Re: Nuclear Weapons Material

In message <paBMkOwscIgG070yn@io.org> Mark Terka writes:
> Not to mention the fact that without tritium, the "trigger" for nuclear
> weapons (and extremely expensive and rare at $ 100m a gram) all you have
> is a radioactive paperweight.

To the best of my knowledge, tritium is not used in nuclear weapons
(meaning A-bombs), only in thermonuclear weapons (H-bombs).  One of
my teachers was involved in the Manhattan project; he never mentioned
any need for tritium.
--
Jim Dixon

At the risk of pushing this even further from cryptography, I should
say that tritium is used in the "boosting" of *fission* weapons. A
mixture of tritium and deuterium is injected into the exploding
fission core to increase the "alpha" (neutron multiplication "gain")
of the system.  The D-T thermonuclear reactions themselves contribute
relatively little energy, but the increase in fission efficiency can
be dramatic.

Thermonuclear boosting was the second major improvement made to US
fission weapons after WWII. The first was the "levitated pit", a gap
between the conventional explosive/tamper assembly and the fissile pit
to allow the former to gain significant momentum before slamming into
the latter.

Both techniques result in considerably more efficient use of fissile
material, but are not absolutely necessary to make a usable weapon (as
shown at Hiroshima and Nagasaki). I believe the simple uranium gun
used at Hiroshima only fissioned a few percent of its U-235. Fat Man
did better, but not that much.

Phil

> At the risk of pushing this even further from cryptography, I should
> say that tritium is used in the "boosting" of *fission* weapons. A
> mixture of tritium and deuterium is injected into the exploding
> fission core to increase the "alpha" (neutron multiplication "gain")
> of the system.  The D-T thermonuclear reactions themselves contribute
> relatively little energy, but the increase in fission efficiency can
> be dramatic.

Been reading our Tom Clancey, have we?  <grin>
-- 
Ed Carp, N7EKG    			Ed.Carp@linux.org, ecarp@netcom.com
Finger ecarp@netcom.com for PGP 2.5 public key		an88744@anon.penet.fi
If you want magic, let go of your armor.  Magic is so much stronger than
steel!        -- Richard Bach, "The Bridge Across Forever"

>Been reading our Tom Clancey, have we?  <grin>

No, actually I have yet to read my first Clancey novel, though I did
see Hunt for Red October.

My information comes from "US Nuclear Weapons" by Chuck Hansen, Orion
Books, 1988. ISBN 0-517-56740-7. I wouldn't be surprised if Clancey
used the same source -- Hansen is the guy who wrote the open letter
that sabotaged the government's case in US vs. Progressive back in 1979.

Now can we return to cryptography? How about a discussion of fast
modular exponentiation algorithms, something we (or at least I) can
put to more immediate and constructive use than nuclear bomb designs?

Phil

Phil Karn says:
> Now can we return to cryptography? How about a discussion of fast
> modular exponentiation algorithms, something we (or at least I) can
> put to more immediate and constructive use than nuclear bomb designs?

Indeed.

I've been wondering recently, by the way, about what advantages doing
some of this stuff on DSPs might have. DSPs are not magical chips, but
they are optimized for a few tasks, including, typically, fast integer
multiplies. IDEA and modular exponentiation both require lots of fast
integer multiplies. Would it make sense to use DSPs as co-processors
to things like Pentiums to speed up these processes?

Phil? You are the resident expert on DSPs, I believe...

Perry

I'm not really an expert on DSPs, but it does seem like they should be
good for modular exponentiation given the number of multiplies required.
But I don't think I'm the first to point that out.

I think I already said that it looks like fast multiply performance is
going to be crucial for secure communications. Modular exponentiation
for public key algorithms, modulo-65537 multiplies in IDEA, and the
many DSP multiplies in CELP speech coding, just to name three.

I recently heard of a FED-STD-1016 CELP implementation that runs in
better than real time on the PowerPC. It runs in much worse than real
time on just about everything else. The PowerPC's multiply performance is
clearly the reason.

Phil

Phil Karn <karn@qualcomm.com> writes:
>Now can we return to cryptography? How about a discussion of fast
>modular exponentiation algorithms, something we (or at least I) can
>put to more immediate and constructive use than nuclear bomb designs?

