In 1919, the atom was first divided at the University of Manchester, England.
Already in the 5th century BC, the Greek philosophers Leucippus and Democritus postulated the theory that all matter is made up of indivisible particles. Their concept of the atom - a term derived from the Greek atoms, meaning "indivisible" - as the smallest component of nature lasted more than 2,000 years; later, in 1919, the atom was first divided at the University of Manchester, England.
This achievement, which heralded the nuclear age, was the culmination of experiments carried out by the physicist Ernest Rutherford, of New Zealand origin, who had investigated the alpha particles emitted by the radioactive element.
In a tube about 20 cm long, he inserted a rod at the end of which was a brass disc coated with radio. The other end of the tube was sealed with a thin metal disc and the outside was covered with zinc sulphide. The tube was filled with different gases.
The metal disc stopped most of the alpha particles emitted by the radio. But any high-energy particle formed by the action of the alpha particles on the gas atoms in the tube went through it. When they hit the zinc screen, they produced small sparks by releasing energy.
When the tube was filled with oxygen or carbon dioxide, the frequency of the sparks decreased because these gases stopped the alpha particles. But when air was used, sparks increased, which was attributed to its nitrogen content.
The hypothesis was confirmed by using pure nitrogen. Rutherford concluded that the alpha particles had disintegrated the nitrogen atoms, and that electrically charged hydrogen atoms had formed. These particles passed through the metal disc. He called them protons, a term derived from the Greek meaning "first".
"We must conclude, Rutherford wrote, that the nitrogen atom has disintegrated. The press expressed this in a more dramatic way: "Rutherford destroys the atom.
Later experiments confirmed Rutherford's conclusions. Alpha particles collided with a nitrogen nucleus and combined with it before disintegrating to produce protons and oxygen atoms.
More efficient means of dividing the atom were soon discovered. In 1928 John Cockcroft and Ernest Walton of Cambridge, England replaced alpha particles with protons. Using a voltage multiplier, a device that increases electrical energy and accelerates particles, they made the protons collide with greater force. In 1932, they fired protons at lithium atoms and produced two helium atoms for each lithium atom.
Their success led to an avalanche of experiments in which various particles were tested, bombarding different "targets".
In January 1939, Otto Hahn and Lise Meitner of McGill University in Toronto, Canada, concluded that by bombarding uranium with neutrons (from the nucleus of the atoms), uranium atoms divided almost in two, producing lighter elements and releasing enormous amounts of energy. When divided, an atom produced at least two neutrons, which in turn could continue to divide other atoms. This was the beginning to create the atomic bomb and nuclear energy.