All physical bodies of nature are built from a type of matter called matter. Substances are divided into two main groups - simple and complex substances.
Complex substances are those substances that can be broken down into other, simpler substances through chemical reactions. In contrast to complex substances, simple substances are those that cannot be chemically decomposed into even simpler substances.
An example of a complex substance is water, which through a chemical reaction can be decomposed into two other, simpler substances - hydrogen and oxygen. As for the last two, they can no longer be chemically decomposed into simpler substances, and therefore are simple substances, or, in other words, chemical elements.
In the first half of the 19th century, there was an assumption in science that chemical elements were unchanging substances that had no common connection with each other. However, the Russian scientist D.I. Mendeleev (1834 - 1907) for the first time in 1869 revealed the connection of chemical elements, showing that the qualitative characteristics of each of them depend on its quantitative characteristics - atomic weight.
While studying the properties of chemical elements, D.I. Mendeleev noticed that their properties periodically repeat depending on their atomic weight. He displayed this periodicity in the form of a table, which was included in science under the name “Mendeleev’s Periodic Table of Elements.”
Below is Mendeleev's modern periodic table of chemical elements.
Atoms
According to modern concepts of science, each chemical element consists of a collection of tiny material (material) particles called atoms.
An atom is the smallest fraction of a chemical element that can no longer be chemically decomposed into other, smaller and simpler material particles.
Atoms of chemical elements that are different in nature differ from each other in their physical and chemical properties, structure, size, mass, atomic weight, intrinsic energy and some other properties. For example, the hydrogen atom differs sharply in its properties and structure from the oxygen atom, and the latter from the uranium atom, etc.
It has been established that atoms of chemical elements are extremely small in size. If we conventionally assume that atoms have a spherical shape, then their diameters should be equal to one hundred millionths of a centimeter. For example, the diameter of a hydrogen atom - the smallest atom in nature - is equal to one hundred millionth of a centimeter (10 -8 cm), and the diameter of the largest atoms, for example, a uranium atom, does not exceed three hundred millionths of a centimeter (3 10 -8 cm). Consequently, a hydrogen atom is as many times smaller than a ball with a radius of one centimeter as the latter is smaller than the globe.
In accordance with the very small size of atoms, their mass is also very small. For example, the mass of a hydrogen atom is m = 1.67 10 -24 g. This means that one gram of hydrogen contains approximately 6 10 23 atoms.
The conventional unit of measurement for the atomic weights of chemical elements is taken to be 1/16 of the weight of an oxygen atom. In accordance with this atomic weight of a chemical element, an abstract number is called, showing how many times the weight of a given chemical element is greater than 1/16 of the weight of an oxygen atom.
The periodic table of elements by D.I. Mendeleev shows the atomic weights of all chemical elements (see the number placed under the name of the element). From this table we see that the lightest atom is the hydrogen atom, which has an atomic weight of 1.008. The atomic weight of carbon is 12, oxygen is 16, etc.
As for heavier chemical elements, their atomic weight exceeds the atomic weight of hydrogen by more than two hundred times. Thus, the atomic weight of mercury is 200.6, radium is 226, etc. The higher the order of number occupied by a chemical element in the periodic table of elements, the greater the atomic weight.
Most of the atomic weights of chemical elements are expressed in fractional numbers. This is to a certain extent explained by the fact that such chemical elements consist of a collection of many types of atoms that have different atom weights, but the same chemical properties.
Chemical elements that occupy the same number in the periodic table of elements, and therefore have the same chemical properties, but different atomic weights, are called isotopes.
Isotopes are found in most chemical elements; it has two isotopes, calcium - four, zinc - five, tin - eleven, etc. Many isotopes are obtained through art, some of them are of great practical importance.
Elementary particles of matter
For a long time it was believed that atoms of chemical elements are the limit of divisibility of matter, i.e., like the elementary “building blocks” of the universe. Modern science has rejected this hypothesis, establishing that the atom of any chemical ale is a collection of even smaller material particles than the atom itself.
According to the electronic theory of the structure of matter, an atom of any chemical element is a system consisting of a central nucleus around which “elementary” material particles called electrons rotate. The nuclei of atoms, according to generally accepted views, consist of a collection of “elementary” material particles - protons and neutrons.
To understand the structure of atoms and the physical and chemical processes in them, it is necessary to at least briefly become familiar with the basic characteristics of the elementary particles that make up the atoms.
Determined that electron is a material particle that has the smallest negative electric charge observed in nature.
If we conventionally assume that an electron as a particle has a spherical shape, then the diameter of the electron should be equal to 4 · 10 -13 cm, i.e. it is tens of thousands of times smaller than the diameter of any atom.
An electron, like any other material particle, has mass. The “rest mass” of an electron, i.e. the mass it has in a state of relative rest, is equal to m o = 9.1 10 -28 g.
The extremely small “rest mass” of the electron indicates that the inert properties of the electron are extremely weak, which means that the electron, under the influence of a variable electric force, can oscillate in space with a frequency of many billions of cycles per second.
The mass of an electron is so small that to obtain one gram of electrons it would be necessary to take 1027 units. To have at least some physical idea of this colossally large number, let us give the following example. If one gram of electrons could be placed in a straight line close to each other, they would form a chain four billion kilometers long.
The mass of an electron, like any other material microparticle, depends on the speed of its movement. An electron, being in a state of relative rest, has a “rest mass”, which is of a mechanical nature, like the mass of any physical body. As for the “mass of motion” of the electron, which increases with increasing speed of its movement, it is of electromagnetic origin. It is due to the presence of an electromagnetic field in a moving electron as a certain type of matter with mass and electromagnetic energy.
The faster the electron moves, the more the inertial properties of its electromagnetic field manifest themselves, and, consequently, the greater the mass of the latter and, accordingly, its electromagnetic energy. Since an electron with its electromagnetic field constitutes a single, organically connected material system, it is natural that the mass of motion of the electromagnetic field of the electron can be directly attributed to the electron itself.
An electron, in addition to the properties of a particle, also has wave properties. Experience has established that the flow of electrons, like a light flow, propagates in the form of a wave-like motion. The nature of the wave motion of the electron flow in space is confirmed by the phenomena of interference and diffraction of electron waves.
Electron interference- this is the phenomenon of superimposing electronic wills on each other, and electron diffraction- this is the phenomenon of electron waves bending around the edges of a narrow gap through which an electron flow passes. Consequently, an electron is not just a particle, but a “particle-wave”, the length of which depends on the mass and speed of the electron.
It has been established that the electron, in addition to its translational motion, also performs a rotational motion around its axis. This type of electron motion is called “spin” (from the English word “spin” - spindle). As a result of such movement, the electron, in addition to the electrical properties due to the electric charge, also acquires magnetic properties, reminiscent in this respect of an elementary magnet.
A proton is a material particle that has a positive electric charge equal in absolute value to the electric charge of an electron.
Proton mass is 1.67 · 10-24 g, i.e. it is approximately 1840 times the “rest mass” of the electron.
Unlike the electron and proton, a neutron does not have an electric charge, i.e. it is an electrically neutral “elementary” particle of matter. The mass of a neutron is almost equal to the mass of a proton.
Electrons, protons and neutrons, being part of atoms, interact with each other. In particular, electrons and protons are mutually attracted to each other as particles with opposite electric charges. At the same time, an electron from an electron and a proton from a proton are repelled as particles having the same electric charges.
The interaction of all these electrically charged particles occurs through their electric fields. These fields represent a special type of matter, consisting of a collection of elementary material particles called photons. Each photon has a strictly defined amount of energy inherent in it (energy quantum).
The interaction of electrically charged material particles is carried out by exchanging photons with each other. The force of interaction between electrically charged particles is usually called electrical force.
Neutrons and protons found in the nuclei of atoms also interact with each other. However, this interaction is no longer carried out through an electric field, since the neutron is an electrically neutral particle of matter, but through the so-called nuclear field.
This field is also a special type of matter, consisting of a collection of elementary material particles called mesons. The interaction of neutrons and protons is carried out by exchanging mesons with each other. The force between neutrons and protons interacting with each other is called the nuclear force.
It has been established that nuclear forces act in the nuclei of atoms within extremely small distances - approximately 10 - 13 cm.Nuclear forces significantly exceed in magnitude the electrical forces of mutual repulsion of protons in the nucleus of an atom. This leads to the fact that they are able not only to overcome the forces of mutual repulsion of protons inside the nuclei of atoms, but also to create very strong systems of nuclei from a combination of protons and neutrons.
The stability of the nucleus of each atom depends on the relationship between two contradictory forces - nuclear (mutual attraction of protons and neutrons) and electrical (mutual repulsion of protons).
Powerful nuclear forces acting in the nuclei of atoms contribute to the transformation of neutrons and protons into each other. These interconversions of neutrons and protons are carried out as a result of the release or absorption of lighter elementary particles, such as mesons.
The particles we have considered are called elementary because they do not consist of a collection of other, simpler particles of matter. But at the same time, we must not forget that they are capable of transforming into each other, arising at the expense of each other. Thus, these particles are some complex formations, i.e. their elementarity is conditional.
Chemical structure of atoms
The simplest atom in its structure is the hydrogen atom. It consists of a collection of only two elementary particles - a proton and an electron. The proton in the hydrogen atom system plays the role of a central nucleus around which the electron rotates in a certain orbit. In Fig. Figure 1 schematically shows a model of the hydrogen atom.
