Iran soon?

Originally Posted by Locke

As far as I understand - enriched uranium is just one of the many steps required to produce a working atomic weapon. Through the use of various pieces of equipment, you seperate the U235 (middle weight isotope) from the mined uranium, usually by gaseous diffusion (uranium tetra-chloride), or centrifuges (iran is using the latter iirc).

If I recall correctly, gaseous diffusion isn't being used anymore, unless the plants are already built. It's inefficient when compared to centrifuges or other somewhat still experimental methods.

Originally Posted by Locke

Even though this is a major step - they are still far away from creating a working weapon - they still have to deal with obtaining the right weights for a critical mass, and perfecting the timers and explosives to the accuracy needed to acheive that critical mass. etc...

Sadly enough, this is not entirely true. What Iran has is enriched uranium, not the usual plutonium which can be produced using U238, in very large quantities. This might look like a good thing, as less material means less bombs, but there are other differences between Pu239 and U235. I explain those in the next paragraph, skip it if you want, it's not absolutely necessary.

(During the production of Pu239 through neutron absorption in a nuclear reactor, a whole load of different nuclear reactions take place in the fuel. You have the fission of U235 itself, used to produce energy, but you have impurities in the fuel which might be tranformed into other elements, or even a minority of "unusual" reactions in the U238, U235 or Pu239. One element resulting of those reaction is a rather uncommon isotope of uranium or plutonium, I can't remember which. I *think* it's Pu240, doesn't really matter. Anyway, that isotope has a somewhat low half-life, meaning it's likely to desintegrate and release a number of products, including neutrons. Neutrons happen to be what is used to split U235 or Pu239 atoms in an atomic bomb. The process is essentially this, you'll have different masses coming together, forming a supercritical mass, meaning more neutrons are produced than lost, leading to a chain reaction. The longer the masses stay together, the more energy you'll have time to release. If the masses do not stay supercritical for long enough, the bomb will fail to work correctly. Now, the thing is, the neutrons liberated by the Pu240 are enough to make the reaction begin much sooner, when the masses are not completely together, or right after they've touched. Enough energy will be generated to separate the masses, but not much else. In the end, the bomb will fizzle out.)

Now, what this means is that to use Pu239 you need to have a much greater force holding the masses of fissile material at first. Those found in an implosion-type device are enough. Those in a gun-type device are not. However, U235 does not have this same problem, meaning a gun-type device will work with U235. And gun-type devices are a whole lot simpler than implosion-type devices. First of all, there's no need to worry about explosion timing, no need to worry about explosive lenses used to focus shockwaves at particular points and all the calculations that follow. Second, the masses of fissile materials don't have to be made as precisely. Figuring out how much you need isn't the toughest thing ever. There are calculations to be made, of course, but they're not complex when compared to other things you encounter in physics or engineering.

This is somewhat similar to the path South Africa followed. They want to get a bomb, any bomb. It doesn't matter if it's inefficient and that they can't make it into an H-bomb afterwards. And they want it soon. Of course, there are other circumstances; unlike North Korea, Iran doesn't have a reprocessing plant or any other source of plutonium, and they're not building an arsenal capable of destroying the US, as the USSR was, so they have no reason NOT to make a gun-type device if they want a bomb.

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Depends.

First of all, there isn't much litterature on nuclear weapons per se. Not technical litterature anyway, meaning you can have a good idea as to how a bomb works, but you won't necessarily have any idea how to make all the calculations. However, a large number of physicists have pretty much all the knowledge you need, so it's possible to fill the holes. For an H-bomb, then it's a whole different matter. Even the non-technical litterature is somewhat scarce. The basic principle is somewhat simple, but the actual "implementation" is harder.

As for what stands between a country and nuclear weapons, it depends on the country. One of the things is secrecy. Quite often, you don't want to tell the world you're making a bomb. If you're a somewhat powerful country, think G7 member, then it's likely easier for you as you already have a large nuclear industry which you can use as a cover for your activities. If you're a smaller country, then anything large is likely to be noticed by someone. Even if you're a walled hell-hole like North Korea, it'll be noticed. That means you're restricted in what you purchase and the size of your program.

Now, secrecy wouldn't be as much of a problem if not for what is essentially the biggest obstacle: obtaining fissile material suitable for bomb construction. Here, you have two options: Highly enriched uranium 235 or plutonium 239. Both have advantages, both have drawbacks. Though in both cases, you'll need large-scale facilities to do the processing. That's one of the biggest challenge. I assume here that no black market for such materials exist, and I think it's fairly safe to assume so (though if there is, any seller is welcome to PM me for offers...). The size of the facilities themselves are one issue, but the actual equipment you need is probably even worse. First, it's expensive. Not much of an issue if you don't mind starving your people to the death, though. Second, it's restricted. Unless you already have a nuclear industry, or are building a large one from scratch, people will wonder why you need those 800 separation centrifuges. There's no reason for you to enrich your own fuel, it doesn't make sense if you have one nuclear plant. Same goes if you choose plutonium instead of uranium; it doesn't make sense for you to have a reprocessing plant for your one nuclear plant. You could try to make the equipment locally, or even develop new methods specifically geared to produce a small amount of material of bomb-grade material, which I think is what Saddam did in the 80s. Or attempted, anyway. But the equipment we're talking about is often quite complex and you'll still need some high-grade material from other countries. Something else you need to add if you don't have a local uranium source is importing the actual ore, which might arouse suspicion too.

Then you have the IAEA and the like. Since you probably can't conceal your facilities, you might decide you want to try to conduct your enrichment or reprocessing in broad daylight and camouflage the whole thing as a civilian operation. For reprocessing, it's somewhat difficult to judge what you'll do with the plutonium you extract, so you shouldn't have much trouble. But the simple fact you built the plant in the first place means everyone know you're full of shit, unless you already have a real nuclear industry. If that is the case, then you're likely going to be able to proceed to the next step. If instead you build an enrichment plant for uranium, then your concerns are different. If you don't have a nuclear industry, then people know you're full of shit. If you do have a nuclear industry, or are building one, then you have yet another problem. Typical civilian fuel is 20% U235. For a bomb, you need at the very least 90%. Whether you obtain one or the other depends on how you configure your centrifuges. Feed the output of each centrifuge in the next until you reach the last and you get a small amount of bomb material. Make 5 centrifuge groups in the same way and run those in parallel and you get a large amount of civilian-grade material. But the problem is, the people inspecting your enrichment plant will know what you're doing. If you throw them out, then you're back at square one, since you wanted to camouflage your operation, except now everyone suspects you.

You got fissile material? Good! Now it's time to make the bomb. If you managed to get uranium, then you might actually be able to make a bomb easily enough, as I've said in my previous post. Congratulation. If you got plutonium, then your physicists will have fun with various calculations involving shockwaves and explosive lenses. It's much more complicated, requires precision and you might even have to develop a number of different technologies along with it. Not to mention you'll have to test it. A uranium bomb is relatively simple, and there probably won't be any need to test it, but not testing a plutonium bomb is insane. Unless you have access to a supercomputer of reasonable power.

So there you have it, this is what stands between a country and the bomb. How hard it is for a particular country, as I said, depends. One with a source of uranium will have an easier time. One with a decent industrial capacity will be able to do so faster than a seventh world agrarian people's republic. Lots of things factor in.

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