Radioactive Fallout: “Radiological Defense” 1961 US Department of Defense, Civil Defense04:33

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Published on January 4, 2018

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Radioactive fallout and how much damage it might cause in the event of a nuclear war. Produced for the Office of Civil and Defense Mobilization by Norwood Studios.

Public domain film from the US National Archives, slightly cropped to remove uneven edges, with the aspect ratio corrected, and one-pass brightness-contrast-color correction & mild video noise reduction applied.
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).

This film was originally in color, but it was faded so badly that it could not be corrected. Therefore the color was removed.

Fallout is the residual radioactive material propelled into the upper atmosphere following a nuclear blast, so called because it “falls out” of the sky after the explosion and shock wave have passed. It commonly refers to the radioactive dust and ash created when a nuclear weapon explodes. This radioactive dust, consisting of material either directly vaporized by a nuclear blast or charged by exposure, is a highly dangerous kind of radioactive contamination. It can lead to the contamination of aquifers and devastate the affected ecosystem years after the initial exposure.


There are many types of fallout, ranging from the global type to the more area-restricted types of fallout.


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.
Atmospheric nuclear weapon tests almost doubled the concentration of radioactive 14C in the Northern Hemisphere, before levels slowly declined following the Partial Test Ban Treaty.

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. Nuclear products that were deposited in the Northern Hemisphere are becoming “far more dangerous than they had originally been estimated[citation needed].”

The radio-biological hazard of worldwide fallout is essentially a long-term one because of the potential accumulation of long-lived radioisotopes (such as strontium-90 and caesium-137) in the body as a result of ingestion of foods containing the radioactive materials. This hazard is less pertinent than local fallout, which is of much greater immediate operational concern.


In a land or water surface burst, heat vaporizes large amounts of earth or water, which is drawn up into the radioactive cloud. This material becomes radioactive when it condenses with fission products and other radiocontaminants that have become neutron-activated. The table below summarizes the abilities of common isotopes to form fallout. Some radiation would taint large amounts of land and drinking water causing formal mutations throughout animal and human life…

A surface burst generates large amounts of particulate matter, composed of particles from less than 100 nm to several millimeters in diameter—in addition to very fine particles that contribute to worldwide fallout. The larger particles spill out of the stem and cascade down the outside of the fireball in a downdraft even as the cloud rises, so fallout begins to arrive near ground zero within an hour. More than half the total bomb debris lands on the ground within about 24 hours as local fallout…

Severe local fallout contamination can extend far beyond the blast and thermal effects, particularly in the case of high yield surface detonations…

Whenever individuals remain in a radiologically contaminated area, such contamination leads to an immediate external radiation exposure as well as a possible later internal hazard from inhalation and ingestion of radiocontaminants, such as the rather short-lived iodine-131, which is accumulated in the thyroid.

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