The neutron detection temperature, also called the neutron energy, indicates a free neutron's kinetic energy, usually given in electron volts. The term temperature is used, since hot, thermal and cold neutrons are moderated in a medium with a certain temperature. The neutron energy distribution is then adapted to the Maxwell distribution known for thermal motion. Qualitatively, the higher the temperature, the higher the kinetic energy of the free neutrons. The momentum and wavelength of the neutron are related through the de Broglie relation. The long wavelength of slow neutrons allows for the large cross section.[1]
But different ranges with different names are observed in other sources.[4]
The following is a detailed classification:
Thermal
A thermal neutron is a free neutron with a kinetic energy of about 0.025 eV (about 4.0×10−21J or 2.4 MJ/kg, hence a speed of 2.19 km/s), which is the energy corresponding to the most probable speed at a temperature of 290 K (17 °C or 62 °F), the mode of the Maxwell–Boltzmann distribution for this temperature, Epeak = 1/2 k T.
After a number of collisions with nuclei (scattering) in a medium (neutron moderator) at this temperature, those neutrons which are not absorbed reach about this energy level.
Neutrons of lower (much lower) energy than thermal neutrons.
Less than 5 meV.
Cold (slow) neutrons are subclassified into cold (CN), very cold (VCN), and ultra-cold (UCN) neutrons, each having particular characteristics in terms of their optical interactions with matter. As the wavelength is made (chosen to be) longer, lower values of the momentum exchange become accessible. Therefore, it is possible to study larger scales and slower dynamics. Gravity also plays a very significant role in the case of UCN. Nevertheless, UCN reflect at all angles of incidence. This is because their momentum is comparable to the optical potential of materials. This effect is used to store them in bottles and study their fundamental properties[5][6] e.g. lifetime, neutron electrical-dipole moment etc... The main limitations of the use of slow neutrons is the low flux and the lack of efficient optical devices (in the case of CN and VCN). Efficient neutron optical components are being developed and optimized to remedy this lack.[7]
A fast neutron is a free neutron with a kinetic energy level close to 1 MeV (100 TJ/kg), hence a speed of 14,000 km/s or higher. They are named fastneutrons 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:
Nuclear fission produces neutrons with a mean energy of 2 MeV (200 TJ/kg, i.e. 20,000 km/s), which qualifies as "fast". However the range of neutrons from fission follows a Maxwell–Boltzmann distribution from 0 to about 14 MeV in the center of momentum frame of the disintegration, and the mode of the energy is only 0.75 MeV, meaning that fewer than half of fission neutrons qualify as "fast" even by the 1 MeV criterion.[8]
Neutron emission occurs in situations in which a nucleus contains enough excess neutrons that the separation energy of one or more neutrons becomes negative (i.e. excess neutrons "drip" out of the nucleus). Unstable nuclei of this sort will often decay in less than one second.
Fast neutrons are usually undesirable in a steady-state nuclear reactor because most fissile fuel has a higher reaction rate with thermal neutrons. Fast neutrons can be rapidly changed into thermal neutrons via a process called moderation. This is done through numerous collisions with (in general) slower-moving and thus lower-temperature particles like atomic nuclei and other neutrons. These collisions will generally speed up the other particle and slow down the neutron and scatter it. Ideally, a room temperature neutron moderator is used for this process. In reactors, heavy water, light water, or graphite are typically used to moderate neutrons.
A chart displaying the speed probability density functions of the speeds of a few noble gases at a temperature of 298.15 K (25 C). An explanation of the vertical axis label appears on the image page (click to see). Similar speed distributions are obtained for neutrons upon moderation.
An increase in fuel temperature also raises uranium-238's thermal neutron absorption by Doppler broadening, providing negative feedback to help control the reactor. When the coolant is a liquid that also contributes to moderation and absorption (light water or heavy water), boiling of the coolant will reduce the moderator density, which can provide positive or negative feedback (a positive or negative void coefficient), depending on whether the reactor is under- or over-moderated.
Intermediate-energy neutrons have poorer fission/capture ratios than either fast or thermal neutrons for most fuels. An exception is the uranium-233 of the thorium cycle, which has a good fission/capture ratio at all neutron energies.
