Mass and charge of the neutron. Big encyclopedia of oil and gas

It is well known to many from school that all matter consisted of atoms. Atoms, in turn, consist of protons and neutrons that form the nucleus of atoms and electrons located at some distance from the nucleus. Many have also heard that light also consists of particles - photons. However, the world of particles is not limited to this. To date, more than 400 different elementary particles are known. Let's try to understand how elementary particles differ from each other.

There are many parameters by which elementary particles can be distinguished from each other:

• Weight.
• Electric charge.
• Lifetime. Almost all elementary particles have a finite lifetime after which they decay.
• Spin. It can be, very approximately, considered as a rotational moment.

A few more parameters, or as they are commonly called in the science of quantum numbers. These parameters do not always have a clear physical meaning, but they are needed in order to distinguish one particle from another. All these additional parameters are introduced as some quantities that are preserved in the interaction.

Almost all particles have mass, except for photons and neutrinos (according to the latest data, neutrinos have a mass, but so small that it is often considered zero). Without mass particles can only exist in motion. The mass of all particles is different. The electron has the minimum mass, apart from the neutrino. Particles that are called mesons have a mass 300-400 times greater than the mass of an electron, a proton and a neutron are almost 2000 times heavier than an electron. Particles that are almost 100 times heavier than a proton have already been discovered. Mass, (or its energy equivalent according to Einstein's formula:

is preserved in all interactions of elementary particles.

Not all particles have an electric charge, which means that not all particles are able to participate in electromagnetic interaction. For all freely existing particles, the electric charge is a multiple of the charge of the electron. In addition to freely existing particles, there are also particles that are only in a bound state, we will talk about them a little later.

Spin, as well as other quantum numbers of different particles are different and characterize their uniqueness. Some quantum numbers are conserved in some interactions, some in others. All these quantum numbers determine which particles interact with which and how.

The lifetime is also a very important characteristic of a particle, and we will consider it in more detail. Let's start with a note. As we said at the beginning of the article, everything that surrounds us consists of atoms (electrons, protons and neutrons) and light (photons). And where, then, are hundreds of different types of elementary particles. The answer is simple - everywhere around us, but we do not notice for two reasons.

The first of them is that almost all other particles live very little, about 10 to minus 10 seconds or less, and therefore do not form structures such as atoms, crystal lattices and so on. The second reason concerns neutrinos, although these particles do not decay, they are subject only to weak and gravitational interaction. This means that these particles interact so little that it is almost impossible to detect them.

Let us visualize what expresses how well the particle interacts. For example, the flow of electrons can be stopped by a rather thin sheet of steel, on the order of a few millimeters. This will happen because the electrons will immediately begin to interact with the particles of the steel sheet, they will sharply change their direction, emit photons, and thus lose energy rather quickly. Everything is wrong with the flow of neutrinos, they can pass through almost without interactions Earth Globe. That is why it is very difficult to find them.

So, most particles live a very short time, after which they decay. Particle decays are the most common reactions. As a result of decay, one particle breaks up into several others of smaller mass, and those, in turn, decay further. All decays obey certain rules - conservation laws. So, for example, as a result of decay, an electric charge, mass, spin, and a number of quantum numbers must be conserved. Some quantum numbers can change during the decay, but also subject to certain rules. It is the decay rules that tell us that the electron and proton are stable particles. They can no longer decay obeying the rules of decay, and therefore it is with them that the chains of decay end.

Here I would like to say a few words about the neutron. A free neutron also decays into a proton and an electron in about 15 minutes. However, when the neutron is in the atomic nucleus, this does not happen. This fact can be explained different ways. For example, when an electron and an extra proton from a decayed neutron appear in the nucleus of an atom, the reverse reaction immediately occurs - one of the protons absorbs an electron and turns into a neutron. This picture is called dynamic equilibrium. She was observed in the universe on early stage its development shortly after the big bang.

