From: Black Unicorn <unicorn@schloss.li>
Date: Fri, 23 Feb 1996 21:04:36 +0800
To: jim bell <jimbell@pacifier.com>
Subject: [Off topic] Re: Easy Nuclear Detonator
In-Reply-To: <m0tpUBd-00098SC@pacifier.com>
Message-ID: <Pine.SUN.3.91.960222191429.9687A-100000@polaris.mindport.net>
MIME-Version: 1.0
Content-Type: text/plain



Way off topic, still....

On Wed, 21 Feb 1996, jim bell wrote:

> At 10:56 PM 2/21/96 -0500, Black Unicorn wrote:
> >On Sun, 18 Feb 1996, jim bell wrote:

[easy nuclear initiation device described, key in design are:]

> >> 
> >> "Multiple very thin flexible hollow tubes (1 mm ID? teflon?) filled with a
> >> homogenous liquid 
> >> explosive (for example, pure nitromethane)

To which I reply:

> >This method is so dependent on the uniformity of the initiator (the cap 
> >in this instance) as to be nearly useless.  Normal blasting caps do not 
> >detonate with the uniformity required to initiate each of the tube paths 
> >at the same time.  In the off chance that you contemplated surrounding 
> >the cap with liquid explosive of a sufficent type, (which still wouldn't 
> >assure proper uniformity with any certainty as the liquid explosive is as 
> >likely to detonate slightly off left to right as up to down) you still have 
> >extremely difficult problems to overcome.
> 
> Re-read my whole statement.  I copy the relevant commentary that you
> sloppily forgot to read:
> 
> >> Detonated from a single cap, with an 
> >> intermediary chamber of liquid explosive to stabilize the shock front,

You, quite inadvertantly I am sure, managed to ignore the following:

> >In the off chance that you contemplated surrounding
> >the cap with liquid explosive of a sufficent type, (which still wouldn't
> >assure proper uniformity with any certainty as the liquid explosive is as
> >likely to detonate slightly off left to right as up to down) you still 
> >have extremely difficult problems to overcome.

And thus boast:

> I already entirely anticipated your objection.  And destroyed it.

Actually, your design still is vulnerable to my objection, as my 
objection was specifically to your intermediary chamber concept.

Your intermediary chamber, if surrounding the blasting cap, is likely to 
detonate to one side first, at a right angle to the axis of the chamber 
to the explosive assembly.  Blasting caps tend to rupture their casings 
on one side before the other.  In this case you will have a left to right 
detonation in the intermediary chamber, as I indicated.  If you have your 
tubes spun off the chamber like a starfish, your initiation times will 
vary, probably significantly.  In the worst case, the duration determined 
by diameter of chamber/velocity of detonation.  In the event your chamber 
is 1/5 of the length of the tubes themselves, you will have one side of 
your explosive assembly detonating when another tube has 1/5 a length to 
go.  As you have not specified any of the dimentions of your chamber or 
tubes, or the exact liquid explosive you intend to use, the delay is 
impossible to quantify exactly.  Attempting to mitigate the delay by 
shortening the tubes brings the explosive assembly closer to the 
intermediary chamber, with associated hazards.  Most problematic, 
disruption of the reflector orientations.

Also note, that if starfished, the worst possible timing error will 
occur, that being, the tubes with the most extreme difference in 
initiation time will be those at opposite poles of the quasi-sphere of 
the explosive assembly.  Bad news for uniform compression.

If you intend to run the intermediary chamber into a funnel before 
seperating into your individual tubes, you have the same problem as if 
you never had a chamber at all, namely the initiation of one or the other 
tubes before the rest.  While the funnel may limit the effect of radial 
differences in initiation timing, it complicates things by requiring 
very precise milling of the connections of the tubes to the intermediary 
chamber as well as such milling at the ends which meet your explosive 
assembly.

> >1>  Interference from the milling shape and accuracy of the openings to 
> >the tubes containing the liquid explosive.
> 
> Quantify, quantify.  How much of a problem?

Clever question given that I am without any information as to the exact 
shape of your tubes, if they are bowled down towards the explosive 
assembly, or what their exact width (excepting your vague 1mm figure) 
might be.  You make some guesses as to material, but these two are fairly 
flimsy even by your own admission.

All you need to realize to appreciate the problem is that if you do not 
have a precisely milled end, with a precise depth into the compressing high 
explosive outer face, you have differences in how and when the various 
faces of the explosive assembly are going to initiate.  If you make your 
tubes narrow, it becomes very hard to mill the ends of your tubes, and if 
you widen the tubes, it exagerates the distortive effect of 
irregularities in the tube ends.

It's very simple, if you don't have a precisely flat end of tube, you 
have a shaped charge in effect.  On the other end, you have problems with 
easy of initiation.

  (Hint:  If you seriously 
> believed there was a problem with this idea, you would be able to give a few 
> examples on how to avoid them.  Reading your commentary, you did none of 
> this.  

