Thread

Nazi Germany had no hope of making an atomic bomb, uranium cubes reveal

137 points · 121 comments · xqcgrek2

WalterBright · 1790963993 · focus · HN ↗
It's generally forgotten that Japan was also developing a nuclear bomb. They were a long ways from making a viable one, though. It was abandoned after the surrender.
1. fusslo · 1790964260 · focus · HN ↗
  I cant remember which, but a documentary about the bombing of Hiroshima and Nagasaki said that after the first bomb, Japanese scientists were deployed to confirm or deny the US's claim of an atomic weapon.
  If I remember right, the Japanese scientists confirmed signs of an atomic explosion, but the leaders were stuck in a debate as to whether or not to accept the findings
  Maybe someone better educated can correct me if I didn't get that history quite right
  Edit:
  <a href="https://en.wikipedia.org/wiki/Yoshio_Nishina#Atomic_bomb" rel="nofollow">https://en.wikipedia.org/wiki/Yoshio_Nishina#Atomic_bomb
  <a href="https://en.wikipedia.org/wiki/Bunsaku_Arakatsu" rel="nofollow">https://en.wikipedia.org/wiki/Bunsaku_Arakatsu (check out his academic advisor!)
  1. 7speter · 1790972386 · focus · HN ↗
    All the people dying from side effects of radiation wasn’t enough proof that an atomic weapon was used?
    AngryData · 1790973475 · focus · HN ↗
    Well the effects of radiation were still poorly understood, but also there wasn't that much radioactive material left over in any concentration. And the gamma ray blast would appear superficially like normal burns from being near a firebomb until atleast a few days later.
    Contrary to Fallout lore, most nuclear bombs dont leave much concentrated radioactive material unless it was done on purpose. You either need a shittier and smaller explosion with the same material, or you need a ground burst which reduces the effective blast area.
    The US was on ground zero in under 2 weeks in Japan and couldn't detect anything over the background in radioactive isotopes.
    Lumich · 1791020983 · focus · HN ↗
    « And the gamma ray blast would appear superficially like normal burns from being near a firebomb until atleast a few days later. »
    Would it? How so?
    First, the notion of “normal burns from being near a firebomb” is inadequate. There are various types of firebombs. The ones “generously” employed by Uncle Sam against the Japanese (primarily civilians, and later idem against the Koreans and the Vietnamese) are napalm bombs. The way they work is that burning napalm is blasted about in lumps and sticks to anything it hits, including clothes and human skin. The injuries caused by napalm lumps are special. They're called keloids.
    Figure 9.3 on page 171 of Palmer's book (free PDF available, link in 49938615, which is among the comments on this topic) shows keloid burns in Hiroshima bombing victims. These have been interpreted as “flash burns”. However, this defies common sense. First, they show characteristically strong locality, irregular shapes, sharply defined edges, and look exactly like napalm burns. Second, how would you explain a hypothetical “flash” (of whatever nature) from a distance more than a couple inches away to produce such conspicuously localized injuries? (And even from ten inches away you'd need strong directionality.) The forensics flatly contradict and preclude such a “flash” interpretation.
    Palmer, who is an MD, found that not much can be found about napalm in the medical literature, which curiously contrasts with its very wide-spread application against humans by the U.S. Air Force (p.140, referred to on p.175 and p.241):
    As of this writing (in 2019), a simple search for “napalm” on PubMed retrieves 29 articles, of which only 7 (seven) are written in English, and none of these provides much useful detail.
  2. WalterBright · 1790984214 · focus · HN ↗
    The leaders knew immediately that it was an atomic bomb.
    Books:
    Code-Name Downfall by Allen
    Downfall by Frank
    The surrender was due to their fear that the US had a third bomb and would drop it on Tokyo.
    defrost · 1791010349 · focus · HN ↗
    They rebuilt Tokyo that fast already ?
