a,
%
burst.
from
As the writer can testify
personal
observation,
J
and so it is greatest directly over
the
the explosion.
Consequently, water thrown up
water in the vicinity of the expio-
over the center rises more rapidly
sion on “Baker Day” was lighted
by a luminosity that could have
and for a longer time than water
farther away. As a result the sides
come only from the intense visible
spectrum of the Ball of Fire.
The general effect had the appearance of light seen through a
of spray dome become steeper as
the water rises.
Its upward mo-
tion is terminated by the effects
of gravity and the resistance of
by
be estimated exactly because the
upper part was surrounded by
soon as the bubble of hot gases
Phenomenon of Plume
The total time of rise and maximum height attained depend on
the energy of the explosion and on
its depth below the surface. For a
very deep burst the spray dome
may not be visible at all.
If the depth of the detonation of
the bomb jis not too great the
the air.
constituting
the
Ball
of
Fire
reached the surface, for then the
gases were eXpelled and cooled.
In the course of its rapid expan-
bubbie of hot gases will remain es-
sion the gas bubble, which now
contains steam and its dissociation
products,
atomic
hydrogen
sentially intact
oxygen, in addition to the fission
jet, carrying some water by
lateral entrainment, will be vented
to the atmosphere,
As the pressure of the bubble
is released water rushes into the
cavity, and the consequent complex phenomena cause the water
to be thrown up as a hollow cylin-
“slick,” is visible jn contrast to the
der, or chimney of spray, known
as the Plume. The radioactive con-
undisturbed water because the ripples or small waves are partially
tents of the gas bubble are vented
through this hollow Plume and
form a gigantic mushroom-shaped
cloud at the top.
calmed by the reflection of the
shock wave as a rarefaction (suction) wave at the surface of the
water.
The part of the shock that passes
into air through the water surface
The Plume and its mushroom
top are without doubt among the
most spectacular and awe-inspiring phenomena to be seen. It was
like watching the birth of a new
causes the compression of the
moist air. When this is followed
continent rising resplendent out of
the sea.
by a suction wave, the conditions
become favorable to the formation
a
spherical
cloud
of
to
point the gases, in the form of a
residue, initiates a shock wave.
The trace of this wave, as it
moves outward from the burst, is
evident, on a reasonably calm surface, aS a rapidly advancing ring,
apparently darker than the surrounding water.
This ring, sometimes called the
of
until it rises
the surface of the water. At this
and
vapor,
A
photograph
of
the
Plume,
taken with a super-speed camera,
knownas the cloud-chamber effect.
This manifested itself almost immediately after the Bikini under-
shows a smalf black smudge on its
right edge. It was the 33,000-ton
battleship Arkansas, lifted out of
the water, suspended vertically in
water burst in a dome-shaped cloud
that formed over the lagoon, This
great dome, set in the midst of the
ring from the shock, looked like
huge garland ringing the top of its
crown.
After the appearance of the ring,
hollow
Plume,
moving with the wind and lasting
for nearly an hour after the explosion, developed from this cloud
through
cloud. It was probably some 8,000
mass. In its early stages the rain
was augmented by the small water
mated that the maximum thick-
descending from the cloud.
feet, and the greatest diameter
was about 2,000 feet. It is now esti-
droplets, equivalent in a sense to
the fall-out of an air burst, still
ness of the walis of the Plume was
about 300 feet, and that about a
million tons of water rose in the
Plume.
Earlier estimates by scientists
on the scene, made soon after the
Were it not for the fact that
base surge is highly radioactive,
because of the presence of fission
products, it would represent merely a curious phenomenon. Because
All Debris Radioactive
burst, placed the quantity of water
of its radioactivity, however, which
raised in the Plume at ten to fifteen million tons.
The cloud, which concealed a
is augmented by that of the water
droplets in the fall-out, it may
represent a serious hazard for a
distance of several miles, especially
in the downwind direction.
There are reasons for believing
that the base surge can be pro-
large part of the upper portion of
the Plume, resembled a cauliflower,
rather than a mushroom, in shape.
It contained some of the fission
products and other bomb constituents, as wel] as water droplets.
In addition, there is evidence that
material
sucked
up
from_ the
bottom of the lagoon was also
present, for calcarous sediment,
which must have been part of the
fall-out, was found on the decks of
ships some distance from the burst.
duced only in fairly deep water.
In the event of a sufficiently deep
underwater atomic burst, the hot
gas bubble would lose its identity
in a mass of turbulent water before it reached the surface and
vented to the atmosphere. In this
case,
the
spray
dome would be
relatively
insignificant
and
no
Plume would be formed. Hence
there would be no formation of a
The Base Surge
As the column of water and
spray constituting the Plume fell
back into the lagoon, there developed, on the surface at the base
of the column, a gigantic wave of
mist about 1,000 feet in height,
completely surrounding the neck of
the Plume.
base-surge
and
no
appreciable
fall-out.
The disintegration of the gas
bubble into a large number of very
small bubbles, which are churned
up with the water, would produce
a radioactive foam or froth. When
this reached the surface, a small
amount of radioactive mist would
be emitted, but most of the activity would be retained in the sea
This wave began to form within
taken less than a millisecond later,
nut-shaped form. The wave or
wall of dense mist, much like the
spray of the base of Niagara Falls
or another waterfall of considerable height, represents the initiation of what is known as the base
surge. It is, in effect, a dense
cloud of liquid droplets which has
the property of flowing almost as
if it were a homogeneous fluid.
highly active foam on a near-by
shore might, however, represent a
hazard.
It seems possible, the handbook
traveled outward at high speed, it
course, be very radioactive,
A
second
photograph,
at Bikini, the conical spray dome
began to form at about four milliseconds (thousandths of a second)
after the explosion. Its initial rate
of rise Was some 2,500 feet per
second, but this was rapidly dimin-
ished by air resistance.
16
the
which the gases vented, could not
ten seconds of
traveled rapidly
shows no trace of the Arkansas.
Like a Cauliflower
In the shailow underwater burst
or slick, a mound or column of
broken water and spray, called the
spray dome, is thrown up directly
over the point of the burst by the
reflection of the biast wave at the
surface. The initial velocity of the
water is proportional to the pressure of the incident shock wave,
which eventually reached a thickness of some thousands of feet.
A moderate to heavy rainfall,
the air for a split second before
it plunged to the bottom of the
lagoon.
a gigantic white derby hat with a
minutes, assumed the appearance
of a mass of strato-cumulus cloud,
The maximum height attained
ground-glass screen, the distortion
from the waves on the surface of
the lagoon preventing any clear
view of the ball. The luminosity
remained for a few thousandths of
a second, but it disappeared as
gradually lifted from the surface of
the lagoon and, after about five
A few milliseconds later, the hot
gas bubble reached the surface of
the lagoon and the Plume began to
form, rapidly overtaking the spray
dome at a height of a few thousand feet.
detonation, and
outward, main-
taining an ever-expanding dough-
As
the
base
surge
at
water.
The
deposition
of
the
adds, that a base surge, made up
of small solid particles, rather
than droplets of water, but still
behaving like a fluid, might result
from an atomic bomb burst below
a soft terrain consisting of sand
Bikini
and
17
mud.
The
debris
would,
of