This experiment proved that anyone could design a nuclear weapon | Hacker News Reader

This experiment proved that anyone could design a nuclear weapon

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112 pointsDanielRibeiro53 comments

>In the 1960s World War II was well over, and the United States and the Soviet Union were both settling into a nice, long, cold war. Both countries were nervous, knowing that each had designed and built nuclear weapons. At least, though, they were the only two countries that could manage it. Nice article but it gets the time-scales slightly wrong.

The Soviet Union tested their first device in 1949.

The United Kingdom in 1952 (and their first thermonuclear bomb in 1957).

France in 1960.

China in 1964.

So by the time this programme began, all the countries in the NPT nuclear club already had fission bombs and at least the UK had a hydrogen bomb. The idea was not to figure out which country would be third but just how many nuclear powers there would be. 1967 is only one year before the first countries signed the NPT so proliferation was clearly on everyone's mind at that time.

Good quote from one of the comments:

>> “With modern weapons-grade uranium, the background neutron rate is so low that terrorists, if they have such material, would have a good chance of setting off a high-yield explosion simply by dropping one half of the material onto the other half. Most people seem unaware that if separated HEU [Highly Enriched Uranium] is at hand it’s a trivial job to set off a nuclear explosion … even a high school kid could make a bomb in short order.” - Luis Alvarez, Nobel Laureate in Physics, 1988

I'm not so sure that it would be quite that simple. You could make the material go supercritical like that but that doesn't necessarily get you a high-yield explosion if the mass blows itself apart too soon.

The so called "Demon Core" went supercritical when Louis Slotin accidentally dropped a neutron reflector onto it (this was the second time out of three that it went critical) and although it killed him, there was no explosion per-se.

From wikipedia: "He quickly knocked the two halves apart, stopping the chain reaction and likely saving the lives of the other men in the laboratory, though it is now known that the heating of the core and shells stopped the criticality within milliseconds of its initiation."

It might go critical, but not supercritial. It's possible to cause a large explosion, although not the same scale as an actual bomb, by making a reactor using control rods and then removing the rods. https://en.wikipedia.org/wiki/SL-1#Accident_and_response

Supercriticality refers to exponential growth in the rate of fission (each fission event in turn causing more than one additional fission event), but unless other conditions are met then going supercritical does not mean you actually get a nuclear bomb style explosion.

There is also the concept of prompt and delayed neutrons. Prompt neutrons are products of the fission of the fuel, while delayed neutrons are products of other fission products and are released shortly after the fission of fuel.

Normally nuclear reactors run prompt-subcritical, delayed critical (meaning that each fission event causes on average less than one other fission event with prompt neutrons, but when you account for delayed neutrons then the average becomes one for one. The lag incurred by relying on delayed neutrons to push you up to critical allows the system to be controlled).

During both the SL-1 accident and the second Demon Core accident, for a very brief moment fission events were causing more than one additional fission events with prompt neutron products. In other words they both went prompt-critical, which is a type of supercritical. Thankfully SL-1 disassembled itself, the Demon Core rapidly heated and expanded, and neither were brought into a supercritical configuration quickly enough. This is the fundamental difference between what happened when the demon core went supercritical when Louis Slotin fucked up and when it went supercritical when the they detonated the bomb made with it over the Pacific.

"one of the design problems to overcome in constructing a bomb is to contract the fissile materials and achieve prompt criticality before the chain reaction has a chance to force the core to expand. A good bomb design must therefore win the race to a dense, prompt critical core before a less-powerful chain reaction (known as a fizzle) disassembles the core without allowing a significant amount of fuel to fission. "

http://en.wikipedia.org/wiki/Prompt_critical#Nuclear_weapons

The second demon core accident was a fizzle. It went supercritical but without involving a significant amount of the fuel.

Indeed, I have spent a lot of time no farther than about 100 feet from an operating nuclear reactor that was technically supercritical.

The demon core was plutonium. The quote was about uranium. The conditions needed to cause a usable explosion are completely different.

