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