3 ms·

Eh, the reason we spent so much effort at Oak Ridge is that we tried all vaguely practical methods of getting weapons grade fissionables, and that was the locat

by hga 11y ago

Eh, the reason we spent so much effort at Oak Ridge is that we tried all vaguely practical methods of getting weapons grade fissionables, and that was the location for uranium enrichment, thermal, caltron, and gaseous diffusion. But the most practical method turned out to be breeding plutonium and separating it, and that was done at Hanford on a vast scale, the largest single WWII construction project. But not inherently super electricity intensive, the piles had to be kept cool, and ... I'm not sure anything was all that power expensive. Ignoring the minor detail that they had 1/166th of the uranium needed for a Hanford style pile, assuming that 1,200 pounds was the first large quantity the might have gotten their hands on ... well, industrially there was no way they could have pulled this method off, we could just barely do it. They couldn't build reliable airplane engines with > ~1,000 hp of output. Niels Bohr dismissed the concept of A-bombs for WWII early on, he thought "you would have to turn the county into a factory". When "Nicholas Baker" showed up in the US, he observed we'd indeed done just that.

sandworm101 11y ago
I would argue that plutonium breeding is only obvious after you have performed some criticality experiments with an appreciable-sized block of enriched uranium. This was new physics at the time, without computer simulations. Bomb theory, critical mass, could only be understood after you get your hands on some enriched uranium.
- hga 11y ago
  Indeed, but there's a chick and egg problem there. We put the plutonium process fully in gear before we even knew the average number of neutrons a Pu-239 fast fission would produce, when we had no more than micrograms or so of cyclotron produced stuff. Which was enough to work out the separation chemistry, ultra-microchemisty is amazing. I guess my point here is that the Germans realized uranium separation was a no-go for them, were trying reactor based approaches, and they might have rolled the dice that way and tried the plutonium path. I'm saying the pieces were in play to possible success, not that it was at all likely without 20/20 hindsight.
- InclinedPlane 11y ago
  This is very much not the case. Bomb theory and critical mass come from a fundamental understanding of neutron chain reactions. You need to have good data on fission properties and neutron mean-free-path distances, but that requires only extremely tiny amounts of Plutonium or natural Uranium, it does not require enriched Uranium. Other than that the other critical factor is coming up with the correct model/theory for nuclear weapons. Something that the Japanese got right, the Americans and British got right, and the Germans (specifically Heisenberg) ended up getting extremely wrong. Fine tuning critical mass calculations was important in optimizing the bomb later on but it wasn't necessary to developing the basic underlying theory of how bombs work or of pointing the way toward implosion assembly and Plutonium breeding.
ufmace 11y ago
Note that the reason why we tried all vaguely practical methods at the same time was that we had no idea which one would turn out to be the best, and we wanted to get the bomb ready ASAP. And of course that we had the resources to do that. It's true that Japan, or some other country, could have built a bomb much cheaper and faster if they used that method alone, but there was no way for anybody to know that. They'd have to be incredibly lucky to happen to guess right the first time, instead of wasting their time going down the wrong rabbit-holes.
paulmd 11y ago
Also you have to remember that by 1944-45 the Japanese economy was a smoking ruin. They'd lost all their overseas territories, we were island-hopping up to their doorstep, and firebombing the shit out of their industrial centers in Honshu. They were incapable of manufacturing sufficient quantities of basic war materiel like rifles, and they could only turn out a very limited quantity of high-end manufacturing like the J2M Raiden and the N1K Shiden interceptor aircraft (which were an known quantity, let alone developing new heavy-bomber type engines like that). Most of that critical production had actually been moved into caves to keep it safe from the firebombing. That's how fucked they were. The idea of them pulling off a Manhattan Project-scale effort - even if they knew exactly what to do - is utterly preposterous. You'd be talking about a very large-scale effort that utilized a great deal of rare resources, energy, and scientific+high-end engineering capacity and it's utterly implausible even if they abandoned everything else. Let alone being able to effectively deliver it in anything except a tactical attack. No heavy bombers, no carrier fleet, no overseas bases? Not gonna happen. Best case is you sneak it into a west-coast harbor with a long-range sub on a one-way trip (if there's one thing that could have made us angrier than Pearl Harbor...). Most likely case you blow it retaking some random island. Worst case, well, they did kinda have the suicide cult thing going on. Now that said they were clearly doing basic research/groundwork on the topic, even if they didn't have the capability to execute mass production or an effective attack. The general concepts of fission were pretty well known even pre-war - it was more of an industrial problem than a conceptual one, in the sense that they would have had to figure out the exact rates/constants involved in fission and the exact technologies/designs needed to cause effective fission, figure out the purification/refining processes and scale them up. The specifics weren't known, but pre-war physicists pretty much understood how to build an atom bomb in principle, looooong before they got their hands on workable quantities of material. Otherwise the US never would have devoted that quantity of expertise and resources.
caf 11y ago
There is also a key insight required for the Plutonium path, which is that Plutonium does not work in a gun-style device - you need to come up with the idea of implosion.
a8da6b0c91d 11y ago
> Niels Bohr dismissed the concept of A-bombs for WWII early on, he thought "you would have to turn the county into a factory". Same thing with breaking enigma and purple. There are some funny contemporaneous enemy quotations floating around about how it would be impossible to break the codes without huge buildings full of computers, which is what was in fact done.

