Free electrons. Extraordinary bricks Where do electrons come from?
The word "electron" in Greek means "amber".
Thales of Miletus (600 BC) noticed that if amber is rubbed hard against a cloth, it will begin to attract light objects. For quite a long time it was believed that only amber had this property. However, the same thing happens with objects made of plastic and other synthetic materials. You can easily observe this phenomenon with a comb and hair: after combing, the comb begins to attract hair (and the combed hair itself, please note, begins to repel each other).
The described phenomena are based on the phenomenon electricity . It consists in the interaction of microscopic particles with a charge - positive or negative. Particles with the same charge repel, and particles with opposite charges attract. Electrons- These are the smallest elementary particles with an electrical charge. The name electrons was given by the Englishman J. J. Stoney. He proposed to call an indivisible particle of charge this way.
As you already know, all substances consist of atoms - microscopic particles. Each atom, in turn, consists of a core and a shell. The core is formed by protons and neutrons, but the shell consists of electrons, and therefore is called electron cloud.
Not only electrons have an electric charge, but also protons (neutrons are electrically neutral, as their name suggests). In an atom, electrons are attracted to the nucleus because it has a positive charge due to the charge of protons, while electrons have a negative charge. But, despite these properties, electrons do not completely combine with the nucleus, since they are in constant motion. And the atom itself is completely electrically neutral, because in an atom the number of protons is equal to the number of electrons.
In metals, some electrons are not bound to atoms and can move freely. The directed movement of these electrons causes a phenomenon without which we can hardly imagine our lives - electric current. That's why metals are called conductors : they can conduct electricity. Substances that cannot conduct current are called insulators , or dielectrics .
Let's return to the beginning of our story and answer the question: why is amber electrified? First of all, note that only insulators can be electrified by friction. When two bodies rub together, some electrons transfer from one body to the other. As a result, the bodies acquire opposite charges. Only insulators can be electrified by friction, because only in these bodies do electrons that move from one body to another remain where they ended up. They begin to move freely in the conductors.
As you probably already guessed, the total charge of a pair of bodies that rubbed against each other is equal to zero, that is, such a floating electrically neutral.
Amber is electrified by friction very easily, just like ebonite, glass or cat fur.
In a metal, as in all solids, each atom occupies a specific place. True, under certain conditions the atoms of solids can leave their places, but in any case they remain “attached” to a certain place for a long time. Depending on the temperature, each atom vibrates more or less strongly around this place, without moving any far from it. Unlike other solids, metals have one interesting feature: free electrons, that is, electrons not associated with certain atoms, move in the space between the metal atoms.
Where do these free electrons come from?
The fact is that in atoms not all electrons are held equally firmly by the nucleus. In the electron shells of metal atoms there are always one, two or three electrons very weakly bound to the nucleus. Therefore, for example, when various salts are dissolved, the metal atoms included in their composition easily give up these electrons to other atoms, and themselves turn into positive ions. The separation of electrons from atoms also occurs in a piece of any metal, but all electrons that have lost connection with the atoms remain in the metal itself between the formed ions.
The number of free electrons in a metal is enormous. There are approximately the same number of them as there are atoms. However, the entire piece of metal remains, of course, uncharged, since the positive charge of all the ions is exactly equal to the negative charge of all the electrons.
Thus, we can imagine the structure of metal in this form. Metal atoms that lost 1-2 electrons became ions. They sit relatively firmly in their places and form, one might say, a rigid “skeleton” of a piece of metal. Electrons move rapidly between the ions in all directions. Some of the electrons are slowed down when moving, others are accelerated, so among them there are always both fast and slow ones.
The movement of free electrons is completely random. You can’t catch any trickles or flows in it, no consistency. Free electrons move in the metal approximately in the same way as midges rush about in the warm air on a summer evening: in a swarm, each of the midges flies on its own, sometimes faster, sometimes slower, and the entire swarm stands still.
Among the randomly moving electrons, there are always those that fly towards the surface of the metal. Will they fly out of the metal? After all, if you leave an open vessel with a gas, the molecules of which are also in random motion, like electrons in a metal, then the gas molecules will quickly disperse in the air. However, electrons do not fly out of the metal under normal conditions. What is holding them back? Attraction by ions. When an electron rises a little above the surface of the metal, there are no longer ions above it, but below, on the surface, there are. These ions attract the rising electron, and it falls back to the surface of the metal, just like a stone thrown upward falls to the ground.
