Misplaced Pages

#319680

116-803: EUROfusion is a consortium of national fusion research institutes located in the European Union, the UK, Switzerland and Ukraine. It was established in 2014 to succeed the European Fusion Development Agreement ( EFDA ) as the umbrella organisation of Europe's fusion research laboratories. The consortium is currently funded by the Euratom Horizon 2020 programme. The EUROfusion consortium agreement has been signed by 30 research organisations and universities from 25 European Union countries plus Switzerland, Ukraine and

232-425: A fermion with intrinsic angular momentum equal to ⁠ 1 / 2 ⁠   ħ , where ħ is the reduced Planck constant . For many years after the discovery of the neutron, its exact spin was ambiguous. Although it was assumed to be a spin  ⁠ 1 / 2 ⁠ Dirac particle , the possibility that the neutron was a spin  ⁠ 3 / 2 ⁠ particle lingered. The interactions of

348-454: A fission-fusion hybrid . In these systems, the power output is enhanced by the fission events, and power is extracted using systems like those in conventional fission reactors. Designs that use other fuels, notably the proton-boron aneutronic fusion reaction, release much more of their energy in the form of charged particles. In these cases, power extraction systems based on the movement of these charges are possible. Direct energy conversion

464-408: A nuclear chain reaction . These events and findings led to the first self-sustaining nuclear reactor ( Chicago Pile-1 , 1942) and the first nuclear weapon ( Trinity , 1945). Dedicated neutron sources like neutron generators , research reactors and spallation sources produce free neutrons for use in irradiation and in neutron scattering experiments. A free neutron spontaneously decays to

580-411: A probability distribution . If the plasma is thermalized , the distribution looks like a Gaussian curve , or Maxwell–Boltzmann distribution . In this case, it is useful to use the average particle cross section over the velocity distribution. This is entered into the volumetric fusion rate: where: The Lawson criterion considers the energy balance between the energy produced in fusion reactions to

696-479: A tokamak -based reactor. The system was able to manipulate the magnetic coils to manage the plasma. The system was able to continuously adjust to maintain appropriate behavior (more complex than step-based systems). In 2014, Google began working with California-based fusion company TAE Technologies to control the Joint European Torus (JET) to predict plasma behavior. DeepMind has also developed

812-473: A 1.5 nanosecond laser fire, 100 times greater than reported in previous experiments. Structural material stability is a critical issue. Materials that can survive the high temperatures and neutron bombardment experienced in a fusion reactor are considered key to success. The principal issues are the conditions generated by the plasma, neutron degradation of wall surfaces, and the related issue of plasma-wall surface conditions. Reducing hydrogen permeability

928-505: A Russian and Japanese company, developed a new manufacturing process for making superconducting YBCO wire for fusion reactors. This new wire was shown to conduct between 700 and 2000 Amps per square millimeter. The company was able to produce 186 miles of wire in nine months. Even on smaller production scales, the containment apparatus is blasted with matter and energy. Designs for plasma containment must consider: Neutron The chemical properties of an atom are mostly determined by

1044-401: A bottle, while the "beam" method employs energetic neutrons in a particle beam. The measurements by the two methods have not been converging with time. The lifetime from the bottle method is presently 877.75 s which is 10 seconds below the value from the beam method of 887.7 s A small fraction (about one per thousand) of free neutrons decay with the same products, but add an extra particle in

1160-456: A cascade known as a nuclear chain reaction . For a given mass of fissile material, such nuclear reactions release energy that is approximately ten million times that from an equivalent mass of a conventional chemical explosive . Ultimately, the ability of the nuclear force to store energy arising from the electromagnetic repulsion of nuclear components is the basis for most of the energy that makes nuclear reactors or bombs possible; most of

1276-461: A control scheme with TCV . The diagnostics of a fusion scientific reactor are extremely complex and varied. The diagnostics required for a fusion power reactor will be various but less complicated than those of a scientific reactor as by the time of commercialization, many real-time feedback and control diagnostics will have been perfected. However, the operating environment of a commercial fusion reactor will be harsher for diagnostic systems than in

SECTION 10

#1732776385320

1392-544: A deuteron is formed by a proton capturing a neutron (this is exothermic and happens with zero-energy neutrons). The small recoil kinetic energy ( E r d {\displaystyle E_{rd}} ) of the deuteron (about 0.06% of the total energy) must also be accounted for. The energy of the gamma ray can be measured to high precision by X-ray diffraction techniques, as was first done by Bell and Elliot in 1948. The best modern (1986) values for neutron mass by this technique are provided by Greene, et al. These give

1508-434: A greater repulsive force. For nuclei lighter than iron-56, the reaction is exothermic , releasing energy when they fuse. Since hydrogen has a single proton in its nucleus, it requires the least effort to attain fusion, and yields the most net energy output. Also since it has one electron, hydrogen is the easiest fuel to fully ionize. The repulsive electrostatic interaction between nuclei operates across larger distances than

1624-407: A machine holding a thermalized and quasi- neutral plasma has to generate enough energy to overcome its energy losses. The amount of energy released in a given volume is a function of the temperature, and thus the reaction rate on a per-particle basis, the density of particles within that volume, and finally the confinement time, the length of time that energy stays within the volume. This is known as

