On Sun, 26 Feb 2012 10:30:27 -0500, Ed Huntress wrote:

On Sun, 26 Feb 2012 05:28:35 +0000 (UTC), Przemek Klosowski
wrote:

On Fri, 24 Feb 2012 13:34:07 -0500, Ed Huntress wrote:

In talking with people about this over the years I find that few
people know that the Hiroshima bomb was an untried gun-trigger device,
but that the Nagasaki bomb was an implosion device based on the Gadget
used in the Trinity test.

Uranium gun was believed to be so reliable that they felt they didn't
need to test it.

Yeah, but it still seems to be an amazing leap of faith. They hadn't
tested uranium in a bomb, and they hadn't actually used the gun trigger
in a bomb test. That's some confidence in the science, all of which was
still pretty uncertain.

In Feynman's memoirs ("Surely You're Joking, Mr. Feynman"), he talks
about the testing that they did to calibrate their math: they had a sub-
critical ring of fissionable material, and another sub-critical sphere.
They'd drop the one through the other, and observe the neutron flux.

So they may not have actually done a gun-type explosion, but it sounds
like there was a whole lot of due-diligence paid to the whole thing.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com