On Sun, 26 Feb 2012 11:57:18 -0600, Tim Wescott
wrote:

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.

Oh, I don't doubt that. I'm not suggesting they just said, "Hey, let's
try this by dropping one on Hiroshima!" g

I still find it remarkable that they relied on those calculations,
when some scientists were still worried that the Earth's entire
atmosphere might go up in a conflagration.

It was a lot of predictive science packed into a short time under
enormous pressure.

--
Ed Huntress