Nuclear Fusion is an energy-producing process which takes
place continuously within the cores of the sun and stars. In the core of
the sun and other stars around the universe the cores can reach extreme
temperatures of 10-15 million degrees Celsius, Hydrogen is converted to Helium
while releasing immense amounts of energy, this reaction produces enough energy
to sustain life on earth. A very similar reaction takes place within nuclear
bombs. This is done by combining Tritium and Deuterium to make a larger
isotope of a helium atom. During this process extreme amounts of energy
are released in a few seconds.
Here on earth different types of fusion reactions are
involved. The most suitable reaction occurs between the nuclei of the two heavy
forms of Hydrogen, these are known as isotopes - Deuterium (D) and Tritium (T);
eventually reactions involving just Deuterium or Deuterium and Helium (3He) may
be used to do the same thing as Tritium and Deuterium.
Most Suitable Fusion Reaction.
For a Deuterium and Tritium reaction temperatures of over 100
Million degrees C are needed for the fuel has changed its state from gas to
PLASMA. In a plasma, the electrons have been separated from the atomic nuclei (usually called the "ions").
Plasma is found in the sun and all of the stars in the universe. The only
natural way that it is found on Earth is in lightning. We can make plasma
by putting Helium atoms under massive amounts of heat and pressure.
Understanding plasma required major developments in physics. Plasmas are now
used widely in industry,
especially for semi-conductor manufacture.
Problems with Fusion Bombs
The problem with fusion is that Deuterium and Tritium are that
they are both gases and are hard to store.
Both gases have to be put under extreme pressure and high temperatures to
start the fusion reaction.
Tritium is also very hard to come by and has a very short half life.
This means that it cannot be kept in a bomb without having to be replenished
constantly.
How These Problems Were
Solved
To solve the problem with Deuterium being hard to store they
chemically combined it with Lithium which makes a solid Lithium-Deuterate
compound which reacts the same except it is able to be stored very well.
To solve the temperature and pressure problem Stanislaw Ulam figured out
that most of the radiation that comes out of a fission reaction was x-rays that
could provide both the high temperatures and pressures that is necessary to
start the fusion reaction. This means that by sticking a fission bomb
inside of a fusion bomb the problem would be solved.
The Tritium problem is solved when they noticed that neutrons from the
fission reaction makes Tritium from Lithium. Lithium-6 plus a neutron
yields Tritium and Helium-4, or Lithium-7 plus a neutron yields Tritium,
Helium-4 and a neutron. This means that the Tritium would not have to be
stored in the bomb but instead become usable when the chemical reaction takes
place.
Fuels
Deuterium is abundant as it can be extracted from all forms of
water. If all the world's city were to be provided by fusion power stations,
Deuterium supplies would blast for millions of years.
Tritium does not occur naturally and will be manufactured from
Lithium within the
machine.
Lithium, the lightest metal, is plentiful in the earth's
crust. If all the world's electricity were to be provided by fusion, known
reserves would last for at least 1000 years.
Once the reaction is established, even though it occurs
between Deuterium and Tritium, the consumables are Deuterium and Lithium.
Interesting facts
For example, 10 grams of Deuterium which can be extracted from
500 liters of water and 15g of Tritium produced from 30g of Lithium would
produce enough fuel for the lifetime electricity needs of an average person in
an industrialized country.
