Half-life
The time in which one half of the atoms of a particular radioactive substance disintegrate into another nuclear form. Measured half-lives vary from millionths of a second to billions of years. Also called physical or radiological half-life.
The time required for the body to eliminate one half of the material taken in by natural biological means.
The time required for a radionuclide contained in a biological system, such as a human or an animal, to reduce its activity by one-half as a combined result of radioactive decay and biological elimination.
The time it takes for an isotope to lose half of its radioactivity.
