K-65 residues
K-65 residues are the very radioactive mill residues resulting from the uniquely concentrated uranium ore discovered before WW II in Katanga province (Shinkolobwe mine) of the Democratic Republic of the Congo (formerly Belgian Congo). According to Zoellner, "Remnants from typical uranium from the southwestern United States give a radioactive signature of about forty picocuries per gram, about ten times the amount of picocuries per liter of air that is considered safe for humans to breathe.