Neutron radiation consists of free neutrons. Neutrons may be emitted during nuclear fission (either spontaneous or triggered), nuclear fusion, very high energy reactions such as in a Spallation Neutron Source, or from certain other reactions, most famously the (α,n) reaction, for example when a beryllium nucleus absorbs an alpha particle and emits a neutron. A free neutron is a neutron that exists outside of an atomic nucleus. ... Properties In physics, the neutron is a subatomic particle with no net electric charge and a mass of 939. ... Sketch of induced nuclear fission, a neutron (n) strikes a uranium nucleus which splits into similar products (F. P.), and releases more neutrons to continue the process, and energy in the form of gamma and other radiation. ... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing fusion power. ... April 2005 aerial photo of the SNS site, Oak Ridge, Tennessee, USA. The Spallation Neutron Source (SNS) is an accelerator-based neutron source being built in Oak Ridge, Tennessee, USA, by the U.S. Department of Energy (DOE). ... An alpha particle is deflected by a magnetic field Alpha particles or alpha rays (named after the first letter in the greek alphabet) are a form of particle radiation which are highly ionizing and have low penetration. ... Properties In physics, the neutron is a subatomic particle with no net electric charge and a mass of 939. ... General Name, Symbol, Number beryllium, Be, 4 Chemical series alkaline earth metals Group, Period, Block 2, 2, s Appearance white-gray metallic Atomic mass 9. ... Nucleus can mean: The Nuclear Envelope The nucleus is enveloped by a pair of membranes enclosing a lumen that is continuous with that of the endoplasmic reticulum. ... An alpha particle is deflected by a magnetic field Alpha particles or alpha rays (named after the first letter in the greek alphabet) are a form of particle radiation which are highly ionizing and have low penetration. ... Properties In physics, the neutron is a subatomic particle with no net electric charge and a mass of 939. ...

Neutron radiation is often called indirectly ionizing radiation. It does not ionize atoms in the same way protons, photons, and electrons do (exciting an electron) because neutrons have no charge, do not interact with electrons. However, neutron interactions are largely ionizing, for example when neutron absorption results in gamma emission and the gamma subsequently removes an electron from an atom, or a nucleus recoiling from a neutron interaction is ionized and causes more traditional subsequent ionization in other atoms. Because neutrons are uncharged, they are more penetrating than alpha radiation or beta radiation. In some cases they are more penetrating than gamma radiation, which is impeded in materials of high atomic number, but in materials made of "lighter" elements, such as hydrogen, oxygen, and nitrogen gamma rays often penetrate farther, depending on their energy . In health physics neutron radiation is considered a fourth radiation hazard alongside these other types of radiation. Another, sometimes more severe, hazard of neutron radiation is neutron activation, the ability of neutron radiation to induce radioactivity in most substances it encounters, including the body tissues of the workers themselves. This occurs through the capture of neutrons by atomic nuclei, which are transformed to another nuclide, frequently a radionuclide. This process accounts for much of the radioactive material released by the detonation of a nuclear weapon. It is also a problem in nuclear fission and nuclear fusion installations, as it gradually renders the equipment radioactive; eventually the hardware must be replaced and disposed of as low-level radioactive waste. Neutrons also degrade materials; intense bombardment with neutrons creates dislocations in the materials, leading to embrittlement of metals and other materials, and to swelling of some of them. This poses a problem for nuclear reactor vessels, and significantly limits their lifetime (which can be somewhat prolonged by controlled annealing of the vessel, reducing the number of the built-up dislocations). Ionizing radiation is a type of particle radiation in which an individual particle (for example, a photon, electron, or helium nucleus) carries enough energy to ionize an atom or molecule (that is, to completely remove an electron from its orbit). ... For alternative meanings see proton (disambiguation). ... In physics, the photon (from Greek φοτος, meaning light) is a quantum of excitation of the quantised electromagnetic field and is one of the elementary particles studied by quantum electrodynamics (QED) which is the oldest part of the Standard Model of particle physics. ... Properties The electron (also called negatron, commonly represented as e−) is a subatomic particle. ... An alpha particle is deflected by a magnetic field Alpha particles or alpha rays are a form of particle radiation which are highly ionizing and have low penetration. ... Beta particles are high-energy electrons emitted by certain types of radioactive nuclei such as potassium-40. ... This article is about electromagnetic radiation. ... The atomic number (Z) is a term used in chemistry and physics to represent the number of protons found in the nucleus of an atom. ... Health physics is the study of the risks of ionizing radiation to people and the environment. ... Neutron activation is the process by which neutron radiation induces radioactivity in materials. ... Radioactivity may mean: Look up radioactivity in Wiktionary, the free dictionary. ... Isotopes are atoms of a chemical element whose nuclei have the same atomic number, Z, but different atomic weights, A. The word isotope, meaning at the same place, comes from the fact that isotopes are located at the same place on the periodic table. ... Atoms of chemical elements may have many isotopes (different forms) with different atomic numbers and different atomic weights. ... The mushroom cloud of the atomic bombing of Nagasaki, Japan, 1945, rose some 18 km (11 mi) above the hypocenter. ... Sketch of induced nuclear fission, a neutron (n) strikes a uranium nucleus which splits into similar products (F. P.), and releases more neutrons to continue the process, and energy in the form of gamma and other radiation. ... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing fusion power. ... A Russian fissile material storage facility Radioactive waste is waste material containing radioactive chemical elements that does not have a practical purpose. ... For the syntaxic operation, see Dislocation (syntax) For the medical term, see Dislocation (medicine) In materials science a dislocation is a linear crystallographic defect, or irregularity, in crystal structure. ... Neutron-induced swelling is the increase of volume and decrease of density of materials subjected to intense neutron radiation. ... The word anneal has several meanings: In metallurgy and materials science annealing is a heat treatment wherein the microstructure of a material is altered, causing changes in its properties such as strength and hardness. ...