1740-488: A magnetic field to separate the neutron spin states. They recorded two such spin states, consistent with a spin  ⁠ 1 / 2 ⁠ particle. As a fermion, the neutron is subject to the Pauli exclusion principle ; two neutrons cannot have the same quantum numbers. This is the source of the degeneracy pressure which counteracts gravity in neutron stars and prevents them from forming black holes. Even though

1856-417: A mass spectrometer, the mass of a neutron can be deduced by subtracting proton mass from deuteron mass, with the difference being the mass of the neutron plus the binding energy of deuterium (expressed as a positive emitted energy). The latter can be directly measured by measuring the energy ( B d {\displaystyle B_{d}} ) of the single 2.224 MeV gamma photon emitted when

1972-416: A mean-square radius of about 0.8 × 10   m , or 0.8  fm , and it is a spin-½ fermion . The neutron has no measurable electric charge. With its positive electric charge, the proton is directly influenced by electric fields , whereas the neutron is unaffected by electric fields. The neutron has a magnetic moment , however, so it is influenced by magnetic fields . The specific properties of

2088-404: A neutron by some heavy nuclides (such as uranium-235 ) can cause the nuclide to become unstable and break into lighter nuclides and additional neutrons. The positively charged light nuclides, or "fission fragments", then repel, releasing electromagnetic potential energy . If this reaction occurs within a mass of fissile material , the additional neutrons cause additional fission events, inducing

2204-448: A neutron mass of: The value for the neutron mass in MeV is less accurately known, due to less accuracy in the known conversion of Da to MeV/ c : Another method to determine the mass of a neutron starts from the beta decay of the neutron, when the momenta of the resulting proton and electron are measured. The neutron is a spin  ⁠ 1 / 2 ⁠ particle, that is, it is

2320-543: A nucleon. The discrepancy stems from the complexity of the Standard Model for nucleons, where most of their mass originates in the gluon fields, virtual particles, and their associated energy that are essential aspects of the strong force . Furthermore, the complex system of quarks and gluons that constitute a neutron requires a relativistic treatment. But the nucleon magnetic moment has been successfully computed numerically from first principles , including all of

2436-489: A nucleus. The observed properties of atoms and molecules were inconsistent with the nuclear spin expected from the proton–electron hypothesis. Protons and electrons both carry an intrinsic spin of ⁠ 1 / 2 ⁠ ħ , and the isotopes of the same species were found to have either integer or fractional spin. By the hypothesis, isotopes would be composed of the same number of protons, but differing numbers of neutral bound proton+electron "particles". This physical picture

SECTION 20

#1732776385320

2552-417: A pair of protons, one with spin up, another with spin down. When all available proton states are filled, the Pauli exclusion principle disallows the decay of a neutron to a proton. The situation is similar to electrons of an atom, where electrons that occupy distinct atomic orbitals are prevented by the exclusion principle from decaying to lower, already-occupied, energy states. The stability of matter

2668-409: A particle accelerator to produce this energy. An atom loses its electrons once it is heated past its ionization energy . An ion is the name for the resultant bare nucleus. The result of this ionization is plasma, which is a heated cloud of ions and free electrons that were formerly bound to them. Plasmas are electrically conducting and magnetically controlled because the charges are separated. This

2784-545: A plasma oscillating device, a magnetically shielded-grid, a penning trap , the polywell , and the F1 cathode driver concept. The fuels considered for fusion power have all been light elements like the isotopes of hydrogen— protium , deuterium , and tritium . The deuterium and helium-3 reaction requires helium-3, an isotope of helium so scarce on Earth that it would have to be mined extraterrestrially or produced by other nuclear reactions. Ultimately, researchers hope to adopt

2900-419: A practical and economical manner. A second issue that affects common reactions is managing neutrons that are released during the reaction, which over time degrade many common materials used within the reaction chamber. Fusion researchers have investigated various confinement concepts. The early emphasis was on three main systems: z-pinch , stellarator , and magnetic mirror . The current leading designs are

3016-423: A proton, an electron , and an antineutrino , with a mean lifetime of about 15 minutes. Free neutrons do not directly ionize atoms, but they do indirectly cause ionizing radiation , so they can be a biological hazard, depending on dose. A small natural "neutron background" flux of free neutrons exists on Earth, caused by cosmic ray showers , and by the natural radioactivity of spontaneously fissionable elements in

3132-419: A rare isotope carbon-13 with 7 neutrons. Some elements occur in nature with only one stable isotope , such as fluorine . Other elements occur with many stable isotopes, such as tin with ten stable isotopes, or with no stable isotope, such as technetium . The properties of an atomic nucleus depend on both atomic and neutron numbers. With their positive charge, the protons within the nucleus are repelled by

3248-476: A scientific reactor because continuous operations may involve higher plasma temperatures and higher levels of neutron irradiation. In many proposed approaches, commercialization will require the additional ability to measure and separate diverter gases, for example helium and impurities, and to monitor fuel breeding, for instance the state of a tritium breeding liquid lithium liner. The following are some basic techniques. Neutron blankets absorb neutrons, which heats

3364-452: A series of D-T tests at JET , the vacuum vessel was sufficiently radioactive that it required remote handling for the year following the tests. In a production setting, the neutrons would react with lithium in the breeding blanket composed of lithium ceramic pebbles or liquid lithium, yielding tritium. The energy of the neutrons ends up in the lithium, which would then be transferred to drive electrical production. The lithium blanket protects

