Hamilton, Joseph H. Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee.
Last reviewed:July 2019
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- Half-life, published October 2016:Download PDF Get Adobe Acrobat Reader
- Half-life, published June 2014:Download PDF Get Adobe Acrobat Reader
- Chemical reactions
- Radioactive decay
- Additional Readings
The time required for one-half of a given material to undergo chemical reactions. As a term, half-life is often used in nuclear physics to quantify the average time interval required for one-half of any quantity of identical radioactive atoms to undergo radioactive decay. For example, the half-life of uranium-238 is approximately 4.5 billion years, meaning that a given quantity X will be reduced to approximately ½ X after that time interval (see illustration). The term half-life is also more broadly used in chemistry and medicine to indicate the time interval within which half of a substance will have decayed or changed in some manner. An example is the biological half-life of a drug, which refers to how many days (typically) it tends to take for biological processes to have removed half of an administered dose from the body. See also: Atom; Chemistry; Nuclear physics; Pharmacology; Radioactivity; Time; Uranium
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