What happens if two subatomic particles collide. Subatomic particles

And nuclear physics.

Subatomic particles are the atomic constituents: electron, neutron and proton. The proton and neutron in turn consist of quarks.

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“Bien faite et la beaute du diable, [Well-built and the beauty of youth," this man said, and when he saw Rostov he stopped talking and frowned.
-What do you want? Request?…
– Qu"est ce que c"est? [What is this?] - someone asked from another room.
“Encore un petitionnaire, [Another petitioner,”] answered the man with the help.
- Tell him what's next. It's coming out now, we have to go.
- After the day after tomorrow. Late…
Rostov turned and wanted to go out, but the man in the arms stopped him.
- From whom? Who are you?
“From Major Denisov,” Rostov answered.
- Who are you? Officer?
- Lieutenant, Count Rostov.
- What courage! Give it on command. And go, go... - And he began to put on the uniform handed to him by the valet.
Rostov went out again into the hallway and noticed that there were already many officers and generals on the porch in full dress uniform, whom he had to pass by.
Cursing his courage, frozen by the thought that at any moment he could meet the sovereign and in his presence be disgraced and sent under arrest, fully understanding the indecency of his act and repenting of it, Rostov, with downcast eyes, made his way out of the house, surrounded by a crowd of brilliant retinue , when someone's familiar voice called out to him and someone's hand stopped him.
- What are you doing here, father, in a tailcoat? – his bass voice asked.
This was a cavalry general who earned the special favor of the sovereign during this campaign, the former head of the division in which Rostov served.
Rostov fearfully began to make excuses, but seeing the good-naturedly playful face of the general, he moved to the side and in an excited voice conveyed the whole matter to him, asking him to intercede for Denisov, known to the general. The general, after listening to Rostov, seriously shook his head.
- It’s a pity, it’s a pity for the fellow; give me a letter.
Rostov barely had time to hand over the letter and tell Denisov’s whole business when quick steps with spurs began to sound from the stairs and the general, moving away from him, moved towards the porch. The gentlemen of the sovereign's retinue ran down the stairs and went to the horses. Bereitor Ene, the same one who was in Austerlitz, brought the sovereign's horse, and a light creaking of steps was heard on the stairs, which Rostov now recognized. Forgetting the danger of being recognized, Rostov moved with several curious residents to the porch itself and again, after two years, he saw the same features he adored, the same face, the same look, the same gait, the same combination of greatness and meekness... And the feeling of delight and love for the sovereign was resurrected with the same strength in Rostov’s soul. The Emperor in the Preobrazhensky uniform, in white leggings and high boots, with a star that Rostov did not know (it was legion d'honneur) [star of the Legion of Honor] went out onto the porch, holding his hat at hand and putting on a glove. He stopped, looking around and that's it illuminating the surroundings with his gaze. He said a few words to some of the generals. He also recognized the former chief of the division, Rostov, smiled at him and called him over.
The entire retinue retreated, and Rostov saw how this general said something to the sovereign for quite a long time.
The Emperor said a few words to him and took a step to approach the horse. Again the crowd of the retinue and the crowd of the street in which Rostov was located moved closer to the sovereign. Stopping by the horse and holding the saddle with his hand, the sovereign turned to the cavalry general and spoke loudly, obviously with the desire for everyone to hear him.
“I can’t, general, and that’s why I can’t because the law is stronger than me,” said the sovereign and raised his foot in the stirrup. The general bowed his head respectfully, the sovereign sat down and galloped down the street. Rostov, beside himself with delight, ran after him with the crowd.

On the square where the sovereign went, a battalion of Preobrazhensky soldiers stood face to face on the right, and a battalion of the French Guard in bearskin hats on the left.
While the sovereign was approaching one flank of the battalions, which were on guard duty, another crowd of horsemen jumped up to the opposite flank and ahead of them Rostov recognized Napoleon. It couldn't be anyone else. He rode at a gallop in a small hat, with a St. Andrew's ribbon over his shoulder, in a blue uniform open over a white camisole, on an unusually thoroughbred Arabian gray horse, on a crimson, gold embroidered saddle cloth. Having approached Alexander, he raised his hat and with this movement, Rostov’s cavalry eye could not help but notice that Napoleon was sitting poorly and not firmly on his horse. The battalions shouted: Hurray and Vive l "Empereur! [Long live the Emperor!] Napoleon said something to Alexander. Both emperors got off their horses and took each other's hands. There was an unpleasantly feigned smile on Napoleon's face. Alexander said something to him with an affectionate expression .
Rostov, without taking his eyes off, despite the trampling of the horses of the French gendarmes besieging the crowd, followed every move of Emperor Alexander and Bonaparte. He was struck as a surprise by the fact that Alexander behaved as an equal with Bonaparte, and that Bonaparte was completely free, as if this closeness with the sovereign was natural and familiar to him, as an equal, he treated the Russian Tsar.
Alexander and Napoleon with long tail The retinues approached the right flank of the Preobrazhensky battalion, directly towards the crowd that stood here. The crowd suddenly found itself so close to the emperors that Rostov, who was standing in the front rows, became afraid that they would recognize him.
“Sire, je vous demande la permission de donner la legion d"honneur au plus brave de vos soldats, [Sire, I ask your permission to give the Order of the Legion of Honor to the bravest of your soldiers,] said a sharp, precise voice, finishing each letter It was the short Bonaparte who spoke, looking straight into Alexander's eyes from below. Alexander listened attentively to what was being said to him, and bowed his head, smiling pleasantly.
“A celui qui s"est le plus vaillament conduit dans cette derieniere guerre, [To the one who showed himself bravest during the war],” Napoleon added, emphasizing each syllable, with a calm and confidence outrageous for Rostov, looking around the ranks of Russians stretched out in front of there are soldiers, keeping everything on guard and motionlessly looking into the face of their emperor.

…God first gave matter the form of solid, massive,

impenetrable, mobile particles of such sizes and shapes

and with such properties and proportions in relation to

space that would be most suitable for the purpose

for which he created them.

I. Newton

In the history of philosophy and science, one can roughly distinguish 3 approaches to understanding the structure of nature at the micro level:

there are indivisible corpuscles or atoms, the world is reduced to fundamental “bricks” (Democritus, Newton);

matter is continuously and endlessly crushed into smaller and smaller pieces, never reaching an indivisible atom (Aristotle);

in the twentieth century a concept arose that explains the world on the basis of the interconnection of all things: a particle is not a “brick” of matter, but a process, link or pattern in the entire Universe (W. Heisenberg, J. Chu, F. Capra).

The first “elementary” particle was discovered in 1897 by J.J. Thomson, while studying cathode rays, he proved the existence electrons . When exposed to substances, negative electricity is easily released, which is recorded as flashes of light on the screen. The particles of negative electricity were called electrons. A minimum amount of electricity equal to the charge of one electron was observed during an electrical discharge in a rarefied gas. Until the 70s. XX century the problem of the internal structure of the electron has not been solved, there is still no hint of its internal structure (Anderson 1968; Weiskopf 1977).

A year earlier, A. Becquerel discovered the radioactive decay of uranium salt - the emission of alpha particles (He nuclei), these particles were used by Rutherford, who experimentally proved the existence of the atomic nucleus. In 1919, E. Rutherford carried out the first artificial nuclear reaction: by irradiating N with alpha particles, he obtained the O isotope, and proved that the nucleus of the atom contains N proton 27 (considered the limiting particle).

In 1932, J. Chadwick discovered another nuclear particle - an uncharged neutron 28. The discovery of the neutron, which laid the foundation for a new science - neutron physics , the basic properties of the neutron, the application of neutrons are devoted to the book by S.F. Shebalina Neutrons . Traces of neutrons were observed in a cloud chamber. The mass of a proton is equal to 1836.1 masses of an electron, the mass of a neutron is 1838.6. V. Heisenberg, and independently of him D.D. Ivanenko, I.E. Tamm, express a hypothesis about the structure of the atomic nucleus from protons and neutrons: nucleus C, for example, consists of 6 protons and 6 neutrons. In the beginning. 30s believed: matter consists of atoms, and atoms consist of 3 “elementary” particles, “building blocks”: protons, neutrons and electrons (Shebalin 1969; Folta, Novy 1987; Capra 1994: 66-67).

In the same year, E.O. Lawrence in California built the first cyclotron (particle accelerator). Particle accelerators are facilities that collide high-energy particles. When subatomic particles moving at high speeds collide, high level energy and the birth of a world of interactions, fields and particles occurs, since the level of elementarity depends on the level of energy. If you accelerate a coin to such speeds, then its energy will be equal to the production of energy worth a thousand million dollars. A ring accelerator with a tunnel circumference of up to 27 km was built near Geneva. Today, to test some theories, for example, the theory of the grand unification of all particles, an accelerator the size of the solar system is needed (Folta, Novy 1987: 270-271; Davis 1989: 90-91).

