PART E -- NATURE OF INDUCED RADIATION
Neutrons are produced in all nuclear weapon detonations.
Some of these
neutrons may be captured by the various elements in the soil under the
burst.
As a result of neutron capture, some of these elements become
radioactive, generally emitting beta particles and gamma radiation for an
extended period following an explosion.
Beta particles are a negligible
hazard unless the radioactive material makes direct contact with the skin
for an extended period of time. In this case, the beta particles can cause
skin irritations varying from reddening to open sores. In contrast, gamma
radiation readily penetrates the body and can cause radiation injury and
even death. Consequently, the external military hazard of induced radiation
is determined substantially through an analysis of dose rate of the emitted
gamma radiation.
1.
Characteristics of Induced Radiation.
The principal characteristics of induced radiation are localized symmetrical
pattern, difficult to decontaminate, and persistent.
a. Localized Symmetrical Pattern.
The pattern of induced radiation is circular around ground zero. The dose
rates within the pattern are highest at ground zero and decrease with
distance from ground zero.
The pattern is much smaller than the fallout
pattern would be if the same weapon were burst on the surface.
Weather
conditions have no influence on the location and size of the pattern or the
dose rate of induced radiation, and there is no shifting of the pattern by
surface winds.
The pattern, if produced, will always be located around
ground zero.
b. Difficult to Decontaminate.
Since the soil in the target area is made radioactive to a depth of about
0.5 meter, decontamination is difficult, requiring the removal of the top 10
centimeters of soil where most of the radiation exists.
In contrast,
fallout is a deposit of radioactive dust on the surface and can be removed
with somewhat more ease than induced radiation. Both types can be covered
by earth.
c. Persistent.
The decay characteristics of induced radiation are considerably different
from those of fallout. Fallout is a mixture of many different substances,
all with different rates of decay. Induced radiation is produced primarily
in aluminum, manganese, and sodium.
Other elements either emit so little
gamma radiation or decay so fast that they are less important. During the
first one
CM5206
5-22
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