In addition to decay reactions, there are also scattering reactions - when two or more particles interact simultaneously, and the result is one or more other particles. There are also absorption reactions, when one is obtained from two or more particles. All reactions occur as a result of a strong weak or electromagnetic interaction. Reactions due to the strong interaction are the fastest, the time of such a reaction can reach 10 to minus 20 seconds. The speed of reactions due to electromagnetic interaction is lower, here the time can be about 10 to minus 8 seconds. For weak interaction reactions, the time can reach tens of seconds and sometimes even years.

At the end of the story about particles, let's talk about quarks. Quarks are elementary particles that have an electric charge that is a multiple of a third of the charge of an electron and which cannot exist in a free state. Their interaction is arranged in such a way that they can live only as part of something. For example, a combination of three quarks of a certain type form a proton. Another combination gives a neutron. A total of 6 quarks are known. Their various combinations give us different particles, and although not all combinations of quarks are allowed by physical laws, there are quite a lot of particles made up of quarks.

Here the question may arise, how can a proton be called elementary if it consists of quarks. Very simply - the proton is elementary, since it cannot be split into its component parts - quarks. All particles that participate in the strong interaction are composed of quarks, and at the same time are elementary.

Understanding the interactions of elementary particles is very important for understanding the structure of the universe. Everything that happens to macro bodies is the result of the interaction of particles. It is the interaction of particles that describes the growth of trees on earth, reactions in the depths of stars, the radiation of neutron stars, and much more.

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The neutron charge is zero. Consequently, neutrons do not play a role in the magnitude of the charge of the nucleus of an atom. The serial number of chromium is equal to the same value.

Proton charge qp e Neutron charge is equal to zero.

It is easy to see that in this case the charge of the neutron is zero, and that of the proton is 1, as expected. All the baryons included in two families are obtained - the eight and the ten. Mesons are made up of a quark and an antiquark. The bar denotes antiquarks; their electric charge differs in sign from that of the corresponding quark. A strange quark does not enter into a pi-meson, pi-mesons, as we have already said, are particles with strangeness and spin equal to zero.

Since the charge of the proton is equal to the charge of the electron and the charge of the neutron is equal to the bullet, then if the strong interaction is turned off, the interaction of the proton with electromagnetic field And it will be the usual interaction of the Dirac particle - Yp / V. The neutron would have no electromagnetic interaction.

Designations: 67 - charge difference between electron and proton; q is the neutron charge; qg is the absolute value of the electron charge.

The nucleus consists of positively charged elementary particles - protons and neutrons that do not carry a charge.

The basis of modern ideas about the structure of matter is the assertion of the existence of atoms of matter, consisting of positively charged protons and chargeless neutrons, forming a positively charged nucleus, and negatively charged electrons rotating around the nucleus. The energy levels of electrons, according to this theory, are discrete, and the loss or acquisition of some additional energy by them is considered as a transition from one allowed energy level to another. In this case, the discrete nature of the electronic energy levels becomes the reason for the same discrete absorption or emission of energy by an electron during the transition from one energy level to another.

We assumed that the charge of an atom or molecule is completely determined by the scalar sum q Z (q Nqn, where Z is the number of electron-proton pairs, (q qp - qe is the difference in the charges of the electron and proton, N is the number of neutrons, and qn is the charge of the neutron.

The nuclear charge is determined only by the number of protons Z, and its mass number A coincides with the total number of protons and neutrons. Since the charge of the neutron is zero, there is no electrical interaction according to the Coulomb law between two neutrons, and also between a proton and a neutron. At the same time, an electrical repulsive force acts between the two protons.

Further, within the limits of measurement accuracy, not a single collision process has ever been registered, in which the charge conservation law would not be observed. For example, the inflexibility of neutrons in uniform electric fields makes it possible to consider the neutron charge as equal to zero with an accuracy of 1 (H7 of the electron charge.

