On Sat, 25 Mar 2000 (15:41:06 -0000) Richard wrote:
>Steven, You wrote:
[Snippage]
>>But, how do these revelations affect my original point? Actually, if
>>anything, they improve it. The question still stands. With the exceptions
>>noted in my first post (and David Bowman's correction of my sunlight/cosmic
>>ray blunder), why are there no naturally-occurring radioactive isotopes
>>having half-lifes of 70 million or less? This question is valid whether
>>all Sm-146 (70 M.Y. half life) has decayed or whether it has simply
>>decayed to the point that we can no longer detect it.
>
>To justify that point, you need to show that the original concentrations
>were well within today's detection limits. That may be obvious to you, but
>not to a layman like me!
If we were only talking about Sm-146 (known as a rare-earth-element), this
justification might be important. But let's look at the problem
statistically. What are the odds that every known isotope in the top half
of the list provided in my original post had an original concentration high
enough that we can still detect it today AND every single element (with
noted exceptions) having a half-life of 70 M.Y. or less did not? Pretty
slim, I'd predict.
As for specific answers, I don't know if we can predict the original
relative concentrations of various isotopes. Possibly. But as an economic
geologist - mineral exploration/environmental geochemist, we are now
approaching topics in physics and atomic theory which are beyond my current
sphere of knowledge.
>By the way, how do we know the half-lives of isotopes which are not found in
>nature? Have they been created artificially?
Yes. The CRC Handbook of Physics and Chemistry tables I mentioned earlier
were compiled at the National Reactor Testing Station of the Idaho Nuclear
Corporation. I'm assuming that some of that work was done there. These
tables contain a lot of measured data beyond just a simple listing of
isotopes and half-lifes.
>>P.S. BTW, although humbling, I consider it an honor to be able to correct
>>my errors. Almost everyone who has written peer-reviewed papers
>>understands and ultimately appreciates correction -- especially before
>>publication.
I just wish that I didn't make so many of them!
>>Perhaps someday, in another post, I will relate the story of person whom
>>I've worked with here -- one of my heros of scientific integrity who
>>personally and very publicly refuted his own published paper after redoing
>>his experiment.
>
>Please do. I look forward to reading it. :-)
Someday. Right now, I can't afford to have too may loose "threads."
Steve
[The opinions expressed herein are my own
and are not to be attributed to my employer.]
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Steven M. Smith, Geologist Office: (303)236-1192
U.S. Geological Survey Fax: (303)236-3200
Box 25046, M.S. 973, DFC smsmith@usgs.gov
Denver, CO 80225
--The USGS National Geochemical Database NURE HSSR Data Web Site--
http://greenwood.cr.usgs.gov/pub/open-file-reports/ofr-97-0492/
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