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Atomic structure: what is a neutron? Neutron (elementary particle)

"The first five fuel assemblies of MOX fuel assemblies for the BN-800 reactor of the Beloyarsk NPP have been produced. Thus, the stage of mastering the production of the MOX MCC technological complex has been completed," the press service of the MCC reported.

Currently, measures are being implemented, developed by the MCC jointly with a number of Rosatom enterprises, and aimed at increasing production productivity in order to fulfill the annual plan of 40 fuel assemblies.

Power unit No. 4 of the Beloyarsk NPP is required to develop a number of technologies for closing the nuclear fuel cycle based on "fast" reactors. In such a closed cycle, due to the expanded reproduction of nuclear "fuel", it is believed that the fuel base of the nuclear power industry will significantly expand, and it will also be possible to reduce the volume of radioactive waste due to the "burning" of hazardous radionuclides. Russia, according to experts, ranks first in the world in technologies for building fast reactors.

Unit 4 of the BNPP with the BN-800 reactor became the prototype of more powerful commercial "fast" power units BN-1200. Earlier it was reported that the decision to build a BN-1200 pilot unit also at the Beloyarsk NPP could be made in the early 2020s.

The BN-800 reactor is designed to use MOX fuel in it, which can use plutonium isolated during the reprocessing of spent nuclear fuel from thermal reactors, which are the basis of modern nuclear power. The industrial production of MOX fuel for BN-800 was built at the MCC with the participation of more than 20 organizations in the Russian nuclear industry.

The initial fuel loading of the BN-800 reactor was formed mainly from traditional uranium oxide fuel. At the same time, some of the fuel assemblies contain MOX fuel manufactured at pilot plants of other Rosatom enterprises - NIIAR (Dimitrovgrad, Ulyanovsk region) and "Mayak Production Association" (ZATO Ozersk, Chelyabinsk region). Over time, the BN-800 reactor should be converted to MOX fuel produced by the MCC.

The Federal State Unitary Enterprise "Mining and Chemical Combine" (part of the division of the final stage of the life cycle of nuclear facilities of Rosatom) has the status of a federal nuclear organization. The MCC is a key enterprise of Rosatom for the creation of a closed nuclear fuel cycle technological complex based on innovative new generation technologies. For the first time in the world, the MCC concentrates three high-tech redistributions at once - storage of spent nuclear fuel from nuclear power plants, its processing and production of new MOX nuclear fuel for fast reactors.

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

Atom structure

Neutrons are in the nucleus - a dense region of an 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 on the proton is matched with the negative charge on the electron to create a neutral atom. Although neutrons in a nucleus do not affect the charge of an atom, they still have many properties that affect an atom, including the level of radioactivity.

Neutrons, isotopes and radioactivity

The particle that is 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, they can have a different number of neutrons. When scientists refer to atomic mass, they mean the average atomic mass. For example, carbon usually has 6 neutrons and 6 protons with an atomic mass of 12, but sometimes it occurs 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 is averaged 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 large isotopes. Now the addition of neutrons does not affect the charge of the atom, since they have no charge. However, they increase the radioactivity of the atom. This can lead to very unstable atoms that can discharge high energy levels.

What is the core?

In chemistry, the nucleus is the positively charged center of the atom, which is made up of protons and neutrons. The word "core" 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 a strong nuclear force. Electrons are attracted to the nucleus, but move so fast that their rotation is carried out at some distance from the center of the atom. Nuclear charge with a plus sign comes from protons, but what is a neutron? It 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 a much greater mass than electrons. The number of protons in an atomic nucleus determines its identity as an element. The number of neutrons means which isotope of an element the atom is.

Atomic nucleus size

The nucleus is much smaller than the overall diameter of the atom because the electrons can be distant from the center. The hydrogen atom is 145,000 times the size of its nucleus, and the uranium atom is 23,000 times the size of 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 compacted together and evenly distributed over spheres. However, this is a simplification of the actual structure. Each nucleon (proton or neutron) can occupy certain level energy and range of locations. While the nucleus can be spherical, it can also be pear-shaped, globular, or disc-shaped.