Fast-neutron reactors use unmoderated fast neutrons to sustain the reaction, and require the fuel to contain a higher concentration of fissile material relative to fertile material (uranium-238). However, fast neutrons have a better fission/capture ratio for many nuclides, and each fast fission releases a larger number of neutrons, so a fast breeder reactor can potentially "breed" more fissile fuel than it consumes.
Fast reactor control cannot depend solely on Doppler broadening or on negative void coefficient from a moderator. However, thermal expansion of the fuel itself can provide quick negative feedback. Perennially expected to be the wave of the future, fast reactor development has been nearly dormant with only a handful of reactors built in the decades since the Chernobyl accident due to low prices in the uranium market, although there is now a revival with several Asian countries planning to complete larger prototype fast reactors in the next few years.[when?]
^de Broglie, Louis. "On the Theory of Quanta" (PDF). aflb.ensmp.fr. Retrieved 2 February 2019.
^Carron, N.J. (2007). An Introduction to the Passage of Energetic Particles Through Matter. p. 308. Bibcode:2007ipep.book.....C.
^"Neutron Energy". www.nuclear-power.net. Retrieved 27 January 2019.
^ H. Tomita, C. Shoda, J. Kawarabayashi, T. Matsumoto, J. Hori, S. Uno, M. Shoji, T. Uchida, N. Fukumotoa and T. Iguchia, Development of epithermal neutron camera based on resonance-energy-filtered imaging with GEM, 2012, quote: "Epithermal neutrons have energies between 1 eV and 10 keV and smaller nuclear cross sections than thermal neutrons."
^"Introduction", Ultracold Neutrons, WORLD SCIENTIFIC, pp. 1–9, 2019-09-23, doi:10.1142/9789811212710_0001, ISBN978-981-12-1270-3, S2CID 243745548, retrieved 2022-11-11
^Jenke, Tobias; Bosina, Joachim; Micko, Jakob; Pitschmann, Mario; Sedmik, René; Abele, Hartmut (2021-06-01). "Gravity resonance spectroscopy and dark energy symmetron fields". The European Physical Journal Special Topics. 230 (4): 1131–1136. arXiv:2012.07472. doi:10.1140/epjs/s11734-021-00088-y. ISSN 1951-6401. S2CID 229156429.
^Hadden, Elhoucine; Iso, Yuko; Kume, Atsushi; Umemoto, Koichi; Jenke, Tobias; Fally, Martin; Klepp, Jürgen; Tomita, Yasuo (2022-05-24). McLeod, Robert R; Tomita, Yasuo; Sheridan, John T; Pascual Villalobos, Inmaculada (eds.). "Nanodiamond-based nanoparticle-polymer composite gratings with extremely large neutron refractive index modulation". Photosensitive Materials and Their Applications II. SPIE. 12151: 70–76. doi:10.1117/12.2623661. ISBN9781510651784. S2CID 249056691.
^Byrne, J. Neutrons, Nuclei, and Matter, Dover Publications, Mineola, New York, 2011, ISBN978-0-486-48238-5 (pbk.) p. 259.
neutron, temperature, neutron, detection, temperature, also, called, neutron, energy, indicates, free, neutron, kinetic, energy, usually, given, electron, volts, term, temperature, used, since, thermal, cold, neutrons, moderated, medium, with, certain, tempera. The neutron detection temperature also called the neutron energy indicates a free neutron s kinetic energy usually given in electron volts The term temperature is used since hot thermal and cold neutrons are moderated in a medium with a certain temperature The neutron energy distribution is then adapted to the Maxwell distribution known for thermal motion Qualitatively the higher the temperature the higher the kinetic energy of the free neutrons The momentum and wavelength of the neutron are related through the de Broglie relation The long wavelength of slow neutrons allows for the large cross section 1 Contents 1 Neutron energy distribution ranges 1 1 Thermal 1 2 Epithermal 1 3 Cadmium 1 4 Epicadmium 1 5 Cold slow neutrons 1 6 Resonance 1 7 Intermediate 1 8 Fast 1 9 Ultrafast 1 10 Other classifications 2 Fast neutron reactor and thermal neutron reactor compared 3 See also 4 References 5 External linksNeutron energy distribution ranges EditNeutron energy range names 2 3 Neutron energy Energy range0 0 0 025 eV Cold slow neutrons0 025 eV Thermal neutrons at 20 C 0 025 0 4 eV Epithermal neutrons0 4 0 5 eV Cadmium neutrons0 5 10 eV Epicadmium neutrons10 300 eV Resonance neutrons300 eV 1 MeV Intermediate neutrons1 20 MeV Fast neutrons gt 20 MeV Ultrafast neutronsBut different ranges with different names are observed in other sources 4 The following is a detailed classification Thermal Edit A thermal neutron is a free neutron with a kinetic energy of about 0 025 eV about 4 0 10 21 J or 2 4 MJ kg hence a speed of 2 