Loyola University Medical Education Network


A generator is a self-contained system housing a parent/daughter mixture in equilibrium, which is designed to yield the daughter for some purpose usually separate from the parent. The principal utility is to produce certain radioisotopes on-site which, because of their short half-lives, 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 the recipient.


1. If intended for clinical use, the output of the generator must be sterile and pyrogen-free.

2. The chemical properties of the daughter must be different than those of the parent to permit separation of daughter from parent. Most often, separations are performed chromatographically.

3. Generator should be eluted with 0.9% saline solution and should involve no violent chemical reactions. Human intervention should be minimal to minimize radiation dose.

4. Daughter isotope should be short-lived gamma-emitting nuclide (physical half-life = hrs-days)

5. Physical half-life of parent should be short enough so daughter regrowth after elution is rapid, but long enough for practicality.

6. Daughter chemistry should be suitable for preparation of a wide variety of compounds, especially those in kit form.

7. Very long-lived or stable granddaughter so no radiation dose is conferred to patient by decay of subsequent generations.

8. Inexpensive, effective shielding of generator, minimizing radiation dose to those using it.

9. Easily recharged (we do NOT recharge Mo/Tc generators, but store them in decay areas after their useful life is over).

Clinically useful, commercially available radionuclide generators are listed below: All of these generators are examples of secular equilibrium, except for the Mo/Tc generator, which is transient equilibrium.

Answer: elution profile of a generator for first five days of the week. Slope of the line represents the decay rate of the parent nuclide.


Stephen Karesh, PhD.

Last Updated: August 14, 1996
Created: March 1, 1996