
The Visible Atomic Bomb - callum85
http://unmakingthebomb.com/visible-bomb/
======
CamperBob2
Coincidentally, I just came across a link someone posted on Reddit to an
annotated copy of the so-called "Farm Hall Transcripts."

I had heard of the ALSOS project before. As WWII was winding down in Europe,
the Allies attempted to interview as many German nuclear physicists as
possible in an effort to learn how far Germany had progressed in their own
bomb-making program. But I didn't realize they (we) had essentially captured
these scientists and isolated them from contact with the rest of the world,
and _bugged the building_ where they were held.

The resulting transcript was declassified in the early 1990s, and it is easily
the most fascinating document I've seen all year:
[http://books.google.com/books?id=pzNjntMMq-
oC&printsec=front...](http://books.google.com/books?id=pzNjntMMq-
oC&printsec=frontcover#v=onepage&q&f=false) You basically get to eavesdrop on
Heisenberg, Hahn, and other household names in the physics community as they
try to figure out why they're being held, wonder what's going to happen to
them, react incredulously to the news of the Hiroshima bombing, blame
themselves for it, try to puzzle out how it was done, and try to predict how
geopolitics will play out over the coming decades.

Do not click that link if you need to do anything else for the next six hours
or so.

~~~
tjradcliffe
There were enormous debates within the nuclear physics community for decades
regarding "the German bomb", which many wanted to exist because the
possibility of it existing was the justification for the Ally's bomb (bombing
Japan was something of an afterthought, albeit one that likely saved tens of
thousands of lives on both sides, not that anyone on the Allied side cared
about Japanese lives at that point in the war.)

There is a quite good play by English playwright and novelist Michael Frane
called "Copenhagen" about Heisenberg's visit to Copenhagen in 1941 to see
Bohr, that to my mind convincingly argues for the non-existence of any German
bomb program, or at least Heisenberg's complete innocence of it.

SPOILER ALERT: don't read the rest of this comment if you want to see the play
and be surprised by the revelation!

================== ================== ==================

I'll bury this in other words so hopefully it'll be difficult for anyone to
see if they don't want to, but the basic argument is drawn from the Farm Hall
transcripts and the reaction that the German physicists had to the bombings in
Japan, which was astonishment, followed fairly quickly by a calculation by
Heisenberg that the mass of the bomb might be as little as a thousand
kilograms or so. He quickly refined this calculation to something more
reasonable, like twenty kilograms, but if he had had any knowledge of or
interest in building a bomb he would have done the calculation long before,
because a first-order, back-of-the-envelope approximation to the chain
reaction based on known properties of uranium is exactly what any physicist
would do the very first day they set out to build a bomb. If Heisenberg had
been part of a programme to build a bomb he would not have already done that
and he wouldn't have needed to do it again. This argument is absolutely
compelling to any working physicist, because that is exactly what any of us
would do under those circumstances, so there is no doubt that if there was a
German bomb program that Heinsenberg was not part of it.

~~~
yeureka
This play was adapted to Portuguese and was played in Lisbon around 2002. I
was working at a company that did interactive installations and I was tasked
to write software that illustrated the characters physics discussions and
projected these on stage under control of the actors via cameras and machine
vision. It was one of the most fun projects I worked in.

