The influence of the wind structure at various altitudes on
the ground distribution of the nearby fallout is qualitatively represented in Figure 2.
The last sketch in Figure 2 illustrates the effects
of the "tshearing" action of the winds when they travel in different
directions and/or speeds at the various altitudes through which the
particles must fall.
Due to these wind conditions, it is possible to
obtain fallout patterns ranging from one looking like an ink blot around
ground zero at one extreme, to other situations where the fallout material is spread in a long thin finger.
In general, the pattern may be
expected to approximate an ellipse.
It is clear that such variables as wind conditions and the
yields of nuclear bombs and their positions of detonations above different types of surface make it impossible to predict fallout patterns
precisely.
In the case of nuclear weapons testing these variables are
either known or can be predicted with good accuracy.
However, in civil
defense planning, certain assumptions concerning these variables must
be used in estimating not only a single fallout pattern, but also
possible overlapping patterns in the event of multiple detonations.
RADIATIONS AND FALLOUT
In describing and evaluating the effects of fallout patterns,
it is necessary to consider the characteristics of the radiations
emitted from the radioactive material.
These are of three types:
rays, beta particles and alpha particles.
gamma
Gamma rays are the emissions
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