Preferred Label : lifetime;
Detailed label : lifetime, τ;
IUPAC definition : Lifetime of a molecular entity, which decays by first-order kinetics, is the time
needed for a concentration of the entity to decrease to 1/e of its original value,
i i.e., /i c(t τ) c(t 0)/e. Statistically, it represents the life expectation
of the entity. It is equal to the reciprocal of the sum of the first-order rate constants
of all processes causing the decay of the molecular entity.;
Scope note : lifetime is used sometimes for processes, which are not first order. however, in such
cases, the lifetime depends on the initial concentration of the entity, or of a quencher
and, therefore, only an initial or a mean lifetime can be defined. in this case it
should be called decay time.; mathematical definition: t 1 k 1
i ki with kithe first-order rate constants for all decay processes of
the decaying state.; occasionally, the term half-life(t1/2) is used, representing the time needed for the
concentration of an entity to decrease to one half of its original value, i.e.,
c t t1/2 c t 0 2 . for
first-order reactions, t1/2 2 t .;
Origin ID : L03515;
See also
Lifetime of a molecular entity, which decays by first-order kinetics, is the time
needed for a concentration of the entity to decrease to 1/e of its original value,
i i.e., /i c(t τ) c(t 0)/e. Statistically, it represents the life expectation
of the entity. It is equal to the reciprocal of the sum of the first-order rate constants
of all processes causing the decay of the molecular entity.
