A quantity is said to be subject to exponential decay if it decreases at a rate proportional to its value. If the decaying quantity, N(t), is the number of discrete elements in a certain set, it is possible to compute the average length of time that an element remains in the set. This is called the mean lifetime.
The mean lifetime can be looked at as a “scaling time”, because we can write the exponential decay equation in terms of the mean lifetime.
|Nt||quantity at time t ( number of discrete elements ) (dimensionless)|
|No||initial quantity (initial population of the assembly) (dimensionless)|
|λ||decay constant (dimensionless)|