It actually began when the Italian-born physicist Enrico Fermi, working in the United States, invented an apparatus which produced the first atomic chain reactions. In 1940 both the Americans and British were researching the atom bomb and when the United States entered WW2, the British joined the American "Manhattan Project" and production of the bomb went on ahead in the US.

The first atom bomb has lead to development such as the hydrogen and nuclear bomb, which are much more powerful than the first atomic bomb. However because of damages to our environment and atmosphere, programmes for such development has been limited and treaty are signed between major countries around the world.

The explosion of an atom bomb consists of an immense release of energy caused by the chain reaction in which more and more atoms are split. The reaction begins when on atom of U-235 or plutonium (a radioactive by-product of nuclear fission) splits under the impact of a single neutron. The atom splits into two fragments and at the same time releases more neutrons, which then split more atoms, and so on, in a self-sustaining sequence. The whole process only takes one millionth of a second to complete, but in order for a chain reaction to occur there has to be a certain quantity of U-235 of plutonium present.