Explanatory dictionary of the Russian language. D.N. Ushakov

neutron

neutron, m. (from Latin neutrum, lit. neither one nor the other) (physical new). A material particle entering the nucleus of an atom, devoid of electric charge, electrically neutral.

Explanatory dictionary of the Russian language. S.I.Ozhegov, N.Yu.Shvedova.

neutron

A, m. (special). Electrically neutral elementary particle with a mass almost equal to the mass of a proton.

adj. neutron, -aya, -oh.

New explanatory dictionary of the Russian language, T. F. Efremova.

neutron

m. Electrically neutral elementary particle.

Encyclopedic Dictionary, 1998

neutron

NEUTRON (English neutron, from Latin neuter - neither one nor the other) (n) a neutral elementary particle with a spin of 1/2 and a mass exceeding the mass of a proton by 2.5 electron masses; refers to baryons. In the free state, the neutron is unstable and has a lifetime of approx. 16 min. Together with protons, a neutron forms atomic nuclei; in nuclei the neutron is stable.

Neutron

(English neutron, from Latin neuter ≈ neither one nor the other; symbol n), a neutral (not having an electric charge) elementary particle with spin 1/2 (in units of Planck's constant) and a mass slightly exceeding the mass of a proton. All atomic nuclei are built from protons and nitrogen. The magnetic moment of a magneton is equal to approximately two nuclear magnetons and is negative, that is, it is directed opposite to the mechanical, spin, angular momentum. N. belong to the class of strongly interacting particles (hadrons) and are included in the group of baryons, that is, they have a special internal characteristic ≈ baryon charge, equal, like that of the proton (p), +

N. were discovered in 1932 by the English physicist J. Chadwick, who established that the penetrating radiation discovered by the German physicists W. Bothe and G. Becker, which occurs when atomic nuclei (in particular, beryllium) are bombarded with a-particles, consists of uncharged particles with a mass , close to the proton mass.

N. are stable only in the composition of stable atomic nuclei. Free N. is an unstable particle that decays into a proton, an electron (e-) and an electron antineutrino:

average lifetime of N. t » 16 min. In matter, free neutrons exist even less (in dense substances, units ≈ hundreds of microseconds) due to their strong absorption by nuclei. Therefore, free neutrons arise in nature or are obtained in the laboratory only as a result of nuclear reactions (see Neutron sources). In turn, free nitrogen is capable of interacting with atomic nuclei, up to the heaviest ones; disappearing, N. causes one or another nuclear reaction, of which special meaning has the fission of heavy nuclei, as well as radiation capture of nitrogen, leading in some cases to the formation of radioactive isotopes. The great efficiency of neutrons in carrying out nuclear reactions and the unique nature of the interaction of very slow nuclei with matter (resonance effects, diffraction scattering in crystals, etc.) make neutrons an extremely important research tool in nuclear physics and physics solid. IN practical applications N. play a key role in nuclear power production transuranic elements and radioactive isotopes ( artificial radioactivity), and are also widely used in chemical analysis(activation analysis) and in geological exploration (neutron logging).

Depending on the energy of N. they are adopted conditional classification: ultracold N. (up to 10-7 eV), very cold (10-7≈10-4 eV), cold (10-4≈5×10-3 eV), thermal (5×10-3≈0.5 eV) , resonant (0.5≈104 eV), intermediate (104≈105 eV), fast (105≈108 eV), high-energy (108≈1010 eV) and relativistic (³ 1010 eV); all N. with energy up to 105 eV are combined common name slow neutrons.

══For methods of registration of neutrons, see Neutron detectors.

Main characteristics of neutrons

Weight. The most accurately determined value is the difference between the masses of nuclei and the proton: mn ≈ mр= (1.29344 ╠ 0.00007) MeV, measured from the energy balance of various nuclear reactions. By comparing this quantity with the mass of the proton, we obtain (in energy units)

mn = (939.5527 ╠ 0.0052) MeV;

this corresponds to mn" 1.6╥10-24g, or mn" 1840 mе, where mе ≈ electron mass.

Spin and statistics. The value 1/2 for spin N is confirmed large aggregate facts. Spin was directly measured in experiments on splitting a beam of very slow neutrons in a nonuniform magnetic field. IN general case the beam should split into 2J+ 1 separate beams, where J ≈ spin H. Splitting into 2 beams was observed in the experiment, which implies that J = 1/

As a particle with half-integer spin, N. obeys Fermi ≈ Dirac statistics (it is a fermion); This was independently established on the basis of experimental data on the structure of atomic nuclei (see Nuclear shells).

Electric charge neutron Q = 0. Direct measurements of Q from the deflection of the N beam in a strong electric field show that at least Q< 10-17e, где е ≈ элементарный электрический заряд, а indirect measurements(based on the electrical neutrality of macroscopic gas volumes) give an estimate Q< 2╥10-22е.

Other quantum numbers neutron. In its properties, N. is very close to the proton: n and p have almost equal masses, the same spin, are capable of mutually transforming into each other, for example in beta decay processes; they manifest themselves in the same way in processes caused by strong interaction, in particular the nuclear forces acting between pairs p≈p, n≈p and n≈n are the same (if the particles are respectively in the same states). Such a deep similarity allows us to consider the neutron and the proton as one particle ≈ nucleon, which can be located in two different states, differing in electric charge Q. A nucleon in a state with Q = + 1 is a proton, with Q = 0 ≈ H. Accordingly, a certain internal characteristic≈ isotonic spin I equal to 1/2, the “projection” of which can take (according to general rules quantum mechanics) 2I + 1 = 2 values: + 1/2 and ≈1/2. Thus, n and p form an isotopic doublet (see Isotopic invariance): a nucleon in a state with the projection of the isotopic spin on the quantization axis + 1/2 is a proton, and with a projection ≈1/2 ≈ H. As components of the isotopic doublet, N. and proton, according to modern taxonomy elementary particles have the same quantum numbers: baryon charge B =+ 1, lepton charge L = 0, strangeness S = 0 and positive internal parity. The isotopic doublet of nucleons is part of a wider group of “similar” particles ≈ the so-called octet of baryons with J = 1/2, B = 1 and positive internal parity; in addition to n and p, this group includes L-, S╠-, S0-, X
--, X0-hyperons, differing from n and p in strangeness (see Elementary particles).

Magnetic dipole neutron moment, determined from nuclear magnetic resonance experiments is equal to:

mn = ≈ (1.91315 ╠ 0.00007) mе,

where mя=5.05×10-24erg/gs ≈ nuclear magneton. A particle with spin 1/2, described by the Dirac equation, must have a magnetic moment equal to one magneton if it is charged, and zero if it is not charged. Availability magnetic moment in N., as well as the anomalous value of the magnetic moment of the proton (mр = 2.79mя), indicates that these particles have a complex internal structure, i.e. inside them there are electric currents, creating an additional “anomalous” magnetic moment of the proton of 1.79 m and approximately equal in magnitude and opposite in sign magnetic moment N. (≈1.9 m) (see below).

Electric dipole moment. WITH theoretical point From the point of view, the electric dipole moment d of any elementary particle should be equal to zero, if the interactions of elementary particles are invariant under time reversal (T-invariance). The search for electric dipole moment in elementary particles are one of the tests of this fundamental position of the theory, and of all elementary particles, N. is the most convenient particle for such searches. Experiments using the method magnetic resonance on a beam of cold N. showed that dn< 10-23см╥e. Это означает, что сильное, электромагнитное и weak interaction are T-invariant with high accuracy.