If the stone had a high enough initial speed, it could overcome the Earth's gravity and
Fly into interplanetary space, like a cannonball flies away in a Jules Verne novel. Very fast electrons can also overcome the forces of electrical attraction and leave the metal. This is what happens when heated.
When a metal is heated, the movement of not only atoms, but also electrons, increases, and at high temperatures so many electrons fly out of the metal that their flow can be detected. Look at fig. 7. It shows an unusual light bulb. In its cylinder, at some distance from the filament, a metal plate is fixed. The plate is called the anode, and the thread is called the cathode. A battery is connected to one end of the thread (it doesn’t matter which one) and to the anode, and between the battery and the anode a device is connected in the so-called “anode” circuit, indicating the presence of electric current. This device is called a galvanometer. The lamp filament itself is connected to the electrical network and is red-hot. If the anode is connected to the negative pole of the battery, and the thread is connected to the positive pole, then there will be no current in the anode circuit (Fig. 7 on the left). Now let's try to change the poles and connect the plate to the “plus” of the battery. A current will immediately appear in the circuit (Fig. 7 on the right). This experiment shows that the hot lamp filament actually emits negative charges - electrons that are repelled from the anode if it is negatively charged (Fig. 7 left), and are carried away by electrical forces to the anode if it is connected to the positive terminal of the battery (Fig. 7 right ).
The emission of electrons by hot metals is of great practical importance. Suffice it to say that it is used in all radio tubes (we will talk about radio tubes in the last section of the book).
You can increase the energy of electrons and make them fly out of the metal not only by heating, but also by lighting. Such phenomena were studied in 1888 by Russian physicist, professor at Moscow University A.G. Stoletov. A stream of light rays carries energy, and if the light falls on a metal, then part of this energy is absorbed by the metal and transferred to electrons. Having received additional energy, some electrons overcome the attraction of the ions and fly out of the metal. This phenomenon is called the photoelectric effect. The photoelectric effect is used in a very important device for technology - the photocell. The photocell diagram is shown in Figure 8.
A glass container from which air has been removed is coated on the inside with a layer of metal, usually sodium, potassium or cesium, which has been subjected to special treatment (electrons are easily ejected from these metals when exposed to visible light); Only a small window for light transmission is not covered with metal. The metal layer serves as the cathode of the photocell (photocathode). In the middle of the cylinder either a thin metal wire or mesh is placed. This is the anode. The photocathode is connected to the negative terminal of the battery, and the anode is connected to the positive terminal. As soon as light rays fall on the photocathode, some electrons acquire greater energy and escape from its surface. The force of electrical attraction drives them towards the anode, and a current appears in the circuit. If the lighting stops, the current disappears). Note that both described methods are able to extract from metals only a very small part of the free electrons present in them.
It is easy to understand that electrification by friction is a process of ejection of electrons. For example, when glass rubs against the skin, electrons extracted from the glass are transferred to the skin.
So we know that electrons can be extracted from atoms. Let's now see how we can control electrons that have left atoms.
To the question Where do electrons come from in a conductor? Why don’t they run out, since the number of electrons in an atom is limited? given by the author Alexander Vladislavovich the best answer is You've probably heard more than once that metals have "free" electrons. So, “free” electrons are not entirely correct. In fact, they are not entirely free. Let's look at a copper conductor, let's say a ring of copper wire. Each copper atom consists of a nucleus with a charge of (+29) and 29 electrons (each with a charge of (-1)). These electrons are not the same; they are distributed across energy levels. The electronic formula of copper is 1s2 2s2 2p6 3s2 3p6 3d10 4s1. Electrons located at the energy levels 1s2 2s2 2p6 3s2 3p6 3d10 are held by the nucleus quite firmly and are each located near their “own” nucleus, but the electron located at the energy level 4s1 is held very weakly. Figuratively speaking, it is enough to “blow” not to tear it off completely, but to move it from one core to another. That other nucleus will have an extra electron, but it (the nucleus) cannot retain the extra electron and transfers it to the third, the next, etc. This transfer of electrons in the absence of external forces is chaotic, without a definite direction. In the end, this extra electron will come to the nucleus from which we “blowed it away”. Thus, electrons located at the 4s1 energy levels of all atoms constantly and very easily move from one atom to another. It is in this sense that they are called free.
