Lifetime (physics)
Lifetime in physics is the mean time of existence of any member of an assembly of identical physical objects, each instance of which lives for a duration that follows a given distribution of which the mean is the lifetime (sometimes calls for this reason the mean lifetime).
Typically one speaks of lifetime for unstable particles, for which the time elapsed before the disintegration follows the exponential distribution (resulting from the fact that a particle has no memory of its past in regard of its lifetime):
with  the associated decay constant (cf. exponential decay). Stated another way, P(t)dt is the infinitesimal probability that the particle disintegrates at time t. Therefore, in an assembly of  particles,  is the rate of particles decaying at time t. (This result is in decays per time unit.)
Computing the average links the lifetime  to the decay constant constant :
The probability for one given atom to disintegrate in any infinitesimal interval of time  is  .
Another quantity of common use is the half life time  , which is the time required for half of the population to disintegrate. It is linked to the lifetime through
See also
Referenced By
Exponential decay
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