From hotrod@Dixie.Com Sun Jan  2 19:41:00 1994
Subject: Re: depleted uranium
From: hotrod@dixie.com (The Hotrod List)
To: hotrod@dixie.com
X-Sequence: 7287
X-Archives: ece.rutgers.edu

-> Yes, depleted Uranium is used in aircraft as counterweights.  Why
-> does that seem strange?

 Weight, mainly.  It seems to me that any control surface needing
counterweights to function would be poorly designed to start with.  But
I guess that's a topic for an airplane list.

Tungsten is some ferociously expensive stuff and hard to work too.  On
the other hand, I don't know that depleted uranium is good for anything.
I wondered if it might be less expensive than tungsten, but John says
it's pretty hard to get.  

[It's not hard to get per se, it just requires a license because it is a
component of THE BOMB.  Uncle Sammy doesn't particularly want to sell U
to people who want to make mushroom clouds.  There's a BUNCH of depleted
uranium around as the result of the weapons programs.  After all, the
U-235 content of natural uranium is only about 0.3 to 0.6% of the whole.
A bit of it is used as tampers and breeding blankets in nuclear weapons
and a bit more is used in nuclear reactor fuel but the bulk of it just
sits around in DOE storage facilities.  So once the license is procured
(and who worries about spending $500 on getting a license for a
bazillion dollar aircraft?), U is plentiful and cheaper than equivalent
heavy materials such as tungsten.  It has a few pesky properties such as
being pyrophoric which means it must be machined in an argon atmosphere
(it burns readily in nitrogen), it is harder'n hell which makes
machining difficult, and it tends to corrode, though a flash of nickel
handles that OK.  JGD]

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Posted by: emory!chaos.lrk.ar.us!dave.williams (Dave Williams)
 


From hotrod@Dixie.Com Mon Jan  3 17:37:12 1994
Subject: Re: depleted uranium
From: hotrod@dixie.com (The Hotrod List)
To: hotrod@dixie.com
X-Sequence: 7290
X-Archives: ece.rutgers.edu


-> component of THE BOMB.  Uncle Sammy doesn't particularly want to sell
-> U to people who want to make mushroom clouds.  There's a BUNCH of

 Waitaminnit.  High school physics was long ago, but I thought the
normal uranium was pretty well worthless; ie only the fancy stuff would
fizz?

[Unfortunately, most of what is common knowledge about atomic bombs is
wrong and is the product of the government's rather intense disinformation
campaign.  Here's a quick summary:

For weapons under about 3/4 megaton and excluding subsurface, deep
penetrating weapons, the typical design is the so-called "boosted implosion"
design.  This design uses multiple spheres of plutoninum surrounded by
high explosive and tamped with either natural or depleted uranium.  When
the weapon is detonated, the high explosives are fired to implode the 
plutonium.  After implosion but before the initiation of the chain reaction,
a small quantity of tritium/deuterium gas is injected under several thousand
pounds of pressure into the core.  Then an external neutron howitzer is
fired to initiate the reaction.  The fission completes in a few nanoseconds
and the conditions in the center of the pit are such that the 
tritium/deuturium undergo fusion reactions. (NOTE: this is NOT a hydrogen
bomb - little to no yield results from this.)  The fusions supply a very
intense flux of fast neutrons which then fast fission the natural uranium
blanket.  All this happens before the weapon casing disassembles.  Typically,
about 40% of the energy release is from the pit, up to perhaps 2% is from
the fusion booster and the rest is from the fission of the blanket/tamper.
BTW, for anyone who read Clancy's "Sum of all Fears", the mechanism of
tritium boosting is one of those details he intentionally mucked up
in order to assuage his conscience.

The basic hydrogen bomb consists of a small boosted fission trigger
stacked atop a cylinder of Lithium Deuteride (LiD).  A thick natural
uranium disk shields the LiD assembly from the thermal effects of the 
trigger.  A hole in the center allows neutrons through.  The center of
the LiD is filled with a plutonium rod.  The whole assembly is suspended
with dense rigid foam inside a thick walled natural uranium cylinder 
that serves as both a tamper and an X-ray reflector.  When the weapon is 
detonated, the bulk of the trigger's energy is released as soft X-rays.
These X-rays travel outward at the speed of light (the explosive effects
are over 10X slower).  They strike the walls of the tamper and spall off
an intense plasma, a plasma so dense that it will exert millions of psi
of pressure on anything it strikes.  At the same time, neutrons traveling
at about half the speed of light stream through the hole in the shield
and initiate bulk fission in the plutonium core of the LiD fusion cylinder.
The spacing is such that the Pu fission and the plasma wave arrive at the
LiD cylinder at the same time.  The plasma compresses inward and the 
fission reaction compresses outward while simultaneously the neutrons
liberated from the fission transmute the Li in the cylinder to tritium.
This compression initiates fusion in the (formerly) LiD cylinder.
The bulk of the energy released in this reaction is fast neutrons which
proceed outward and fast fission the natural uranium tamper/blanket.
This "single stage" design is good for up to about 1.5 megaton.
About 15-20% of the yield comes from the initiator, about 30-40% from
the fusion reaction and the rest from the fission of the tamper.
This design is sometimes referred to as a "fission-fusion-fission" device.