Neutron interactions

N. participate in all known interactions of elementary particles—strong, electromagnetic, weak, and gravitational.

Strong interaction of neutrons. N and proton participate in strong interactions as components of a single isotopic doublet of nucleons. The isotopic invariance of strong interactions leads to a certain connection between the characteristics various processes with the participation of a proton and a proton, for example, the effective cross sections for the scattering of a p+ meson on a proton and p
-meson on N. are equal, since the p+p and p-n systems have the same isotopic spin I = 3/2 and differ only in the values ​​of the projection of the isotopic spin I3 (I3 = + 3/2 in the first and I3 = ≈ 3/2 in in the second cases), the scattering cross sections of K+ on a proton and K╟ on H are identical, etc. The validity of this kind of relationship has been experimentally verified in a large number of experiments at accelerators high energy. [Due to the absence of targets consisting of neutrons, data on the interaction of various unstable particles with nuclei are extracted mainly from experiments on the scattering of these particles on the deuteron (d) ≈ ​​the simplest nucleus containing nuclei.]

At low energies, the actual interactions of neutrons and protons with charged particles and atomic nuclei differ greatly due to the presence of an electric charge on the proton, which determines the existence of long-range Coulomb forces between a proton and other charged particles at distances at which short-range nuclear forces are practically absent. If the collision energy of a proton with a proton or atomic nucleus is below the height of the Coulomb barrier (which for heavy nuclei is about 15 MeV), proton scattering occurs mainly due to electrostatic repulsion forces, which do not allow particles to approach to distances on the order of the radius of action nuclear forces. N.'s lack of electric charge allows it to penetrate the electronic shells of atoms and freely approach atomic nuclei. This is what determines unique ability N. of relatively low energies causes various nuclear reactions, including the fission reaction of heavy nuclei. For methods and results of studies of the interaction of N. with nuclei, see the articles Slow neutrons, Neutron spectroscopy, Atomic fission nuclei, Scattering of slow neutrons on protons at energies up to 15 MeV is spherically symmetrical in the center of inertia system. This indicates that scattering is determined by the interaction n ≈ p in the state relative motion with orbital angular momentum l = 0 (the so-called S-wave). Scattering in the S-state is a specifically quantum mechanical phenomenon that has no analogue in classical mechanics. It prevails over scattering in other states when the de Broglie wavelength is H.

order or greater than radius action of nuclear forces (≈ Planck’s constant, v ≈ N. velocity). Since at an energy of 10 MeV the wavelength is H.

This feature of nuclear scattering on protons at such energies directly provides information about the order of magnitude of the radius of action of nuclear forces. Theoretical consideration shows that scattering in the S-state weakly depends on the detailed shape of the interaction potential and is described with good accuracy by two parameters: the effective radius of the potential r and the so-called scattering length a. In fact, to describe scattering n ≈ p the number of parameters is twice as large, since the np system can be in two states with different meanings full spin: J = 1 (triplet state) and J = 0 (singlet state). Experience shows that the scattering lengths of hydrogen by a proton and the effective radii of interaction in the singlet and triplet states are different, i.e., nuclear forces depend on the total spin of the particles. It also follows from experiments that the bound state of the system np (deuterium nucleus) can exist only when the total spin is 1, while in the singlet state the magnitude of nuclear forces is insufficient to form a bound state H. ≈ proton. The length of nuclear scattering in the singlet state, determined from experiments on the scattering of protons on protons (two protons in the S-state, according to the Pauli principle, can only be in a state with zero total spin), is equal to the scattering length n≈p in the singlet state. This is consistent with the isotopic invariance of strong interactions. Absence connected system pr in the singlet state and the isotopic invariance of nuclear forces lead to the conclusion that a bound system of two neutrons ≈ the so-called bineutron cannot exist (similar to protons, two neutrons in the S-state must have a total spin equal to zero). Direct experiments on n≈n scattering were not carried out due to the absence of neutron targets, however, indirect data (properties of nuclei) and more direct ≈ studies of the reactions 3H + 3H ╝ 4He + 2n, p- + d ╝ 2n + g ≈ are consistent with the hypothesis of isotopic invariance nuclear forces and the absence of a bineutron. [If a bineutron existed, then in these reactions peaks in the energy distributions of a-particles (4He nuclei) and g-quanta, respectively, would be observed at quite certain energy values.] Although nuclear interaction in the singlet state is not large enough to form a bineutron, this does not exclude the possibility of the formation of a bound system consisting of large number N. alone ≈ neutron nuclei. This issue requires further theoretical and experimental study. Attempts to experimentally detect nuclei of three to four nucleotides, as well as 4H, 5H, and 6H nuclei, have not yet yielded positive result, Despite the lack of a consistent theory of strong interactions, on the basis of a number of existing ideas it is possible to qualitatively understand some regularities of strong interactions and the structure of neutrons. According to these ideas, the strong interaction between nuclei and other hadrons (for example, a proton) is carried out through the exchange of virtual hadrons (see . Virtual particles) ≈ p-mesons, r-mesons, etc. This interaction picture explains the short-range nature of nuclear forces, the radius of which is determined by the Compton wavelength of the lightest hadron ≈ p-meson (equal to 1.4 × 10-13 cm). At the same time, it indicates the possibility of virtual transformation of neutrons into other hadrons, for example, the process of emission and absorption of the p-meson: n ╝ p + p- ╝ n. The intensity of strong interactions known from experience is such that N. must spend the vast majority of time in such “dissociated” states, being, as it were, in a “cloud” of virtual p-mesons and other hadrons. This leads to the spatial distribution of the electric charge and magnetic moment inside the N., physical dimensions which is determined by the size of the “cloud” virtual particles(see also Form factor). In particular, it turns out to be possible to qualitatively interpret the above-mentioned approximate equality in terms of absolute value anomalous magnetic moments of the neutron and the proton, if we assume that the magnetic moment of the neutron is created orbital motion charged p
--mesons emitted virtually in the process n ╝ p + p- ╝ n, and the anomalous magnetic moment of the proton ≈ the orbital motion of a virtual cloud of p+ mesons, created by the processр ╝ n + p+ ╝ р.

Electromagnetic interactions neutron. Electromagnetic properties N. are determined by the presence of a magnetic moment, as well as the distribution of positive and negative charges and currents. All these characteristics, as follows from the previous one, are associated with N.’s participation in strong interaction, which determines its structure. The magnetic moment of the N. determines the behavior of the N. in external electromagnetic fields: N beam splitting in a non-uniform magnetic field, spin precession N. Internal electromagnetic structure N. manifests itself during the scattering of high-energy electrons on N. and in the processes of production of mesons on N. by g-quanta (meson photoproduction). Electromagnetic interactions of neutrons with the electron shells of atoms and atomic nuclei lead to a number of phenomena that have important to study the structure of matter. Interaction of the magnetic moment of N. with magnetic moments electron shells atoms manifests itself significantly for neutrons, the wavelength of which is of the order of or greater than atomic dimensions (energy E< 10 эв), и широко используется для исследования магнитной структуры и элементарных возбуждений (спиновых волн) магнитоупорядоченных кристаллов (см. Нейтронография). Интерференция с ядерным рассеянием позволяет получать пучки поляризованных медленных Н. (см. Поляризованные нейтроны).

Interaction of the magnetic moment of N. with electric field nuclei causes specific dispersion of N., indicated for the first time American physicist Yu. Schwinger and therefore called “Schwinger”. The total cross section for this scattering is small, but at small angles (~ 3╟) it becomes comparable to the cross section for nuclear scattering; N., scattered at such angles, in strong degree polarized.

The interaction of magnetism ≈ electron (n≈e), which is not associated with the electron’s own or orbital momentum, is reduced mainly to the interaction of the magnetism magnetic moment with the electron’s electric field. Another, apparently smaller, contribution to the (n≈e) interaction may be due to the distribution of electric charges and currents inside the N. Although the (n≈e) interaction is very small, it has been observed in several experiments.

Weak neutron interaction manifests itself in processes such as the disintegration of N.:

capture of an electron antineutrino by a proton:

and muon neutrino (nm) by neutron: nm + n ╝ р + m-, nuclear capture of muons: m- + р ╝ n + nm, decays of strange particles, for example L ╝ p╟ + n, etc.