In the Crypto 93 proceedings, there is an article by Bosselaers, Govaerts,
and Vandewalle comparing the speed of three algorithms for modular reduction
which is the main time-consuming step in modular exponentiation.  They
compared the classical algorithm from Knuth, a modification to it by Barrett
which speeds up the estimate of the first digit of the quotient, and 
Montgomery multiplication (which is inherently modular).

Montgomery was the fastest for taking 1024 bit numbers modulo 512 bit
numbers, but not by a lot.  For exponentiation, though, where the reduction
happens a lot, Montgomery was fastest for all but the very smallest exponents.
512 bit exponents took  about 2.93 seconds for the classical algorithm,
2.85 seconds for the Barrett improvement, and 2.55 seconds for Montgomery.
The crossover point (below which Barrett is best) is exponents of about 32
bits.

So, Montgomery multiplication was best, but the percentage improvement is
not that large.

Sometimes, as I mentioned yesterday, you can restrict the size of the exponents
without losing security (as in DSS), but it depends on the algorithm.

Hal

An interesting discussion. Thanks.

How about a basic tutorial on these various modexp algorithms, with
particular attention to how many of each arithmetic operation
(add/subtract/multiply/divide) are needed as a function of the modexp
input parameter sizes?  I don't really understand all the details yet,
especially how they relate to which algorithm is best for a given
machine.

I.e., if I come up with a list of clock counts for each basic
arithmetic instruction, how can I tell which algorithm is probably
best for my machine?

Phil

> An interesting discussion. Thanks.
> 
> How about a basic tutorial on these various modexp algorithms, with
> particular attention to how many of each arithmetic operation

I want to tie this in to that other hot Cypherpunks topic: Pretty Good
Nukes.

Even though the topic is nearly depleted, and the sabots have jammed
the list machine pretty thoroughly, how much faster would a fast
modular exponentiation go if the inner loops were encased in a layer
of deleted unobtainium?


--Klaus! von Future Prime

On Tue, 23 Aug 1994 khijol!erc@apple.com wrote:

> > At the risk of pushing this even further from cryptography, I should
> > say that tritium is used in the "boosting" of *fission* weapons. A
> > mixture of tritium and deuterium is injected into the exploding
> > fission core to increase the "alpha" (neutron multiplication "gain")
> > of the system.  The D-T thermonuclear reactions themselves contribute
> > relatively little energy, but the increase in fission efficiency can
> > be dramatic.
> 
> Been reading our Tom Clancey, have we?  <grin>

  I would recommend 'The Secret that Exploded' by Howard Morland

  Describes H-Bombs in a language that we can all understand.

  Brian

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> 
> In message <paBMkOwscIgG070yn@io.org> Mark Terka writes:
> > Not to mention the fact that without tritium, the "trigger" for nuclear
> > weapons (and extremely expensive and rare at $ 100m a gram) all you have
> > is a radioactive paperweight.
> 
> To the best of my knowledge, tritium is not used in nuclear weapons
> (meaning A-bombs), only in thermonuclear weapons (H-bombs).  One of
> my teachers was involved in the Manhattan project; he never mentioned
> any need for tritium.
> --
> Jim Dixon

I agree.  Fission bombs I thought just needed shaped metal with a
conventional charge to force compression and make it go critical.

Fusion bombs I thought used tritium as fuel and needed a Plutonium
trigger or something.  They are supposedly set off with some kind of
inner mirrored ball with high powered lasers.  Fission then fusion I
believe.


sdw
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Stephen D. Williams says:
> Fusion bombs I thought used tritium as fuel and needed a Plutonium
> trigger or something.

Sort of.

> They are supposedly set off with some kind of
> inner mirrored ball with high powered lasers.

No. A reality check would tell you that H bombs preceeded the
development of the laser by many years.

H Bombs use a fission reaction to compress and heat the hydrogen or
other fuel until it begins to undergo fusion.

Perry

> 
> Fusion bombs I thought used tritium as fuel and needed a Plutonium
> trigger or something.  They are supposedly set off with some kind of
> inner mirrored ball with high powered lasers.  Fission then fusion I
> believe.
> 

	The plutonium trigger is set off using conventional explosives
to implode a hollow sphere of the material. While this technique is
superficially similar to the gun-type triggering used by U-235 fuelled
bombs, the geometry prevents the Pu-239 from fissioning prematurely.
	The tritium is used as a neutron source - it releases neutrons
when sufficiently motivated to do so.