Particles are also discovered in natural accelerators, cosmic rays collide with atoms of an experimental device, and the results of the impact are studied (this is how the predicted positron, muon and meson were discovered). With the help of accelerators and cosmic radiation research, a large and diverse world of subatomic particles has been revealed. In 1932, 3 particles were discovered, in 1947 – 14, in 1955 – 30, 1969 – more than 200. Simultaneously with the experiments, theoretical research was also carried out. Particles often move at the speed of light,  , it is necessary to take into account the theory of relativity. The creation of a general theory of particles remains an unsolved problem in physics (Capra 1994: 67).

In 1967, a hypothesis appeared about the existence tachyons – particles whose speed of movement is higher than the speed of light. New “building blocks” of matter were discovered, many unstable, short-lived (“resonances” live 10-27 s.) particles that decay into ordinary particles. Later it became clear that the new particles: resonances and hyperons, mesons – excited states of other particles: proton and leptons. Just like an excited H atom in various states, which appears as 3 spectral lines, is not another atom (Born 1967: 127-129).

It turned out that particles do not decay, but transform into each other or into the energy of field quanta, transform into “their other”, any particle can be integral part any other. Particles can “disappear” into radiation and exhibit wave properties. After the first artificial transformation, when the Li nuclei were converted into He nuclei, a atomic, nuclear physics (Born 1967; Weiskopf 1977: 50).

In 1963, M. Gell-Mann and J. Zweig proposed a hypothesis quarks . All hadrons are built from smaller particles - quarks of 3 types and their antiquarks. A proton and a neutron are made up of 3 quarks (they are also called baryons - heavy or nucleons - nuclear particles). The proton is stable, positively charged, the neutron is unstable, turns into a proton. Quark-antiquark pairs (each particle has an antiparticle) form mesons (intermediate in mass between electron and proton). In order to explain the diversity of hadronic patterns, physicists had to postulate the existence of extra quarks. There are now 12 quarks: 4 varieties or flavors (upper, downward, strange and charming), each of which can exist in 3 colors. Most physicists consider quarks to be truly elementary, without structure. Although all hadrons are characterized by quark symmetries, hadrons often behave as if they were actually made of point components, but the mystery of quarks still exists (Davis 1989: 100; Hawking 1990: 69; Capra 1994: 228, 229).

In accordance with bootstrap hypothesis nature cannot be reduced to “building blocks” of matter such as quarks, but must be understood on the basis of connectivity. Heisenberg, who did not believe in the quark model, agreed with the bootstrap picture of particles as dynamic patterns in an interconnected network of events (Capra 1996: 43-49).

All known particles of the Universe can be divided into two groups: particles of “solid” matter and virtual particles, carriers of interactions , having no “rest” mass. Particles of matter are also divided into two groups: hadrons 29 , nucleons 30 , baryons or heavy particles and leptons 31 .

Leptons include the electron, muon , tau lepton and 3 types neutrino . Today it is customary to consider an electron to be an elementary, point-like object. The electron is negatively charged, 1836 times lighter than the proton (Weiskopf 1997: 79; Davis 1989: 93-102; Hawking 1990: 63; Feynman, Weinberg 2000).

In 1931, W. Pauli predicted the existence of a neutral particle neutrino , in 1955, in a nuclear reactor, a neutrino was born from a proton to form an electron and a neutron.

This is the most amazing particle: with BV, the neutrino almost does not interact with matter, being the lightest of leptons. Its mass is less than one ten-thousandth the mass of an electron, but it is perhaps the most abundant particle in the Universe and can cause its collapse. Neutrinos hardly interact with matter, penetrating through it as if it were not there at all (an example of the existence of non-one-dimensional forms). A gamma quantum travels 3 m in lead and interacts with the nucleus of a lead atom, and a neutrino must travel 4·10 13 km to interact. Neutrinos participate only in weak interactions. It has not yet been established precisely whether neutrinos actually have a “rest” mass. There are 3 types of neutrinos: electron, muon and tau.

In 1936, in the products of interaction of cosmic rays they discovered muon , an unstable particle that decays into an electron and 2 neutrinos. In the late 70s, the heaviest particle, the lepton, was discovered. tau lepton (Davis 1989: 93-95).

In 1928, P. Dirac predicted, and in 1932, discovered a positively charged electron ( positron – antiparticle of the electron.): from one γ-quantum an electron and a positron – a positively charged electron – are born. When an electron collides with a positron, two gamma rays are produced, since to maintain zero at annihilation 32 two photons are needed, scattering in different directions.

Later it turned out: all particles have antiparticles , interacting, particles and antiparticles annihilate with the formation of energy quanta. Every particle of matter has an antiparticle. When a particle and an antiparticle collide, they annihilate, as a result of which energy is released and other particles are born. In the early Universe there were more particles than antiparticles, otherwise annihilation would have filled the Universe with radiation, and there would have been no matter (Silk 1982: 123-125; Hawking 1990: 64, 71-72).

The state of electrons in an atom is determined using a series of numbers called quantum numbers , and indicate the location and shape of the orbits:

number (n) – this is the orbital number, which determines the amount of energy that an electron must have in order to be in orbit, radius;

number (ℓ) determines the exact shape of the electron wave in orbit;

number (m) called magnetic and determines the charge of the field that surrounds the electron;

number(s) , so-called spin (rotation) determines the speed and direction of rotation of the electron, which is determined by the shape of the electron wave in terms of the probability of the particle existing at certain points in the orbit.

Since these characteristics are expressed in integers, this means that the amount of rotation of the electron does not increase gradually, but abruptly - from one fixed value to another. Particles are characterized by the presence or absence of mass, electric charge, spin (rotational characteristic, particles of matter have spin +1/2, –1/2, particles that carry interactions 0, 1 and 2) and Lifetime (Erdei-Gruz 1976; Davis 1989 : 38-41, 92; Hawking 1990: 62-63; Capra 1994: 63).

In 1925, W. Pauli asked the question: why do electrons in an atom occupy a strictly defined position (2 in the first orbit, 8 in the second, 32 in the fourth)? Analyzing the spectra, he revealed a simple principle: two identical particles cannot be in the same state , i.e. they cannot have the same coordinates, velocities, quantum numbers. All particles of matter obey W. Pauli's exclusion principle .

This principle emphasizes a clear organization of structures, outside of which the particles would turn into a homogeneous and dense jelly. The exclusion principle made it possible to explain the chemical properties of elements determined by the electrons of the outer unfilled shells, which provided the basis for the periodic table of elements. The Pauli principle led to new discoveries and understanding of the thermal and electrical conductivity of metals and semiconductors. Using the exclusion principle, the electronic shells of atoms were built, and Mendeleev’s system of elements became clear (Dubnishcheva 1997: 450-452).

But there are particles that do not obey W. Pauli’s exclusion principle (there is no limit on the number of exchanged particles, the interaction force can be any), carrier particles or virtual particles that do not have a “rest” mass and create forces between particles of matter (Hawking 1990: 64 -65).

6. The world of subatomic particles

Splitting the atom

It is often said that there are two types of sciences - big sciences and small ones. Atom splitting - big science. It has gigantic experimental facilities, colossal budgets and receives the lion's share of Nobel Prizes.

Why did physicists need to split the atom? The simple answer - to understand how the atom works - contains only part of the truth, but there is a more general reason. It is not entirely correct to speak literally about the splitting of the atom. In reality, we are talking about the collision of high-energy particles. When subatomic particles moving at high speeds collide, a new world of interactions and fields is born. The fragments of matter carrying enormous anergy, scattering after collisions, conceal the secrets of nature, which from the “creation of the world” remained buried in the depths of the atom.

The installations where high-energy particles collide - particle accelerators - are striking in their size and cost. They reach several kilometers across, making even laboratories that study particle collisions seem tiny in comparison. In other areas of scientific research, the equipment is located in a laboratory; in high-energy physics, laboratories are attached to an accelerator. Recently European Center Nuclear Research (CERN), located near Geneva, allocated several hundred million dollars for the construction of a ring accelerator. The circumference of the tunnel being built for this purpose reaches 27 km. The accelerator, called LEP (Large Electron-Positron ring), is designed to accelerate electrons and their antiparticles (positrons) to speeds that are only a hair's breadth away from the speed of light. To get an idea of ​​the scale of energy, imagine that instead of electrons, a penny coin is accelerated to such speeds. At the end of the acceleration cycle, it would have enough energy to produce $1,000 million worth of electricity! No wonder that similar experiments is usually referred to as “high energy” physics. Moving towards each other inside the ring, beams of electrons and positrons experience head-on collisions, in which the electrons and positrons annihilate, releasing energy sufficient to produce dozens of other particles.

What are these particles? Some of them are the very “building blocks” from which we are built: protons and neutrons that make up atomic nuclei, and electrons orbiting around the nuclei. Other particles are usually not found in the matter around us: their lifespan is extremely short, and after it expires they disintegrate into ordinary particles. The number of varieties of such unstable short-lived particles is amazing: several hundred of them are already known. Like stars, unstable particles are too numerous to be identified by name. Many of them are indicated only by Greek letters, and some by just numbers.

It is important to keep in mind that all these numerous and varied unstable particles are by no means literally components protons, neutrons or electrons. When colliding, high-energy electrons and positrons do not scatter into many subatomic fragments. Even in collisions of high-energy protons, which obviously consist of other objects (quarks), they, as a rule, are not split into their component parts in the usual sense. What happens in such collisions is better viewed as the direct creation of new particles from the energy of the collision.

