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Encyclopedia > Free neutron
Free neutron

General
Name, symbol free neutron,1n
Neutrons 1
Protons 0
Nuclide Data
Natural abundance synthetic
Half-life 613 ± 0.6 seconds
Isotope mass 1.0086649 u
Spin 1/2+
Excess energy 8071.323± 0.002 keV
Binding energy 0.000± 0.000 keV
Decay mode Decay energy
Beta emission 0.782353 MeV

$hbox{n}tohbox{p}+hbox{e}^-+overline{nu}_{mathrm{e}}$

Even though it is not a chemical element, the free neutron is often included in tables of nuclides. It is then considered to have an atomic number of zero and a mass number of one. The periodic table of the chemical elements A chemical element, or element for short, is a type of atom that is defined by its atomic number; that is, by the number of protons in its nucleus. ... It has been suggested that List of elements by atomic number be merged into this article or section. ... The mass number (A), also called atomic mass number or nucleon number, is the number of nucleons (protons and neutrons) in an atomic nucleus. ...

Various nuclides become more stable by expelling neutrons as a decay mode; this is known as neutron emission, and happens commonly during spontaneous fission. ... In physics, the decay mode describes a particular way a particle decays. ... Neutron emission is a type of radioactive decay in which an atom contains excess neutrons and a neutron is simply ejected from the nucleus. ... Spontaneous fission (SF) is a form of radioactive decay characteristic of very heavy isotopes, and is theoretically possible for any atomic nucleus whose mass is greater than or equal to 100 amu (elements near ruthenium). ...

Cosmic radiation interacting the earth's atmosphere continuously generates neutrons that can be detected at the surface. Cosmic rays can loosely be defined as energetic particles originating outside of the Earth. ...

Nuclear fission reactors naturally produce free neutrons; their role is to sustain the energy-producing chain reaction. The intense neutron radiation can also be used to produce various radioisotopes through the process of neutron activation. Core of a small nuclear reactor used for research. ... A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions. ... Neutron radiation consists of free neutrons. ... Neutron activation is the process by which neutron radiation induces radioactivity in materials. ...

Experimental nuclear fusion reactors produce free neutrons as a waste product. However, it is these neutrons that possess most of the energy, and converting that energy to a useful form has proved a difficult engineering challenge to nuclear physicists. This also explains why this form of energy is likely to create around twice the amount of radioactive waste of a fission reactor, but with a short (50-100 years) decay period (as opposed to the 10,000 years for fission waste). [1] [2] Internal view of the JET tokamak superimposed with an image of a plasma taken with a visible spectrum video camera. ...

Thermal neutron

A thermal neutron is a free neutron that is Boltzmann distributed with kT = 0.024 eV (4.0×10-21 J) at room temperature. This gives characteristic (not average, or median) speed of 2.2 km/s. The name 'thermal' comes from their energy being that of the room temperature gas or material they are permeating. (see kinetic theory for energies and speeds of molecules). After a number of collisions (often in the range of 10–20) with nuclei, neutrons arrive at this energy level, provided that they are not absorbed. A chart displaying the speed probability density functions of the speeds of a few noble gases at a temperature of 298. ... The Maxwellâ€“Boltzmann distribution is a probability distribution with applications in physics and chemistry. ... The joule (IPA pronunciation: or ) (symbol: J) is the SI unit of energy. ... Kinetic theory attempts to explain macroscopic properties of gases, such as pressure, temperature, or volume, by considering their molecular composition and motion. ... This article or section does not adequately cite its references or sources. ...

In many substances, thermal neutrons have a much larger effective cross-section than faster neutrons, and can therefore be absorbed more easily by any atomic nuclei that they collide with, creating a heavier — and often unstableisotope of the chemical element as a result. The nucleus of an atom is the very small dense region, of positive charge, in its centre consisting of nucleons (protons and neutrons). ... A radionuclide is an atom with an unstable nucleus. ... Isotopes are any of the several different forms of an element each having different atomic mass (mass number). ... The periodic table of the chemical elements A chemical element, or element for short, is a type of atom that is defined by its atomic number; that is, by the number of protons in its nucleus. ...

Most fission reactors use a neutron moderator to slow down, or thermalize the neutrons that are emitted by nuclear fission so that they are more easily captured, causing further fission. Others, called fast breeder reactors, use fission energy neutrons directly. Core of a small nuclear reactor used for research. ... This does not adequately cite its references or sources. ... For the generation of electrical power by fission, see Nuclear power plant An induced nuclear fission event. ... The fast breeder or fast breeder reactor (FBR) is a type of fast neutron reactor that produces more fissile material than it consumes. ...

Cold neutrons

These neutrons are thermal neutrons that have been equilibrated in a very cold substances such as liquid deuterium. These are produced in neutron scattering research facilities. Deuterium, also called heavy hydrogen, is a stable isotope of hydrogen with a natural abundance in the oceans of Earth of approximately one atom in 6500 of hydrogen (~154 PPM). ... The term Neutron Scattering encompasses all scientific techniques whereby neutrons are used as a scientific probe. ...