Plutonium cannot be used in gun-type bombs because of P-240 contamination, but the basics are still the same. If you do not get the U-235 into the correct configuration quickly enough you will have a fizzle. The difference between plutonium and uranium in a gun type bomb is that there really isn't a practical "quickly enough" with plutonium.

The more pure you get your U-235 the more you can reduce the amount of time that you have to get it into a proper configuration. Pure enough to just drop together though? I find that incredibly unlikely. Keep in mind that even with incredibly pure U-235 your fuel is going to start to become critical when the two halves are still a few inches apart. Once that happens you have a very short period of time to close the gap and 9.8m/s^2 is pretty shoddy. The two halves are also quite massive, so being strong enough to slam them together by hand fast enough is not really reasonable either, they have too much inertia.

Maybe you could make a gun-type bomb using gravity if you dropped one half down a long evacuated tube... easier just to make it properly though. Of course refining pure enough U-235 that "simpler" gun designs become possible would be more difficult than actually just building the rest of the bomb correctly anyway.

I think Luis Alvarez was exaggerating "high yield" (you could certainly create a very damaging fizzle), or more likely "dropping", since constructing the gun is rather trivial with highly pure U-235.

Yes, I understand all that. I don't share your intuition that it's gravity over a man-sized drop is obviously too weak to cause a large explosion. You haven't made an order of magnitude estimate to back it up.

My point is that there are many orders of magnitude difference between the relevant parameters of plutonium vs. uranium, so the fact that dropping plutonium cores against each other is insufficient to produce a large explosions tells us essentially nothing about that possibility for uranium.

Yes, but obtaining "separated HEU [Highly Enriched Uranium]" is highly non-trivial. Enriching Uranium is a specialised process that needs equipment (like centrifuges) manufactured to precise tolerances operated by skilled and well-trained people.

There's a catch. While it's trivial to design a gun-type bomb (Little Boy), it's very difficult to produce weapon grade uranium for it. As for implosion-type bomb (Fat Man), it's relatively easy to get a hold of plutonium, but the design is extremely complex.

Good point - Little Boy's design was not even tested prior to its detonation.

Except the Nth country experiment participants designed an implosion-type bomb. The people running the experiment understood that designing a gun-type bomb would have been too easy. Nonetheless, you're right that obtaining the fissile material is much harder than the bomb's design.

> As for implosion-type bomb (Fat Man), it's relatively easy to get a hold of plutonium, but the design is extremely complex.

Relatively easy as in, you need a chemistry lab and a working breeder reactor. To elaborate a bit, for Uranium the main task is isotope separation, this is quite complicated since different Uranium isotopes are chemically identical and have a mass difference of just 1%. On the other hand, more or less all plutonium isotopes are fissile, and the task is to chemically separate them from other elements. ( And that one needs to work with spend nuclear fuel.) On the other hand, Plutonium does not occur naturally, so one needs a breeder reactor to produce it first.

But Pu240 undergoes a lot of spontaneous fission, and if you have too much of it your bomb will fizzle. Pu238 generates a lot of decay heat, which makes it great for NASA missions but not so great for bombs. For a while it was used in pacemakers.

Bombs are generally made from fairly pure Pu239, which can be made by bombarding U238 with neutrons. But if you leave the plutonium in the reactor, you get a mix of isotopes that's pretty much useless for bombs. Separating the isotopes is harder then enriching uranium.

For these reasons, nuclear waste from reactors, even with reprocessing, isn't actually much of a proliferation concern.

These problems are discussed in considerable detail in [1], specifically:

    While reactor grade plutonium would probably be of no 
    interest to a nation with access to better grade 
    material, it could be effectively used by a nation 
    capable of good weapon design, but without access to 
    better fissile material. Even a low technology nation 
    could fashion powerful weapons from it, after all even 
    a 1 kt device greatly exceeds the destruction of any 
    conventional weapon.

So yes, recognized nuclear states are using very pure Pu239, but this is done for engineering convenience and not an absolute necessity. And the calculation probably changes for a state with a clandestine nuclear program, since it is much easier to hide the additional computing capacity to make a working reactor grade plutonium design, than it is to hide a breeder reactor.