Rice. 1. Scheme of the structure of the hydrogen atom
This model is only a rough approximation of reality. The fact is that the electron as a “particle-wave” does not have a volume sharply delimited from the external environment. This means that we should not talk about some exact linear orbit of the electron, but about a kind of electron cloud. In this case, the electron most often occupies some middle line of the cloud, which is one of its possible orbits in the atom.
It must be said that the orbit of the electron itself is not strictly unchanged and motionless in the atom - it, too, due to changes in the mass of the electron, undergoes some rotational motion. Consequently, the movement of an electron in an atom is relatively complex. Since the nucleus of a hydrogen atom (proton) and the electron rotating around it have opposite electric charges, they are mutually attracted.
At the same time, the electron, spinning around the nucleus of the atom, develops a centrifugal force that tends to remove it from the nucleus. Consequently, the electric force of mutual attraction between the nucleus of an atom and the electron and the centrifugal force acting on the electron are contradictory forces.
At equilibrium, their electron occupies a relatively stable position in a certain orbit in the atom. Since the mass of an electron is very small, in order to balance the force of attraction to the nucleus of an atom, it must rotate at an enormous speed, equal to approximately 6 10 15 revolutions per second. This means that the electron in the system of the hydrogen atom, like any other atom, moves along its orbit with a linear speed exceeding a thousand kilometers per second.
Under normal conditions, an electron rotates in an atom of its kind in the orbit closest to the nucleus. At the same time, it has the minimum possible amount of energy. If, for one reason or another, for example, under the influence of some other material particles that have invaded the atomic system, the electron moves to an orbit more distant from the atom, then it will already have a slightly larger amount of energy.
However, the electron remains in this new orbit for an insignificantly short time, after which it again rotates to the orbit closest to the atomic nucleus. During this move, it gives off its excess energy in the form of a quantum of electrical magnetic radiation - radiant energy (Fig. 2).
Rice. 2. An electron, when moving from a distant orbit to one closer to the nucleus of an atom, emits a quantum of radiant energy
The more energy an electron receives from outside, the more distant the orbit it moves from the nucleus of the atom, and the greater the amount of electromagnetic energy it emits when it rotates into the orbit closest to the nucleus.
By measuring the amount of energy emitted by an electron when moving from various orbits to the one closest to the nucleus of the atom, it was possible to establish that an electron in the system of the hydrogen atom, as in the system of any other atom, can not move to any arbitrary orbit, but to a strictly defined one in accordance with the energy that it receives under the influence of an external force. The orbits that an electron can occupy in an atom are called allowed orbits.
Since the positive charge of the nucleus of a hydrogen atom (proton charge) and the negative charge of the electron are numerically equal, their total charge is zero. This means that the hydrogen atom, being in its normal state, is an electrically neutral particle.
This is true for atoms of all chemical elements: an atom of any chemical element in a normal state is an electrically neutral particle due to the numerical equality of its positive and negative charges.
Since the nucleus of a hydrogen atom contains only one “elementary” particle - a proton, the so-called mass number of this nucleus is equal to one. The mass number of the nucleus of an atom of any chemical element is the total number of protons and neutrons included in the composition of this nucleus.
Natural hydrogen mainly consists of a collection of atoms with a mass number equal to one. However, it also contains another type of hydrogen atoms, with a mass number equal to two. The nuclei of the atoms of this heavy hydrogen, called deuterons, consist of two particles - a proton and a neutron. This isotope of hydrogen is called deuterium.
Natural hydrogen contains very small amounts of deuterium. For every six thousand atoms of light hydrogen (mass number equal to one), there is only one atom of deuterium (heavy hydrogen). There is another isotope of hydrogen - superheavy hydrogen, called tritium. In the nuclei of an atom of this hydrogen isotope there are three particles: a proton and two neutrons, bound to each other by nuclear forces. The mass number of the nucleus of a tritium atom is three, i.e., a tritium atom is three times heavier than a light hydrogen atom.
Although the atoms of hydrogen isotopes have different masses, they still have the same chemical properties. For example, light hydrogen, entering into a chemical interaction with oxygen, forms a complex substance with it - water. Similarly, the isotope of hydrogen, deuterium, combines with oxygen to form water, which, unlike ordinary water, is called heavy water. Heavy water is widely used in the process of producing nuclear (nuclear) energy.
Consequently, the chemical properties of atoms do not depend on the mass of their nuclei, but only on the structure of the electron shell of the atom. Because light hydrogen, deuterium, and tritium atoms have the same number of electrons (one for each atom), these isotopes have the same chemical properties.
It is no coincidence that the chemical element hydrogen occupies the first number in the periodic table of elements. The fact is that there is some connection between the number of any element in the periodic table of elements and the charge value of the nucleus of an atom of this element. It can be formulated like this: the serial number of any chemical element in the periodic table of elements is numerically equal to the positive charge of the nucleus of this element, and, consequently, to the number of electrons rotating around it.
Since hydrogen occupies the first number in the periodic table of elements, this means that the positive charge of the nucleus of its atom is equal to one and that one electron rotates around the nucleus.
The chemical element helium occupies number two in the periodic table of elements. This means that it has a positive electric charge of the nucleus equal to two units, i.e., its nucleus must contain two protons, and the electron shell of the atom must contain two electrodes.
Natural helium consists of two isotopes - heavy and light helium. The mass number of heavy helium is four. This means that the nucleus of a heavy helium atom, in addition to the above-mentioned two protons, must include two more neutrons. As for light helium, its mass number is three, i.e., its nucleus, in addition to two protons, must include one more neutron.
It has been established that in natural helium the number of light helium atoms is approximately one millionth of the heavy helium atoms. In Fig. Figure 3 shows a schematic model of the helium atom.
Rice. 3. Scheme of the structure of the helium atom
Further complexity of the structure of atoms of chemical elements occurs due to an increase in the number of protons and neutrons in the nuclei of these atoms and at the same time due to an increase in the number of electrons rotating around the nuclei (Fig. 4). Using the periodic table of elements, it is easy to determine the number of electrons, protons and neutrons that make up various atoms.
Rice. 4. Schemes of the structure of atomic nuclei: 1 - helium, 2 - carbon, 3 - oxygen
The atomic number of a chemical element is equal to the number of protons located in the nucleus of an atom, and at the same time the number of electrons rotating around the nucleus. As for the atomic weight, it is approximately equal to the mass number of the atom, i.e., the number of protons and neutrons combined in the nucleus. Therefore, by subtracting from the atomic weight of an element a number equal to the atomic number of the element, one can determine how many neutrons are contained in a given nucleus.
It has been established that the nuclei of light chemical elements, which contain equal parts of protons and neutrons, are distinguished by very high strength, since the nuclear forces in them are relatively large. For example, the nucleus of a heavy helium atom is extremely strong because it is made up of two protons and two neutrons bound together by powerful nuclear forces.
The nuclei of atoms of heavier chemical elements contain an unequal number of protons and neutrons, so their bond in the nucleus is weaker than in the nuclei of light chemical elements. The nuclei of these elements can be relatively easily split when bombarded with atomic “projectiles” (neutrons, helium nuclei, etc.).
As for the heaviest chemical elements, in particular radioactive ones, their nuclei are so weak that they spontaneously disintegrate into their component parts. For example, atoms of the radioactive element radium, consisting of a combination of 88 protons and 138 neutrons, spontaneously decay, turning into atoms of the radioactive element radon. The atoms of the latter, in turn, disintegrate into their component parts, turning into atoms of other elements.
Having briefly familiarized ourselves with the components of the nuclei of atoms of chemical elements, let us consider the structure of the electronic shells of atoms. As is known, electrons can rotate around atomic nuclei only in strictly defined orbits. Moreover, they are so grouped in the electron shell of each atom that individual layers of electrons can be distinguished.
Each layer can contain a number of electrons that does not exceed a strictly defined number. So, for example, in the first electron layer closest to the nucleus of an atom there can be a maximum of two electrons, in the second - no more than eight electrons, etc.
Those atoms whose outer electron layers are completely filled have the most stable electron shell. This means that this atom firmly holds all its electrons and does not need to receive an additional amount from the outside. For example, a helium atom has two electrons that completely fill the first electron layer, and a neon atom has ten electrons, of which the first two completely fill the first electron layer, and the rest - the second (Fig. 5).
Rice. 5. Scheme of the structure of the neon atom
Consequently, helium and neon atoms have completely stable electronic shells and do not strive to somehow modify them quantitatively. Such elements are chemically inert, that is, they do not interact chemically with other elements.
However, most chemical elements have atoms in which the outer electron layers are not entirely filled with electrons. For example, a potassium atom has nineteen electrons, of which eighteen completely fill the first three layers, and the nineteenth electron is alone in the next, unfilled electron layer. The weak filling of the fourth electron layer with electrons leads to the fact that the nucleus of the atom very weakly holds the outermost electron, the nineteenth electron, and therefore the latter can be easily torn out of the atom. .
Or, for example, an oxygen atom has eight electrons, two of which completely fill the first layer, and the remaining six are located in the second layer. Thus, to completely complete the construction of the second electron layer in the oxygen atom, it only needs two electrons. Therefore, the oxygen atom not only firmly holds its six electrons in the second layer, but also has the ability to attract the two electrons it lacks to fill its second electron layer. He achieves this by chemically combining with atoms of elements whose outer electrons are weakly bound to their nuclei.
