[Also: Half-Life Time, Radioactive Half-Life] The half-life is the time in which half the atoms (always a fraction, not a number) of a given radionuclide disintegrate from the amount of atoms present when measurement starts. From 200 atoms of a radionuclide with a half-life of one minute will 100 atoms disintegrate in the first minute, 50 in the second minute, etc. The half-life is a characteristic property of radioactive isotopes. The effective half-life includes all processes of elimination, including radioactive decay.
Different half-life terms:
- Physical Radioactive Half-Life
- Biological Radioactive Half-Life
- Effective Radioactive Half-Life.

See also Decay Constant, Decay.

The biological half-life is the time required for the concentration of a substance in a biological system to be reduced by one half. A biological half-life includes usual processes for eliminating substances without radioactive decay.

See also Biological Radioactive Half-Life.

Time in which 50% of the atoms of a radioactive substance transform/disintegrate (decay) to another nuclear form.

See also Half-Life, Biological Radioactive Half-Life and Effective Radioactive Half-Life.

Time in which 50% of a radioactive substance through biological (physiological) processes and decay is removed.
The effective radioactive half-life is shorter or equal than the physical or the biological radioactive half-life alone.

Effective Radioactive Half-Life (t_eff) =
(Biological Radioactive Half-Life x Physical Radioactive Half-Life) /
(Biological Radioactive Half-Life + Physical Radioactive Half-Life)

See also Half-Life, Biological Half-Life, Physical Radioactive Half-Life.

Time in which 50% of an administered dosage of a radioactive substance through biological (physiological) processes is removed.

See also Half-Life, Physical Radioactive Half-Life and Effective Radioactive Half-Life.