[1] http://nuclearweaponarchive.org/Nwfaq/Nfaq6.html (In section 6.2.2.10 Reactor Grade Plutonium)

From that section of your link: "Using this material in a bomb would be a challenge. Continual active cooling would be needed to prevent deterioration and damage to the core, explosives, and other components. The high rate of neutron emission means that predetonation is inevitable, even with a very efficient implosion system. However, even the relatively primitive Fat Man design would have produced a 0.5 kt or so yield with this material. With optimal implosion design yields in the range of at least several kilotons are possible. If fusion boosting is used, then the adverse effects properties of reactor grade plutonium can be completely overcome"

Yield restricted to a couple kilotons is generally considered a fizzle. It's big compared to chemical explosives but only about a tenth as big as Hiroshima. And the experiment in OP's article only talked about making a working bomb, not an optimal one.

The point on fusion is interesting, though. It might be worth repeating the experiment for thermonuclear bomb designs.

There's a book from the 70s, _The Curve of Binding Energy_, by John McPhee, which is about how easy it was at that time to acquire weapons-grade materials and design and build a device. I found it pretty interesting.

Of course, I read it in the 1980s, and here we are in the 2010s, and there's never been a private nuclear explosion of any kind, nor apparently any nuclear blackmail. That says something about either difficulty, or about how effective (covert?) non-proliferation efforts have been, or about how rare is the desire to use a nuclear weapon. Not sure which.

I think the article is pretty misleading given that the British carried out their first nuclear bomb test in 1952 and the French in 1960, it was pretty obvious already that other countries could build a bomb.

Reading the original report they assumed a reactor capable of producing plutonium was available so I'd say the real reasons for the experiment is to answer questions like, "if we sell countries reactors how big a step would it be for them to build a bomb". Given smart (but not Einstein smart) trained physicists with access to the publicly available literature, the answer they come to is 3 man years. Thats for an implosion device, a gun design would have been "finished much sooner".

Reading between the lines I guess there was also an element of trying to figure out how much of other countries nuclear programmes was based on espionage (the British were partners in the Manhattan Project, and the Soviets had had several spies there). They conclude that "its not surprising China has progressed so rapidly".

Finally its also worth noting that the reviewers were less confident in the design then the scientists were, they dont say it wouldn't work, just that it would need testing to work out the kinks (which the designers also say they just seem to expect less bugs :)

There's a more in-depth article on this here:

http://www.guardian.co.uk/world/2003/jun/24/usa.science

I suppose the reassuring thing is that it took two fairly smart people a significant amount of time, and that was without management giving them too much agro, and with the ability to run experiments more or less as they pleased via asking their supervisors to run the tests and getting the results back.

'They were to explain at length, on paper, what part of their developing design they wanted to test, and they would pass it, through an assigned lab worker, into Livermore's restricted world. Days later, the results would come back - though whether as the result of real tests or hypothetical calculations, they would never know.'

(Quote taken from the Guardian article.)

The appendix from the scientists documenting where they learned various things is a thrilling read.

And, TIL that you should not use classified material as a paperweight.

"Marv Williamson (whose office was just down the hall from us) kept an interesting paperweight on his desk.

[REDACTED: several hundred words, presumably describing it.]

We still have no idea what it really is because we don't want to ask! It was probably because we found it here in the Laboratory that we were led to speculate about it in the first place."

I'm sure that part right there has spawned a lot of conspiracy theories, especially concerning aliens. :)

Maybe it was a sphere.

http://nuclearsecrecy.com/blog/2012/08/29/forbidden-spheres/

> [REDACTED: several hundred words, presumably describing it.]

How to build the Super using a conventional initiator?

Its an interesting trivia question. One of Feynman's many autobiographical books described how they had spheres and hemispheres of all manner of crazy stuff to test neutron flux and explosive lens issues. He specifically mentioned gold and silver, because normally it would be pretty insane to have giant lumps of that stuff laying around, but given the level of perceived security, using a hemisphere of solid 24kt gold as a desk paperweight isn't so crazy after all. Its probably more secure on his desk than in a normal bank vault or merely ft knox or whatever.