by hga 11y ago

sandworm101 11y ago

I would argue that plutonium breeding is only obvious after you have performed some criticality experiments with an appreciable-sized block of enriched uranium. This was new physics at the time, without computer simulations. Bomb theory, critical mass, could only be understood after you get your hands on some enriched uranium.

hga 11y ago
Indeed, but there's a chick and egg problem there. We put the plutonium process fully in gear before we even knew the average number of neutrons a Pu-239 fast fission would produce, when we had no more than micrograms or so of cyclotron produced stuff. Which was enough to work out the separation chemistry, ultra-microchemisty is amazing. I guess my point here is that the Germans realized uranium separation was a no-go for them, were trying reactor based approaches, and they might have rolled the dice that way and tried the plutonium path. I'm saying the pieces were in play to possible success, not that it was at all likely without 20/20 hindsight.
InclinedPlane 11y ago
This is very much not the case. Bomb theory and critical mass come from a fundamental understanding of neutron chain reactions. You need to have good data on fission properties and neutron mean-free-path distances, but that requires only extremely tiny amounts of Plutonium or natural Uranium, it does not require enriched Uranium. Other than that the other critical factor is coming up with the correct model/theory for nuclear weapons. Something that the Japanese got right, the Americans and British got right, and the Germans (specifically Heisenberg) ended up getting extremely wrong. Fine tuning critical mass calculations was important in optimizing the bomb later on but it wasn't necessary to developing the basic underlying theory of how bombs work or of pointing the way toward implosion assembly and Plutonium breeding.

ufmace 11y ago

Note that the reason why we tried all vaguely practical methods at the same time was that we had no idea which one would turn out to be the best, and we wanted to get the bomb ready ASAP. And of course that we had the resources to do that. It's true that Japan, or some other country, could have built a bomb much cheaper and faster if they used that method alone, but there was no way for anybody to know that. They'd have to be incredibly lucky to happen to guess right the first time, instead of wasting their time going down the wrong rabbit-holes.

paulmd 11y ago

Also you have to remember that by 1944-45 the Japanese economy was a smoking ruin. They'd lost all their overseas territories, we were island-hopping up to their doorstep, and firebombing the shit out of their industrial centers in Honshu. They were incapable of manufacturing sufficient quantities of basic war materiel like rifles, and they could only turn out a very limited quantity of high-end manufacturing like the J2M Raiden and the N1K Shiden interceptor aircraft (which were an known quantity, let alone developing new heavy-bomber type engines like that). Most of that critical production had actually been moved into caves to keep it safe from the firebombing. That's how fucked they were. The idea of them pulling off a Manhattan Project-scale effort - even if they knew exactly what to do - is utterly preposterous. You'd be talking about a very large-scale effort that utilized a great deal of rare resources, energy, and scientific+high-end engineering capacity and it's utterly implausible even if they abandoned everything else. Let alone being able to effectively deliver it in anything except a tactical attack. No heavy bombers, no carrier fleet, no overseas bases? Not gonna happen. Best case is you sneak it into a west-coast harbor with a long-range sub on a one-way trip (if there's one thing that could have made us angrier than Pearl Harbor...). Most likely case you blow it retaking some random island. Worst case, well, they did kinda have the suicide cult thing going on. Now that said they were clearly doing basic research/groundwork on the topic, even if they didn't have the capability to execute mass production or an effective attack. The general concepts of fission were pretty well known even pre-war - it was more of an industrial problem than a conceptual one, in the sense that they would have had to figure out the exact rates/constants involved in fission and the exact technologies/designs needed to cause effective fission, figure out the purification/refining processes and scale them up. The specifics weren't known, but pre-war physicists pretty much understood how to build an atom bomb in principle, looooong before they got their hands on workable quantities of material. Otherwise the US never would have devoted that quantity of expertise and resources.

caf 11y ago

There is also a key insight required for the Plutonium path, which is that Plutonium does not work in a gun-style device - you need to come up with the idea of implosion.

a8da6b0c91d 11y ago

> Niels Bohr dismissed the concept of A-bombs for WWII early on, he thought "you would have to turn the county into a factory". Same thing with breaking enigma and purple. There are some funny contemporaneous enemy quotations floating around about how it would be impossible to break the codes without huge buildings full of computers, which is what was in fact done.