    The strikes conducted by the USAAF on the night of 9–10 March 1945, codenamed Operation Meetinghouse, constitute the single deadliest and most destructive aerial bombing raid in human history. Sixteen square miles (41 km2; 10,000 acres) of central Tokyo was destroyed, leaving an estimated 100,000 civilians dead and over one million homeless.
    ~ <a href="https://en.wikipedia.org/wiki/Bombing_of_Tokyo" rel="nofollow">https://en.wikipedia.org/wiki/Bombing_of_Tokyo
    Perhaps that "third bomb on Tokyo" fear was a bit made up and ahistoric.
  3. Lumich · 1791015468 · focus · HN ↗
    « signs of an atomic explosion »
    I'm curious. We know that there's a lot of energy in the atom. Some of it can be released by fission, which results in fission products, radiation, and heat.
    However, there doesn't seem to be anything in the process that would account for any sort of explosion. Radiation doesn't contribute. Heat alone is insufficient. In addition, you need an instant and manyfold increase in the volume of matter generated on the other side of the reaction. With TNT, for example, this increase is three orders of magnitude. Fission products are completely insignificant in this respect.
    So nothing comparable exists for nuclear fission, else it would be a problem for reactors. So how can it explode? What is the mechanism?
    womble2 · 1791019321 · focus · HN ↗
    Heat alone is not insufficient, the heat generated is so intense that is turns the surrounding air into a plasma which then absorbs the x-rays emitted creating a stupendous over-pressure in the air which drives the shockwave.
    Reactors don't explode because the amount of heat then generate is carefully monitored and matched the the rate at which that heat can be pulled from the reactor and converted into work.
    Lumich · 1791027824 · focus · HN ↗
    Thanks. This is a novel explanation to me. So to rephrase, some volume of air (~1,2 kg/m³ at sea level) is “plasmarized” and then eats the X-rays, upon which it expands in a shockwave.
    It is usually stated, however, that the X-rays go first, and at the speed of light. Plasmarization, OTOH, would be subject to some inertia, however little, wouldn't it. So there'd be a delay before plasma formation, and the X-rays would already be “over the horizon” (joke – they wouldn't follow Earth's curvature, would they).
    womble2 · 1791040059 · focus · HN ↗
    The x-rays aren't just emitted in a single moment, they are the result of the initial core heating up to millions of degrees, so the light they emit just as a result of being hot is in the x-ray and lasts for some amount of time. This is long enough to generate the ionised air which continues to expand and absorb more x-rays until the initial core cools down somewhat. At that point you have a large amount of incredibly hot, incredibly high pressure plasma which then expands and causes the shockwave.
    Someone · 1791030686 · focus · HN ↗
    The extreme radiation of the bomb almost instantly vaporizes everything near it (water in the air, earth, parts of the bomb, etc), expanding it in volume.
    That’s what causes the shockwave.
    As a corollary, having more material around the bomb that can capture some of its radiation means a bigger shockwave, but less radiation further away from the detonation.
    Lumich · 1791123537 · focus · HN ↗
    [dead]
2. colechristensen · 1790966157 · focus · HN ↗
  Hideki Yukawa was the first Japanese Nobel Prize winner for his work on strong-force related physics in the 1930s.
  >It was abandoned after the surrender.
  Japan is strongly believed to be on the order of months away from assembling a nuclear weapon, and not just one, they have the materials for many. For them it is not geopolitically useful to actually finish a weapon, but they are more than capable.
  1. buildsjets · 1790966956 · focus · HN ↗
    Do you have a reliable source you can share which supports that claim? Because el wiki says nothing of the sort. It discusses two main projects, "Ni-Go" and "F-Go", neither of which successfully enriched fissile material. One was built but did not operate successfully, the other was not built.
    <a href="https://en.wikipedia.org/wiki/Japanese_nuclear_weapons_programs" rel="nofollow">https://en.wikipedia.org/wiki/Japanese_nuclear_weapons_progr...
    rawling · 1790967096 · focus · HN ↗
