They're handing out potassium iodide (KI) pills near the nuclear power plants in PA. This tells a bit about why.
It mentions the Chernobyl accident, and 1000 cases of thyroid cancer that allegedly resulted from it (other sources, including the previous link, differ).
Whatever the right number is, it's a shame. If the Russian Communists had given a damn about civil defense and passed out such pills, most of those could have been prevented. Instead, they chose to deny the existence of a problem that was visible from outer space and set off radiation alarms in Scandinavia.
Incidentally, these pills will be radioactive. Never mind the poll.