After the parent nuclide decays, the daughter nuclide produced can also be radioactive. In this way, a single nuclide can undergo several radioactive decay processes, one after the other in a chain. We call this a decay series. As the chain progresses, more material and energy are ejected, making the daughter nuclides lighter and less energetic than their parents.

This image is complex. It shows a parent nuclide of Neptunium-237 decaying by alpha decay, indicated by an arrow, into Protactinium-233, which decays into Uranium-233 by Beta decay, then Thorium-229 by alpha, Radium-225 by alpha, and finally Actinium-225 by Beta. An arrow in between each event shows the direction of the decay series. At the end of the series another arrow indicates that this is not in fact the end and that it will continue until a stable nuclide is reached.

For example, neptunium-237 decays by alpha decay to become protactinium-233, which itself undergoes beta decay to become uranium-233. This process continues until the nuclide reaches a special balance of protons and neutrons producing a stable nuclide.