Have you designed an atomic bomb?

[f95toli]

A while back I talking with some friends about just how difficult it would be to design a nuke.

I was arguing that if we limit ourself to a 15-20 kT uranium bomb using a canon to shoot the two pieces of the core together (similar to the Hiroshima-bomb) it is a fairly simple design.

A plutonium bomb is much more complicated because of the implosion problem (but I guess that is much easier to solve today with the help of a computer), hydrogen bombs are even more complicated.

My point was that a group of regular engineers and physicist should be able to design a working atomic bomb using only public sources of information, my estimate was that it would take one year at most.

AS far as I understand (I took a course in subatomic physics a few years ago) there is no real "secret" to an uranium bomb (I think there even was a sketch in one of the books we used, in the chapter about applicatios) , the real problem is producong enough uranium.

Am I wrong? That is, is there some big "problem" with uranium bombs that I am unaware of.

 

[CTho9305]

I'm told it's very hard to come across/produce pure enough U235.

 

[f95toli]

True, and my point is that this is as far as I know the only "real" problem.
The phrase "capable of producing WMD" would then apply to every nation that manages to get their hands on some U235.

 

[cquark]

Originally posted by: f95toli
True, and my point is that this is as far as I know the only "real" problem.
The phrase "capable of producing WMD" would then apply to every nation that manages to get their hands on some U235.

You're right about U235 being the difficulty in producing atomic bombs. It also doesn't take much thought to make a layer cake hydrogen bomb of around 500 kT. The difficult one to build is the Teller-Ulam hydrogen bomb (around 10MT explosive power), but even that's based on science that's half a century old.

 

[thelordemperor]

When I was digging through some old magazines I found an issue of Sci-Fi digest and right on the front page it said:

"How to build a nuclear bomb"

Naturally interested I read it, it was very detailed and instructed exactly how to build a very low-yield weapon.

The author even detailed the process of refining uranium, and described in detail how hundreds of would-be bombers would die unpleasant deaths attempting to refine without the proper equipment.

 

[MtnMan]

I was trained by one of the branches of our militiary to work on nuclear weapon warheads. Getting the necessary stuff to build it and the guts to work with that stuff is the hard part.

 

[Shalmanese]

Originally posted by: thelordemperor
When I was digging through some old magazines I found an issue of Sci-Fi digest and right on the front page it said:

"How to build a nuclear bomb"

Naturally interested I read it, it was very detailed and instructed exactly how to build a very low-yield weapon.

The author even detailed the process of refining uranium, and described in detail how hundreds of would-be bombers would die unpleasant deaths attempting to refine without the proper equipment.

That might be an old New Scientist, I have the same article tucked away somewhere.

Another problem is that you will need a design that MUST work first time as you don't have the luxury of testing your beta version before going into mass production. This means you must neccesarily sacrifice some yield for relability.

 

[f95toli]

Mtmman: I thought most modern nukes were plutonium-based?
And as I wrote above, I am not thinking of an optimized 500 kT warhead, 15-20 kT is "enough" for most purposes.

And rembember that the uranium bomb had actually never been tested before Hiroshima. I guess Oppenheimer&Co were reasonably sure that the design was so simple that there was not much that could go wrong.

 

[Shalmanese]

They tested them at least twice in the Nevada desert before they dropped them on Hiroshima. Even then, it was massively under-yielding. I think i read somewhere that a modern design could yeild 50 times the megatonnage from the same amount of uranium

 

[f95toli]

Twice?
As far as I know the bomb at "Trinity" was a plutonium-bomb and that was the only test.
Of course there might have been a second bomb but I can't see why they would have kept that a secret.

 

[cquark]

Originally posted by: Shalmanese
They tested them at least twice in the Nevada desert before they dropped them on Hiroshima. Even then, it was massively under-yielding. I think i read somewhere that a modern design could yeild 50 times the megatonnage from the same amount of uranium

There was only one test before Hiroshima and it was of a plutonium-based bomb at the Trinity site in New Mexico. Little Boy was the uranium gun device dropped on Hiroshima, while Fat Man was the plutonium implosion device dropped on Nagasaki.

While both were small yield devices (10-20kT), I wouldn't call them underyielding, as modern fission devices with megaton fission yields obtain their increased yield through secondary fission via an intermediate fusion stage and no one had fusion capability in 1945.

 

[Peter]

Boy messing around with radioactives

 

[K1052]

The Trinity test actually surpassed nearly all the scientist?s expectations in terms of yield. Their estimations were way under.

Modern nuclear weapons are more efficient than the originals due to extensive testing and improved designs. Not to mention the various advances in explosives, electronics, and other areas that let weapons designers shrink the physical size of the device.

 

[Mark R]

I'm just wondering how powerful a 'bad' atomic bomb would be. My conclusion, so far, is that it would be powerful enough to be worrying.

The simplest scenario I can imagine is a gun-type, plutonium device, built from reactor-grade plutonium extracted from commercial MOX fuel. This is a far from optimal situation - poor isotope profile and slow core approach to criticality. However, anyone with knowledge of chemistry, explosives and metalworking skills would probably be able to build one.

