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.
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.