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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. 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.

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