We have already said that the difference between the magnetic moment of a proton and one nuclear magneton is an amazing result. Even more surprising (It seems that there is a magnetic moment for a neutron without a charge.

It is easy to see that these forces are not reduced to any of the types of forces considered in the previous parts of the physics course. Indeed, if we assume, for example, that gravitational forces act between nucleons in nuclei, then it is easy to calculate from the known proton and neutron masses that the binding energy per particle will be negligible - it will be 1036 times less than that observed experimentally. The assumption about the electric character also disappears. nuclear forces. Indeed, in this case it is impossible to imagine a stable nucleus consisting of a single charged proton and no charge of a neutron.

The strong bond that exists between nucleons in the nucleus indicates the presence in atomic nuclei of special, so-called nuclear forces. It is easy to see that these forces are not reduced to any of the types of forces considered in the previous parts of the physics course. Indeed, if we assume, for example, that gravitational forces act between nucleons in nuclei, then it is easy to calculate from the known masses of the proton and neutron that the binding energy per particle will be negligible - it will be 1038 times less than that observed experimentally. The assumption about the electric nature of nuclear forces also disappears. Indeed, in this case it is impossible to imagine a stable nucleus consisting of a single charged proton and no charge of a neutron.

An atom is the smallest particle chemical element, which preserves all Chemical properties. An atom consists of a positively charged nucleus and negatively charged electrons. The charge of the nucleus of any chemical element is equal to the product of Z by e, where Z is the serial number of this element in the periodic system of chemical elements, e is the value of the elementary electric charge.

Electron- this is the smallest particle of a substance with a negative electric charge e=1.6·10 -19 coulombs, taken as an elementary electric charge. Electrons, rotating around the nucleus, are located on the electron shells K, L, M, etc. K is the shell closest to the nucleus. The size of an atom is determined by the size of its electron shell. An atom can lose electrons and become a positive ion, or gain electrons and become a negative ion. The charge of an ion determines the number of electrons lost or gained. The process of turning a neutral atom into a charged ion is called ionization.

atomic nucleus(the central part of the atom) consists of elementary nuclear particles - protons and neutrons. The radius of the nucleus is about a hundred thousand times smaller than the radius of the atom. The density of the atomic nucleus is extremely high. Protons- These are stable elementary particles having a unit positive electric charge and a mass 1836 times greater than the mass of an electron. The proton is the nucleus of the lightest element, hydrogen. The number of protons in the nucleus is Z. Neutron is a neutral (not having an electric charge) elementary particle with a mass very close to the mass of a proton. Since the mass of the nucleus is the sum of the mass of protons and neutrons, the number of neutrons in the nucleus of an atom is A - Z, where A is the mass number of a given isotope (see). The proton and neutron that make up the nucleus are called nucleons. In the nucleus, nucleons are bound by special nuclear forces.

The atomic nucleus has a huge store of energy, which is released during nuclear reactions. Nuclear reactions occur when interacting atomic nuclei with elementary particles or with the nuclei of other elements. As a result of nuclear reactions, new nuclei are formed. For example, a neutron can transform into a proton. In this case, a beta particle, i.e., an electron, is ejected from the nucleus.

The transition in the nucleus of a proton into a neutron can be carried out in two ways: either a particle with a mass equal to the mass of an electron, but with a positive charge, called a positron (positron decay), is emitted from the nucleus, or the nucleus captures one of the electrons from the nearest K-shell (K -capture).

Sometimes the formed nucleus has an excess of energy (it is in an excited state) and, turning into normal condition, releases excess energy in the form electromagnetic radiation with very short wavelength. The energy released during nuclear reactions is practically used in various industries.

