7 ms·

Plus the two armed nuclear weapons that were dropped on North Carolina when a bomber exploded mid flight, and amazingly did not detonate.

gear54rus 4y ago
Should they have exploded? I was under the impression that to actually get the powerful chain reaction you have to spend a lot of energy bringing pieces of fuel together (to the point that explosives are used for that) otherwise they'd just melt and not explode. Can anyone more knowledgeable chime in here?
- TheOtherHobbes 4y ago
  It's quite hard to get a nuclear bomb to go boom. A lot of things have to happen in a carefully controlled and timed sequence. A big part of that is indeed forcing bits of fuel to stay together for long enough to allow the chain reaction to work its way through a significant proportion of the fuel. Without the force you get various intensities of fizzle explosions and radiation bursts. Hitting the ground with a "doink" after falling out of a plane is more likely to break something than trigger a full-scale explosion.
- yccs27 4y ago
  I believe the highest risk is that some unplanned external influence sets off the trigger mechanism. As you said, the nuclear core itself will not spontaneously explode from an impact, but there are surrounding explosives designed to mke the core achieve criticality - can we be sure they don't accomplish their goal unintentionally?
  - samus 4y ago
    The activation of the explosives has to be precisely aligned, else it will just explode and distribute the nuclear material over the surrounding area. Events that happen on the scale of microseconds determine the success and final yield of the nuclear chain reaction. Therefore, an uncontrolled detonation of the explosions is likely to thwart the reaction from happening.
    - yccs27 4y ago
      I‘m with you there, it‘s very unlikely. Still, it doesn’t feel comfortable when failing to successfully detonate might become the only thing preventing a nuclear disaster.
- justin66 4y ago
  > I was under the impression that to actually get the powerful chain reaction you have to spend a lot of energy bringing pieces of fuel together (to the point that explosives are used for that) otherwise they'd just melt and not explode. When it comes to the original fission weapons, you’d use a spherical arrangement of high explosives to force a carefully crafted, solid core to implode and achieve the critical mass (fat man) or you’d fire a gun with fissionable material as the bullet into a fissionable target that would achieve critical mass once the bullet whacked into it (little boy). Your description is super interesting because it sounds like maybe you were conflating the two. I can’t imagine the gun method really takes a lot of energy (more than a shotgun shell, but not much more?) but the high explosive arrangement for the spherical method was probably a scary, powerful work of art, in its way. I expect with the more developed weapons, not to mention the hydrogen bombs, the warheads are quite sturdy and it’s the arming systems and fuses that prevent disaster. The bombs might sometimes be expected to hit the earth from a great height and then detonate, after all.
  - puffoflogic 4y ago
    > The bombs might sometimes be expected to hit the earth from a great height and then detonate, after all. I'm under the impression that this is not how aircraft-carried nuclear bombs would be detonated. The Little Boy detonated at Hiroshima did so 580 meters from the ground.
    - detaro 4y ago
      Depends on the goal. Air burst optimizes for area of blast effect on the surface, ground burst is more effective against underground targets and causes way more fallout and contamination.
  - sbierwagen 4y ago
