Re: half-life of stable isotopes


mmeron@xxxxxxxxxxxxxxxxxx wrote:
> In article <doaqmi$p8g$1@xxxxxxxxxxxxxxxx>, keith@xxxxxxxxxxxxxxxxxxx (Keith A. Schneider) writes:
>
> >How stable are "stable" isotopes? A proton is stable but has a
> >theoretical half-life of 10^32 years at least.
>
> The limit by now has been raised, at least to 10^35 as I recall. And
> it may be infinite as well.
>
> > I assume that stable isotopes have half-lives less than this (but
> >still not easily measureable).
>
> Not necessarily, may be longer.
>
> > What is the half-life of, say, Oxygen-16? Anyone know?
> >
> All you can say is "no decay has been measured". There is no clear
> defining line between stable and unstable. When the lifetime is too
> long (even if finite), you just won't detect decays.

Can you not say that a particular decay mode of a particular isotope is
or is not energetically possible? And use the absence of any
energetically possible decay as "proof" of an isotopes stability?

By this definition, the dividing line between stable and unstable
isotopes is as clear as the dividing line between exothermic and
endothermic in chemical reactions.

OTOH, my most recent (16thEdition) Chart of the Nuclides still lists
Bismuth 209 as stable... Sigh...

.

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