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On August 8th 1945,
the world woke to the startling news that
two days earlier, much of the Japanese city
of Hiroshima had been destroyed by a single
bomb dropped from a US aircraft. A few days
later came the news that the city of Nagasaki
had suffered a similar fate. Shortly after,
the Japanese surrendered.
60
YEARS
of the
ATOMIC
BOMB
8 Silicon
ilicon Chip
hip
by Keith Walters
siliconchip.com.au
M
uch has been written about
the first atomic bomb to be
used in warfare – and it is
interesting to compare the newspaper
reports of the time with more recent
historical descriptions of the same
event.
Recent accounts reports tend to
dwell on the terrible death toll . But
that wasn’t really what the citizens of
the time were so shocked about.
After all, at that point in the war
there were almost nightly raids on
Japanese cities by huge fleets of B29
bombers, which inflicted similar
amounts of damage with similar casualty figures. The after-effects of radiation and fallout are often mentioned
these days but these weren’t really
understood at the time.
An awful realization
No, the real shock was that here at
last was an explanation for one of the
greatest puzzles of WWII: What was
the purpose of the V2 rocket?
Toward the end of WWII the Nazis
launched approximately 5,000 V2
rockets, mostly aimed at Antwerp and
London. At first sight, the V2 sounds
like a formidable weapon: carrying a
one-tonne payload, it could climb to
a height of about 100km and then fall
back to Earth at supersonic speed,
seemingly appearing out of nowhere
before destroying one or at most, two
buildings.
As a military weapon, the V2 was
ludicrously inefficient. They cost more
to build than a conventional bomber,
which could deliver much more explosive punch, far more accurately, and
with a more than half-decent chance of
coming back for another load! Terrifying though the V2 may have sounded,
the vast majority of them simply failed
to hit anything important.
But after August 6th 1945, the whole
world realised what the US and British
military had known for some years:
theV2 was merely one part of a radical
new weapons system, the other part
being the atomic bomb.
Armed with a nuclear warhead, the
V2’s targeting accuracy would cease
to be an issue! Heinrich Himmler (in
charge of Hitler’s dreaded SS) had
actually made occasional references
to such so-called “miracle weapons”
which could “destroy London or New
York with a single stroke.”
Fortunately, as it turned out, building a workable nuclear weapon, particularly one that a V2 could carry,
was far beyond the capabilities of the
Nazi Military Industrial complex. But
nobody had any way of knowing that
at the start of the war.
Manhattan Project
As it was, the amount of industrial
and scientific muscle that was applied
in the USA to the top-secret “Manhattan Project” is simply unbelievable.
Over half a million people worked on
the project at one time or another, the
vast majority having absolutely no idea
what they were working on!
The true cost will probably never be
known, as several large corporations
donated large amounts of time and
resources at cost or for free, and the
thousands of engineers and scientists
were rarely paid overtime. An oftenquoted guesstimate is about $US30
billion (about $A42 billion) in today’s
currency.
Another little-appreciated fact is
that the two bombs that were dropped
used two completely different technologies. The Hiroshima device used
relatively simple “gun-type” bomb
construction but required a staggering amount of equipment and time to
produce the highly enriched uranium
it needed.
This photograph of the damage to Hiroshima is
also historically significant because it is signed by
Col. Paul Tibbets, Pilot of the “Enola Gay” which
dropped the first Atomic Bomb on Japan on August
6th, 1945.
siliconchip.com.au
August 2005 9
The Nagasaki device used plutonium, which costs far less to manufacture but the sophistication of the
necessary implosion detonator device
is, even to this day, far beyond the
technological capabilities of most
countries.
Virtually all of this happened within
a space of about three years, with most
of the critical work done in the final
12 months!
Why?
Much has been written over the last
60 years about the actual reasons the
atomic bombs were used on Japan, a
large part of it being speculation presented as fact.
One fact often overlooked is that the
people making those decisions were
all born in the much tougher world
of the 19th century. They had already
lived through one world war and the
worst economic recession in recorded
history.
The world was a very different place
then. At the time, most Americans
knew virtually nothing about Japan
or its people, apart from the single
fact that the Japanese air force had
launched an unprovoked attack on
Pearl Harbour.
The Allied Powers were also coming
to terms with a massive humanitarian
crisis in Europe, most of it the result
of a drawn-out and futile war that the
recently defeated Axis powers had
effectively lost years before.