-- 
*       *       Mikolaj J. Habryn
                dichro@tartarus.uwa.edu.au
    *           "I'm just another sniper on the information super-highway."
                PGP Public key available by finger
    *           #include <standard-disclaimer.h>

Mikolaj Habryn says:
> > 
> > Fusion bombs I thought used tritium as fuel and needed a Plutonium
> > trigger or something.  They are supposedly set off with some kind of
> > inner mirrored ball with high powered lasers.  Fission then fusion I
> > believe.
> 
> 	The plutonium trigger is set off using conventional explosives
> to implode a hollow sphere of the material. While this technique is
> superficially similar to the gun-type triggering used by U-235 fuelled
> bombs, the geometry prevents the Pu-239 from fissioning prematurely.
> 	The tritium is used as a neutron source - it releases neutrons
> when sufficiently motivated to do so.

In a fusion, or H Bomb, the tritium (which is just hydrogen with an
extra two neutrons) is that which produces the boom -- the main fuel,
as it were. Its a "neutron source" only in the weakest possible sense
-- the same way dynamite might be considered to need nitroglycerine as
a "neutron source". (I'm not sure that people outside of the bomb
building industry really know *for sure* what the geometries used in
the atomic weapon that sets off the fusion reaction.)

Perry

> In a fusion, or H Bomb, the tritium (which is just hydrogen with an
> extra two neutrons) is that which produces the boom -- the main fuel,
> as it were. Its a "neutron source" only in the weakest possible sense
> -- the same way dynamite might be considered to need nitroglycerine as
> a "neutron source". (I'm not sure that people outside of the bomb
> building industry really know *for sure* what the geometries used in
> the atomic weapon that sets off the fusion reaction.)

I don't understand your point.  The earliest devices used a pie shape 
with a wedge cut out.  The actual geometry is rather unimportant to 
getting a fission reaction - but it *is* important if you want to 
maximize your yield.
-- 
Ed Carp, N7EKG    			Ed.Carp@linux.org, ecarp@netcom.com
Finger ecarp@netcom.com for PGP 2.5 public key		an88744@anon.penet.fi
If you want magic, let go of your armor.  Magic is so much stronger than
steel!        -- Richard Bach, "The Bridge Across Forever"

Ed Carp [Sysadmin] says:
> > In a fusion, or H Bomb, the tritium (which is just hydrogen with an
> > extra two neutrons) is that which produces the boom -- the main fuel,
> > as it were. Its a "neutron source" only in the weakest possible sense
> > -- the same way dynamite might be considered to need nitroglycerine as
> > a "neutron source". (I'm not sure that people outside of the bomb
> > building industry really know *for sure* what the geometries used in
> > the atomic weapon that sets off the fusion reaction.)
> 
> I don't understand your point.  The earliest devices used a pie shape 
> with a wedge cut out.  The actual geometry is rather unimportant to 
> getting a fission reaction - but it *is* important if you want to 
> maximize your yield.

We aren't discussing fission bombs. Please reread.

.pm

>We aren't discussing fission bombs. Please reread.

Sigh. At the risk of furthering a way-off-topic discussion, I should
elaborate on what I said earlier. My understanding is that the tritium
produced for nuclear weapons is used only to "boost" the *fission*
reactions in the "primary" that is in turn used to trigger the main
fusion reaction in the "secondary".

Although the main fusion reaction in a thermonuclear device *is*
between tritium and deuterium, the much larger quantities of tritium
needed for this stage are produced during the actual detonation by
neutron irradiation of lithium-6. That's why lithium-6 deuteride is
used as the fusion fuel.

Once again, these materials are distinct from the small amounts of
gaseous tritium and deuterium used in the fission boosting stage.

To summarize the steps (page 22, "US Nuclear Weapons" by Hansen):

1. High explosives detonate and compress the fission fuel in the primary.

2. At the right moment, neutrons are injected from an external
generator to start the chain reaction.

3. Small amounts of gaseous tritium and deuterium are injected into
the exploding fission core to boost the fission reaction, resulting in
much more rapid and complete fission.

4. X-rays from the exploding primary, traveling at the speed of light,
are focused onto a physically separated "secondary", the fusion fuel
assembly, rapidly compressing and heating it by radiation pressure.
Physical separation is essential to give the secondary time to react
before the exploding primary physically blows it apart. *This* is the
"breakthrough" that Ulam came up with that made the H-bomb practical;
before then, Teller had wanted to simply pile deuterium closely around
an A-bomb, which clearly wouldn't work.

