From: owner-cypherpunks@toad.com
Date: Fri, 23 Feb 1996 02:47:06 +0800
Subject: No Subject
Message-ID: <QQadzy29491.199602221135@relay3.UU.NET>
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At 11:00 PM 2/21/96 -0500, Black Unicorn wrote:
>On Mon, 19 Feb 1996, Brian Davis wrote:
>
>> On Mon, 19 Feb 1996, jim bell wrote:
>> 
>> > it just didn't occur to me that you'd object to this.  "Nettiquette" is new
>> > to me.
^^^^^^^^^^^^^^^^^^ > 
>>   ^^^^^^
>> 
>> No shit.
>
>So, it would seem, is nuclear weapons design.

I wrote this just a few hours ago.  Let's have a vote:  Who thinks I have 
some idea about the subject?


>> A hell of a lot easier, I'm sure!  Multiple krytrons and coaxial capacitors 
>> is WAY too complicated.
>
>I've often wondered why not one circuit and all in series. If you had
>enough juice to fire them all, the exploding wire forms a conductive
>plasma to maintain the circuit. That, as I understand it, is what makes
>them so effective. Is it just a power limitation, or would it be
>impossible to match up the resistances between the wires well enough to
>get the proper timing?

It's probably a partly practical consideration.  For a given (reasonable) 
size of wire, it's going to take a certain amount of current to explode it 
sufficiently rapidly, and that translates into an approximate voltage.  For 
argument's sake, assume that the voltage necessary is 5000 volts.  (I don't 
know what the "real" number is...)  Capacitors of 5000 volts are reasonably 
easily "doable."  However, if you try to hook all those wires together, and 
if you have a couple of dozen trigger locations, that works out to 125,000 
volts total, which is a rather impractically high voltage for "routine" use. 
(to say nothing of the ability to SWITCH such high voltages).   I suspect 
that "parts availability" drives nuclear detonators just as it does most 
more innocuous electronics. 'course, their budgets are a lot higher!

In addition (and this is probably at least as important a reason, if not 
more so),  if you put multiple wires in series, while the current through 
them is equal, the voltage across each one may vary.  Thus, the energy put 
into each wire will also vary, and those where the voltage is higher get 
more power, and get hotter, and higher resistance, and more voltage, and 
more power, etc.

In other words, it's an unstable equilibrium, and this would almost 
certainly lead to a situation where some some triggers happened 
substantially later than the others.  Putting them all in PARALLEL would 
avoid this, sorta, but that has its own problems.

>> That's right, the "lenses" would still be necessary. I'm not clear on what 
>> kind of "transformer" they use to efficiently couple the blast energy into 
>> the dense plutonium;  I would guess that it would be the shock-wave 
>> equivalent of an "anti-reflection coating," which might require a material 
>> with the geometric mean of the mechanical impedance between the detonating 
>> explosive and the plutonium. 
>
>Well, there is a spacer or air gap between the core and "hammer" but
>I've never read what the hammer is made of. This part could be
>simulated in one dimension, and an optimization function used to find
>the best density. 

A few weeks ago, I downloaded a GIF of the H-bomb, and it shows an element 
which it referred to as a "shock absorber" (at the appropriate location)and 
identified the material as graphite.  Graphite is very stiff; a high modulus 
of elasticity (Young's modulus).  But it isn't very dense.  I would imagine 
that the velocity of sound in graphite is about as high as you can get in a 
solid material.  I haven't done any math to determine how effective a match 
this would be, but maybe it doesn't really matter.

Oh, one more thing.  What the lay person (or even the person who THINKS he 
"knows it all", as opposed to US, who do.  <G>!) doesn't realize about bomb
design 
is that the "highest tech" bombs are not the largest, but are in fact the 
SMALLEST bombs.  Chances are good that a Hiroshima-sized bomb was just about 
the smallest that was technically do-able in the 1940's.   I would imagine 
that most of the work that has gone into bomb design in the last 30 years 
has been the technology to develop smaller (LESS explosive power) bombs,  
aside from making them physically small enough to fit in a launch bus.