3480-481: A series of experiments that showed that the new radiation consisted of uncharged particles with about the same mass as the proton. These properties matched Rutherford's hypothesized neutron. Chadwick won the 1935 Nobel Prize in Physics for this discovery. Models for an atomic nucleus consisting of protons and neutrons were quickly developed by Werner Heisenberg and others. The proton–neutron model explained

3596-413: A shell, driving the shell to radiate x-rays , which then implode the pellet. The beams are commonly laser beams, but ion and electron beams have been investigated. Electrostatic confinement fusion devices use electrostatic fields. The best known is the fusor . This device has a cathode inside an anode wire cage. Positive ions fly towards the negative inner cage, and are heated by the electric field in

EUROfusion - Misplaced Pages Continue

3712-404: A simple nonrelativistic , quantum mechanical wavefunction for baryons composed of three quarks. A straightforward calculation gives fairly accurate estimates for the magnetic moments of neutrons, protons, and other baryons. For a neutron, the result of this calculation is that the magnetic moment of the neutron is given by μ n = 4/3 μ d − 1/3 μ u , where μ d and μ u are

3828-422: A surface of the device, and transfer a portion of their kinetic energy to the other atoms. The rate of conduction is also based on the temperature and density. Radiation is energy that leaves the cloud as light. Radiation also increases with temperature as well as the mass of the ions. Fusion power systems must operate in a region where the rate of fusion is higher than the losses. The Lawson criterion argues that

3944-423: A variety of heating methods that were developed in the early 1970s. In modern machines, as of 2019 , the major remaining issue was the confinement time. Plasmas in strong magnetic fields are subject to a number of inherent instabilities, which must be suppressed to reach useful durations. One way to do this is to simply make the reactor volume larger, which reduces the rate of leakage due to classical diffusion . This

4060-413: Is a consequence of these constraints. The decay of a neutron within a nuclide is illustrated by the decay of the carbon isotope carbon-14 , which has 6 protons and 8 neutrons. With its excess of neutrons, this isotope decays by beta decay to nitrogen-14 (7 protons, 7 neutrons), a process with a half-life of about 5,730 years . Nitrogen-14 is stable. "Beta decay" reactions can also occur by

4176-471: Is also common in research. The optimum energy to initiate this reaction is 15 keV, only slightly higher than that for the D-T reaction. The first branch produces tritium, so that a D-D reactor is not tritium-free, even though it does not require an input of tritium or lithium. Unless the tritons are quickly removed, most of the tritium produced is burned in the reactor, which reduces the handling of tritium, with

4292-497: Is called "tritium suppressed fusion". The removed tritium decays to He with a 12.5 year half life. By recycling the He decay into the reactor, the fusion reactor does not require materials resistant to fast neutrons. Assuming complete tritium burn-up, the reduction in the fraction of fusion energy carried by neutrons would be only about 18%, so that the primary advantage of the D-D fuel cycle

4408-403: Is essential to the production of nuclear power. In the decade after the neutron was discovered by James Chadwick in 1932, neutrons were used to induce many different types of nuclear transmutations . With the discovery of nuclear fission in 1938, it was quickly realized that, if a fission event produced neutrons, each of these neutrons might cause further fission events, in a cascade known as

4524-448: Is for one of the neutron's quarks to change flavour (through a Cabibbo–Kobayashi–Maskawa matrix ) via the weak interaction . The decay of one of the neutron's down quarks into a lighter up quark can be achieved by the emission of a W boson . By this process, the Standard Model description of beta decay, the neutron decays into a proton (which contains one down and two up quarks), an electron, and an electron antineutrino . The decay of

4640-428: Is formed by oxidation alone. Alternative methods utilize specific gas environments with strong magnetic and electric fields. Assessment of barrier performance represents an additional challenge. Classical coated membranes gas permeation continues to be the most reliable method to determine hydrogen permeation barrier (HPB) efficiency. In 2021, in response to increasing numbers of designs for fusion power reactors for 2040,

4756-525: Is seen as crucial to hydrogen recycling and control of the tritium inventory. Materials with the lowest bulk hydrogen solubility and diffusivity provide the optimal candidates for stable barriers. A few pure metals, including tungsten and beryllium, and compounds such as carbides, dense oxides, and nitrides have been investigated. Research has highlighted that coating techniques for preparing well-adhered and perfect barriers are of equivalent importance. The most attractive techniques are those in which an ad-layer

EUROfusion - Misplaced Pages Continue

4872-611: Is still considerably higher compared to fission reactors. Because the confinement properties of the tokamak and laser pellet fusion are marginal, most proposals for aneutronic fusion are based on radically different confinement concepts, such as the Polywell and the Dense Plasma Focus . In 2013, a research team led by Christine Labaune at École Polytechnique , reported a new fusion rate record for proton-boron fusion, with an estimated 80 million fusion reactions during

4988-404: Is that tritium breeding is not required. Other advantages are independence from lithium resources and a somewhat softer neutron spectrum. The disadvantage of D-D compared to D-T is that the energy confinement time (at a given pressure) must be 30 times longer and the power produced (at a given pressure and volume) is 68 times less. Assuming complete removal of tritium and He recycling, only 6% of

5104-420: Is the nuclear magneton . The neutron's magnetic moment has a negative value, because its orientation is opposite to the neutron's spin. The magnetic moment of the neutron is an indication of its quark substructure and internal charge distribution. In the quark model for hadrons , the neutron is composed of one up quark (charge +2/3  e ) and two down quarks (charge −1/3  e ). The magnetic moment of