    >into a fissionable target that would achieve critical mass once the bullet whacked into it [...] I can’t imagine the gun method really takes a lot of energy (more than a shotgun shell, but not much more?) The gun type is mechanically simple, but impossible to scale up. If you're smacking two subcritical spheres together, each sphere can't be more than 15kg.¹ But wait, Little Boy used 64kg of uranium. How did it do that? "Critical mass" is a function of mass and surface area. A sphere packs the most atoms together, a long skinny rod spreads them out. To increase the amount of uranium used and thus the explosive yield, Little Boy actually fired a 38.5kg cylinder onto a stationary 25.6kg plug. Each half of the pit would have been supercritical, if they were spherical. Gun types also need to assemble quickly, since as soon as any part of the assembly reaches critical mass it will start blowing itself apart. It had 64kg of uranium but 2,300kg of neutron reflecting material and tamper, and the launching charge used 3.6 kilograms of cordite! That would be a hell of a shotgun shell. --- ¹: For pure U-233, which Little Boy didn't actually have, since it was only enriched to 80%. Wartime contingencies and all.
- kennend3 4y ago
  > to actually get the powerful chain reaction you have to spend a lot of energy bringing pieces of fuel together (to the point that explosives are used for that) otherwise they'd just melt and not explode. This isn't really how it works because you are not "putting energy" into the system via explosives.. You are compressing a plutonium core to cause it to become "supercritical". To your point, this is very difficult because if the explosive lenses are not perfectly timed, the core will not compress properly. This could cause anything from a total "fizzle" where the plutonium is spread over a large area due to "conventional explosives" to a yield far below expectations. To get the "powerful chain reaction" you need to hold this compressed "supercritical" core together as long as possible, to consume the plutonium fuel. This is challenging because the fission reactions increase at an exponential rate, so obviously it cant be held supercritical for long. See: https://en.wikipedia.org/wiki/Critical_mass https://en.wikipedia.org/wiki/Critical_mass
hedora 4y ago
It's pretty easy to design a nuclear bomb to tolerate a plane crash / accidental drop without detonating. Perhaps more amazingly, both bombs' failsafes failed. One acted like it was armed when it wasn't. The other's fail safe switch flipped to the arm position, but didn't actually arm the bomb. https://www.atlasobscura.com/articles/nuclear-bombs-dropped-on-north-carolina https://www.atlasobscura.com/articles/nuclear-bombs-dropped-...
- sitkack 4y ago
  The linked article supports the OPs claim. > As it fell, one bomb deployed its parachute: a bad sign, as it meant the bomb was acting as if it had been deployed deliberately. It started flying through the seven-step sequence that would end in detonation. The last step involved a simple safety switch. When a military crew found the bomb, it was nose-down in the dirt, with its parachute caught in the tree, still whole. As the Orange County Register writes, that last switch was still turned to SAFE. Perhaps you are saying the same thing arriving from different paths. OP didn't say why it was amazing they didn't detonate. Maybe they read the same article. Are you assuming that they think nukes just go boom in an explosion? It is amazing they didn't detonate, given how far along in the arming sequence they seam to have been. It is not hard to conceive of something bumping that switch during the destruction of the plane ... world might be a very different place had that happened. US thought it was nuked (by the Soviets), launches attack, Soviets launch counter attack.
  - sitkack 4y ago
    https://youtu.be/0GQc_SwSp_U?t=68 https://youtu.be/0GQc_SwSp_U?t=68
kyriakos 4y ago
I'd be more surprised had they detonated. Unlike conventional bombs the actual assembly is very delicate and minor misalignments will render them inoperable. They could blow up because they contain explosives but won't produce fission.
implements 4y ago
Well, neither were fully armed armed - fortunately! There were multiple arming points / switches. One bomb was ‘Safe’, and the other ‘Armed’ (but with an intermediate high voltage switch ‘off’). Bits of the latter one are still buried 150ft down, including nuclear material: https://en.wikipedia.org/wiki/1961_Goldsboro_B-52_crash https://en.wikipedia.org/wiki/1961_Goldsboro_B-52_crash

