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high into the air by the heat and force of the nuclear explosion,
Larger
particles and those in the lower levels of the cloud fall nearby.
(Graphics No. 2)
Smaller particles in the upper levels are carried
away to be spread worldwide.
The worldwide distribution of these radio-
active particles follows the same pattern as would occur with any other
injected
small particles/into the same regions of the atmosphere -- radioactivity has almost no effect on the pattern of distribution.
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Roughly, a nuclear detonation of one-half a million tons or less,
fired at a low altitude - but high enough so the fireball does not
intersect the ground - results in most of the fission products remain-
ing in the lower atmosphere (called the troposphere) .
unt
They are -
deposited on the earth's surface at such a rate that one-half of the
amount remaining in the atmosphere at any one time falls in 3-4 weeks
{called tropospheric residence half-time).
As the nuclear detonations
increase in energy yield more and more of the fission products are
swept higher and higher into the stratosphere - the zone above the
troposphere.
The residence half-time now becomes more like one-half
a year for injection into the lower stratosphere in the polar regions
and one year at the equator.
Radioactive debris from nuclear deto-
nations occurring at very high altitudes (about 30 miles and higher)
may have a residence half-time of five years or more.
(Graphics No.4)
Roughly two-thirds of the radioactive particulate debris injected
into the lower stratosphere at the north polar regions has been ob-
served to fall in the 30°-60° North latitude zone (where about 80 percent of the world's population live).
Injection at the equatorial regions
has been observed to result in a more even distribution between the
two hemispheres.
(Graphics 3)
.