13.7 NUCLEAR ENERGY

The curve of binding energy per nucleon Ebn, given in Fig. . , has a long flat middle region between A = and A = . In this region the binding energy per nucleon is nearly constant ( .

MeV). For the lighter nuclei region, A < , and for the heavier nuclei region, A > , the binding energy per nucleon is less than . MeV, as we have noted earlier. This feature of the binding energy curve means that nuclei in the middle region & A & are more tightly bound than nuclei with A < and A > .

Energy then can be released if less tightly bound nuclei are transmuted into more tightly bound nuclei. Two such processes, which we have already referred to, are fission and fusion. In conventional energy sources like coal or petroleum, energy is released through chemical reactions. The energies involved are of the order of electron volts per atom.

As we have seen, energies involved in FIGURE . Energy level diagram showing the emission of " rays by a 60Co nucleus subsequent to beta decay. nuclear processes are million times larger (in MeVs per nucleon). This means that for the same quantity of matter, nuclear sources will give a million times larger energy than conventional sources.

One kilogram of coal on burning gives J of energy, whereas kg of uranium, which undergoes fission, will generate on fission J of energy. . . Fission Soon after the discovery of neutron by Chadwick, Enrico Fermi found that when neutrons bombard various elements, new radioactive elements are produced.

However, when a neutron was bombared on a uranium target, the uranium nucleus broke into two nearly equal fragments releasing great amount of energy. An example of such a reaction is