19 km s which is the energy corresponding to the most probable speed at a temperature of 290 K 17 C or 62 F the mode of the Maxwell Boltzmann distribution for this temperature Epeak 1 2 k T After a number of collisions with nuclei scattering in a medium neutron moderator at this temperature those neutrons which are not absorbed reach about this energy level Thermal neutrons have a different and sometimes much larger effective neutron absorption cross section for a given nuclide than fast neutrons and can therefore often be absorbed more easily by an atomic nucleus creating a heavier often unstable isotope of the chemical element as a result This event is called neutron activation Epithermal Edit example needed Neutrons of energy greater than thermal Greater than 0 025 eVCadmium Edit example needed Neutrons which are strongly absorbed by cadmium Less than 0 5 eV Epicadmium Edit example needed Neutrons which are not strongly absorbed by cadmium Greater than 0 5 eV Cold slow neutrons Edit example needed Neutrons of lower much lower energy than thermal neutrons Less than 5 meV Cold slow neutrons are subclassified into cold CN very cold VCN and ultra cold UCN neutrons each having particular characteristics in terms of their optical interactions with matter As the wavelength is made chosen to be longer lower values of the momentum exchange become accessible Therefore it is possible to study larger scales and slower dynamics Gravity also plays a very significant role in the case of UCN Nevertheless UCN reflect at all angles of incidence This is because their momentum is comparable to the optical potential of materials This effect is used to store them in bottles and study their fundamental properties 5 6 e g lifetime neutron electrical dipole moment etc The main limitations of the use of slow neutrons is the low flux and the lack of efficient optical devices in the case of CN and VCN Efficient neutron optical components are being developed and optimized to remedy this lack 7 Resonance Edit example needed Refers to neutrons which are strongly susceptible to non fission capture by U 238 1 eV to 300 eVIntermediate Edit example needed Neutrons that are between slow and fast Few hundred eV to 0 5 MeV Fast Edit A fast neutron is a free neutron with a kinetic energy level close to 1 MeV 100 TJ kg hence a speed of 14 000 km s or higher They are named 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 Nuclear fission produces neutrons with a mean energy of 2 MeV 200 TJ kg i e 20 000 km s which qualifies as fast However the range of neutrons from fission follows a Maxwell Boltzmann distribution from 0 to about 14 MeV in the center of momentum frame of the disintegration and the mode of the energy is only 0 75 MeV meaning that fewer than half of fission neutrons qualify as fast even by the 1 MeV criterion 8 Spontaneous fission is a mode of radioactive decay for some heavy nuclides Examples include plutonium 240 and californium 252 Nuclear fusion deuterium tritium fusion produces neutrons of 14 1 MeV 1400 TJ kg i e 52 000 km s 17 3 of the speed of light that can easily fission uranium 238 and other non fissile actinides Neutron emission occurs in situations in which a nucleus contains enough excess neutrons that the separation energy of one or more neutrons becomes negative i e excess neutrons drip out of the nucleus Unstable nuclei of this sort will often decay in less than one second Fast neutrons are usually undesirable in a steady state nuclear reactor because most fissile fuel has a higher reaction rate with thermal neutrons Fast neutrons can be rapidly changed into thermal neutrons via a process called moderation This is done through numerous collisions with in general slower moving and thus lower temperature particles like atomic nuclei and other neutrons These collisions will generally speed up the other particle and slow down the neutron and scatter it Ideally a room temperature neutron moderator is used for this process In reactors heavy water light water or graphite are typically used to moderate neutrons A chart displaying the speed probability density functions of the speeds of a few noble gases at a temperature of 298 15 K 25 C An explanation of the vertical axis label appears on the image page click to see Similar speed distributions are obtained for neutrons upon moderation Ultrafast Edit example needed Relativistic Greater than 20 MeVOther classifications Edit Pile Neutrons of all energies present in nuclear reactors 0 001 eV to 15 MeV