Now consider the same copper ring, one section of which is placed in a magnetic field and, under the action of an external (mechanical) force, moves in it across the magnetic field lines (this part of the ring is a generator, and the remaining parts are wires and a consumer, for example a light bulb). In fact, if you go down to the atomic level, nuclei and electrons move under the influence of applied mechanical force. According to the law, I don’t remember who (I have completely forgotten physics) charges moving in a magnetic field are acted upon by a force that is directed perpendicular to the direction of movement of the conductor as a whole. This force cannot cause the nuclei (they are very heavy) and the electrons associated with them to move, located at the energy levels 1s2 2s2 2p6 3s2 3p6 3d10. But it forces the so-called “free electrons” (at the 4s level) to move along the conductor. Now the movement of “free” electrons is not chaotic, but strictly directed. An electron moves from the first atom to the second, from the second to the third, from the third... and so on. Finally, the electron from the last atom moves to the first (do not forget that our conductor is coiled into a ring.
Thus, each copper atom again has 29 electrons, but the 4s electrons are not their own, but from their neighbor. At the next moment of time, all “free” electrons will shift another 1 position in the same direction. The operation of alternating current generators is organized in such a way that, roughly speaking, the frame with current rotates in a constant magnetic field (in industrial ones with a frequency of 50 hertz). Therefore, in the first half of the revolution, the conductor (one side of the frame) crosses the lines of force near the north pole of the magnet, and the electrons move in one direction. During the second half of the frame's revolution, the conductor in question crosses the lines of force near the south pole of the magnet, and the electrons move in the opposite direction, and so on 50 times per second. True, in fact, the intensity of the magnetic field that the conductor crosses is not constant, but varies along a sinusoid, but this does not change the essence of what is happening. The result is an alternating electric current, i.e. the electrons actually do not go far from their nuclei, but “dangle” back and forth, as if on a swing. Something like this. Thank you very much, I’ve been tormented by this question all my life.
However, I did not understand how then all sorts of Tesla transformers distribute electricity in the air, or the same lightning, or the air also transmits these “free” electrons, but in this case they will not be able to return to the source, because there is no circuit.
In general, I would like to ask you, or can you recommend some literature?
Answer from Dr. Dick[guru]
so in place of those who left, others come. Current flows only in a closed circuit, remember? That is, electrons circulate in a circle
Answer from Alexander Shevchenko[active]
electrons do not run anywhere, they remain in place, they transfer charge along the chain to each other.
Answer from Pinochet[guru]
Let these electrons not run anywhere.
If I tell you that not a single scientist knows exactly what e-mail is. current, then you will lose faith in humanity.))
There are only hypotheses, that is, assumptions, so that at least some calculations can be made.
And you can come up with a bunch of hypotheses yourself.
The electrons don’t run anywhere, they just beat each other in the ass to see who flies farthest.
Kind of like the balls in billiards.
And when should they run? -The speed of current is equal to the speed of light. They simply transfer charge to each other and that’s all.
Answer from Potato dad[guru]
free electrons.
They do not end because electric current is always a closed circle process. If something has left, something has arrived.
Answer from Globe[guru]
I don't know what the phrase "electrons transfer charge" means, but in my humble understanding this is the case.
When we flip a switch, a disturbance travels through the conductor at the speed of light. You've probably seen a freight train leaving the station? The locomotive pulls the first car, which pulls the second, and so the clanging of the automatic coupler sweeps along the entire chain (and the speed of this clanging is much higher than the speed of both the locomotive and the cars). So it is here - electrons rush to the plus, neighboring ones move in their place, etc. An electromagnetic pulse runs through a conductor at the speed of light.
Let us further remember that current strength is the charge that passes through a certain cross-section of a conductor per unit time. The speed of an individual electron may be tiny - but it crossed this cross section, and, therefore, made its contribution to the current.