Chemical elements whose atoms do not have outer electron layers completely filled with electrons are, as a rule, chemically active, that is, they readily enter into chemical interactions.
So, electrons in the atoms of chemical elements are arranged in a strictly defined order, and any change in their spatial arrangement or quantity in the electron shell of the atom leads to a change in the physicochemical properties of the latter.
The equality of the number of electrons and protons in the atomic system is the reason that its total electric charge is zero. If the equality of the number of electrons and protons in the atomic system is violated, then the atom becomes an electrically charged system.
An atom in whose system the balance of opposite electric charges is disturbed due to the fact that it has lost some of its electrons or, conversely, acquired an excess amount of them, is called an ion.
On the contrary, if an atom gains some extra electrons, it becomes a negative ion. For example, a chlorine atom that has gained one extra electron turns into a singly charged negative chlorine ion Cl -. An oxygen atom that has received an extra two electrons turns into a doubly charged negative oxygen ion O, etc.
An atom that has turned into an ion becomes an electrically charged system in relation to the external environment. This means that the atom began to have an electric field, together with which it constitutes a single material system and through this field it carries out electrical interaction with other electrically charged particles of matter - ions, electrons, positively charged atomic nuclei, etc.
The ability of unlike ions to be mutually attracted to each other is the reason that they chemically combine, forming more complex particles of matter - molecules.
In conclusion, it should be noted that the dimensions of an atom are very large compared to the dimensions of the material particles of which they are composed. The nucleus of the most complex atom, together with all the electrons, occupies a billionth of the volume of the atom. A simple calculation shows that if one cubic meter of platinum could be compressed so tightly that the intraatomic and interatomic spaces disappeared, then the volume would be equal to approximately one cubic millimeter.
First of all, it is necessary to understand that there are four separate types of energy released:
1) chemical energy that powers our cars, as well as most of the devices of modern civilization;
2) nuclear fission energy, used to generate about 15% of the electricity we consume;
3) the energy of hot nuclear fusion, which powers the sun and most stars;
4) cold nuclear fusion energy, which is observed by some experimenters in laboratory studies and the existence of which is rejected by most scientists.
The amount of nuclear energy released (heat/lb of fuel) of all three types is 10 million times greater than that of chemical energy. How are these types of energy different? In order to understand this issue, some knowledge of chemistry and physics is required.
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Nature has given us two types of stably charged particles: protons and electrons. A proton is a heavy, usually very small, positively charged particle. The electron is usually light, large, with fuzzy boundaries and has a negative charge. Positive and negative charges attract each other, just as the north pole of a magnet attracts the south pole. If a magnet with its north pole is brought close to the south pole of another magnet, they will collide. The collision will release a small amount of energy in the form of heat, but it is too small to be easily measured. To separate the magnets, you will have to do work, that is, expend energy. It's about the same as lifting a stone back up a hill.
Rolling a stone down a hill produces a small amount of heat, but lifting the stone back up requires energy.
In the same way, the positive charge of a proton collides with the negative charge of an electron, they “stick together”, releasing energy. The result is a hydrogen atom, designated H. A hydrogen atom is nothing more than a fuzzy electron enveloping a small proton. If you knock an electron out of a hydrogen atom, you get a positively charged H+ ion, which is nothing more than the original proton. "Ion" is the name applied to an atom or molecule that has lost or gained one or more electrons and is therefore no longer neutral.
As you know, there is more than one type of atom in nature. We have oxygen atoms, nitrogen atoms, iron atoms, helium atoms and others. How are they all different? They all have different types of nuclei, and all nuclei contain different numbers of protons, which means they have different positive charges. The helium nucleus contains 2 protons, which means it has a charge of plus 2, and in order to neutralize the charge, 2 electrons are required. When 2 electrons “stick” to it, a helium atom is formed. The oxygen nucleus contains 8 protons and has a charge of 8. When 8 electrons “stick” to it, an oxygen atom is formed. A nitrogen atom has 7 electrons, an iron atom has about 26. However, the structure of all atoms is approximately the same: a small, positively charged nucleus located in a cloud of diffuse electrons. The difference in size between the nucleus and electrons is enormous.
The diameter of the Sun is only 100 times the diameter of the Earth. The diameter of the electron cloud in an atom is 100,000 times greater than the diameter of the nucleus. In order to get the difference in volumes, you need to cube these numbers.
Now we are ready to understand what chemical energy is. The atoms, being electrically neutral, can actually bond together, releasing more energy. In other words, they can connect into more stable configurations. The electrons already in the atom are trying to be distributed in such a way as to get as close as possible to the nucleus, but due to their diffuse nature they require a certain space. However, when they combine with electrons from another atom, they usually form a closer configuration, allowing them to move closer to the nuclei. For example, 2 hydrogen atoms can combine into a more compact configuration if each hydrogen atom gives up its electron to a cloud of 2 electrons, which is shared between two protons.
Thus, they form a group consisting of two electrons in a single cloud and two protons, separated from each other by space, but nevertheless located inside the cloud of electrons. As a result, a chemical reaction occurs that occurs with the release of heat: H + H => H G (The sign “=>” means “turns into” or “becomes”). The H2 configuration is a hydrogen molecule; when you buy a cylinder of hydrogen, you get nothing more than H molecules. Moreover, by combining, two H 2 electrons and 8 electrons of an O atom can form an even more compact configuration - a water molecule H O plus heat. In reality, a water molecule is a single cloud of electrons, inside of which there are three point nuclei. Such a molecule is the minimum energy configuration.
Thus, when we burn oil or coal, we redistribute electrons. This leads to the formation of more stable configurations of point nuclei inside electron clouds and is accompanied by the release of heat. This is the nature of chemical energy.
In the previous discussion we missed one point. Why do nuclei in nature initially contain two or more protons? Each proton has a positive charge, and when the distance between the positive charges is so small that it is comparable to the space surrounding the nucleus, they strongly repel each other. The repulsion of like charges is similar to the repulsion that occurs between the north poles of two magnets when they are tried to be connected incorrectly. There must be something that overcomes this repulsion, otherwise only hydrogen atoms would exist. Fortunately, we see that this is not the case.
There is another type of force that acts on the proton. This is nuclear power. Due to the fact that it is very large, the particles are firmly held almost on top of each other. In addition, there is a second type of heavy particle, which differs from the proton only in that it has neither a positive nor a negative charge. They are not repelled by the positive charge of the proton. These particles are called "neutrons" because they are electrically neutral. The peculiarity is that the unchanged state of particles is possible only inside the nucleus. Once the particle is outside the nucleus, within about 10 minutes it turns into a proton, an electron and a very light antineutrino. However, inside the core it can remain unchanged for as long as desired. Be that as it may, the neutron and proton are very strongly attracted to each other. Having approached a sufficient distance, they combine, forming a very strong pair, the so-called deuteron, which is designated D+. A single deuteron combines with a single electron to form an atom of heavy hydrogen, or deuterium, designated D.
The second nuclear reaction occurs when two deuterons interact. When two deuterons are forced to interact, they combine to form a particle that has a double charge. A group of two protons and two neutrons is even more stable than the proton-neutron group in a deuteron. The new particle, neutralized by 2 electrons, becomes the nucleus of a helium atom, which is designated He. In nature, there are also large groups that are the nuclei of carbon, nitrogen, oxygen, iron and other atoms. The existence of all these groups is possible due to the nuclear force that arises between particles when they interact with each other or share a total volume of space equal to the size of the nucleus.
We can now understand the nature of ordinary nuclear energy, which is actually nuclear fission energy. Throughout the early history of the universe, massive stars formed. When such massive stars exploded, many types of nuclei were formed and exploded again into space. Planets and stars, including the Sun, were formed from this mass.
It is possible that during the explosion all possible stable configurations of protons and neutrons appeared, as well as such practically stable groups as the uranium nucleus. There are actually three varieties of uranium atom nuclei: uranium-234, uranium-235 and uranium-238. These “isotopes” differ in the number of neutrons, however, they all contain 92 protons. The nuclei of any type of uranium atom can change into lower energy configurations by escaping helium nuclei, however, this process occurs so rarely that terrestrial uranium retains its properties for about 4 billion years.
However, there is another way to disrupt the configuration of the uranium nucleus. In general, groups of protons and neutrons are most stable if they contain about 60 proton-neutron pairs. The number of such pairs contained in the uranium nucleus is three times this figure. As a result, it tends to split into two parts, releasing a large amount of heat. However, nature does not allow it to separate. In order to do this, it first needs to move to a higher energy configuration. However, one type of uranium - uranium-235, designated 235 U - obtains the necessary energy by capturing a neutron. Having thus received the necessary energy, the nucleus decays, releasing a huge amount of energy and releasing additional neutrons. These additional neutrons can in turn split the uranium-235 nuclei, leading to a chain reaction.
This is exactly what happens in nuclear power plants, where heat from nuclear decay is used to boil water, create steam, and turn an electrical generator. (The disadvantage of this method is the release of radioactive waste, which must be safely disposed of.)
