expressions one encounters are "annihilation", "fission", "fusion", "thermonuclear reaction", "triggering", etc. Without a comprehensive scientific background it is difficult to understand the detailed meaning of such terms, but an attempt will nevertheless be made in the next few pages to outline the general significance of such terminologies, albeit-in a crude fashion.
    In the first place, the obvious prerequisite quality of any explosive substance is that it shall yield energy in vast quantities and in a very short period of time, e.g. kilotons in microseconds. Scientists for many centuries were aware of the fact that work, electricity, heat and light were forms of energy, but the most revolutionary concept of all resulted from Einstein's - work on the special theory of relativity. According to this theory the mass of a body should vary with the velocity at which it was travelling and hence that mass is a form of energy. This fantastic concept has been proved true in numerous ways by the elaborate experiments of many eminent scientists; one of the earliest confirmations of the theory being provided by Sir John Cockcroft, now, Director, A.E.R.E. Harwell, during his experiments on the bombardment of Lithium nuclei by protons.

                Einstein's celebrated equation is usually written in the form:
                Energy in Ergs' = Mass in grams X (Velocity of light in cms/sec.) 2 
                E = Mc2.

Scientists are rather prone to express energy values in more precise but rather abstruse terms such as "ergs" or "million electron volts" (MeV). For our present purposes it might be better to write the Einstein equation in the more understandable form:

I gram of matter = 20,000 tons T.N.T. (approximately)

     This suggests that during the detonation of a nominal atomic bomb, one gram of the substance composing its vital part has been completely annihilated and turned into energy. How has this been achieved?  
    It is generally accepted that in the kiloton weapons, the vital parts consist of either uranium, U235 metal or plutonium, Pu239 metal, and we may presume that it is some portion of these metals which has been consumed by the process called "fission". In order to understand more fully what happens during fission we must now examine the general structure of atoms and nuclei in a little more detail. 
    During the present century, scientists have established that all the elements, iron, oxygen, carbon, etc., known to mankind are composed of particulate agglomerates built up from three primary particles which are so arranged as to preserve a state of electrical neutrality. These ultimate particles of matter are shown in symbolic form in the following table and it is observed that the proton is positively charged, the electron is negatively charged and the neutron is electrostatically uncharged.
    Over a hundred elements are now known to science and all the atoms of these elements possess a very similar atomic structure which is most easily illustrated by reference to one simple atom type. The accompanying diagram is representative of the structure of a beryllium atom and scientific notation writes it as, 4Be9. The upper right-hand number gives the number of nucleons (neutrons and protons) in the hard central core

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