What is half-life?
Half-life is the time it takes for half of a substance to decay or be eliminated. After one half-life, 50% remains; after two, 25% remains.
Radioactive decay explained
Radioactive decay is exponential, not linear. The same fraction decays in each equal half-life period, so the quantity approaches zero but never reaches it exactly in the model.
Half-life in medicine
Drug half-life describes how long it takes the body to remove half of a dose. It helps clinicians understand dosing intervals and how long a medicine remains active.