5220-404: Is unaffected by the confinement scheme. In most designs, it is captured in a thick "blanket" of lithium surrounding the reactor core. When struck by a high-energy neutron, the blanket heats up. It is then actively cooled with a working fluid that drives a turbine to produce power. Another design proposed to use the neutrons to breed fission fuel in a blanket of nuclear waste , a concept known as

5336-416: Is used by several fusion devices to confine the hot particles. A reaction's cross section , denoted σ, measures the probability that a fusion reaction will happen. This depends on the relative velocity of the two nuclei. Higher relative velocities generally increase the probability, but the probability begins to decrease again at very high energies. In a plasma, particle velocity can be characterized using

5452-404: Is why ITER is so large. In contrast, inertial confinement systems approach useful triple product values via higher density, and have short confinement intervals. In NIF , the initial frozen hydrogen fuel load has a density less than water that is increased to about 100 times the density of lead. In these conditions, the rate of fusion is so high that the fuel fuses in the microseconds it takes for

5568-713: The Chicago Pile-1 at the University of Chicago in 1942, the first self-sustaining nuclear reactor . Just three years later the Manhattan Project was able to test the first atomic bomb , the Trinity nuclear test in July 1945. The mass of a neutron cannot be directly determined by mass spectrometry since it has no electric charge. But since the masses of a proton and of a deuteron can be measured with

5684-603: The Earth's crust . An atomic nucleus is formed by a number of protons, Z (the atomic number ), and a number of neutrons, N (the neutron number ), bound together by the nuclear force . Protons and neutrons each have a mass of approximately one dalton . The atomic number determines the chemical properties of the atom, and the neutron number determines the isotope or nuclide . The terms isotope and nuclide are often used synonymously , but they refer to chemical and nuclear properties, respectively. Isotopes are nuclides with

5800-676: The United Kingdom Atomic Energy Authority published the UK Fusion Materials Roadmap 2021–2040 , focusing on five priority areas, with a focus on tokamak family reactors: In a plasma that is embedded in a magnetic field (known as a magnetized plasma) the fusion rate scales as the magnetic field strength to the 4th power. For this reason, many fusion companies that rely on magnetic fields to control their plasma are trying to develop high temperature superconducting devices. In 2021, SuperOx,

5916-705: The tokamak and inertial confinement (ICF) by laser . Both designs are under research at very large scales, most notably the ITER tokamak in France and the National Ignition Facility (NIF) laser in the United States. Researchers are also studying other designs that may offer less expensive approaches. Among these alternatives, there is increasing interest in magnetized target fusion and inertial electrostatic confinement , and new variations of

SECTION 50

#1732776385320

6032-415: The uranium enrichment process. Tritium is a natural isotope of hydrogen, but because it has a short half-life of 12.32 years, it is hard to find, store, produce, and is expensive. Consequently, the deuterium-tritium fuel cycle requires the breeding of tritium from lithium using one of the following reactions: The reactant neutron is supplied by the D-T fusion reaction shown above, and the one that has

6148-410: The "triple product": the plasma density, temperature, and confinement time. In magnetic confinement, the density is low, on the order of a "good vacuum". For instance, in the ITER device the fuel density is about 1.0 × 10 m , which is about one-millionth atmospheric density. This means that the temperature and/or confinement time must increase. Fusion-relevant temperatures have been achieved using

6264-486: The 1920s, physicists assumed that the atomic nucleus was composed of protons and "nuclear electrons", but this raised obvious problems. It was difficult to reconcile the proton–electron model of the nucleus with the Heisenberg uncertainty relation of quantum mechanics. The Klein paradox , discovered by Oskar Klein in 1928, presented further quantum mechanical objections to the notion of an electron confined within

6380-457: The 1940s, but as of 2024, no device has reached net power, although net positive reactions have been achieved. Fusion processes require fuel and a confined environment with sufficient temperature , pressure , and confinement time to create a plasma in which fusion can occur. The combination of these figures that results in a power-producing system is known as the Lawson criterion . In stars

6496-512: The 1944 Nobel Prize in Chemistry "for his discovery of the fission of heavy atomic nuclei". The discovery of nuclear fission would lead to the development of nuclear power and the atomic bomb by the end of World War II. It was quickly realized that, if a fission event produced neutrons, each of these neutrons might cause further fission events, in a cascade known as a nuclear chain reaction. These events and findings led Fermi to construct

6612-558: The American chemist W. D. Harkins first named the hypothetical particle a "neutron". The name derives from the Latin root for neutralis (neuter) and the Greek suffix -on (a suffix used in the names of subatomic particles, i.e. electron and proton ). References to the word neutron in connection with the atom can be found in the literature as early as 1899, however. Throughout

6728-590: The EUROfusion umbrella aims to prepare for ITER experiments and develop concepts for the fusion power demonstration plant DEMO . EUROfusion is in charge of the fusion-related research carried out at JET, the Joint European Torus , which is housed in the Culham Centre for Fusion Energy, UK. Other fusion devices in Europe that devote some amount of time towards research under the EUROfusion framework include

6844-523: The Lawson criterion requirements with less extreme conditions. Most designs aim to heat their fuel to around 100 million kelvins, which presents a major challenge in producing a successful design. Tritium is extremely rare on Earth, having a half life of only ~12.3 years. Consequently, during the operation of envisioned fusion reactors, known as breeder reactors, helium cooled pebble beds (HCPBs) are subjected to neutron fluxes to generate tritium to complete