Gravitational interaction of the neutron. N. is the only elementary particle with a rest mass for which it was directly observed gravitational interaction≈ curvature of the trajectory of a well-collimated beam of cold neutrons in the terrestrial gravitational field. The measured gravitational acceleration of neutrons, within the limits of experimental accuracy, coincides with gravitational acceleration macroscopic bodies.

Neutrons in the Universe and near-Earth space

The question of the amount of neutrons in the Universe in the early stages of its expansion plays important role in cosmology. According to the model of the hot Universe (see Cosmology), a significant part of the initially existing free neutrons manage to decay during expansion. The part of hydrogen that is captured by protons should ultimately lead to approximately 30% content of He nuclei and 70% protons. Experimental determination The percentage composition of He in the Universe is one of the critical tests of the hot Universe model.

The evolution of stars in some cases leads to the formation neutron stars, which include, in particular, the so-called pulsars.

Due to their instability, neutrons are absent from the primary component of cosmic rays. However, the interactions of cosmic ray particles with atomic nuclei earth's atmosphere lead to the generation of nitrogen in the atmosphere. The reaction 14N (n, р)14С, caused by these N., is the main source radioactive isotope carbon 14C in the atmosphere, from where it enters living organisms; based on determination of 14C content in organic residues radiocarbon dating geochronology. Decay of slow neutrons diffusing from the atmosphere into the near-Earth space, is one of the main sources of electrons filling the inner region of the Earth's radiation belt.

Bombardment of uranium nuclei neutrons the beryllium rod took much more energy than was released during primary fission.

Therefore, for the reactor to operate, it was necessary that each atom be split neutrons

Therefore, for the reactor to operate, it was necessary that each atom split neutrons beryllium rod, in turn, caused the splitting of other atoms.

Good source neutrons was affordable even for a poor laboratory: a little radium and a few grams of beryllium powder.

The same amount could be obtained in a cyclotron in two days if we used neutrons, knocked out of a beryllium target by accelerated deuterons.

Then it was possible to show that beryllium radiation actually consists of gamma rays and a flux neutrons.

You see, the original flow neutrons will be a simple spherical expansion from the primary explosion, but it will be captured by beryllium,” Fromm explained, standing next to Kuati.

Hell, akasha, alcoholism, Angel, antimatter, antigravity, antiphoton, asthenia, astrology, atom, Armageddon, aura, autogenic training, delirium tremens, insomnia, dispassion, God, divine, divine path, Buddhism, buddhi, future, future of the Universe, future solar system, vacuum, Great vow, substance, virtual, influence on fate, extraterrestrial civilization, Universe, global flood, incarnation, time, Higher intelligence, Higher Knowledge, galaxy, geological periods, Hermes Trismegistus, hyperon, hypnosis, brain, horoscope, gravitational waves, gravity, guna, Tao, double, depersonalization, mass defect, demon, Zen Buddhism, good evil, DNA, Ancient Knowledge, continental drift, Spirit, soul, dhyana, devil, Unified Theory Fields, life, mental illness, origin of life, star, earthly life, knowledge of the future, knowledge, zombies, zombification, change of fate, altered states of consciousness, measurement of matter, Emerald Tablet, immune system, instinct, intelligence, intuition, bending of light, artificial intelligence

To the boron carbide rod, highly absorbent neutrons, suspended a graphite displacer 4.5 m long.

Replacing these pillars with a graphite displacer that is less absorbent neutrons, and creates a local reactor.

Minimum size Minimum size of living inert natural body natural body is determined by dispersion determined by breathing, matter-energy - atom, mainly gas electron, corpuscle, biogenic migration of atoms neutron etc.

The idea of ​​a long-lived compound nucleus allowed Bohr to foresee that even very slow ones would be suitable. neutrons.

Structural difference between them is reduced to the number of protons included in them, neutrons, mesons and electrons, however, each successive addition of a proton-electron pair to the system sharply changes the functional properties of the entire aggregate unit as a whole and this is a clear confirmation of the regulation of the number of fnl.

The RBMK-1000 reactor is a channel type reactor, moderator neutrons- graphite, coolant - ordinary water.

NEUTRON

NEUTRON

(English neutron, from Latin neuter - neither one nor the other) (n), electrically neutral element. particle with spin 1/2 and mass slightly exceeding the mass of a proton; belongs to the class of hadrons and is part of the group of baryons. All atomic nuclei are built from protons and nitrogen. N. opened in 1932. physicist J. Chadwick, who established that what was discovered was by physicists V. Bothe and G. Becker, penetrating, which occurs during the bombardment of at. nuclei a-particles, consists of uncharged. ch-ts with a mass close to proton.

N. are stable only in the composition of stable at. cores. Free N. is an unstable particle that decays according to the scheme: n®p+e-+v=c (beta decay of N.); Wed N. t=15.3 min. In substances, free neutrons exist even less (in dense substances - units - hundreds of microseconds) due to their strong absorption by nuclei. Therefore, free N. occur in nature or are obtained in the laboratory only as poison. reactions. Free N., interacting with at. nuclei, cause dif. . Greater efficiency of N. in the implementation of poison. reactions, the uniqueness of the interaction with slow N. (resonance effects, diffraction scattering in crystals, etc.) make N. an extremely important tool for research in poison. physics and physics TV. body (see NEUTRONOGRAPHY). In practice N. applications play a key role in poison. energy, in the production of transuranium elements and radioactivity. isotopes (artificial), and are also used in chemistry. analysis (activation analysis) and in geol. exploration (neutron logging).

Basic characteristics of neutrons.

Weight. The difference between the masses of neutron and proton is most accurately determined: mn--mp=1.29344(7) MeV, measured by energy. balance diff. I. reactions. Hence (and the known mp) mn = 939.5731(27) MeV or mn»1.675X10-24 g»1840me (me - el-na).

Spin and statistics. The N. J spin was measured by splitting a beam of very slow N. in an inhomogeneous magnetic field. . According to quant. mechanics, the beam should split into 2J+1 parts. bunches. Splitting into two beams was observed, i.e. for N. J = 1/2 and N. obeys Fermi - Dirac statistics (this was independently established on the basis of experimental data on the structure of at. nuclei).

The scattering of slow neutrons by protons at energies up to 15 MeV is spherically symmetrical in the center of inertia system. This indicates that scattering is determined by the action of np in the relative state. movements from orbits. moment l=0 (so-called S-wave). S-scattering prevails over scattering in other states when de Broglie N. ?? radius of action of poison. strength Since at an energy of 10 MeV for N.?2 10-13 cm, this feature of the scattering of N. on protons at such energies gives information about the order of magnitude of the radius of action of the poison. strength From the theory of scattering of microparticles it follows that scattering in the S-state weakly depends on the detailed shape of the action potential and is described with good accuracy by two parameters: eff. radius r of the potential and scattering length a. To describe np scattering, the number of parameters is twice as large, since the system can be in two states with different meanings total spin: 1 (triplet state) and 0 (singlet state). Experience shows that the scattering lengths of N. by a proton and eff. the radii of action in the singlet and triplet states are different, i.e. poison. forces depend on the total back h-ts. In particular, communications. state of the np system - the deuterium nucleus can exist only at spin 1. The scattering length in the singlet state, determined from pp-scattering experiments (two protons in the S-state, according to the Pauli principle, can only be in a state with zero total spin), is equal to length of np scattering in the singlet state. This is consistent with isotopic invariance of strong action. Lack of connections. np systems in singlet state and isotopic. invariance poison. forces lead to the conclusion that a connection cannot exist. systems of two N-- so-called. bineutron. Direct experiments on nn-scattering were not carried out due to the lack of neutron targets, but indirectly. data (the properties of nuclei) and more direct ones - the study of the reactions 3H+3H®4He+2n, p-+d®2n+g are consistent with the isotopic hypothesis. invariance poison. forces and the absence of a bineutron. (If the bineutron existed, then in these reactions peaks in the energy distributions of the corresponding a-particles and g-quanta would be observed at quite certain energies.) Although poison. The effect in the singlet state is not strong enough to form a bineutron; this does not exclude the possibility of bond formation. systems consisting of a large number of neutron nuclei alone (nuclei of three or four neutrons have not been detected).

