Monasite sands typically contain 3 to 7% Th-232 and minor amounts of U decay change nuclides, 10% the Th-232 activity, in my experience, as well as gadolinium, lanthium and neodynium. ************************************************************************ The RADSAFE Frequently Asked Questions list, archives and subscription information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html