You are not the first (nor I suspect will you be the last) to report such things. Again, I recommend NCRP Report 95. Page 24 has information on radioactive materials commonly found in building materials. Ed Tupin RSO, Center for Devices and Radiological Health EAT@fdadr.cdrh.fda.gov (301) 827-1230 Fax: (301) 594-4760