There are a lot of free electrons in a conductor: approximately 10^23 (on the order of Avogadro’s constant). And although the charge of one electron is about 10^-19 C, it is enough for 0.01% of all electrons to start moving - and a current of 1A will flow through the conductor.
This is with constant current. In a variable, everything is even simpler - there the electrons can not move anywhere, but simply oscillate in accordance with the periodic change in the direction of the electric field.
And finally, about the decline. If there are fewer electrons in the conductor, then it will become positively charged, and either the current will stop, or it will begin to attract electrons from the minus of the battery.
Answer from Gennady Karpov[guru]
The electrons are running and running.
And the electric field makes them run.
An electron has a charge and moves under the influence of an elfield.
In conductors (metals, for example, in electrolytes, semiconductors.... a slightly different picture) due to the peculiarities of their structure, there are free electrons.
Some run away, and others come running in their place, from another conductor connected (for example, a switch when turned on). That conductor is connected to a current source, and the source drives them in a circle.
This happens with constant current.
If the current is alternating (remember about 50 Hz in the network), then they oscillate “this way and that” 50 times per second. And they remain almost in place.
The electric field in a conductor propagates quickly, at the speed of light (speed of propagation of the electric field). And the electrons themselves travel much slower.
Answer from Evgeny M.[guru]
When something runs in a circle, it never decreases.
Why didn’t such a simple thought occur to you? (Or your teacher?)
The mechanism of the process is not at all important, the details are not at all important. For example, it does not matter whether one specific electron manages to fly around the entire conductor along a closed path and return back, or whether it only flies into a neighboring atom and takes the place of the emitted electron there.
The main thing is that direct current ALWAYS flows only along a closed path. If the path is not closed, then the current always stops (electrons run out).
If the path is not closed, then only alternating current can exist in such a system. (For example, the path can be broken by a capacitor.) With alternating current, electrons generally do not fly away anywhere. They are located close to their atoms and only perform oscillatory movements at the frequency of alternating current.
Answer from Doctor[guru]
There are electrons in a conductor - they are in orbitals around the nuclei of atoms. But in conductors they are free. This means that under the influence of external forces they can move without hindrance. . They are on their own.
When an electric field arises, they begin to move in an orderly manner.
According to Kirkhoff's law, the sum of the currents is zero. That's why they don't end - they aren't wasted anywhere - but go around in circles in a closed chain.
Second, there are no orbits in atoms)
There are orbitals - a set of points where the location of the electron is more likely. You are using an old model of the boron atom.
Answer from MwenMas[guru]
In short, electrons do not escape from a conductor. They always remain in it and move under the influence of an electric field, either in one direction with direct current, or back and forth with alternating current. Imagine that in a heating system the pump drives water, but it doesn’t go anywhere, it doesn’t get smaller. Same with electrons.
Answer from Oriy Semykin[guru]
The resurrection of Einstein is for biologists and doctors.
There is no need for physics here, just common sense to figure it out. Electrons do not disappear, but only shift. Otherwise, a section of the circuit would quickly become positively charged. Since it remains neutral, the charge is compensated. It is clear that they are electrons. In reality, electrons do not “flow” in the form of a current, but an electromagnetic wave moves. This will be more difficult to understand.
Answer from Alex[newbie]
And to all that has been said, how is the charge (energy) of electrons renewed in a closed circuit, given that part of the energy is spent on heat during the operation of the consumer?
Answer from Maxim Diamonds[guru]
there is a word called resonance...
Answer from Yergey[active]
Science is unable to explain many phenomena using electron theory. These include the manifestation and disappearance of static electricity, the phenomenon of magnetism, the neutrality of the conductor, conductivity and non-conductivity of electric current substances, the piezoelectric effect, the presence of electric current in an open circuit, the absence of positrons in the generation of electric current and their presence in the generation of electric discharge, the manifestation of dualism by particles and much more.
Answer from Yura Ezhov[newbie]
And if there is an incandescent light bulb in the circuit. It spends energy in light and heat, so it turns out that the electrons are charged and transfer the charge to the light bulb. So then where do they get a new charge? From a magnetic field? Or because they continue to kick themselves in a circle
?
Free electron model on Wikipedia
Look at the Wikipedia article about Free electron model
– In Europe no one plays the piano now,
play with electricity.