5. At the center of the rapidly imploding *secondary* is a "sparkplug"
of fissionable material. Neutrons from the primary cause this material
to fission, producing even more neutrons that breed large amounts of
tritium from the lithium-6 in the fusion fuel.

6. The newly produced tritium fuses with the deuterium in the main
fusion reaction.

7. Fast neutrons from the fusion reaction may then fission a jacket
of U-238 (yes, U-238) surrounding the secondary, producing an even
greater yield using material that would otherwise be useless.

8. Additional fusion stages may then react (if present).

As you can see, the fission and fusion reactions in a modern
thermonuclear weapon are very closely interwined.

Just to bring this back somewhat to cryptography, an interesting topic
for speculation is the operation of the "permissive action links"
(PALs) that control these weapons. The complexity of the procedure
suggests that the precise timing of many events is crucial if a
high-yield nuclear explosion is to result. This is particularly true
for the timing of the many HE detonators, the neutron generator and
the fusion boost injector.  Perhaps these parameters are stored in
encrypted form in the weapon and can be decrypted for use only with
the proper externally-provided key? Considering that a brute force key
search would consume one weapon per trial key, perhaps this technique
isn't too bad against dictionary attacks? :-)

Phil

> 
> > the atomic weapon that sets off the fusion reaction.)
> 
> I don't understand your point.  The earliest devices used a pie shape 
> with a wedge cut out.  The actual geometry is rather unimportant to 
> getting a fission reaction - but it *is* important if you want to 
> maximize your yield.
> -- 

	Wrong. If you are using a uranium fuelled bomb, then you are
right. As long as you thump together two barely sub-critical masses, it
will go boom. However, if you try this with plutonium, it will fizzle.
In the time that it takes for a standard gun type triggering mechanism
to operate, the plutonium will become critical, and then release most of
it's energy harmlessly, instead of going super-critical. This is the
reason for using fast-triggering bomb geometries.

-- 
*       *       Mikolaj J. Habryn
                dichro@tartarus.uwa.edu.au
    *           "I'm just another sniper on the information super-highway."
                PGP Public key available by finger
    *           #include <standard-disclaimer.h>

> > > the atomic weapon that sets off the fusion reaction.)
> > 
> > I don't understand your point.  The earliest devices used a pie shape 
> > with a wedge cut out.  The actual geometry is rather unimportant to 
> > getting a fission reaction - but it *is* important if you want to 
> > maximize your yield.
> > -- 
> 
> 	Wrong. If you are using a uranium fuelled bomb, then you are
> right. As long as you thump together two barely sub-critical masses, it
> will go boom. However, if you try this with plutonium, it will fizzle.
> In the time that it takes for a standard gun type triggering mechanism
> to operate, the plutonium will become critical, and then release most of
> it's energy harmlessly, instead of going super-critical. This is the
> reason for using fast-triggering bomb geometries.

Wrong.  If you will notice, I said "the earliest devices".  They didn't 
use plutonium for nuclear devices until much later.
-- 
Ed Carp, N7EKG    			Ed.Carp@linux.org, ecarp@netcom.com
Finger ecarp@netcom.com for PGP 2.5 public key		an88744@anon.penet.fi
If you want magic, let go of your armor.  Magic is so much stronger than
steel!        -- Richard Bach, "The Bridge Across Forever"

> Wrong.  If you will notice, I said "the earliest devices".  They didn't 
> use plutonium for nuclear devices until much later.

Much as I hate continuing to inject facts into an off-topic
discussion...  

I wouldn't call it "much later".

The first bomb *design* was the uranium gun-type bomb.  They thought
that they could use the same design with Pu239, but discovered when
their first significant samples of Pu showed up that it just wouldn't
work.

The first bomb ever *detonated* (at Alamogordo, NM, on 16 July 1945)
was an implosion bomb using plutonium.  You see, the implosion design
was sufficiently hairy that they needed to test it before using it for
real.

The "Los Alamos Primer" I cited yesterday contains a photo captioned:

   "Sgt. Herbert Lehr delivering plutonium core of first test bomb in its
   shock mounted case to the assembly room at McDonald Ranch, on the
   Trinity test site in the desert northwest of Alamogordo, NM, July 12
   1945."

(The "shock mounted case" in question is a rectangular box, roughly
6"x6"x8")


						- Bill

> Wrong.  If you will notice, I said "the earliest devices".  They didn't 
> use plutonium for nuclear devices until much later.