We are now ready to understand the essence of hot nuclear fusion. As discussed in Lesson 5, groupings of protons and neutrons are most stable when the number of protons and neutrons approximately matches the number in the nucleus of the iron atom. Just like uranium, which normally contains too many neutron-proton pairs, light elements such as hydrogen, helium, carbon, nitrogen and oxygen contain too few such pairs.
If the necessary conditions are created for these nuclei to interact, they will unite into more stable groups with the release of heat. This is how the synthesis process occurs. It occurs naturally in stars such as the Sun. In nature, compressed hydrogen becomes very hot, and after some time, a synthesis reaction occurs. If the process initially occurred with deuterons, which already contain doubled protons and neutrons, the reactions in stars would proceed relatively easily. The speed at which any particular type of atom moves within a cloud of similar atoms depends directly on temperature. The higher the temperature, the higher the speed, and the closer the atoms are to each other, making an instantaneous collision.
In stars, the temperature is high enough for electrons to escape from the core. Thus, we can say that in reality we are dealing with a mixed cloud of electrons and nuclei. At very high temperatures, the nuclei at the moment of collision are so close to each other that the nuclear force is activated, attracting them to each other. As a result, the nuclei can “stick together” and turn into a lower-energy group of protons and neutrons, releasing heat. Hot nuclear fusion is an attempt to carry out this process in a laboratory setting using deuterium and ternary hydrogen (the nucleus of which contains 1 proton and 2 neutrons) as a gas. Hot fusion requires maintaining gas temperatures of hundreds of millions of degrees, which can be achieved using a magnetic field, but only for 1-2 seconds. It is hoped that it will be possible to maintain the temperature of the gas for a longer period of time. As long as the temperature is high enough, a nuclear reaction occurs when nuclei collide.
The main form in which energy is released is the release of high-energy neutrons and protons. Protons are converted into heat very quickly. Neutron energy can also be converted into heat, however, after this the equipment becomes radioactive. Decontamination of equipment appears to be very difficult, so hot fusion is not suitable as a method for commercial energy production. In any case, hot fusion energy is a dream that has been around for at least 50 years. However, most scientists view hot fusion as the only way to produce fusion energy. The process of hot fusion produces less radiation than fission, it is an environmentally friendly and practically unlimited source of fuel on Earth (relative to modern energy consumption, it would be enough for many millions of years).
Finally, we come to the explanation of cold fusion. Cold fusion could be a simple and non-radioactive way to release fusion energy. During cold fusion, the protons and neutrons of one nucleus interact with the protons and neutrons of another in a completely different way.
At the same time, nuclear force helps them form a more stable configuration. For any nuclear reaction it is necessary that the reacting nuclei have a common volume of space. This requirement is called particle alignment. In hot fusion, the combination of particles occurs for a short time, when the repulsive force of two positive charges is overcome, and the nuclei collide. During cold fusion, the condition of particle fusion is achieved by forcing deuterium nuclei to behave as fuzzy particles, like electrons, rather than as tiny point particles. When light or heavy hydrogen is added to a heavy metal, each hydrogen "atom" occupies a position where it is surrounded on all sides by heavy metal atoms.
This form of hydrogen is called intermediate. The electrons of the hydrogen atoms, together with the intermediate hydrogen, become part of the mass of electrons in the metal. Each hydrogen nucleus oscillates like a pendulum as it passes through the metal's negatively charged cloud of electrons. Such vibration occurs even at very low temperatures, in accordance with the postulates of quantum mechanics. This kind of movement is called zero point movement. In this case, the nuclei become blurry objects, like electrons in an atom. However, such vagueness is not enough to allow one hydrogen nucleus to interact with another.
Another condition is necessary that two or more hydrogen nuclei have the same common space. Electric current carried by electrons in a metal behaves like a vibrating matter wave rather than like point particles. If electrons did not behave like waves in solids, neither transistors nor modern computers would exist today. An electron in the form of a wave is called a Bloch function electron. The secret of cold fusion is the need to obtain a deuteron of the Bloch function. In order for two or more deuterons to have a common volume of space, wave deuterons must be produced inside or on the surface of a solid. As soon as Bloch function deuterons are created, the nuclear force begins to act, and the protons and neutrons that make up the deuteron are reorganized into a more stable Bloch function helium configuration, which is accompanied by the release of heat.
To study cold fusion, an experimenter needs to force deuterons into a wave state and maintain them in this state. Cold fusion experiments demonstrating the release of excess heat prove that this is possible. However, no one still knows how to carry out such a process in the most reliable way. Using cold fusion promises to provide an energy resource that will last for millions of years, without the problems of global warming or radioactivity - which is why serious efforts should be made to study this phenomenon.
- 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 consisting of anything smaller in size). But to them later.
Surprisingly, protons and neutrons have almost the same mass - accurate to within a percentage:
- 0.93827 GeV/c 2 for the 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 called 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 discovered around 1933. It was realized almost immediately that protons and neutrons are so similar to each other. But the fact that they have a measurable size comparable to the size of a nucleus (about 100,000 times smaller in radius than an atom) was not known until 1954. That they consist of quarks, antiquarks and gluons was gradually understood from the mid-1960s to the mid-1970s. By the late 70s and early 80s, 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. Not to say that atoms are in principle simple, but at least one can say without thinking 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 is inside it?” that an atom is like an elegant minuet, and a nucleon is like a wild party.
The complexity of the proton and neutron appears to be genuine, and does not stem from incomplete knowledge of physics. We have equations used to describe quarks, antiquarks, and gluons, and the strong nuclear interactions that occur between them. These equations are called QCD, from quantum chromodynamics. The accuracy of the equations can be tested in a variety of ways, including measuring the number of particles produced at the Large Hadron Collider. By plugging the QCD equations into a computer and running calculations on the properties of protons and neutrons and other similar particles (collectively called "hadrons"), we obtain predictions of the properties of these particles that closely approximate observations made in the 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:
- Simple equations can have very complex solutions,
- Sometimes it is impossible to describe complex decisions 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, it will most likely not bring you satisfaction: 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 in until the last one. Each level raises questions that I can partially answer in the next one, 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 obtained in real experiments, to various influential theoretical arguments, and computer simulations.
First level of understanding
What are protons and neutrons made of?Rice. 1: an overly simplified version of protons, consisting of only two up quarks and one down quark, and neutrons, consisting of only two down quarks and one up quark
To simplify matters, many books, articles and websites indicate that protons consist of three quarks (two up quarks and one down quark) and draw something like Fig. 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. 1 may appear. 2, where gluons are drawn as springs or strings holding quarks. Neutrons are the same, only with one up quark and two down quarks.
Rice. 2: improvement fig. 1 due to the emphasis on the important role of the strong nuclear force, which holds quarks in the proton
This is not such a bad way to describe nucleons, since it emphasizes the important role of the strong nuclear force, which holds quarks in a proton at the expense of gluons (just as the photon, the particle that makes up light, is associated with the electromagnetic force). But this is 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 consists 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 as well) . 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 demonstrated this in Fig. 3. Neutrons are again the same, but with one up and two down quarks; The quark that changed its identity is indicated by an arrow.
Rice. 3: more realistic, although still imperfect, representation of protons and neutrons
These quarks, anti-quarks and gluons not only rush back and forth wildly, 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.
- The neutron has one up quark and two down quarks (plus something else).
- The “something else” of neutrons coincides with the “something else” of protons. That is, the nucleons have the same “something else”.
- 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 top quarks the electric charge is equal to 2/3 e (where e is the charge of a proton, -e is the charge of an electron),
- bottom 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, an antidown quark has a charge of +1/3e, so a down quark and a down quark will have a charge of –1/3 e +1/3 e = 0),
- the total electric charge of the proton is 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” is inside the nucleon,
- what is it doing there
- where does 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 are essentially a third of a nucleon - much like a proton or neutron is 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 light) with relatively weak interactions 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 the proton. But this 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 around in it at speeds close to light. These particles collide with each other, and in these collisions, some of them are annihilated and others are created in their place. Gluons have no mass, the masses of the top quarks are on the order of 0.004 GeV/c 2 , and the masses of the bottom quarks are on the order of 0.008 GeV/c 2 - hundreds of times less than a proton. Where the energy of the proton mass comes from is a complex question: part of it comes from the energy of the mass of quarks and antiquarks, part from the energy of motion of quarks, antiquarks and gluons, and part (possibly positive, perhaps negative) from the energy stored in the strong nuclear interaction, holding quarks, antiquarks and gluons together.
In a sense, Fig. 2 attempts to resolve the difference between Fig. 1 and fig. 3. It simplifies the figure. 3, removing many quark-antiquark pairs, which, in principle, can be called ephemeral, since they constantly appear 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 together. And it doesn't explain where the proton's mass comes from.
In Fig. 1 there is another drawback, in addition to the narrow frames of the proton and neutron. It does not explain some properties of other hadrons, for example, pion and rho meson. Fig. has the same problems. 2.
These restrictions led to the fact that I give my students and on my website the picture from Fig. 3. But I want to warn you that it also has many limitations, which I will discuss later.
It is worth noting that the extreme complexity of the structure implied by Fig. 3 would be expected from an object held together by a force as powerful as 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 quark-antiquark pairs 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 a proton, and look at a particular quark, you could immediately tell whether it was part of the sea or a valence one. This cannot be done, there is simply no such way.
