C70:arms-d (05/11/82)
>From HGA@MIT-MC Tue May 11 00:22:08 1982
Arms-Discussion Digest Volume 0 : Issue 103
Today's Topics:
The Sinking of the General Belgrano
Falklands
Build an H-bomb and wake up the neighborhood
Time-urgent hard-target kill capability
----------------------------------------------------------------------
Date: 9 May 1982 22:30:41-EDT
From: zrm at mit-mc
Thought you might like to know: The Globe reported yesterday that the
General Belgrano was carrying its full complement of 1042 men at the
time it was sunk. It was hit by two torpedoes (which indicates both
the torpedoes that reports say were fired worked). The engine room was
hit, and a fuel fire started. The explosion from the torpedoes was
just below the mess hall -- almost all casualties were among crew that
was off duty at the time and relaxing in that area of the ship. (This
seems to imply a war alert was NOT on at the time) "Everyone on the
deck was saved." "It was vital to move the rafts away from the ship
to avoid being sucked under..." (Indicating the ship was sinking
fast.) 680 men are officially accounted for but rescue efforts are
continuing. Quotes in the above paragraph are from the captain of the
General Belgrano, Hector Bonzo(!).
The Economist ran a short item on the circumstances surrounding the
sinking of the General Belgrano. Two points seem very interesting: The
cruiser's escort fled when she was hit and Argentine rescue efforts
did not pull any crewmen from the lifeboats until 24 hours after the
General Belgrano sank. Second, elements of the British task force made
no rescue efforts of their own, although if any ships were nearby,
they would be required to do so under the 1949 Geneva convention. If
no ships were nearby, then how could the General Belgrano have been
"threatening British ships"? Everything is wierd.
Cheers,
Zig
------------------------------
Date: 10 May 1982 0922-EDT
From: WDOHERTY at BBNG
Subject: FALKLANDS
I have heard something about the US and Britain sharing an airfield
used by the Brits to send their planes to the Falklands. Apparently,
Reagan claims that we had no knowledge of plans for the British
airstrike. How could this be if we share the airfield with them?
(I've heard this second-hand so it may be total rumor.)
Will Doherty (WDOHERTY@BBNG)
------------------------------
Date: 10 May 1982 1156-PDT
From: Paul Dietz <DIETZ at USC-ECL>
Subject: Build an H-bomb and wake up the neighborhood
I just read "The Secret That Exploded" by Howard Morland, the author
of the Progressive's article about the details of the H-bomb. The
book covers the search theat led Morland to his design, the errors he
made and the legal hassles with the government. I found the technical
details of H-bomb construction to be the most interesting part.
The principles behind H-bomb design are relatively simple. A mixture
of deuterium and tritium must be compressed and heated so that much
fusion occurs in the microseconds before the bomb is blown apart.
Simply surrounding a fission bomb with DT doesn't work -- no
compression occurs. There is no room inside a fission bomb to put
much DT, at least not enough to get bombs in the multimegaton range.
Severe constraints follow from the physical dimensions of actual
warheads. For example, the warhead in the cruise missile is a tapered
cylinder 29 inches long, the large end 16 inches in diameter and the
small 14 inches. It weighs 270 pounds.
The actual fusion fuel is lithium deuteride, which is compressed into
a hard ceramic-like material and machined to the proper dimensions.
The lithium is actually lithium-6, which the government separates from
lithium-7. Neutrons transmute the lithium to tritium during
detonation.
A study of the nuclear rections involved reveal something interesting.
In a clean fusion bomb (if such a thing were possible) 80% of the
energy comes out in the form of neutrons. If allowed to escape these
neutrons will not contribute to the blast: they will travel about half
a mile in the air, gradually heating it. This wasteful situation is
remedied by putting U238 in the way of the neutrons. The fast
neutrons cause fission reactions in the U238. In a large device
(multimegaton) up to 50% of the energy comes from the U238.
The real problem is how to compress the LiD fuel. The actual
arrangement of LiD in a bomb is interesting: it is arranged in a
narrow cylinder pointing away from the fission trigger. Running down
the middle of the fusion fuel is a rod of plutonium: the "sparkplug".