About twenty years ago, physicists were completely baffled by the number and variety of new subatomic particles, which seemed to have no end. It was impossible to understand For what so many particles. Perhaps elementary particles are like the inhabitants of a zoo, with their implicit family affiliation, but without any clear taxonomy. Or perhaps, as some optimists have believed, elementary particles hold the key to the universe? What are the particles observed by physicists: insignificant and random fragments of matter or the outlines of a vaguely perceived order emerging before our eyes, indicating the existence of a rich and complex structure of the subnuclear world? Now there is no doubt about the existence of such a structure. There is a deep and rational order to the microworld, and we begin to understand the meaning of all these particles.

The first step towards understanding the microworld was made as a result of the systematization of all known particles, just as in the 18th century. biologists compiled detailed catalogs of plant and animal species. The most important characteristics of subatomic particles include mass, electric charge, and spin.

Because mass and weight are related, particles with high mass are often called "heavy." Einstein's relation E =mc^ 2 indicates that the mass of a particle depends on its energy and, therefore, on its speed. A moving particle is heavier than a stationary one. When they talk about the mass of a particle, they mean it rest mass, since this mass does not depend on the state of motion. A particle with zero rest mass moves at the speed of light. The most obvious example of a particle with zero rest mass is the photon. It is believed that the electron is the lightest particle with a non-zero rest mass. The proton and neutron are nearly 2,000 times heavier, while the heaviest particle created in the laboratory (the Z particle) is about 200,000 times the mass of the electron.

The electric charge of particles varies in a rather narrow range, but, as we noted, it is always a multiple of the fundamental unit of charge. Some particles, such as photons and neutrinos, have no electrical charge. If the charge of a positively charged proton is taken to be +1, then the charge of the electron is -1.

In ch. 2 we introduced another characteristic of particles - spin. It also always takes values ​​that are multiples of some fundamental unit, which for historical reasons is chosen to be 1 /2. Thus, a proton, neutron and electron have a spin 1/2, and the photon's spin is 1. Particles with spin 0, 3/2 and 2 are also known. Fundamental particles with spin greater than 2 have not been discovered, and theorists believe that particles with such spins do not exist.

The spin of a particle is an important characteristic, and depending on its value, all particles are divided into two classes. Particles with spins 0, 1 and 2 are called "bosons" - after the Indian physicist Chatyendranath Bose, and particles with half-integer spin (i.e. with spin 1/2 or 3/2 - "fermions" in honor of Enrico Fermi. Belonging to one of these two classes is probably the most important in the list of characteristics of a particle.

Another important characteristic of a particle is its lifetime. Until recently, it was believed that electrons, protons, photons and neutrinos were absolutely stable, i.e. have endlessly big time life. The neutron remains stable while it is "locked" in the nucleus, but a free neutron decays in about 15 minutes. All other known particles are highly unstable, their lifetimes range from a few microseconds to 10-23 s. Such time intervals seem incomprehensibly small, but we should not forget that a particle flying at a speed close to the speed of light (and most particles born in accelerators move at precisely such speeds) manages to fly a distance of 300 m in a microsecond.

Unstable particles undergo decay, which is a quantum process, and therefore there is always an element of unpredictability in the decay. The lifespan of a particular particle cannot be predicted in advance. Based on statistical considerations, only the average lifetime can be predicted. Usually they talk about the half-life of a particle - the time during which the population of identical particles is reduced by half. The experiment shows that the decrease in population size occurs exponentially (see Fig. 6) and the half-life is 0.693 of the average life time.

It is not enough for physicists to know that this or that particle exists - they strive to understand what its role is. The answer to this question depends on the properties of particles listed above, as well as on the nature of the forces acting on the particle from outside and inside it. First of all, the properties of a particle are determined by its ability (or inability) to participate in strong interactions. Particles participating in strong interactions form a special class and are called androns. Particles that participate in weak interactions and do not participate in strong interactions are called leptons, which means "lungs". Let's take a brief look at each of these families.

Leptons

The best known of the leptons is the electron. Like all leptons, it appears to be an elementary, point-like object. As far as is known, the electron has no internal structure, i.e. does not consist of any other particles. Although leptons may or may not have an electrical charge, they all have the same spin 1/2, therefore, they are classified as fermions.

Another well-known lepton, but without a charge, is the neutrino. As already mentioned in Chap. 2, neutrinos are as elusive as ghosts. Since neutrinos do not participate in either the strong or electromagnetic interactions, they almost completely ignore matter, penetrating through it as if it were not there at all. The high penetrating ability of neutrinos for a long time made it very difficult to experimentally confirm their existence. It was only almost three decades after the neutrinos were predicted that they were finally discovered in the laboratory. Physicists had to wait for the creation of nuclear reactors, during which a huge number of neutrinos are emitted, and only then were they able to register the head-on collision of one particle with a nucleus and thereby prove that it really exists. Today it is possible to carry out much more experiments with neutrino beams, which arise from the decay of particles in an accelerator and have the necessary characteristics. The vast majority of neutrinos “ignore” the target, but from time to time neutrinos still interact with the target, which makes it possible to obtain useful information about the structure of other particles and the nature of weak interaction. Of course, conducting experiments with neutrinos, unlike experiments with other subatomic particles, does not require the use of special protection. The penetrating power of neutrinos is so great that they are completely harmless and pass through the human body without causing the slightest harm to it.

Despite their intangibility, neutrinos occupy a special position among other known particles because they are the most abundant particles throughout the Universe, outnumbering electrons and protons by a billion to one. The universe is essentially a sea of ​​neutrinos, with occasional inclusions in the form of atoms. It is even possible that the total mass of neutrinos exceeds the total mass of stars, and therefore it is neutrinos that make the main contribution to cosmic gravity. According to a group of Soviet researchers, neutrinos have a tiny, but not zero, rest mass (less than one ten thousandth the mass of an electron); if this is true, then gravitational neutrinos dominate the Universe, which in the future may cause its collapse. Thus, neutrinos, at first glance the most “harmless” and incorporeal particles, are capable of causing the collapse of the entire Universe.

Among other leptons, one should mention the muon, discovered in 1936 in the products of the interaction of cosmic rays; it turned out to be one of the first known unstable subatomic particles. In all respects except stability, the muon resembles an electron: it has the same charge and spin, participates in the same interactions, but has a larger mass. In about two millionths of a second, the muon decays into an electron and two neutrinos. Muons are widespread in nature and account for a significant portion of the background cosmic radiation that is detected on the Earth's surface by a Geiger counter.

For many years, the electron and the muon remained the only known charged leptons. Then, in the late 1970s, a third charged lepton was discovered, called the tau lepton. With a mass of about 3500 electron masses, the tau lepton is obviously the “heavyweight” of the trio of charged leptons, but in all other respects it behaves like an electron and a muon.

This list of known leptons is by no means exhausted. In the 60s it was discovered that there are several types of neutrinos. Neutrinos of one type are born together with an electron during the decay of a neutron, and neutrinos of another type are born during the birth of a muon. Each type of neutrino exists in pairs with its own charged lepton; therefore, there is an "electron neutrino" and a "muon neutrino". In all likelihood, there should also be a third type of neutrino - accompanying the birth of the tau lepton. In this case, the total number of neutrino varieties is three, and the total number of leptons is six (Table 1). Of course, each lepton has its own antiparticle; thus the total number of different leptons is twelve.

Table 1

Six leptons correspond to charged and neutral modifications (antiparticles are not included in the table). Mass and charge are expressed in units of electron mass and charge, respectively. There is evidence that neutrinos may have low mass

Hadrons

In contrast to the handful of known leptons, there are literally hundreds of hadrons. This alone suggests that hadrons are not elementary particles, but are built from smaller components. All hadrons participate in strong, weak and gravitational interactions, but are found in two varieties - electrically charged and neutral. Among hadrons, the most famous and widely distributed are the neutron and the proton. The remaining hadrons are short-lived and decay either in less than one millionth of a second due to the weak interaction, or much faster (in a time of the order of 10-23 s) - due to the strong interaction.

In the 1950s, physicists were extremely puzzled by the number and diversity of hadrons. But little by little, particles were classified according to three important characteristics: mass, charge and spin. Gradually, signs of order began to appear and a clear picture began to emerge. There are hints that there are symmetries hidden behind the apparent chaos of the data. A decisive step in unraveling the mystery of hadrons came in 1963, when Murray Gell-Mann and George Zweig of the California Institute of Technology proposed the theory of quarks.

Fig.10 Hadrons are built from quarks. A proton (top) is made up of two up quarks and one d quark. The lighter pion (bottom) is a meson, consisting of one u-quark and one d-antiquark. Other hadrons are all sorts of combinations of quarks.