gear54rus 4y ago

Should they have exploded? I was under the impression that to actually get the powerful chain reaction you have to spend a lot of energy bringing pieces of fuel together (to the point that explosives are used for that) otherwise they'd just melt and not explode. Can anyone more knowledgeable chime in here?

TheOtherHobbes 4y ago
It's quite hard to get a nuclear bomb to go boom. A lot of things have to happen in a carefully controlled and timed sequence. A big part of that is indeed forcing bits of fuel to stay together for long enough to allow the chain reaction to work its way through a significant proportion of the fuel. Without the force you get various intensities of fizzle explosions and radiation bursts. Hitting the ground with a "doink" after falling out of a plane is more likely to break something than trigger a full-scale explosion.
yccs27 4y ago
I believe the highest risk is that some unplanned external influence sets off the trigger mechanism. As you said, the nuclear core itself will not spontaneously explode from an impact, but there are surrounding explosives designed to mke the core achieve criticality - can we be sure they don't accomplish their goal unintentionally?
- samus 4y ago
  The activation of the explosives has to be precisely aligned, else it will just explode and distribute the nuclear material over the surrounding area. Events that happen on the scale of microseconds determine the success and final yield of the nuclear chain reaction. Therefore, an uncontrolled detonation of the explosions is likely to thwart the reaction from happening.
  - yccs27 4y ago
    I‘m with you there, it‘s very unlikely. Still, it doesn’t feel comfortable when failing to successfully detonate might become the only thing preventing a nuclear disaster.
justin66 4y ago
> I was under the impression that to actually get the powerful chain reaction you have to spend a lot of energy bringing pieces of fuel together (to the point that explosives are used for that) otherwise they'd just melt and not explode. When it comes to the original fission weapons, you’d use a spherical arrangement of high explosives to force a carefully crafted, solid core to implode and achieve the critical mass (fat man) or you’d fire a gun with fissionable material as the bullet into a fissionable target that would achieve critical mass once the bullet whacked into it (little boy). Your description is super interesting because it sounds like maybe you were conflating the two. I can’t imagine the gun method really takes a lot of energy (more than a shotgun shell, but not much more?) but the high explosive arrangement for the spherical method was probably a scary, powerful work of art, in its way. I expect with the more developed weapons, not to mention the hydrogen bombs, the warheads are quite sturdy and it’s the arming systems and fuses that prevent disaster. The bombs might sometimes be expected to hit the earth from a great height and then detonate, after all.
- puffoflogic 4y ago
  > The bombs might sometimes be expected to hit the earth from a great height and then detonate, after all. I'm under the impression that this is not how aircraft-carried nuclear bombs would be detonated. The Little Boy detonated at Hiroshima did so 580 meters from the ground.
  - detaro 4y ago
    Depends on the goal. Air burst optimizes for area of blast effect on the surface, ground burst is more effective against underground targets and causes way more fallout and contamination.
- sbierwagen 4y ago
  >into a fissionable target that would achieve critical mass once the bullet whacked into it [...] I can’t imagine the gun method really takes a lot of energy (more than a shotgun shell, but not much more?) The gun type is mechanically simple, but impossible to scale up. If you're smacking two subcritical spheres together, each sphere can't be more than 15kg.¹ But wait, Little Boy used 64kg of uranium. How did it do that? "Critical mass" is a function of mass and surface area. A sphere packs the most atoms together, a long skinny rod spreads them out. To increase the amount of uranium used and thus the explosive yield, Little Boy actually fired a 38.5kg cylinder onto a stationary 25.6kg plug. Each half of the pit would have been supercritical, if they were spherical. Gun types also need to assemble quickly, since as soon as any part of the assembly reaches critical mass it will start blowing itself apart. It had 64kg of uranium but 2,300kg of neutron reflecting material and tamper, and the launching charge used 3.6 kilograms of cordite! That would be a hell of a shotgun shell. --- ¹: For pure U-233, which Little Boy didn't actually have, since it was only enriched to 80%. Wartime contingencies and all.
kennend3 4y ago
> to actually get the powerful chain reaction you have to spend a lot of energy bringing pieces of fuel together (to the point that explosives are used for that) otherwise they'd just melt and not explode. This isn't really how it works because you are not "putting energy" into the system via explosives.. You are compressing a plutonium core to cause it to become "supercritical". To your point, this is very difficult because if the explosive lenses are not perfectly timed, the core will not compress properly. This could cause anything from a total "fizzle" where the plutonium is spread over a large area due to "conventional explosives" to a yield far below expectations. To get the "powerful chain reaction" you need to hold this compressed "supercritical" core together as long as possible, to consume the plutonium fuel. This is challenging because the fission reactions increase at an exponential rate, so obviously it cant be held supercritical for long. See: https://en.wikipedia.org/wiki/Critical_mass https://en.wikipedia.org/wiki/Critical_mass

hedora 4y ago

It's pretty easy to design a nuclear bomb to tolerate a plane crash / accidental drop without detonating. Perhaps more amazingly, both bombs' failsafes failed. One acted like it was armed when it wasn't. The other's fail safe switch flipped to the arm position, but didn't actually arm the bomb. https://www.atlasobscura.com/articles/nuclear-bombs-dropped-on-north-carolina https://www.atlasobscura.com/articles/nuclear-bombs-dropped-...

sitkack 4y ago
The linked article supports the OPs claim. > As it fell, one bomb deployed its parachute: a bad sign, as it meant the bomb was acting as if it had been deployed deliberately. It started flying through the seven-step sequence that would end in detonation. The last step involved a simple safety switch. When a military crew found the bomb, it was nose-down in the dirt, with its parachute caught in the tree, still whole. As the Orange County Register writes, that last switch was still turned to SAFE. Perhaps you are saying the same thing arriving from different paths. OP didn't say why it was amazing they didn't detonate. Maybe they read the same article. Are you assuming that they think nukes just go boom in an explosion? It is amazing they didn't detonate, given how far along in the arming sequence they seam to have been. It is not hard to conceive of something bumping that switch during the destruction of the plane ... world might be a very different place had that happened. US thought it was nuked (by the Soviets), launches attack, Soviets launch counter attack.
- sitkack 4y ago
  https://youtu.be/0GQc_SwSp_U?t=68 https://youtu.be/0GQc_SwSp_U?t=68

kyriakos 4y ago

I'd be more surprised had they detonated. Unlike conventional bombs the actual assembly is very delicate and minor misalignments will render them inoperable. They could blow up because they contain explosives but won't produce fission.

implements 4y ago

Well, neither were fully armed armed - fortunately! There were multiple arming points / switches. One bomb was ‘Safe’, and the other ‘Armed’ (but with an intermediate high voltage switch ‘off’). Bits of the latter one are still buried 150ft down, including nuclear material: https://en.wikipedia.org/wiki/1961_Goldsboro_B-52_crash https://en.wikipedia.org/wiki/1961_Goldsboro_B-52_crash