Nuclear Fission: Discovery and Technological Development

In the 1890s Henri Becquerel (pictured at left) was investigating phosphorescent minerals, those which after exposure to light would glow in the dark. He wrapped photographic plates in black paper and tried placing various materials against the wrapped plates. Nothing happened until one day in 1896 when he tested uranium minerals and their salts. These caused strong darkening of the wrapped photographic plate, the first indication of the existence of a new form of radiation that could pass through paper and darken the photographic plate. Becquerel had discovered radioactivity.

Radioactivity can occur naturally, or, as learned through many investigations during the first half of the 20th Century, radioactive isotopes can be produced artificially by bombarding a target nucleus with a sub-atomic-size particle, a process called transmutation. Whether it’s the parent or the target nucleus which changes into a daughter, the change is relatively small; the daughter has a mass only a small amount different from the parent or target. Then suddenly, late in 1938, Otto Hahn (pictured at right with Lisa Meitner) and Fritz Strassmann (pictured at left) discovered a fundamentally new and unexpected exception. After irradiating uranium with neutrons, they were surprised to detect barium, an element only about half of the mass of uranium. The conclusion was inescapable; they had split the uranium atom into two parts. They had discovered nuclear fission -- the splitting of the atom.

Two physical properties of nuclear fission are particularly exciting and important; splitting the uranium nucleus with a neutron releases energy and a few additional neutrons. Almost immediately, Siegfried Flügge and Leo Szilard, independently, realized that those two properties meant the possibility of a nuclear chain reaction. A nuclear chain reaction, if it could be made to occur very quickly, meant the possibility of a new weapon of war, the atom bomb. A slow, controlled chain reaction might be used to generate electric power or to produce fissionable material for atom bombs. As the clouds of World War II darkened over Europe and the rest of the world, scientists focused attention on learning what was need to design and manufacture atom bombs. Enrico Fermi (pictured at right) built the first man-made nuclear fission reactor under the stands of Stagg Field at the University of Chicago, which became operational on December 2, 1942. At the time, Fermi and everyone else thought that was the first self-sustaining nuclear chain reaction, but they were wrong; Mother Nature had beat them to the punch. Interestingly, just months after the discovery of nuclear fission, Siegfried Flügge speculated on the possibility of nuclear explosions in uranium deposits. But, as you will see by perusing this website, there is much more to the story of natural nuclear fission.

Nuclear Fission Resources
Concerning the basics of nuclear fission -- this is a short list of some of the best links, selected by the education committee of the Canadian Nuclear Society.

The Virtual Nuclear Tourist !  has some fission basics (including more links) at

The US Nuclear Energy Institute has a web site called Science Club - Nuclear World at   ...specifically, their "Splitting the Atom" page (with animation) is at
Another one of the better web sites is "What is Uranium? How does it work?" - from the UIC, at

and a similar one at the World Nuclear Association :

The ABCs of Nuclear Science (educational site from Lawrence Livermore National Laboratory) is at     ....the part about fission is at

Our own AECL has a nice fission animation at
....and AECL's Kid's Zone has another fission animation (about half-way down the page) at

The Particle Adventure (another, more general, educational site from Lawrence Livermore National Laboratory) is at

Natural Radioactive Decay animation is at

Virtual Radiation Museum is at

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