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Aucb.1056 fa.arms-d utzoo!decvax!ucbvax!C70:arms-d Tue May 11 00:26:37 1982 Arms-Discussion Digest V0 #103 >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

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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)

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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.

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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.

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Date: 11 May 1982 01:29-EDT From: Robert Elton Maas <REM MIT-MC AT> 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.

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End of Arms-D Digest ********************

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