The main idea of ​​this theory is very simple. All hadrons are made of smaller particles called quarks. Quarks can connect to each other in one of two possible ways: either in triplets or in quark-antiquark pairs. Relatively heavy particles are made up of three quarks - baryons, which means "heavy particles". The best known baryons are the neutron and the proton. Lighter quark-antiquark pairs form particles called mesons -"intermediate particles". The choice of this name is explained by the fact that the first discovered mesons occupied an intermediate position in mass between electrons and protons. To take into account all the then known hadrons, Gell-Mann and Zweig introduced three different types (“flavors”) of quarks, which received rather fancy names: And(from up- upper), d(from down - lower) and s (from strange- strange). By allowing for the possibility of various combinations of flavors, the existence of a large number of hadrons can be explained. For example, a proton consists of two And- and one d-quark (Fig. 10), and the neutron is made up of two d-quarks and one u-quark.

For the theory proposed by Gell-Mann and Zweig to be effective, it is necessary to assume that quarks carry a fractional electric charge. In other words, they have a charge whose value is either 1/3 or 2/3 of the fundamental unit - the charge of the electron. A combination of two and three quarks can have a total charge of zero or one. All quarks have spin 1/2. therefore they are classified as fermions. The masses of quarks are not determined as accurately as the masses of other particles, since their binding energy in a hadron is comparable to the masses of the quarks themselves. However, it is known that the s-quark is heavier And- and d-quarks.

Inside hadrons, quarks can be in excited states, much like the excited states of an atom, but with much higher energies. The excess energy contained in an excited hadron increases its mass so much that before the creation of the quark theory, physicists mistakenly took excited hadrons for completely different particles. It has now been established that many of the seemingly different hadrons are in fact only excited states of the same fundamental set of quarks.

As already mentioned in Chap. 5, quarks are held together by strong interaction. But they also participate in weak interactions. The weak interaction can change the flavor of a quark. This is how neutron decay occurs. One of the d-quarks in the neutron turns into a u-quark, and the excess charge carries away the electron that is born at the same time. Similarly, by changing the flavor, the weak interaction leads to the decay of other hadrons.

The existence of s-quarks is necessary for the construction of so-called “strange” particles - heavy hadrons, discovered in the early 50s. The unusual behavior of these particles, which suggested their name, was that they could not decay due to strong interactions, although both themselves and their decay products were hadrons. Physicists have puzzled over why, if both the mother and daughter particles belong to the hadron family, the strong force does not cause them to decay. For some reason, these hadrons "preferred" the much less intense weak interaction. Why? Quark theory naturally solved this riddle. The strong interaction cannot change the flavor of quarks - only the weak interaction can do this. And without a change in flavor, accompanied by the transformation of the s-quark into And- or d-quark, decay is impossible.

In table Figure 2 presents the various possible combinations of three-flavor quarks and their names (usually just a Greek letter). Numerous excited states are not shown. The fact that all known hadrons could be obtained from various combinations of the three fundamental particles symbolized the main triumph of the quark theory. But despite this success, only a few years later it was possible to obtain direct physical evidence of the existence of quarks.

This evidence was obtained in 1969 in a series of historical experiments conducted at the large linear accelerator at Stanford (California, USA) - SLAC. The Stanford experimenters reasoned simply. If there really are quarks in the proton, then collisions with these particles inside the proton can be observed. All that is needed is a subnuclear “projectile” that could be directed directly into the depths of the proton. It is useless to use another hadron for this purpose, since it has the same dimensions as a proton. An ideal projectile would be a lepton, such as an electron. Since the electron does not participate in the strong interaction, it will not “get stuck” in the medium formed by quarks. At the same time, an electron can sense the presence of quarks due to the presence of an electric charge.

table 2

The three flavors of quarks, u, d and s, correspond to charges +2/3, -1/3 and -1/3; they combine in threes to form the eight baryons shown in the table. Quark-antiquark pairs form mesons. (Some combinations, such as sss, are omitted.)

In the Stanford experiment, the three-kilometer accelerator essentially acted as a giant electron "microscope" that produced images of the inside of a proton. A conventional electron microscope can distinguish details smaller than one millionth of a centimeter. A proton, on the other hand, is several tens of millions of times smaller, and can only be “probed” by electrons accelerated to an energy of 2.1010 eV. At the time of the Stanford experiments, few physicists adhered to the simplified theory of quarks. Most scientists expected the electrons to be deflected by the electrical charges of the protons, but the charge was assumed to be evenly distributed within the proton. If this were really so, then mainly weak electron scattering would occur, i.e. When passing through protons, electrons would not undergo strong deflections. The experiment showed that the scattering pattern differs sharply from the expected one. Everything happened as if some electrons flew into tiny solid inclusions and bounced off them at the most incredible angles. Now we know that such solid inclusions inside protons are quarks.

In 1974, the simplified version of the theory of quarks, which by that time had gained recognition among theorists, was dealt a sensitive blow. Within a few days of each other, two groups of American physicists - one at Stanford led by Barton Richter, the other at Brookhaven National Laboratory led by Samuel Ting - independently announced the discovery of a new hadron, which was called the psi particle. In itself, the discovery of a new hadron would hardly be particularly noteworthy if not for one circumstance: the fact is that in the scheme proposed by the theory of quarks there was no room for a single new particle. All possible combinations of up, d, and s quarks and their antiquarks have already been “used up.” What does a psi particle consist of?

The problem was solved by turning to an idea that had been in the air for some time: there should be a fourth scent that no one had ever observed before. The new fragrance already had its name - charm (charm), or s. It has been suggested that a psi particle is a meson consisting of a c-quark and a c-antiquark (c), i.e. cc. Since antiquarks are carriers of anti-flavor, the charm of the psi particle is neutralized, and therefore experimental confirmation of the existence of a new flavor (charm) had to wait until mesons were discovered, in which charm quarks were paired with anti-quarkamps of other flavors . A whole string of enchanted particles is now known. They are all very heavy, so the charm quark turns out to be heavier than the strange quark.

The situation described above was repeated in 1977, when the so-called upsilon meson (UPSILON) appeared on the scene. This time, without much hesitation, a fifth flavor was introduced, called b-quark (from bottom - bottom, and more often beauty - beauty, or charm). The upsilon meson is a quark-antiquark pair made up of b quarks and therefore has a hidden beauty; but, as in the previous case, a different combination of quarks made it possible to ultimately discover “beauty.”

The relative masses of quarks can be judged at least by the fact that the lightest of mesons, the pion, consists of pairs And- and d-quarks with antiquarks. The psi meson is about 27 times, and the upsilon meson is at least 75 times heavier than the pion.

The gradual expansion of the list of known flavors occurred in parallel with the increase in the number of leptons; so the obvious question was whether there would ever be an end. Quarks were introduced to simplify the description of the entire variety of hadrons, but even now there is a feeling that the list of particles is again growing too quickly.

Since the time of Democritus, the fundamental idea of ​​atomism has been the recognition that, on a sufficiently small scale, there must exist truly elementary particles, the combinations of which make up the matter around us. Atomism is attractive because indivisible (by definition) fundamental particles must exist in a very limited number. The diversity of nature is due to a large number not their constituent parts, but their combinations. When it was discovered that there were many different atomic nuclei, the hope disappeared that what we today call atoms corresponded to the ancient Greeks' idea of ​​\u200b\u200bthe elementary particles of matter. And although, according to tradition, we continue to talk about various chemical “elements,” it is known that atoms are not elementary at all, but consist of protons, neutrons and electrons. And since the number of quarks turns out to be too large, it is tempting to assume that they too are complex systems consisting of smaller particles.

Although for this reason there is some dissatisfaction with the quark scheme, most physicists consider quarks to be truly elementary particles - point-like, indivisible and without internal structure. In this respect they resemble peptones, and it has long been assumed that there must be a deep relationship between these two distinct but structurally similar families. The basis for this point of view arises from a comparison of the properties of leptons and quarks (Table 3). Leptons can be grouped in pairs by associating each charged lepton with a corresponding neutrino. Quarks can also be grouped in pairs. Table 3 is composed in such a way that the structure of each cell repeats the one located directly in front of it. For example, in the second cell the muon is represented as a "heavy electron" and the charm and strange quarks are represented as heavy variants And- and d-quarks. From the next box you can see that the tau lepton is an even heavier "electron", and the b quark is a heavier version of the d quark. For a complete analogy, we need one more (tau-leptonium) neutrino and a sixth flavor of quarks, which has already received the name true (truth, t). At the time this book was being written, the experimental evidence for the existence of top quarks was not yet convincing enough, and some physicists doubted that top quarks existed at all.

Table 3

Leptons and quarks naturally pair up. as shown in the table. The world around us consists of the first four particles. But the following groups, apparently, repeat the upper one and consist, in the crown of neutrinos, of extremely unstable particles.

Can there be a fourth, fifth, etc. vapors containing even heavier particles? If so, the next generation of accelerators will likely give physicists the opportunity to detect such particles. However, an interesting consideration is expressed, from which it follows that there are no other pairs except the three named. This consideration is based on the number of neutrino types. We will soon learn that at the moment of the Big Bang, which marked the emergence of the Universe, there was an intense creation of neutrinos. A kind of democracy guarantees each type of particle the same share of energy as the others; therefore, the more various types neutrinos, the more energy is contained in the sea of ​​neutrinos filling outer space. Calculations show that if there were more than three varieties of neutrinos, then the gravity created by all of them would have a strong disturbing effect on the nuclear processes that occurred in the first few minutes of the life of the Universe. Consequently, from these indirect considerations a very plausible conclusion follows that the three pairs shown in table. 3, all quarks and leptons that exist in nature are exhausted.