Electromagnetic interaction. El.-magnetic. Saints of N. are determined by the presence of magnesium. moment, as well as the distribution existing inside the N. will put. and deny. charges and currents. Magn. N.'s moment determines N.'s behavior in external situations. el.-magn. fields: splitting of the N. beam in an inhomogeneous magnetic field. field, spin precession N. Int. el.-magn. the structure of a neutron (see FORM FACTOR) manifests itself during the scattering of high-energy electrons on a neutron and in the processes of production of mesons on a neutron by g-quanta. Magnetic effect moment N. with magnet. moments of the electron shells of atoms is significantly manifested for N., the de Broglie length of which?? at. sizes (? NEUTRONOGRAPHY). Magnetic interference scattering with nuclear allows one to obtain beams of polarized slow N. Magnetic effects. moment N. with electric the nuclear field causes a specific Schwinger scattering (indicated for the first time by the American physicist Yu. Schwinger). The total scattering is small, but at small angles (= 3°) it becomes comparable to the poison cross section. scattering; N., scattered at such angles, are highly polarized. N.'s relationship with e-nom, not related to his own. or orbits. moment el-na, comes down to the main. to the rise of the magnet. moment N. with electric email field. Although this effect is very small, it was possible to observe it in the investigation. experiments.

Weak (I. manifests itself in processes such as the disintegration of N.: n®p+e-+v=e, capture electron proton: v=e+p®n+e+ and muon neutron: vm+n®p+m-, poison. capture of muons: m-+р®n+vm, decays of strange particles, e.g. L®p°+n, as well as in poison. reactions caused by II. and walking in violation of spaces. parity.

Gravitational interaction. N. is the only element that has a rest mass. h-ts, for the cut the gravitational force was directly observed. deflection - curvature of the trajectory of a well-collimated beam of cold N in the terrestrial gravitational field. Measured gravitation. N., within the accuracy of the experiment, coincides with gravity. acceleration macroscopic tel.

Neutrons in the Universe and near-Earth space.

The question of the number of particles in the Universe in the early stages of its expansion plays an important role in cosmology. According to the hot Universe model, that means. Some of the initially existing free N. has time to disintegrate during expansion. The part of N. that ends up being captured by protons should ultimately lead to approx. to a 30% content of He nuclei and a 70% content of protons. Let's experiment. determination of the percentage of He in the Universe is one of the critical. tests of the hot Universe model. The evolution of stars in some cases leads to the formation of neutron stars (which include, in particular, pulsars). In the primary component of the cosmos. There are no N. rays due to their instability. However, the effect of the cosmos. rays with the nuclei of atoms of the earth's atmosphere leads to the generation of nitrogen in the atmosphere. The reaction 14N (n, p) 14C, caused by these N., is the main. radioact source carbon isotope 14C in the atmosphere, from where it enters living organisms; on determining the content of 14C in organic matter. The remains are based on the radiocarbon dating method of geochronology. Decay of slow neutrons diffusing from the atmosphere into the near-Earth space. pr-vo, yavl. one of the sources of emails filling the internal region radiation belts Earth.

Physical encyclopedic Dictionary. - M.: Soviet Encyclopedia. . 1983 .

NEUTRON

(n) (from Latin neuter - neither one nor the other) - an elementary particle with zero electric power. charge and mass, insignificant greater mass proton. Along with the proton under the general name. The nucleon is part of atomic nuclei. H. has spin 1/2 and therefore obeys Fermi - Dirac statistics(is a fermion). Belongs to the family adra-nov; has baryon number B= 1, i.e. included in the group baryons.

Discovered in 1932 by J. Chadwick, who showed that hard penetrating radiation arising from the bombardment of beryllium nuclei by a-particles consists of electrically neutral particles with a mass approximately equal to that of a proton. In 1932, D. D. Ivanenko and W. Heisenberg put forward the hypothesis that atomic nuclei consist of protons and H. Unlike charges. particles, H. easily penetrates into nuclei at any energy and with high probability causes nuclear reactions capture (n,g), (n,a), (n, p), if the energy balance in the reaction is positive. Probability of exothermic nuclear reaction increases as H slows down. Inversely proportional. his speed. An increase in H. capture reactions when they are slowed down in hydrogen-containing media was discovered by E. Fermi and co-workers in 1934. The ability of H. to cause the fission of heavy nuclei, discovered by O. Hahn and F. Strassmann (F. Strassman) in 1938 (see Nuclear fission), served as the basis for the creation nuclear weapons And nuclear power. The peculiarity of the interaction with matter of slow neutrons, which have a de Broglie wavelength on the order of atomic distances (resonance effects, diffraction, etc.), serves as the basis for the widespread use of neutron beams in solid state physics. (Classification of H. by energies - fast, slow, thermal, cold, ultra-cold - see Art. Neutron physics.)

In the free state, H. is unstable - it undergoes B-decay; n p + e - + v e; its life t n = = 898(14) s, the limiting energy of the electron spectrum is 782 keV (see. Neutron beta decay). IN bound state in the composition of stable nuclei, H. is stable (according to experimental estimates, its lifetime exceeds 10 32 years). According to astr. It is estimated that 15% of the visible matter of the Universe is represented by H., which is part of the 4 He nuclei. H. is the main component neutron stars. Free H. in nature are formed in nuclear reactions, caused by a-particles radioactive decay, cosmic rays and as a result of spontaneous or forced fission of heavy nuclei. Art. sources of H. are nuclear reactors, nuclear explosions, accelerators of protons (average energy) and electrons with targets from heavy elements. The sources of monochromatic H. beams with an energy of 14 MeV are low-energy. deuteron accelerators with a tritium or lithium target, and in the future intensive sources of such H. may turn out to be thermonuclear installations UTS. (Cm. Neutron sources.)

Main characteristics of H.

Mass H. t p = 939.5731(27) MeV/s 2 = = 1.008664967(34) at. units mass 1.675. 10 -24 g. The difference between the masses of H. and the proton was measured from the max. accuracy from energy. balance of the reaction of H. capture by a proton: n + p d + g (g-quantum energy = 2.22 MeV), m n- m p = 1.293323 (16) MeV/c 2 .

Electric charge H. Q n = 0. Most accurate direct measurements Q n are made by deflecting beams of cold or ultra-cold H. into electrostatic. field: Q n<= 3·10 -21 her - electron charge). Kosv. electrical data neutrality macroscopic. amount of gas they give Q n<= 2·10 -22 e.

Spin H. J= 1/2 was determined from direct experiments on splitting a H beam in an inhomogeneous magnetic field. field into two components [in the general case, the number of components is equal to (2 J + 1)].

Internal parity H. positive. Isotopic spin I = 1 / 2, while the projection isotopic. back H. I 3 = - 1/2. Within S.U.(3)-symmetry H. is included in the baryon octet (see. Unitary symmetry).

Magnetic moment H. Despite the electrical neutrality of H., its magnetic moment. the moment is significantly different from zero: m n = - 1.91304184(88)m I, where m I = e/ 2m p c- nuclear magneton(m p - proton mass); magnet sign moment is determined relative to the direction of its spin. Magnetic comparison moments of the proton (m p = 2.7928456) and H. made it possible to hypothesize the role of the p-meson environment (coat) of the “naked” nucleon in the formation of the nucleon structure. The ratio of m p and m n (m p / m n - 3 / 2) can be explained within the framework of ideas about the quark structure of nucleons (see below). Naib. exactly m n measured by comparison with m p method nuclear magnetic resonance on a bunch of cold H.

