[phkahler]

I was going to say it fired a slug through a cylindrical piece of material, but decided to verify this on Wikipedia. It turns out:

>> For the first fifty years after 1945, every published description and drawing of the Little Boy mechanism assumed that a small, solid projectile was fired into the center of a larger, stationary target.[31] However, critical mass considerations dictated that in Little Boy the larger, hollow piece would be the projectile.

I had never heard this before and was in denial reading the part above that. So either this key detail was kept secret for 50 years, or somehow history has been changed to confuse would-be bomb makers. I wonder how this detail came to light.

Edit: Following the reference is was this guy: https://en.wikipedia.org/wiki/John_Coster-Mullen

[ramesh31]

>So either this key detail was kept secret for 50 years, or somehow history has been changed to confuse would-be bomb makers. I wonder how this detail came to light.

Making a nuclear bomb has nothing to do with the knowledge of its' construction. Detailed plans are freely available to anyone who is interested. The reason you can't make a nuke is that the enrichment process of a suitable amount of fissile material requires nation-state level of industrial output. It is physically impossible for a small rogue actor to make a bomb from scratch. Germany during WWII, for example, was far advanced toward a bomb years before the Manhattan project, but their industrial capacity was simply never sufficient to build it.

[mandevil]

The Nth Country Experiment, in 1964, took three freshly minted Physics Ph.D's without any security clearances of any kind, gave them access to a reasonably sized unclassified physics library, and asked them to design an implosion weapon. After approximately three man-years of effort (along with some basic calculation assistance from some 1964 unclassified calculators) those Ph.D's designed a workable implosion bomb. So by 1964 it is clear that design was not the limitation: every real country can scrape together a few Physics Ph.D's for three man years of effort.

I would STRONGLY disagree that the Germans were ever more advanced than the Manhattan project. The British were a bit (~9 months) ahead of the US before S-1 started (December 1941), but I've never seen any evidence that the Germans were ahead of either country at any point. Certainly the fact that they never managed to replicate CP-1, which went critical in December 1942 (and was still years of hard work away from an actual nuclear bomb) suggests that they were never very close at all.

The closest I can come up with is that the discovery of nuclear fission in 1938. In that work, there were five people who collaborated closely enough that today they would have all had their names on the one paper (because of Nazis the work was published in two papers, Aryans on one, Jews on the other): Otto Hahn, Fritz Strassman, Lise Meitner, Otto Frisch, and Wilhelm Traube. Hahn and Strassman were considered Aryan enough to stay in Germany. Meitner and Frisch escaped- Frisch ended up working on the MAUD report and then at Los Alamos, Meitner stayed in neutral Sweden. Traube did not manage to escape and died in Gestapo custody in 1942. So 20% of this team ended up at Los Alamos, and only 40% managed to stay in Germany, which does somewhat point to some of the underlying problems any German bomb project would have had.

[phkahler]

>> Making a nuclear bomb has nothing to do with the knowledge of its' construction. Detailed plans are freely available to anyone who is interested.

Yes, but you don't know if those plans are viable and correct. This whole thing about the gun firing a cylinder is a case in point. People *thought" they knew how it was built sans some detailed measurements and such, but it turns out they were completely wrong on a rather critical aspect of the design.

[acchow]

> The reason you can't make a nuke is that the enrichment process of a suitable amount of fissile material requires nation-state level of industrial output

Is this still true in the 2020s?

[sbierwagen]

Supposedly the laser enrichment process is smaller and cheaper, though it's also kept secret.

You still need thousands of kilograms of natural metallic uranium, which is a rare heavy metal with few commercial uses and one really salient illegal one, or thousands of tons of uranium ore, which, see previous. It's hard to buy this stuff secretly, because not many people have it, and people who do have it have a big, salient, vested interests in not selling it to people who want to make nukes! It's not like selling drones to Saudi Arabia and saying "oh well guess it'll suck to be a Houthi". You might get nuked!