“You can’t play on electricity—it’ll electrocute you.”
-And they play with rubber gloves...
-Eh! You can wear rubber gloves!
"Mimino"
It’s strange... They play with electricity, but for some reason they kill with some kind of current... Where does the current come from in electricity? And what kind of current is this? Hello, dear ones! Let's figure it out.
Well, first of all, let's start with why it is still possible to play with electricity in rubber gloves, but, for example, in iron or lead gloves, it is impossible, although metal ones are stronger? The thing is that rubber does not conduct electricity, but iron and lead do, so they will give you an electric shock. Stop, stop... We are going in the wrong direction, let's turn around... Yeah... We need to start with the fact that everything in our Universe consists of tiny particles - atoms. These particles are so small that, for example, a human hair is several million times thicker than the smallest hydrogen atom. An atom consists (see Figure 1.1) of two main parts - a positively charged nucleus, which in turn consists of neutrons and protons and electrons rotating in certain orbits around the nucleus.
Figure 1.1 – Structure of the electron
The total electric charge of an atom is always (!) equal to zero, that is, the atom is electrically neutral. Electrons have a fairly strong bond with the atomic nucleus, however, if you apply some force and “pluck” one or more electrons from the atom (through heating or friction, for example), then the atom will turn into a positively charged ion, since the positive charge of its nucleus will be greater the magnitude of the negative total charge of the remaining electrons. And vice versa - if one or more electrons are somehow added to the atom (but not through cooling...), the atom will turn into a negatively charged ion.
The electrons that make up the atoms of any element are absolutely identical in their characteristics: charge, size, mass.
Now, if you look at the internal composition of any element, you can see that not the entire volume of the element is occupied by atoms. Always, in any material there are also both negatively charged and positively charged ions, and the process of conversion “negatively charged ion–atom–positively charged ion” occurs constantly. During this transformation, so-called free electrons are formed - electrons that are not associated with any of the atoms or ions. It turns out that different substances have different amounts of these free electrons.
It is also known from the physics course that around any charged body (even something as insignificant as an electron) there is a so-called invisible electric field, the main characteristics of which are intensity and direction. It is conventionally accepted that the field is always directed from a point of positive charge to a point of negative charge. Such a field arises, for example, when rubbing an ebonite or glass rod on wool, and in the process you can hear a characteristic crackling sound, the phenomenon of which we will consider later. Moreover, a positive charge will form on the glass rod, and a negative charge on the ebonite rod. This will precisely mean the transfer of free electrons from one substance to another (from a glass rod to wool and from wool to an ebonite rod). The transfer of electrons means a change in charge. To evaluate this phenomenon, there is a special physical quantity - the amount of electricity, called a coulomb, with 1C = 6.24 10 18 electrons. Based on this relationship, the charge of one electron (or otherwise called the elementary electric charge) is equal to: 
So what does all these electrons and atoms have to do with it... But here’s what it has to do with it. If you take a material with a large content of free electrons and place it in an electric field, then all the free electrons will move in the direction of the positive point of the field, and the ions - since they have strong interatomic (interionic) bonds - will remain inside the material, although in theory they should move to that point in the field whose charge is opposite to the charge of the ion. This was proven with a simple experiment.
Two different materials (silver and gold) were combined with each other and placed in an electric field for several months. If the movement of ions between the materials had been observed, then a diffusion process should have occurred at the point of contact and gold would have formed in a narrow zone of silver, and silver in a narrow zone of gold, but this did not happen, which proved the immobility of “heavy” ions. Figure 2.1 shows the movement of positive and negative particles in an electric field: negatively charged electrons move against the direction of the field, and positively charged particles move in the direction of the field. However, this is only true for particles that are not included in the crystal lattice of any material and are not interconnected by interatomic bonds. 
Figure 1.2 – Motion of a point charge in an electric field
The movement occurs in this way, because like charges repel, and unlike charges attract: two forces always act on a particle: the force of attraction and the force of repulsion.
So, it is the ordered movement of charged particles that is called electric current. There is a funny fact: it was initially believed (before the discovery of the electron) that the electric current was generated precisely by positive particles, so the direction of the current corresponded to the movement of positive particles from “plus” to “minus”, but later the opposite was discovered, but it was decided to leave the direction of the current the same, and This tradition has remained in modern electrical engineering. So it's actually the other way around! 