6960-494: The Nobel Prize in Physics "for his demonstrations of the existence of new radioactive elements produced by neutron irradiation, and for his related discovery of nuclear reactions brought about by slow neutrons". In December 1938 Otto Hahn , Lise Meitner , and Fritz Strassmann discovered nuclear fission , or the fractionation of uranium nuclei into lighter elements, induced by neutron bombardment. In 1945 Hahn received

7076-714: The United Kingdom. The EUROfusion's Programme Management Unit offices located in Garching, near Munich (Germany), are hosted by the Max Planck Institute of Plasma Physics (IPP). The IPP is also the seat for the co-ordinator of EUROfusion. EUROfusion funds fusion research activities in accordance with the Roadmap to the realisation of fusion energy . The Roadmap outlines the most efficient way to realise fusion electricity by 2050. Research carried out under

SECTION 60

#1732776385320

7192-406: The beta decay process. The neutrons and protons in a nucleus form a quantum mechanical system according to the nuclear shell model . Protons and neutrons of a nuclide are organized into discrete hierarchical energy levels with unique quantum numbers . Nucleon decay within a nucleus can occur if allowed by basic energy conservation and quantum mechanical constraints. The decay products, that is,

7308-410: The blanket. Power can be extracted from the blanket in various ways: Confinement refers to all the conditions necessary to keep a plasma dense and hot long enough to undergo fusion. General principles: To produce self-sustaining fusion, part of the energy released by the reaction must be used to heat new reactants and maintain the conditions for fusion. Magnetic mirror effect. If a particle follows

7424-400: The capture of a lepton by the nucleon. The transformation of a proton to a neutron inside of a nucleus is possible through electron capture : A rarer reaction, inverse beta decay , involves the capture of a neutrino by a nucleon. Rarer still, positron capture by neutrons can occur in the high-temperature environment of stars. Three types of beta decay in competition are illustrated by

7540-438: The common chemical element lead , Pb, has 82 protons and 126 neutrons, for example. The table of nuclides comprises all the known nuclides. Even though it is not a chemical element, the neutron is included in this table. Protons and neutrons behave almost identically under the influence of the nuclear force within the nucleus. They are therefore both referred to collectively as nucleons . The concept of isospin , in which

7656-441: The complex behavior of quarks to be subtracted out between models, and merely exploring what the effects would be of differing quark charges (or quark type). Such calculations are enough to show that the interior of neutrons is very much like that of protons, save for the difference in quark composition with a down quark in the neutron replacing an up quark in the proton. The neutron magnetic moment can be roughly computed by assuming

7772-496: The configuration of electrons that orbit the atom's heavy nucleus. The electron configuration is determined by the charge of the nucleus, which is determined by the number of protons, or atomic number . The number of neutrons is the neutron number . Neutrons do not affect the electron configuration. Atoms of a chemical element that differ only in neutron number are called isotopes . For example, carbon , with atomic number 6, has an abundant isotope carbon-12 with 6 neutrons and

7888-552: The difference in mass represents the mass equivalent to nuclear binding energy, the energy which would need to be added to take the nucleus apart. The nucleus of the most common isotope of the hydrogen atom (with the chemical symbol H) is a lone proton. The nuclei of the heavy hydrogen isotopes deuterium (D or H) and tritium (T or H) contain one proton bound to one and two neutrons, respectively. All other types of atomic nuclei are composed of two or more protons and various numbers of neutrons. The most common nuclide of

8004-405: The disadvantage of producing more, and higher-energy, neutrons. The neutron from the second branch of the D-D reaction has an energy of only 2.45 MeV (0.393 pJ), while the neutron from the D-T reaction has an energy of 14.1 MeV (2.26 pJ), resulting in greater isotope production and material damage. When the tritons are removed quickly while allowing the He to react, the fuel cycle

8120-459: The electron fails to gain the 13.6  eV necessary energy to escape the proton (the ionization energy of hydrogen ), and therefore simply remains bound to it, forming a neutral hydrogen atom (one of the "two bodies"). In this type of free neutron decay, almost all of the neutron decay energy is carried off by the antineutrino (the other "body"). (The hydrogen atom recoils with a speed of only about (decay energy)/(hydrogen rest energy) times

8236-405: The emitted particles, carry away the energy excess as a nucleon falls from one quantum state to one with less energy, while the neutron (or proton) changes to a proton (or neutron). For a neutron to decay, the resulting proton requires an available state at lower energy than the initial neutron state. In stable nuclei the possible lower energy states are all filled, meaning each state is occupied by

8352-448: The energy being lost to the environment. In order to generate usable energy, a system would have to produce more energy than it loses. Lawson assumed an energy balance , shown below. where: The rate of fusion, and thus P fusion , depends on the temperature and density of the plasma. The plasma loses energy through conduction and radiation . Conduction occurs when ions , electrons , or neutrals impact other substances, typically

8468-593: The energy released from fission is the kinetic energy of the fission fragments. Neutrons and protons within a nucleus behave similarly and can exchange their identities by similar reactions. These reactions are a form of radioactive decay known as beta decay . Beta decay, in which neutrons decay to protons, or vice versa, is governed by the weak force , and it requires the emission or absorption of electrons and neutrinos, or their antiparticles. The neutron and proton decay reactions are: where p , e , and ν e denote