    > Today, Japan is considered to be a latent or threshold nuclear state, capable of developing weapons in a short timespan. It is unique among non-nuclear weapons states in that it possesses a full nuclear fuel cycle and plutonium stockpile, as part of its civilian nuclear energy industry, and advanced developments in the industries necessary to make nuclear weapons.
    mmmBacon · 1790970884 · focus · HN ↗
    While your comment is true today. It doesn’t support the GP’s claim that Japan was near a nuclear weapon at the end of WW2 and only lacked the will to do so.
    OJFord · 1790971951 · focus · HN ↗
    That was not the claim. They said 'is on the order of months away', not 'was'.
    colechristensen · 1791135470 · focus · HN ↗
    correct
  2. Lumich · 1790977488 · focus · HN ↗
    « For them it is not geopolitically useful to actually finish a weapon »
    Why, they could take their revenge, couldn't they.
    This whole thing is stories built upon stories built upon stories. It's stories all the way down till you reach The World Set Free by British propaganda writer H.G. Wells, published in 1913–14 as part of the British war propaganda preparations against Germany. I don't recommend the book, it's psychologically dull and constructed, but that's where Leo Szilárd picked up the idea of an “atomic superbomb” in 1932 when reading the novel, which led to the Einstein letter in 1939. Well, according to the story anyway.
    [deleted] · 1790981687 · focus · HN ↗
    [deleted]
    WalterBright · 1790984509 · focus · HN ↗
    A more reliable account is "The Making of the Atomic Bomb" by Rhodes.
    Lumich · 1791009906 · focus · HN ↗
    [dead]
    Lumich · 1791119875 · focus · HN ↗
    [dead]
  3. WalterBright · 1790984330 · focus · HN ↗
    I'm skeptical. To generate the enriched uranium requires a lot of time and an enormous investment of money. Consider Iran has been doing that for years and years.
    philipkglass · 1791044475 · focus · HN ↗
    Japan has a large inventory of plutonium recycled from used power reactor fuel:
    <a href="https://www.aec.go.jp/bunya/04/plutonium/20260805_e.pdf" rel="nofollow">https://www.aec.go.jp/bunya/04/plutonium/20260805_e.pdf
    As of the end of 2025, the total amount of Japan’s separated plutonium managed both within and outside Japan was approximately 44.4 tons, of which approximately 9.9 tons were held domestically and approximately 34.5 tons were held abroad.
    Despite the nomenclature, weapons grade plutonium is not necessary to make nuclear weapons. Reactor grade plutonium has more problems with predetonation ("fizzle") and decay heat management, but both obstacles can be bypassed by design changes. In particular, "boosting" with a mixture of deuterium and tritium overcomes predetonation problems and can ensure repeatable high yields even with plutonium containing a high fraction of Pu-240.
    <a href="https://en.wikipedia.org/wiki/Boosted_fission_weapon#Gas_boosting" rel="nofollow">https://en.wikipedia.org/wiki/Boosted_fission_weapon#Gas_boo...
    The fusion reaction rate typically becomes significant at 20 to 30 megakelvins. This temperature is reached at very low efficiencies, when less than 1% of the fissile material has fissioned (corresponding to a yield in the range of hundreds of tons of TNT). Since implosion weapons can be designed that will achieve yields in this range even if neutrons are present at the moment of criticality, fusion boosting allows the manufacture of efficient weapons that are immune to predetonation. Elimination of this hazard is a very important advantage in using boosting.
    This design hardens weapons against neutrons from nuclear interceptors and against neutrons generated within the core itself, e.g. spontaneous fission from "dirty" reactor plutonium.
    Gas boosted bombs are more mechanically complex than the bombs of the 1940s, but the US started building them in the 1950s. Japan could easily manage the complexity today. Japan has also operated its Tritium Process Laboratory since the late 1980s, with capacity to handle 16 grams of tritium at a time. That's not much, but an individual boosted warhead may need only 3 grams of tritium.

Open on Hacker News to reply ↗

Unofficial Hacker News client; not affiliated with Y Combinator.