North Korea is believed to possess fission bombs. They are now claiming that they also possess hydrogen bomb technology.
AIUI, fission bombs haven’t proliferated much because they are difficult to make. The export of fissile material and the technology required to assemble it into a supercritical mass are tightly controlled, and it is difficult to develop these things from scratch without massive investments of time and money.
But if a nation has already cleared that hurdle - if they already possess fission bomb technology and materials - how hard is it to make a fusion bomb? Wikipedia makes it look like you don’t need any more electronics or explosives engineering; you just need a few other materials like U-238, lithium-6 deuteride, and plutonium (of unspecified isotope), all packed in Styrofoam.
I assume plutonium is difficult to come by, but if you’ve already got some for the fission device, how much more do you need for the fusion “spark plug?” Just a little more (i.e. now you have a use for the scraps from your fission core), or a lot more (i.e. sacrifice one of your other fission bomb cores)?
I’m guessing that U-238 is available as depleted uranium. Is that controlled for export?
What about lithium-6 deuteride? difficult to acquire or synthesize?
You need a hohlraum cylinder that will be just right for directing the primary’s energy to compress the secondary the right way. You might not get fusion otherwise.
First of all, you need a very efficient fission bomb.
The crappy ones that N. Korea has won’t work.
Secondly, you need a lot of technology to figure out how to direct the x-rays to implode your secondary. It’s probably not too hard to make one that could fit on a truck, but getting one small enough to fit inside a missile warhead is another story.
Infamous article from The Progressive magazine in the late 1970s, discussing details of H-bomb construction. Infamous, because the US Gov’t tried to enjoin its publication. The article mentions constructing the “radiation reflector-casing” out of thousands of finely machined pieces of U-238. It also mentions that some of the Secondary’s fuel is tritiated, not just deuterated. I had also thought that the foam filling the radiation channel was also something quite exotic, not just the polystyrene mentioned in the article.
You’re basically trying to manage the radiation output from an atomic bomb, whose pressure is described in the article as 8 billion tons per square inch, and redirect some of it onto a chunk of deuterium and tritium in such a way that the chunk is squeezed, then heated to fusion. Not that easy.
OTOH, is there a member of the nuclear club that isn’t also a member of the multi-stage device club? Besides North Korea? I had thought that India and Pakistan also had multi-stage weapons?
The spark plug is a problem, too. Unless you built your Stage 1 device from scratch and have a goodly chunk of U-235 or PU-239 left over. Seems to me that that would be the most exotic and hard-to-procure material in stage 2, simply by virtue of being controlled as the primary active material of a fission weapon.
IMO the most important thing, or ‘secret’, that the *Progressive *article released in 1979 was the concept of radiation implosion. This really is the key idea that allows thermonuclear bombs to work. Originally, the smaller group of scientists in The Manhattan Project who were assigned to ‘The Super’ as the H-bomb was then referred to, thought that it would just be a matter of setting off an A-bomb near a supply of hydrogen and that the immense heat alone would cause a fusion reaction. Turned out this wasn’t the case, it was much more difficult and complicated than that. However, once this was worked out the idea of a ‘third stage’ tamper (which the *Progressive *article also revealed) was discovered, which made the yield of H-bombs potentially unlimited.
Interestingly, both the US and the Soviets hit upon radiation implosion at around the same time (Teller & Ulam in the US, Sakharov in the USSR). And although the Soviets relied heavily on espionage of the US program I don’t think this was something they totally got from spying.
The problem is not that they are difficult to make for a state with a fission device capability (they are not) the problem is that unlike a fission bomb, to validate your design an end to end test is necessary, otherwise you don’t have the high confidence needed that your device will work when you have an annoying enemy city you wish to give urban renewal to.
It should be pointed out that there are types of devices which use fusion reactions which do not need testing. Boosted fission devices employ small amounts of Tritium to increase the yield of the fission reaction and a device known as “layer cake” where alternating layers of U238 and Li H are used to set off a small fusion reaction.
[QUOTE=Grey Ghost]
I had thought that India and Pakistan also had multi-stage weapons
[/QUOTE]
India claims to have tested one in 1998, but the small yield; about 40Kt casts doubt on that, maybe its secondary failed to ignite.
You might get some fusion, but mostly just a lot of vaporized (extremely expensive) tritium. The Greenhouse George test used a fission bomb to cause fusion in a small vial of Deuterium-Tritium remote from the explosion.
It’s tricky. You need the surface of the pusher to ablate at a sufficiently even rate that the fusion fuel is uniformly compressed. Otherwise it just squirts off in whichever direction is being squeezed slower (where “slower” = behind by a few jiffies) and won’t fuse. You have to do a very good simulation to get everything right. The computing power is no longer a challenge, but the code includes some nontrivial algorithms and a wad of empirical data on a variety of materials under unusual conditions that would take years of experiment to rediscover, if you needed to.
