Decay chain

[Rennhack]

The series of decays that certain radioisotopes go through before reaching a stable form. For example, the decay chain that begins with Uranium-238 culminates in Lead-206, after forming intermediates such as Uranium-234, Thorium-230, Radium-226, and Radon-222.  Also called the "decay series."

http://www.epa.gov/radiation/understand/chain.htm