title: Comments on equilibrium, transient equilibrium, and secular equilibrium in serial radioactive decay.
abstract: Equations describing serial radioactive decay are reviewed along with published descriptions of transient and secular equilibrium. It is shown that terms describing equilibrium are not used in the same way by various authors. Specific definitions are proposed; they suggest that secular equilibrium is a subset of transient equilibrium.
mesh_terms: D006207:Half-Life; D008433:Mathematics; D055585:Physical Phenomena; D010825:Physics; D011851:Radioactivity; D011876:Radionuclide Generators