# Exponential decay

A very similar equation will be seen below, which arises when the base of the exponential is chosen to be 2, rather than *e*. In that case the scaling time is the "half-life".

For example, polonium-210 has a half-life of 138 days, and a mean lifetime of 200 days.

or, by rearranging (applying the technique called separation of variables),

For a decay by three simultaneous exponential processes the total half-life can be computed as above:

In the pharmacology setting, some ingested substances might be absorbed into the body by a process reasonably modeled as exponential decay, or might be deliberately formulated to have such a release profile.

Exponential decay occurs in a wide variety of situations. Most of these fall into the domain of the natural sciences.