The neutron is a subatomic hadron particle that has the symbol n or n0. Neutrons have no net electric charge and a massslightly larger than that of a proton. With the exception of hydrogen-1, the nucleus of every atom consists of at least one or more of both protons and neutrons. Protons and neutrons are collectively referred to as “nucleons”. Since interacting protons have a mutual electromagnetic repulsion that is stronger than their attractive nuclear interaction, neutrons are often a necessary constituent within the atomic nucleus that allows a collection of protons to stay atomically bound (see diproton &neutron-proton ratio). Neutrons bind with protons and one another in the nucleus via the nuclear force, effectively stabilizing it. The number of neutrons in the nucleus of an atom is referred to as its neutron number, which reveals the specific isotopeof that atom. For example, the abundant carbon-12 isotope has 6 protons and 6 neutrons, whereas the rare radioactivecarbon-14 isotope also has 6 protons but, instead, 8 neutrons. Elements may be found in nature as only one isotope or with as many as 10 isotopes (Manganese and Tin, respectively).

While the bound neutrons in nuclei can be stable (depending on the nuclide, free neutrons are unstable; they undergo beta decay with a mean lifetime of just under 15 minutes (881.5±1.5 s). Free neutrons are produced in nuclear fission and fusion. Dedicated neutron sources like neutron generators, research reactors and spallation sources produce free neutrons for use in irradiation and in neutron scatteringexperiments. Even though it is not a chemical element, the free neutron is sometimes included in tables of nuclides.

The neutron has been key to the production of nuclear power. The neutron was discovered in 1932, and in 1933, it was realized that it might mediate a nuclear chain reaction. In the 1930s, neutrons were used to produce many different types ofnuclear transmutations. When nuclear fission was discovered in 1938, it became clear that, if the process also produced neutrons, this might be the mechanism to produce the neutrons for a chain reaction. This was proven in 1939, opening the path to nuclear power production. These events and findings led directly to the first self-sustaining, man-made, nuclear chain reaction (Chicago Pile-1, 1942) and to the first nuclear weapons (1945).


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By Trinh Manh Do

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