Fusion is the process by which light elements combine to produce heavier
ones. Nuclei must be joined together, but all nuclei have positive charges
and thus repel each other. For nuclei to fuse, they must be brought so
close together that the stronger n uclear forces of attraction can overcome
the electric repulsion. This can only occur when the two nuclei are no
more than approximately 10-15m apart.
In order for nuclei to come within 10-15m of each other, the repulsion between their protons must be overcome. This can occur only if the atoms containing the nuclei are moving towards each other fast enough. If the atoms of a material are to move fast enough for their nuclei to fuse when they collide, the temper ature of the material must be very high indeed. This reaction is the primary source of the world's energy. It has been taking place on the sun for at least 5.0 X 109 years. At 1 000 000oC, 1 g of deuterium can undergo fusion and r elease enough energy to supply the electrical needs of an average North American home for nearly 40 years.
Accurate measurements of atomic mass have shown that the mass of products is less than the mass of the reactants. Just as in the fission reaction, it is the amount of the loss in mass that is converted into energy.
The first manufactured use of the energy of nuclear fission was in the fusion bomb, popularly called the thermonuclear or hydrogen bomb. It was devised by a team led by the American physicist Edward Teller(1908-) and exploded in 1952. After a series of fission bombs had been exploded it was discovered that the temperatures created exceeded 108oC, high enough to sustain the fusion reaction.
The advantages of fusion power are that the fuel is cheap and easy to obtain (probably deuterium from water), and the by-products are harmless(primarily helium nuclei and a few neutrons). With these advantages, fusion power would seem to be the answer to the world's energy needs. However, human-made fusion has so far been accomplished only in the fusion bomb.