I forgot about the beryllium.  Beryllium, I understand, is described as a 
"neutron reflector".   Now how GOOD a neutron reflector it is I don't know, 
but if you're trying to make a bomb with the smallest amount of material at 
the primary's core it would help a great deal to have a neutron reflector.  
Presumably, it would be used to coat the inside of the "hammer."  If 
beryllium were a "perfect" neutron reflector, you could use arbitrarily low 
amounts of plutonium or U-235 as the core (analogy:  If you were in a room 
with walls which were perfect mirrors, and "you" were invisible, you would 
see "forever" and the volume of space you were in would appear to be 
infinite), and you could make the core as small as you want.  (But it isn't, 
so the improvement effected by beryllium is limited.)

It might also help to make the "pit" hollow, but I don't know about that.  
This might assist in the mechanical impedance match, too.  If you could get 
the chemical implosion timed  "just right" you might be able to get away 
with using a really THIN layer of plutonium that crashes together at the 
core.  This might provide optimum densification because you would be able to 
accelerate the hollow plutonium sphere centrally at near-detonation-velocity 
speeds, which would result in very effective density increases.

There is also supposed to be a beam trigger in modern bombs.  It ionizes
helium to 
form alphas, which are fired at beryllium targets which releases neutrons at 
"just the right time" to start the compacted core going at just the right 
time.  (More on this if you're interested...)


(BTW, keep in mind as you read what I'm writing that I've never had a nuke-E 
course, never talked to a bomb maker or anyone who ever talked to one (and 
probably never talked to anyone who talked to a person who talked to a 
bomb-maker, etc), have had zero access to classified information of any type 
(including non-nuclear).   So take what I'm saying with a grain of sodium 
chloride.  

Actually, I'm not particularly interested in bomb design anyway, so I really 
don't know why I started this thread?!?  <G>


>Using high-density explosives (RDX/HMX based I would
>think) would provide a better 'impedance match'.

That's probably true, but it's still likely to be a very mismatched system.  
The density of plutonium is really high.  Now we know why computers were so 
important in the 1960's and 1970's to bomb design (and still are, I guess!): 
 Doing a quasi-3 dimensional simulation of the trigger is vastly cheaper 
than actually exploding a bomb, and you can get far more information from 
the simulation as well.  Probably the only reason they kept setting off real 
bombs was to ensure that their mathematics represented reality. (Well, also 
to test the reliability of "working" warheads...)

BTW, a few years ago I heard about a new explosive material, 
octanitrocubane.  If you are familiar with chemistry, you'll suspect from 
the name what it is:  A cube-shaped arrangement of eight carbon atoms, each 
connected to a nitro (NOT nitrate) group.  It has at least two things going 
for it:

1.  It is stoichiometric internal to the molecule.

2.  It has ENORMOUS ring strain, which translates into a dramatically 
greater detonation energy.    It is probably the current record-holder for 
carbon/nitrogen/hydrogen/oxygen explosives, by a long shot.

Its main disadvantage is predictable, if you know any organic chemistry:  It 
is an extremely difficult compound to synthesize, or at least to develop the 
synthesis for.  Thus, it is probably exceedingly expensive.  That means that 
for "ordinary" use, almost any common explosive is better.  This material is 
only going to be practical for the "highest-level" usages of explosives, and 
nuclear detonators are one of these.  Of course, since we're DISMANTLING 
bombs and not building them (at least as much as we used to!) then new 
technology to build bombs isn't  particularly useful.  I'm "sure" Los Alamos 
has probably simulated an octanitrocubane-triggered bomb, for curiosity's 
sake if nothing else.  


>Also, how do they keep the core at the exact center of the air gap?
>Thin wires or pins to hold it there? Or is the "gap" actually some
>Styrofoam-like low-density but rigid material?

The B-28 (?) H-bomb GIF identified this gap as being "vacuum," but we know 
there is no reason to have an actual vacuum there.  In fact, as I have read, 
plutonium "pits" get warm to the touch due to radioactive decay.  If it were 
REALLY put in a "vacuum" it would be so well insulated that it would get 
EXTREMELY hot before radiative cooling equilibrated the temperature.  Since 
air is 99.9% of the way to a perfect vacuum compared to a solid, air (in a 
foam) is plausible, like a harder version of styrofoam.  Plenty of such 
foams exist today.  And it's possible they augment and stabilize the 
position by embedding a few relatively thin carbon rods radially between the 
pit and the hammer.