It is interesting to note that all ordinary matter in the Universe consists of only two lightest leptons (electron and electron neutrino) and two lightest quarks ( And And d). If all the other leptons and quarks suddenly ceased to exist, then very little would probably change in the world around us.

Perhaps heavier quarks and leptons play the role of a kind of backup for the lightest quarks and leptons. All of them are unstable and quickly disintegrate into particles located in the upper cell. For example, the tau lepton and the muon decay into electrons, while the strange, charmed, and beautiful particles decay quite quickly into either neutrons or protons (in the case of baryons) or leptons (in the case of mesons). The question arises: For what Are there all these second and third generation particles? Why did nature need them?

Particles are carriers of interactions

The list of known particles is by no means exhausted by six pairs of leptons and quarks, which form the building material of matter. Some of them, such as the photon, are not included in the quark circuit. The particles “left overboard” are not “building blocks of the universe”, but form a kind of “glue” that does not allow the world to fall apart, i.e. they are associated with four fundamental interactions.

I remember being told as a child that the moon causes the oceans to rise and fall during the daily tides. It has always been a mystery to me how the ocean knows where the Moon is and follows its movement in the sky. When I learned about gravity at school, my bewilderment only intensified. How does the Moon, having overcome a quarter of a million kilometers of empty space, manage to “reach” the ocean? The standard answer - the Moon creates a gravitational field in this empty space, the action of which reaches the ocean, setting it in motion - of course, made some sense, but still did not completely satisfy me. After all, we cannot see the gravitational field of the Moon. Maybe that's just what they say? Does this really explain anything? It always seemed to me that the moon must somehow tell the ocean where it is. There must be some kind of signal exchange between the moon and the ocean so that the water knows where to move.

Over time, it turned out that the idea of ​​force transmitted through space in the form of a signal is not so far from the modern approach to this problem. To understand how this idea arises, we must consider in more detail the nature of the force field. As an example, let's choose not ocean tides, but a simpler phenomenon: two electrons approach each other, and then, under the influence of electrostatic repulsion, fly apart in different directions. Physicists call this process the scattering problem. Of course, electrons don't literally push each other. They interact at a distance, through the electromagnetic field generated by each electron.

Fig. 11. Scattering of two charged particles. The trajectories of particles are bent as they approach each other due to the action of electrical repulsion.

It is not difficult to imagine the picture of electron-on-electron scattering. Initially, the electrons are separated by a large distance and have little effect on each other. Each electron moves almost rectilinearly (Fig. 11). Then, as repulsive forces come into play, the electron trajectories begin to bend until the particles are as close as possible; after this, the trajectories diverge, and the electrons fly apart, again beginning to move along rectilinear, but already diverging trajectories. A model of this kind can easily be demonstrated in the laboratory using electrically charged balls instead of electrons. And again the question arises: how does a particle “know” where another particle is, and accordingly changes its movement.

Although the picture of curved electron trajectories is quite visual, it is completely unsuitable in a number of respects. The fact is that electrons are quantum particles and their behavior obeys the specific laws of quantum physics. First of all, electrons do not move in space along well-defined trajectories. We can still determine in one way or another the starting and ending points of the path - before and after scattering, but the path itself in the interval between the beginning and end of the movement remains unknown and uncertain. In addition, the intuitive idea of ​​​​a continuous exchange of energy and momentum between the electron and the field, as if accelerating the electron, contradicts the existence of photons. Energy and momentum can be transferred field only in portions, or quanta. We will obtain a more accurate picture of the disturbance introduced by the field into the motion of the electron by assuming that the electron, absorbing a photon from the field, seems to experience a sudden push. Therefore, at the quantum level, the act of scattering an electron on an electron can be depicted as shown in Fig. 12. The wavy line connecting the trajectories of two electrons corresponds to a photon emitted by one electron and absorbed by the other. Now the act of scattering appears as a sudden change in the direction of movement of each electron

Fig. 12. Quantum description of the scattering of charged particles. The interaction of particles is due to the exchange of an interaction carrier, or virtual photon (wavy line).

Diagrams of this kind were first used by Richard Feynman to visually represent the various terms of an equation, and initially they had a purely symbolic meaning. But then Feynman diagrams began to be used to diagrammatically depict particle interactions. Such pictures seem to complement the physicist’s intuition, but they should be interpreted with a certain amount of caution. For example, there is never a sharp break in the electron trajectory. Since we only know the initial and final positions of the electrons, we do not know exactly when the photon is exchanged and which particle emits and which absorbs the photon. All these details are hidden by a veil of quantum uncertainty.

Despite this caveat, Feynman diagrams have proven to be an effective means of describing quantum interactions. The photon exchanged between the electrons can be thought of as a kind of messenger from one of the electrons telling the other: “I’m here, so get moving!” Of course, all quantum processes are probabilistic in nature, so such an exchange occurs only with a certain probability. It may happen that electrons exchange two or more photons (Fig. 13), although this is less likely.

It is important to realize that in reality we do not see photons scurrying from one electron to another. Interaction carriers are the “internal matter” of two electrons. They exist solely to tell electrons how to move, and although they carry energy and momentum, the corresponding conservation laws of classical physics do not apply to them. Photons in this case can be likened to a ball that tennis players exchange on the court. Just as a tennis ball determines the behavior of tennis players on the playground, a photon influences the behavior of electrons.

The successful description of interaction using a carrier particle was accompanied by an expansion of the concept of a photon: a photon turns out to be not only a particle of light visible to us, but also a ghostly particle that is “seen” only by charged particles undergoing scattering. Sometimes the photons we observe are called real, and photons carrying the interaction are virtual, which reminds us of their fleeting, almost ghostly existence. The distinction between real and virtual photons is somewhat arbitrary, but nevertheless these concepts have become widespread.

The description of electromagnetic interaction using the concept of virtual photons - its carriers - in its significance goes beyond just illustrations of a quantum nature. In reality, we are talking about a theory thought out to the smallest detail and equipped with a perfect mathematical apparatus, known as quantum electrodynamics, Abbreviated as QED. When QED was first formulated shortly after World War II, physicists had at their disposal a theory that satisfied the basic principles of both quantum theory and relativity. This is a wonderful opportunity to see the combined manifestations of two important aspects of new physics and. check them experimentally.

Theoretically, the creation of QED was an outstanding achievement. Earlier studies of the interaction of photons and electrons had very limited success due to mathematical difficulties. But as soon as the theorists learned to carry out calculations correctly, everything else fell into place. QED proposed a procedure for obtaining the results of any no matter how complex process involving photons and electrons.

Fig. 13. Electron scattering is caused by the exchange of two virtual photons. Such processes constitute a small amendment to the main process shown in Fig. eleven

To test how well the theory matched reality, physicists focused on two effects that were of particular interest. The first concerned the energy levels of the hydrogen atom, the simplest atom. QED predicted that the levels should be slightly shifted from the position they would occupy if virtual photons did not exist. The theory predicted the magnitude of this shift very accurately. The experiment to detect and measure displacement with extreme accuracy was carried out by Willis Lamb from the University of State. Arizona. To everyone's delight, the calculation results perfectly coincided with the experimental data.

The second decisive test of QED concerned the extremely small correction to the electron's own magnetic moment. And again, the results of theoretical calculations and experiment completely coincided. Theorists began to refine their calculations, and experimenters began to improve their instruments. But, although the accuracy of both theoretical predictions and experimental results has continuously improved, the agreement between QED and experiment has remained impeccable. Nowadays, the theoretical and experimental results still agree within the limits of the achieved accuracy, which means a coincidence of more than nine decimal places. Such a striking correspondence gives the right to consider QED the most advanced of the existing natural science theories.

Needless to say, after such a triumph, QED was adopted as a model for the quantum description of the other three fundamental interactions. Of course, fields associated with other interactions must correspond to other carrier particles. To describe gravity it was introduced graviton, playing the same role as a photon. During the gravitational interaction of two particles, gravitons are exchanged between them. This interaction can be visualized using diagrams similar to those shown in Fig. 12 and 13. It is gravitons that carry signals from the Moon to the oceans, following which they rise during high tides and fall during low tides. Gravitons scurrying between the Earth and the Sun keep our planet in orbit. Gravitons firmly chain us to the Earth.

Like photons, gravitons travel at the speed of light, hence gravitons are particles with “zero rest mass.” But this is where the similarities between gravitons and photons end. While a photon has a spin of 1, a graviton has a spin of 2.

Table 4

Particles that carry four fundamental interactions. Mass is expressed in proton mass units.

This is an important difference because it determines the direction of the force: in electromagnetic interaction, similarly charged particles, such as electrons, repel, while in gravitational interaction, all particles are attracted to each other.

Gravitons can be real or virtual. A real graviton is nothing more than a quantum of a gravitational wave, just as a real photon is a quantum of an electromagnetic wave. In principle, real gravitons can be “observed”. But because the gravitational interaction is incredibly weak, gravitons cannot be detected directly. The interaction of gravitons with other quantum particles is so weak that the probability of scattering or absorption of a graviton, for example, by a proton is infinitely small.

