At 11:00 PM 2/21/96 -0500, Black Unicorn wrote:

On Mon, 19 Feb 1996, Brian Davis wrote:

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On Mon, 19 Feb 1996, jim bell wrote:

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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?

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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.

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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?)

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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?!?

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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.

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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