Figure 1.3 – Structure of the atom
An electric field, although characterized by the magnitude of the intensity, is created around any charged body. For example, if the same glass and ebonite rods are rubbed on wool, an electric field will arise around them. An electric field exists near any object and affects other objects, no matter how far they are located. However, as the distance between them increases, the field strength decreases and its magnitude can be neglected, so that two people standing next to each other and having a certain charge, although they create an electric field, and an electric current flows between them, but it is so small that its value is difficult to record even with special instruments.
So, it’s time to talk more about what this characteristic is – electric field strength. It all starts with the fact that in 1785, the French military engineer Charles Augustin de Coulomb, taking a break from drawing military maps, derived a law describing the interaction of two point charges:
The modulus of the force of interaction between two point charges in a vacuum is directly proportional to the product of the moduli of these charges and inversely proportional to the square of the distance between them.
We will not delve into why this is so, we will simply take Mr. Coulomb at his word and introduce some conditions for compliance with this law:
- point-like charges - that is, the distance between charged bodies is much larger than their sizes - however, it can be proven that the force of interaction of two volumetrically distributed charges with spherically symmetrical non-intersecting spatial distributions is equal to the force of interaction of two equivalent point charges located at centers of spherical symmetry;
- their immobility. Otherwise, additional effects come into force: the magnetic field of a moving charge and the corresponding additional Lorentz force acting on another moving charge;
- interaction in a vacuum.
Mathematically, the law is written as follows: 
where q 1 , q 2 are the values of interacting point charges,
r is the distance between these charges,
k is a certain coefficient describing the influence of the environment.
The figure below provides a graphical explanation of Coulomb's law. 
Figure 1.4 – Interaction of point charges. Coulomb's law
Thus, the force of interaction between two point charges increases as these charges increase and decreases as the distance between the charges increases, and doubling the distance leads to a fourfold decrease in the force. However, such a force arises not only between two charges, but also between a charge and a field (and again an electric current!). It would be logical to assume that the same field has different effects on different charges. So the ratio of the force of interaction between the field and the charge to the magnitude of this charge is called the electric field strength. Provided that the charge and field are stationary and do not change their characteristics over time. 
where F is the interaction force,
q – charge.
Moreover, as mentioned earlier, the field has a direction, and this arises precisely from the fact that the interaction force has a direction (it is a vector quantity: like charges attract, unlike charges repel).
After I wrote this lesson, I asked my friend to read it, evaluate it, so to speak. In addition, I asked him one interesting question, in my opinion, precisely on the topic of this material. Imagine my surprise when he answered incorrectly. Try to answer this question (it is placed in the tasks section at the end of the lesson) and argue your point of view in the comments.
And lastly, since a field can move a charge from one point in space to another, it has energy, and therefore can do work. This fact will be useful to us later when considering issues of the operation of electric current.
With this, the first lesson is over, but we still have an unanswered question: why, wearing rubber gloves won’t kill you with an electric shock. Let's leave it as an intrigue for the next lesson. Thank you for your attention, see you again!
- Let's assume that in the hero city of Moscow there is a certain outlet, the same ordinary outlet that you have at home. Let’s also assume that we stretched wires from Moscow to Vladivostok and connected a light bulb in Vladivostok (again, the lamp is completely ordinary, the same one now illuminates the room for both me and you). So, what we have is: a light bulb connected to the ends of two wires in Vladivostok and a socket in Moscow. Now let’s insert the “Moscow” wires into the socket. If we do not take into account a lot of different conditions and simply assume that the light bulb in Vladivostok lights up, then try to guess whether the electrons that are currently in the socket in Moscow will reach the filament of the light bulb in Vladivostok? What happens if we connect a light bulb not to a socket, but to a battery?
Kikoin A.K. Two mysteries of beta decay // Quantum. - 1985. - No. 5. - P. 30-31, 34.