8584-485: The field line and enters a region of higher field strength, the particles can be reflected. Several devices apply this effect. The most famous was the magnetic mirror machines, a series of devices built at LLNL from the 1960s to the 1980s. Other examples include magnetic bottles and Biconic cusp . Because the mirror machines were straight, they had some advantages over ring-shaped designs. The mirrors were easier to construct and maintain and direct conversion energy capture

8700-402: The following: Nuclear fusion power Fusion power is a proposed form of power generation that would generate electricity by using heat from nuclear fusion reactions . In a fusion process, two lighter atomic nuclei combine to form a heavier nucleus, while releasing energy. Devices designed to harness this energy are known as fusion reactors. Research into fusion reactors began in

8816-445: The form of an emitted gamma ray: Called a "radiative decay mode" of the neutron, the gamma ray may be thought of as resulting from an "internal bremsstrahlung " that arises from the electromagnetic interaction of the emitted beta particle with the proton. A smaller fraction (about four per million) of free neutrons decay in so-called "two-body (neutron) decays", in which a proton, electron and antineutrino are produced as usual, but

8932-427: The fuel cycle. As a source of power, nuclear fusion has a number of potential advantages compared to fission . These include reduced radioactivity in operation, little high-level nuclear waste , ample fuel supplies (assuming tritium breeding or some forms of aneutronic fuels ), and increased safety. However, the necessary combination of temperature, pressure, and duration has proven to be difficult to produce in

9048-410: The fusion energy is carried by neutrons. The tritium-suppressed D-D fusion requires an energy confinement that is 10 times longer compared to D-T and double the plasma temperature. A second-generation approach to controlled fusion power involves combining helium-3 ( He) and deuterium ( H): This reaction produces He and a high-energy proton. As with the p- B aneutronic fusion fuel cycle, most of

9164-455: The greatest energy yield. The reaction with Li is exothermic , providing a small energy gain for the reactor. The reaction with Li is endothermic , but does not consume the neutron. Neutron multiplication reactions are required to replace the neutrons lost to absorption by other elements. Leading candidate neutron multiplication materials are beryllium and lead , but the Li reaction helps to keep

9280-406: The heat generated by the reactions to blow the fuel apart. Although NIF is also large, this is a function of its "driver" design, not inherent to the fusion process. Multiple approaches have been proposed to capture the energy that fusion produces. The simplest is to heat a fluid. The commonly targeted D-T reaction releases much of its energy as fast-moving neutrons. Electrically neutral, the neutron

9396-474: The long-range electromagnetic force , but the much stronger, but short-range, nuclear force binds the nucleons closely together. Neutrons are required for the stability of nuclei, with the exception of the single-proton hydrogen nucleus. Neutrons are produced copiously in nuclear fission and fusion . They are a primary contributor to the nucleosynthesis of chemical elements within stars through fission, fusion, and neutron capture processes. The neutron

9512-437: The magnetic moments for the down and up quarks, respectively. This result combines the intrinsic magnetic moments of the quarks with their orbital magnetic moments, and assumes the three quarks are in a particular, dominant quantum state. The results of this calculation are encouraging, but the masses of the up or down quarks were assumed to be 1/3 the mass of a nucleon. The masses of the quarks are actually only about 1% that of

9628-453: The most common fuel is hydrogen , and gravity provides extremely long confinement times that reach the conditions needed for fusion energy production. Proposed fusion reactors generally use heavy hydrogen isotopes such as deuterium and tritium (and especially a mixture of the two ), which react more easily than protium (the most common hydrogen isotope ) and produce a helium nucleus and an energized neutron , to allow them to reach

9744-597: The most reactive aneutronic fuel is He. However, obtaining reasonable quantities of He implies large scale extraterrestrial mining on the Moon or in the atmosphere of Uranus or Saturn. Therefore, the most promising candidate fuel for such fusion is fusing the readily available protium (i.e. a proton ) and boron . Their fusion releases no neutrons, but produces energetic charged alpha (helium) particles whose energy can directly be converted to electrical power: Side reactions are likely to yield neutrons that carry only about 0.1% of

9860-406: The neutron and its magnetic moment both indicate that the neutron is a composite , rather than elementary , particle. The quarks of the neutron are held together by the strong force , mediated by gluons . The nuclear force results from secondary effects of the more fundamental strong force . The only possible decay mode for the neutron that obeys the conservation law for the baryon number

9976-401: The neutron and its properties is central to the extraordinary developments in atomic physics that occurred in the first half of the 20th century, leading ultimately to the atomic bomb in 1945. In the 1911 Rutherford model , the atom consisted of a small positively charged massive nucleus surrounded by a much larger cloud of negatively charged electrons. In 1920, Ernest Rutherford suggested that

10092-461: The neutron are described below in the Intrinsic properties section . Outside the nucleus, free neutrons undergo beta decay with a mean lifetime of about 14 minutes, 38 seconds, corresponding to a half-life of about 10 minutes, 11 s. The mass of the neutron is greater than that of the proton by 1.293 32   MeV/ c , hence the neutron's mass provides energy sufficient for the creation of

10208-401: The neutron can be modeled as a sum of the magnetic moments of the constituent quarks. The calculation assumes that the quarks behave like point-like Dirac particles, each having their own magnetic moment. Simplistically, the magnetic moment of the neutron can be viewed as resulting from the vector sum of the three quark magnetic moments, plus the orbital magnetic moments caused by the movement of

