Re: Natural Thorium

[DWMCCARN@aol.com]

Just another note:
      I have always used "NATURAL" as in "NATURAL URANIUM" to mean the 
naturally occuring (unprocessed) form, but then I'm just a geologist.

Isotopic Abundance from the "Nuclear Wallet Card", 5th Edition, July 1995, 
Jagdish K. Tuli National Nuclear Data Center, Brookhaven National Laboratory	
	U-238	      	U-235		U-234	      Total
	99.2745%		0.720%		0.0055%	100.0000%

Because "Natural Uranium" decay adds activity to the total thorium activity, 
and because each mineral species at any locality may vary significantly in 
both uranium and thorium concentration, the total thorium activity would have 
to be measured.

As an example, the thorium-rich monazite beach sands (Monazite	(Ce,La,Th) 
(PO4) )
also contains minor amounts of Uranium. U-238 / Pb-206 ratios can be used to 
date monazite along with U-235 / Pb-207, Pb-207 / Pb-206, and Th-232 / Pb-208 
ratios.

D. McCarn
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