By special agreement with the editorial board and editors of the journal "Kvant"
As is known, natural beta-radioactive decay consists of the fact that the nuclei of atoms of one element spontaneously emit beta particles, that is, electrons, and at the same time turn into the nuclei of another element with an atomic number one greater, but with the same mass (“Physics 10 ", § 103). Symbolically this transformation is written like this:
\(~^M_ZX \to \ ^M_(Z+1)Y +\ ^0_(-1)e\) .
Here X- the original core, Y- decomposition product, e- electron (the superscript “0” shows that the mass of the electron compared to the atomic mass unit is very small).
A careful study of beta decay has shown that this phenomenon is fraught with two mysteries.
Riddle one: “loss” of energy
If the core X spontaneously turns into a nucleus Y, then this means that the energy W X cores X more than energy W Y core Y. And the energy of the beta particle emitted in this case should be equal to the energy difference W X- W Y (if we neglect recoil energy).
Since all the original kernels X are identical, as well as all the resulting nuclei are identical Y, all emitted beta particles must have the same energy. Experiments show that the energy of almost all beta particles is less than the energy difference W X- W Y. More precisely: β -particles have different energies, and they all range from zero to a maximum value equal to W X- W Y. For example, for beta particles emitted by \(~\ ^(210)_(83)Bi\) nuclei (half-life 5 days), the maximum energy value is about 1 MeV, and the average energy per particle is less than 0.4 MeV.
It seemed that beta decay is a process in which, in violation of the law of conservation of energy, energy disappears without a trace. Some physicists were inclined to think that the law of conservation of energy, which is certainly true in the world of macroscopic processes, is “not necessary” for some processes associated with elementary particles. Even such a physicist as Niels Bohr was inclined to this idea (about the possibility of violating the law of conservation of energy). Other opinions were also expressed that there may be processes in which energy does not disappear without a trace (as in the case of beta decay), but rather appears from nothing.
Neutrino
The law of conservation of energy was, however, “saved” by the Swiss theoretical physicist Wolfgang Pauli. In 1930, he suggested that during beta decay, not only an electron is emitted from the nucleus, but also another particle, which accounts for the missing energy. But why does this particle not reveal itself in any way: it does not ionize the gas, as an electron does; its energy during collisions with atoms does not turn into heat, etc.? Pauli explained this by saying that the particle he invented was electrically neutral and had no rest mass.
This particle, to which the Italian physicist Enri Co Fermi gave the name neutrino, seemed very strange. The whole purpose of the neutrino was to “save” the law of conservation of energy. Physicists have never had to deal with such particles before. Nevertheless, Pauli's idea of a new particle quickly gained universal acceptance. Soviet physicist A.I. Leypunsky already in 1936 came up with a way to detect it. However, its real existence was finally proven only in 1956, almost 26 years after it was “born” in the brain of the imaginative physicist B. Pauli.
Riddle two: where do electrons come from?
This mystery of beta decay (it could be put in first place) consisted of this.
As is known (“Physics 10”, § 107), the atomic nuclei of all elements consist only of protons and neutrons. How can electrons, which are not there, and neutrinos, which are not there either, fly out of nuclei?
This amazing fact (something that is not there flies out of the nucleus) can only be explained by the fact that the particles - protons and neutrons that form the nucleus - are capable of mutually transforming into each other. In particular, beta decay is when one of the neutrons entering the nucleus of a radioactive element turns into a proton.
In this case, there is one more proton in the nucleus than there was, and the total number of particles remains the same. Just one of the neutrons became a proton. But if the matter were limited to that, the law of conservation of electric charge would be violated. Nature does not allow such processes! So, it turns out that along with the transformation of a neutron into a proton, an electron is born in the nucleus, the negative charge of which compensates for the positive charge of the emerging proton, and a neutrino, which carries away a certain amount of energy. Thus, during beta decay in the nucleus, one of the neutrons transforms into a proton and the birth of two particles - an electron and a neutrino. The proton remains in the nucleus, but the electron and neutrino, which “are not supposed to be in the nucleus,” fly out of it.
Note that the process of beta radioactive decay is somewhat reminiscent of the process of emission of a light quantum (photon). A beta particle and a neutrino are born at the moment of transition of a nucleus from one state to another, similar to how a photon is emitted by an atom when an electron, which is part of the electron shell of the atom, transitions from one energy level to another.