[seqfan] Re: Another chemistry related sequence?
chaosorder4 at gmail.com
Thu Sep 3 15:51:20 CEST 2009
Perhaps if the lengths of half-lives on a logarithmic scale cluster near a
high node (stableish) and near a low node (unstableish), leaving a sea of
non-used range, then the cutoff line could be placed tentatively and
hopefully in the middle of that sea.
On Wed, Sep 2, 2009 at 11:18 PM, Charles Greathouse <
charles.greathouse at case.edu> wrote:
> I would be very happy to have sequences like these in the OEIS, if
> only they were well-defined and not arbitrary. Stable at "the normal
> room temperature conditions" is ill-defined; half-life over 10^20
> years is arbitrary.
> Perhaps isotopes by stability, except that that's not defined on the
> lower end unless/until all (or all but one) of 'stable' isotopes are
> found to have finite half-lives.
> Charles Greathouse
> Case Western Reserve University
> On Wed, Sep 2, 2009 at 8:24 PM, <franktaw at netscape.net> wrote:
> > See http://en.wikipedia.org/wiki/Bismuth-209. Bismuth 209 was long
> > thought to be stable, but actually has a half-life of 1.9e19 years. It
> > is likely that other isotopes will be found to be slightly unstable;
> > perhaps all are (proton decay is still a theoretical concept).
> > Frankly, I think this whole area ought to be left out of the OEIS; but
> > as long as A007656 is present, I suppose there's no reason to exclude
> > it.
> > Franklin T. Adams-Watters
> > -----Original Message-----
> > From: David Wilson <davidwwilson at comcast.net>
> > a(43) = 0 as well.
> > I think "stable" once meant "will never spontaneously decay." The
> > poster boy
> > for stability was the proton.
> > Wikipedia states that protons are now thought to have minimum half-life
> > of
> > 10^36 years, yet are still called stable.
> > I don't find a defined half-life cutoff point where unstable becomes
> > stable,
> > maybe it's a matter of application.
> > ----- Original Message -----
> > From: "Antti Karttunen" <antti.karttunen at gmail.com>
> >> Here is an idea for atomic elements related sequence that should
> >> be reasonably well defined:
> >> a(n) = The number of stable isotopes the element number n has.
> >> If the information in Wikipedia is correct, the sequence should start
> > as:
> >> 2,2,2,1,2,2,2,3,1,3,...
> >> Note that both a(83) ( http://en.wikipedia.org/wiki/Bismuth )
> >> and a(92) ( http://en.wikipedia.org/wiki/Uranium ) should be 0.
> >> (Or is it? Okay, we can speculate about the eventual decaying of
> > protons,
> >> but... Also, I mean stable at "the normal room temperature
> > conditions",
> >> not
> >> inside
> >> a particle accelerator.)
> >> Cheers,
> >> Antti.
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