So one of the factors would have
been the growing realization that without an order of unconditional surrender
from the Japanese Top Brass, there
seemed little possibility of any quick
end to hostilities in the Pacific.
There was already a massive aerial
bombing campaign under way that
was expected to have destroyed all
of Japan’s military manufacturing capability by early 1946, carried out by
huge fleets of B-29 bombers.
Although there was little question
that the Japanese military would soon
cease to be a major threat, there was
no telling how it long it would be
before the Pacific would again be safe
for shipping.
The Japanese soldiers’ (or probably more correctly, their officers’)
“fight-to-the death” Bushido code was
already resulting in unacceptably high
Allied casualties just trying to secure
some small Pacific islands; the death
toll from an invasion of the Japanese
10 Silicon Chip
mainland would be immeasurably higher.
Hiroshima:
August 6 1945
The only thing that
seemed likely to change
the situation was direct
intervention by the Emperor, and the only thing
that might prod him
into such an unheard-of
breach of protocol would
be a massive display of
overwhelming force.
Originally a “demonstration” explosion in
Tokyo harbour had been
proposed but perhaps
surprisingly this was rejected on the basis that it The blast from a nuclear bomb normally extends far
probably would not look beyond the fire zone. But Hiroshima suffered from a
all that impressive. It huge number of fires fed by gas leaks, exacerbated
by the light construction of the majority of buildings.
might sink a few boats and
cause a mini-tidal wave,
but overall the damage inflicted would plicity of the design, and the shortage
probably be relatively slight.
of further U235 supplies, they decided
A list of potential military targets that testing of the Little Boy design
was drawn up, the list gradually dwin- might be an unnecessary luxury.
dling as city after city was destroyed
The final “combat ready” Little
by conventional bombing raids!
Boy assembly was 3.2 metres long,
By August 1945 there were only two 71cm in diameter and weighed about
working atomic bombs actually avail- 4 tonnes, most of this being made
able, one of each type, and although up by the steel tamper backplate. By
there was some talk of reshaping mid-July the major bomb components
Little Boy’s U235 core to make four had been shipped out to Tinian Island
more implosion bombs, the War Office in several sections on the USS Indievidently decided it didn’t want any anapolis, under intense secrecy. The
further delays. Due to the relative sim- uranium-containing sections were
A few moments ago, there
was a city under there.
About 30 seconds after the
explosion (8.15.15am local
time on August 6, 1945),
the Enola Gay circled
Hiroshima at 30,000 feet –
and the mushroom cloud
was already above them.
The city itself was already
completely obscured by
the thick black smoke
seen at the bottom of the
picture.
siliconchip.com.au
photographs was simply due to conventional fires caused by burning gas
jets when large numbers of wooden
factory buildings collapsed. More
substantial brick and stone structures
even directly under the blast were still
left standing, although no one inside
them would have survived.
Actually the initial death toll wasn’t
all that different from what had already been experienced in dozens
of conventional bombing missions,
although admittedly those didn’t
have the added later complication of
radiation exposure. Visitors to both
sites reported that weeds and grass
had started to sprout again within a
few days, so the effect was more like
that of a savage forest fire.
Nagasaki: August 9 1945
Backup-plane view of the mushroom cloud over Nagasaki, August 9, 1945,
Nagasaki was in fact the backup target, the primary target of Kokura being
obscured by clouds. So too was Nagasaki – but it “earned” its place in history.
flown out separately on three C-54
transport planes.
The projected date of the first bombing mission was August 1 1945, with
a second mission ten days later on
August 11. However, bad weather
delayed the first mission until August
6. Although their primitive on-board
radar systems could establish the general location of a city, if there was substantial cloud cover, there was simply
no way of finding your actual target!
The B-29 “super fortress” finally
selected was piloted by 30-year-old
Colonel Paul Tibbets and christened
“Enola Gay” after his mother. Tibbets is still alive incidentally; you
can read a recent interview with
him at www.guardian.co.uk/g2/
story/0,3605,769634,00.html
You can also visit his website www.
theenolagay.com
The co-pilot was Captain Robert
Lewis, and the weapons specialist
supervising the bombing was US Navy
Captain William “Deke” Parsons.
The 12-man crew also included an
assistant weaponeer, a bombardier, a
navigator, two radar specialists, two
flight engineers, a radio operator and
a tail gunner.