The nuclei of protons and neutrons are baryons, composed of the smallest ones called quarks. The gravitational 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). The English physicist who was a student of Rutherford should be thankful for this. What is a neutron? This is an unstable particle, which in a free state in just 15 minutes is capable of decaying into a proton, an electron and a neutrino, the so-called massless neutral particle.

The particle got its name due to the fact that it has no electric 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, then 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 own 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 may differ. An atom of a given element with a certain number of neutrons in its nucleus is called an isotope.

Are single neutrons dangerous?

What is a neutron? This is a particle that, along with a proton, enters into, however, sometimes they can exist on their own. When neutrons are outside the nuclei of atoms, they acquire potentially harmful properties. When they move at high speed, they produce deadly radiation. The so-called neutron bombs, known for their ability to kill people and animals, while having minimal impact 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 an extraordinary destructive force and energy. As a consequence, they can alter or even tear apart the nuclei of the atoms that strike. Although the neutron has a pure, neutral electric charge, it is composed of charged components that cancel each other out 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 this is the only way to explain the behavior of atoms. Neutrons are very important for ensuring the stability of an atom, however, outside of its atomic center, they cannot exist for a long time and decay on average in just 885 seconds (about 15 minutes).

A neutron (Latin neuter - neither one nor the other) is an elementary particle with zero electric charge and a mass slightly larger than the mass of a proton. Neutron mass m n=939,5731(27) Mev / s 2 =1,008664967 a.m.. =1,675 10 -27Kg... Electric charge = 0. Spin = 1/2, neutron obeys Fermi statistics. Internal parity is positive. Isotopic spin T = 1/2. Third isospin projection T 3 = -1/2. Magnetic moment = -1.9130. Binding energy in the core 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), a neutron lives forever. "The exclusive 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 into the nucleus and causes a variety of nuclear transformations.

Approximate neutron classification for energies 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).

Radiation capture reactions ( n, γ) neutron with subsequent emission of γ-quantum are on slow neutrons with energies from 0 ÷ 500 kev.

Example: Mev.

Elastic neutron scattering ( n, n) is widely used for registration of fast neutrons by the method of recoil nuclei in track methods and for slowing down neutrons.

In the case of inelastic neutron scattering ( n, n ') a neutron is captured with the formation of a compound nucleus, which decays, ejecting a neutron with an energy lower than the original neutron had. 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 with the formation of protons ( n, p) occurs under the action of fast neutrons with energies of 0.5 ÷ 10 meV. The most important are the reactions for obtaining the isotope of tritium from helium-3:

Mev with a cross section σ heat = 5400 barn,

and registration of neutrons by the method of photoemulsions:

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

Neutron reactions ( n,α) with the formation of α-particles effectively proceed on neutrons with energies of 0.5 ÷ 10 MeV. Sometimes the reactions run on thermal neutrons: the reaction of tritium production in thermonuclear devices.

Chapter one. PROPERTIES OF STABLE NUCLEI

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

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

where X is the name of the element to which the nucleus belongs (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, the type of radioactive transformations, the energy of the emitted particles, and a number of other special properties, which will be discussed below.

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

§ 1. BASIC CHARACTERISTICS OF PROTON AND NEUTRON

Weight. In units of electron mass: the mass of the proton is the mass of the neutron.

In atomic mass units: proton mass neutron mass

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

Electric charge. q is a parameter characterizing the interaction of a particle with electric field, expressed in units of the 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 equal to zero.

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

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

The quantity is called the nuclear magneton. It could be assumed, by analogy with the electron, that the spin magnetic moment of the proton is equal.However, experience has shown that the intrinsic magnetic moment of the proton 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 different from zero and equal to

The presence of a magnetic moment in the neutron and such a large value of the magnetic moment in the proton contradict the assumptions about the point nature of these particles. A number of experimental data obtained in last years, indicates that both the proton and the neutron have a complex inhomogeneous structure. In this case, there is a positive charge at the center of the neutron, and at the periphery, 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 they create will not be equal. Therefore, a neutron can have a magnetic moment while remaining generally neutral.

Mutual transformations of nucleons. The mass of the neutron is greater than the mass of the proton by 0.14%, or by 2.5 masses of the electron,

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

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

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

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

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

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