From: utzoo!decvax!harpo!eagle!mhuxt!mhuxa!mhb5b!smb
Newsgroups: net.physics
Title: Re: Any nuke designers out there?
Article-I.D.: mhb5b.270
Posted: Wed Apr  6 22:36:33 1983
Received: Thu Apr  7 07:14:07 1983
References: <832@sri-arpa.UUCP>

Because of the inevitable presence of plutonium 240 (as opposed to the
desired isotope plutonium 239), there's a higher background neutron
density in a plutonium bomb; hence, the "gun-barrel" detonator can't work
fast enough.  This was discovered during the Manhattan Project, and caused
much consternation -- they couldn't get an implosion detonator to work,
but couldn't produce enough U-235 for more than one bomb.  (Source:
"Oppenheimer -- Shatterer of Worlds", by Peter Goodchild.)

		--Steve