Fission energy neutron

A fast neutron is a free neutron with a kinetic energy level close to 2 MeV (20 TJ/kg), hence a speed of 28,000 km/s. They are named fission energy or fast neutrons to distinguish them from lower-energy thermal neutrons, and high-energy neutrons produced in cosmic showers or accelerators. Fast neutrons are produced by nuclear processes such as nuclear fission. A chart displaying the speed probability density functions of the speeds of a few noble gases at a temperature of 298. ... mega- (symbol M) is an SI prefix in the SI system of units denoting a factor of 106, i. ... The electronvolt (symbol eV, or, rarely and incorrectly, ev) is a unit of energy. ... tera- (symbol: T) is a prefix in the SI system of units denoting 1012, or 1 000 000 000 000. ... The joule (IPA pronunciation: or ) (symbol: J) is the SI unit of energy. ... The U.S. National Prototype Kilogram, which currently serves as the primary standard for measuring mass in the U.S. It was assigned to the United States in 1889 and is periodically recertified and traceable to the primary international standard, The Kilogram, held at the Bureau International des Poids et... km redirects here. ... Look up second in Wiktionary, the free dictionary. ... This article or section does not adequately cite its references or sources. ... For the generation of electrical power by fission, see Nuclear power plant An induced nuclear fission event. ...

Fast neutrons can be made into thermal neutrons via a process called moderation. This is done with a neutron moderator. In reactors, typically heavy water, light water, or graphite are used to moderate neutrons. This does not adequately cite its references or sources. ... Heavy water is dideuterium oxide, or D2O or 2H2O. It is chemically the same as normal water, H2O, but the hydrogen atoms are of the heavy isotope deuterium, in which the nucleus contains a neutron in addition to the proton found in the nucleus of any hydrogen atom. ... Light water, in the terminology of nuclear reactors, is ordinary water. ... Graphite (named by Abraham Gottlob Werner in 1789 from the Greek Î³ÏÎ±Ï†ÎµÎ¹Î½ (graphein): to draw/write, for its use in pencils) is one of the allotropes of carbon. ...

Intermediate neutrons

A fission energy neutron that is slowing down is often said to have intermediate energy. There are not many non-elastic reactions in this energy region, so most of what happens is just slowing to thermal speeds before eventual capture.

High-energy neutrons

These neutrons have more energy than fission energy neutrons and generated in accelerators or in the atmosphere from cosmic particles. They can have energies as high as tens of joules per neutron.

Neutron radiation consists of free neutrons. ... The term Neutron Scattering encompasses all scientific techniques whereby neutrons are used as a scientific probe. ... A chart displaying the speed probability density functions of the speeds of a few noble gases at a temperature of 298. ... This is a list of particles in particle physics, including currently known and hypothetical elementary particles, as well as the composite particles that can be built up from them. ... In nuclear physics, a nuclear reaction is a process in which two nuclei or nuclear particles collide to produce products different from the initial particles. ... A thermal reactor is the most common category of nuclear reactor. ... A dineutron is a particle consisting of two neutrons that is considered to have a transitory existence in nuclear reactions produced by helions that result in the formation of a proton and a nucleus having the same atomic number as the target nucleus but a mass number two units greater. ... A fast neutron is a free neutron with a kinetic energy level close to 1 MeV (10 TJ/kg, hence a speed of 14,000 km/s. ... Radiation hazard symbol. ... Isotopes are any of the several different forms of an element each having different atomic mass (mass number). ... neutron flux n : the rate of flow of neutrons; the number of neutrons passing through a unit area in unit time via dictionary. ... A neutron star is one of the few possible endpoints of stellar evolution. ... Neutronium is a term used in science fiction and popular literature to refer to an extremely dense phase of matter composed primarily of neutrons. ... A tetraneutron is a hypothesised stable cluster of four neutrons. ...

References

1. ^ [Particle Data Group's Review of Particle Physics 2006]
• Krane, K. S. (1998) Introductory Nuclear Physics
• G. L. Squires (1997) Introduction to the Theory of Thermal Neutron Scattering
• M. S. Dewey, D. M. Gilliam, J. S. Nico, M. S. Snow and F. E. Wietfeldt NIST Neutron Lifetime Experiment
 Nothing Isotopes of neutron Dineutron Produced from: Many nuclear reactions Decay chain Decays to: Hydrogen-1

Results from FactBites:

 Neutron - Wikipedia, the free encyclopedia (1172 words) The neutron and proton are instances of a nucleon. Although the neutron has zero net charge, it may interact electromagnetically in two ways: first, the neutron has a magnetic moment of the same order as the proton; second, it is composed of electrically charged quarks. Free neutron beams are obtained from neutron sources by neutron transport.
 Free neutron - Wikipedia, the free encyclopedia (190 words) A free neutron is a neutron that exists outside of an atomic nucleus. While neutrons can be stable when bound inside nuclei, free neutrons are unstable and decay with a half-life of just under 15 minutes. Nuclear reactors are designed to produce free neutrons in copious amounts; their role is to sustain the energy-producing chain reaction.
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