Actually, to pick a nit, the first a-bomb exploded (Alamogordo) was a
plutonium device.  The U235 design was dropped on Hiroshima untested.

Paul

> Actually, to pick a nit, the first a-bomb exploded (Alamogordo) was a
> plutonium device.  The U235 design was dropped on Hiroshima untested.

The media was making a big deal last night about the seizure of 
twenty pounds of U-238.  This, of course, is the non-radioactive
isotope of uranium in which trade is relatively unrestricted.  It does
make excellent shell casings and has a few other mundane industrial 
uses.

I wonder why the issue of bomb parts is now being given such a
huge push in the press?

-- 
     Mike Duvos         $    PGP 2.6 Public Key available     $
     mpd@netcom.com     $    via Finger.                      $

Mike Duvos says:
> The media was making a big deal last night about the seizure of 
> twenty pounds of U-238.  This, of course, is the non-radioactive
> isotope of uranium in which trade is relatively unrestricted.

Its plenty radioactive. It just isn't fissionable. Not all isotopes
are fissionable.

> It does make excellent shell casings

Actually, depleted uranium tends to be used in place of lead in rounds
used for things like Phalanx (sp?) anti-missile gattling guns. Its
also used in some sorts of armor. I don't think anyone in their right
mind would make a shell CASING from it.

> I wonder why the issue of bomb parts is now being given such a
> huge push in the press?

Because its a real issue. Lots of nuclear material is floating around,
and some of it is going to end up in the hands of terrorists at some
point. However, as I said in the second message in this thread, this
will not be a reasonable excuse to stop strong cryptography, as anyone
with the resouces to build a bomb can also buy or build a good
cryptosystem.

Perry

Perry E. Metzger <perry@imsi.com> writes:]

 >> The media was making a big deal last night about the
 >> seizure of twenty pounds of U-238.  This, of course, is the
 >> non-radioactive isotope of uranium in which trade is
 >> relatively unrestricted.

 > Its plenty radioactive. It just isn't fissionable. Not all
 > isotopes are fissionable.

Uranium is not particularly radioactive, being a long lived alpha
emitter.  This is true of plutonium and some other fissionable
materials as well.  I can handle clad uranium or plutonium
reactor or bomb components in complete safety with no protective
clothing needed. The only hazard is from ingestion of the
material, or from accumulation of decay products such as radon in
a badly ventilated area.

Workers in nuclear fuel fabrication facilities have been known to
use small disks of plutonium sintered into a ceramic base as
poker chips.

Although U-238 can decay both by spontaneous fission and alpha
emission, its astronomically long half-life of many billions of
years results in a very low level of radioactivity for both these
modes of decay.  For all practical purposes, we may consider it a
stable isotope.

 >> It does make excellent shell casings

 > Actually, depleted uranium tends to be used in place of
 > lead in rounds used for things like Phalanx (sp?)
 > anti-missile gattling guns. Its also used in some sorts of
 > armor. I don't think anyone in their right mind would make a
 > shell CASING from it.

Uranium is used in munitions because of its mass, which allows it
to go through less massive materials like steel or concrete like
a hot knife through butter.  It is used both for bullets and
shell casings.  Especially anti-tank rounds and shells designed
to penetrate hardened military facilities.  The idea is that the
uranium penetrates the armor and the charge then explodes once
the round is inside.

-- 
     Mike Duvos         $    PGP 2.6 Public Key available     $
     mpd@netcom.com     $    via Finger.                      $

> 
> Uranium is used in munitions because of its mass, which allows it
> to go through less massive materials like steel or concrete like
> a hot knife through butter.  It is used both for bullets and
> shell casings.  Especially anti-tank rounds and shells designed
> to penetrate hardened military facilities.  The idea is that the
> uranium penetrates the armor and the charge then explodes once
> the round is inside.
> 
I would like to request some reference on the use of Uranium in the casing
of a shell or round. The casing gets thrown out on the ground (by both
aircraft and tanks) when the round goes off. There is no reason to use
anything other than brass or steel for this.

As to the use in a round, the idea is like a sabot. When the ke of the shell
is conserved on impact the more massive core goes right on into the target.
          
I can find no reference any U-core round being HE or otherwise carrying a 
charge. In all cases that I am aware of and can find reference to it is simply
a KE attack on the target where the by products of the impact bounce around
inside the target grinding up whatever is in there.

Take care.

