ee163cz (04/04/83)
Are there any experienced nuclear warhead designers out there? I would
like a minor point cleared up:
There seems to be a common belief (recently expressed in an article in
the "Opinion" section of the \L.A. Times/, and, so I hear, on that "Special
Bulletin" thing on TV) that nuclear warheads are subject to sympathetic
detonation: that an attempt to destroy a nuclear warhead by violent means,
such as dynamite, will result in a *nuclear* explosion.
It has always been my impression that fission bombs (such as the fission
trigger for a fusion bomb) are marvelously finicky beasts, requiring near-
perfect synchronization of many detonators to get a halfway decent yield
(typically ~20 detonators synchronized to within ~300 ns). This implies that
an asymmetric detonation (any *not* initiated by the firing circuit) would
cause a modest-sized chemical explosion and a nasty great plume of plutonium
oxide, uranium oxide, and (in the case of a thermonuclear bomb) tritiated
water; while hardly good for the health of those downwind, this would be
vastly less destructive than even a small nuclear explosion.
Is this correct? Was it ever tested, back in the good old days of
unrestrained testing? Any further information or comments?
(not (afraid (to use) (parentheses))),
Eric J. Wilner,
sdcsvax!sdccsu3!ee163czfaustus (04/05/83)
I'm no nuke designer, but as I understand it, a bomb made with Uranium (I forget the isotope #) can be detonated very easily, as all you need is a lot of uranium to come into close proximity reasonably fast. But with plutonium, you have to cause the critical mass to be formed much faster as the stuff tends to go off before a chain reaction involving most of the material can begin and it just blows the stuff apart and creates a big plutonium cloud, etc. That is why it is infinitely less difficult to build bombs out of uranium than plutonium. Wayne
DCP@MIT-MC (04/05/83)
From: David C. Plummer <DCP @ MIT-MC> Please have this discussion on some other mailing list.
JGA@MIT-MC (04/05/83)
From: John G. Aspinall <JGA @ MIT-MC>
Date: 4 Apr 83 17:20:56-PST (Mon)
From: faustus (Wayne Christopher) at Ucb-Vax
Article-I.D.: ucbvax.203
In-Reply-To: Article sdccsu3.456
Received: from Usenet.uucp by SRI-Unix.uucp with rs232; 5 Apr 83 2:51-PST
I'm no nuke designer, but as I understand it...
I'm no nuke designer either, but the fast fission cross
sections of U-235 and Pu-239 are similar enough. In BOTH cases, the
super-critical mass has to be assembled pretty fast.soreff (04/06/83)
Also not a nuke designer, but I was under the impression that the assembly time of a plutonium weapon must be much shorter than for a U-235 weapon, not for fast fission cross section reasons, but because of neutron backround reasons. Depending on how long the uranium used to make Pu-239 is irradiated, there will be varying amounts of Pu-240 mixed in with it, and this has a substantial spontaneous fission rate, thus raising the neutron backround. Does anyone out there have any numbers? If a hollow sphere with a radius of ~10 cm is being imploded at a few km/sec (typical for high explosives), the implosion time is going to be 10-100 usec or so. Does anyone know what the typical fraction of Pu-240 in weapons-grade plutonium would be? That, together with the spontaneous fission half life should show how important this effect is. I've been told that natural backround neutron flux is very low, of the order of one per square cm per minute, so if that were the only problem it would be possible to assemble a very supercritical assembly slowly and wait many seconds till the first neutron came along to trigger it. Does anyone out there know if this is true, or completely off the wall? -Jeffrey Soreff (hplabs!hplabsb!soreff)
smb (04/07/83)
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
ld (04/09/83)
Our department once had a seminar on graphics given by an engineer from Lawrence Livermore Lab and he said (paraphrasing): We no longer refer to nuclear weapon engineers as `nuclear weapon engineers'. We now refer to them as `quick release, high energy system engineers'. Larry Dwyer ucbvax!hpda!ld
ee163cz (04/12/83)
THIS DISCUSSION IS NOT GOING IN THE DIRECTION I INTENDED!!!
For those of you who missed it, the original article, 'Any nuke designers
out there?', asked about the possibility of sympathetic detonation of nuclear
bombs. This question has been answered (in the negative, as expected) in two
letters to me; meanwhile, the net.physics discussion is on the subject of
'how to build a bomb', which is most definitely NOT what I asked, so please
don't use Re: <MY article title> to discuss it!
Seriously, there are several of us in netland who know some of the nasty
little details of how to build a nuclear bomb; if we pool our knowledge, we
can probably provide all the necessary information. I don't happen to think
this is a good idea. The BEHAVIOR of nukes is certainly a fit subject for
public discussion; I don't happen to think the detailed DESIGN of them is.
<censored by author>, essential to the construction of a workable bomb,
IS a tricky process, but it is one which could conceivably be accomplished
by a moderately well-financed terrorist group. I don't think we should be
giving them any encouragement and/or information.
Not really as ill-tempered as this makes me sound,
but this worries me a bit,
Eric J. Wilner, sdcsvax!sdccsu3!ee163cz