Re: thorium abundance?

["Dale E. Boyce" <dale@radpro.uchicago.edu>]

Tough question, Melissa.  Th-232 is listed as 100%, but that is
100% - epsilon.  Th-228 in equilibrium with it contributes
1.9/1.4e10 to the abundance (ratio of half lives).  Th-230 
from U-234 decay would contribute something like 
0.0017% * [Uranium abund.]/[Thorium abund.].  Similarly, one could
calculate the abundance of Th-227, Th-231, and Th-234 from the
relative abundances of the parent nuclides.  Hope this helps.

Dale