l hour after the burst would be expected to be 0.1 R/hr after ff hours and
0.01 R/hr after 49 hours.
This rule seems to be valid for abdut 6 months
following an explosion, after which the obServed decay is som
than that predicted by this relationship.
The activation pro
general, decay at a faster rate than the fission products.
Fission products and the activation products, along with
uranium or plutonium from the device, are the components of t
fissioned
radioactive
material in the fallout cloud, and this cloud is the primary
tential exposure to residual radiation.
In a nuclear airburst in which the central core of
intens
terial, or fireball, does not touch the surface, the bomb res
ing the fission products, the activation products resulting f
interaction with device materials, and unfissioned uranium an
nium)
are vaporized.
These vapors condense as the fireball r
cools, and the particles formed by the condensation are small
like.
They are carried up with the cloud to the altitude at
rise stops, usually called the cloud stabilization altitude.
of this material then depends on the winds and weather.
If tlle burst size
is small, the cloud stabilization altitude will be in the lowdr atmosphere
and the material will act like dust and return to the Earth's|surface in a
matter of weeks.
Essentially all debris from bursts with yie
lent to kilotons of TNT will be down within 2 months (Referen
areas in which this fallout material will be deposited will agfpear on maps
as bands following the wind's direction.
Larger bursts (yields equivalent
to megatons of TNT) will have cloud stabilization altitudes ig’
the strato-
sphere (above about 10 miles [16 km] in the tropics); the radgoactive material from such altitudes will not return to Earth for many
its distribution will be much wider.
@onths and
Thus, airbursts contribgte little
potential for radiation exposure to personnel at the testing grea, although
there may be some residual and short-lived radiation coming fom activated
surface materials under the burst if the burst altitude is sufficiently low
for neutrons
to reach the surface.
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