Both the East Coast and west coast, have planes and helicopters equiped with radiation detecting equipment. They are capable of detecting the rad from nature stone such as headstones. They have background map of rad of all major cities to compare any different future readings. I know this for a fact and any major event, the surrounding area is scanned ahead to monitor differences in readings. If such an event was to happen it would be because they let it happen. Former CBRN specialist.