Nuclear fallout, or simply fallout, also known as Black Rain, 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. Some basic information
It commonly refers to the radioactive dust and ash created when a nuclear weapon explodes, but this dust can also be originated in a damaged nuclear plant. 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 or soil and devastate the affected ecosystems years after the initial exposure. Worldwide effect
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 10kt.
Atmospheric nuclear weapon tests almost doubled the concentration of radioactive C14 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. 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...