An atom (Greek atomos - indivisible) is the smallest particle of a chemical element that has its chemical properties. Every element is made up of atoms a certain kind. The structure of an atom includes the kernel carrying a positive electric charge, and negatively charged electrons (see), forming its electronic shells. The value of the electric charge of the nucleus is equal to Z-e, where e is the elementary electric charge, equal in magnitude to the charge of the electron (4.8 10 -10 e.-st. units), and Z is the atomic number of this element in the periodic system of chemical elements (see .). Since a non-ionized atom is neutral, the number of electrons included in it is also equal to Z. The composition of the nucleus (see. Atomic nucleus) includes nucleons, elementary particles with a mass approximately 1840 times greater than the mass of an electron (equal to 9.1 10 - 28 g), protons (see), positively charged, and chargeless neutrons (see). The number of nucleons in the nucleus is called the mass number and is denoted by the letter A. The number of protons in the nucleus, equal to Z, determines the number of electrons entering the atom, the structure of the electron shells and the chemical properties of the atom. The number of neutrons in the nucleus is A-Z. Isotopes are called varieties of the same element, the atoms of which differ from each other in mass number A, but have the same Z. Thus, in the nuclei of atoms of different isotopes of one element there are a different number of neutrons with the same number of protons. When designating isotopes, the mass number A is written at the top of the element symbol, and the atomic number at the bottom; for example, isotopes of oxygen are denoted:

The dimensions of the atom are determined by the dimensions of the electron shells and for all Z are about 10 -8 cm. Since the mass of all the electrons of the atom is several thousand times less mass nucleus, the mass of an atom is proportional to the mass number. The relative mass of an atom of a given isotope is determined in relation to the mass of an atom of the carbon isotope C 12, taken as 12 units, and is called the isotopic mass. It turns out to be close to the mass number of the corresponding isotope. The relative weight of an atom of a chemical element is the average (taking into account the relative abundance of the isotopes of a given element) value of the isotopic weight and is called the atomic weight (mass).

An atom is a microscopic system, and its structure and properties can only be explained with the help of quantum theory, created mainly in the 20s of the 20th century and intended to describe phenomena on an atomic scale. Experiments have shown that microparticles - electrons, protons, atoms, etc. - in addition to corpuscular ones, have wave properties that manifest themselves in diffraction and interference. In quantum theory, a certain wave field characterized by a wave function (Ψ-function) is used to describe the state of micro-objects. This function determines the probabilities of possible states of a micro-object, i.e., it characterizes the potential possibilities for the manifestation of one or another of its properties. The law of variation of the function Ψ in space and time (the Schrödinger equation), which makes it possible to find this function, plays the same role in quantum theory as Newton's laws of motion in classical mechanics. The solution of the Schrödinger equation in many cases leads to discrete possible states of the system. So, for example, in the case of an atom, a series of wave functions for electrons is obtained corresponding to different (quantized) energy values. The system of energy levels of the atom, calculated by the methods of quantum theory, has received brilliant confirmation in spectroscopy. The transition of an atom from the ground state corresponding to the lowest energy level E 0 to any of the excited states E i occurs when a certain portion of energy E i - E 0 is absorbed. An excited atom goes into a less excited or ground state, usually with the emission of a photon. In this case, the photon energy hv is equal to the difference between the energies of an atom in two states: hv= E i - E k where h is Planck's constant (6.62·10 -27 erg·sec), v is the frequency of light.

In addition to atomic spectra, quantum theory has made it possible to explain other properties of atoms. In particular, the valency, nature chemical bond and the structure of molecules, a theory was created periodic system elements.

• Translation

At the center of every atom is the nucleus, a tiny collection of particles called protons and neutrons. In this article, we will study the nature of protons and neutrons, which consist of even smaller particles - quarks, gluons and antiquarks. (Gluons, like photons, are their own antiparticles.) Quarks and gluons, as far as we know, can be truly elementary (indivisible and not composed of something smaller). But to them later.

Surprisingly, protons and neutrons have almost the same mass - up to a percentage:

• 0.93827 GeV/c 2 for a proton,
• 0.93957 GeV/c 2 for a neutron.