Electric dipole moment H. Dynamic, i.e. induced, dipole moment H. can arise in a strong electric. field, e.g. during the scattering of H. on a heavy nucleus, or during the scattering of g-rays on a deuteron. Change in particle energy in electrical energy. the field is determined by the relation D = -(a o 2 /2). E 2, where a 0 is the polarizability of the particle, E - field strength. Experiments give estimates a 0<= 10 -42 см 3 (принята , в к-рой = With= 1).

Static electric the dipole moment (EDM) of an elementary particle must be identically equal to zero if the interactions it experiences are invariant with respect to time reversals(T-invariants). EDM is different from zero if T-invariance is broken, which, according to CPT theorem(i.e. charge conjugation, spatial inversion and time reversal), is equivalent to violation SR-in-variance. Although the violation SR-invariance was discovered back in 1964 in the decay of K 0 L-meson, still SR-non-invariant effects for other particles (or systems) were not observed. In modern unified gauge theories of elementary particles violation T(or C.P.)-invariance can occur in electroweak interaction, although the effect size is extremely small. Diff. violation models SR-invariances predict the value of EDM H. at the level (10 -24 -10 -32) e. see Because of its electrical neutrality H. is a very convenient object for searching SR-non-invariance. Naib. sensitive and reliable method - NMR method with electrical field superimposed on the magnetic field. iole. Changing the direction of electrical field while maintaining all other characteristics of the resonant NMR spectrometer causes a shift in the NMR frequency by the value D v = - 4dE, Where d- EDM. For d ~ 10 -25 e. cm Dv ~10 -6 Hz. Using the method of retaining ultracold H. in an NMR spectrometer, it is possible to achieve such sensitivity. Received max. exact limitation on EDM H.: d n<= 2·10 -25 e. cm .

H structure.

H., along with the proton, belongs to the lightest baryons. According to modern ideas, it consists of the three lightest valence quarks(two d-quarks and one u-quark) of three colors forming a colorless combination. In addition to valence quarks and the ones that bind them gluons a nucleon contains a “sea” of virtual quarks, including heavy ones (strange, charmed, etc.). Quantum numbers H. are entirely determined by the set of valence quarks, and spaces. structure - the dynamics of interaction of quarks and gluons. A feature of this interaction is the increase in eff. interaction constants ( effective charge)with increasing distance, so that the size of the interaction area is limited by the so-called area. confinement of quarks - a region of confinement of colored objects, the radius of which is ~10 -13 cm (see. Color retention).

Consistent description of the structure of hadrons based on modern theory of strong interaction - quantum chromodynamics - while meeting theoretical. difficulties, however, for many will completely satisfy the tasks. the results are given by a description of the interaction of nucleons, represented as elementary objects, through the exchange of mesons. Let's experiment. exploration of spaces. H. structure is carried out using the scattering of high-energy leptons (electrons, muons, neutrinos, considered in modern theory as point particles) on deuterons. The contribution of scattering on a proton is measured in dep. experiment and can be subtracted using the definition. will calculate. procedures.

Elastic and quasi-elastic (with deuteron splitting) scattering of electrons on a deuteron makes it possible to find electrical densities. charge and magnetic moment H. ( form factor H.). According to the experiment, the magnetic density. moment H. with an accuracy of the order of several. percent coincides with the distribution of electrical density. proton charge and has a root-mean-square radius of ~0.8·10 -13 cm (0.8 F). Magn. H. form factor is described quite well by the so-called. dipole f-loy G M n = m n (1 + q 2 /0.71) -2, where q 2 - square of the transferred momentum in units (GeV/c) 2.

A more complex question is about the magnitude of the electric current. (charge) form factor H. G E n. From deuteron scattering experiments we can conclude that G E n ( q 2 ) <= 0.1 in the interval of squares of transmitted impulses (0-1) (GeV/c) 2. At q 2 0 due to the equality to zero electric. charge H. G E n- > 0, however, it can be determined experimentally dG E n ( q 2 )/dq 2 | q 2=0 . This value is max. exactly found from measurements scattering lengths H. on the electron shell of heavy atoms. Basic Part of this interaction is determined by the magnetic field. moment H. Max. precise experiments give the ne-scattering length A ne = -1.378(18) . 10 -16 cm, which differs from the calculated value determined by the magnetic field. moment H.: a ne = -1.468. 10 -16 cm. The difference between these values ​​gives the mean square electric. radius H.<r 2 E n >= = 0.088(12) Fili dG E n ( q 2)/dq 2 | q 2=0 = -0.02 F 2 . These figures cannot be considered final due to the large scatter of data, decomposition. experiments exceeding the reported errors.

IN deeply inelastic process scattering (interaction with the creation of many secondary hadrons, predominantly pions), an incident point particle (lepton) interacts directly with the point components of the nucleon - quarks. Quark composition H. ( ddu)max. is clearly revealed in experiments with the interaction of high-energy neutrinos and antineutrinos with proton and neutron (containing deuterium) targets. For example, the total reaction cross section s v m n m - X (where X is the set of hadrons) is approximately twice the total reaction cross section v m p m - X, since v m interacts only with d-quark [quark composition of the proton ( uud)]. Likewise Corrections to these simple relations of total cross sections are related in the main. with the presence of a “sea” of virtual quark-antiquark pairs.

Interactions H.

Strong interaction of H. with nucleons. As a consequence, isotopic Invariance is the equality of the cross sections for neutron-neutron and proton-proton interactions, if in the latter case the contribution of the Coulomb interaction is taken into account. At the quark-gluon level isotope. is a consequence of the small mass difference d- And u-quarks (if the quark mass itself is small). This also explains the smallness of the difference between the masses of the proton and H., as well as the magnitude and sign of this difference ( d- quark is heavier u-quark).

At low energies (up to 15 MeV), the scattering of H. on a proton is isotropic in the center of mass system, i.e., the interaction is determined mainly. S-wave (relative motion with orbital momentum L= 0). For S-wave interaction, the scattering cross section can be characterized by two parameters - eff. radius of the interaction potential and scattering length. Dependence on relates. the direction of the spins of H. and the proton doubles the number of parameters, since the scattering lengths for the singlet (total spin of the system 0) and triplet (total spin 1) states are different (differ several times). Modern values ​​of scattering lengths and eff. radii (in F): = 1,70(3), r os= 2.67(3). The parameters of np scattering cannot be directly compared with pp and nn scattering, since the pp and nn systems, in accordance with Pauli principle cannot be in the triplet state. The singlet length of pp scattering is equal to: A pp = -7.815(8) F, r 0 = 2.758 F. Calculation of the Coulomb contribution to a pp allows one to obtain a purely nuclear pp scattering length a I pp, edge turns out to be equal to -17.25 F. According to isotopic. invariance, A i pp = A nn. Determining the parameters of nn-scattering is a difficult problem, since direct interaction of free H. has not yet been observed due to the difficulty of the experiment. Several have been proposed. experimental options for searching for direct nn-scattering in beams of high-flux pulsed or stationary reactors.

Naib. certain information about A pp . obtained by studying the reaction p-d 2ng: a nn = - 18.45(46) F, and reactions nd p2n: a nn = - 16.73(45) F. The discrepancy in the results is due to the ambiguity of the extrapolation procedure to zero energy H. and the insufficient description of the deuteron. Comparing A nn and a pp, we can conclude that isotopic. invariance is observed, although experimental. insufficient.

At the early stage of the development of nuclear physics, fundamentals played a major role in understanding the properties of nuclear forces. characteristics of the deuteron. The deuteron is a bound triplet state with a binding energy of -2.224 MeV. The singlet state is positive. binding energy 64 keV and is a resonance. Dr. There are no resonances and bound states in the low energy region in the np system. These two parameters make it possible to determine the nucleon-nucleon interaction and the radius of nuclear forces. The presence of a quadrupole electric in the deuteron. moment Q = 2.859. 10 -27 cm 2 leads to the conclusion about the existence of tensor nuclear forces.

Radiation the capture of H. by a proton, nр dg, is the simplest nuclear reaction. The capture cross section at low energies H depends on the speed H as 1 / u . For thermal H. (with l = 1.73) s n g = 0.311 barn.

