Re: H bombs

Eugene Leitl (
Tue, 3 Mar 1998 17:30:51 +0300 (MSK)

On Mon, 2 Mar 1998, John K Clark wrote:

> On Mon, 2 Mar 1998 Eugene Leitl <> Wrote:
> >The reflecting plane is not flat, most photons do not get reflected
> >but absorbed (xRay mirror they are not)
> It doesn't make much difference, if the photons are reflected the target will
> receive twice the photons momentum, if it is absorbed it will still receive

What is the energy flux upon a square meter of surface 300 m away from a
10 m-radius sphere radiating as a 100 MK blackbody? (Of course these
parameters are ad hoc, and emitting sphere surface grows bigger while
cooling off, &c&c, but this should give us at least some ballpark
figures). Are you really proposing that the peak forces generated are
sufficient to deformate a macroscopic object made of, say, 1 cm sheet
steel? If we assume above energy flux to persist for 0.5 s, what would the
final travel velocity of a 1 x 1 x 0.01 m steel sheet be? I'd say
negligeably small, few 10 cm/s at best.

> the photon's momentum and its energy too.

Ok, I have a cloud of excited atoms over the surface (=not part of it
anymore) which relaxate by radiation into vacuum. How much of it sees the

> >causing the surface material to turn into a gas cloud exploding
> >outwards.
> Right, and that will cause the inner material to implode inward and compress.
> Ouch.

What I am saying that this effect contributes 99.999% of the pressure the
surface sees.

> >Surface turned into gas expands into vacuum, relaxating by EM
> >radiation into the environment, which, if not sol-proximal, is few-K
> >(Big Bang echo) cold space.
> Yes, but so what?

Excited atom, not part of target, emits a photon. Photon whizzes off, atom
whizzes off. Probability of any of them striking the surface below is <1.
In any case the half-life time must be taken into account, diluting the
energy spike temporally.

> [...]
> >Is 100 MT small enough? The difficulties we are talking about is
> >hitting a flurry of habitats/mosaic of subterranous settlings
> >semisimultaneously, requring a large number of brilliant warheads.
> Going underground won't help much, during the gulf war bunker busting bombs
> penetrated 30 feet of steel reinforced concrete to destroy installations, and
> they just had chemical explosives, H bombs could do much better. I suggest

You are talking about direct hits again. What I was saying is that, say, 1
Gpeople distributed over vacuum-separated spatially distributed 100 k
habitats (lunar surface would offer an enrichment, and ground would allow
energy coupling while also enhancing shielding) are drastically more
difficult to kill with nukes since essentially requiring direct habitat
hit each. Since, contrary to antimatter nukes, fissible material requires
a noticeable critical mass (using other transurans than Pu won't help
much) the resulting kill efficiency will be too low for practical use.

> you visit the island of Elugelab, that's where the USA detonated a bomb that
> was expected to be of less than 5 megatons but actually produced 15 megatons.

I thought the Russies peaked that on Novaya Zhemlya (20 MT expected, 60 MT
estimated real yield). This has been no ground blast, though.

> They blew it up in 1954 on top of a short tower, it produced a fireball 4
> miles in diameter, it terrified the scientists who set it off and trapped
> them in their bunker for several days on an island 10 miles away, and it
> killed the Japanese sailors on the fishing boat Fukuryu Maru- The lucky
> Dragon, who were far from the official danger area and well inside the
> "safety" zone. Actually I'm being unfair, you can't visit Elugelab anymore,

Uh, wasn't that lethality supposed to be due to the fallout solely
(activated coral sand)?

> but if you have a submarine you can look at the crater on the sea floor 250
> feet deep and 6500 feet across where Elugelab once was.

A typical atoll's elevation is just few m above the sea surface. Even the
largest devices do not change the landscape noticeably -- you could level
only a very small mountain with them.

> [...]
> Maybe, but then the design would be inefficient because if the foam was that
> ephemeral then most of the X rays energy would pass through all the foam and
> be wasted, it would not be available to compress the fusion cylinder. Why not
> use radiation pressure?

Maybe all they wanted was to compress the material to the critical density
to be ignited by the fission primer.

I must take your word for that that the radiation pressure is the
determinant, as I cannot prove your numbers.

> I found a quotation that gives some support to my theory that the polymer
> foam's main function was to protect vital parts made of heavy atoms for a few
> extra nanoseconds, and its use as a plasma generator of only secondary
> importance. Jacob Wechsler was a H bomb engineer and he's talking about
> Carson Mark, the chief designer of the first H bomb:
> "He was really concerned about higher Z materials [elements with higher
> atomic number] being exposed. In a radiation environment with high energy
> radiation coming down from the primary, anything like steel because it's
> so dense will cause a pressure spike when it vaporizes. Carson was trying
> to sustain a deuterium burn and he was afraid that if things blew off at
> higher Z that might chop up the fuel, its temperature wouldn't stay high
> enough [...] the surface of the lead would blow off so we covered the lead
> with plastic, with polyethylene. That was low Z, just CH2 [hydrogen and
> carbon]. From a time point of view the radiation ionization of the heavy
> materials with all that shielding would be so late that it would have
> zilch effect on the overall system."

Interesting quote. Are you aware of any high-quality online resources?

> >There's a reason thermonuclear devices are so difficult to build.
> I wonder, are they difficult to build? Over 100,000 of the damn things have
> been made and several hundred have exploded in tests, some with very unusual
> designs, and yet there has not been one dud and most turned out to be more
> powerful than expected.

Yeah, but while I could build a working crude gun assembler nuke on a very
modest budget, the threshold for a fusion nuke from scratch is worth
man-centuries of high-paid experts.