Because they are so similar, and because these particles make up nuclei, protons and neutrons are often referred to as nucleons.

Protons were identified and described around 1920 (although they were discovered earlier; the nucleus of a hydrogen atom is just a single proton), and neutrons were found around 1933. The fact that protons and neutrons are so similar to each other was understood almost immediately. But the fact that they have a measurable size comparable to the size of the nucleus (about 100,000 times smaller than an atom in radius) was not known until 1954. That they are made up of quarks, antiquarks, and gluons was gradually understood from the mid-1960s to the mid-1970s. By the late 70's and early 80's, our understanding of protons, neutrons, and what they are made of had largely settled down, and has remained unchanged ever since.

Nucleons are much more difficult to describe than atoms or nuclei. This is not to say that atoms are in principle simple, but at least one can say without hesitation that a helium atom consists of two electrons in orbit around a tiny helium nucleus; and the helium nucleus is a fairly simple group of two neutrons and two protons. But with nucleons, everything is not so simple. I already wrote in the article "What is a proton, and what does it have inside?" that the atom is like an elegant minuet, and the nucleon is like a wild party.

The complexity of the proton and neutron seems to be real, and does not stem from incomplete physical knowledge. We have equations used to describe quarks, antiquarks, and gluons, and the strong nuclear forces that go on between them. These equations are called QCD, from "quantum chromodynamics". The accuracy of the equations can be tested in various ways, including measuring the number of particles that appear at the Large Hadron Collider. Substituting the QCD equations into a computer and running calculations on the properties of protons and neutrons, and other similar particles (with common name"hadrons"), we obtain predictions of the properties of these particles that approximate well the observations made in real world. Therefore, we have reason to believe that the QCD equations do not lie, and that our knowledge of the proton and neutron is based on the correct equations. But just having the right equations is not enough, because:

• At simple equations can be very difficult decisions.
• Sometimes it is not possible to describe complex solutions in a simple way.

Because of the inherent complexity of nucleons, you, the reader, will have to make a choice: how much do you want to know about the complexity described? No matter how far you go, you will most likely not be satisfied: the more you learn, the clearer the topic will become, but the final answer will remain the same - the proton and neutron are very complex. I can offer you three levels of understanding, with increasing detail; you can stop after any level and move on to other topics, or you can dive to the last. Each level raises questions that I can partly answer in the next, but new answers raise new questions. In the end - as I do in professional discussions with colleagues and advanced students - I can only refer you to data from real experiments, various influential theoretical arguments, and computer simulations.

First level of understanding

Rice. 1: an oversimplified version of protons, consisting of only two up quarks and one down, and neutrons, consisting of only two down quarks and one up

To simplify matters, many books, articles and websites state that protons are made up of three quarks (two up and one down) and draw something like a figure. 1. The neutron is the same, only consisting of one up and two down quarks. This simple image illustrates what some scientists believed, mostly in the 1960s. But it soon became clear that this point of view was oversimplified to the point that it was no longer correct.

From more sophisticated sources of information, you will learn that protons are made up of three quarks (two up and one down) held together by gluons - and a picture similar to Fig. 2, where gluons are drawn as springs or strings that hold quarks. Neutrons are the same, with only one up quark and two down quarks.

Rice. 2: improvement fig. 1 due to the emphasis on important role strong nuclear force that holds the quarks in the proton

Not such a bad way to describe nucleons, as it emphasizes the important role of the strong nuclear force, which holds quarks in a proton at the expense of gluons (just like the photon, the particle that makes up light, is associated with the electromagnetic force). But that's also confusing because it doesn't really explain what gluons are or what they do.

There are reasons to go ahead and describe things the way I did in : a proton is made up of three quarks (two up and one down), a bunch of gluons, and a mountain of quark-antiquark pairs (mostly up and down quarks, but there are a few weird ones too) . They all fly back and forth at very high speeds (approaching the speed of light); this entire set is held together by the strong nuclear force. I have shown this in Fig. 3. Neutrons are again the same, but with one up and two down quarks; the quark that has changed ownership is indicated by an arrow.

