A generator is a self-contained system housing a parent/daughter mixture in equilibrium. There must be a method of removing the daughter and leaving the parent behind to regenerate more daughter activity. It is designed to produce the daughter for some purpose separate from the parent.

Generators produce certain short-lived radioisotopes on-site which cannot be shipped by commercial sources. To be useful, the parent's half-life must be long compared to the travel time required to transport the generator to recipient. The typical shelf-life of a Mo/Tc generator is 2 weeks, as is the expiration date.

The process of removing the daughter from the generator is referred to as elution; the solution used to remove the daughter is called the eluent; and the solution collected from the generator containing the daughter radioisotope is called the eluate.

A photograph of the Bristol Meyers Squibb generator is shown below.