- the constant time period required for the disintegration of half of the atoms in a sample of some specific radioactive substancealso half life
- the time it takes for half of something to decompose, reduce in strength or effectiveness, etc.: often, specif., used of the diminishing concentration of a medication in the body
- life ()
- Physics The time required for half the nuclei in a sample of a specific isotopic species to undergo radioactive decay.
- Biology a. The time required for half the quantity of a drug or other substance deposited in a living organism to be metabolized or eliminated by normal biological processes. Also called biological half-life.b. The time required for the radioactivity of material taken in by a living organism to be reduced to half its initial value by a combination of biological elimination processes and radioactive decay.
- Alternative spelling of half-life.
- (physics) The time required for half of the nuclei in a sample of a specific isotope to undergo radioactive decay.
- (chemistry) In a chemical reaction, the time required for the concentration of a reactant to fall from a chosen value to half that value.
- (medicine) The time it takes for a substance (drug, radioactive nuclide, or other) to lose half of its pharmacological, physiologic, or radiological activity.
- The time it takes for an idea or a fashion to lose half of its influential power.
half-life - Investment & Finance Definition
The point at which half of the principal has been repaid in a mortgage-backed security. A typical time assumed for half-life is 12 years. If interest rates fall, that time decreases because more homeowners will refinance their mortgages, which will have the effect of paying off the principal more quickly than normal. If interest rates rise and refinancing slows, then the inverse is true.