Proton mass and neutron mass
Since the masses of the proton and neutron are so similar, and since the proton and neutron differ only in the replacement of the up quark by the down quark, it seems likely that their masses are provided in the same way, come from the same source, and their difference lies in the slight difference between the up and down quarks . But the three figures above indicate the presence of three very different views on the origin of the proton mass.Rice. 1 says that the up and down quarks simply make up 1/3 of the mass of the proton and neutron: on the order of 0.313 GeV/c 2, or because of the energy required to hold 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. How much of a proton's mass is due to gluons? But, in principle, it follows from the figure that most of the proton mass still comes from the mass of quarks, as in Fig. 1.
Rice. 3 reflects a more nuanced approach to how the proton's mass actually comes about (as we can test directly through computer calculations of the proton, and indirectly using other mathematical methods). It is very different from the ideas presented in Fig. 1 and 2, and it turns out not so simple.
To understand how this works, you need to 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. Conceptually, the correct question is not “where does the mass of the proton m come from,” after which you can calculate E by multiplying m by c 2 , but vice versa: “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) 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) 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 high speed, and that it is full of massless gluons, so the contribution of B) is greater than A). Typically, in most physical systems B) and C) turn out to be comparable, while C) is often negative. So the mass energy of the proton (and neutron) mainly comes 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 they contain, 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 familiar to us, the energy balance is distributed differently. For example, in atoms and in the solar system A) dominates, and B) and C) are much smaller and comparable in magnitude.
To summarize, we point out that:
- Rice. 1 assumes that the proton mass energy comes from contribution A).
- Rice. 2 assumes that both contributions A) and B) are important, with B) making a small contribution.
- Rice. 3 suggests that B) and C) are important, and the contribution of A) turns out to be insignificant.
If fig. 3 does not lie, 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 the up quark is difficult to measure and varies due to subtle effects, so it may be much less than 0.005 GeV/c2). The mass of the bottom quark is approximately 0.004 GeV/s 2 greater than the mass of the top quark. 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 down quark to up quark mass does not approach unity! The mass of the down quark is at least twice the mass of the up quark. The reason that the masses of the neutron and proton are so similar is not because the masses of the up and down quarks are similar, but because 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. Remember that to turn a proton into a neutron, you simply need to replace one of its up quarks with a down quark (Figure 3). This replacement 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 the various particles inside the proton collide with each other, and are constantly appearing and disappearing, does not affect the things we are discussing - energy is conserved in any collision. The mass energy and energy of motion of quarks and gluons can change, as can 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 the 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 strong nuclear interactions that hold the nucleon in its entire state. Yes: our planet, our bodies, our breath are the result of such quiet, and, until recently, unimaginable pandemonium.
Aktobe, 2014
Hadron. A class of elementary particles participating in the strong interaction. Hadrons consist of quarks and are divided into two groups: baryons (from three quarks) and mesons (from a quark and an antiquark). Most of the matter we observe consists of baryons: protons and nucleons that are part of the nuclei of atoms.
Radioactive source activity- the ratio of the total number of decays of radioactive nuclei in a radioactive source to the decay time.
Alpha radiation- a type of ionizing radiation - a stream of positively charged particles (alpha particles) emitted during radioactive decay and nuclear reactions. The penetrating power of alpha radiation is low (it is blocked by a sheet of paper). It is extremely dangerous for sources of alpha radiation to enter the body through food, air, or through damaged skin.
Alpha decay(or α-decay) - spontaneous emission of alpha particles (helium atom nuclei) by atomic nuclei
Alpha particle- a particle consisting of two protons and two neutrons. Identical to the nucleus of a helium atom.
Annihilation- the interaction of an elementary particle and an antiparticle, as a result of which they disappear, and their energy is converted into electromagnetic radiation.
Annihilation is the reaction of a particle and antiparticle transforming into other particles upon collision.
Antiparticle is a particle that has the same values of mass, spin, charge and other physical properties as its “twin” particle, but differs from it in the signs of some interaction characteristics (for example, the sign of the electric charge).
Antiparticles are twins of ordinary elementary particles, which differ from the latter in the sign of their electric charge and the signs of some other characteristics. The particle and antiparticle have the same masses, spins, and lifetimes.
AC- nuclear power plant - an industrial enterprise for the production of electrical or thermal energy using one or more nuclear power reactors and a set of necessary systems, devices, equipment and structures with the necessary personnel,
Atom- the smallest particle of a chemical element that retains its properties. Consists of a nucleus with protons and neutrons and electrons moving around the nucleus. The number of electrons in an atom is equal to the number of protons in the nucleus.
Atomic mass- the mass of an atom of a chemical element, expressed in atomic mass units (amu). For 1 amu 1/12 of the mass of the carbon isotope with atomic mass 12 is accepted. 1 amu = 1.6605655·10-27 kg. Atomic mass is the sum of the masses of all the protons and neutrons in a given atom.
Atomic nucleus- the positively charged central part of the atom, around which electrons rotate and in which almost the entire mass of the atom is concentrated. Consists of protons and neutrons. The nuclear charge is determined by the total charge of the protons in the nucleus and corresponds to the atomic number of the chemical element in the periodic table of elements.
Baryons– particles consisting of three quarks, which determine their quantum numbers. All baryons, with the exception of the proton, are unstable.
Storage pool- an installation located at the reactor site of a nuclear power plant for the temporary storage of spent nuclear fuel under a layer of water in order to reduce radioactivity and decay heat.
Becquerel(Bq) is the SI unit of activity of a radioactive substance. 1 Bq is equal to the activity of a radioactive substance in which one decay event occurs in 1 s.
β γ rays- flow of fast electrons.
α-rays- flow of helium nuclei.
γ-rays- electromagnetic waves with a very short wavelength (L ~ 10 -10 m).
Beta radiation- a type of ionizing radiation - a flow of electrons or positrons emitted during nuclear reactions or radioactive decay. Beta radiation can penetrate body tissues to a depth of 1 cm. It poses a danger to humans from both the point of view of external and internal exposure.
Beta particles– electrons and positrons emitted by atomic nuclei, as well as a free neutron during beta decay. During the electronic beta decay of an atomic nucleus, an electron e - (as well as an antineutrino) is emitted; during the positron decay of nuclei, a positron e + (and a neutrino ν) is emitted. The decay of a free neutron (n) produces a proton (p), an electron and an antineutrino: n → p + e - + .
Electron and positron– stable particles with spin J = 1/2 (internal mechanical angular momentum), belonging to the class of leptons. A positron is an antiparticle to an electron.
Biological protection- a radiation barrier created around the reactor core and its cooling system to prevent the harmful effects of neutron and gamma radiation on personnel, the public and the environment. At a nuclear power plant, the main material for biological protection is concrete. For high-power reactors, the thickness of the concrete protective screen reaches several meters.
Bosons(from the name of the Indian physicist S. Bose) – elementary particles, atomic nuclei, atoms with zero or integer spin (0ћ, 1ћ, 2ћ, …).
Fast neutrons- neutrons whose kinetic energy is higher than a certain certain value. This value can vary over a wide range and depends on the application (reactor physics, protection or dosimetry). In reactor physics, this value is most often chosen to be 0.1 MeV.
Wilson chamber– a track detector of elementary charged particles, in which the track (trace) of a particle is formed by a chain of small droplets of liquid along the trajectory of its movement.
Gamma radiation- a type of ionizing radiation - electromagnetic radiation emitted during radioactive decay and nuclear reactions, propagating at the speed of light and having high energy and penetrating ability. Effectively weakened when interacting with heavy elements, such as lead. To attenuate gamma radiation in nuclear reactors at nuclear power plants, a thick-walled protective screen made of concrete is used.
Law of Radioactive Decay- the law by which the number of undecayed atoms is found: N = N 0 2 -t/T.
Deuterium- “heavy” isotope of hydrogen with atomic mass 2.
Ionizing radiation detector- a sensitive element of a measuring instrument designed to register ionizing radiation. Its action is based on phenomena that occur when radiation passes through matter.
Radiation dose- in radiation safety - a measure of the impact of ionizing radiation on a biological object, in particular a person. There are exposure, absorbed and equivalent doses.
Excess mass(or mass defect) – expressed in energy units, the difference between the mass of a neutral atom and the product of the number of nucleons (the total number of protons and neutrons) in the nucleus of this atom per atomic mass unit
Isotopes- nuclides that have the same atomic number but different atomic masses (for example, uranium-235 and uranium-238).
Isotopes– atomic nuclei having the same number of protons Z, a different number of neutrons N and, therefore, a different mass number A = Z + N. Example: isotopes of calcium Ca (Z = 20) - 38 Ca, 39 Ca, 40 Ca, 41 Ca, 42 Ca.
Radioactive isotopes are isotope nuclei that undergo radioactive decay. Most known isotopes are radioactive (~3500).
Wilson chamber- a device for observing traces of microparticles moving at high speed (electrons, protons, alpha particles, etc.). Created in 1912 by the English physicist Wilson.
A quark is an elementary charged particle participating in the strong interaction. Protons and neutrons each consist of three quarks.
Cosmic radiation- background ionizing radiation, which consists of primary radiation coming from outer space and secondary radiation resulting from the interaction of primary radiation with the atmosphere.
Cosmic rays are streams of charged elementary particles of high energy (mainly protons, alpha particles and electrons) propagating in interplanetary and interstellar space and continuously “bombarding” the Earth.
