Neutron

Nuclear Fission: Nuclear fission is the process of splitting large nuclei into smaller nuclei. Generally atoms with a proton number of more than 92 are unstable and are able to increase stability by randomly splitting into two. This process is both spontaneous (if occurs naturally) or induced (if caused by the actions of man). Induced fission occurs when a neutron is made to collide with the nucleus of an unstable atom. This causes the nucleus to become very unstable and ultimately results in it splitting in an attempt to gain greater stability. The neutron that is directed at the atom must be of low energy otherwise it would not be captured correctly. A neutron at this speed is called a thermal neutron. This induced fission can result in a number of different products, and also produces three free neutrons which can then go on to collide with other unstable nuclei in the same way creating a chain reaction. The sum of the nucleon number of the products must add up to the nucleon number of the original nuclei. When nuclear fission occurs energy is released as the new nuclei have a higher binding energy per nucleon. Larger nuclei are more likely to undergo fission as they have greater instability. The products of fission are often radioactive as they have a proportionally higher number of neutrons than nuclei of a similar atomic number. They therefore undergo radioactive to gain stability.

Nuclear Reactors: The energy produced from fission can be harnessed in nuclear reactors. These reactors use uranium rods (mainly 235 but some use plutonium). When they undergo fission they release neutrons which then go on to collide with further uranium atoms (known as a chain reaction). The fuel rods are placed in a moderator such as water to slow down the neutrons so they are slow enough to be absorbed. The chain reaction however must also be controlled otherwise too many fission reactions will occur releasing huge amount of energy in a short time. Excess neutrons are therefore absorbed by control rods, often made of carbon. Reactants also require coolants to removes the heat produced by fission. This moderator is often water but may be a gas such as carbon dioxide. The heat that is removed is used to move a turbine linked to a generator.

Nuclear Fusion: Nuclear fusion is the process of combing two light nuclei into one larger nucleus. The process releases a lot of energy as the produced nucleus has a higher binding energy per nucleon. The nuclei of all atoms are positively charged due to the protons and therefore the electrostatic repulsion between nuclei must be overcome so they are able to get close enough to each other that the strong force can hold them together. This energy is about 1 MeV (1.6x10-13J). This energy comes from very high temperatures (hence fusion reactions occur on the sun).