the series of decays that certain radioisotopes go through before reaching a stable form. For example, the decay chain that begins with uranium-238 (U-238) ends in lead-206 (Pb-206), after forming isotopes, such as uranium-234 (U-234), thorium-230 (Th-230), radium-226 (Ra-226), and radon-222 (Rn-222).
In nuclear science, the decay chain refers to the radioactive decay of different discrete radiocative decay products as a chained series of transformations. Most radioactive substances do not decay directly to a stable state, but rather undergo a series of decays until eventually a stable isotope is reached.