As is the case in many fields, designing != building.

For example I ride bikes. A friend of mine designed a bike for me. But since neither of us could (at the time) weld, I had to pay someone else to assemble it.

Just because you can design a bomb that would work doesn't mean you'd have the ability to actually build it. Even if you were given refined uranium (and that's 80% of the job) there's still quite a lot of work to tolerance everything correctly, machine it all without killing yourself, assemble it, procure the primary explosives, put together a precise enough detonation system to allow the chain reaction to happen and then build a system to trigger the detonation. All of that is no joke.

The complexity really depends on the design. There are 2 basic types for a fission bomb; cannon and implosion. By far the simplest is the cannon which is pretty much as simple as taking a cannon and firing one lump into another. Implosion is trickier but only really because you have to get the timing of the explosions right to get good compression.

The tricky part is enriching the Uranium. The better your enriching process is the easier it is to make a bomb because the material is closer to critical.

No, getting a sufficient quantity of highly enriched uranium is 99.9% of the job. It's pretty easy to fashion a crude nuclear weapon once you have sufficiently high quantity of fissile material.

All I know is what I read in Tom Clancy's Sum of All Fears, which has a hell of a lot of detail about building a nuclear bomb. The thing that struck me was all the very high precision machining required, and how hard that was to achieve.

As you suggest, design principle, easy, actually engineering it is the tricky bit.

Plutonium is harder to machine that other metals, as it's density tends to be non-uniform: http://en.wikipedia.org/wiki/Plutonium#Allotropes

You go along milling a hard spot, then hit a soft spot and--oops! You took off too much.

And your bike example is given ready to manipulate refined materials. Its a much bigger problem if you're given a mountain containing some coal and some iron ore and told good luck. Oh and when you're done with that, to paint it, here's some land where you could probably dig an oil well and build a refinery and a complete petrochemical industry.

I've been interested in this topic for a long time and it seems the biggest non-obvious problems relate to the initiator design.

The hardest part of making a nuclear weapon is acquiring weapons grade (highly enriched) uranium and/or plutonium. The actual designing/making of the bomb itself is relatively trivial compared to the materials enrichment process (you can easily find detailed diagrams of good bomb designs online).

Even at the time of the Manhattan Project, the vast majority of the cost, facilities and workers on the project were involved in creating the fissionable materials rather than the better-known design work at Los Alamos. Remember that even then, they were confident enough in the gun-type Little Boy design that they didn't even need to test it.

Building a nuke requires purified uranium or plutonium. Making that is a massive industrial operation. Then comes casting, machining, etc. Only a determined nation-state has a chance of success, in spite of movies. Given that, design hasn't been a obstacle for decades.

Design is still a major obstacle for advanced multi-stage hydrogen bombs. How they work exactly is still a major secret that isn't public knowledge AFAIK.

Yeah, but you don't need that to get people's attention. Any nuclear bomb at all is a Big Deal.

If your going for attention you don't even need to go critical. A dirty bomb should be enough for that.

Not exactly. A good primer on multi-stage design was published in a magazine called "The Progressive" in 1979.

http://www.progressive.org/images/pdf/1179.pdf

Seriously misleading title. It seems to me that this particular experiment did not prove that "anyone could make a nuclear bomb". Rather, it demonstrated that a group of highly-educated physicists, when provided with the necessary resources and enough time, could develop one.

I sincerely doubt that reading this study would lead one to conclude that a member of a hunter-gatherer tribe could do the same. Perhaps "anyone" should have been substituted with "any industrialized country" in the title.

Fortunately, designing one doesn't mean you'll successfully build one, and building one doesn't mean you'll have something that actually works.

I'm guessing the fact that it was a design for a "working atomic bomb" (from the article) is the bit that means you'd "have something that actually works."

The generic design might be something that works, but if you don't account for materials, tolerances, etc that are associated with the building of the device, it could be broken.

