Half-life

{
  "id": "MLC-T-ENV-012786",
  "term": "Half-life",
  "field": "Environment",
  "definition": "1. The length of time required for the mass, concentration, or activity of a chemical or physical agent to be reduced by one-half.\n\n2. The time in which the concentration of a substance will be reduced by half\n\n3. The time required for a pollutant to lose one-half of its original coconcentration or for example, the biochemical half-life of DDT in the environment is 15 years.\n\n4. The time required for half of the atoms of a radioactive element to undergo self-transmutation or decay (half-life of radium is 1620 years).\n\n5. The time required for the elimination of half a total dose from the body.\n\n6. Radioactively, half-life is the time required for half of a given quantity of material to decay. Chemically, it is the time required for half of a given quantity of material to undergo a chemical reaction.\n\n7. The time required for half of the quantity of a radioactive isotope to decay. Half-lives are different for each radionuclide and range from fractions of a second to billions of years.\n\n8. 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.\n\n9. (a) The time required for a pollutant to lose one-half of its original concentration. For example, the biochemical half-life of DDT in the environment is 15 years. (b) The time required for half of the atoms of a radioactive element to undergo self-transmutation or decay (half-life of radium is 1620 years). (c) The time required for the elimination of half a total dose from the body.\n\n10. Time required for one-half of the original mass of the chemical to be degraded, transformed, or destroyed in a particular medium.",
  "abbreviation": "t½",
  "subject": "Chemicals, toxics and pesticides",
  "references": [
    "Drinking Water Technical & Legal Terms",
    "Chemical Emergency Preparedness and Prevention Glossary",
    "Terms of Environment",
    "Environmental Geophysics Glossary",
    "RadNet Glossary; Radiation Protection Radiation Glossary; RadTown Glossary",
    "ATSDR 2004",
    "EPA 2005b",
    "EPA ExpoBox Terminology"
  ],
  "url": "https://mlchart.com/terminology/environment/half-life/"
}