[ Still waiting to be slapped down by someone who's pissed off about
this crypto-free thread, or else for the NSA to have the FBI arrest
all us mad bombers :-) ]

Mike Duvos writes:
 >                                          The idea is that the
 > uranium penetrates the armor and the charge then explodes once
 > the round is inside.

I don't know much about modern munitions, but I do know that armor
piercing rounds may have no charge in them at all.  Generally, when a
round pierces one side of a vehicle, it loses enough energy and is
suitably deformed to prevent exit from the opposite wall.  It does,
however, bounce around quite a bit, which can be plenty of fun in a
tank loaded with equipment, munitions, and soldiers.

It was discovered in the second world war that (with then-current
metallurgical techniques) introduction of a high-explosive charge into
the armor piercing round tended to reduce its effectiveness by
weakening the structure.

| GOOD TIME FOR MOVIE - GOING ||| Mike McNally <m5@tivoli.com>       |
| TAKE TWA TO CAIRO.          ||| Tivoli Systems, Austin, TX:        |
|     (actual fortune cookie) ||| "Like A Little Bit of Semi-Heaven" |

Mike McNally says:
> Mike Duvos writes:
>  >                                          The idea is that the
>  > uranium penetrates the armor and the charge then explodes once
>  > the round is inside.
> 
> I don't know much about modern munitions, but I do know that armor
> piercing rounds may have no charge in them at all.

The Illustrated Encyclopedia of Ammunition, a book that I actually
possess, makes this claim. According to it, there are two basic kinds
of armor piercing rounds -- one that involves having a potent thin
metal projectile usually made of a material like tungsten, that
penetrates the armor, and one involving having a shaped charge that
squirts a jet of hot metal through the armor. No one seems to have
attempted to get explosives through the armor in many many decades.

None of the forms of modern shells described in this book involve the
use of depleted uranium in shell casings.

Perry

> 
> None of the forms of modern shells described in this book involve the
> use of depleted uranium in shell casings.
> 
> Perry
> 
The ammo used by the A-10 chain gun uses a depleted uranium core that is
designed to defeat Chobam and other types of reactive armor. It is also 
used in F-14, F-15, F-16, and F-18's that are tasked with ground attack
missions where active armor tanks are expected to be encountered. The ammo
was specificaly developed for use in the late 70's for use against Soviet
T-72's in a Fulda Gap scenario.

I know of no ammo that uses anything other than brass or steel (in the 
case of mini-guns and other motor driven guns) for the case. The reason
that the Uranium is used is because of its high density.

Jim choate says:
> > None of the forms of modern shells described in this book involve the
> > use of depleted uranium in shell casings.
> > 
> The ammo used by the A-10 chain gun uses a depleted uranium core that is
> designed to defeat Chobam and other types of reactive armor.

Thats a core, not a casing. Plenty of things use such cores -- phalanx
guns, for instance.

> I know of no ammo that uses anything other than brass or steel (in the 
> case of mini-guns and other motor driven guns) for the case. The reason
> that the Uranium is used is because of its high density. 

Excactly.

Perry

-----BEGIN PGP SIGNED MESSAGE-----

> The ammo used by the A-10 chain gun uses a depleted uranium core that is
> designed to defeat Chobam and other types of reactive armor. It is also 
> used in F-14, F-15, F-16, and F-18's that are tasked with ground attack
> missions where active armor tanks are expected to be encountered. The ammo
> was specificaly developed for use in the late 70's for use against Soviet
> T-72's in a Fulda Gap scenario.

1. The DU tank & 25mm ammo used by the US military is sabot ammo,
meaning that the "bullet" is of significantly smaller diameter than
the shell itself; an adaptor, or sabot (from the French for "shoe"),
mates the projectile & the shell and falls off after the projectile
leaves its barrel.

2. Chobham, not Chobam. Chobham armor refers to a specific type of
layered armor, the precise composition and fabrication of which is
classified. It's named for the British works which first built it.
Reactive armor, such as is presently used by the Israelis and some
xUSSR units, is different; it consists of many small charges which
explode outward when hit by an incoming round.

2. Of the aircraft listed above, none can carry the 30mm round used by
the A-10. There is a 25mm round for the Bradley AFV chain gun;
presumably it can also be fired from the Apache. I don't know of a
20mm DU round. (Of course, there's also a 120mm APDS round for the M-1
tank.)

