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TeachMeFinance.com - explain Half-life Half-life The term 'Half-life' as it applies to the area of hazardous materials can be defined as 'The time it takes for half the original amount of a substance to disappear. In the environment, the half-life is the time it takes for half the original amount of a substance to disappear when it is changed to another chemical by bacteria, fungi, sunlight, or other chemical processes. In the human body, the half-life is the time it takes for half the original amount of the substance to disappear, either by being changed to another substance or by leaving the body. In the case of radioactive material, the half life is the amount of time necessary for one half the initial number of radioactive atoms to change or transform into another atom (that is normally not radioactive). After two half lives, 25% of the original number of radioactive atoms remain'. The term 'Half-life' as it applies to the area of nuclear science can be defined as ' 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 term 'Half-life' as it applies to the area of energy can be defined as ' The time it takes for an isotope to lose half of its radioactivity'. Previous 5 Terms: Hail Size - Pea Hail Spike Haines Index halcocline halcyonine Next 5 Terms: Half-life (radiological) Half-life, biological Half-life, effective Half-thickness half-tide level About the author Mark McCracken Author: Mark McCracken is a corporate trainer and author living in Higashi Osaka, Japan. He is the author of thousands of online articles as well as the Business English textbook, "25 Business Skills in English". Copyright © 2005-2011 by Mark McCracken, All Rights Reserved. TeachMeFinance.com is an informational website, and should not be used as a substitute for professional medical, legal or financial advice. Information presented at TeachMeFinance.com is provided on an "AS-IS" basis. Please read the disclaimer for details.