The bomb was assembled on Tinian
Island and checked out on August 5th
ready for a 2:45 AM takeoff the next
day. It was supposed to be left in fullyoperational form but Parsons removed
siliconchip.com.au
the explosive charge from the gun for
re-fitting immediately after takeoff, in
case of a crash.
The mission went off without a
hitch, unlike the trouble-plagued
Nagasaki mission a few days later. At
7:30AM Hiroshima was in plain sight
and so the bomb’s electronic systems
were activated. (Because of the enormous power drain of the valve-based
electronics, the bomb could not be
armed for much more than two hours
before its intended use).
At about 8AM local time the “aim
point”, the Aioi Bridge, was lined up
by Parsons. About 15 minutes later,
Little Boy was released and when
the Enola Gay was safely clear, a
1.3GHz arming signal was transmitted, switching on the bomb’s main
control electronics. When the bomb
fell below 7,000 feet, the onboard radar
altimeters were enabled by the barometric safety switch and when they
detected a height of 1,900 feet above
ground, the cordite explosive charge
was detonated. The U235 “bullet” then
slammed into the tamper/target in
less than six milliseconds, producing
the nuclear explosion only about 150
metres short of the aim point.
Most accounts of the event report
that the city was completely destroyed by the initial explosion but
this is something of an exaggeration.
Most of the devastation seen on later
The actual Fat Man bomb assembly
was fitted into a relatively conventional bomb casing with the necessary
remote control electronics and its batteries. The whole assembly was 3.25
metres long, 1.5 metres in diameter
and weighed about 4.5 tonnes, more
than half of this being the TNT explosive lens system. The B-29 selected
for the mission was had already been
named “Bocks Car” after Frederick C.
Bock, the man who usually piloted it.
It was piloted for the Nagasaki mission
by Major Charles Sweeney. The intended target was the massive arsenal
complex at the city of Kokura, where
the bulk of Japan’s weapons R&D and
manufacture was carried out.
Things started to go wrong right from
the start. (Ironically, the only thing that
worked flawlessly was the bomb itself,
despite the necessity of skipping many
of its final checkout procedures due to
the revised timetable)!
Soon after takeoff they discovered
that the fuel pump attached to the
auxiliary tank was not working, and
although this did not necessarily mean
they had to abandon the mission, it severely limited the amount of time they
could spend searching for their target.
When they reached Kokura, the city was
hidden in clouds so thick that they lost
sight of the other two escort/decoy B29s.
After three fruitless passes over Kokura,
Sweeney decided to try for Nagasaki, the
only other target in range.
There was only enough fuel available for a single pass over Nagasaki,
and since they would have to jettison
Continued on P14
August 2005 11
ANATOMY
OF THE
ATOMIC
BOMBS
The basic theory of an atomic fission
bomb is well known to most scientifically
literate people these days, and was certainly understood by nuclear physicists
by the late 1930s.
Essentially, if a sizeable quantity of
a suitably radioactive material could be
suddenly crushed together into a small
volume, the probability of any particular
neutron colliding with another nucleus
and releasing two or more further neutrons would be greatly increased.
With a suitable “fissile” material the
classic runaway chain reaction would
take place resulting in almost instantaneous splitting of a large proportion
of the nuclei and an enormous burst of
heat and radiation.
“Little Boy”
At first, the only material that seemed
workable for a bomb was the scarce uranium isotope U235, which has a nucleus
consisting of 92 protons and 143 neutrons. Calculations showed it would need
to be refined (that is separated from the
other uranium isotopes) to at least 90%
purity, otherwise the more radioactive
U238 atoms would cause the critical
mass to “jump the gun”, destroying the
bomb after only a very small percentage
of atoms had fissioned.
It was quickly realised that the greater
the amount of compression that could be
applied to the fissile mass, the smaller
the minimum amount that would be
required to produce a true nuclear
explosion.
However the amount of compression that could be practically applied
was heavily dependent on the physical
properties of the strongest available
materials at the time.
The only workable approach envisioned in the early 1940s was a “gun”
design where the fissile material is
made in two separate pieces which are
12 Silicon Chip
slammed together by an explosive charge.
The limitations of tungsten carbide, the
strongest workable material at the time,
meant that a practical weapon would also
need about 65kg of the 90% pure U235 –
there was simply no conceivable method
of applying sufficient compression to any
smaller amount.