Isotopic the invariance of nuclear forces and the known singlet np state make it possible to justify the absence of a bound nn state (di-neutron). Let's experiment. searches for this in reactions of type A + B C + 2n confirm this conclusion: dineutron production cross section<=10 -29 см 2 . Не найдены также связанные состояния трёх и четырёх H. Для большего числа H. существование связанных состояний не исключено, хотя вероятность их образования в исследованных ядерных реакциях должна быть крайне мала.

At high energies of nucleon-nucleon interaction, its character changes. At energies of incident nucleons (200-400) MeV, corresponding to their approach at a distance of ~0.3 F, repulsive reactions appear in the interaction. strength. This phenomenon is usually compared with the existence of a rigid repulsive core (core) of nucleons and is attributed to the dominant role at short distances of exchange of heavy vector mesons, for example. w-mesons. This explanation is not the only possible one. In the “quark bag” model (see Quark models) the same phenomenon is explained by the fusion at short distances of two nucleons into one six-quark bag, the properties of which are qualitatively different from the properties of individual nucleons; This leads to the fact that two individual nucleons are not observed experimentally at short distances.

At higher energies, interactions become essentially inelastic and are accompanied by multiples. the creation of p-mesons and heavier particles (see. Multiple processes). The properties of quarks and gluons play a decisive role in the dynamics of interaction, causing the formation of jets of secondary hadrons (see Fig. Hadron jet)and etc.

Interaction of H. with nuclei and matter. As with the interaction with a proton, the interaction of H. with nuclei is described by rather short-range forces compared to the de Broglie wavelength of H. For low energies, the interaction is described by the scattering length and the radius of the potential. pits. The absence of a barrier to the penetration of H. into the nucleus leads to what is low energy for H. the role is played by the reaction channel going through the formation of a compound kernels(compound cores). Neutron resonances determined by the states of the compound nucleus at the so-called. resonant energies of H., are well separated (see. Neutron spectroscopy). At ~ (0.1 - 1) MeV in medium and heavy nuclei overlap and the behavior of the cross section is described statistically. Phenomenologically, the behavior of the cross section for the interaction of H. with nuclei is described by force functions s, p, d neutron resonances with characteristic fluctuations. At higher energies phenomenological. description of averaged sections is achieved using optical model, core. The interaction of high-energy H. with nuclei is similar to the interaction of protons with nuclei.

For slow H., its wave properties and coherent interaction with ordered condensers become decisive. Wednesdays. H. with a wavelength close to interatomic distances are the most important means of studying the structure of solids and the dynamics of excitation in them. The presence of H. mag. moment makes beams of polarizers. H. is extremely sensitive. a tool for studying the distribution of magnetization in matter (see. Neutronography).

A feature of H.'s interaction with most nuclei is positive. , which leads to coefficient. refraction< 1. Благодаря этому H., падающие из вакуума на границу вещества, могут испытывать полное внутр. отражение. При скорости u. < (5-8) м/с (ультрахолодные H.) H. испытывают полное отражение от границы с углеродом, никелем, бериллием и др. при любом угле падения и могут удерживаться в замкнутых объёмах. Это свойство ультрахолодных H. широко используется в экспериментах (напр., для поиска ЭДМ H.) и позволяет реализовать нейтронооптич. устройства (см. Neutron optics).

H. and weak (electroweak) interaction. An important source of information about the electroweak interaction is the b-decay of free H. At the quark level, this process corresponds to the transition. The reverse process of interaction of an electron antineutrino with a proton is called. reverse b-decay. This class of processes includes electronic capture, occurring in nuclei, re - n v e.

Decay of free H. taking into account kinematics. parameters are described by two constants - vector GV, resulting from vector conservation current univers. weak interaction constant, and axial-vector G A , the value of the cut is determined by the dynamics of the strongly interacting components of the nucleon - quarks and gluons. Wave functions of the initial H. and final proton and n p transition due to isotopic. invariances are calculated quite accurately. As a result, the calculation of the constants G V And G A from the decay of free H. (in contrast to calculations from the b-decay of nuclei) is not associated with taking into account nuclear structural factors.

The lifetime of H. without taking into account certain corrections is equal to: t n = k(G 2 V+ 3G 2 A) -1 , where k includes kinematic factors and Coulomb corrections depending on the boundary energy of b-decay and radiation corrections.

Probability of polarizer decay. H. with spin S , energies and momenta of the electron and antineutrino and R e, is generally described by the expression:

Coef. correlations a, A, B, D can be represented as a function from a parameter a =(G A/G V,)exp( i f). Phase f is different from zero or p if T-invariance is broken. In table experimental data are given. values ​​for these coefficients. and the resulting meanings a and f.

There is a noticeable difference between these data. experiments for t n, reaching several. percent.

The description of the electroweak interaction involving H. at higher energies is much more complicated due to the need to take into account the structure of nucleons. For example, m - -capture, m - p n v m, is described by at least twice the number of constants. H. is also tested with other hadrons without the participation of leptons. Such processes include the following.

1) Decays of hyperons L np 0, S + np +, S - np -, etc. The reduced probability of these decays is several. times less than for non-strange particles, which is described by introducing the Cabibbo angle (see. Cabibbo corner).

2) Weak interaction n - n or n - p, which manifests itself as not preserving spaces. parity. The usual magnitude of the effects caused by them is of the order of 10 -6 -10 -7.

H.'s interaction with medium and heavy nuclei has a number of features, leading in some cases to mean. enhancing effects non-conservation of parity in nuclei. One of these effects is related. the difference in the absorption cross section of H. with polarization in the direction of propagation and against it, edges in the case of the 139 La nucleus is equal to 7% at = 1.33 eV, corresponding to R- wave neutron resonance. The reason for the increase is the combination of low energy. the width of the states of the compound nucleus and the high density of levels with opposite parities in this compound nucleus, which provides 2-3 orders of magnitude greater mixing of components with different parities than in low-lying states of nuclei. The result is a number of effects: asymmetry of the emission of g-quanta relative to the spin of the captured polarizers. H. in the reaction (n, g), asymmetry of charge emission. particles during the decay of compound states in the reaction (n, p) or the asymmetry of the emission of a light (or heavy) fission fragment in the reaction (n, f). The asymmetries have a value of 10 -4 -10 -3 at thermal energy H. V R-wave neutron resonances are realized in addition. enhancement associated with the suppression of the probability of the formation of a parity-conserving component of this compound state (due to the small neutron width R-resonance) with respect to the impurity component with opposite parity, which is s-resonance-som. It is the combination of several. amplification factors allow an extremely weak effect to manifest itself with a magnitude characteristic of nuclear interaction.

Interactions with baryon number violation. Theoretical models grand unification And superunifications predict the instability of baryons - their decay into mesons. These decays can be noticeable only for the lightest baryons - p and n, which are part of atomic nuclei. For interaction with a change in baryon number by 1, D B= 1, one would expect a H. type transformation: n e + p - , or a transformation with the emission of strange mesons. The search for processes of this kind was carried out in experiments using underground detectors with a mass of several. thousand tons. Based on these experiments, we can conclude that the decay time of H. with baryon number violation is more than 10 32 years.

Dr. possible type of interaction with D IN= 2 can lead to the phenomenon of interconversion of H. and antineutrons in a vacuum, i.e. to . In the absence of external fields or at their low magnitude, the states of H. and the antineutron are degenerate, since their masses are the same, therefore even an ultra-weak interaction can mix them. The criterion of small external fields is the smallness of the interaction energy magnetic. moment H. with magnet. field (n and n ~ have opposite magnetic signs) compared to the energy determined by time T observations H. (according to the uncertainty relation), D<=hT -1 . When observing the production of antineutrons in an H beam from a reactor or other source T is the time of flight H. to the detector. The number of antineutrons in the beam increases quadratically with increasing time of flight: /N n ~ ~ (T/t osc) 2, where t osc is the oscillation time.