Rice. 3: more realistic, though still not ideal, depiction of protons and neutrons

These quarks, antiquarks, and gluons not only scurry back and forth, but also collide with each other and turn into each other through processes such as particle annihilation (in which a quark and an antiquark of the same type turn into two gluons, or vice versa) or absorption and emission of a gluon (in which a quark and a gluon can collide and produce a quark and two gluons, or vice versa).

What do these three descriptions have in common:

• Two up quarks and a down quark (plus something else) for a proton.
• One up quark and two down quarks (plus something else) for a neutron.
• The “something else” for neutrons is the same as the “something else” for protons. That is, nucleons have “something else” the same.
• The small difference in mass between the proton and the neutron appears due to the difference in the masses of the down quark and the up quark.

• for up quarks, the electric charge is 2/3 e (where e is the charge of the proton, -e is the charge of the electron),
• down quarks have a charge of -1/3e,
• gluons have a charge of 0,
• any quark and its corresponding antiquark have a total charge of 0 (for example, the anti-down quark has a charge of +1/3e, so the down quark and down antiquark will have a charge of –1/3 e +1/3 e = 0),

• total electric charge of the proton 2/3 e + 2/3 e – 1/3 e = e,
• the total electric charge of the neutron is 2/3 e – 1/3 e – 1/3 e = 0.

• how much "something else" inside the nucleon,
• what is it doing there
• where do the mass and mass energy (E = mc 2 , the energy present there even when the particle is at rest) of the nucleon come from.

Rice. 1 says that quarks, in fact, represent a third of a nucleon - much like a proton or a neutron represents a quarter of a helium nucleus or 1/12 of a carbon nucleus. If this picture were true, the quarks in the nucleon would move relatively slowly (at speeds much slower than the speed of light) with relatively weak forces acting between them (albeit with some powerful force holding them in place). The mass of the quark, up and down, would then be on the order of 0.3 GeV/c 2 , about a third of the mass of a proton. But this is a simple image, and the ideas it imposes are simply wrong.

Rice. 3. gives a completely different idea of ​​the proton, as a cauldron of particles scurrying through it at speeds close to the speed of light. These particles collide with each other, and in these collisions some of them annihilate and others are created in their place. Gluons have no mass, the masses of the upper quarks are about 0.004 GeV/c 2 , and the masses of the lower quarks are about 0.008 GeV/c 2 - hundreds of times less than a proton. Where does the mass energy of the proton come from, the question is complex: part of it comes from the mass energy of quarks and antiquarks, part comes from the energy of motion of quarks, antiquarks and gluons, and part (perhaps positive, perhaps negative) from the energy stored in the strong nuclear interaction, holding quarks, antiquarks, and gluons together.

In a sense, Fig. 2 tries to eliminate the difference between fig. 1 and fig. 3. It simplifies the rice. 3, removing many quark-antiquark pairs, which, in principle, can be called ephemeral, since they constantly arise and disappear, and are not necessary. But it gives the impression that the gluons in the nucleons are a direct part of the strong nuclear force that holds the protons. And it doesn't explain where the mass of the proton comes from.

At fig. 1 has another drawback, besides the narrow frames of the proton and neutron. It does not explain some of the properties of other hadrons, such as the pion and the rho meson. The same problems exist in Fig. 2.

These restrictions have led to the fact that I give my students and on my website a picture from fig. 3. But I want to warn you that it also has many limitations, which I will consider later.

It should be noted that the extreme complexity of the structure, implied in Fig. 3 is to be expected from an object that holds together such powerful force like the strong nuclear force. And one more thing: three quarks (two up and one down for a proton) that are not part of a group of quark-antiquark pairs are often called "valence quarks", and pairs of quark-antiquarks are called a "sea of ​​quark pairs." Such a language is technically convenient in many cases. But it gives the false impression that if you could look inside the proton, and look at a particular quark, you could immediately tell if it was part of the sea or a valence. This cannot be done, there is simply no such way.

