It is believed that the maximum
height attainable by an atomic
cloud will be limited by the height
of the base of the stratosphere.
If the radioactive cloud should
pass through a temperature inversion layer, a layer at which the
How to Recognize Nuclear Blast
temperature begins to increase
again after it had been falling with
increasing altitude in the atmos-
There is a sound reason why the | great disorganization in the life of
a city.
officia] handbook on the effects of
atomic weapons, issued by the DeDepending on the height of the
partment of Defense
and
the
burst of the atomie bomb and on
Atomic Energy Commission as a
the nature of the terrain, high
guide in planning and executing
winds will occur in the immediate
effective civilian defense measures vicinity of the explosion. These,
against possible attacks by atomic
together with the air blast from
bombs, describes in detail the varithe shock wave, will cause various
ous spectacular phenomena accomamounts of dirt and other particles
panying an atomic explosion.
from the earth’s surface to be
Very few people alive have seen
sucked up.
an atomic explosion, and to know
At first the rising Bail of Fire
what it looks like is an essential
carries the particles upward, but
for the education of large masses
after a time they begin to fall un-
of people, so they would know how
to behave in an emergency with
calm and precision and, above all,
without panic.
The phenomena of an atomic eXplosion are so spectacular, and
they take place in such incredibly
short time, measured in split sec-
onds, that individuals surprised by
the awe-inspiring, dazzling spec-
tacle may lose precious seconds
that might mean the difference between life and death.
Knowledge in advance what the
phenomenaare, will serve to elimi-
nate the element of surprise. In an
effective
civilian defense,
mental
preparation is of equal importance
with
physical
means
of
defense.
The unprepared mind is the one
most likely to succumb to panic
and hysteria, and, when that happens all physical measures are
likely to become disorganized.
Distinction of Explosions
It also is necessary for the average person to learn to distinguish
between an atomic and an ordinary
explosion. To mistake an atomic
explosion for an ordinary one
would lead to the needless loss of
many lives.
On the other hand, the mistaken
identification of the explosion of
an ordinary TNT bomb, or an incendiary, aS an atomic explosion
might lead to needless panic on the
part of tens of thousands and to
der the influence of gravity at
various rates dependent on their
size. Consequently, an ascending
and expanding column of smokeis
observed to form. It consists of
water droplets, radioactive oxides
of the fission products, and more
or less debris, largely determined
by the height of the explosion.
The Mushroom Cloud
This is the spectacular mush-
room-shaped cloud which rose to
40,000
feet
at
Alamogordo
to 60,000 feet at Nagasaki.
and
At the beginning its rate of rise
is about 200 miles per hour, reaching 10,000 feet in 48 seconds. It
reaches 15,000 feet in 1.5 minutes,
when its rate of rise has dropped
to 50 miles per hour; goes to 20,000
feet in 2.6 minutes, a rate of rise
33 miles per hour; 25,000 feet in
4.6 minutes, rising at the rate of
20 miles per hour, and to 30,000
feet in 8.5 minutes when its rate
of rise has dropped to 12 miles per
hour.
The height to which an atomic
cloud will rise depends on the
thermal energy emitted by the
bomb, the temperature of the surrounding air, and the density of
the air. The greater the energy
liberated as heat, the larger will be
the buoyancy thrust on the rising
cloud, and hence the greater will
be the distance it ascends.
phere, it will tend to “mushroom”
to a small extent.
Because the air in the inversion
layer is fairly stagnant, some of
the particles in the cloud will tend
Sy -
no
hie
}
~
would be sucked into the cloud.
The importance of the “fall-out,”
the handbook points out, lies in
its radioactivity. Only in exceptional circumstances would the in-
tensity of the activity be great
enough to constitute a hazard upon
reaching the ground.
The evidence from the Hiro-
shima and Nagasaki explosions,
where the height of the burst was
about 2,000 feet, is that casualties
ascribable to the radioactive ‘‘fall-
out” were completely absent.
to spread out horizontally instead
of continuing to move vertically.
Hazard of Fall-Out
However, the handbook adds,
if the bomb burst occurred rela-
enormous heat energy of the hot
ation that would be uneconomical
usually pass through an inversion
structive effect, and considerable
amounts of dirt and other debris
were sucked into the radioactive
cloud, the fall-out would have to
be considered as a danger.
The fall-out, consisting mostly
Nevertheless,
as
a
result of
the
gas bubble, most of the cloud will
layer.
Upon attaining a region where
the density of the gas bubble is
the same as that of the surrounding air, or upon reaching the base
of
the stratosphere,
at
about
40,000 to 60,000 feet, where the
tively close to the ground, a situ-
from the standpoint of the
de-
of water drops, would also be im-
room-shaped cloud,
portant if the detonation took
place at a iow level above the
surface of the water; and the
presence of salt in the water would
enhance the hazard.
There was at one time considerable speculation about the possible effects on the weather of an
until it is dispersed by the winds
into the surrounding atmosphere.
water, some forecasting violent
weather reactions. Actually no
such effects have been observed.
The handbook declares that a
temperature of the atmosphere is
almost constant and there is practically no motion to convection,
the radioactive column will spread
out for a distance of several miles
and form the characteristic mushHaving reached the final stage
of its development, the cloud remains visible for an hour or more,
atomic burst, especially one over
When the radioactive, metallic
oxide particles in the cloud collide
with the particles of dirt, which
are in general considerably larger,
careful
they
adhere.
Consequently,
examination
of
all
the
available evidence would iead to
the conclusion that an atomic bomb
burst has a negligible effect on the
weather. It would appear that the
the
atom bomb coujid not be used as
a rainmaker,
So far, only one underwater
atomic burst, the Bikini “Baker”
test, has been reported. The burst
dirt particles in the cloud become
contaminated with radioactivity.
When the violence of the disturb-
ance from the bomb has subsided,
the contaminated dirt particles
gradually fall back to earth, giving rise to the phenomenon known
was made well below the surface
of
the
lagoon,
which
was
about
200 feet deep. From the results of
as the “fall-out.”
this test many of the effects of
a deep underwater burst can be
The extent and nature of the
“fall-out” will be detérmined by
the combination of circumstances
associated with the height of the
explosion, with the nature of the
surface beneath, and with the
meteorological conditions. If the
height of the bomb burst exceeds
a certain value, it is possible that
there would be no detectable fali-
inferred. Although there are certain characteristic effects, the details would vary with the depth
and area of the water and the distance below the surface at which
detonation occurred.
The Underwater Blast
In the underwater detonation a
Ball of Fire is formed as in an air
out, since no extraneous particles
15