Reproduction rate- the most important characteristic of a fission chain reaction, showing the ratio of the number of neutrons of a given generation to the number of neutrons of the previous generation in an infinite environment. Another definition of the multiplication factor is often used - the ratio of the rates of generation and absorption of neutrons.
Critical mass- the smallest mass of fuel in which a self-sustaining nuclear fission chain reaction can occur given a certain design and composition of the core (depends on many factors, for example: fuel composition, moderator, core shape, etc.).
Curie (Ci)- extrasystemic unit of activity, initially the activity of 1 g of the radium-226 isotope. 1Ci=3.7·1010 Bq.
Critical mass(tk) - the smallest mass of nuclear fuel (uranium, plutonium) at which a nuclear chain reaction occurs.
Curie(Ci) is an off-system unit of activity of a radioactive substance. 1 Ci = 3.7 10 10 Bq.
Leptons(from the Greek leptos - light, small) - a group of point particles with a spin of 1/2ћ that do not participate in strong interactions. Lepton size (if it exists)<10 -17 см. Лептоны считаются точечными бесструктурными частицами. Существует три пары лептонов:
- electron (e –) and electron neutrino (ν e),
- muon (μ –) and muon neutrino (ν μ),
- tau lepton (τ –) and tau neutrino (ν τ),
Magic nuclei are atomic nuclei containing the so-called magic numbers of protons or neutrons.
| Z | |||||||
| N |
These nuclei have a binding energy greater than neighboring nuclei. They have a higher nucleon separation energy and are more common in nature.
Mass number(A) - the total number of nucleons (protons and neutrons) in the atomic nucleus; one of the main characteristics of the atomic nucleus.
Dose rate- the ratio of the increment in radiation dose over a time interval to this interval (for example: rem/s, Sv/s, mrem/h, mSv/h, μrem/h, μSv/h).
Neutron- a neutral elementary particle with a mass close to the mass of a proton. Together with protons, neutrons form the atomic nucleus. In the free state it is unstable and decays into a proton and an electron.
Nuclide- a type of atom with a certain number of protons and neutrons in the nucleus, characterized by atomic mass and atomic (ordinal) number.
Enrichment (by isotope):
2. A process that results in an increase in the content of a particular isotope in a mixture of isotopes.
Uranium ore enrichment- a set of processes for the primary processing of mineral uranium-containing raw materials, with the goal of separating uranium from other minerals that make up the ore. In this case, there is no change in the composition of the minerals, but only their mechanical separation to produce ore concentrate.
Enriched nuclear fuel- nuclear fuel, in which the content of fissile nuclides is greater than in the original natural raw materials.
Enriched uranium- uranium, in which the content of the uranium-235 isotope is higher than in natural uranium.
Half life(T) is the time interval during which half of the original number of nuclei will decay.
Half life– the time during which half of the radioactive nuclei decay. This quantity, denoted T 1/2, is a constant for a given radioactive nucleus (isotope). The value T 1/2 clearly characterizes the rate of decay of radioactive nuclei and is equivalent to two other constants characterizing this rate: the average lifetime of a radioactive nucleus τ and the probability of decay of a radioactive nucleus per unit time λ.
Absorbed radiation dose- the ratio of the absorbed energy E of ionizing radiation to the mass of the substance irradiated by it.
Bohr's postulates- basic assumptions introduced without proof by N. Bohr, which form the basis of the quantum theory of the atom.
Offset rule: during a-decay, the nucleus loses its positive charge 2e, and its mass decreases by approximately 4 amu; During b-decay, the charge of the nucleus increases by 1e, but the mass does not change.
Half-life of a radionuclide- the time during which the number of nuclei of a given radionuclide as a result of spontaneous decay will decrease by half.
Positron- an antiparticle of an electron with a mass equal to the mass of the electron, but a positive electric charge.
Proton- a stable positively charged elementary particle with a charge of 1.61·10-19 C and a mass of 1.66·10-27 kg. The proton forms the nucleus of a “light” isotope of the hydrogen atom (protium). The number of protons in the nucleus of any element determines the charge of the nucleus and the atomic number of that element.
Radioactivity- spontaneous transformation (radioactive decay) of an unstable nuclide into another nuclide, accompanied by the emission of ionizing radiation.
Radioactivity- the ability of some atomic nuclei to spontaneously transform into other nuclei, emitting various particles.
Radioactive decay- spontaneous nuclear transformation.
Breeder reactor- a fast reactor in which the conversion factor exceeds 1 and expanded reproduction of nuclear fuel is carried out.
Geiger counter(or Geiger-Muller counter) is a gas-filled counter of charged elementary particles, the electrical signal from which is amplified due to the secondary ionization of the gas volume of the counter and does not depend on the energy left by the particle in this volume.
Fuel element- fuel element. The main structural element of the core of a heterogeneous reactor, in the form of which fuel is loaded into it. In fuel elements, heavy nuclei U-235, Pu-239 or U-233 fission occurs, accompanied by the release of energy, and thermal energy is transferred from them to the coolant. Fuel elements consist of a fuel core, cladding and end parts. The type of fuel element is determined by the type and purpose of the reactor, and the parameters of the coolant. The fuel element must ensure reliable heat removal from the fuel to the coolant.
Working body- medium (coolant) used to convert thermal energy into mechanical energy.
Dark matter− invisible (non-emitting and non-absorbing) substance. Its existence is definitely evidenced by gravitational effects. Observational data also suggests that this dark matter-energy is divided into two parts:
- the first is the so-called dark matter with a density
W dm = 0.20–0.25, – unknown, weakly interacting massive particles (not baryons). These could be, for example, stable neutral particles with masses from 10 GeV/c2 to 10 TeV/c2, predicted by supersymmetric models, including hypothetical heavy neutrinos;
the second is the so-called dark energy with a density
W Λ = 0.70–0.75), which is interpreted as vacuum. This refers to a special form of matter - physical vacuum, i.e. the lowest energy state of physical fields that permeate space.
Thermonuclear reactions− reactions of fusion (synthesis) of light nuclei occurring at high temperatures. These reactions usually involve the release of energy, since in the heavier nucleus formed as a result of the merger the nucleons are more strongly bound, i.e. have, on average, a higher binding energy than in the original merging nuclei. The excess total binding energy of nucleons is released in the form of kinetic energy of reaction products. The name “thermonuclear reactions” reflects the fact that these reactions occur at high temperatures ( > 10 7 –10 8 K), since for fusion light nuclei must come together to distances equal to the radius of action of nuclear attractive forces, i.e. up to distances of ≈10 -13 cm.
Transuranic elements− chemical elements with a charge (number of protons) greater than that of uranium, i.e. Z>92.
Fission chain reaction- a self-sustaining fission reaction of heavy nuclei, in which neutrons are continuously produced, dividing more and more new nuclei.
Fission chain reaction- the sequence of the fission reaction of the nuclei of heavy atoms when they interact with neutrons or other elementary particles, as a result of which lighter nuclei, new neutrons or other elementary particles are formed and nuclear energy is released.
Nuclear chain reaction- a sequence of nuclear reactions excited by particles (for example, neutrons) born in each reaction event. Depending on the average number of reactions following one previous one - less than, equal to or greater than one - the reaction is called decaying, self-sustaining or increasing.
Nuclear chain reactions– self-sustaining nuclear reactions in which a chain of nuclei is sequentially involved. This occurs when one of the products of a nuclear reaction reacts with another nucleus, the product of a second reaction reacts with the next nucleus, and so on. A chain of nuclear reactions follows one after another occurs. The most famous example of such a reaction is the nuclear fission reaction caused by a neutron
Exothermic reactions- nuclear reactions that occur with the release of energy.
Elementary particles- the smallest particles of physical matter. Ideas about elementary particles reflect the stage in knowledge of the structure of matter that has been achieved by modern science. Along with antiparticles, about 300 elementary particles have been discovered. The term "elementary particles" is conditional, since many elementary particles have a complex internal structure.
Elementary particles– material objects that cannot be divided into their component parts. In accordance with this definition, molecules, atoms and atomic nuclei that can be divided into component parts cannot be classified as elementary particles - an atom is divided into a nucleus and orbital electrons, a nucleus into nucleons.
Energy output of a nuclear reaction- the difference between the rest energies of nuclei and particles before and after the reaction.
Endothermic reactions- nuclear reactions that occur with the absorption of energy.
Binding energy of an atomic nucleus(E St) - characterizes the intensity of the interaction of nucleons in the nucleus and is equal to the maximum energy that must be expended in order to divide the nucleus into individual non-interacting nucleons without imparting kinetic energy to them.
Mössb effect uaera - the phenomenon of resonant absorption of gamma quanta by atomic nuclei without loss of energy due to momentum return.
Nuclear (planetary) model of the atom- in the center there is a positively charged nucleus (diameter about 10 -15 m); around the core, like the planets of the solar system, electrons move in circular orbits.
Nuclear models– simplified theoretical descriptions of atomic nuclei, based on the representation of the nucleus as an object with previously known characteristic properties.
Nuclear fission reaction- reaction of fission of atomic nuclei of heavy elements under the influence of neutrons.
Nuclear reaction- the reaction of transformation of atomic nuclei as a result of interaction with each other or with any elementary particles.
