How easy is it to build a nuclear bomb?

[Dancing David]

As long as one is able to finish the bomb and blow it up I'd guess the amount of radiation poisoning one is affected by is unimportant. How dangerous is to be around the fissionable material before the explosion?

Well if you don't get them sub critical you can take some exposure before you get real sick.

like this?

Yup or this one:
http://www.world-nuclear.org/info/inf37.html

 

[Skwinty]

Hmm. What is the correct shape? How much of fissile material is needed?

look at this link for more detail regarding shapes and types etc.

http://en.wikipedia.org/wiki/Nuclear_weapon_design

 

[catsmate]

Ah yes. Where do states like NK get their material from? How hard is it to "enrich" the material so much that it's actually usable in a weapon? Is it something that one could do in a garage at home or is a large industry required?

Most nuclear weapons use either entirely Plutonium (Pu) cores ("pits") or a mix of Pu and Highly Enriched Uranium (HEU, >80% U²³⁵). "Enriching" Uranium increases the proportion of U²³⁵ in it as the more common U²³⁸ isotope has limited applications in nuclear weapons due to the energy levels of the neutrons needed to induce fission.
Pu is separated chemically from "unburned" Uranium and other fission byproducts after cycling through a nuclear reactor.
As for the reactor, they can be fuelled using natural (unenriched) Uranium; there are many designs.
However this method isn't suitable for small scale operations; steal some Plutonium. You'll need 5-6kg for a basic bomb, less than 3kg if you're clever.

As long as one is able to finish the bomb and blow it up I'd guess the amount of radiation poisoning one is affected by is unimportant. How dangerous is to be around the fissionable material before the explosion?

No that dangerous unless you ingest some fissile material or are in prolonged physical contact. You might pick up a couple of Sieverts but that wouldn't kill you for years. Actually inhale or otherwise ingest Plutonium and you are in real trouble.

Pretty much all nuclear weapons use plutonium 239. It is made in a nuclear reactor and somehow separated from the other material (don't ask me how they do this, I dunno). This is most certainly not something that an individual could do in his garage. You can also make a nuclear bomb using uranium 235. But it is very hard to enrich from natural uranium in the necessary quantities. The entire Manhattan project only made enough for one bomb.

The usual separation process is chemical in nature (called PUREX) and the operation is usually done robotically with human oversight from a distance.
It's very nasty from a radiological and chemical view.

 

[Dancing David]

Hmm. What is the correct shape? How much of fissile material is needed? All the whilst avoiding predetonation. What is the relationship between the required velocity of the bullit/implosion, the rate of spontanious fission , the ambient neutron level and the likelyhood of predetonation? On a related note, how can we ensure that the chain reaction starts at the moment of maximum supercriticallit?. What device is needed to achieve that? What is the required precission in symmetry for an implosion type of device? How do we achieve such a level of symmetry?

Methinks making a nuclear weapon is quite a bit more difficult than that is popularly believed.

Not really, I talked to a professor at the U of I about this, he says the hard part is getting the fissile material. Other than that it is basically a chimney and some tracks and explosives. You can use just gravity and a tube, three to four stories and a chimney.

This gentleman here:
http://cstsp.aaas.org/content.html?contentid=6

 

[geni]

Isn't the amount needed variable with the speed of impact? That implosion concept is used to allow smaller amounts. So the trade off is, lots more precision in an implosion device, vs lots less Plutonium.

No.

Implosion increases the density so which does allow for less material to be used but thats not why you use it for plutonium. Contamination from plutonium 240 means that it isn't possible to build a halfway practical gun type plutonium weapon since you have to assmeble the critical mass very fast indeed to avoid fizzel.

In Tom Clancy's novel, they used lens grinding machines, and it still fizzled. Not many lens grinding machines in home shops.

Unlikely to be an issue. Correctly modeling the lenses and getting the electronics right is likely to be more of a headache.

 

[TubbaBlubba]

Pretty much all nuclear weapons use plutonium 239. It is made in a nuclear reactor and somehow separated from the other material (don't ask me how they do this, I dunno).

They use some kind of centrifuge, I think.

 

[catsmate]

Depends on how many kilotonne your yield need to be.

10K thereabout (hiroshima) is quite well documented and easy to do, from cannon type to sphere type.

