Explaining the unimaginable: How do nuclear bombs work?
on
Get link
Facebook
X
Pinterest
Email
Other Apps
By Graham Templeton
So, this is a bit of a touchy question. From the beginning,
even before the true destructive and killing power of The Bomb was
clear to its own creators, one thing was certain: Nobody should ever
acquire nuclear weapons if those who do have them can help it. That may be a hypocritical stance for current nuclear powers to take — but they’re live hypocrites, so whatever.
The justified fear over nuclear technology led to the creation of one
of the weirder bits of legislation: the classification of “born
secret.” This refers to the fact that, under a certain reading of the
law, information on the design and function of nuclear weapons is
considered stolen classified information even if you come up with it yourself.
As a result of this and more reasonable secrecy plans, the
fine details of all but the earliest nuclear weapons are still unknown
to the public. To be fair, those details wouldn’t help anyone but a
state actor, one with access to nuclear material, enrichment facilities,
tons of money, and at least a few world-class engineers, but it’s still
probably for the best. So rather than learning how to actually build
nuclear weapons (darn…), we’ll have to settle for a basic conceptual
understanding of the two basic nuclear weapon types: the old, and the
new.
Fat Man, the bomb which was detonated over Nagasaki. Shirts probably wouldn’t have helped anyway…
The old type of nuclear weapons, still in use all over the world, are called fission bombs, or simply atomic weapons.
The latter term can be used as an umbrella, or to specifically refer to
the first sort of bombs created during the Second World War. Scientists
load the bomb with a “super-critical mass” of enriched fissile
material, usually uranium, which can create a self-sustaining chain
reaction of fission events. Though it’s created differently, this is
basically the same chain reaction that occurs in a nuclear reactor, but
more uncontrollably due to the amount and enrichment (isotope purity) of
the sample used.
The ups and downs of this classical nuke-type are well
known. The explosions are big, the fallout horrifying. Even hardened
military men, who did not blink at the idea of wiping whole sections of
world cities from existence, were taken aback by the continuing impact
of radioactivity. This radioactivity comes from various sources, but
much like the Chernobyl nuclear disaster, the majority of the long-term
damage comes from how the explosion physically distributes radioactive
material over a wide radius. This material comes from the bomb itself,
and if detonated near the surface (not high in the air) the reaction
will also vaporize and disperse a huge amount of ground and/or water as a
highly radioactive (mushroom) cloud. Traces of the fallout from some
such explosions can be detected by scientific instruments all over the
world.
The other type of nuclear weapon is called a thermonuclear weapon, or sometimes a hydrogen bomb. While
no nuclear weapon could ever be said to be humanitarian, if there ever
is a nuclear war between great powers, we’ll be happy they have these,
rather than the old kind. “Hydrogen bomb” gets the point across: The
primary destructive sample is not uranium or plutonium or even thorium,
but heavy isotopes of the most abundant element in the universe. And
rather than breaking these atoms apart, thermonuclear weapons generate
their outward force through the process of nuclear fusion.
Thermonuclear weapons basically contain
a conventional nuclear weapon, but much smaller than its overall yield
would seem to require. The power of this small fission reaction is
directed onto two on-board samples of hydrogen isotopes — one deuterium,
the other tritium — and these samples are forced together so violently
that they fuse. Again, the main difference between the fusion going on
here and in a fusion reactor (beyond that we had to explode a bomb to
get it started) is that a bomb has many tens of thousands of times more
fusion material.
Now, doing fusion also releases a ton of radiation,
but this release is short-lived compared with the radioactive half-life
of material strewn around after a fission explosion. So, by eliminating
the vast majority of the fissile material in the bomb, distributing
this sample around the environment via a fusion explosion has a much
less toxic effect. Thermonuclear weapons can deliver a much higher yield
than pure fission bombs, but they crucially produce less fallout while
doing so. They are also more natural fits as so-called “tactical nukes,”
allowing targeted destruction of an installation without having to make
the whole area uninhabitable for a while.
Other types of nukes include neutron bombs, which
intentionally let high-intensity neutron radiation out of the bomb’s
case. While most bombs have a thick case of lead or some other material
to stop the release of neutron radiation, neutron bombs are designed to
be as thin and permeable as possible. They were specifically invented to
counter the thick shielding on Soviet tanks, which was thought to
provide too much protection against pure heat and concussion, but
they’re also sometimes thought of as pure anti-personnel weapons, since
neutron radiation can be extremely deadly to biological material without
destroying infrastructure.
There’s also a concept called a salted bomb, which
encases the nuclear device in a metal like gold that can be
neutron-blasted into a much more radioactive isotope, producing a huge
additional amount of radioactive material upon detonation. The concept
was named for the phrase “salt the Earth;” thankfully, so far as we know
no salted bomb has ever actually been tested.
None of these are to be confused with dirty bombs,
which are the real threat posed when low-tech groups like terrorists
come into nuclear material. Rather than creating an actual nuclear bomb,
they would simply strap a regular explosive device to a sample
of radioactive material and blow it up. This cannot cause a nuclear
reaction, but it can contaminate large areas by distributing an aerosol
version of the radioactive substance. The destructive power isn’t very
great, but the loss of life could still be substantial due to health
problems in the years and decades after the explosion.
Check out our ExtremeTech Explains series for more in-depth coverage of today’s hottest tech topics.
Comments
Post a Comment