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NUCLEAR FISSION
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What is Nuclear Fission? |
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The word nuclear means 'of atoms' and the word fission means 'to split up'. Therefore, nuclear fission literally means the 'splitting up of atoms'. The animation shows an atom (lots of protons & neutrons) splitting up. The blue balls are neutrons and the red balls are protons. When the atom splits up neutrons and radiation (energy) are released. |
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The Nuclear Fission of Uranium Atoms |
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When we talk about nuclear fission we are generally referring to the splitting up of very 'heavy', radioactive Uranium atoms. Uranium is the heaviest naturally occurring element. It has an atomic number 92, which means there are 92 protons in the nucleus of each atom. There are several isotopes of Uranium. This means there are atoms of Uranium that all have 92 protons in the nucleus but different numbers of neutrons. Three examples are atoms having 143, 146 & 147 neutrons in the nucleus, giving mass numbers of 235, 238 and 239 respectively. Generally the nuclear fission of Uranium-235 is the basis of how all nuclear reactors and power stations work. A neutron is bombarded into an atom of Uranium-235. Fission occurs, i.e. the Uranium atom splits up to give two smaller atoms. A huge amount of energy (heat) is released. |
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The picture below shows the nuclear fission of Uranium-235. |
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The nuclear fission of a 'heavy', radioactive Uranium-235 atom is animated below. |
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A neutron (small green particle in this animation) hits a Uranium-235 atom. |
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The Uranium-235 atom becomes unstable and splits up into two smaller atoms: Barium-140 and Krypton-93. These are themselves radioactive and are known as nuclear waste (radioactive material that is difficult and expensive to dispose of). |
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Three neutrons and a huge amount of energy are released in the fission process. |
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Each of the three neutrons released hits another Uranium-235 atom and so on… |
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Another animation of Uranium-235 fission is shown below. |
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This animation shows that when the neutron is absorbed Uranium-236 is formed. |
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Fission of the unstable Uranium-236 atom gives Barium-142 and Krypton-92. |
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In this case only two neutrons are released. |
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The two animations show what can happen when a Uranium-235 atom splits up. |
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The Chain Reaction |
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The fission of a Uranium-235 atom gives two or three neutrons and a huge amount of energy. Each of the neutrons produced can hit another Uranium-235 atom giving yet more neutrons and more energy. This process can continue forever. We call it a chain reaction because it does not stop. |
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The animation below shows a chain reaction of the fission of Uranium-235 atoms. |
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Each time fission occurs a lot of energy is released, much more energy compared to the amount you get when a chemical bond forms. |
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A nuclear fission chain reaction gives a massive amount of energy. Nuclear bombs give up this energy causing destruction. Bombs made with chemicals are much less powerful. |
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