Direct experiments on observing the production in beams of cold H. from a high-flux reactor give a limit on t osc > 10 7 s. In the experiments being prepared, one can expect an increase in sensitivity to the level of t osc ~ 10 9 s. The limiting circumstances are max. intensity of H. beams and simulation of antineutron annihilation phenomena in the cosmic detector. rays.

Dr. method of observing oscillations - observing the annihilation of antineutrons, which can be formed in stable nuclei. Moreover, due to the large difference in the interaction energies of the emerging antineutron in the nucleus from the binding energy H. eff. the observation time becomes ~ 10 -22 s, but the large number of observed nuclei (~ 10 32) partially compensates for the decrease in sensitivity compared to the experiment on H beams. From the data of underground experiments searching for proton decay, the absence of events with an energy release of ~ 2 GeV can be concluded with a certain uncertainty, depending on ignorance of the exact type of interaction of the antineutron inside the nucleus, that t osc > (1-3). 10 7 p. Creatures the increase in the limit of t osc in these experiments is hampered by the background caused by the interaction of cosmic particles. neutrinos with nuclei in underground detectors.

It should be noted that the search for nucleon decay with D B= 1 and the search for -oscillations are independent experiments, since they are caused by fundamentally different types of interactions.

Gravitational interaction H. The neutron is one of the few elementary particles that fall into gravity. The Earth's field can be observed experimentally. The direct acceleration of gravity for H. is carried out with an accuracy of 0.3% and does not differ from the macroscopic one. The issue of compliance remains relevant equivalence principle(equality of inertial and gravitational masses) for H. and protons.

The most accurate experiments were carried out using the Et-weight method for bodies with different averages. ratio values A/Z Where A - at. number, Z- charge of nuclei (in units of elementary charge e). From these experiments it follows that the acceleration of gravity for H. and protons is identical at the level of 2·10 -9, and the equality of gravity. and inert masses at the level of ~10 -12.

Gravity acceleration and deceleration are widely used in experiments with ultracold H. Application of gravity. A refractometer for cold and ultracold H. allows one to measure with great accuracy the lengths of coherent scattering of H. on a substance.

H. in cosmology and astrophysics

According to modern ideas, in the Hot Universe model (see. Hot Universe theory)The formation of baryons, including protons and hydrogen, occurs in the first minutes of the life of the Universe. Subsequently, a certain part of the H., which did not have time to decay, is captured by protons with the formation of 4 He. The ratio of hydrogen and 4 He is 70% to 30% by weight. During the formation of stars and their evolution, further nucleosynthesis, up to iron nuclei. The formation of heavier nuclei occurs as a result of supernova explosions with the birth of neutron stars, creating the possibility of successive. capture of H. by nuclides. In this case, the combination of the so-called. s-process - slow capture of H. with b-decay between successive captures and r-process - fast sequential. capture during explosions of stars mainly. may explain the observed prevalence of elements in space objects.

In the primary component of the cosmic H. rays are probably absent due to their instability. H., formed at the surface of the Earth, diffusing into space. and decaying there, apparently, contribute to the formation of the electron and proton components radiation belts Earth.

Lit.: Gurevich I.S., Tarasov L.V., Physics of Low Energy Neutrons, M., 1965; Alexandrov Yu. A.,. Fundamental properties of the neutron, 2nd ed., M., 1982.

V. M. Lobashov.

Physical encyclopedia. In 5 volumes. - M.: Soviet Encyclopedia. Editor-in-Chief A. M. Prokhorov. 1988 Big Encyclopedic Dictionary Dictionary of synonyms

A neutral elementary particle with a mass close to the mass of a proton. Together with protons, neutrons form the atomic nucleus. In a free state, a neutron is unstable and decays into a proton and an electron. Nuclear energy terms. Rosenergoatom Concern,... ... Nuclear energy terms

Neutron- (n), a neutral elementary particle with a mass slightly greater than the mass of a proton. Discovered and named by the English physicist J. Chadwick in 1932. Neutrons are stable only within nuclei. The mass of a neutron is 1.7 x 10 24 g. A free neutron... ... Illustrated Encyclopedic Dictionary

NEUTRON, neutron, husband. (from Latin neutrum, lit. neither one nor the other) (physical neol.). A material particle entering the nucleus of an atom, devoid of electric charge, electrically neutral. Dictionary Ushakova. D.N. Ushakov. 1935 1940 ... Ushakov's Explanatory Dictionary

NEUTRON, huh, husband. (specialist.). An electrically neutral elementary particle with a mass almost equal to that of a proton. | adj. neutron, oh, oh. Ozhegov's explanatory dictionary. S.I. Ozhegov, N.Yu. Shvedova. 1949 1992 … Ozhegov's Explanatory Dictionary

neutron- Neutral elementary particle with a mass close to the mass of a proton. Together with protons, neutrons form the atomic nucleus. In the free state it is unstable and decays into a proton and an electron. Topics... ... Technical Translator's Guide

Chapter first. PROPERTIES OF STABLE NUCLEI

It was already said above that the nucleus consists of protons and neutrons bound by nuclear forces. If we measure the mass of a nucleus in atomic mass units, it should be close to the mass of a proton multiplied by an integer called the mass number. If the charge of a nucleus is a mass number, this means that the nucleus contains protons and neutrons. (The number of neutrons in the nucleus is usually denoted by

These properties of the kernel are reflected in symbolic notation, which will be used later in the form

where X is the name of the element whose atom the nucleus belongs to (for example, nuclei: helium - , oxygen - , iron - uranium

The main characteristics of stable nuclei include: charge, mass, radius, mechanical and magnetic moments, spectrum of excited states, parity and quadrupole moment. Radioactive (unstable) nuclei are additionally characterized by their lifetime, type of radioactive transformations, energy of emitted particles and a number of other special properties, which will be discussed below.

First of all, let's consider the properties of the elementary particles that make up the nucleus: proton and neutron.

§ 1. BASIC CHARACTERISTICS OF THE PROTON AND NEUTRON

Weight. In units of electron mass: proton mass, neutron mass.

In atomic mass units: proton mass, neutron mass

In energy units, the rest mass of a proton is the rest mass of a neutron.

Electric charge. q is a parameter characterizing the interaction of a particle with an electric field, expressed in units of electron charge where

All elementary particles carry an amount of electricity equal to either 0 or The charge of a proton The charge of a neutron is zero.

Spin. The spins of the proton and neutron are equal. Both particles are fermions and obey Fermi-Dirac statistics, and therefore the Pauli principle.

Magnetic moment. If we substitute the proton mass into formula (10), which determines the magnetic moment of the electron instead of the electron mass, we obtain

The quantity is called nuclear magneton. It could be assumed by analogy with the electron that the spin magnetic moment of the proton is equal to However, experience has shown that the proton’s own magnetic moment is greater than the nuclear magneton: according to modern data

In addition, it turned out that an uncharged particle - a neutron - also has a magnetic moment that is different from zero and equal to

The presence of a magnetic moment in a neutron and such a large value of the magnetic moment in a proton contradict assumptions about the point nature of these particles. A number of experimental data obtained in recent years indicate that both the proton and the neutron have a complex inhomogeneous structure. At the center of the neutron there is a positive charge, and at the periphery there is a negative charge equal in magnitude distributed in the volume of the particle. But since the magnetic moment is determined not only by the magnitude of the flowing current, but also by the area covered by it, the magnetic moments created by them will not be equal. Therefore, a neutron can have a magnetic moment while remaining generally neutral.

Mutual transformations of nucleons. The mass of a neutron is 0.14% greater than the mass of a proton, or 2.5 times the mass of an electron,

In a free state, a neutron decays into a proton, electron and antineutrino: Its average lifetime is close to 17 minutes.