Nuclear power- this is the energy released as a result of the internal restructuring of atomic nuclei. Nuclear energy can be obtained from nuclear reactions or radioactive decay of nuclei. The main sources of nuclear energy are fission reactions of heavy nuclei and fusion (combination) of light nuclei. The latter process is also called thermonuclear reactions.
Nuclear forces- forces acting between nucleons in atomic nuclei and determining the structure and properties of nuclei. They are short-range, their range is 10 -15 m.
Nuclear reactor- a device in which a controlled chain reaction of nuclear fission is carried out.
A self-sustaining fission chain reaction is a chain reaction in a medium for which the multiplication factor k >= 1.
Nuclear accident- a nuclear accident is the loss of control of the chain reaction in the reactor, or the formation of a critical mass during reloading, transportation and storage of fuel elements. As a result of a nuclear accident, due to an imbalance of generated and removed heat, fuel rods are damaged with the release of radioactive fission products. In this case, dangerous exposure of people and contamination of the surrounding area becomes potentially possible. .
Nuclear safety- a general term that characterizes the properties of a nuclear installation during normal operation and in the event of an accident to limit the radiation impact on personnel, the public and the environment to acceptable limits.
Nuclear fission- a process accompanied by the splitting of the nucleus of a heavy atom when interacting with a neutron or other elementary particle, as a result of which lighter nuclei, new neutrons or other elementary particles are formed and energy is released.
Nuclear material- any source material, special nuclear material and sometimes ores and ore waste.
Nuclear transformation- transformation of one nuclide into another.
Nuclear reactor- a device in which a controlled nuclear chain reaction occurs. Nuclear reactors are classified by purpose, neutron energy, type of coolant and moderator, core structure, design and other characteristic features.
Nuclear reaction- transformation of atomic nuclei caused by their interaction with elementary particles, or with each other and accompanied by a change in the mass, charge or energy state of the nuclei.
Nuclear fuel- material containing fissile nuclides, which, when placed in a nuclear reactor, allows a nuclear chain reaction to occur. It has a very high energy intensity (with the complete fission of 1 kg of U-235, energy equal to J is released, while the combustion of 1 kg of organic fuel releases energy of the order of (3-5) J, depending on the type of fuel).
Nuclear fuel cycle- a set of measures to ensure the functioning of nuclear reactors carried out in a system of enterprises interconnected by the flow of nuclear material and including uranium mines, plants for processing uranium ore, uranium conversion, enrichment and fuel production, nuclear reactors, spent fuel storage facilities, spent fuel reprocessing plants fuels and associated intermediate storage facilities and radioactive waste disposal facilities
Nuclear installation- any facility at which radioactive or fissile materials are generated, processed or handled in such quantities that it is necessary to take into account nuclear safety issues.
Nuclear power- internal energy of atomic nuclei released during nuclear fission or nuclear reactions.
Nuclear power reactor- a nuclear reactor whose main purpose is to generate energy.
Nuclear reactor- a nuclear reactor is a device designed to organize a controlled self-sustaining fission chain reaction - a sequence of nuclear fission reactions in which free neutrons are released, necessary for the fission of new nuclei.
Fast neutron nuclear reactor- reactors differ significantly in the spectrum of neutrons - the distribution of neutrons by energy, and, consequently, in the spectrum of absorbed (causing nuclear fission) neutrons. If the core does not contain light nuclei specifically designed for moderation as a result of elastic scattering, then almost all moderation is due to inelastic scattering of neutrons by heavy and medium-mass nuclei. In this case, most fissions are caused by neutrons with energies of the order of tens and hundreds of keV. Such reactors are called fast neutron reactors.
Thermal neutron nuclear reactor- a reactor whose core contains such an amount of moderator - a material designed to reduce the energy of neutrons without appreciably absorbing them - that most fissions are caused by neutrons with energies less than 1 eV.
Nuclear forces- forces that hold nucleons (protons and neutrons) in the nucleus.
Nuclear forces are short-acting . They appear only at very small distances between nucleons in the nucleus of the order of 10 -15 m. The length (1.5 - 2.2) 10 -15 is called range of nuclear forces .
Nuclear forces discover charge independence , i.e., the attraction between two nucleons is the same regardless of the charge state of the nucleons - proton or neutron.
Nuclear forces have saturation property , which manifests itself in the fact that a nucleon in a nucleus interacts only with a limited number of neighboring nucleons closest to it. Almost complete saturation of nuclear forces is achieved in the α-particle, which is a very stable formation.
Nuclear forces depend on the orientation of the spins of interacting nucleons . This is confirmed by the different nature of neutron scattering by ortho- and hydrogen vapor molecules.
Nuclear forces are not central forces .
By studying the structure of matter, physicists found out what atoms are made of, got to the atomic nucleus and split it into protons and neutrons. All these steps were given quite easily - you just had to accelerate the particles to the required energy, push them against each other, and then they themselves would fall apart into their component parts.
But with protons and neutrons this trick no longer worked. Although they are composite particles, they cannot be “broken into pieces” in even the most violent collision. Therefore, it took physicists decades to come up with different ways to look inside the proton, see its structure and shape. Today, the study of the structure of the proton is one of the most active areas of particle physics.
Nature gives hints
The history of studying the structure of protons and neutrons dates back to the 1930s. When, in addition to protons, neutrons were discovered (1932), having measured their mass, physicists were surprised to find that it was very close to the mass of a proton. Moreover, it turned out that protons and neutrons “feel” nuclear interaction in exactly the same way. So identical that, from the point of view of nuclear forces, a proton and a neutron can be considered as two manifestations of the same particle - a nucleon: a proton is an electrically charged nucleon, and a neutron is a neutral nucleon. Swap protons for neutrons and nuclear forces will (almost) notice nothing.
Physicists express this property of nature as symmetry - nuclear interaction is symmetrical with respect to the replacement of protons with neutrons, just as a butterfly is symmetrical with respect to the replacement of left with right. This symmetry, in addition to playing an important role in nuclear physics, was actually the first hint that nucleons had an interesting internal structure. True, then, in the 30s, physicists did not realize this hint.
Understanding came later. It began with the fact that in the 1940–50s, in the reactions of collisions of protons with the nuclei of various elements, scientists were surprised to discover more and more new particles. Not protons, not neutrons, not the pi-mesons discovered by that time, which hold nucleons in nuclei, but some completely new particles. For all their diversity, these new particles had two common properties. Firstly, they, like nucleons, very willingly participated in nuclear interactions - now such particles are called hadrons. And secondly, they were extremely unstable. The most unstable of them decayed into other particles in just a trillionth of a nanosecond, not even having time to fly the size of an atomic nucleus!
For a long time, the hadron “zoo” was a complete mess. At the end of the 1950s, physicists had already learned quite a lot of different types of hadrons, began to compare them with each other, and suddenly saw a certain general symmetry, even periodicity, in their properties. It was suggested that inside all hadrons (including nucleons) there are some simple objects called “quarks”. By combining quarks in different ways, it is possible to obtain different hadrons, and of exactly the same type and with the same properties that were discovered in the experiment.
What makes a proton a proton?
After physicists discovered the quark structure of hadrons and learned that quarks come in several different varieties, it became clear that many different particles could be constructed from quarks. So no one was surprised when subsequent experiments continued to find new hadrons one after another. But among all the hadrons, a whole family of particles was discovered, consisting, just like the proton, of only two u-quarks and one d-quark. A sort of “brother” of the proton. And here the physicists were in for a surprise.
Let's first make one simple observation. If we have several objects consisting of the same “bricks”, then heavier objects contain more “bricks”, and lighter ones contain fewer. This is a very natural principle, which can be called the principle of combination or the principle of superstructure, and it works perfectly both in everyday life and in physics. It even manifests itself in the structure of atomic nuclei - after all, heavier nuclei simply consist of a larger number of protons and neutrons.
However, at the level of quarks this principle does not work at all, and, admittedly, physicists have not yet fully figured out why. It turns out that the heavy brothers of the proton also consist of the same quarks as the proton, although they are one and a half or even two times heavier than the proton. They differ from the proton (and differ from each other) not composition, and mutual location quarks, by the state in which these quarks are relative to each other. It is enough to change the relative position of the quarks - and from the proton we will get another, noticeably heavier, particle.
What will happen if you still take and collect more than three quarks together? Will there be a new heavy particle? Surprisingly, it won’t work - the quarks will break up in threes and turn into several scattered particles. For some reason, nature “does not like” combining many quarks into one whole! Only very recently, literally in recent years, hints began to appear that some multi-quark particles do exist, but this only emphasizes how much nature does not like them.
A very important and deep conclusion follows from this combinatorics - the mass of hadrons does not at all consist of the mass of quarks. But if the mass of a hadron can be increased or decreased by simply recombining its constituent bricks, then it is not the quarks themselves that are responsible for the mass of hadrons. And indeed, in subsequent experiments it was possible to find out that the mass of the quarks themselves is only about two percent of the mass of the proton, and the rest of the gravity arises due to the force field (special particles - gluons) that bind the quarks together. By changing the relative position of quarks, for example, moving them further away from each other, we thereby change the gluon cloud, making it more massive, which is why the hadron mass increases (Fig. 1).
What's going on inside a fast-moving proton?