The neutrons in reactors are generally categorized as slow (thermal) neutrons or fast neutrons depending on their energy. Thermal neutrons are similar to a gas in thermodynamic equilibrium but are easily captured by atomic nuclei and are the primary means by which elements undergo atomic transmutation. A thermal neutron is a free neutron with a kinetic energy level of ca. ... 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. ... Transmutation is the conversion of one object into another. ...

In order to achieve an effective fission chain reaction, the neutrons produced during fission must be captured by fissionable nuclei, which then split, releasing more neutrons. In most fission reactor designs, the nuclear fuel is not sufficiently refined to be able to absorb enough fast neutrons to carry on the fission chain reaction, due to the lower cross section for higher-energy neutrons, so a neutron moderator must be introduced to slow the fast neutrons down to thermal velocities to permit sufficient absorption. Common neutron moderators include graphite, light water and heavy water. A few reactors (fast neutron reactors) and all nuclear weapons rely on fast neutrons. This requires certain changes in the design and in the required nuclear fuel. The element beryllium is particularly useful due to its ability to act as a neutron reflector or lens. This allows smaller quantities of fissile material to be used and is a primary technical development that led to the creation of neutron bombs. In scattering, a differential cross section is defined by the probability to observe a scattered particle in a given quantum state per solid angle unit (i. ... In nuclear engineering, a neutron moderator is a medium which reduces the velocity of fast neutrons, thereby turning them into thermal neutrons capable of sustaining a nuclear chain reaction. ... Graphite (named by Abraham Gottlob Werner in 1789, from the Greek γραφειν: to draw/write, for its use in pencils) is one of the allotropes of carbon. ... In speaking of nuclear reactors, light water is ordinary water. ... 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. ... A fast neutron reactor or simply a fast reactor is a category of nuclear reactor in which the fission chain reaction is sustained by fast neutrons. ... General Name, Symbol, Number beryllium, Be, 4 Chemical series alkaline earth metals Group, Period, Block 2, 2, s Appearance white-gray metallic Atomic mass 9. ... A neutron bomb is a type of nuclear weapon specifically designed to release a relatively large portion of its energy as energetic neutron radiation. ...

Cosmogenic neutrons, neutrons produced from cosmic radiation in the earth's atmosphere or surface, and those produced in particle accelerators can be significantly higher energy than those encountered in reactors. Most of them decay into a proton, an electron, and an antineutrino before reaching the ground; a few react with nuclei in the air. The reactions with Nitrogen 14 lead to the formation of Carbon 14, widely used in radiocarbon dating. Cosmic rays can loosely be defined as energetic particles originating outside of the Earth. ... Carbon-14, or 14C, is a radioactive isotope of carbon discovered February 27, 1940, by Martin Kamen and Sam Ruben. ... Radiocarbon dating is a radiometric dating method that uses the naturally occurring isotope carbon-14 to determine the age of carbonaceous materials up to ca 60,000 years. ...

Neutron radiation protection relies on radiation shielding. In comparison with conventional ionizing radiation based on photons or charged particles, neutrons are absorbed in light nuclei, so a large mass of hydrogen-rich material is needed. The most effective materials are eg. water, polyethylene, paraffin wax, or concrete, where a considerable amount of water molecules is chemically bound to the cement. The light atoms serve to slow down the neutrons by elastic scattering, so they can then be absorbed by nuclear reactions. However, gamma radiation is often produced in such reactions, so additional shielding has to be provided to absorb it. Radiation protection, sometimes known as radiological protection, is the science of protecting people and the environment from the harmful effects of radiation. ... Radiation protection, sometimes known as radiological protection, is the science of protecting people and the environment from the harmful effects of both particle radiation and ionizing radiation. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... Water (from the Old English word wæter; c. ... Polyethylene or polyethene is a thermoplastic commodity heavily used in consumer products (over 60M tons are produced worldwide every year). ... Paraffin is a common name for a group of high molecular weight alkane hydrocarbons with the general formula CnH2n+2, where n is greater than about 20. ... Placing a concrete floor for a commercial building Installing rebar in a floor during a concrete pour In construction, concrete is a composite building material made from the combination of aggregate and cement binder. ... In scattering theory and in particular in particle physics, elastic scattering is one of the specific forms of scattering. ... In nuclear physics, a nuclear reaction is a process in which two nuclei or nuclear particles collide, to produce products different to the initial products. ... This article is about electromagnetic radiation. ...

See also

• Neutron activation
• Neutron bomb

Neutron activation is the process by which neutron radiation induces radioactivity in materials. ... A neutron bomb is a type of nuclear weapon specifically designed to release a relatively large portion of its energy as energetic neutron radiation. ...

External links

• Radiological hazards and their control
• EPA definitions of various terms