As it turned out, only one such “gun
type” uranium weapon was ever built,
codenamed “Little Boy”, the design becoming obsolete before the weapon was
ever tested.
Bomb mechanism
The actual bomb mechanism was made
from a modified anti-aircraft gun. The 65kg
fissile mass was made into two distinct
sections: a 100mm diameter “plug” that
would be fired down the barrel of the gun
and a series of 100mm diameter rings
(constructed like ferrite speaker magnets)
that the plug would “collect” on the way. The
75mm barrel was machined out to 100mm
and a conventional explosive charge would
fire the U235 plug toward the “tamper”.
The tamper consisted of a tungsten
carbide plate mounted in a 2.5 tonne steel
block. This steel block and the gun barrel
had matching threads cut into them so
they could simply be screwed together.
When the explosive charge was fired the
U235 plug and the collected uranium rings
would smash into the tamper, producing a
modestly compressed critical mass of uranium vapour, hopefully compact enough to
start a runaway chain reaction.
The “production” bomb’s control mechanism was amazingly sophisticated for
something built 60 years ago. The bomb
received its final arming signal (after it
had been released from the aircraft),
via a then state-of-the-art 1.3GHz radio
control system. The bomb also contained
a newly developed radar altimeter and a
“fail-safe” atmospheric pressure switch,
which prevented the bomb from detonating
above 7,000 feet.
Only one operational bomb of this type
was ever produced, since by the time it
was ready for combat use, the much more
technically demanding but inherently more
efficient plutonium implosion system had
been successfully tested. Five complete
“Little Boy” bomb mechanisms were actually built by August 1945 but there was only
enough U235 for one of them.
As far as operational safety was concerned, Little Boy was a ludicrously unsafe
weapon! Anything that could have accidentally ignited the cordite charge (a plane
crash or similar vehicle accident) could
have set off a full-yield nuclear explosion.
Although it was always transported with the
explosive charge removed, it was only later
realised that the design had no provision
for waterproofing. Any water entering the
device (in a shipwreck for example) could
have acted as a crude moderator for the
highly enriched uranium.
While this could not produce a true nuclear explosion, it still would cause massive
damage to the surrounding area as well as
delivering a lethal dose of gamma rays and
Here’s something you
can never see again,
because it disappeared
in less than the blink
of an eye. This is a
photo of the actual
“Little Boy” atomic
bomb, ready for
loading aboard the
Enola Gay on Tinian
Island, August 5, 1945.
An interesting aside
– one which would
undoubtedly have
changed history:
would you believe that
just four days after
unloading its topsecret cargo on Tinian,
the US aircraft carrier
“Indianapolis” was
sunk by a Japanese
submarine?
siliconchip.com.au
neutrons to any crew members nearby.
Created under the pressure of wartime
emergency, the Little Boy bomb was a
very inefficient design, in that less than
2% of the 65kg of U235 actually underwent
useful fission. The superior compression
system used on Fat Man allowed a similar
explosive yield (18 - 21kt) using only about
6kg of plutonium.
Another piece
of history: “Fat
Man” being
transported to
the B29 bomber
“Bocks Car”
for its oneway journey to
Nagasaki, August
9, 1945
“Fat man”
So the uranium bomb that was dropped
on Hiroshima (Little Boy) was really
something of an “orphan”. It was originally
undertaken as the atomic fission device
“most likely to work”, on the basis of what
was known in the early 1940s.
To the best of anyone’s knowledge at
the time, the only material in existence that
was suitable for building a fission bomb
was uranium 235. However, as the initial
research got underway, it was realized that
a then-theoretical element with 94 protons
and 145 neutrons might also be suitable.
This was verified after a minute sample
of the element was eventually created
by bombarding U238 with a high-speed
neutron beam from an early model cyclotron. Ultimately, this element was named
“plutonium”.
But while the scientists soon realized
that it might still be possible to base a bomb
design on plutonium, it would require the
development of a vastly more sophisticated
explosive trigger mechanism.
No tamper made from any known substance would be anywhere near strong
enough to withstand the force of the collision that would be necessary to initiate
successful plutonium fission. The only
solution was to shape the plutonium into
a hollow sphere and completely surround
it with a spherical layer of high explosive.
