Could thermonuclear reactions be made to take place on earth? The
conditions that exist in the center of the sun would be extremely
difficult to duplicate on the earth, so there was a natural search for
any kind of nuclear fusion that would produce similar energies to those
going on in the sun but which would be easier to bring about.
There are 3 hydrogen isotopes known to exist. Ordinary hydrogen is
almost entirely hydrogen-1, with a nucleus made up of a single proton.
Small quantities of hydrogen-2 (deuterium) with a nucleus made up of a
proton plus a neutron also exist and such atoms are perfectly stable.
In 1934 Rutherford, along with the Australian physicist Marcus Laurence
Elwin Oliphant (1901- ) and the Austrian chemist Paul Harteck
(1902- ) sent hydrogen-2 nuclei flying into hydrogen-2 targets and
formed hydrogen-3 (also called “tritium” from the Greek word for
“third”) with a nucleus made up of a proton plus 2 neutrons. Hydrogen-3
is mildly radioactive.
Hydrogen-2 fuses to helium more easily than hydrogen-1 does and, all
things being equal, hydrogen-2 will do so at lower temperatures than
hydrogen-1. Hydrogen-3 requires lower temperatures still. But even for
hydrogen-3 it still takes millions of degrees.
Hydrogen-3, although the easiest to be forced to undergo fusion, exists
only in tiny quantities.
Hydrogen-2, therefore, is the one to pin hopes on especially in
conjunction with hydrogen-3. Only 1 atom out of every 6000 hydrogen
atoms is hydrogen-2, but that is enough. There exists a vast ocean on
earth that is made up almost entirely of water molecules and in each
water molecule 2 hydrogen atoms are present. Even if only 1 in 6000 of
these hydrogen atoms is deuterium that still means there are about
35,000 billion tons of deuterium in the ocean.
What’s more, it isn’t necessary to dig for that deuterium or to drill
for it. If ocean water is allowed to run through separation plants, the
deuterium can be extracted without very much trouble. In fact, for the
energy you could get out of it, deuterium from the oceans, extracted by
present methods and without allowing for future improvement, would be
only one-hundredth as expensive as coal.
The deuterium in the world’s ocean, if allowed to undergo fusion little
by little, would supply mankind with enough energy to keep us going at
the present rate for 500,000,000,000 years. To be sure, to make
deuterium fusion practical, it may be necessary to make use of rarer
substances such as the light metal lithium. This will place a sharper
limit on the energy supply but even if we are careful, fusion would
probably supply mankind with energy for as long as mankind will exist.
Then, too, there would seem to be no danger of hydrogen fusion plants
running out of control. Only small quantities of deuterium would be in
the process of fusion at any one time. If anything at all went wrong,
the deuterium supply could be automatically cut off and the fusion
process, with so little involved, would then stop instantly. Moreover,
there would be less reason to worry about atomic wastes, for the most
dangerous products—hydrogen-3 and neutrons—could be easily taken care
of.
It seems ideal, but there is a catch. However clear the theory, before a
fusion power station can be established some practical method must be
found to start the fusion process, which means finding some way for
attaining temperatures in the millions of degrees.
One method for obtaining the necessary temperature was known by 1945. An
exploding fission bomb would do it. If, somehow, the necessary
hydrogen-2 was combined with a fission bomb, the explosion would set off
a fusion reaction that would greatly multiply the energy released. You
would have in effect a “thermonuclear bomb”. (To the general public,
this was commonly known as a “hydrogen bomb” or an “H-bomb”.)
In 1952 the first fusion device was exploded by the United States in the
Marshall Islands. Within months, the Soviet Union had exploded one of
its own and in time thermonuclear bombs thousands of times as powerful
as the first fission bomb over Hiroshima were built and exploded.
All thermonuclear bombs have been exploded only for test purposes. Even
testing seems to be dangerous, however, at least if it is carried on in
the open atmosphere. The radioactivity liberated spreads over the world
and may do slow but cumulative damage.