[seqfan] Another chemistry related sequence?
antti.karttunen at gmail.com
Thu Sep 3 11:38:38 CEST 2009
On Thu, Sep 3, 2009 at 3:30 AM, <seqfan-request at list.seqfan.eu> wrote:
> Message: 10
> Date: Wed, 02 Sep 2009 20:24:16 -0400
> From: franktaw at netscape.net
> Subject: [seqfan] Re: Another chemistry related sequence?
> To: seqfan at list.seqfan.eu
> Message-ID: <8CBFA44015A488B-4550-B63B at webmail-m012.sysops.aol.com>
> Content-Type: text/plain; charset="us-ascii"; format=flowed
> 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
Hmm, it's getting complicated. Exactly defined sequences seem to mix poorly
with the real-life physics and chemistry. See also:
with the longest known half-life, 2.2×1024 years.
So, instead, I propose an arbitrary cut-point:
"Number of isotopes of the element with atomic number n, whose half-life is
>= half-life of Uranium-238"
(i.e. 4.468x10^9 years). This age-limit is convenient also because
it's an approximate age of the Earth and our Solar system.
Then only problem would come if there were some isotope
of another element than Uranium, with half-life so near to U-238
that it would be beyond the reach of our measurements to determine
whether it's shorter or longer than with U-238. But that is unlikely?
Then, a(92)=1 and also a(83)=1.
Question to Neil: Should I submit this sequence?
> 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
> 10^36 years, yet are still called stable.
> I don't find a defined half-life cutoff point where unstable becomes
> 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
> > 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
> > but... Also, I mean stable at "the normal room temperature
> > not
> > inside
> > a particle accelerator.)
> > Cheers,
> > Antti.
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