To produce a precisely spherical shock
wave, thousands of experiments were carried out with “explosive lenses” made from
fast and slow-burning TNT mixtures.
The individual explosions had to be
synchronised to within nanoseconds, and
so conventional hot wire electrical fuses
could not be used. Instead, special “exploding wire” detonators were developed.
These were combined with sophisticated
spark-gap triggers driven from a newly
developed portable regulated 8,000V DC
power supply made by Raytheon. The
spark gaps were all fed from a network
of precision RC networks with exactly the
same time-constant. 32 large high voltage
capacitors were needed, and the capacitor/spark gap assembly alone weighed
siliconchip.com.au
over 200 kilograms!
Apart from all this, the scientists and
engineers had only a few months to learn
the entire metallurgy of the brand-new element, plutonium. Initially they had problems
with the plutonium sphere halves warping
after casting and machining, until they
discovered that an alloy of 3% gallium and
97% plutonium was dimensionally stable.
Although, like uranium, plutonium 239
is only weakly radioactive in the “unmoderated” state, chemically it is an extremely
toxic substance and spontaneously bursts
into flame when exposed to air. All the
machining had to be carried out in an
atmosphere of nickel carbonyl gas, which
plated any newly exposed surfaces with a
protective layer of nickel.
The final wartime implosion-type bomb
used about 2.5 tons of TNT-based shaped
charges precision-fitted around a series of
nested shells of various materials. (See
diagram). The entire assembly was housed
in a spherical aluminium alloy shell about
100mm thick and 1,500 mm diameter.
There were 32 separate explosive lens
assemblies, 20 hexagonal and 12 pentagonal, in the same pattern as a soccer ball.
Each assembly consisted of two precision
castings of fast-burning and one casting of
slow-burning explosive. The slow-burning
segment fitted into a conical cavity in the
larger of the fast-burning pieces, and a
further piece of fast-burning explosive was
fitted under this.
The actual plutonium “pit” was machined
into two precision hemispheres that formed
a hollow sphere 90mm in diameter (about
the size of a cricket ball). The 20mm polonium/beryllium neutron initiator fitted
precisely inside the hollow centre.
Surrounding the pit was a 70mm thick
“tamper/reflector” made from natural
uranium. Its purpose was mostly to keep
the pit from rebounding before the full fis-
sion reaction could be completed, but
it also served as a neutron reflector to
enhance the chain reaction. Also a small
part of the “yield” of the bomb (about
20%) would come from fast fission of
the tamper.
Surrounding the tamper was a
115mm “Pusher/Neutron absorber” shell
made from a boron/aluminium alloy.
This was actually part of the mechanism
that “tuned” the implosive shock wave,
although what the neutron absorption
function of the boron actually accomplishes has never been made entirely
clear. The shock waves would move
more slowly through the lightweight
aluminium than they would through the
uranium, and the timing was such that
any reflected energy would be returned
to the core just as the actual chain reaction began, something after the fashion
of a Yagi antenna.
For safety, a 20mm hole was cut
through the plutonium pit and the pusher
and tamper shells to allow the neutron
initiator to be fitted just prior to combat
use. For transport, a dummy sphere of
cadmium removed any possibility of a
chain reaction. Removable precisionmachined aluminium and uranium plugs
allowed this to be withdrawn and the
initiator fitted in its place.
Each of the 32 exploding-wire detonators was connected to an SO239
“UHF” socket, the same type that is
still found today on AM CB radios. (In
those days, “UHF” meant pretty much
anything above about 50MHz!) Since the
detonators had to be fired within +/-10
nanoseconds of each other, 32 precisely
matched lengths of coaxial cable were
required. (Ironically, the necessary polythene dielectric co-ax was yet another
technology that just “happened along”
at the right time!)
August 2005 13
Perhaps more by (bad?) luck than management, the Mitsubishi arms
plant in Nagasaki became ground zero. Here’s what was left of it.
the bomb anyway if they were going to
make it back, the bombardier decided
that if necessary they would attempt
to aim the bomb using the onboard
radar system. Nagasaki turned out
to be covered in even thicker clouds
than Kokura but just as they were
about to release the bomb for a “pot
luck” strike, a small opening appeared
above a large industrial complex that
turned out to be the Mitsubishi arms
manufacturing plant.