The basic idea of ​​the exchange of carrier particles also applies to other interactions (Table 4) - weak and strong. However, there are important differences in detail. Let us recall that the strong interaction provides the connection between quarks. Such a connection can be created by a force field similar to an electromagnetic one, but more complex. Electric forces lead to the formation of a bound state of two particles with charges of opposite signs. In the case of quarks, bound states of three particles arise, which indicates a more complex nature of the force field, to which three types of “charge” correspond. Particles - carriers of interaction between quarks, connecting them in pairs or triplets, are called gluons.

In the case of weak interaction the situation is somewhat different. The radius of this interaction is extremely small. Therefore, the carriers of the weak interaction must be particles with large rest masses. The energy contained in such a mass has to be “borrowed” in accordance with the Heisenberg uncertainty principle, which has already been discussed on p. 50. But since the "borrowed" mass (and therefore energy) is so large, the uncertainty principle requires that the repayment period of such a loan be extremely short - only about 10^-28s. Such short-lived particles do not have time to move very far, and the radius of interaction they carry is very small.

There are actually two types of weak force transporters. One of them is similar to a photon in everything except rest mass. These particles are called Z particles. Z particles are essentially a new kind of light. Another type of weak force carrier, W particles, differ from Z particles by the presence of an electric charge. In ch. 7 we will discuss in more detail the properties of Z and W particles, which were discovered only in 1983.

The classification of particles into quarks, leptons and carriers of interactions completes the list of known subatomic particles. Each of these particles plays its own, but decisive role in the formation of the Universe. If there were no carrier particles, there would be no interactions, and each particle would remain in the dark about its partners. Complex systems could not arise, any activity would be impossible. Without quarks there would be no atomic nuclei or sunlight. Without leptons, atoms could not exist, chemical structures and life itself would not arise.

What are the goals of particle physics?

The influential British newspaper The Guardian once published an editorial questioning the wisdom of developing particle physics, an expensive undertaking that consumes not only a significant share of the nation's science budget, but also the lion's share of the best minds. “Do physicists know what they’re doing?” asked the Guardian. “Even if they do, what’s the use of it? Who, other than physicists, needs all these particles?”

A few months after this publication, I had the opportunity to attend a lecture in Baltimore by George Keyworth, the US President's adviser on science. Keyworth also addressed particle physics, but his lecture took a completely different tone. American physicists were impressed by a recent report from CERN, Europe's leading particle physics laboratory, about the discovery of fundamental W and Z particles, which were finally obtained at a large proton-antiproton colliding beam collider. Americans are accustomed to the fact that all sensational discoveries are made in their high-energy physics laboratories. Isn't the fact that they lost the palm a sign of scientific and even national decline?

Keyworth had no doubt that for the United States in general and the American economy in particular to prosper, the country needed to be at the forefront of scientific research. Main projects basic research, Keyworth said, are at the forefront of progress. The United States must regain its supremacy in particle physics,

That same week, news channels circulated reports about an American project for a giant accelerator designed to conduct a new generation of experiments in particle physics. The main cost was estimated at $2 billion, making this accelerator the most expensive machine ever built by man. This giant of Uncle Sam, in comparison with which even the new CERN LEP accelerator will seem like a dwarf, is so large that the entire state of Luxembourg could fit inside its ring! Giant superconducting magnets are designed to create intense magnetic fields that will curl a beam of particles, directing it along a ring-shaped chamber; it is such a huge structure that the new accelerator is supposed to be located in the desert. I would like to know what the editor of the Guardian newspaper thinks about this.

Known as the Superconducting Super Collider (SSC), but more often referred to as "de-zertron" (from the English. desert - desert. - Ed.), this monstrous machine will be able to accelerate protons to energies approximately 20 thousand times higher than the rest energy (mass). These numbers can be interpreted in different ways. At maximum acceleration, particles will move at a speed of only 1 km/h less speed light - the maximum speed in the Universe. The relativistic effects are so great that the mass of each particle is 20 thousand times greater than at rest. In the system associated with such a particle, time is stretched so much that 1 s corresponds to 5.5 hours in our frame of reference. Each kilometer of the chamber through which the particle sweeps will “seem” to be compressed to only 5.0 cm.

What kind of extreme need forces states to expend such enormous resources on the ever more destructive fission of the atom? Is there any practical benefit to such research?

Any great science, of course, is not alien to the spirit of struggle for national priority. Here, just like in art or sports, it’s nice to win prizes and global recognition. Particle physics has become a kind of symbol of state power. If it develops successfully and produces tangible results, then this indicates that science, technology, as well as the country’s economy as a whole, are basically at the proper level. This supports confidence in the high quality of products from other more general technology branches. Creating an accelerator and all associated equipment requires a very high level of professionalism. The valuable experience gained from developing new technologies can have unexpected and beneficial effects on other areas of scientific research. For example, research and development on superconducting magnets needed for the “desertron” has been carried out in the USA for twenty years. However, they do not provide direct benefits and are therefore difficult to value. Are there any more tangible results?

One sometimes hears another argument in support of fundamental research. Physics tends to be about fifty years ahead of technology. Practical application of one or another scientific discovery Although not obvious at first, few of the significant achievements of fundamental physics have not found practical applications over time. Let's remember Maxwell's theory of electromagnetism: could its creator have foreseen the creation and success of modern telecommunications and electronics? And Rutherford's words that nuclear power is unlikely to ever find practical application? Is it possible to predict what the development of elementary particle physics can lead to, what new forces and new principles will be discovered that will expand our understanding of the world around us and give us power over a wider range of people? physical phenomena. And this could lead to the development of technologies no less revolutionary in nature than radio or nuclear energy.

Most branches of science eventually found some military application. In this respect, particle physics (as opposed to nuclear physics) has so far remained untouchable. By coincidence, Keyworth's lecture coincided with the publicity hype around President Reagan's controversial project to create an anti-missile, so-called beam, weapon (this project is part of a program called the Strategic Defense Initiative, SDI). The essence of this project is to use high-energy particle beams against enemy missiles. This application of particle physics is truly sinister.

The prevailing opinion is that the creation of such devices is not feasible. Most scientists working in the field of elementary particle physics consider these ideas absurd and unnatural and speak out sharply against the president's proposal. Condemning the scientists, Keyworth urged them to “consider what role they can play” in the project beam weapons. Keyworth's appeal to physicists (purely by chance, of course) followed his words regarding the financing of high-energy physics.

It is my firm belief that high-energy physicists do not need to justify the need for fundamental research by citing applications (especially military ones), historical analogues, or vague promises of possible technical miracles. Physicists conduct these studies primarily in the name of their ineradicable desire to find out how our world works, the desire to understand nature in more detail. Particle physics is unparalleled among other human activities. For two and a half millennia, humanity has been striving to find the original “building blocks” of the universe, and now we are close to the final goal. Giant installations will help us penetrate into the very heart of matter and wrest from nature its deepest secrets. Humanity can expect unexpected applications of new discoveries, previously unknown technologies, but it may turn out that high-energy physics will not give anything for practice. But even a majestic cathedral or concert hall has little practical use. In this regard, one cannot help but recall the words of Faraday, who once remarked: “What good is a newborn baby?” Types of human activity that are far from practice, which include the physics of elementary particles, serve as evidence of the manifestation of the human spirit, without which we would be doomed in our overly material and pragmatic world.

On the topic "Properties of the Atom"

Completed by a 1st year student

Groups Ke-DLI-401

Eliseev Vladislav

Checked:

Medvedeva Olga Alekseevna

Kemerovo 2015

The structure of the atom.

In the distant past, philosophers of Ancient Greece assumed that all matter is one, but acquires certain properties depending on its “essence.” Some of them argued that matter consists of tiny particles called atoms. The scientific foundations of atomic-molecular teaching were laid later in the works of the Russian scientist M.V. Lomonosov, French chemists L. Lavoisier and J. Proust, English chemist D. Dalton, Italian physicist A. Avogadro and other researchers.

Periodic law D.I. Mendeleev shows the existence of a natural relationship between all chemical elements. This suggests that all atoms have something in common. Until the end of the 19th century, the prevailing belief in chemistry was that an atom is the smallest indivisible particle of a simple substance. It was believed that during all chemical transformations, only molecules are destroyed and created, while atoms remain unchanged and cannot be broken into parts. And finally, at the end of the 19th century, discoveries were made that showed the complexity of the structure of the atom and the possibility of transforming some atoms into others.

