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points by rjsw 4 hours ago | 0 comments
The US built a reactor first too [1], followed by others [2] as part of the Manhattan Project.

[1] https://en.wikipedia.org/wiki/Chicago_Pile-1 [2] https://en.wikipedia.org/wiki/Hanford_Site

[–] defrost 4 hours ago
In the context of the time, those US scientists that built a reactor were all in for nuclear energy and absolutely 100% did not think that a nuclear weapon was economically feasible.

"Economically feasible" meaning maybe, perhaps, theoretically possible but even if so astronomically expensive in time, money, and physical resources.

It took the UK/CA/AU Tube Alloys group to find ways to make a weapon more practical, and multiple letters, attempts, and a one on one press the flesh tour to convince the US nuclear types that a weapon was both possible and achievable.

[–] bluGill 4 hours ago
If you go to the Los Alamos Science Museum you can see an original letter from Albert Einstein where he proposed that a nuclear bomb could be fit on a ship and sailed into harbor in 1938. A ship-sized nuclear bomb was not of interest to President Roosevelt at the time for a likely good reason. It's only when the UK realized that it wasn't a ship size. It was something that you could drop from a conventional airplane bomber of the day that the US became interested.
[–] defrost 3 hours ago
Seen it, read it, and aware of why it was ignored at the time - the ability to make such a weapon, as relayed by Einstein, was a hearsay tale of speculation.

Some time later Mark Oliphant visited the US in person and walked key people through a circles and arrows on chalkboard breakdown of how such a thing would be actually possible.

[–] lazide 3 hours ago
It was also a failure of imagination. A ship sized tsar bomba at the time would still be quite interesting - armor the ship like a Iowa class (or more), and give it an automated navigator (very doable at the time, plus or minus a mile or two), and it’s a war ender.
[–] gonzalohm 3 hours ago
And sail the ship into Berlin?
[–] lazide 3 hours ago
Wait until the wind is right, add some of the right contaminants, and you wouldn’t need to do so to poison all of Germany for at least a generation.

Also, Tokyo Bay.

For the Axis powers, it would be an even easier sell of course.

At least if any of them could believe - or even imagine - that it actually could exist or be as devastating as it was of course. And frankly, unless you saw the footage of an actual Tsar Bomba, how could anyone?

[–] defrost 3 hours ago
Footage of the actual Tsar Bomba has no scale, detonating as it did high up in the atmosphere - for anyone watching it might have been a really big or really small explosion.

For the first bomb ever made to immediately jump to Tsar Bomba size, or for it to utilise an understanding of fallout and contaminants that didn't exist prior to the Castle Bravo tests seems ... unlikely.

[–] chasil 3 hours ago
The plutonium bomb was vastly more difficult to design than the uranium version.

Were both judged infeasible for different reasons? Perhaps uranium purification challenges and the implosion required for plutonium?

[–] defrost 3 hours ago
In general the take was that human created nuclear weapons were infeasible (regardless of design) because of what was thought to be the barrier to cross to achieve a chain reaction.

The Frisch–Peierls memorandum changed that understanding ... provided that reading of the FP-memorandum was convincingly conveyed to people that made things happen, what Einstein put to paper (and was ignored) and that Oliphant pushed through in person.

Little Boy on Hiroshima was a gun design, a grossly inefficient McGyver that used some 64 kilograms of enriched uranium to successfully convert less than half a gram to energy.

Fat Man on Nagasaki was an implosion device - a necessary design change due to simply not having enough uranium or an enrichment pipeline to sustain the needs of a gun design.

The first device detonated, at Trinity in the USofA, was an implosion device, created to test the more difficult design.

Further, there was an abandoned / discarded "Thin Man" device IIRC.

These were all alternative implementations that were pursued after the FP-memorandum was pushed about to make the case that weapons were apparently possible rather than not yet achievable - the prevailing belief in the US prior to Oliphant doing the rounds.

[–] rjsw 3 hours ago
Trinity and Fat Man were plutonium bombs, they needed to be implosion designs because it was realized that a gun wouldn't work using plutonium [1].

[1] https://en.wikipedia.org/wiki/Thin_Man_(nuclear_bomb)

[–] defrost 3 hours ago
As I said above - and perhaps you might like to try a primary source rather than wikipedia ?

  These weapons were, however, as different as their monikers imply. Little Boy was a uranium, gun-type weapon, whereas Fat Man was a plutonium, implosion-style weapon. Two types were needed because there was only enough uranium for one gun-type weapon, and the U.S. government knew it would need to make more than one weapon.
~ Los Alamos Nuclear Lab https://www.lanl.gov/media/publications/the-vault/1023-a-tal...