Fallout 4 pdf francais article needs additional citations for verification. Nuclear fallout, or simply 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 the shock wave have passed.
This radioactive dust, usually consisting of fission products mixed with bystanding atoms that are neutron activated by exposure, is a highly dangerous kind of radioactive contamination. 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. A ground burst can produce possibly much more severe, local 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. 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. In a land or water surface burst, heat vaporizes large amounts of earth or water, which is drawn up into the radioactive cloud. Per capita thyroid doses in the continental United States resulting from all exposure routes from all atmospheric nuclear tests conducted at the Nevada Test Site from 1951-1962. 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. Severe local fallout contamination can extend far beyond the blast and thermal effects, particularly in the case of high yield surface detonations.
The ground track of fallout from an explosion depends on the weather from the time of detonation onwards. In stronger winds, fallout travels faster but takes the same time to descend, so although it covers a larger path, it is more spread out or diluted. 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. There are two main considerations for the location of an explosion: height and surface composition. A nuclear weapon detonated in the air, called an air burst, produces less fallout than a comparable explosion near the ground. In case of water surface bursts, the particles tend to be rather lighter and smaller, producing less local fallout but extending over a greater area.