For higher yields, the fusion pits are simply stacked so that the first
one servers as the initiator for the second and so on.  Both our and
the Soviet high yield (up to 10 megaton) weapons are 3 stage weapons,
that is, three LiD fusion assemblies.  Oh, and to answer a common
question, the Dial-A-Yield facility, whereby the weapons officer
can select the bomb's yield before delivery, simply varies the 
amount of Du/T injected into the trigger.  This varies the yield
of the trigger which varies the yield of the fusion package, etc.

More modern designs use X-ray mirrors to focus the energy from much smaller
yield triggers on the LiD fusion package.  How these mirrors are made
are still highly classified so I can't talk about it.  Probably freely
available in the literature, however :-) JGD]

-> (and who worries about spending $500 on getting a license for a
-> bazillion dollar aircraft?), U is plentiful and cheaper than

 I've seen Mallory metal priced at $50 to $100 per inch for 1" bar.
If you ran a crank shop you'd use a lot of stuff doing strokers,
internal balancing, etc.  Does the license restrict what you do with the
metal?  Specifically, would it prohibit selling cranks with slugs of
uranium in them?

[Yes, the license requires you to account for any SNM you might possess.
The auditing process is commonly referred to as Safeguards.  Several
companies, D.S. Davidson among them, make portable Safeguards monitors
whereby an inspector can examine a cache of SNM and by analyzing the 
gamma ray spectrum with some proven heuristics, can determine with
great accuracy how much SNM is present.  If you built a crankshaft
using an SNM as a balancing weight, your customer would also have to
be licensed and would have to submit to Safeguards.  That means 
that when the engine blows up and the U burns up, he's gonna have to
account for where it went.  If you observe that this is structured
to discourage ownership of said material, you would be correct.  JGD]

-> heavy materials such as tungsten.  It has a few pesky properties such
-> as being pyrophoric which means it must be machined in an argon
-> atmosphere (it burns readily in nitrogen), it is harder'n hell which
-> makes machining difficult, and it tends to corrode, though a flash of
-> nickel handles that OK.  JGD]

 My Machinery's Handbook doesn't mention all that neat stuff.  <grin>
Seriously, is it more likely to catch fire than aluminum or magnesium?
Would directing argon at the cutting edge be sufficient, or would it
require a chamber, like welding titanium?

[More likely.  Uranium is really strange stuff.  Plutonium even more so.
There are a pair of thick books still in print called "The Metallurgy of 
{Uranium, Plutonium}" that detail all the weirdnesses.  Both metals
exist in numerous allotropes and the transition from one to the other
can be fairly energetic.  I don't know if an argon purge on the 
cutting tool would be enough or not.  I do know that the government's 
machining centers that I've seen are contained either in argon glove boxes 
or in tents.  JGD]

 I never considered corrosion, but I guess you're right, since uranium's
"natural" form is an oxide.


 Considering the way today's safety nazis act, half the government would
probably shit bricks if someone actually used uranium in a crank, but I
have this curiosity problem...
                           
[Me too :-)  For strictly practical reasons, I'm not sure I'd want to 
try to use U.  I have a small square of depleted U.  This stuff is 
as hard as a rock.  A carbide scribe will mar the surface but not much.
About the only way I've found to cut it is to fracture off a chunk and
even that takes some effort.  Nuclear properties aside, it is not a friendly
metal.  JGD]
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Posted by: emory!chaos.lrk.ar.us!dave.williams (Dave Williams)
 


From hotrod@Dixie.Com Tue Jan  4 15:43:08 1994
Subject: Re: depleted uranium
From: hotrod@dixie.com (The Hotrod List)
To: hotrod@dixie.com
X-Sequence: 7298
X-Archives: ece.rutgers.edu

JGD:

>Unfortunately, most of what is common knowledge about atomic bombs is
>wrong and is the product of the government's rather intense disinformation
>campaign.  Here's a quick summary:  [surprising burse of knowledge deleted]

  John, I'm surprised you haven't applied this knowledge to the old
Lawnmowers From Hell thread.  Bet you could come up with one hell of
a stump chewer ;) .

  Ron "Well, I Enjoyed It Anyway" Rader

[ :-)  Well I always have regarded nukes as simply hotrod firecrackers :-)
Only problem is getting and keeping the goodies.  I once worked on a 
helicoptor-borne instrument used by NEST that could detect a kg of plutonium
in a 100 ft deep well while the helo was flying over the area at full tac.  
I figured that I'd never have the opportunity to collect a critical mass
or live to tell about it.  On the other hand, what a show it would be!
Imagine my little firecracker set off in front of 1600 Pennsylvania Avenue :-)
JGD]
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Posted by: emory!bbt.com!rlr (Powdered Toast Man)