Ultracold Neutrons with sufficiently low energy to be reflected and trapped Upper bound of 335 neVFast neutron reactor and thermal neutron reactor compared EditMost fission reactors are thermal neutron reactors that use a neutron moderator to slow down thermalize the neutrons produced by nuclear fission Moderation substantially increases the fission cross section for fissile nuclei such as uranium 235 or plutonium 239 In addition uranium 238 has a much lower capture cross section for thermal neutrons allowing more neutrons to cause fission of fissile nuclei and propagate the chain reaction rather than being captured by 238U The combination of these effects allows light water reactors to use low enriched uranium Heavy water reactors and graphite moderated reactors can even use natural uranium as these moderators have much lower neutron capture cross sections than light water 9 An increase in fuel temperature also raises uranium 238 s thermal neutron absorption by Doppler broadening providing negative feedback to help control the reactor When the coolant is a liquid that also contributes to moderation and absorption light water or heavy water boiling of the coolant will reduce the moderator density which can provide positive or negative feedback a positive or negative void coefficient depending on whether the reactor is under or over moderated Intermediate energy neutrons have poorer fission capture ratios than either fast or thermal neutrons for most fuels An exception is the uranium 233 of the thorium cycle which has a good fission capture ratio at all neutron energies Fast neutron reactors use unmoderated fast neutrons to sustain the reaction and require the fuel to contain a higher concentration of fissile material relative to fertile material uranium 238 However fast neutrons have a better fission capture ratio for many nuclides and each fast fission releases a larger number of neutrons so a fast breeder reactor can potentially breed more fissile fuel than it consumes Fast reactor control cannot depend solely on Doppler broadening or on negative void coefficient from a moderator However thermal expansion of the fuel itself can provide quick negative feedback Perennially expected to be the wave of the future fast reactor development has been nearly dormant with only a handful of reactors built in the decades since the Chernobyl accident due to low prices in the uranium market although there is now a revival with several Asian countries planning to complete larger prototype fast reactors in the next few years when See also EditAbsorption hardening List of particles Neutron detection Neutron source Nuclear reaction ScintillatorReferences Edit de Broglie Louis On the Theory of Quanta PDF aflb ensmp fr Retrieved 2 February 2019 Carron N J 2007 An Introduction to the Passage of Energetic Particles Through Matter p 308 Bibcode 2007ipep book C Neutron Energy www nuclear power net Retrieved 27 January 2019 H Tomita C Shoda J Kawarabayashi T Matsumoto J Hori S Uno M Shoji T Uchida N Fukumotoa and T Iguchia Development of epithermal neutron camera based on resonance energy filtered imaging with GEM 2012 quote Epithermal neutrons have energies between 1 eV and 10 keV and smaller nuclear cross sections than thermal neutrons Introduction Ultracold Neutrons WORLD SCIENTIFIC pp 1 9 2019 09 23 doi 10 1142 9789811212710 0001 ISBN 978 981 12 1270 3 S2CID 243745548 retrieved 2022 11 11 Jenke Tobias Bosina Joachim Micko Jakob Pitschmann Mario Sedmik Rene Abele Hartmut 2021 06 01 Gravity resonance spectroscopy and dark energy symmetron fields The European Physical Journal Special Topics 230 4 1131 1136 arXiv 2012 07472 doi 10 1140 epjs s11734 021 00088 y ISSN 1951 6401 S2CID 229156429 Hadden Elhoucine Iso Yuko Kume Atsushi Umemoto Koichi Jenke Tobias Fally Martin Klepp Jurgen Tomita Yasuo 2022 05 24 McLeod Robert R Tomita Yasuo Sheridan John T Pascual Villalobos Inmaculada eds Nanodiamond based nanoparticle polymer composite gratings with extremely large neutron refractive index modulation Photosensitive Materials and Their Applications II SPIE 12151 70 76 doi 10 1117 12 2623661 ISBN 9781510651784 S2CID 249056691 Byrne J Neutrons Nuclei and Matter Dover Publications Mineola New York 2011 ISBN 978 0 486 48238 5 pbk p 259 Some Physics of Uranium Accessed March 7 2009External links EditLanguage of the Nucleus Retrieved from https en wikipedia org w index php title Neutron temperature amp oldid 1170912396 Epithermal, wikipedia, wiki, book, books, library,
