Absorbed dose The energy passed on to matter by ionizing radiation per unit mass of material of interest. One Gy (gray) is an absorbed dose of 1 Joule/kg or 100 rads. One rad is an absorbed dose of 100 ergs/g or 0.01 joule/kg, equal to 0.01 Gy.
Dose rate The amount of radiation given per unit of time, such as Gy/min.
Electromagnetic radiation A self-propagating wave in space that has both electric and magnetic components.
Excitation Elevation of the energy level of an atom to an excited state by raising the energy level of an electron without actually ejecting it.
Gamma rays Electromagnetic radiation with a specific frequency produced by interaction of subatomic particles, such as electron-positron annihilation or radioactive decay. Gamma rays are an ionizing type of radiation. They have the highest energy and shortest wavelength in the electromagnetic spectrum, and are close in property to x rays.
Ionization Converting an atom or molecule to an ion by altering the difference between the numbers of protons and electrons.
Ionizing radiation Energetic particles or waves that can ionize an atom or molecule (i.e., completely remove an electron) as a result of atomic interactions.
Linear Energy Transfer (LET) A measure of the energy transferred to material as an ionizing particle passes through.
Non-ionizing radiation Electromagnetic radiation whereby the indivisible unit of energy is not energetic enough to cause ionization, although an excitation can occur and induce a biological effect.
Photon An elementary particle that has both wave and particle properties, and is responsible for electromagnetic phenomena. It can be absorbed by matter and transfer energy as well as momentum proportional to its frequency.
Radiation Energy in the form of waves or moving subatomic particles.
Ultraviolet (UV) light Electromagnetic radiation having a wavelength less than that of visible light but longer than soft x-rays.
X rays A form of electromagnetic radiation with a characteristic wavelength between 10 and 0.01 nanometers. This type of radiation is ionizing, and similar in property to gamma rays.