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.



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.

I'm sure that there are purely mechanical ways of building your gun
mechanism that would put some redundancy in. The one that comes to mind
first would be load a honkin' big round -- cartridge, primer, powder, and
U-235 "bullet" -- that gets automatically loaded into the gun (with
interlocks) and won't do s**t outside of it. Perhaps better, have the
U-235 in the tube, but keep the explosive physically separate until the
minute that it is needed.

But -- the Iranians do appear crazy. Or at least fanatical, which looks
like insanity to anyone who doesn't share their particular brand of
fanaticism.

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