4 ms·

It's almost a certainty that at least enriched U-235 gun-type weapons would be made regardless of the Manhattan Project as the relatively simple technology of u

It's almost a certainty that at least enriched U-235 gun-type weapons would be made regardless of the Manhattan Project as the relatively simple technology of uranium enrichment came online. It's almost literally a cannon shooting a U-235 bullet into a U-235 sphere welded to the end of the cannon. Given the pure material (which you can make by spinning natural uranium in a tube), it's basically easy. Heck, the Manhattan Project people didn't even bother testing it like they did with the far more complex plutonium implosion device (Trinity).

stan_rogers 5y ago
The outer part was the projectile; the slug was the target. Making it the other way around - the way most of us always assumed it would have worked - would have forced the ring into criticality. So it is an easy concept, but the first guess is almost bound to be the wrong one.
- dtgriscom 5y ago
  Interesting: citation?
  - int0x2e 5y ago
    https://en.wikipedia.org/wiki/Gun-type_fission_weapon https://en.wikipedia.org/wiki/Gun-type_fission_weapon Look at the diagram on the right - it's the cylinder that's the target.
- deleted 5y ago
  [deleted]
- wrycoder 5y ago
  Where did you hear that? It seems to me that the only thing that matters is the relative speed of the two components. Was the ring much lower mass than the core? Edit: it was more. Nonetheless, accelerating the ring had advantages, according to WP! I didn’t know that.
  - stan_rogers 5y ago
    It's not the mass per se, but the need for the thing to be contained at the target end. If the ring is already at the target end, you have a relatively large mass of enriched uranium surrounded by a neutron reflector. That's not going to make things go bang, but it is enough to be rather exciting. By sitting the core cylinder in the middle of the containment vessel with a gap around it and filling that gap with the ring on firing, nothing goes critical until it's supposed to go supercritical. (The ring is carried on a sort of sabot.)
supperburg 5y ago
Is it easy? You have to spin the tube at 50k rpm and flow a gaseous form of uranium through it. It’s dangerous and expensive and certainly hard if you’ve never built a centrifuge before.
- sudosysgen 5y ago
  Sure but centrifuges were going to be built to that standard anyways, they're a necessary basic technology.
  - pfdietz 5y ago
    The issue, as I understand it, is that even slight vibration mixes the UF6 enough to ruin things. Getting the centrifuges to rotate absolutely smoothly is difficult.
    - kaba0 5y ago
      Compared to very finely controlled explosions to all meet in the center with high enough velocity and accuracy, it is trivial.
int0x2e 5y ago
I hope you understand that enriching Uranium isn't as simple as "spinning natural uranium in a tube". The Manhattan project used multiple different processes at the time, simply because time was of the essence and they didn't know which would work and which would be most efficient when they started. At peak, they used 10-15% of total US electrical power, as well as quite a bit of important material (mostly metals for particle accelerators). They didn't have access to centrifuge or laser based enrichment processes, which are significantly more power efficient, but neither of these are simple plants to build. Centrifuges in particular are very delicate pieces of machinery, constructed of special materials and balanced in an extremely delicate way. Oils from your hands would be enough to destroy a unit due to the crazy speeds involved. Not to mention you're still working with gaseous uranium hexafluoride which isn't OSHA approved :-). TL;DR - even if bomb design is trivial for a gun type bomb, generating enough enriched U235 for a proper bomb requires a significant, prolonged, well funded effort. I agree we would probably have nukes at some point, but I'm not sure when.
- jjk166 5y ago
  Centrifuges are delicate but they're not especially difficult for an industrial society to produce. They are comparable to jet engine shafts in terms of both loading and components. The manhattan project didn't utilize them because a single individual overlooked a simple method of making them more stable - you add a flexible section so any vibrations damp themselves out. German scientists claimed to have figured out this trick during the war, and the soviets implemented it shortly thereafter in their nuclear program, allowing them to enrich enough material for their weapons with only a fraction of industrial effort of the American project. Gas centrifuges for enrichment of chlorine isotopes had already been in use since 1934. Much smaller nation states have since been able to effectively generate enough uranium for nuclear weapons programs in short periods of time using centrifuges. The main challenge for them has not been production itself, but hiding the activity from international scrutiny. Tracking shipments of materials and parts necessary for centrifuge construction has been one of the leading methods of avoiding nuclear proliferation, but still centrifuges are so effective that even a small number is enough. North Korea, for example, is believed to have two buildings worth of centrifuges, but we only know where one of them is, and only because they have given international inspectors a tour of that location. For context, North Korea's current GDP is about 1/64th of the US's GDP in 1939.

