In nuclear physics, transient equilibrium is a situation in which equilibrium is reached by a parent-daughter radioactive isotope pair where the half-life of the daughter is shorter than the half-life of the parent.
An example of this is a molybdenum-99 generator producing technetium-99 for nuclear medicine diagnostic procedures.
Such a generator is sometimes called a cow because the daughter product, in this case technetium-99, is milked at regular intervals.
[1] Transient equilibrium occurs after four half-lives, on average.
are the half-lives (inverses of reaction rates
in the above equation modulo ln(2)) of the parent and daughter, respectively, and BR is the branching ratio.
In transient equilibrium, the Bateman equation cannot be simplified by assuming the daughter's half-life is negligible compared to the parent's half-life.
) is approximately 24 hours, which makes it convenient for medical use.