Nation-states can pull this off, since they have both land and state security apparatuses. Empirically, private groups or terrorist cells haven't been able to do it. The rumors I've read and the impression I've received is that AQA spent decades trying, lost a lot of lieutenants and trucks full of cash to CIA honeypots, and eventually gave up. Too hard, too expensive, too many dead ends and entrapment schemes.

[R0b0t1]

Is enriching uranium in the US actually illegal? Seems like the answer is no.

[colechristensen]

The Atomic Energy Act put a licensing requirement on all civilian use of nuclear materials, in this case for uranium concentrations above what is found in nature. Enriching is definitely in this category.

To enrich uranium legally in the US you would have to get a license by justifying why you were doing it and there are not many legitimate reasons to do so outside slightly enriched uranium for power plants or highly enriched for a few medical isotopes.

But if you just decide to do it, yes it’s illegal and the NRC will probably find you.

https://www.nrc.gov/about-nrc/governing-laws.html#aea-1954

[sbierwagen]

I would be interested to see what you’ve read to lead you to that conclusion.

[R0b0t1]

Well, after much searching I didn't find the parts of the Atomic Energy Act that required certification for any and all materials processing.

By default things are legal.

I've also spoken with scientists who do research that, at times, abuts nuclear science, and have heard stories of them just... not doing paperwork because it's annoying.

[ramesh31]

>Is this still true in the 2020s?

The laws of physics haven't changed in 80 years. Even if you started with yellow cake uranium (~70% enriched, and itself already nearly impossible for a non-state actor to acquire), to reach weapons grade at >95% you'd need hundreds of tons of it, and massive industrial scale chemical facilities to convert that into uranium hexafluoride and pull out the U235 isotopes [0], where the ratio of U235 to U238 (the non-fissile isotope) is 99:1. The vast majority of the Manhattan Project was in the engineering challenges required to do this, not really in the construction of the bomb. So far, only 5 countries in the world have been able to do it.

[0] https://web.evs.anl.gov/uranium/guide/uf6/index.cfm#:~:text=....

[djrogers]

> So far, only 5 countries in the world have been able to do it.

I think you’re a tad optimistic there - sadly we have many more than 5 nuclear powers today.

[speed_spread]

5 countries have developed Uranium enrichment facilities.

[colechristensen]

Argentina, Brazil, China, France, Germany, India, Iran, Japan, the Netherlands, North Korea, Pakistan, Russia, the United Kingdom, and the United States

There’s the list of “known” meaning publicly acknowledged countries with operating enrichment facilities, more than 5.

Notice it doesn’t include Israel which more or less everyone believes has nuclear weapons meaning enrichment facilities. There are several other countries which are very reasonably believed to have or have had enrichment programs.

[acchow]

I was thinking more that the industrial production has increased 10x in 70 years. Private companies can now build rockets that go to space...

[samus]

Private companies could indeed do it. Heck, the mining and refining part is probably done by private entities these days. However, the only legal customers are nuclear power plants and governments.

[samus]

The process has gotten a bit more efficient, but it still is nothing that can be run effectively in a garage. We are talking about separating not two elements, but two isotopes that behave chemically indentical and just differ in mass by 1.3% of the weight of the heavier one.

Another possibity is building a breeder reactor first to breed Plutonium.

Also, where to get Uranium ores in the first place? You can be sure that governments keep close tabs on who takes funny stones out of certain mines.

[mandevil]

http://blog.nuclearsecrecy.com/2011/11/08/the-mysterious-des...

Especially take note of Carey Sublette's comment on the design history in the blog comments: Mr. Sublette is definitely a name to be reckoned with, as far as unclassified nuclear analysis goes. His thought, that the design was basically taken direct from the Thin Man bomb design, is an especially interesting one.

As for why the unclassified world thought what it thought for so long, I always presumed it was because men in the 1940's naturally assumed that the rod moves into the long tube, not the tube moves to surround the rod. (Cut to shot of train going into tunnel.)

[dylan604]

You mean a shot of the tunnel engulfing the train?

[ncmncm]

Moreso: a set of hollow rings. So, maybe the rings didn't nest together until they hit the target.

[wolverine876]

> decided to verify this on Wikipedia

Please, please don't say that. :(