Proton mass and neutron mass

Rice. 1 says that the up and down quarks simply make up 1/3 of the mass of the proton and neutron: about 0.313 GeV/c 2 , or because of the energy needed to keep the quarks in the proton. And since the difference between the masses of a proton and a neutron is a fraction of a percent, the difference between the masses of an up and down quark must also be a fraction of a percent.

Rice. 2 is less clear. What fraction of the mass of a proton exists due to gluons? But, in principle, it follows from the figure that most of the mass of the proton still comes from the mass of quarks, as in Fig. 1.

Rice. 3 reflects a more subtle approach to how the mass of the proton actually comes about (as we can check directly through the proton's computer calculations, and not directly using other mathematical methods). It is very different from the ideas presented in Fig. 1 and 2, and it turns out to be not so simple.

To understand how this works, one must think not in terms of the proton's mass m, but in terms of its mass energy E = mc 2 , the energy associated with mass. The conceptually correct question is not “where does the proton mass m come from”, after which you can calculate E by multiplying m by c 2 , but the opposite: “where does the energy of the proton mass E come from”, after which you can calculate the mass m by dividing E by c 2 .

It is useful to classify contributions to the proton mass energy into three groups:

A) The mass energy (rest energy) of the quarks and antiquarks contained in it (gluons, massless particles, do not make any contribution).
B) Energy of motion (kinetic energy) of quarks, antiquarks and gluons.
C) The interaction energy (binding energy or potential energy) stored in the strong nuclear interaction (more precisely, in the gluon fields) holding the proton.

Rice. 3 says that the particles inside the proton move at a high speed, and that it is full of massless gluons, so the contribution of B) is greater than A). Usually, in most physical systems, B) and C) are comparable, while C) is often negative. So the mass energy of the proton (and neutron) is mostly derived from the combination of B) and C), with A) contributing a small fraction. Therefore, the masses of the proton and neutron appear mainly not because of the masses of the particles contained in them, but because of the energies of motion of these particles and the energy of their interaction associated with the gluon fields that generate the forces that hold the proton. In most other systems we are familiar with, the balance of energies is distributed differently. For example, in atoms and in solar system A dominates), while B) and C) are much smaller and comparable in size.

Summing up, we point out that:

• Rice. 1 suggests that the mass energy of the proton comes from the contribution A).
• Rice. 2 suggests that both contributions A) and C) are important, and B) makes a small contribution.
• Rice. 3 suggests that B) and C) are important, while the contribution of A) is negligible.

If fig. 3 is not lying, the masses of the quark and antiquark are very small. What are they really like? The mass of the top quark (as well as the antiquark) does not exceed 0.005 GeV/c 2 , which is much less than 0.313 GeV/c 2 , which follows from Fig. 1. (The mass of an up quark is difficult to measure and varies due to subtle effects, so it could be much less than 0.005 GeV/c2). The mass of the bottom quark is approximately 0.004 GeV/c 2 greater than the mass of the top one. This means that the mass of any quark or antiquark does not exceed one percent of the mass of a proton.

Note that this means (contrary to Fig. 1) that the ratio of the mass of the down quark to the up quark does not approach unity! The mass of the down quark is at least twice that of the up quark. The reason that the masses of the neutron and proton are so similar is not that the masses of the up and down quarks are similar, but that the masses of the up and down quarks are very small - and the difference between them is small, relative to the masses of the proton and neutron. Recall that to convert a proton into a neutron, you simply need to replace one of its up quarks with a down quark (Figure 3). This change is enough to make the neutron slightly heavier than the proton, and change its charge from +e to 0.

