We have completed the review of the development of the theory of atom over a period of more than 2500 years. It would, however, be highly improper to close the chapter with a sense of utter doom, which the above paragraph may forebode. Enormous progress has also been made in the direction of utilising nuclear energy for the benefit of mankind, and it is our duty to give the reader a glimpse of the nuclear research and development work in which some tens of thousands of scientists are busy all over the world today.
At Atomic Research Centres in the United States of America, Russia, the United Kingdom, France, the Federal Republic of Germany and International Centre a' Geneva, thousands of research teams are engaged in probing the heart of the atom.
Research work in the sub-nuclear world is based on a law of nature that the smaller the dimensions of the particles to be studied, the higher must be the energies of the beams serving as a probe. By way of comparison, consider the forces that hold the nucleus of an atom together. In order to learn something about the structure of the nuclei, one needs energies about 100 times greater than the binding energy of a proton in a nucleus. But to carry out research into the structure of proton or neutron, one requires energies 1000 times greater i.e. of the order of one thousand million electron volts. No wonder elementary 'particle physics' is, therefore, sometimes called 'high energy physics.'