stan_rogers 5y ago

The outer part was the projectile; the slug was the target. Making it the other way around - the way most of us always assumed it would have worked - would have forced the ring into criticality. So it is an easy concept, but the first guess is almost bound to be the wrong one.

dtgriscom 5y ago
Interesting: citation?
- int0x2e 5y ago
  https://en.wikipedia.org/wiki/Gun-type_fission_weapon https://en.wikipedia.org/wiki/Gun-type_fission_weapon Look at the diagram on the right - it's the cylinder that's the target.
deleted 5y ago
[deleted]
wrycoder 5y ago
Where did you hear that? It seems to me that the only thing that matters is the relative speed of the two components. Was the ring much lower mass than the core? Edit: it was more. Nonetheless, accelerating the ring had advantages, according to WP! I didn’t know that.
- stan_rogers 5y ago
  It's not the mass per se, but the need for the thing to be contained at the target end. If the ring is already at the target end, you have a relatively large mass of enriched uranium surrounded by a neutron reflector. That's not going to make things go bang, but it is enough to be rather exciting. By sitting the core cylinder in the middle of the containment vessel with a gap around it and filling that gap with the ring on firing, nothing goes critical until it's supposed to go supercritical. (The ring is carried on a sort of sabot.)

supperburg 5y ago

Is it easy? You have to spin the tube at 50k rpm and flow a gaseous form of uranium through it. It’s dangerous and expensive and certainly hard if you’ve never built a centrifuge before.

sudosysgen 5y ago
Sure but centrifuges were going to be built to that standard anyways, they're a necessary basic technology.
- pfdietz 5y ago
  The issue, as I understand it, is that even slight vibration mixes the UF6 enough to ruin things. Getting the centrifuges to rotate absolutely smoothly is difficult.
  - kaba0 5y ago
    Compared to very finely controlled explosions to all meet in the center with high enough velocity and accuracy, it is trivial.

int0x2e 5y ago

I hope you understand that enriching Uranium isn't as simple as "spinning natural uranium in a tube". The Manhattan project used multiple different processes at the time, simply because time was of the essence and they didn't know which would work and which would be most efficient when they started. At peak, they used 10-15% of total US electrical power, as well as quite a bit of important material (mostly metals for particle accelerators). They didn't have access to centrifuge or laser based enrichment processes, which are significantly more power efficient, but neither of these are simple plants to build. Centrifuges in particular are very delicate pieces of machinery, constructed of special materials and balanced in an extremely delicate way. Oils from your hands would be enough to destroy a unit due to the crazy speeds involved. Not to mention you're still working with gaseous uranium hexafluoride which isn't OSHA approved :-). TL;DR - even if bomb design is trivial for a gun type bomb, generating enough enriched U235 for a proper bomb requires a significant, prolonged, well funded effort. I agree we would probably have nukes at some point, but I'm not sure when.

jjk166 5y ago
Centrifuges are delicate but they're not especially difficult for an industrial society to produce. They are comparable to jet engine shafts in terms of both loading and components. The manhattan project didn't utilize them because a single individual overlooked a simple method of making them more stable - you add a flexible section so any vibrations damp themselves out. German scientists claimed to have figured out this trick during the war, and the soviets implemented it shortly thereafter in their nuclear program, allowing them to enrich enough material for their weapons with only a fraction of industrial effort of the American project. Gas centrifuges for enrichment of chlorine isotopes had already been in use since 1934. Much smaller nation states have since been able to effectively generate enough uranium for nuclear weapons programs in short periods of time using centrifuges. The main challenge for them has not been production itself, but hiding the activity from international scrutiny. Tracking shipments of materials and parts necessary for centrifuge construction has been one of the leading methods of avoiding nuclear proliferation, but still centrifuges are so effective that even a small number is enough. North Korea, for example, is believed to have two buildings worth of centrifuges, but we only know where one of them is, and only because they have given international inspectors a tour of that location. For context, North Korea's current GDP is about 1/64th of the US's GDP in 1939.