Absorbed dose The energy imparted by ionizing radiation
to a suitably small volume of matter divided by the mass of that volume. Unit
gray, symbol Gy.
1 Gy = 1 joule per kilogram.
Actinides A group of 15 elements with atomic number from that of actinium (89) to lawrencium (103) inclusive. All are radioactive. Group includes uranium, plutonium, americium, and curium.
Activity The rate at which nuclear transformations occur in a radioactive material. Used as a measure of the amount of a radionuclide present.
Unit becquerel, symbol Bq. 1 Bq = 1 transformation per second.
Alpha particle A particle consisting of two protons plus two neutrons
(i.e. the nucleus of a helium atom) emitted by a radionuclide.
Atom Unit of matter consisting of a single nucleus surrounded by a number of electrons equal to the number of protons in the nucleus. The smallest portion of an element that can combine chemically with other atoms.