A proton is a stable particle. However, inside the nucleus it can turn into a neutron; in this case the reaction proceeds according to the scheme

The difference in the masses of particles on the left and right is compensated by the energy imparted to the proton by other nucleons in the nucleus.

A proton and a neutron have the same spins, almost the same masses, and can transform into each other. It will be shown later that the nuclear forces acting between these particles in pairs are also identical. Therefore, they are called by a common name - nucleon and they say that a nucleon can be in two states: proton and neutron, differing in their relationship to the electromagnetic field.

Neutrons and protons interact due to the existence of nuclear forces that are non-electrical in nature. Nuclear forces owe their origin to the exchange of mesons. If we depict the dependence of the potential energy of interaction between a proton and a low-energy neutron on the distance between them, then approximately it will look like the graph shown in Fig. 5, a, i.e. it has the shape of a potential well.

Rice. 5. Dependence of potential interaction energy on the distance between nucleons: a - for neutron-neutron or neutron-proton pairs; b - for a proton-proton pair

What is a neutron? What are its structure, properties and functions? Neutrons are the largest of the particles that make up atoms, the building blocks of all matter.

Atomic structure

Neutrons are found in the nucleus, a dense region of the atom also filled with protons (positively charged particles). These two elements are held together by a force called nuclear. Neutrons have a neutral charge. The positive charge of the proton is matched with the negative charge of the electron to create a neutral atom. Even though the neutrons in the nucleus do not affect the charge of the atom, they still have many properties that affect the atom, including the level of radioactivity.

Neutrons, isotopes and radioactivity

A particle that is located in the nucleus of an atom is a neutron that is 0.2% larger than a proton. Together they make up 99.99% of the total mass of the same element and may have different numbers of neutrons. When scientists refer to atomic mass, they mean average atomic mass. For example, carbon typically has 6 neutrons and 6 protons with an atomic mass of 12, but it is sometimes found with an atomic mass of 13 (6 protons and 7 neutrons). Carbon with atomic number 14 also exists, but is rare. So the atomic mass for carbon averages out to 12.011.

When atoms have different numbers of neutrons, they are called isotopes. Scientists have found ways to add these particles to the nucleus to create larger isotopes. Now adding neutrons does not affect the charge of the atom since they have no charge. However, they increase the radioactivity of the atom. This can result in very unstable atoms that can discharge high levels of energy.

What is the core?

In chemistry, the nucleus is the positively charged center of an atom, which consists of protons and neutrons. The word "kernel" comes from the Latin nucleus, which is a form of the word meaning "nut" or "kernel". The term was coined in 1844 by Michael Faraday to describe the center of an atom. The sciences involved in the study of the nucleus, the study of its composition and characteristics, are called nuclear physics and nuclear chemistry.

Protons and neutrons are held together by the strong nuclear force. The electrons are attracted to the nucleus, but move so fast that their rotation occurs at some distance from the center of the atom. The nuclear charge with a plus sign comes from protons, but what is a neutron? This is a particle that has no electrical charge. Almost all the weight of an atom is contained in the nucleus, since protons and neutrons have much more mass than electrons. The number of protons in an atomic nucleus determines its identity as an element. The number of neutrons indicates which isotope of the element the atom is.

Atomic nucleus size

The nucleus is much smaller than the overall diameter of the atom because the electrons can be further away from the center. A hydrogen atom is 145,000 times larger than its nucleus, and a uranium atom is 23,000 times larger than its center. The hydrogen nucleus is the smallest because it consists of a single proton.

Arrangement of protons and neutrons in the nucleus

The proton and neutrons are usually depicted as being packed together and evenly distributed into spheres. However, this is a simplification of the actual structure. Each nucleon (proton or neutron) can occupy a specific energy level and range of locations. While the nucleus can be spherical, it can also be pear-shaped, spherical, or disc-shaped.

The nuclei of protons and neutrons are baryons, consisting of smallest ones called quarks. The attractive force has a very short range, so protons and neutrons must be very close to each other to be bound. This strong attraction overcomes the natural repulsion of charged protons.

Proton, neutron and electron

A powerful impetus in the development of such a science as nuclear physics was the discovery of the neutron (1932). We should thank for this the English physicist who was a student of Rutherford. What is a neutron? This is an unstable particle that, in a free state, can decay into a proton, electron and neutrino, the so-called massless neutral particle, in just 15 minutes.

The particle gets its name because it has no electrical charge, it is neutral. Neutrons are extremely dense. In an isolated state, one neutron will have a mass of only 1.67·10 - 27, and if you take a teaspoon densely packed with neutrons, the resulting piece of matter will weigh millions of tons.

The number of protons in the nucleus of an element is called the atomic number. This number gives each element its unique identity. In the atoms of some elements, such as carbon, the number of protons in the nuclei is always the same, but the number of neutrons can vary. An atom of a given element with a certain number of neutrons in the nucleus is called an isotope.

Are single neutrons dangerous?

What is a neutron? This is a particle that, along with the proton, is included in However, sometimes they can exist on their own. When neutrons are outside the nuclei of atoms, they acquire potentially dangerous properties. When they move at high speeds, they produce deadly radiation. So-called neutron bombs, known for their ability to kill people and animals, yet have minimal effect on non-living physical structures.

Neutrons are a very important part of the atom. The high density of these particles, combined with their speed, gives them extreme destructive power and energy. As a result, they can alter or even tear apart the nuclei of the atoms they strike. Although a neutron has a net neutral electrical charge, it is composed of charged components that cancel each other with respect to charge.

A neutron in an atom is a tiny particle. Like protons, they are too small to be seen even with an electron microscope, but they are there because that is the only way to explain the behavior of atoms. Neutrons are very important for the stability of an atom, but outside its atomic center they cannot exist for long and decay on average in only 885 seconds (about 15 minutes).

Properties of the neutron

Neutron (Latin neuter - neither one nor the other) is an elementary particle with zero electrical charge and a mass slightly greater than the mass of a proton. Neutron mass m n=939,5731(27) MeV/s 2 =1,008664967 a.e.m. =1,675 10 -27kg. Electric charge =0. Spin =1/2, the neutron obeys Fermi statistics. The internal parity is positive. Isotopic spin T=1/2. Third isospin projection T 3 = -1/2. Magnetic moment = -1.9130. Binding energy in the nucleus rest energy E 0 =m n c 2 = 939,5 Mev. A free neutron decays with a half-life T 1/2= 11 min through the channel due to weak interaction. In a bound state (in the nucleus), the neutron lives forever. “The exceptional position of the neutron in nuclear physics is similar to the position of the electron in electronics.” Due to the absence of an electric charge, a neutron of any energy easily penetrates the nucleus and causes various nuclear transformations.

Approximate neutron classification by energy is given in Table 1.3

Reactions under the influence of neutrons are numerous: ( n, γ), (n,p), (n,n'), (n,α), ( n,2n), (n,f).

Radiative capture reactions( n, γ) neutron followed by the emission of a γ-quantum are based on slow neutrons with energies from 0÷500 kev.

Example: Mev.

Elastic neutron scattering ( n, n) is widely used for detecting fast neutrons using the recoil nuclei method in track methods and for moderating neutrons.

For inelastic neutron scattering ( n,n') a neutron is captured to form a compound nucleus, which decays, emitting a neutron with an energy lower than that of the original neutron. Inelastic neutron scattering is possible if the neutron energy is several times higher than the energy of the first excited state of the target nucleus. Inelastic scattering is a threshold process.

Neutron reaction producing protons ( n,p) occurs under the influence of fast neutrons with energies of 0.5÷10 meV. The most important reactions are the production of the tritium isotope from helium-3:

Mev with cross section σ heat = 5400 barn,

and registration of neutrons using the photoemulsion method:

0,63 Mev with cross section σ heat = 1.75 barn.

Neutron reactions ( n,α) with the formation of α-particles effectively occur on neutrons with an energy of 0.5÷10 MeV. Sometimes reactions occur with thermal neutrons: the reaction to produce tritium in thermonuclear devices.