Everything described above concerns a stationary proton; in the language of physicists, this is the structure of the proton in its rest frame. However, in the experiment, the structure of the proton was first discovered under other conditions - inside fast flying proton.
In the late 1960s, in experiments on particle collisions at accelerators, it was noticed that protons traveling at near-light speed behaved as if the energy inside them was not distributed evenly, but was concentrated in individual compact objects. The famous physicist Richard Feynman proposed to call these clumps of matter inside protons partons(from English part - Part).
Subsequent experiments examined many of the properties of partons—for example, their electrical charge, their number, and the fraction of proton energy each carries. It turns out that charged partons are quarks, and neutral partons are gluons. Yes, those same gluons, which in the proton’s rest frame simply “served” the quarks, attracting them to each other, are now independent partons and, along with quarks, carry the “matter” and energy of a fast-moving proton. Experiments have shown that approximately half of the energy is stored in quarks, and half in gluons.
Partons are most conveniently studied in collisions of protons with electrons. The fact is that, unlike a proton, an electron does not participate in strong nuclear interactions and its collision with a proton looks very simple: the electron emits a virtual photon for a very short time, which crashes into a charged parton and ultimately generates a large number of particles ( Fig. 2). We can say that the electron is an excellent scalpel for “opening” the proton and dividing it into separate parts - however, only for a very short time. Knowing how often such processes occur at an accelerator, one can measure the number of partons inside a proton and their charges.
Who are the Partons really?
And here we come to another amazing discovery that physicists made while studying collisions of elementary particles at high energies.
Under normal conditions, the question of what this or that object consists of has a universal answer for all reference systems. For example, a water molecule consists of two hydrogen atoms and one oxygen atom - and it does not matter whether we are looking at a stationary or moving molecule. However, this rule seems so natural! - is violated if we are talking about elementary particles moving at speeds close to the speed of light. In one frame of reference, a complex particle may consist of one set of subparticles, and in another frame of reference, of another. It turns out that composition is a relative concept!
How can this be? The key here is one important property: the number of particles in our world is not fixed - particles can be born and disappear. For example, if you push together two electrons with a sufficiently high energy, then in addition to these two electrons, either a photon, or an electron-positron pair, or some other particles can be born. All this is allowed by quantum laws, and this is exactly what happens in real experiments.
But this “law of non-conservation” of particles works in case of collisions particles. How does it happen that the same proton from different points of view looks like it consists of a different set of particles? The point is that a proton is not just three quarks put together. There is a gluon force field between the quarks. In general, a force field (such as a gravitational or electric field) is a kind of material “entity” that permeates space and allows particles to exert a forceful influence on each other. In quantum theory, the field also consists of particles, albeit special ones - virtual ones. The number of these particles is not fixed; they are constantly “budding off” from quarks and being absorbed by other quarks.
Resting A proton can really be thought of as three quarks with gluons jumping between them. But if we look at the same proton from a different frame of reference, as if from the window of a “relativistic train” passing by, we will see a completely different picture. Those virtual gluons that glued the quarks together will seem less virtual, “more real” particles. They, of course, are still born and absorbed by quarks, but at the same time they live on their own for some time, flying next to the quarks, like real particles. What looks like a simple force field in one frame of reference turns into a stream of particles in another frame! Note that we do not touch the proton itself, but only look at it from a different frame of reference.
Further more. The closer the speed of our “relativistic train” is to the speed of light, the more amazing the picture we will see inside the proton. As we approach the speed of light, we will notice that there are more and more gluons inside the proton. Moreover, they sometimes split into quark-antiquark pairs, which also fly nearby and are also considered partons. As a result, an ultrarelativistic proton, i.e. a proton moving relative to us at a speed very close to the speed of light, appears in the form of interpenetrating clouds of quarks, antiquarks and gluons that fly together and seem to support each other (Fig. 3).
A reader familiar with the theory of relativity may be concerned. All physics is based on the principle that any process proceeds the same way in all inertial frames of reference. But it turns out that the composition of the proton depends on the frame of reference from which we observe it?!
Yes, exactly, but this in no way violates the principle of relativity. The results of physical processes - for example, which particles and how many are produced as a result of a collision - do turn out to be invariant, although the composition of the proton depends on the frame of reference.
This situation, unusual at first glance, but satisfying all the laws of physics, is schematically illustrated in Figure 4. It shows how the collision of two protons with high energy looks in different frames of reference: in the rest frame of one proton, in the frame of the center of mass, in the rest frame of another proton . The interaction between protons is carried out through a cascade of splitting gluons, but only in one case is this cascade considered the “inside” of one proton, in another case it is considered part of another proton, and in the third it is simply some object that is exchanged between two protons. This cascade exists, it is real, but to which part of the process it should be attributed depends on the frame of reference.
3D portrait of a proton
All the results that we just talked about were based on experiments performed quite a long time ago - in the 60–70s of the last century. It would seem that since then everything should have been studied and all questions should have found their answers. But no - the structure of the proton still remains one of the most interesting topics in particle physics. Moreover, in recent years, interest in it has increased again because physicists have figured out how to obtain a “three-dimensional” portrait of a fast-moving proton, which turned out to be much more difficult than a portrait of a stationary proton.
Classic experiments on proton collisions tell only about the number of partons and their energy distribution. In such experiments, partons participate as independent objects, which means that it is impossible to find out from them how the partons are located relative to each other, or how exactly they add up to a proton. We can say that for a long time only a “one-dimensional” portrait of a fast-moving proton was available to physicists.
In order to construct a real, three-dimensional portrait of a proton and find out the distribution of partons in space, much more subtle experiments are required than those that were possible 40 years ago. Physicists learned to carry out such experiments quite recently, literally in the last decade. They realized that among the huge number of different reactions that occur when an electron collides with a proton, there is one special reaction - deep virtual Compton scattering, - which can tell us about the three-dimensional structure of the proton.
In general, Compton scattering, or the Compton effect, is the elastic collision of a photon with a particle, for example a proton. It looks like this: a photon arrives, is absorbed by a proton, which goes into an excited state for a short time, and then returns to its original state, emitting a photon in some direction.
Compton scattering of ordinary light photons does not lead to anything interesting - it is simply the reflection of light from a proton. In order for the internal structure of the proton to “come into play” and the distribution of quarks to be “felt,” it is necessary to use photons of very high energy - billions of times more than in ordinary light. And just such photons - albeit virtual ones - are easily generated by an incident electron. If we now combine one with the other, we get deep virtual Compton scattering (Fig. 5).
The main feature of this reaction is that it does not destroy the proton. The incident photon does not just hit the proton, but, as it were, carefully feels it and then flies away. The direction in which it flies away and what part of the energy the proton takes from it depends on the structure of the proton, on the relative arrangement of the partons inside it. That is why, by studying this process, it is possible to restore the three-dimensional appearance of the proton, as if to “sculpt its sculpture.”
True, this is very difficult for an experimental physicist to do. The required process occurs quite rarely, and it is difficult to register it. The first experimental data on this reaction were obtained only in 2001 at the HERA accelerator at the German accelerator complex DESY in Hamburg; a new series of data is now being processed by experimenters. However, already today, based on the first data, theorists are drawing three-dimensional distributions of quarks and gluons in the proton. A physical quantity, about which physicists had previously only made assumptions, finally began to “emerge” from the experiment.
Are there any unexpected discoveries awaiting us in this area? It is likely that yes. To illustrate, let's say that in November 2008 an interesting theoretical article appeared, which states that a fast-moving proton should not look like a flat disk, but a biconcave lens. This happens because the partons sitting in the central region of the proton are compressed more strongly in the longitudinal direction than the partons sitting at the edges. It would be very interesting to test these theoretical predictions experimentally!
Why is all this interesting to physicists?
Why do physicists even need to know exactly how matter is distributed inside protons and neutrons?
Firstly, this is required by the very logic of the development of physics. There are many amazingly complex systems in the world that modern theoretical physics cannot yet fully cope with. Hadrons are one such system. By understanding the structure of hadrons, we are honing the abilities of theoretical physics, which may well turn out to be universal and, perhaps, will help in something completely different, for example, in the study of superconductors or other materials with unusual properties.
Secondly, there is direct benefit for nuclear physics. Despite the almost century-long history of studying atomic nuclei, theorists still do not know the exact law of interaction between protons and neutrons.
They have to partly guess this law based on experimental data, and partly construct it based on knowledge about the structure of nucleons. This is where new data on the three-dimensional structure of nucleons will help.
Thirdly, several years ago physicists were able to obtain no less than a new aggregate state of matter - quark-gluon plasma. In this state, quarks do not sit inside individual protons and neutrons, but walk freely throughout the entire clump of nuclear matter. This can be achieved, for example, like this: heavy nuclei are accelerated in an accelerator to a speed very close to the speed of light, and then collide head-on. In this collision, temperatures of trillions of degrees arise for a very short time, which melts the nuclei into quark-gluon plasma. So, it turns out that theoretical calculations of this nuclear melting require a good knowledge of the three-dimensional structure of nucleons.
Finally, these data are very necessary for astrophysics. When heavy stars explode at the end of their lives, they often leave behind extremely compact objects - neutron and possibly quark stars. The core of these stars consists entirely of neutrons, and maybe even cold quark-gluon plasma. Such stars have long been discovered, but one can only guess what is happening inside them. So a good understanding of quark distributions can lead to progress in astrophysics.