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|Definition of radioactive fallout|
|How it occurs|
|Two types of fallout:||Tropospheric fallout|
Radioactive fallout is the term used for the radioactive particles that settle themselves on the earth and that are released into the atmosphere after nuclear discharge from nuclear power plants, nuclear explosions or nuclear weapons. This can lead to excess radioactivity and radiation. These are explained in other parts of the site. (Go to Radiation).
The radioactive fallout material is formed by the splitting of nuclei (centre part of atoms), this splitting of nuclei is called "nuclear fission" and is how, presently, all nuclear power plants produce energy to generate electricity. When nuclear fission is carried out, amounts of radioactive waste is produced activating soil, air, water and any other substances near where fission took place. So when a nuclear weapon is used close to the surface of the earth, the force of the explosion causes the earth's surface to be destroyed. Material from the surface are sucked up into a fireball which, in turn, rises to form a cloud.
If the force of the explosion is low, or possibly a medium power the cloud formed by the explosion does not go past the atmospheric layer between the troposphere and stratosphere, this layer is called the tropopause. The particles from the explosion float about the earth at the latitude of the fallout and precipitation brings these particles back to earth, cleansing the atmosphere.
If the force of the explosion is great enough to penetrate particles beyond the tropopause, the atmosphere cannot be cleansed as the smaller particles float in the stratosphere and there is no precipitation of any form here. These particles can remain in the stratosphere for a very long time. They spread themselves apart, horizontally so eventually particles are found throughout the whole of the stratosphere. In polar regions during winter and early spring, vertical mixing occurs bringing material down into the troposphere which, in turn, is then cleansed by precipitaion.
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