While it wouldn't be a particularly impressive demonstration, it would probably knock the windows out for a few city blocks.

Uranium would be a much better material for such a bomb, but you need large quantities at very high enrichment. The equipment to enrich the uranium to that degree is probably beyond the reach of most members of this board, as indeed it is beyond the reach of many governments.

 

[f95toli]

I might be wrong but I don't think it is possible to build a "gun-typ" plutonium bomb, that only works with uranium. With plutonium the reaction would start before the "wedge-shaped" piece is complettely inserted into the core resulting in a smaller explosion, with U-235 this is less of a problem (I think).

But, again, I don't remember the details so I might be wrong.

The first uranium bomb used about 15 kg of U-235 surrounded by a shell of natural uranium.

 

[K1052]

Originally posted by: Mark R
I'm just wondering how powerful a 'bad' atomic bomb would be. My conclusion, so far, is that it would be powerful enough to be worrying.

The simplest scenario I can imagine is a gun-type, plutonium device, built from reactor-grade plutonium extracted from commercial MOX fuel. This is a far from optimal situation - poor isotope profile and slow core approach to criticality. However, anyone with knowledge of chemistry, explosives and metalworking skills would probably be able to build one.

While it wouldn't be a particularly impressive demonstration, it would probably knock the windows out for a few city blocks.

Uranium would be a much better material for such a bomb, but you need large quantities at very high enrichment. The equipment to enrich the uranium to that degree is probably beyond the reach of most members of this board, as indeed it is beyond the reach of many governments.

It would still be a real pain to extract the Plutonium back out of the MOX fuel and also rather dangerous without proper facilities. The Plutonium recoverd would be throwing off enough radiation to really screw with other weapon componets.

 

[dnuggett]

Originally posted by: f95toli
True, and my point is that this is as far as I know the only "real" problem.
The phrase "capable of producing WMD" would then apply to every nation that manages to get their hands on some U235.

Yes, and your point would be..?

 

[thelordemperor]

If you think about it, you don't really even need to cause a reaction to make an effective weapon with a radioactive substance. Just pack lots of uranium in with a whole bunch of conventional explosives and blow the thing up. Bits of uranium or uranium dust would be spread quite far.

Everybody who is exposed just dies of radiation poisoning or cancer. It's not like they're any less dead.

 

[f95toli]

dnugget: Just that I thinks most people (and many politicians) seem to believe that nukes are extremely complicated devices and that only a few countries have the technology and knowledge to build even a simple one.

K1052; AFAIK plutonium is not that dangerous, it is extremely toxic but as long as you don't inhale it eat it that is not a problem.

 

[Falloutboy]

all this talk is about building actual nuke, with a decent explosion. but how hard would it to be a dirty bomb (no big explosions but crap loads of radiation) I think this is proubly much easier

 

[K1052]

K1052; AFAIK plutonium is not that dangerous, it is extremely toxic but as long as you don't inhale it eat it that is not a problem.

The various separation processes and the machining of the Plutonium into the required shape are dangerous without proper safety equipment.

Also, the ?reactor-grade? Plutonium has a large quantity of undesirable isotopes that cause problems with spontaneous fission.

 

[Mark R]

An important point is that for an improvised nuclear weapon doesn't have to be good. If you could achieve explosive prompt criticality then you already have a weapon far more powerful than anything which could be built with similar effort.

While I don't pretend to understand the mathematics involved in developing such a device - there have been projects to examine the possibility of using reactor-grade material - their conclusions were that such a weapon would be unlikely to yield less than 1 kT. This is terrible performance compared to a properly designed and implemented weapon which could yield 20 kT.

However, such a yield neverthless makes a reactor-grade plutonium bomb a fearsome weapon.

 

[silverpig]

Just unleash the Spice Girls on whatever you want to destroy.

atomic power << girl powah!!!

 

[Matthias99]

Originally posted by: f95toli
K1052; AFAIK plutonium is not that dangerous, it is extremely toxic but as long as you don't inhale it eat it that is not a problem.

Uranium is not that dangerous, unless you ingest it or have tons of it lying around (at which point the radiation it emits starts to get to you).

Plutonium is *incredibly* toxic from what I've read if inhaled, and the danger of a dirty bomb is that it blows radioactive dust over a fairly large radius (several hundred yards, I would think, more for an airburst)... if it was built using plutonium, you'd likely kill everyone anywhere near it. Plus the area would be uninhabitable for weeks (if not months or years) -- it would be a horrible ecological disaster, and cleaning it up would be nearly impossible. Uranium decays relatively quickly, but plutonium sticks around essentially forever.

 

[cquark]

Common uranium isotopes have much longer half-lifes than common Plutonium isotopes. U-235 is 700 million years and U-238 is 4.5 billion years, whereas Pu-239 is 24000 years. This is to be expected, as Uranium can be found naturally on Earth, whereas Plutonium cannot, all of it having decayed away long before humanity existed.

There's a good online Plutonium Fact Sheet, which shows that it's dangerous but not nearly as bad as some peole make it out to be.