>Interesting that in 'The Curve of Binding Energy' the author hinted at
>this as in "I can't be specific, but I can say this: if you drive a
>nail, do you put the hammer against the nail and push?" At that time,
>it (the air gap) was still classified. Now it's widely known.

After a while, things become obvious, don't they?

Even so, and even though my "mechanical engineering" background is weak, I 
find it hard to believe that modern technology can't provide some sort of 
"graded impedance" covering that acts like a broadband anti-reflection 
coating.  (the mechanical equivalent to the covering for the Stealth bomber 
and fighter plane.)   The main problem would have been simulating such a 
complex material on a computer, at least in the 1960's.  Something tells me 
they would have pursued this at least theoretically,  perhaps lacking 
anything else to do.

The real problem, it seems to me, is that to do this simulation would 
require a pressure-versus-density curve for plutonium up to nearly a million 
atmospheres.  This is, of course, hard to test, and that is one reason it 
would be useful to have deeper atomic physics background.  Perhaps 
physicists would have been able to estimate such a curve on theoretical grounds.


>In reading about this one gets the feeling that bomb design is as much
>art as science, and that if a reasonably sharp person had the
>opportunity to experiment, with real explosives but not necessarily
>real plutonium, they would get the hang of it after a while.

That's exactly what computer simulation is intended to avoid the need for.  
I'm sure instrumentation is a real headache for the testers.

>Alternatively, a Nuclear Bomb Construction Kit - a freeware program
>that helps you to accurately design and play with simulated bombs -
>would be a very interesting political experiment. Combine this with a
>searchable database of available information on the subject. There must
>be lots of publicly available information that, combined and made
>searchable, would be of considerable help to the prospective
>bomb-maker. That would make one hell of a thesis for someone, if
>nothing else.

But not for me.  I have no "nuke E" credentials, and don't enjoy 
programming, and I'm busily working on my "Assassination Politics" debate.  
(which, incidentally, will (I believe) force the dismantling of all nuclear 
weapons in the world, if you've followed the debate, as well as eliminating 
all wars and militaries and governments.  Tell me, who do you think will win?)


>> You're pretty sharp; the version I've read is that amines (substituted 
>> ammonia, but possibly ammonia as well) makes nitromethane 
>> supersonic-rifle-bullet sensitive, but just barely.  Haven't tried this, 
>> however.  I would imagine that a blasting cap would set off pure 
>> nitromethane with no amine contamination at all.
>
>Let's see: Nitromethane and sawdust gives you a medium-power explosive
>that requires a compound detonator. 

Why put it in sawdust?  The only reason I can think of is to keep it from 
flowing like a liquid.  Nitromethane is "oxygen-poor" to start out with.

>Nitromethane with ammonium nitrate
>gives you "a direct substitute for TNT" which can be set off with a
>blasting cap.

Easily.  And even better, ammonium nitrate is "oxygen rich" so tht you can 
get efficient use of the nitromethane.  A 2-1 mixture by weight (AN, 2,
nitromethane, 
1) is stoichiometric, as I recall.  They are not miscible in all 
proportions, however, so you'd have to settle for a finely-powdered slurry.

That's why I specified a HOMOGENOUS liquid as the tube-filler.  At least 
that way you know it's a consistent mix, as opposed to a slurry which would 
settle.


>) The liquid if sensitized can be detonated with a blasting
>cap but a compound detonator produces higher velocity. They claim that
>nitromethane won't detonate in its pure state,

I doubt this.  I'll test it, however, within the next year or so.

> but if sensitized is more powerful than TNT.

That wouldn't be surprising.  TNT is EXTRAORDINARILY 'oxygen-poor.'  It's 
about as far as you get from being an "efficient" explosive. 

>Nitromethane is used for racing fuel and other high-volume purposes,
>and must be transported in tanker-truck quantities. If someone wanted
>to make a very large conventional bomb quickly, such a truck is about
>as close as you get to a ready-made bomb. It could be ready within
>hours after the truck was hijacked.

