charged electrons in motion around the nucleus.

One-twelfth of the mass of a carbon-12 atom. It is approximately equal to the mass of a single proton or neutron.