Since questions arose, just before I declared a moratorium,
concerning the conditions under which a nuclear weapon will explode I thought I
would say a few words of explanation. I am no kind of physicist but back in the
day when I spent a good deal of my time as part of the Campaign for Nuclear
Disarmament I had to learn some of this stuff up and it sort of stays with you.
The crucial point to remember is that the mass of an atom is
determined both by the number of protons and neutrons it contains and also by
the amount of energy, in the form of mass, required to hold it together. Some
atoms either in their standard form or in their isotope form are sufficiently
unstable to break down periodically, giving off an amount of energy determined
by the famous formula e=mc2. Since the constant c stands for the
speed of light which is 300,000 km/s, the energy equivalent of even a very
small bit of mass is obviously very large.
Very heavy atoms like uranium and plutonium are unstable and
break down into their component parts regularly without external prodding.
Sometimes when one of those atoms spontaneously breaks down, it gives off an
alpha particle that hits another atom of the same material and causes it to
break up as well. But since, contrary to intuition, most of supposedly solid
matter is actually empty space, the likelihood of this happening is rather
small. If you cram enough uranium or plutonium into a small enough space you
can raise the likelihood of a series of such break ups, called a chain
All of this was well understood theoretically at the time
during the second world war when both the allies and the axis had a go at
creating a weapon out of nuclear materials. All the physicists involved knew
that the amount of energy that could be released by such a chain reaction was
enormous but the engineering problem was how to get the chain reaction to start
and carry on for some period of time (a microsecond, actually) before the
explosion produced scattered the material and stopped the chain reaction.
The amount of energy produced by even a primitive so-called
atomic bomb was beyond anything human beings had ever produced. The super big
conventional bombs carried by Allied bombers in the air raids over Germany were
as large as 1 ton or 2000 pounds of TNT. That is a monster big bomb but the
atom bombs dropped on Hiroshima and Nagasaki were rated not in equivalent
thousands of pounds of TNT but in equivalent thousands of tons of TNT – hence
the invention of the term kiloton.
The secret of making the damn thing work turned out to be
creating a sheath of conventional explosive around two components of uranium or
plutonium, neither one large enough all by itself to produce a chain reaction,
and then exploding the sheath inward, or imploding it, so that the two
components were jammed together by the explosion and held there just long
enough to produce a chain reaction of enormous explosive power.
Blowing up a functional atomic bomb by hitting it with a missile would scatter the material harmlessly (setting aside for the moment the
effect of the radiation produced by the components). The likelihood that such a
missile attack would literally trigger the explosive mechanism and cause the
atomic bomb to explode as intended is virtually nil.
So what on earth is a hydrogen bomb? Well, it turns out that
if you arrange all the elements in order of their atomic weight from the very
lightest, which is hydrogen, to the very heaviest which is uranium or
plutonium, in each case the heavier atom is a trace heavier than the combined
component atoms resulting from a breakup, the additional weight consisting of
the mass form of the energy holding the parts of the atom together.
Except one case. If you break up one atom of helium, which
has an atomic weight of four, which is to say two protons and two neutrons,
into two atoms of so-called heavy hydrogen, which is to say an isotope of
hydrogen with one proton and one neutron, the two atoms of heavy hydrogen weigh more than the one atom of helium! This means that if you could find a way of
combining two atoms of heavy hydrogen into one atom of helium, energy would be
released. The amount of energy, it turned out, is enormous even by atom bomb
standards. But there is a problem: this process of combining hydrogen atoms
into helium – the same process, by the way, that generates the energy of the
sun – requires enormous temperatures. But the yield is vast – measured not in
thousands of tons of TNT equivalent but in millions of tons. Hence the new term
Heavy hydrogen exists in nature in very small quantities in
ocean water and if you are willing to take the trouble of processing huge
amounts of that ocean water you can extract heavy hydrogen and use it to make
an H – bomb, with an A-bomb trigger. During the second world war the scientists
gathered at Los Alamos undertook to create a uranium bomb, and they solve the
problem of how to trigger it with a covering of conventional explosive (this
was of course an international group of scientists and it turns out that the
shape of the conventional explosive that is optimally effective is roughly that
of a soccer ball!) The Germans made the mistake of trying to create a fusion
bomb, not realizing that it would require an atomic bomb trigger. They had a
big plant processing ocean water at Peenemünde, which was raided by the allies
in an important air raid.
Well, that just about exhausts my understanding of these
matters but readers of this blog might find this interesting.