Strontium-90, Iodine-129 and other lethal particles across a broad swath of the country. Infants who were bottle-fed, which was then considered the modern approach, were particularly vulnerable to the Strontium-90 that ended up in cows' milk.

In 1961, as John Kennedy was poised to resume atmospheric testing after a two-year moratorium, he met with White House science adviser Jerome Wiesner in the Oval Office one rainy day. The president wondered how fallout reached the earth. Wiesner explained that it was washed out of the clouds by rain. "You mean," Kennedy asked, "it's in the rain out there?" As Wiesner tells it, the president then "looked out the window, looked very sad and didn't say a word for several minutes." Nonetheless JFK, fearful that the Soviet Union might score a nuclear breakthrough, authorized a new round of above-ground testing before negotiating the Nuclear Test Ban Treaty in 1963.