------
tdicola
This is really cool, is there anything similar for hydrogen bombs? I've always
been curious how they are different from fission bombs (although obviously a
lot of their true workings are still classified).

~~~
VonGuard
IANANP (I an not a nuclear physicist) but I have read a great deal, and your
best bet is to read
[http://nuclearweaponarchive.org/](http://nuclearweaponarchive.org/) which is
chock full of interesting information, including a comprehensive list of every
nuclear detonation, ever. Go read there about how Hydrogen bombs work.

TLDR for that site; there are two major factors in play with an H-bomb. The
first is the addition of a fair amount of deuterium (Hydrogen with an extra
neutron) around the explosive core. This acts as a large source of potential
energy, and after the initial fission reaction is kicked off, the deuterium
ignites and fussion occurs, similar to that which happens on the sun: 2
Hydrogens become 1 Helium, and 2 neutrons go flying off.

The Fission reaction has to be managed differently, however, as there needs to
be a secondary reflector system in use. This secondary core reflector system
captures the X-rays after the initial fission begins. These x-rays are
reflected back into the core, causing the implosion to have a second stage.
This "second stage" ignites the third stage fuel, and boom. The documentation
will call it only 2 stages, though that x-ray reflection device is an
essential part of kickstarting fusion.

The first H-Bomb detonation was essentially a A-bomb surrounded by liquid
deuterium in a massive cooling system. The cooling system was actually the
size of a building.
[http://nuclearweaponarchive.org/Usa/Tests/Ivy.html](http://nuclearweaponarchive.org/Usa/Tests/Ivy.html)

Of interesting side note is the second H-bomb Castle Bravo:
[http://nuclearweaponarchive.org/Usa/Tests/Castle.html](http://nuclearweaponarchive.org/Usa/Tests/Castle.html)
) included a Lithium-deuteride solid fuel around the detonation device. The
detonation was accidentally the largest ever conducted by the United States.
It irradiated a huge swath of the Pacific ocean, and it's follow-up test had
similar results.

Devices which used Lithium-6 or enriched Lithium instead of Deuterium would
also be considered H-bombs, despite their not having Hydrogen. That's why we
call them thermonuclear.

This was because of the added Lithium in the solid fuel. You're basically
tripling the amount of neutrons available to the fusion reaction, and thus,
the detonation was completely out of hand and exceeded calculations by an
exponential factor.

~~~
vibrolax
Your description also leaves out the strictly optional, but common 3rd stage
of a thermonuclear device: the thick Uranium blanket surrounding the entire
assembly. Even "depleted" U-238 will undergo fast neutron fission, which the
deuterium / tritium fusion reaction produces in extreme abundance. In most TN
weapons, most of the explosive yield results from fission of the Uranium
blanket, not the fusion reaction. In a "neutron bomb", or "enhanced radiation
warhead", neutrons are the desired product rather than explosive yield, so
these typically omit the U casing.

Richard Rhodes' "Dark Sun: The Making of the Hydrogen Bomb" provides an
excellent description and paper bibliography.

------
lisper
This diagram only shows one type of weapon design, and in particular, the type
used in the Fat Man bomb. The Little Boy bomb had a different design:

[http://en.wikipedia.org/wiki/Gun-
type_fission_weapon](http://en.wikipedia.org/wiki/Gun-type_fission_weapon)

[EDIT: Originally had FM and LB reversed. Thanks to droopybuns for pointing
this out.]

~~~
droopybuns
You're inverted. Little boy is the gun bomb.

Another interesting anecdote is that Little Boy's design was a fall back. The
"Thin Man" was plutonium based and discovered to be unlikely to yield an
efficient explosion, so they changed to Uranium and made the gun bigger.

~~~
lisper
You're right. I fixed it. Thanks!

------
notastartup
so the explosives cause the jawbreaker like layers of radioactive materials to
compress creating nuclear fission that unleashes ton of energy?

