Neutron source
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Neutron scattering |
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Neutron facilities |
A neutron source is any device that emits neutrons, irrespective of the mechanism used to produce the neutrons. Neutron sources are used in physics, engineering, medicine, nuclear weapons, petroleum exploration, biology, chemistry, and nuclear power.
Neutron source variables include the energy of the neutrons emitted by the source, the rate of neutrons emitted by the source, the size of the source, the cost of owning and maintaining the source, and government regulations related to the source.
Small devices
Spontaneous fission (SF)
Some
Radioisotopes which alpha decay; mixed with a light element
Neutrons are produced when alpha particles hit any of several light isotopes including isotopes of beryllium, carbon, or oxygen. Thus, one can make a neutron source by mixing an alpha-emitter such as radium, polonium, or americium with a low-atomic-weight isotope, usually by blending powders of the two materials. Alpha neutron sources typically produce ~106–108 neutrons per second. An alpha-beryllium neutron source may produce about 30 neutrons per 106 alpha particles. The useful lifetime for such sources depends on the half-life of the radioisotope. The size and cost of these neutron sources are comparable to spontaneous fission sources. Usual combinations of materials are plutonium-beryllium (PuBe), americium-beryllium (AmBe), or americium-lithium (AmLi).
Radioisotopes which decay with high-energy photons co-located with beryllium or deuterium
Gamma radiation with an energy exceeding the neutron binding energy of a nucleus can eject a neutron (
Sealed-tube neutron generators
Some accelerator-based
Medium-sized devices
Plasma focus and plasma pinch devices
The dense plasma focus neutron source produces controlled nuclear fusion by creating a dense plasma within which heats ionized deuterium and/or tritium gas to temperatures sufficient for creating fusion.
Inertial electrostatic confinement
Light ion accelerators
Traditional particle accelerators with hydrogen (H), deuterium (D), or tritium (T) ion sources may be used to produce neutrons using targets of deuterium, tritium, lithium, beryllium, and other low-Z materials.[citation needed] Typically these accelerators operate with energies in the > 1 MeV range.
High-energy bremsstrahlung photoneutron/photofission systems
Neutrons are produced when photons above the nuclear binding energy of a substance are incident on that substance, causing it to undergo
Large devices
Nuclear fission reactors
Nuclear fission within a reactor, produces many neutrons and can be used for a variety of purposes including power generation and experiments. Research reactors are often specially designed to allow placement of material samples into a high-neutron-flux environment.
Nuclear fusion systems
Nuclear fusion, the fusing of heavy isotopes of hydrogen, also has the potential to produces large numbers of neutrons. Small scale fusion systems exist for (plasma) research purposes at many universities and laboratories around the world. A small number of large scale fusion experiments also exist including the National Ignition Facility in the US, JET in the UK, and soon the ITER experiment currently under construction in France. None are yet used as neutron sources.
High-energy particle accelerators
A
Neutron flux
For most applications, higher neutron flux is better (since it reduces the time needed to do the experiment, acquire the image, etc.). Amateur fusion devices, like a fusor, generate only about 300 000 neutrons per second. Commercial fusor devices can generate on the order of 109 neutrons per second, hence a usable flux of less than 105 n/(cm2 s). Large neutron beams around the world achieve much greater flux. Reactor-based sources now produce 1015 n/(cm2 s), and spallation sources generate > 1017 n/(cm2 s).
See also
- Neutron emission
- Neutron generator, commercial devices
- Neutron temperature ('fast' or 'slow')
- Startup neutron source
- Zetatron
- A subcritical nuclear reactor relies on an "external" neutron source
References
- ^ Giant Dipole Resonance Neutron Yields Produced by Electrons as a Function of Target Material and Thickness
- S2CID 42506679.
- ^ "SUF Spallation Neutron Source (S... | U.S. DOE Office of Science (SC)". science.osti.gov. 29 April 2022. Retrieved 19 October 2022.