This was the impetus for the formation and development of a new section of chemistry, “Structure of the Atom.” The first indication of the complex structure of the atom were experiments on the study of cathode rays generated during an electrical discharge in highly rarefied gases. To observe these rays, as much air as possible is pumped out of a glass tube into which two metal electrodes are soldered, and then a high voltage current is passed through it. Under such conditions, “invisible” cathode rays propagate from the cathode of the tube perpendicular to its surface, causing a bright green glow in the place where they hit. Cathode rays have the ability to cause movement. On their way, easily moving bodies deviate from their original path in the magnetic and electric fields (in the latter towards the positively charged plate). The effect of cathode rays is detected only inside the tube, since glass is impenetrable to them. Studies of the properties of cathode rays have led to the conclusion that they consist of tiny particles that carry a negative charge and travel at speeds reaching half the speed of light. It was also possible to determine the mass and magnitude of their charge. The mass of each particle was equal to 0.00055 carbon particles. The charge is equal to 1.602 to the power of 10 to the minus 19. It is especially remarkable that the mass of the particles and the magnitude of their charge do not depend either on the nature of the gas remaining in the tube, or on the substance from which the electrodes are made, or on other experimental conditions. In addition, cathode particles are known only in a charged state and cannot exist without their charges, cannot be converted into electrically neutral particles: electric charge constitutes the very essence of their nature. These particles are called electrons. In cathode tubes, electrons are separated from the cathode under the influence of an electrical charge. But they can also arise without any connection with an electric charge. Thus, for example, during electron emission, metals emit electrons; During the photoelectric effect, many substances also emit electrons. The release of electrons by a wide variety of substances indicates that these particles are part of all atoms; therefore, atoms are complex formations built from smaller “component parts”.

The study of the structure of the atom practically began in 1897-1898, after the nature of cathode rays as a stream of electrons was finally established and the charge and mass of the electron were determined. The fact that electrons are released by a wide variety of substances led to the conclusion that electrons are part of all atoms. But the atom, as is known, is electrically neutral, from this it followed that its composition should have included another component that balanced the sum of the negative charges of the electrons. This positively charged part of the atom was discovered in 1911. Rutherford in motion studies

particles in gases and other substances.

Rutherford Ernest (1871-1937)

particles emitted by substances of active elements are positively charged helium ions, the speed of which reaches 20,000 km/sec. Thanks to such enormous speed, particles flying through the air and colliding with gas molecules knock out electrons from them. Molecules that have lost electrons become positively charged, while the knocked-out electrons immediately join other molecules, charging them negatively. Thus, positively and negatively charged gas ions are formed in the air along the path of particles. The ability of particles to ionize air was used by an English physicist Wilson in order to make visible the paths of movement of individual particles and photograph them.

Subsequently, the apparatus for photographing particles was called a cloud chamber. (The first track detector of charged particles. Invented by Charles Wilson in 1912. The action of the Wilson chamber is based on the condensation of supersaturated vapor (the formation of small droplets of liquid) on ions appearing along the track (track) of a charged particle. Later it was replaced by other track detectors.)

While studying the paths of particle motion using a camera, Rutherford noticed that in the chamber they are parallel (paths), but when a beam of parallel rays is passed through a layer of gas or a thin metal plate, they do not come out parallel, but somewhat diverge, i.e. particles deviate from their original path. Some particles were deflected very strongly, some did not pass through the thin plate at all.

Based on these observations, Rutherford proposed his own diagram of the structure of the atom: at the center of the atom there is a positive nucleus, around which negative electrons rotate in different orbitals. The centripetal forces that arise during their rotation keep them in their orbits and prevent them from flying away. This atomic model easily explains the phenomenon of particle deflection. The dimensions of the nucleus and electrons are very small compared to the dimensions of the entire atom, which are determined by the orbits of the electrons farthest from the nucleus; therefore, most particles fly through the atoms without noticeable deflection. Only in cases where the particle comes very close to the nucleus does electrical repulsion cause it to deviate sharply from its original path. Thus, the study of particle scattering laid the foundation for the nuclear theory of the atom. One of the tasks facing the theory of atomic structure at the beginning of its development was to determine the magnitude of the nuclear charge of various atoms. Since the atom as a whole is electrically neutral, by determining the charge of the nucleus, it would be possible to establish the number of electrons surrounding the nucleus. In solving this problem, the study of the spectra of X-rays was of great help. X-rays are produced when rapidly moving electrons hit a solid body and differ from visible light rays only in their significantly shorter wavelength. While short light waves have a length of about 4000 angstroms (violet rays), wavelengths of X-rays range from 20 to 0.1 angstroms. To obtain an X-ray spectrum, you cannot use an ordinary prism or diffraction grating. (Diffraction GRATING, optical device; set large quantity parallel slits in an opaque screen or reflective mirror strips (stripes), equally spaced from each other, on which light diffraction occurs. A diffraction grating decomposes a beam of light incident on it into a spectrum, which is used in spectral instruments.)

X-rays required a grating with a very large number of divisions per millimeter (approximately 1 million/1 mm). It was impossible to artificially prepare such a lattice. In 1912, the Swiss physicist Laue The idea arose to use crystals as a diffraction grating for X-rays.

The ordered arrangement of atoms in a crystal and the small distance between them gave reason to assume that crystals would be suitable for the role of the required diffraction grating.

The experiment brilliantly confirmed Laue's assumption; soon it was possible to build instruments that made it possible to obtain the X-ray spectrum of almost all elements. To obtain X-ray spectra, the anticathode in X-ray tubes is made of the metal whose spectrum is to be obtained, or a compound of the element being studied is applied. The screen for the spectrum is photographic paper; After development, all lines of the spectrum are visible on it. In 1913, the English scientist Moseley, studying X-ray spectra, found a relationship between the wavelengths of X-rays and the serial numbers of the corresponding elements - this is called Moseley's law and can be formulated as follows: The square roots of the reciprocal values ​​of the wavelengths are linearly dependent on the serial numbers elements.

Even before Moseley's work, some scientists assumed that the atomic number of an element indicates the number of charges on the nucleus of its atom. At the same time, Rutherford, studying the dispersion of particles when passing through thin metal plates, found that if the charge of an electron is taken as a unit, then the nuclear charge expressed in such units is approximately equal to half the atomic weight of the element. The atomic number, at least of the lighter elements, is also equal to approximately half the atomic weight. All taken together led to the conclusion that the charge of the nucleus is numerically equal to the serial number of the element. Thus, Moseley's law made it possible to determine the charges of atomic nuclei. Thus, due to the neutrality of atoms, the number of electrons rotating around the nucleus in the atom of each element was established. Rutherford's nuclear model of the atom was further developed thanks to the work of Niels Bora, in which the doctrine of the structure of the atom is inextricably linked with the doctrine of the origin of spectra.

Line spectra are obtained by decomposing light emitted by hot vapors or gases. Each element has its own spectrum, different from the spectra of other elements. Most metals give very complex spectra containing a huge number of lines (in iron up to 5000), but relatively simple spectra are also found.

Developing Rutherford's nuclear theory, scientists came to the idea that the complex structure of line spectra is due to electron vibrations occurring inside atoms. According to Rutherford's theory, each electron rotates around a nucleus, and the force of attraction of the nucleus is balanced by the centrifugal force that arises when the electron rotates. The rotation of an electron is completely analogous to its rapid oscillations and should cause the emission of electromagnetic waves. Therefore, we can assume that a rotating electron emits light of a certain wavelength, depending on the electron’s orbital frequency. But, emitting light, the electron loses part of its energy, as a result of which the balance between it and the nucleus is disturbed; To restore equilibrium, the electron must gradually move closer to the nucleus, and the frequency of revolution of the electron and the nature of the light emitted by it will also gradually change. Eventually, having exhausted all the energy, the electron must “fall” onto the nucleus, and the emission of light will stop. If in fact such a continuous change in the motion of the electron occurred, then the spectrum would always be continuous, and not with rays of a certain wavelength. In addition, the “fall” of an electron onto the nucleus would mean the destruction of the atom and the cessation of its existence. Thus, Rutherford’s theory was powerless to explain not only the patterns in the distribution

lines of the spectrum, nor the very existence of line spectra. In 1913, Bohr proposed his theory of the structure of the atom, in which he managed with great skill to reconcile spectral phenomena with the nuclear model of the atom, applying to the latter the so-called quantum theory of radiation, introduced into science by the German physicist Planck. The essence of the quantum theory comes down to the fact that radiant energy is emitted and absorbed not continuously, as was previously accepted, but in separate small, but well-defined portions - energy quanta. The energy reserve of a radiating body changes abruptly, quantum by quantum; The body can neither emit nor absorb a fractional number of quanta. The magnitude of the energy quantum depends on the frequency of the radiation: the higher the frequency of the radiation, the greater the magnitude of the quantum. Quanta of radiant energy are also called photons. Having applied quantum concepts to the rotation of electrons around a nucleus, Bohr based his theory on very bold assumptions, or postulates. Although these postulates contradict the laws of classical electrodynamics, they find their justification in the amazing results they lead to, and in the complete agreement that is found between the theoretical results and a huge number of experimental facts. Bohr's postulates are as follows: An electron can move around not in any orbits, but only in those that satisfy certain conditions arising from quantum theory. These orbits are called stable or quantum orbits. When an electron moves along one of the stable orbits possible for it, it does not radiate. The transition of an electron from a distant orbit to a closer one is accompanied by a loss of energy. The energy lost by the atom during each transition is converted into one quantum of radiant energy. The frequency of the light emitted in this case is determined by the radii of the two orbits between which the electron transition occurs. The greater the distance from the orbit in which the electron is located to the one to which it moves, the greater the frequency of the radiation. The simplest atom is the hydrogen atom; around the nucleus of which only one electron rotates. Based on the above postulates, Bohr calculated the radii of possible orbits for this electron and found that they are related as the squares of natural numbers: 1: 2: 3: ... n The value n was called the principal quantum number. The radius of the orbit closest to the nucleus in a hydrogen atom is 0.53 angstroms. The frequencies of radiations calculated from this, accompanying the transitions of an electron from one orbit to another, turned out to exactly coincide with the frequencies found experimentally for the lines of the hydrogen spectrum. Thus, the correctness of the calculation of stable orbits was proven, and at the same time the applicability of Bohr's postulates for such calculations. Bohr's theory was subsequently extended to the atomic structure of other elements, although this was associated with some difficulties due to its novelty.

