Created at the height of the Cold War, “Radiological Defense” presents the scenario of the USA dealing with a “fallout situation” as a result of an atomic attack. According to the film, 100 million people who were not affected by the atomic blast or heat effects, might be affected by the spread of fallout.

Nuclear fallout, or simply fallout, is the residual radioactive material propelled into the upper atmosphere following a nuclear blast or a nuclear reaction conducted in an unshielded facility, so called because it “falls out” of the sky after the explosion and shock wave have passed.

After an air burst, fission products, un-fissioned nuclear material, and weapon residues vaporized by the heat of the fireball condense into a fine suspension of small particles 10 nm to 20 µm in diameter. These particles may be quickly drawn up into the stratosphere, particularly if the explosive yield exceeds 10 kt.

Initially little was known about the dispersion of nuclear fallout on a global scale. The AEC assumed that fallout would be dispersed evenly across the globe by atmospheric winds and gradually settle to the Earth’s surface after weeks, months, and even years as worldwide fallout.