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?
 A: In a sense, this question is unanswerable. (Still a good question!) 
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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.  
A: Just made a small Python that builds a graph from a "decay.txt" file I found somewhere. Longest path in it is:
Sg263->Rf259->Lr259->No259->Md259->Es255->Bk251->Cf251->Cm247->Pu243->Am243->Np239->Pu239->U235->Th231->Pa231->Ac227->Fr223->At219->Rn219->Po215->Pb211->Bi211->Tl207->Pb207
A: I've done some research on this, and the longest decay chain is Og-293*→Lv-289→Fl-285→Cn-281→Ds-277→Hs-273→Sg-269→Rf-265→No-261→Fm-257→Cf-253→Es-253→Bk-249→Cf-249→Cm-245→Pu-241→Am-241→Np-237→Pa-233→U-233→Th-229→Ra-225→Ac-225→Fr-221→At-217→Bi-213→Po-213→Pb-209→Bi-209→Tl-205
*Og-293, although theoretically more stable than the only discovered isotope of Oganesson (Og-294), has not been discovered, but it will probably be in the not too distant future. I have also checked decay chains for other theoretical isotopes of Oganesson such as Og-300, but their decay chains are very short due to spontaneous fission. If you want the longest decay chain for isotopes that are known to exist, then just remove the Og-293 from the decay chain.
