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.



I find it scary that Iran went for uranium.

Well, there's no other way though: the only way to get plutonium is to
refine it from spent fuel created in a conventional U235 reactor. In
short, neutrons from U235 fission hit the normally inert U238 and convert
it to Pu239 http://en.wikipedia.org/wiki/Plutonium

Right. But producing weapons-grade uranium is a vastly bigger project,
in comparison with using a reactor to produce plutonium.

Again, what seems to be missing in the press accounts is these points:
1) If you have 90%+ enriched uranium, you can make a bomb with a
simple gun trigger that requires none of the sophisticated engineering
of an implosion trigger. After Hiroshima, the whole world knows that
it works.

2) You have to be a little crazy to use a gun trigger unless you have
complete control of everything: a delivery system that allows you to
arm it at the last minute, far from the launch site, etc.

3) The Iranians appear to be a little crazy.

--
Ed Huntress