H bombs

John K Clark (johnkc@well.com)
Mon, 9 Mar 1998 13:27:43 -0800 (PST)


On Mon, 9 Mar 1998 mark@unicorn.com Wrote:

>A while ago there was a discussion about the role of plastic foam in
>H-bombs; I think I've deleted most of the messages, but over the
>weekend I was able to collect my copy of Richard Rhode's book 'Dark
>Sun: The Making Of The Hydrogen Bomb', and look up what he said on
>the subject. He claims that the plastic on the original H-bomb test
>was placed around the inside of the bomb casing, not on the fusion
>core itself as I've read elsewhere. The X-rays from the initiator
>turn the plastic to plasma, which re-radiates X-rays onto the U-238
>tamper, creating a rocket effect which implodes the fusion core.
>This also compresses the fission trigger in the middle of the fusion

Rhodes was somewhat contradictory about this because he also said that the
plastic foam was used to keep pressure spikes from destroying key components
of the bomb before they can do their job, in fact "Dark Sun" is the book
where I found the quote that I posted on the subject.

I found another interesting quotation that gives more support to my hunch
that a light fluid like that produced from foam could not evenly compress a
heavy plasma fluid from Uranium, but that X rays could. It's from Kip Thorne's
recent book "Black Holes and Time Warps". Thorne never worked on weapons but
he is one of the world's greatest experts on neutron stars and the accretion
disks around Black Holes, and they have many of the same conditions as
H bombs.

The Soviet physicist Borisovich Yakov Zeldovich (who worked on the Russian
H Bomb) proposed a model for the accretion diskaround Black Holes that
involved X rays compressing gas. Thorne says this on page 241:

"This picture of the flow of gas and X rays disturbed me. I knew full well
that on Earth, if one tries to hold a dense fluid such as liquid mercury up
be means of a less dense fluid such as water below it, tongues of mercury
quickly eat their way down into the water, the mercury goes whooshing down,
and the water goes whooshing up. This phenomenon is called Rayleigh- Taylor
instability. In Zeldovich's picture, the X rays were like the low density
water and the gas was like high density mercury. Wouldn't tongues of gas
eat their way into the X rays, and wouldn't the gas then fall freely down
those tongues? A detailed calculation with the laws of physics would tell
me whether this happened, but such a calculation would be very complex and
time consuming: so rather than calculate, I asked Zeldovich one afternoon
in 1969, when we were discussing physics in his apartment in Moscow."

"Zeldovich looked a bit uncomfortable when I rased the question, but his
answer was firm: "No Kip, that doesn't happen. There are no tongues into
the X rays. The flow of gas is stable. " How do you know Borisovich Yakov?"
I asked. Amazingly, I could not get an answer. It seemed clear that
Zeldovich or somebody had done a detailed calculation or experiment showing
that X rays can push hard on a gas without Rayleigh- Taylor tongues
destroying the push, but Zeldovich could not point me to any such
calculation or experiment in the published literature, nor would he
describe for me the detailed physics that goes on. How uncharacteristic of

"A few months later I was hiking in the high Sierras in California with
Stirling Colgate. (Colgate is one of the best American experts on the flows
of fluids and radiation and was deeply involved in the late stages of the
American superbomb effort, and he was one of the Livermore physicists who
had simulated a star's implosion on a computer). As we hiked I posed to
Colgate the same question I had asked of Zeldovich, and he gave me the same
answer: The flow is stable; the gas cannot escape the force of the X rays
by developing tongues. "How do you know, Stirling?" I asked "It has been
shown" he replied. "Where can I find the calculations or experiments?" I
asked. "I don't know... ""

"That's very peculiar," I told Stirling. "Zeldovich told me precisely the
same thing- the flow is stable. But he, like you, would not point to any
proofs" "Oh! That's fascinating. So Zeldovich really knew" said Stirling."

"And then I knew as well. I hadn't wanted to know. But the conclusion was
unavoidable. The Teller - Ulam idea must be the use of X rays emitted in
the first microsecond of the fission (atom bomb) trigger to heat, help
compress, and ignite the superbomb's fusion fuel. That this is, indeed, part
of the Teller-Ulam idea was confirmed in the 1980's in several unclassified
American publications, otherwise I wouldn't mention it here."

>Interestingly, he also says that most of the yield in that test came
>from the U-238, as the fusion byproducts converted it into other,
>unstable, elements which then fissioned.

When a SLOW neutron, such as one from a fission reaction, hits U238 it does
not split, instead it absorbs the neutron and turns into U239, this has a
half life of 24 minutes and it decays into neptunium 239, this has a half life
of 2.3 days and it decays into plutonium 239, and plutonium 239 has a half
life of 14,000 years and works great in bombs. This is fine for manufacturing
plutonium but far too slow to play a part in a nuclear explosion.

However, when a FAST neutron, like those produced in a fusion reaction hits
U238 it will split and make lots of energy. So in an H bomb about 70% of the
energy comes from the fission of common U238, but that wouldn't be possible
without the fast neutrons from the fusion reaction.

John K Clark johnkc@well.com

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