10324-434: The neutron is a neutral particle, the magnetic moment of a neutron is not zero. The neutron is not affected by electric fields, but it is affected by magnetic fields. The value for the neutron's magnetic moment was first directly measured by Luis Alvarez and Felix Bloch at Berkeley, California , in 1940. Alvarez and Bloch determined the magnetic moment of the neutron to be μ n = −1.93(2)  μ N , where μ N

10440-415: The neutron population high. Natural lithium is mainly Li, which has a low tritium production cross section compared to Li so most reactor designs use breeding blankets with enriched Li. Drawbacks commonly attributed to D-T fusion power include: The neutron flux expected in a commercial D-T fusion reactor is about 100 times that of fission power reactors, posing problems for material design . After

10556-431: The neutron's magnetic moment with an external magnetic field were exploited to finally determine the spin of the neutron. In 1949, Hughes and Burgy measured neutrons reflected from a ferromagnetic mirror and found that the angular distribution of the reflections was consistent with spin  ⁠ 1 / 2 ⁠ . In 1954, Sherwood, Stephenson, and Bernstein employed neutrons in a Stern–Gerlach experiment that used

10672-431: The nucleus consisted of positive protons and neutrally charged particles, suggested to be a proton and an electron bound in some way. Electrons were assumed to reside within the nucleus because it was known that beta radiation consisted of electrons emitted from the nucleus. About the time Rutherford suggested the neutral proton-electron composite, several other publications appeared making similar suggestions, and in 1921

10788-420: The nucleus via the nuclear force , effectively moderating the repulsive forces between the protons and stabilizing the nucleus. Heavy nuclei carry a large positive charge, hence they require "extra" neutrons to be stable. While a free neutron is unstable and a free proton is stable, within nuclei neutrons are often stable and protons are sometimes unstable. When bound within a nucleus, nucleons can decay by

10904-446: The original particle is not composed of the product particles; rather, the product particles are created at the instant of the reaction. "Free" neutrons or protons are nucleons that exist independently, free of any nucleus. The free neutron has a mass of 939 565 413 .3  eV/ c , or 939.565 4133   MeV/ c . This mass is equal to 1.674 927 471 × 10   kg , or 1.008 664 915 88   Da . The neutron has

11020-574: The outer portions of the reactor from the neutron flux. Newer designs, the advanced tokamak in particular, use lithium inside the reactor core as a design element. The plasma interacts directly with the lithium, preventing a problem known as "recycling". The advantage of this design was demonstrated in the Lithium Tokamak Experiment . Fusing two deuterium nuclei is the second easiest fusion reaction. The reaction has two branches that occur with nearly equal probability: This reaction

11136-453: The power, which means that neutron scattering is not used for energy transfer and material activation is reduced several thousand-fold. The optimum temperature for this reaction of 123 keV is nearly ten times higher than that for pure hydrogen reactions, and energy confinement must be 500 times better than that required for the D-T reaction. In addition, the power density is 2500 times lower than for D-T, although per unit mass of fuel, this

11252-420: The process. If they miss the inner cage they can collide and fuse. Ions typically hit the cathode, however, creating prohibitory high conduction losses. Fusion rates in fusors are low because of competing physical effects, such as energy loss in the form of light radiation. Designs have been proposed to avoid the problems associated with the cage, by generating the field using a non-neutral cloud. These include

11368-447: The protium–boron-11 reaction, because it does not directly produce neutrons, although side reactions can. The easiest nuclear reaction, at the lowest energy, is D+T: This reaction is common in research, industrial and military applications, usually as a neutron source. Deuterium is a naturally occurring isotope of hydrogen and is commonly available. The large mass ratio of the hydrogen isotopes makes their separation easy compared to

11484-400: The proton and neutron are viewed as two quantum states of the same particle, is used to model the interactions of nucleons by the nuclear or weak forces. Because of the strength of the nuclear force at short distances, the nuclear energy binding nucleons is many orders of magnitude greater than the electromagnetic energy binding electrons in atoms. In nuclear fission , the absorption of

11600-406: The proton to a neutron occurs similarly through the weak force. The decay of one of the proton's up quarks into a down quark can be achieved by the emission of a W boson. The proton decays into a neutron, a positron, and an electron neutrino. This reaction can only occur within an atomic nucleus which has a quantum state at lower energy available for the created neutron. The story of the discovery of

11716-409: The proton, electron and electron anti- neutrino decay products, and where n , e , and ν e denote the neutron, positron and electron neutrino decay products. The electron and positron produced in these reactions are historically known as beta particles , denoted β or β respectively, lending the name to the decay process. In these reactions,

11832-464: The proton, electron, and anti-neutrino. In the decay process, the proton, electron, and electron anti-neutrino conserve the energy, charge, and lepton number of the neutron. The electron can acquire a kinetic energy up to 0.782 ± 0.013 MeV . Still unexplained, different experimental methods for measuring the neutron's lifetime, the "bottle" and "beam" methods, produce different values for it. The "bottle" method employs "cold" neutrons trapped in

11948-519: The puzzle of nuclear spins. The origins of beta radiation were explained by Enrico Fermi in 1934 by the process of beta decay , in which the neutron decays to a proton by creating an electron and a (at the time undiscovered) neutrino. In 1935, Chadwick and his doctoral student Maurice Goldhaber reported the first accurate measurement of the mass of the neutron. By 1934, Fermi had bombarded heavier elements with neutrons to induce radioactivity in elements of high atomic number. In 1938, Fermi received