Surrounding the LiD is a casing of U238. Interposed between the
fission trigger (the "primary") and the fusion secondary is a thick
piece of U238 to shield the fusion fuel from the radiation produced by
the primary.
The radiation we want is X-radiation. The primary puts out most (80%)
of its energy as X-rays. These X-rays travel from the primary towards
the secondary. Surrounding the secondary is a special plastic.
Embedded in the plastic is a carefully controlled mixture of dense
particles. The plastic is essentially transparent to X-rays. The
particles, on the other hand, absorb the hard x-rays, softening them.
By carefully tailoring the density of the particles we can get the
plastic to implode upon the LiD/Pu secondary.
The implosion causes the Pu sparkplug to go supercritical. It
detonates, further compressing the LiD fuel. Neutrons from the Pu and
from fusion reactions convert the lithium into tritium. Fusion occurs
and the resulting neutrons cause fission in the U238 casing of the
secondary.
Tritium itself is also used in at least two places. First, every
warhead has a small one-shot electrostatic accelerator. Adsorbed onto
the anode are tritium atoms: one the cathode are deuterium atoms. The
tritium atoms are accelerated towards to cathode by a potential of 150
Kev. This generates neutrons, which are injected into the primary to
start the whole thing (older bombs had a polonium/berylium neutron
generator: alpha particles from the polonium cause the berylium to
give off neutrons. This has the disadvantage that you can't turn it
off.)
Tritium and deuterium are also used as "boosters" in the primary. As
part of the arming sequence high pressure tritium and deuterium is
injected into the plutonium primary. Apparently the fusion neutrons
generated during the explosion increase the percentage of Pu atoms
that fission. It also allows us to construct a "dial-a-bomb" with
programmable yield: just inject different amounts of DT into the
primary.
Both the tube and the booster are field replaceable, so a bomb will
not go bad because its tritium decays away.
------------------------------------------------------------
Of course, knowing all this will not enable you to build an H-bomb.
You need special machine tools, and all sorts of special isotopes
(Li6, Pu239, U238, D, T). You also need to do a lot of
experimentation to work out the bugs in your design, and a lot of
compute power to get the design in the first place.
This information makes me skeptical of the claim that US bombs are
cleaner than Russian bombs becuase we don't use steel casings. The
fallout comes from fission products, and if you leave out the U238 the
bomb is *much* less efficient.
It was suggested in the book that the neutron bomb does not have a
sparkplug. The fusion fuel would have to contain tritium, so N-bombs
would have to be refurbished periodically.
Also interesting is what this says about bomb testing. We can today
test a fission bomb without any fission taking place: just replace the
fissile material with nonfissile isotopes and wire the thing with very
fast cameras and instruments. This gives enough data to tell you if
the thing would actually work. Testing a fusion bomb is slightly more
difficult: we must actually detonate the primary. The secondary can
be replaced with an instrument package, however, so we can get some
idea about how a very large (multimegaton) bomb would work without
actually firing it.
------------------------------
Date: 11 May 1982 01:29-EDT
From: Robert Elton Maas <REM at MIT-MC>
Subject: time-urgent hard-target kill capability
I'm not a hawk, but I'll provide a guess.
If you're in a war, you'd like to be able to fire half your missiles,
wait to see which strike their targets, then retarget your remaining
weapons to hit anything that was missed the first time around. This
eliminates the need to send multiple warheads to each major target,
allowing you to achieve a higher kill ratio than independent random
probability theory would provide. You can actually achieve 100% kill
rather than only exponentially reducing the non-kill to close to zero.
On the other side, you'd like to prevent your enemy from retargeting a
second wave by forcing all the enemy weapons to be used in the first
strike. One way to do this is by destroying their silos during the
first exchange. Thus while silo-killers may have the disadvantage of
forcing a full strike (they must throw everything at us the first
time; if they try to be nice to us by making a limited strike, we
destroy their weapons in the silos), they have the advantage of
preventing retargeting and thus reducing total damage to our side
during a full exchange.
------------------------------
End of Arms-D Digest
********************