Although the bomb itself was of a
completely different design from Little
Boy, the arming sequence was exactly
the same. The bomb was released, and
when the plane was far enough away,
the 1.3GHz arming signal was transmitted, activating the firing electronics. At about 7,000 feet, the barometric
safety switch kicked in, allowing the
radar altimeter/trigger to function.
At 1,650 feet, the radar altimeter
closed a contactor inside the 8,000V
power supply, feeding this voltage to
the RC spark gap array. A couple of
milliseconds later, all 32 spark gaps
arced over within 10 nanoseconds of
each other, sending 32 identical high
voltage pulses to the array of exploding
wire fuses. An instant later 32 identical convex flame fronts were shaped
and merged into a single spherical
imploding shock wave. The various
metal layers were vaporised as the
wave travelled through them, the
surface area of the spherical shock
wave decreasing by a factor of about 16
times, thus increasing the pressure by
a similar amount. The plutonium pit
14 Silicon Chip
Nagasaki suffered less damage than Hiroshima, due
largely to the city’s topography.
was compressed by a factor of about
2.5 times, a remarkable figure for a
virtually solid ball of metal!
When the shock wave reached the
centre, the neutron initiator assembly
was instantly converted to a series of
high pressure jets of beryllium/polonium vapour which mixed with the
vaporised plutonium to “kick-start”
the chain reaction.
Once the chain reaction was under
way a massive burst of high-speed
neutrons struck the surrounding cloud
of uranium vapour, fissioning some of
the U238 atoms and adding about 20%
to the explosive yield.
The yield of the explosion was
estimated at about 21,000 tonnes,
completely destroying the largely corrugated iron structures of Mitsubishi
plant, with an initial death toll estimated at about 70,000. As was the case
with Hiroshima, the death toll would
have been a lot lower if people had
retreated to the simple but effective
bomb shelters dug into the hillsides.
Because of the small number of aircraft
involved, they probably assumed it
was a reconnaissance mission.
It may seem incredible now, to think
that it took the Japanese over a week
to surrender after the massive devastation of the initial Hiroshima blast, but
the sad fact was that communications
were so poor at the time that most of
the populace (military included) simply had no idea that the attacks had
taken place! All that they knew at the
nearby army bases was that all communication (radio, telephone or tele-
graph) from the bombed cities abruptly
ceased, all at the same moment. Petrol
was only available for military use, and
civilian transport between cities was
virtually non-existent.
There are numerous accounts from
Japanese Air Force pilots who were
sent to investigate and who simply
had no idea what had happened, since
there was no sign of the cratering seen
on conventional bombardments.
The immediate post-war period
When the war ended on August 15
1945 obviously there was an abrupt
change of priorities. Now that the
plants were up and running, operating
costs fell dramatically and so production of weapons-grade uranium and
plutonium continued, but few actual
working bombs were constructed. By
October 1945 there were 60 Fat Man
assemblies (without plutonium pits)
available but by July 1946 there were
still only seven fully operational Fat
Man type weapons in the US arsenal.
Presumably the US government had
more pressing things to spend its money on at the time and so the nuclear
weapons program was put on the back
burner. However in 1949 the detection
of traces of radioactive fallout drifting
across from Siberia indicated that the
Soviet Union had successfully tested a
nuclear weapon of its own. As it turned
out, this was basically a direct copy of
Fat Man, constructed using information supplied by spies operating inside
Los Alamos. From that point the Arms
Race began in earnest.
SC
siliconchip.com.au
10 SECONDS IN THE LIFE OF AN ATOMIC BOMB
This amazing series of photographs is of the world’s first atomic bomb blast – at Alamagordo, New Mexico, USA on July 16, 1945.
(Photos in this feature courtesy atomicarchive.com)
6: The mushroom cloud
starts to form – two seconds
after detonation.
1: The early fireball, taken
just sixteen milliseconds after
detonation.
7: And grows –
three seconds after
detonation.
2: Another nine milliseconds
later, (at 0.025s) not much
appears to have changed.
8: Again at four seconds
after detonation.
3: Here’s the fireball
at 53 milliseconds.
9: The head starts to take on
the familiar mushroom form –
seven seconds after detonation.
4: And at 62
milliseconds it’s
growing . . .
10: The mushroom head
fully formed ten seconds
after detonation.
5: Less than one
tenth of a second
after
detonation.
5: And
again at 90
milliseconds.
siliconchip.com.au
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August
ugust 2005 15
2005 15
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