Also, after a year it is estimated that a sizable quantity of fission products move from the northern to the southern stratosphere. By the time that stratospheric fallout has begun to reach the earth, the radioactivity is very much decreased. Long-term fallout can sometimes occur from deposition of tiny particles carried in the stratosphere. The intermediate time scale results from fallout that has been put into the troposphere and ejected by precipitation during the first month. Exposure can be on an intermediate time scale or long term.

Starting from 1951 people may have gotten exposure, depending on whether they were outside, the weather, and whether they consumed contaminated milk, vegetables or fruit. Fallout accumulates on vegetation, including fruits and vegetables. Radioactive fallout has occurred around the world for example, people have been exposed to iodine-131 from atmospheric nuclear testing. Elevated atmospheric radioactivity remains measurable after the widespread nuclear testing of the 1950s. Its radioactive characteristics increase the statistical cancer risk. This size of particulate matter, lifted to the stratosphere, may take months or years to settle, and may do so anywhere in the world. Its amount can be estimated from the fission-fusion design and yield of the weapon.Īfter the detonation of a weapon at or above the fallout-free altitude (an air burst), fission products, un-fissioned nuclear material, and weapon residues vaporized by the heat of the fireball condense into a suspension of particles 10 nm to 20 µm in diameter. When the nuclear fireball does not reach the ground, this is the only fallout produced. These materials are limited to the original mass of the device, but include radioisotopes with long lives. The second, depending on the height of detonation, is a large quantity of radioactive dust and sand with a short half-life.Īll nuclear explosions produce fission products, un-fissioned nuclear material, and weapon residues vaporized by the heat of the fireball.

The first is a small amount of carcinogenic material with a long half-life.

Types of fallout 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.įallout comes in two varieties. This radioactive dust, usually consisting of fission products mixed with bystanding atoms that are neutron-activated by exposure, is a form of radioactive contamination. Fallout may get entrained with the products of a pyrocumulus cloud and fall as black rain (rain darkened by soot and other particulates, which fell within 30–40 minutes of the atomic bombings of Hiroshima and Nagasaki). The amount and spread of fallout is a product of the size of the weapon and the altitude at which it is detonated. It commonly refers to the radioactive dust and ash created when a nuclear weapon explodes. Nuclear 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 has passed.

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