A generator must always have a parent nuclide with a longer half-life than the daughter nuclide. Transient equilibrium occurs when the parent half-life is 10-100 times greater than the daughter half-life, while secular equilibrium occurs when the parent half life is at least 100 times over that of the daughter. Finally, the parent nuclide must remain tightly bound to the column over the generator so that the daughter nuclide may be eluted for use.
