[seqfan] Re: Atomic number of n-th element in the "neptunium series"

[Chris Thompson]

On Apr 20 2018, Marc LeBrun wrote:

>Maybe, rather than counting down, it should be increasing, with a(1) = the
>the final stable decay product? That way, any "trans-neptunian" elements
>discovered in the future would simply extend the sequence.

Ah, but what counts as "stable"? Felix's series counted Bi^209 as unstable
and added Tl^205 at the end of the chain, although the alpha decay of Bi^209,
with a half life of 1.9*10^19 years, was not actually detected until 2003,
although a value of that order of magnitude had previously been predicted.

After all, nearly all of the heavier nuclei are *theoretically* unstable,
one way or another. Even the ultra-"stable" doubly-magic Pb^208 has a
computed positive alpha decay energy of about 0.34 Mev, which I think gives
one an estimated alpha-decay half-life of something like 10^300 years...

-- 
Chris Thompson
Email: cet1 at cam.ac.uk