H bombs

John K Clark (johnkc@well.com)
Sat, 28 Feb 1998 21:13:14 -0800 (PST)


On Sat, 28 Feb 1998 Eugene Leitl <eugene@liposome.genebee.msu.su> Wrote:

>Unless you are a massive, unstructured superalloy sphere you won't
>survive a nuke fireball from a few m distance virtually unscathed.

It wouldn't matter what you did, at that distance nothing would be unscathed,
not even atoms.

>nukes are pretty useless in space, especially against rad-shielded
>floating and underground habitats.

I think that's a big overstatement. It's true that in a vacuum you wouldn't
get hit by a shock wave caused by the pressure of matter, but you would have
to worry about the enormous shock from radiation pressure. We usually think
of radiation pressure as being very weak, after all, we'd need a solar sail
miles across to slowly accelerate a small space ship, the feebleness is
partly because the sun has a small angular size near the Earth but mostly
because the of the sun is so cold, less than 10,000 degrees at the surface.
When things get really hot the pressure becomes astronomical, literally
astronomical, because just a small increase in temperature means a huge
increase in radiation pressure, the two are related to the FOURTH power.

If you heat up a tin can to temperature T the Black Body radiation pressure
inside the can is 1/3 [QT^4] , Q is the radiation constant
7.56591* 10^-15 erg cm-3 Kelvin -4 . If you heated up the can to 90,000,000
degrees the radiation pressure inside the can would be equal to the total
pressure found at the center of the sun! Yes your target wouldn't be
completely enveloped and would only receive the radiation from one side, but
on the other hand, an H bomb can produce temperatures well over 200,000,000
degrees, and the shock would be further enhanced because the outer layer of
the target would vaporize and rocket outward and because momentum is
conserved the inner parts would rocket inward.

Incidentally, without radiation pressure an H bomb wouldn't work, the
radiation from the fission trigger is the only way to compress deuterium
enough to achieve fusion. You might think that photons of light couldn't
evenly compress matter because of Rayleigh - Taylor instability, that's what
would happen if you tried to support heavy mercury with a column of water,
tiny tongs of mercury would force their way a small way into the water and
then grow exponentially until the mercury had entirely fallen through the
water. It's not at all obvious that the same thing wouldn't happen with light
and matter, however detailed calculations by the military on the largest
super computers of their day showed that this instability does not happen,
photons really can compress matter evenly. This fact was kept top secret for
many years, and when it was finally revealed, after painstakingly piecing it
together in the early 1980's from hundreds of unclassified documents and
after several people nearly went to jail, astronomers found it very

The interior of the sun is at a chilly 14 million degrees so radiation
pressure is not very important, the gas pressure is about 1700 times greater,
the same is true for most stars but not all, it is vitally important in
super giantstars, supernovas, the accretion cloud around Black Holes, and in
the H bomb it's the entire ball game.

>What we should worry right now are not nukes nor nerve agents, but
>engineered bioweapons (mostly viruses, not bacteriological bioweapons).

That does worry me, another thing that worries me are the thousands of H bombs
in the former USSR guarded by angry unhappy men who drink too much and make
about a thousand dollars a year.

John K Clark johnkc@well.com

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