Now multi stage yield is a tad bit more complicated (i think above 50kt would need to check that), and as faras I know not well documented above 3rd stage, as it involve special material or layering of different material for the reflection of neutron. Much more difficult.

You can build a fairly straightforward pure fission weapon up to ~50kt using a simple implosion design with ~6kg of Pu¹. Beyond that the 'pit' needs to be larger and thus the implosion system becomes more complicated with more lenses.
Without the resources of a small state or large-ish organisation this would be difficult. Unless you obtain detailed blueprints of a working design course...
A pure fission device can reach ~200kt with a good design; mixed Pu/HEU core, complex implosion lens system and good engineering². Adding boosting features such as a good fission tamper and a Be/Po "howitzer" system can push this further, to over 500kt³ though this usually requires a HEU core and isn't generally worth the trouble as Tritium boosting is easier and cheaper for most users.



¹ The US Model 1561 (MK 3 Mod 2) for example.
² The US MK 5 and Mk 6 for example.
³ The US MK 18 (Ivy King)for example.

 

[I Ratant]

This thread reminds me of similar threads on model airplane forums where someone in Syria or Lebanon asks how to build a model plane that can carry 10 kgs.
The number of responses that try to be helpful are interesting, and the number that get upset when the OP's location is mentioned, and the payload's potential use.
The upset guys see only the hobby side of the situation, and will tell anyone anything they want to know, disregarding the circumstances.
.
If anyone needs to know how to make a nuke, let -them- look it up!
Don't assist them!

 

[Skwinty]

They use some kind of centrifuge, I think.

No, see link in this post. A centrifuge is used for uranium enrichmment.

http://www.internationalskeptics.com/forums/showpost.php?p=6878572&postcount=10

 

[geni]

If anyone needs to know how to make a nuke, let -them- look it up!
Don't assist them!

Except http://en.wikipedia.org/wiki/Nuclear_weapon_design is rather more helpful than this thread. You sure you want people looking it up?

 

[NutCracker]

Not really, I talked to a professor at the U of I about this, he says the hard part is getting the fissile material. Other than that it is basically a chimney and some tracks and explosives. You can use just gravity and a tube, three to four stories and a chimney.

This gentleman here:
http://cstsp.aaas.org/content.html?contentid=6

Ok, your argument from authority works. I still have my doubts, though. Maybe he means that such an improvised nuiclear device has a sufficient likelyhood of producing a big anough fizzle to wreak havoc on its vincinity.

Ok, I'll shift goalposts. The point I am trying to make is that I believe that constructing nukes that perform reliably and optimally is a bit more convoluted than is popularly believed, 'cause theire is quite a bit more to it.

To throw in my own argument from authority: I once saw an interview with a guy who actually designed the darn things: he agreed with me.

That NK's first nuclear test was a dud , though, is consistent with my position.

 

[temporalillusion]

*waves to the FBI*

 

[geni]

That NK's first nuclear test was a dud , though, is consistent with my position.

That was a plutonium based implosion device and it has been suggested they were trying to build one with a less than ideal amount of plutonium which makes things harder.

 

[noreligion]

Well how hard is it? I have some knowledge about particle physics and related things but i have no practical knowledge about hard it would be. Let's discard the missile.

What things would you need? How easy would it be for people to discover the project? I mean you see the US and the Soviets having thousands upon thousands of nuclear weapons but then you see a country like north korea struggle to achieve just a little fizzle...

Based on the thread title I was wondering if there was a budding terrorist in our midst (outside of the 9/11 forum I mean).

 

[catsmate]

Hmm. What is the correct shape?

The "correct" shape for an implosion bomb is usually a sphere, this is dictated by basic solid geometry. With a sophisticated implosion lens system other shapes can be collapsed sufficiently quickly for a chain reaction; some artillery shell delivered fission weapons use a teardrop shaped pit¹.
Usually the pit is constructed by casting or machining Plutonium elements and assembling them² into a hollow sphere which is surrounded by the implosion lenses, carefully machined pieces of explosives that are detonated in a sequence to compress the pit sufficiently so that neutrons released by spontaneous fission will tend to strike other nuclei and induce fission, leading to an uncontrolled chain reaction.
Really, the basic idea isn't difficult a bright undergraduate could work out the details.