Bohr's theory made it possible to resolve a very important question about the arrangement of electrons in the atoms of various elements and to establish the dependence of the properties of elements on the structure of the electron shells of their atoms. At present, schemes for the structure of atoms of all chemical elements have been developed. However, keep in mind that all these schemes are only a more or less reliable hypothesis that allows us to explain many physical and Chemical properties elements. As was said earlier, the number of electrons revolving around the nucleus of an atom corresponds to the atomic number of the element in the periodic table. Electrons are arranged in layers, i.e. Each layer has a certain number of electrons that fill it or, as it were, saturate it. Electrons of the same layer are characterized by almost the same energy reserve, i.e. are at approximately the same energy level. The entire shell of the atom disintegrates

to several energy levels. The electrons of each subsequent layer are at a higher energy level than the electrons of the previous layer. Largest number electrons N that can be at a given energy level is equal to twice the square of the layer number:

where n is the layer number. In addition, it was found that the number of electrons in the outer layer for all elements except palladium does not exceed eight, and in the penultimate layer - eighteen. The electrons of the outer layer, being the most distant from the nucleus and, therefore, least tightly bound to the nucleus, can be detached from the atom and attached to other atoms, becoming part of the outer layer of the latter. Atoms that have lost one or more electrons become positively charged, since the charge of the atomic nucleus exceeds the sum of the charges of the remaining electrons. On the contrary, atoms that have gained electrons become negatively charged. The charged particles formed in this way are qualitatively different from the corresponding atoms. are called ions. Many ions, in turn, can lose or gain electrons, turning into either electrically neutral atoms or new ions with a different charge. Bohr's theory provided enormous services to physics and chemistry, approaching, on the one hand, the discovery of the laws of spectroscopy and explaining the mechanism of radiation emission, and, on the other, elucidating the structure of individual atoms and establishing connections between them. However, there were still many phenomena in this area that Bohr's theory could not explain.

Bohr presented the movement of electrons in atoms as simple mechanical, but it is complex and unique. This peculiarity was explained by a new quantum theory. This is where it came from: “Carpuscular-wave dualism.”

And so, an electron in an atom is characterized by:

1. The main quantum number n, indicating the energy of the electron;

2. Orbital quantum number l, indicating the nature of the orbit;

3. Magnetic quantum number, characterizing the position of clouds in space;

4. And the spin quantum number, which characterizes the spindle-shaped motion of the electron around its axis.

In the distant past, philosophers of Ancient Greece assumed that all matter is one, but acquires certain properties depending on its “essence.” And now, in our time, thanks to great scientists, we know exactly what it actually consists of.

Used Books:

1) General chemistry course (N.V. Korovin)

2) Course of general chemistry (A.N. Kharin)

3) Structure of matter (V.K. Vasiliev, A.N. Shuvalova)

4) Physical chemistry (A.L. Daineko)

The structure of the atomic nucleus. Subatomic particles. Elements. Isotopes.

An atom consists of a nucleus and an electron “cloud” surrounding it. Located in the electronic cloud electrons carry negative electric charge. Protons, included in the core, carry positive charge.

In any atom, the number of protons in the nucleus is exactly equal to the number of electrons in the electron cloud, so the atom as a whole is a neutral particle that carries no charge.

An atom can lose one or more electrons or, conversely, gain electrons from others. In this case, the atom acquires a positive or negative charge and is called ion.

Almost the entire mass of an atom is concentrated in its nucleus, since the mass of an electron is only 1/1836 of the mass of a proton. The density of the substance in the core is fantastically high - about 10 13 - 10 14 g/cm 3 . A matchbox filled with a substance of this density would weigh 2.5 billion tons!

The external dimensions of an atom are the dimensions of a much less dense electron cloud, which is approximately 100,000 times larger than the diameter of the nucleus.

In addition to protons, the nuclei of most atoms include neutrons, which do not carry any charge. The mass of a neutron is practically no different from the mass of a proton. Together protons and neutrons are called nucleons(from the Latin nucleus - core).

Electrons, protons and neutrons are the main "building blocks" of atoms and are called subatomic particles. Their charges and masses in kg and special “atomic” mass units (amu) are shown in Table 2-1.

Table 2-1. Subatomic particles.

From Table 2-1 it is clear that the masses of subatomic particles are extremely small. The exponent (for example, ten to the minus twenty-seventh power) shows how many zeros after the decimal point must be written to form a decimal fraction expressing the mass of a subatomic particle in kilograms. This is the tiniest fraction of a kilogram, so it is more convenient to express the mass of subatomic particles in atomic mass units(abbreviated as a.e.m.). An atomic mass unit is taken to be exactly 1/12 of the mass of a carbon atom, the nucleus of which contains 6 protons and 6 neutrons. A schematic representation of such a “reference” carbon atom is shown in Fig. 2-5 (b). The atomic mass unit can also be expressed in grams: 1 amu. = 1.660540·10 -24 g.

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Rice. 2-5. Atoms consist of a positively charged nucleus and an electron cloud. A) The nucleus of a hydrogen atom contains only 1 proton, and the electron cloud is filled with one electron. b) There are 6 protons and 6 neutrons in the nucleus of a carbon atom, and 6 electrons in the electron cloud. V) There is also isotopic carbon, the nucleus of which is 1 neutron more. The content of this isotope in natural carbon is slightly more than 1% (for isotopes, see below). The linear dimensions of atoms are very small: their radii range from 0.3 to 2.6 angstroms (1 angstrom = 10 –8 cm). The radius of the core is about 10–5 angstroms, that is, 10–13 cm. This is 100,000 times smaller sizes electronic shell. Therefore, it is impossible to correctly show the relative proportions of nuclei and electron shells in the figure. If an atom were to grow to the size of the Earth, the nucleus would only be about 200 feet in diameter and could fit on a football field.

The mass of an atom, expressed in kilograms or grams, is called absolute atomic mass. Used more often relative atomic mass, which is expressed in atomic mass units (amu). Relative atomic mass is the ratio of the mass of an atom to the mass of 1/12 of a carbon atom. Sometimes they say more briefly: atomic weight. The last term is not at all outdated, as is sometimes written in textbooks - it is widely used in modern scientific literature, so we will also use it. Relative atomic mass and atomic weight are, in fact, dimensionless quantities (the mass of any atom is divided by the mass of part of the carbon atom), therefore the designation “a.u.m.” after the numerical value it is usually omitted (but you can write it, there will be no mistake). Terms “ relative atomic mass”, “atomic mass”, “atomic weight" in scientific chemical language they are usually used equally and there is simply no distinction made between them. The International Union of Chemists (IUPAC) has a Commission on Isotopic Abundances and Atomic Weights, or CIAAW for short, but not a "Commission on Relative Atomic Weights". However, all chemists are well aware that we are talking about the same thing.

In Russian textbooks and Unified State Exam assignments use the term relative atomic mass , which is denoted by the symbol A r. Here "r" is from the English "relative" - ​​relative. For example, A r= 12.0000 – the relative atomic mass of carbon 12 6 C is 12.0000. In modern scientific literature relative atomic mass And atomic weight – synonyms.

** From the physics course you remember that the weight of a physical body is a variable quantity. For example, on the Earth and on the Moon the same physical body has different weight, but body weight is a constant value. Therefore the term “ relative atomic mass" considered more strict. For many calculations, it is convenient to use the proton and neutron masses on the amu scale. consider rounded equal unit.

In Fig. 2-5 show atoms of two different types. The question may arise: why two, and not three types - after all, the figure shows three atoms? The fact is that atoms (b) and (c) belong to the same chemical element carbon, while atom (a) is a completely different element (hydrogen). What are chemicals? elements and how do they differ from each other?

Hydrogen and carbon are different number of protons in the nucleus and, therefore, the number of electrons in the electron shell. The number of protons in the nucleus of an atom is called nuclear charge atom and is denoted by the letter Z. This is a very important quantity. When we move on to studying the Periodic Law, we will see that the number of protons in the nucleus coincides with serial number atom in D.I. Mendeleev’s Periodic Table.

As we have already said, the charge of the nucleus (the number of protons) coincides with the number of electrons in the atom. When atoms come together, they first interact with each other not with nuclei, but with electrons. The number of electrons determines the ability of an atom to form bonds with other atoms, that is, its chemical properties. Therefore, atoms with the same nuclear charge (and the same number of electrons) behave chemically almost identically and are considered as atoms of the same chemical element.