The basic idea behind a nuclear bomb is a ridiculously simple one. Bring enough fissionable material together, and it goes boom. There’s no nanotech, no microbots, semiconductors, electromagnetic containment vessels, or finely designed mechanisms. There’s just two lumps of (special) material brought together. We first got it done in '45, just 20 years after realizing that it could be done and decades before we were able to create much of our modern technology.
The first bomb to ever be built and tested… worked. (As a programmer, or as a plain engineer, that just blows my mind – if you know what I mean.)
So why are nukes considered hard to build? What’s stopping a future when everyone has them and the world is in chaos?
First, it requires large quantities of highly fissionable material (U-235) that has to be separated from from large quantities of less desirable material (U-238). This takes mile of centrifuges and tons of electricity. Or you need plutonium created in a stable reactor, which requires a good deal of tech. Plutonium is also toxic and reactive in addition to the radioactive danger. It’s also worth noting that early nuclear weapons were huge and heavy, requiring a large bomber to deliver them. Though if you could put it in a shipping container, you might have some luck delivering it.
That’s the best I can do without serious research.
It’s very, very engineering-intensive to refine or create the fissionable material.
It’s also not so simple to make the bomb go “boom” - the critical mass must be achieved in a very short amount of time. Do a search - there was a thread on this recently.
The easy-to-build design needs hard to get material - enriched Uranium. Plutonium is easier to get hold of (if you have a nuclear reactor about) but harder to use in a bomb.
If it weren’t so hard, a lot more would have gone off since 1945. Tel Aviv, Jerusalem, New York City, London, Damascus, Tehran, Islamabad and New Delhi would probably be no more.
To get much of a yield, the fissionable masses must be brought from a nowhere-near-critical distribution in space to a very-compactly-critical union very quickly. Doing this requires multiple subcritical masses in something like a spherical shell configuration, with high explosives driving them toward the center at almost the same instant for all of them.
FWIW the Hiroshima bomb had the equivalent of about a 5 inch sphere of fissionable mass, and it had a yield of only about 1%, IIRC.
The challenge is bringing the pieces together fast enough. If they come together too slowly the reaction starts prematurely and blows the assembly apart before most of the fissile material has a chance to split.
It’s true that a gun-type device like Little Boy is still pretty easy to get right. But gun-type devices are limited to relatively low yields. And they only work with Uranium. If you want a high-yield Plutonium device you have to use an implosion-type device like Trinity or Fat Man. Those are wickedly hard to engineer, because they rely on precisely-shaped explosive charges to produce the spherical shock wave that assembles the critical mass.
The only easy nukes are the little boy/gun type devices and they are not efficient and tend to waste its fuel by dispersing it before it fissions. Also they are limited to using difficult to produce enriched uranium-235. The harder to build fat man/implosian type device fissions more of its fuel and is able to use easy to produce plutonium-239/240.
It required the combined efforts of many of the world’s leading physicists for years plus the full weight of the US government under wartime conditions to produce the atomic bomb. As others have said the engineering required just for the implosion device is extremely challenging. Plutonium is not readily available. In Richard Rhodes’ book Dark Sun about the Manhattan Project he describes the scale of the plants that produced the fissile material and compares it to creating the entire US automobile industry, from scratch, in a couple of years.
A rocket is pretty simple too. Why don’t more people just slap together a Saturn 5 and go to the moon?
U-238 isn’t used in atomic weapons. U-235 was used for Little Boy (Hiroshima), Plutonium for the Trinity test and Fat Man (Nagasaki).
U-238 just doesn’t undergo fission as readily as U-235, and it makes up something like 99.3% of naturally occurring uranium, so you have to separate out the U-235 and that’s not a simple process.
Don’t forget in 1945 they had no computers to simulate explosions or to do any calculations. I think that probably slowed the process down at least some.
It’s OK to put U-238 in a bomb, but it doesn’t produce a runaway chain reaction like U-235. Without a certain concentration of 235, you won’t get any reaction. Since that concentration is several times higher than you find in nature, refinement is a challenge.
To provide a great example of the importance of timing, critical mass was accidentally achieved during the Manhattan project in a lab. The uranium started putting out a lot of heat and radiation and killed three people due to the radiation exposure. But there was no giant fireball explosion or significant danger to people outside the room. A terrorist can kill more people more easily with a homemade IED, or by grinding the uranium up and putting it in your food. Without the careful timing and directing of explosives, you just don’t have a weapon.
It seems to me that after the end of the Soviet Union, there was enough chaos in Eastern Europe that already existing nukes or fissionable materials could have gone missing without anyone knowing or caring.
You don’t NEED that. You need that to design a fancy bomb that is as small as it can be and is as efficient as it can be and will give you the amount of bang you expected/predicted it would. Most precise and largest bang for the buck so to speak.
If you have a decent amount of plutonium or fissionable uranium and you assemble them RIGHT, you will get a big bang. Terrorist or pissed off postal workers dont really care EXACTLY how big the bang is as long as its big.
The biggest thing that slowed down building the first bombs was accumulating the required amount of plutonium or uranium.
All the fancy calcs do is tell you whether you need 5 or 10 pounds and how critical your design/construction tolerances are.
Having claimed that, assembing that stuff RIGHT aint easy. It aint remotely easy IMO.
After all these years, the best description I’ve ever read of how to build a nuclear bomb (admittedly, I’ve not read many) is in Tom Clancy’s “Sum of All Fears”.
My understanding is that’s true for a uranium bomb, but not for one using plutonium. In that case, it’s really hard to make a usefully large blast. It seems like it takes the entire engineering skills of a superpower to produce megaton yields out of a given lump of plutonium… but North Korea only managed a kiloton. While that’s still a hugely destructive device, that still required a large engineering investment from a small nation. IMO, I doubt a small team of non-expert engineers could get ten or hundred ton yields – to the point where it would be just effective to load a semitrailer with fertilizer and fuel oil.
To be clear, any bomb with a megaton yield is going to be a fusion bomb, not a fission bomb. Admittedly, once you have the capability to build a fission bomb, it’s not all that much harder to build a fusion bomb, but you still have to take it one step at a time.
Has it ever actually been confirmed that the North Korea test was a genuine nuke? There was some speculation at the time that they just made a huge pile of chemical explosives and set it all off at once as a bluff.
IMO its more a precision/construction problem. At least when it comes to bomber bobs or north koreas.
If you have a fixed amount of fissionable material, you have to either squeeze a subcritical mass into a critical mass in the case of plutonium. Or you have to assemble sub critical masses into one critical mass in the case of enriched uranium.
So, with a fixed amount of bang material, and a relatively fixed amount of money, you do everything the best you can with what you got and hope for the best.
Lemons and lemonade and all that…
Being “smart” about the process is going to make a big difference between no chance of it working and at least some chance of a big boom.
I’ll agree that plutonium sucks tough wise. I “think” a small group of people with the right skills could pull off a heavy ass uranium device. A plutonium device, not nearly so easy IMO.
Of course its not like I am some certified bang designer either. Mostly just a gut technical feel here.