I'm not in the business of designing nuclear initiators.  I expose poorly 
thought out explosive engineering as a hobby.  Your best solution is to 
mill each tube exactly alike, right down the the degree of bend and slope 
of arc as well as shape of either end.  But you could have figured that 
out without me spelling it our for you.

> >2>  Mild to obscure impurities in the liquid explosives causing 
> >differences in velocity with respect to other tubes. 
> 
> All the tubes can be filled at the last minute by pulling a vacuum on the
> system and letting atmospheric pressure fill all the tubes.  No impurities,
> or at least it's a perfectly homogeneous mixture.

Hard to prevent with a hydrazine explosive.  Hydrazine based explosives 
may vary as much as 10-15% in velocity of detonation with mere .1% 
changes in pressure and 1% changes in temp.  I don't know how impurity 
comes into play exactly, but I suspect they are very sensitive to such 
changes as well.

> > Even small changes 
> >in pressures within the tubes might cause enough timing problems to make 
> >uniform initiation of the primary high explosive assembly impossible.
> 
> "might"?  Well, could you be more specific?  How many nanoseconds would be
> too many?

What is the mass of your subcritial material?  What shape are you using?  
Simple sphere or multifaceted polygon?  What is the thickness of your 
compressive explosive?  What kind of explosive is it?  How deep are the 
initiators inserted into the compressive explosive?  What is the material 
of your tubes?  Glass or metalic?  (Metalic will be force conductive 
before failure, glass will merely shatter, the difference in initiation 
points in the compressive explosive will be equal to the depth of the 
tubes when comparing glass and metalic tubes.  Glass is likely to 
initiatite at the surface, metalic tubes at the point of tube terminus.

> >3>  Interference from the milling shape and accuracy of the terminus of 
> >the tubes containing the liquid explosive.
> 
> So what's your point?

You might have signifincantly different characteristics in the initiation 
of your compressive explosive.  As I said before, anything but a 
precisely milled flat end on your tubes will effectively be a shaped charge.
The effects of various shapes at the ends of tubes are left as an 
exercise for the reader.

> >4>  Overpressure in the device causing premature detonation of the near 
> >portion of the high explosive assembly.
> 
> Sure about that?

Quite.  It was a big problem in the first compressive devices.  Some 
early experimentation produced mushroom like shapes in the compressed 
material (inert for experimentation) because one side of the compressive 
explosive was initiated by presure of the impact of the casing itself.  
Supercriticality would not have been achieved in these instances of 
failure.
  
Further experimentation attempted to rectify the problem by placing the 
entire inner chamber at .25 of an atmosphere.  I think their eventual 
solution got around overpressure initiation in a simplier way, but I 
don't recall what it was.  (Might have been new explosives for the 
compression phase)

> 
> >All of these might cause enough timing error to prevent uniform pressure 
> >and thus prevent uniform compression and make supercriticality impossible.
> 
> Pigs might fly.

But they don't.  The timing problem is quite significant.  Why do you 
think high speed and superaccurate switches are so well guarded?  There 
isn't an easy grassroots substitute, if there were, the switches would be 
fairly useless.

> >Remember, kryonic switiches are necessary even when dealing with the 
> >speeds of electric conductivity.  The velocities of even hydrazine based 
> >explosives are signigicantly lower.  The margin for error is similarly lower.
> 
> How low?  Be specific.

Again, I don't know what your dimentions are.  Hydrazine explosives tend 
to detonate around 8500-10000 m/s.  The speed of transmission of electric 
impulses through a given conductive medium is certainly much higher.

> >Plutonium gun is still the easiest method for the home grown nuclear 
> >device, even if it requires more fissile material.
> 
> The "gun" design wasn't used with the plutonium, because IT WOULD NOT HAVE 
> WORKED! "Fat Man," the bomb dropped on Nagasaki, used the implosion method.  
> "Little Boy," the gun-method bomb, used U-235.   Plutonium detonates far too 
> rapidly to use the "gun" method.   The 
> scientists knew that in 1945.  You seem to be at least 50 years behind the 
> times.

You are correct this time.  My fault.  Uranium should have been in there.  
Typo on my part.  Doesn't change the fact that it's much easier as an initiator.

> Sheesh!  I guess we now know what field YOU don't know about, huh?  Or, 
> perhaps more likely, this is a specific DIS-information campaign.   You want 
> someone to waste a critical-mass worth of plutonium.   

Hey, be my guest.  If you had a critical mass worth of plutonium you're 
playing around with the wrong list, and, I might add, wasting your time 
with anything but the black market for the material.

---
My prefered and soon to be permanent e-mail address: unicorn@schloss.li
"In fact, had Bancroft not existed,       potestas scientiae in usu est
Franklin might have had to invent him."    in nihilum nil posse reverti
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