How much of fissile material is needed?

Depends on the material used, its purity and the sophistication of the design. For Pu²³⁹ containing less than 7% Pu²⁴⁰ about 5.5kg without tamping or boosting. With a good design less than one kilogram.
There are many other fissile (as opposed to fissionable) isotopes;
Pu²⁴¹, U²³³, Pu²³⁸, U²³⁵, Pu²⁴⁰, Np²³⁷, Cm²⁴³, Pu²⁴², Cf²⁵¹, Am²⁴¹

All the whilst avoiding predetonation.

Only generally a problem with gun-barrel designs; spherical implosion designs require a complex series of actions to occur, in sequence, to function.

What is the relationship between the required velocity of the bullit/implosion, the rate of spontanious fission , the ambient neutron level and the likelyhood of predetonation?

This again depends on the materials or mix of materials used in the pit and is generally complex.
For example a Plutonium gun-barrel bomb is possible but not practical as the presence of Pu²⁴⁰ as an impurity at any significant level leads to too great a level of spontaneous fission and thus would cause a pre-detonation ('fizzle'). However using Uranium this is less of a problem as the most common impurity in HEU (U²³⁸) isn't fissile using thermal neutrons. Nor is this a significant concern with implosion designs.

On a related note, how can we ensure that the chain reaction starts at the moment of maximum supercriticallit?. What device is needed to achieve that?

I'm not sure what you mean by this.

What is the required precission in symmetry for an implosion type of device? How do we achieve such a level of symmetry?

The fissile material is imploded by a number (typically 32 to ~120) of lenses made from explosives with different detonation velocities and detonated either simultaneously or at microsecond intervals depending o the design.

Methinks making a nuclear weapon is quite a bit more difficult than that is popularly believed.

No not really. As I said a bright undergrad with access to a good library and CAD software could to better than the Manhattan project; the science has been done.
You'd need specific engineering skills for working with the Plutonium (and Beryllium and Polonium is used) and the explosives.





¹ The US W48 for example. This "linear implosion" allows for smaller diameter weapons.
² Carefully. Very, very carefully.

 

[I Ratant]

Except http://en.wikipedia.org/wiki/Nuclear_weapon_design is rather more helpful than this thread. You sure you want people looking it up?

.
It's probably better to not assist in any manner.
The paranoid net of suspicion can be thrown pretty wide, when the nuke goes off.
Let'em do their own work.

 

[I Ratant]

*waves to the FBI*

.
Might be surprised at who is reading this stuff.
Free speech and country and all that, but aiding and abetting is a pretty serious charge.

 

[Dancing David]

This thread reminds me of similar threads on model airplane forums where someone in Syria or Lebanon asks how to build a model plane that can carry 10 kgs.
The number of responses that try to be helpful are interesting, and the number that get upset when the OP's location is mentioned, and the payload's potential use.
The upset guys see only the hobby side of the situation, and will tell anyone anything they want to know, disregarding the circumstances.
.
If anyone needs to know how to make a nuke, let -them- look it up!
Don't assist them!

The genie is out of the bottle, it won't go back, and we have used our three wishes. There are many more details than a rough schematic, like critical mass, distance for sub critical events and the like.

 

[Dancing David]

Ok, your argument from authority works. I still have my doubts, though. Maybe he means that such an improvised nuiclear device has a sufficient likelyhood of producing a big anough fizzle to wreak havoc on its vincinity.

Ok, I'll shift goalposts. The point I am trying to make is that I believe that constructing nukes that perform reliably and optimally is a bit more convoluted than is popularly believed, 'cause theire is quite a bit more to it.

To throw in my own argument from authority: I once saw an interview with a guy who actually designed the darn things: he agreed with me.

That NK's first nuclear test was a dud , though, is consistent with my position.

Sure, it takes engineering, you bet. The fact that the NKs first test was a dud is no suprise, they didn't want to poison themselves in the process. having it work is always a trick as any home chemist knows.

Besides, off the shelf bombs are not very secure in some parts of the world.

 

[Dancing David]

Based on the thread title I was wondering if there was a budding terrorist in our midst (outside of the 9/11 forum I mean).

They would do better to run for office and get power that way.