12064-448: The reaction energy is released as charged particles, reducing activation of the reactor housing and potentially allowing more efficient energy harvesting (via any of several pathways). In practice, D-D side reactions produce a significant number of neutrons, leaving p- B as the preferred cycle for aneutronic fusion. Both material science problems and non-proliferation concerns are greatly diminished by aneutronic fusion . Theoretically,

12180-429: The same atomic number, but different neutron number. Nuclides with the same neutron number, but different atomic number, are called isotones . The atomic mass number , A , is equal to the sum of atomic and neutron numbers. Nuclides with the same atomic mass number, but different atomic and neutron numbers, are called isobars . The mass of a nucleus is always slightly less than the sum of its proton and neutron masses:

12296-469: The single isotope copper-64 (29 protons, 35 neutrons), which has a half-life of about 12.7 hours. This isotope has one unpaired proton and one unpaired neutron, so either the proton or the neutron can decay. This particular nuclide is almost equally likely to undergo proton decay (by positron emission , 18% or by electron capture , 43%; both forming Ni ) or neutron decay (by electron emission, 39%; forming Zn ). Within

12412-429: The speed of light, or 250  km/s .) Neutrons are a necessary constituent of any atomic nucleus that contains more than one proton. As a result of their positive charges, interacting protons have a mutual electromagnetic repulsion that is stronger than their attractive nuclear interaction , so proton-only nuclei are unstable (see diproton and neutron–proton ratio ). Neutrons bind with protons and one another in

12528-639: The spheromak, attempt to combine the advantages of toroidal magnetic surfaces with those of a simply connected (non-toroidal) machine, resulting in a mechanically simpler and smaller confinement area. Inertial confinement is the use of rapid implosion to heat and confine plasma. A shell surrounding the fuel is imploded using a direct laser blast (direct drive), a secondary x-ray blast (indirect drive), or heavy beams. The fuel must be compressed to about 30 times solid density with energetic beams. Direct drive can in principle be efficient, but insufficient uniformity has prevented success. Indirect drive uses beams to heat

12644-407: The stellarator. Fusion reactions occur when two or more atomic nuclei come close enough for long enough that the nuclear force pulling them together exceeds the electrostatic force pushing them apart, fusing them into heavier nuclei. For nuclei heavier than iron-56 , the reaction is endothermic , requiring an input of energy. The heavy nuclei bigger than iron have many more protons resulting in

12760-457: The strong force, which has a range of roughly one femtometer —the diameter of a proton or neutron. The fuel atoms must be supplied enough kinetic energy to approach one another closely enough for the strong force to overcome the electrostatic repulsion in order to initiate fusion. The " Coulomb barrier " is the quantity of kinetic energy required to move the fuel atoms near enough. Atoms can be heated to extremely high temperatures or accelerated in

12876-417: The theoretical framework of the Standard Model for particle physics, a neutron comprises two down quarks with charge − ⁠ 1 / 3 ⁠ e and one up quark with charge + ⁠ 2 / 3 ⁠ e . The neutron is therefore a composite particle classified as a hadron . The neutron is also classified as a baryon , because it is composed of three valence quarks . The finite size of

12992-435: The three charged quarks within the neutron. In one of the early successes of the Standard Model, in 1964 Mirza A.B. Beg, Benjamin W. Lee , and Abraham Pais calculated the ratio of proton to neutron magnetic moments to be −3/2 (or a ratio of −1.5), which agrees with the experimental value to within 3%. The measured value for this ratio is −1.459 898 05 (34) . The above treatment compares neutrons with protons, allowing

13108-585: Was gamma radiation . The following year Irène Joliot-Curie and Frédéric Joliot-Curie in Paris showed that if this "gamma" radiation fell on paraffin , or any other hydrogen -containing compound, it ejected protons of very high energy. Neither Rutherford nor James Chadwick at the Cavendish Laboratory in Cambridge were convinced by the gamma ray interpretation. Chadwick quickly performed

13224-418: Was a contradiction, since there is no way to arrange the spins of an electron and a proton in a bound state to get a fractional spin. In 1931, Walther Bothe and Herbert Becker found that if alpha particle radiation from polonium fell on beryllium , boron , or lithium , an unusually penetrating radiation was produced. The radiation was not influenced by an electric field, so Bothe and Becker assumed it

13340-800: Was developed at Lawrence Livermore National Laboratory (LLNL) in the 1980s as a method to maintain a voltage directly using fusion reaction products. This has demonstrated energy capture efficiency of 48 percent. Plasma is an ionized gas that conducts electricity. In bulk, it is modeled using magnetohydrodynamics , which is a combination of the Navier–Stokes equations governing fluids and Maxwell's equations governing how magnetic and electric fields behave. Fusion exploits several plasma properties, including: Many approaches, equipment, and mechanisms are employed across multiple projects to address fusion heating, measurement, and power production. A deep reinforcement learning system has been used to control

13456-417: Was easier to implement. Poor confinement has led this approach to be abandoned, except in the polywell design. Magnetic loops bend the field lines back on themselves, either in circles or more commonly in nested toroidal surfaces. The most highly developed systems of this type are the tokamak , the stellarator, and the reversed field pinch. Compact toroids , especially the field-reversed configuration and

#319680