Half Life

Is defined as the time required for half of any initial quantity of something to decay. Commonly used in radioactive decay but also used in pharmacological decay. The half-life is defined in terms of probablitlity based on the number of disintegrations per second of a material to decrease by one-half. In terms of radioactive material alpha and beta are generally slower at decay than gamma. Some radiological decay or half lifes are listed below:
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History of Half Life

The original term, dating to 1907, was "half-life period", which was later shortened to "half-life" in the early 1950s. The name was originally used to describe a characteristic of unstable atoms radioactive decay, but it may apply to any quantity which follows a set-rate decay.
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Application of Half Life

The decay of many physical quantities is not exponential—for example, the evaporation of water from a puddle, or (often) the chemical reaction of a molecule. In such cases, the half-life is defined the same way as before: as the time elapsed before half of the original quantity has decayed. However, unlike in an exponential decay, the half-life depends on the initial quantity, and the prospective half-life will change over time as the quantity decays.

The decay of many physical quantities is not exponential—for example, the evaporation of water from a puddle, or (often) the chemical reaction of a molecule. In such cases, the half-life is defined the same way as before: as the time elapsed before half of the original quantity has decayed. However, unlike in an exponential decay, the half-life depends on the initial quantity, and the prospective half-life will change over time as the quantity decays.


References
  1. Beiser, A. (1988). Physical Science (2nd Edition) . New York, NY: McGraw Hill
  2. Half-life. (2012, February 29). In Wikipedia, The Free Encyclopedia. Retrieved 14:54, March 1, 2012, from http://en.wikipedia.org/w/index.php?title=Half-life&oldid=479517289
  3. half-life. In (2010). Volume 5 (15 ed. p. 633). Chicago: Encyclopaedia Britannica, Inc.

This WikiPage developed by Alice Quinn - 2012SP
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