By the way, the fact that different particles inside a proton are colliding with each other, and constantly appearing and disappearing, does not affect the things we are discussing - energy is conserved in any collision. The mass energy and the energy of motion of quarks and gluons can change, as well as the energy of their interaction, but the total energy of the proton does not change, although everything inside it is constantly changing. So the mass of a proton remains constant, despite its internal vortex.

At this point, you can stop and absorb the information received. Amazing! Virtually all the mass contained in ordinary matter comes from the mass of nucleons in atoms. And most of this mass comes from the chaos inherent in the proton and neutron - from the energy of motion of quarks, gluons and antiquarks in nucleons, and from the energy of the work of strong nuclear interactions that hold the nucleon in its whole state. Yes: our planet, our bodies, our breath are the result of such a quiet and, until recently, unimaginable pandemonium.

As soon as it happens to meet with an unknown object, the mercantile-everyday question necessarily arises - how much does it weigh. But if this unknown is an elementary particle, what then? But nothing, the question remains the same: what is the mass of this particle. If someone were to count the costs incurred by mankind to satisfy their curiosity for research, more precisely, measurements, the masses of elementary particles, then we would find out that, for example, the mass of a neutron in kilograms with a mind-boggling number of zeros after the decimal point, cost mankind more, than most expensive construction with the same number of zeros before the decimal point.

And it all started very casually: in the laboratory led by J. J. Thomson in 1897, studies of cathode rays were carried out. As a result, a universal constant for the Universe was determined - the value of the ratio of the mass of an electron to its charge. Before determining the mass of an electron, there is very little left - to determine its charge. After 12 years he managed to do it. He conducted experiments with oil droplets falling in an electric field, and he managed not only to balance their weight with the magnitude of the field, but also to make the necessary and extremely delicate measurements. Their result is the numerical value of the electron mass:

me = 9.10938215(15) * 10-31kg.

By this time, studies of the structure also belong to where the pioneer was Ernest Rutherford. It was he who, observing the scattering of charged particles, proposed a model of an atom with an external electron shell and positive core. The particle, to which the role of the nucleus of the simplest atom was proposed, was obtained by bombarding nitrogen. This was the first nuclear reaction, obtained in the laboratory - as a result, oxygen and nuclei of the future called protons were obtained from nitrogen. However, alpha rays are composed of complex particles: in addition to two protons, they contain two more neutrons. The neutron mass is almost equal to and total weight the alpha particle turns out to be quite solid in order to destroy the oncoming nucleus and split off a “piece” from it, which happened.

The flow of positive protons was deflected by the electric field, compensating for its deflection caused by these experiments. It was no longer difficult to determine the proton mass. But the most interesting was the question of what ratio the proton and electron masses have. The riddle was immediately solved: the mass of the proton exceeds the mass of the electron by a little more than 1836 times.

So, initially, the atom model was supposed, according to Rutherford, as an electron-proton set with the same number of protons and electrons. However, it soon turned out that the primary nuclear model does not fully describe all the observed effects on the interactions of elementary particles. Only in 1932 did he confirm the hypothesis of additional particles in the composition of the nucleus. They were called neutrons, neutral protons, because. they had no charge. It is this circumstance that determines their great penetrating ability - they do not spend their energy on the ionization of oncoming atoms. The mass of a neutron is very slightly greater than the mass of a proton - only about 2.6 electron masses more.

The chemical properties of substances and compounds that are formed by a given element are determined by the number of protons in the nucleus of an atom. Over time, the participation of the proton in strong and other fundamental interactions was confirmed: electromagnetic, gravitational and weak. In this case, despite the fact that the charge of the neutron is absent, with strong interactions, the proton and neutron are considered as an elementary particle, the nucleon in different quantum states. In part, the similarity in the behavior of these particles is also explained by the fact that the mass of the neutron differs very little from the mass of the proton. The stability of protons allows them to be used after accelerating to high speeds, as bombarding particles for nuclear reactions.