# Isotope with longest decay chain to reach a stable isotope

Which decay chain of a radioactive isotope has the most 'steps' before reaching a stable isotope, i.e. decays into the most other isotopes before becoming stable?

• for clarity, not about the time taken to decay. – stanley dodds Feb 12 '15 at 17:34
• Who gave here a minus? And why? – Sofia Feb 12 '15 at 17:39

In a sense, this question is unanswerable. (Still a good question!) } Consider the natural decay chain of $_{92}U^{238}$. This isotope goes through 14 steps, along various routes, to decay to $_{82}Pb^{206}$. This $4n+2$ series is the longest naturally occurring one. See http://en.wikipedia.org/wiki/Decay_chain
However, someone could immediately claim that they have some $_{94}Pu^{242}$ which decays almost at once by $\alpha$-emission to $_{92}U^{238}$. The someone jumps up with some $_{96}Cm^{246}$, and so on, and so on.