Neutron

=**Neutrons**= The **neutron** is a [|subatomic] [|hadron] particle which has the symbol n or n 0
 * , no net [|electric charge] and a [|mass] slightly larger than that of a [|proton] . With the exception of [|hydrogen], [|nuclei] of [|atoms] consist of [|protons] and neutrons, which are therefore collectively referred to as [|nucleons] . The number of protons in a nucleus is the [|atomic number] and defines the type of [|element] the atom forms. Neutrons are necessary within an atomic nucleus as they bind with protons via the [|strong force] ; protons are unable to bind with each other due to their mutual [|electromagnetic repulsion] being stronger than the attraction of the strong force. The number of neutrons is the [|neutron number] and determines the [|isotope] of an element. For example, the abundant [|carbon-12] isotope has 6 protons and 6 neutrons, while the very rare radioactive [|carbon-14] isotope has 6 protons and 8 neutrons.**

While bound neutrons in stable nuclei are stable, free neutrons are unstable; they undergo [|beta decay] with a [|mean lifetime] of just under 15 minutes (881.5 ± 1.5 s). [|[4]] Free neutrons are produced in [|nuclear fission] and [|fusion]. Dedicated [|neutron sources] like [|research reactors] and [|spallation sources] produce free neutrons for use in [|irradiation] and in [|neutron scattering] experiments. Even though it is not a [|chemical element], the free neutron is sometimes included in tables of nuclides. [|[5]] It is then considered to have an [|atomic number] of zero and a [|mass number] of one, and is sometimes referred to as [|neutronium] .[// [|citation needed] //] The neutron has been the key to nuclear power production. After the neutron was discovered in 1932, it was realized in 1933 that it might mediate a [|nuclear chain reaction]. In the 1930s, neutrons were used to produce many different types of [|nuclear transmutations]. When [|nuclear fission] was discovered in 1938, it was soon realized that this might be the mechanism to produce the neutrons for the chain reaction, if the process also produced neutrons, and this was proven in 1939, making the path to nuclear power production evident. These events and findings led directly to the first man-made nuclear chain reaction which was self-sustaining ( [|Chicago Pile-1], 1942) and to the first [|nuclear weapons] (1945).


 * **neutrons have no electrical charge**
 * The mass of a neutron is slightly larger than that of a proton.
 * The nuclei of an atom consists of protons and neutrons, commonly referred to as nucleons.
 * Since protons are unable to bind with themselves, neutrons are the binding force.
 * The neutron number determines the isotope of the element, in that you add the proton number to the number of neutrons.
 * For example, Carbon-14 has 6 protons and 8 neutrons.

Stability and beta decay
The [|Feynman diagram] for beta decay of a neutron into a [|proton], [|electron] , and [|electron antineutrino] via an intermediate heavy [|W boson] Under the [|Standard Model] of particle physics, because the neutron consists of three [|quarks], the only possible decay mode without a change of [|baryon number] is for one of the quarks to [|change] [|flavour] via the [|weak interaction]. The neutron consists of two [|down quarks] with charge − 1⁄3 [|e] and one [|up quark] with charge + 2⁄3 e, and the decay of one of the down quarks into a lighter up quark can be achieved by the emission of a [|W boson]. By this means the neutron decays into a [|proton] (which contains one down and two up quarks), an [|electron], and an [|electron antineutrino]. Outside the nucleus, free neutrons are unstable and have a [|mean lifetime] of 881.5± 1.5 s (about 14 minutes, 42 seconds); therefore the [|half-life] for this process (which differs from the mean lifetime by a factor of [|ln] (2) = 0.693 ) is 611.0± 1.0 s (about 10 minutes, 11 seconds). [|[4]] Free neutrons decay by emission of an electron and an electron antineutrino to become a proton, a process known as [|beta decay] : [|[8]] n 0 → p + + e − + ν e Neutrons in unstable nuclei can also decay in this manner. However, inside a nucleus, protons can also transform into a neutron via [|inverse beta decay]. This transformation occurs by emission of an [|antielectron] (also called positron) and an electron [|neutrino] : p + → n 0 + e + + ν e The transformation of a proton to a neutron inside of a nucleus is also possible through [|electron capture] : p + + e − → n 0 + ν e Positron capture by neutrons in nuclei that contain an excess of neutrons is also possible, but is hindered because positrons are repelled by the nucleus, and quickly [|annihilate] when they encounter electrons. When bound inside of a nucleus, the instability of a single neutron to beta decay is balanced against the instability that would be acquired by the nucleus as a whole if an additional proton were to participate in repulsive interactions with the other protons that are already present in the nucleus[// [|clarification needed] //]. As such, although free neutrons are unstable, bound neutrons are not necessarily so. The same reasoning explains why protons, which are stable in empty space, may transform into neutrons when bound inside of a nucleus.

Uses
[|//Cold//, //thermal// and //hot//] [|neutron radiation] is commonly employed in [|neutron scattering] facilities, where the radiation is used in a similar way one uses [|X-rays] for the analysis of [|condensed matter]. Neutrons are complementary to the latter in terms of atomic contrasts by different scattering [|cross sections] ; sensitivity to magnetism; energy range for inelastic neutron spectroscopy; and deep penetration into matter.The neutron plays an important role in many nuclear reactions. For example, neutron capture often results in [|neutron activation], inducing [|radioactivity]. In particular, knowledge of neutrons and their behavior has been important in the development of [|nuclear reactors] and [|nuclear weapons]. The [|fissioning] of elements like [|uranium-235] and [|plutonium-239] is caused by their absorption of neutrons. The development of "neutron lenses" based on total internal reflection within hollow glass capillary tubes or by reflection from dimpled aluminum plates has driven ongoing research into neutron microscopy and neutron/gamma ray tomography. [|[16]] [|[17]] [|[18]] A major use of neutrons is to excite delayed and prompt [|gamma rays] from elements in materials. This forms the basis of [|neutron activation analysis] (NAA) and [|prompt gamma neutron activation analysis] (PGNAA). NAA is most often used to analyze small samples of materials in a [|nuclear reactor] whilst PGNAA is most often used to analyze subterranean rocks around [|bore holes] and industrial bulk materials on conveyor belts. Another use of neutron emitters is the detection of light nuclei, particularly the hydrogen found in [|water] molecules. When a fast neutron collides with a light nucleus, it loses a large fraction of its energy. By measuring the rate at which slow neutrons return to the probe after reflecting off of hydrogen nuclei, a [|neutron probe] may determine the water content in soil.