On 01/05/18 15:35, Chris Hogg wrote:
On Tue, 01 May 2018 15:07:46 +0100, Tim Streater
wrote:

In article , Chris Hogg
wrote:

So my question remains: where has the uranium and thorium in coal,
come from? I doubt there will be an answer, unless some lab somewhere
has ground up some coal samples _very_ fine and done a density
separation, or more probably a flotation, to separate the organic
component from the inorganic, and measured the radioactivity in each.

I suggested a possible answer.

Oklo, IIRC. While I realise that uranium and thorium might be
transported by groundwater, that doesn't really explain why they
should be incorporated into deposits that eventually became coal,
especially as coal deposits are widely distributed across the world.

OK so in the Carboniferous, the land masses were very differently
distributed to what they are today*, but I still find that explanation
unlikely. It would require a rather unique set of circumstances to
apply to may large areas of Everglade-type swamp, and why don't other
non-coal deposits of similar age also contain raised levels of U and
Th. Or perhaps they do.

I think 'perhaps they do' is about right.

All plants contain uranium and are thereby radioactive. Its a very
common element and occurs almsot everywhere, but is more pravalent in
rocks that have been extruded from deeper in the mantle - i.e. volcanic
rocks like granite and the like.





* https://en.wikipedia.org/wiki/Pangaea



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