Wilhelm Röntgen, of Germany, discovered x-rays in 1885 and by 1934 Enrico Fermi had split the nucleus of the uranium atom. At that time he was unable to explain the results. In 1938 Fermi’s experiment was repeated by Otto Hahn and Fritz Strassmann, and they were still unable to explain the results. One of their former colleagues, Lise Meitner was able to come up with the fission explanation, and her nephew Otto Frisch coined the word “fission” in 1939. By this time, physicists and chemists like Niels Bohr, Albert Einstein, James Chadwick, Ernest Rutherford, and Marie Curie were able to accurately describe the structure of the atom and properties of radioactivity. It was a period of intense and exciting scientific research.
Nuclear fission can be described as the reaction that occurs when the nucleus of an atom splits into two smaller nuclides having similar masses. This process releases one or more neutrons in the case of the fissioning of a nucleus with a high mass number. A neutron with a suitable energy may interact with a nucleus to induce fission. A nucleus may undergo spontaneous fission very rarely — without any help at all.
During the fission process, energy is released as less energy is required to hold two smaller nuclei together than for the large nucleus. The energy release in one fission is about a million times greater than that of the most energetic chemical reactions because it involves the nuclear Strong Force rather than the Electromagnetic Force. The energy release is sufficiently large that for a large number of fissions, it is possible to demonstrate the loss of mass based on Einstein’s equation: e=mc2.
Of the naturally-occurring nuclides, the uranium-235 atom is the most fissioned using low energy neutrons. When a neutron traveling at just the right speed interacts with the nucleus of a uranium-235 atom, the nucleus splits into two smaller parts, producing a pair of atoms of different elements. The fission process also releases two or three neutrons. The new atoms are radioactive isotopes.
If the neutrons released during fission can be made to go on to split more uranium-235 atoms which in turn, create more radioactive isotopes and release more neutrons, this cycle is known as a nuclear fission chain reaction. This process will continue until either the uranium-235 is used up or until the flow of neutrons is stopped. Learning how to control the fission process in uranium-235 and produce other radioactive elements gave birth to an entirely new industry – The Nuclear Industry.