Yes, the gap between the theoretical knowledge of how nuclear weapons work, and the practical ability to build one, is large. There's an interesting article about the possibility of "uninventing" nuclear weapons by stopping to make them, thereby losing the practical knowledge that is required to produce them: http://www.jstor.org/stable/2782506 (requires registration to read).

This will NEVER happen.

For one thing, it would be trivial for us to re-learn how to make one. The folks that had NEVER invented one did it in short order without computers and specialized equipment. They weren't even sure they'd be successful the first go around.

Possessing this knowledge would be very useful in a world where other nations didn't have it. Just look at history to know the reason why.

The only thing stopping the spread of this knowledge is the early warning provided by watching for the attempts of governments to acquire it themselves. Once you know they are trying, you use political/economic/military pressure to force them to abandon the effort. In some cases that works (South Africa). In some cases it doesn't (North Korea).

covered by the guardian 6 years ago

http://www.guardian.co.uk/world/2003/jun/24/usa.science

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

thanks bloggers!

Yes, you're right. Because it has been talked about before we should never talk about it again. Makes sense to me. ;)

These seems to be a growing trend whereby general interest stories and articles have someone calling them out as not hacking, not allowed (they are), or dismissing them as discussed some time ago. If people up vote and its within the guidelines isn't that all that matters?

That was 60-ies. I wonder about results of this would-be nuke design these days. I have a clue that current physics grads are unable to produce anything like their granddads did when it comes to nukes.

'Course, there's an Emacs command to do that.

Probably are a few out there in private hands.

:-/

There are few things in the world as useless as a nuclear weapon nobody else knows you have. All of the game theory, and that is where the advantage comes from, derives from the fact people will go to extremes to keep themselves from getting nuked even once. Keeping a Doomsday Device a secret defeats the whole point.

And yet Israel has a policy of not confirming or denying they have a working weapon, although everyone knows they do.

I think a lot of these things are whether you want to. It's just like people do the impossible with strong will and when there is a complete lack of will they simply never will. And building weapons and military infrastructure was something the US always wanted - something they learned, because they learned war, weapons and military brings money, power and a form of social infrastructure, while still being able to call it non-socialist. Those are all benefits. Hope that doesn't sound negative, but as a matter of fact the US has really much power, especially with their agencies and real problems with preventing enemy nations from building atomic bombs.

On the other hands smaller countries, like Lichtenstein, Luxembourg, Monaco, Austria, ... probably have the resources, monetary and scientifically (else they could buy them), but have a complete lack of interest, just like the ordinary physics student has a complete lack of interest. In fact I even know someone with a startup who is really scared of their technology being used for weapons and he does everything to prevent this (they make amazing drones and Hollywood and stuff are already really interested, cause it has a camera that allows to make pictures/films that could not be done before). He also lost friends because they got into military stuff - like they were killed.

Anyway, this article states that these were people who studied physics and were not into weapons and did only use public information, but that's really far from reality of someone who would target and have the real will to create a nuclear weapon. Many circumstances would most likely be way better for someone who really wants to.

Now one can do some research on this topic, but the US, kinda as part of their military system also has a huge army when it comes to agencies and invests like an unlimited amount of money into them, so it can pretty much flood Iranian science institutions with agents. I mean, they often had agents that got into way higher political positions than they intended and stuff like that. And military spending is just extreme in the US (look it up on Wikipedia if you haven't seen the figures yet).

So basically nuclear weapons are a lot about will, but also fear. I mean looking at the world and how the official US tends to act a lot of states that could have interests in such weapons doesn't want to, cause it would result into a nearly automatic invasion, be it by agents or military from the US.

Okay, I don't know how hard it really is. I mean according to the US the Iran was really close (weeks/months away) from the atomic bomb since the eighties or so. I don't know what stopped them, whether it really just were agents or whether there were other reasons, but given these facts and how much the Iran (according to the US! (not saying you can trust the other side more though)) wants this weapons there has to be more than a bit of cyber war, which really was more like public "look how cool we are" thing. I mean they put in agents there to place that worm and I am pretty sure he could have done many things and they just did it for the public.

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