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  #1  
Old March 26th 09, 11:37 PM posted to sci.astro.amateur
Wonton Lee
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Default isotopes

Why isn't there far more radiogenic matter making up the planets? How is it
that massive stars create far less isotopes than stable mattter?


  #2  
Old March 27th 09, 12:23 AM posted to sci.astro.amateur
Brian Tung[_5_]
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Default isotopes

Wonton Lee wrote:
Why isn't there far more radiogenic matter making up the planets? *How is it
that massive stars create far less isotopes than stable mattter?


Haven't you just answered your own question? The unstable isotopes
(an
isotope is just a particular species of an element--some are stable
and
some unstable) are made just as stable ones are, but by and large they
don't last as long. So the matter that lasts is made largely of
stable
isotopes--some originally made in the stars, but others that are the
stable products of radioactive isotopes. Those radioactive isotopes
that
do have long half-lives are well represented in planetary mass.

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  #3  
Old March 31st 09, 07:15 AM posted to sci.astro.amateur
jerry warner[_26_]
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Default isotopes



Wonton Lee wrote:

Why isn't there far more radiogenic matter making up the planets? How is it
that massive stars create far less isotopes than stable mattter?


far less unstable matter (isotopes) than stable mattter.


  #4  
Old March 31st 09, 08:58 AM posted to sci.astro.amateur
Martin Brown
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Posts: 1,707
Default isotopes

Wonton Lee wrote:
Why isn't there far more radiogenic matter making up the planets? How is it
that massive stars create far less isotopes than stable mattter?


At the time of a supernova explosion they do create lots of exotic
neutron rich species that in part power the luminous decay. They don't
stay around for long without decaying into more stable elements.
See for example:

http://www.pha.jhu.edu/~qzhang/seminar1bfigs/node3.html

A fresh young planet would have a higher proportion of medium half life
radioisotope species. U235 was once common enough on Earth that a
natural water moderated nuclear reactor formed in the Gabon.

http://www.ocrwm.doe.gov/factsheets/doeymp0010.shtml

These days we only see natural species with half lives of the order of
10^9 years or decay products of things with that sort of lifetime.

Isolating short lived Promethium from a stock solution of Uranium is a
classic wet chemistry radioisotope lab experiment for students.

Regards,
Martin Brown
 




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