Hours?  Aw, C'mon!  Minutes!  Maybe even 60 seconds.   The biggest 
impediment is figuring out how to open the tank, but even that could be 
avoided by drilling through the wall with a self-sealing "screw" assembly, 
one that would drain a bit of liquid into a detonator channel...    These 
tankers are probably usually made either of aluminum or stainless steel, and 
they could probably be pierced comparatively easily with a screw or a 
pointed  probe, or even a drill arranged to seal after the flukes had 
pierced. (Makita's are REALLY useful!) Drilling aluminum is easy; drilling 
stainless steel's normally a bitch because it work-hardens, but you're not 
looking for a pretty result so you'd just design with a nicely-sharpened 
carbide tip (a little work with a masonry bit and a sacrificial grinding 
wheel will work wonders) and be prepared for anything up to and including 
tool steel.  The hole would only have to be 1/8" or even smaller (or maybe 
not even necessary, triggering through the wall is certainly possible, too, 
but it would require more than a lowly cap.) and you can apply enormous 
forces to a short drill bit.

>
>If you had more time to kill, so to speak, mix it with a larger
>quantity of ammonium nitrate to get a lot more bang for your buck.

I don't think it would be worth it.  If the tanker was full, you'd merely be 
replacing one fair explosive with another, and it would take a lot of work 
to grind up the AN and mix it with the contents of the tank.   You'd be 
wasting time, risking the operation of an anti-highjacking alarm system,  
and risking detection and leaving evidence of intent.  Just highjacking the 
truck, later followed  by a huge explosion, would "leave 'em guessing" about 
what really happened.

I guess the world is fortunate I'm not into this sorta stuff, huh?!?


>> > I'm not sure what the
>> >minimum cross-sectional area is for a proper detonation.
>> 
>> That's a good question; I really don't know.  It ought to be rather low for 
>> a liquid explosive, but when the opportunity presents itself I'll do my own 
>> experiments.
>
>What would be the simplest way to compare relative arrival times
>between two tubes? Since the result of an explosion is a plasma,
>electrodes placed in the tube at the far end should become conductive
>as the wave reaches them. So a dual channel oscilloscope, with the
>sweep triggered as the cap is detonated, should be able to compare the
>propagation through two tubes detonated by the same cap.

Me, I'd do it digitally.  Set up a master 100 MHz clock, for 10 nsec time 
resolution, feed it to a master counter made up of modern 74ACXXX 
synchronous counters, then take the count chain and buffer it into a bus 
connected to a slew of edge-triggered latches, with appropriate amplifiers 
and  extra circuitry to guard against double-clocking.  You could connect up 
as many latches as you wanted, fed from various points in a triggered 
system.  ("fanout limited," but then again, multiple buffering is easy to 
do, as well.)   "All" the data could be taken in one shot, maybe.  Dozens or 
even hundreds of locations.

I'd test simultaneity after multiple long lenths of parallel fine tubing, 
variations in velocity with diameter, effect of curvature, everything.  One 
"bang" and I'm done.  It would be easy to measure the detonation velocities 
of the "lens" explosives as well, probably to well under 0.1% accuracy.  (I 
wonder if nitromethane could act as one of them?!? Would it dissolve or 
weaken a solid explosive?  Can a solid explosive with a "compatible" 
detonation velocity be found?)

I only have a fair background in optics, but since the principle of the 
lensing effect is general it should be easy to figure out what the shape of 
the lenses would be.  Casting the lenses is probably the technique I'd use, 
since surprisingly enough most nitrated organic explosives will melt long 
before they might be inclined to explode.  TNT, for instance, has long been 
poured as a liquid into artillery shells, melted in steam-jacketed kettles.

At least four molds would be necessary:  Pentagonal and hexagonal versions 
of the inner and outer explosive.

>> Again, that's a matter I'm unsure of.  Part of the reason I specifi
ed THIN 
>> tubing is so it "appears" to be linear, from a detonation-velocity point of 
>> view.  All of this should be easily measureable, however.  I'd probably 
also 
>> want to measure the relative velocity in two different-sized tubes, to find 
>> out if there is a significant difference that could be exploited or avoided.
>
>This would be fun to play with, and the kind of thing the government
>would not like to see written up. Measure the speed versus tube
>diameter and radius of curvature. If radius has a significant effect,
>things get complex.

True, but I suspect that the variation is going to be smaller than is 
significant, or at least it can be measured and compensated for.  Chances 
are that "military-grade" accuracies are straightforwardly possible.

BTW, feel free to keep and forward this note to anyone you feel would be 
interested in this information.  I'd appreciate getting confirmation or 
corrections, for curiosity's sake if nothing else.


Jim Bell
jimbell@pacifier.com