> I know of no ammo that uses anything other than brass or steel (in the 
> case of mini-guns and other motor driven guns) for the case. The reason
> that the Uranium is used is because of its high density. 

3. It is interesting to note that US Army tanks are now being equipped
with depleted uranium _armor_ precisely because its density makes a
great backstop. DU armor can pretty much shrug off most medium AT
weapons; it is quite heavy, but that's not a problem for vehicles
which already weigh as much as tanks.

- -Paul

- -- 
Paul Robichaux, KD4JZG        |  Demand that your elected reps support the
perobich@ingr.com             |  Constitution, the whole Constitution, and
Not speaking for Intergraph.  |  nothing but the Constitution.

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> 2. Chobham, not Chobam. Chobham armor refers to a specific type of
> layered armor, the precise composition and fabrication of which is
> classified. It's named for the British works which first built it.
> Reactive armor, such as is presently used by the Israelis and some
> xUSSR units, is different; it consists of many small charges which
> explode outward when hit by an incoming round.
>
If your spelling is correct then several of my books have mis-spellings.

As to Chob(h)am bing classified, this was true till the late 80's. It is
a ceramic based layered with cintered metallics that dissipate the KE
of the incoming round.      

The Russians also developed this method for the T-72's at about the same
time. It was discovered that the 'applique' armor on the T-72 was really
this type of armor that could be bolted on. The reason that I lump the
two together is that they both require a dual warhead to defeat.

> 2. Of the aircraft listed above, none can carry the 30mm round used by
> the A-10. There is a 25mm round for the Bradley AFV chain gun;
> presumably it can also be fired from the Apache. I don't know of a
> 20mm DU round. (Of course, there's also a 120mm APDS round for the M-1
> tank.)
>
I have seen the exact same chain-gun mounted on F-16's and A-10's here at
Bergstron AFB in Austin at at least two different air shows. I am going on
this alone. I do not know if this was ever an active use of the gun.

> > I know of no ammo that uses anything other than brass or steel (in the 
> > case of mini-guns and other motor driven guns) for the case. The reason
> > that the Uranium is used is because of its high density. 
> 
> 3. It is interesting to note that US Army tanks are now being equipped
> with depleted uranium _armor_ precisely because its density makes a
> great backstop. DU armor can pretty much shrug off most medium AT
> weapons; it is quite heavy, but that's not a problem for vehicles
> which already weigh as much as tanks.
> 
Could you provide references for this application? I did technical support
for Desert Storm and know of no use of such depleted armor in that campaign.
Has Chrysler started putting applique style blocks on the M1 Abhrams?

Take care.

> I have seen the exact same chain-gun mounted on F-16's and A-10's here at
> Bergstron AFB in Austin at at least two different air shows. I am going on
> this alone. I do not know if this was ever an active use of the gun.
> 

	Are we thinking of the same A-10? Tank-killer? The one that
houses a multi-barrel gun the size of a small car, and fires shells
which could pass for milk bottles in a dark room? I've seen an F-16, and
i don't think it could carry the chain gun off an A-10 - or have i
missed the point somewhere?

-- 
*       *       Mikolaj J. Habryn
                dichro@tartarus.uwa.edu.au
    *           "I'm just another sniper on the information super-highway."
                PGP Public key available by finger
    *           #include <standard-disclaimer.h>

>   Mike McNally says:
>   > Mike Duvos writes:
>   >  >                                          The idea is that the
>   >  > uranium penetrates the armor and the charge then explodes once
>   >  > the round is inside.

>   > I don't know much about modern munitions, but I do know that armor
>   > piercing rounds may have no charge in them at all.

>   The Illustrated Encyclopedia of Ammunition, a book that I actually
>   possess, makes this claim. According to it, there are two basic kinds
>   of armor piercing rounds -- one that involves having a potent thin
>   metal projectile usually made of a material like tungsten, that
>   penetrates the armor, and one involving having a shaped charge that
>   squirts a jet of hot metal through the armor. No one seems to have
>   attempted to get explosives through the armor in many many decades.

>   None of the forms of modern shells described in this book involve the
>   use of depleted uranium in shell casings.

out of curiousity, what does it say under 'sabot'?

josh

> >   > Mike Duvos writes:
> >   >  >                                          The idea is that the
> >   >  > uranium penetrates the armor and the charge then explodes once
> >   >  > the round is inside.
> 
> >   > I don't know much about modern munitions, but I do know that armor
> >   > piercing rounds may have no charge in them at all.