So what stops so many other countries from creating such seemingly simple
device? Is it the trouble in acquiring the materials?

~~~
tjradcliffe
Nothing.

Remember: this was done the first time in less than four years, from 9 October
1941 to 16 July 1945, using technology from the stone age.

No solid-state electronics beyond crude diodes. No electronic computation.
Approximate estimates on most of the cross-sections. Hopeful guesses on many
of the processes (including multiply redundant approaches to some things,
including the basic design, because people weren't sure what would work or
what would be possible to build.)

Today, a team of reasonably intelligent engineering students with a budget of
a few billion dollars could build a bomb in a year, simply because they would
know vastly more than the original team.

Again: it took _three years_ and _$2 billion_ ($30 billion in today's dollars)
to build the very first bomb from scratch knowing almost nothing about the
process and having to custom build and design and _invent_ almost every
component.

To suggest that any particularly rare expertise today would be required or
that the cost would be more than a tenth of the original development is
implausible.

Remember this the next time you hear about Iran's nuclear program, which has
been going on for twenty years, supposedly in mad pursuit of nuclear weapons.
It's a ridiculous claim: if the Iranians wanted a Bomb very badly they would
have one by now. If they don't have one by now the only reasonable conclusion
is that they don't want one very badly.

The extreme disapprobation they get from the rest of the world on this issue
may well contribute to their tepid enthusiasm, but no amount of Stuxnet and
the like is going to put a dent in a strongly committed program. The Iranian's
commitment just isn't that strong.

Gas centrifuge technology in particular has been a game-changer in the
lowering the nuclear bar over the past couple of decades. People were warning
about it in the '80's, and their warnings seem to have had some prescience. It
makes practical enrichment of natural uranium to weapons grade, bypassing the
need for a reactor program to breed plutonium, and all the nasty, difficult
chemistry involved in plutonium extraction.

And unlike plutonium weapons, uranium weapons are ridiculously easy to
detonate. Trinity was a plutonium test. Little Boy was one of the very few
uranium weapons ever detonated, and it was live tested because the scientists
were as certain as anything it would actually explode.

There are uraninite (pitchblende) ores that are getting on for 10% uranium, or
0.07% 235U, so a tonne of ore would yield 7 kg of 235U. It'll only get worse
as seawater extraction gets better (it's already capable of producing
macroscopic amounts of uranium from the relatively uranium-rich Japan Current,
although post-Fukushima the primary research, which was Japanese, has likely
been curtailed.)

Processing a couple of tonnes of ore is sub-industrial. It isn't that hard to
hide. On the other hand, if countries want to go the plutonium route,
plutonium producing reactors aren't hard to hide either: the Russians were
running them underground--a few hundred metres below the surface--in the 80's
and 90's.

~~~
notastartup
Following your reasoning, it makes sense why North Korea was able to produce a
small amount of it in a relatively short time. They were well funded thanks to
the left-leaning South Korean administrations from 1998-2008 who practiced
Sunshine policy. The last bit is that they certainly want it bad enough but
have failed to produce a nuclear weapon with significant power (nothing in the
range of WW2 nuclear weapons). So if a country that wants it so bad like North
Korea have been able to produce a controlled nuclear explosion, why can't they
produce anything significant enough to be recognized as a nuclear state? The
only thing that would stop them seems to be either expertise or lack of key
material or perhaps lack of monies.

~~~
dfox
Producing some kind of nuclear explosion is mostly only about procuring the
raw materials. Getting to significant yield is the actual hard part as it
involves precision machining, measurements and timing.

Machining heavy metals is complex problem in itself even without requirement
of extreme precision. It is hard to procure machining equipment with
sufficient precision and tooling capable of machining hard metals without
raising lots of red flags.

Almost anything that is capable of switching of significant powers with small
or repeatable latency is essentially non-exportable with the reasoning that it
is not useful for much else than triggering nuclear weapons (one could think
of lots of other applications, but the devices are too bulky and expensive for
most of them).

------
gmarx
tres cool

------
ThompJackie
This is pretty cool.

------
sytelus
Here's the funny thing: If you had 6kg of U-235 and through it forcefully on
the ground it would most likely explode. This almost happened at Las Alamos.
All the machinery in nuclear fission bomb essentially just to protect
unintentional explosion and make sure explosion is symmetrical and as vigorous
as possible when triggered. The triggering mechanism is essentially firing
usual explosives around the sphere of fission material.

~~~
lisper
> If you had 6kg of U-235 and through it forcefully on the ground it would
> most likely explode.

First, you mean "threw", not "through." And second, this is absolutely not
true. To achieve an explosion you have to induce super-criticality with very
precise timing. Otherwise the uranium will melt and become sub-critical before
it explodes.

> This almost happened at Las Alamos

No, it didn't. You are almost certainly thinking of these incidents:

[http://en.wikipedia.org/wiki/Demon_core](http://en.wikipedia.org/wiki/Demon_core)

but those were completely different. It was a plutonium core, not uranium, and
it went critical not because it was thrown forcefully to the floor, but
because it was inadvertently enclosed in a neutron reflector that caused it to
become critical.

~~~
abruzzi
>To achieve an explosion you have to induce super-criticality with very
precise timing. Otherwise the uranium will melt and become sub-critical before
it explodes.

True, but the complexity of the Fat Man plutonium bomb (shown in the link
here) belies the simplicity of Little Boy uranium bomb.

