First thing to review is this "Radiation Emergency Medical Management" page, with a list of different contaminants and appropriate therapies.

http://www.remm.nlm.gov/int_contamination.htm

The discussion for Potassium Iodide is here:

http://www.remm.nlm.gov/potassiumiodide.htm

Which provides a link to this FDA page:

http://www.fda.gov/Drugs/EmergencyPreparedness/BioterrorismandDrugPreparedness/ucm072265.htm

And there's always the wikipedia page:

http://en.wikipedia.org/wiki/Potassium_iodide