> >   None of the forms of modern shells described in this book involve the
> >   use of depleted uranium in shell casings.
> 
The U after is goes through the armor is pyrophoric, and there is quite a 
fireball as a result - lots of hot burning particles flying around. quite 
spectacular from the downstream side (I've seen it - the back side of a 
target plate)
L

> I don't know much about modern munitions, but I do know that armor
> piercing rounds may have no charge in them at all.  Generally, when a
> round pierces one side of a vehicle, it loses enough energy and is
> suitably deformed to prevent exit from the opposite wall.  It does,
> however, bounce around quite a bit, which can be plenty of fun in a
> tank loaded with equipment, munitions, and soldiers.

	I was under the impression that the most common techniquoe for
creating armour-piercing munitions was to use shaped-charges. While
depleted uranium has it's uses (being, as someone said, rather dense),
mass alone will not get through everything. A shaped charge will get
through more things more violently :)

-- 
*       *       Mikolaj J. Habryn
                dichro@tartarus.uwa.edu.au
    *           "I'm just another sniper on the information super-highway."
                PGP Public key available by finger
    *           #include <standard-disclaimer.h>

> > > 
> > > I don't understand your point.  The earliest devices used a pie shape 
> > > with a wedge cut out.  The actual geometry is rather unimportant to 
> > > getting a fission reaction - but it *is* important if you want to 
> > > maximize your yield.
> > > -- 
> 
> Wrong.  If you will notice, I said "the earliest devices".  They didn't 
> use plutonium for nuclear devices until much later.

	That may be what you had in mind - what you wrote was that
geometry is irrelevant in fusion reactions, which is incorrect.

-- 
*       *       Mikolaj J. Habryn
                dichro@tartarus.uwa.edu.au
    *           "I'm just another sniper on the information super-highway."
                PGP Public key available by finger
    *           #include <standard-disclaimer.h>

On Wed, 24 Aug 1994, Perry E. Metzger wrote:
> 
> In a fusion, or H Bomb, the tritium (which is just hydrogen with an
> extra two neutrons) is that which produces the boom -- the main fuel,
> as it were. Its a "neutron source" only in the weakest possible sense
> -- the same way dynamite might be considered to need nitroglycerine as
> a "neutron source". (I'm not sure that people outside of the bomb
> building industry really know *for sure* what the geometries used in
> the atomic weapon that sets off the fusion reaction.)
> 
> Perry
> 
Since the bomb thread won't die a seemly death I thought I'd throw in my
.00000002 megabucks.  Modern H bombs are actually fission-fusion-fission
devices. The traditional U-235 (or Pu-239) atomic bomb sets off a fusion 
reaction burning the tritium, producing alot of fast neutrons that in turn
sets off another fission explosion in the otherwise non-fissile U-238 
that is wrapped around the outside of the bomb.  More bang for the buck, 
and it gives you something to do with all that U-238 you got while 
purifying the U-235.

C. J. Leonard                     (    /      "DNA is groovy"
                                   \ /                - Watson & Crick
<cjl@welchlink.welch.jhu.edu>      / \     <--  major groove
                                  (    \
Finger for public key               \   )
Strong-arm for secret key             /    <--  minor groove
Thumb-screws for pass-phrase        /   )

> In a fusion, or H Bomb, the tritium (which is just hydrogen with an
> extra two neutrons) is that which produces the boom -- the main fuel,
> as it were. Its a "neutron source" only in the weakest possible sense
> -- the same way dynamite might be considered to need nitroglycerine as
> a "neutron source". (I'm not sure that people outside of the bomb
> building industry really know *for sure* what the geometries used in
> the atomic weapon that sets off the fusion reaction.)
> 

	This also depends on the type of bomb. In a two-stage fusion
bomb, you are quite correct - the tritium-deuterium/tritium fusion
reaction gives the boom. However, in a three-stage bomb, there is an
additional fission reaction, this due to the fact that the neutrons
produced by the fusion reaction have the precise energy required to
fission U-238. Since U-238 is vastly easier to obtain than enriched
U-235, there is no great problem with sticking in half a tonne of it.
Around that you can add cobalt jackets, etc, for more interesting
effects.

-- 
*       *       Mikolaj J. Habryn
                dichro@tartarus.uwa.edu.au
    *           "I'm just another sniper on the information super-highway."
                PGP Public key available by finger
    *           #include <standard-disclaimer.h>