Lesson outline
on this topic
"The concept
about elementary particles"
(Grade 11)
Physics teacher
Cherpita Valery Nikolaevich
GBOU School 2051
Moscow cities
The concept of elementary particles.
Classification of elementary particles.
/data/files/u1514922328.pptx (Presentation for the lesson on the topic “The concept of element particles”)
Lesson objectives: to acquaint students with elementary particles as the only representatives of matter at a level less than 10¯ ¹⁵ m spatial dimensions and distances; reveal the general properties of elementary particles, give their classification.
Lesson Plan
| Lesson steps | Time, min | Methods and techniques |
| Introduction: setting educational problems for the lesson | 3 - 5 | Teacher's story and formulation |
| Studying new material: the concept of elementary particles, classification of particles, quarks, etc. | 30 - 35 | Teacher's story using conversation elements. Working with the textbook. Textbook material. Table. Notebook entries |
| Summing up, highlighting the main thing. Homework | 5 - 7 | Conversation on issues. Formulation of conclusions |
1. Throughout the physics course, students encountered elementary particles more than once. Already at the first stage electrons were studied; further the concept of electron was used in many cases. In quantum physics, students learned about the proton and neutron.
Final lessons can be conducted in the form of school lectures, including elements of conversation and short presentations by students on individual issues. To maintain the cognitive activity of students in the lesson, it is necessary to ensure a change in their activity, to combine informational material (story, message) with reproductive (answering questions, independent work with a textbook) and problematic (posing a problem, putting forward hypotheses, etc.). When preparing lessons, you should take care of visual aids, prepare tables, photographs of tracks, etc. There is no longer time in the course for repeated application of introduced concepts, so it is necessary to connect the new with the previously learned as much as possible.
2. Presentation of new material.As science delved deeper into the structure of matter, it discovered molecules, atoms, found out that an atom consists of a nucleus and electrons, and finally established the complex structure of the nucleus, which includes protons and neutrons.
If we consider the structure of matter taking into account this information, then in the microcosm at the level of small distances, about 10¯¹⁴ - 10¯¹⁵ m, we can conclude that matter consists of protons, neutrons and electrons. But matter is represented in nature not only by matter, but also by an electromagnetic field. The electromagnetic field also consists of microparticles - photons.
Microparticles - photons, electrons, protons, neutrons - are called elementary particles. The word “elementary” means the simplest element underlying matter: all material objects - bodies, fields - consist of these particles. When this term was introduced, it was assumed that elementary particles had no internal structure, i.e. they no longer consist of anything. Now the concept of elementaryity has been clarified, as will be discussed below.
Currently, more than 400 microparticles have been discovered, similar in size, mass, electric charge (and some other properties) to those listed above. All of them are also called elementary.
A characteristic feature of most elementary particles is theirinstability. All particles, except photons in the void, electrons, protons, neutrons (in the nucleus) and neutrino particles, decay spontaneously, eventually becoming stable. These processes are similar to the radioactive decay of nuclei. Average lifetime of unstable elementary particles; particles whose lifetime are extremely short-lived or relatively stable are considered to be10 ¯ ⁶ - 10 ¯ ¹⁴ s, athere are also particles that live only10 ¯ ²² - 10 ¯ ²³ With.
A neutron outside the nucleus is also unstable: its average lifetime is 16 minutes, but compared to the lifetime of short-lived particles this is a very long time.
It is clear that if the Universe once arose, then during its existence to the present day all unstable elementary particles would have decayed, turned into stable ones or disappeared, giving up their energy to the thermal motion of stable particles of matter. Where do short-lived particles come from? They were discovered and obtained both in nuclear reactions and in various reactions with stable elementary particles. A reaction occurs when one elementary particle collides with another or spontaneously disintegrates. As a result of the reaction, new particles are formed, and the mutual transformation of particles occurs.
As an example of a decomposition reaction, we give the following reaction:
n → p + e¯+ ṽ ,
where a neutron decays into a proton, electron and antineutrino.
Antineutrinos and neutrinos are particles with a very low rest mass, thousands of times smaller than the lightest particle - the electron. They are electrically neutral. Neutrino is a stable particle. For a long time, after theoretical prediction, the actions of neutrinos could not be recorded experimentally. Finally, in 1956, the reaction was carried out
p + ṽ → n + e˖
in which a neutron and a positively charged electron - a positron - were formed.
A positron is discovered in experience when it encounters an electron; it “disappears” along with the electron:
e˖ + e¯ → 2y
The reaction is calledannihilationelectron-positive pair; As a result, two photons are formed, which are recorded by special counters.
Mutual convertibilityelementaryparticles during interactions is their second feature.
The third feature inherent in all elementary particles isEach particle has a twin - an antiparticle.If a particle is electrically charged, then the antiparticle carries a charge of the opposite sign. But uncharged particles also have antiparticles. When they meet, the interaction between a particle and an antiparticle leads to their annihilation, i.e. to disappearance, to transformation into photons or other particles. Currently, antiparticles have been discovered for almost all known particles, including the antiproton and antineutron. Even an atom consisting of antiparticles, antihelium, has been obtained, so in principle we can talk about the possibility of the existence of antimatter. The combination of matter with antimatter should lead to the transition of matter into a field, to the annihilation of matter within the framework of the laws of conservation of energy, momentum, and electric charge; this releases energy equivalent to rest massmc². But it is now known that the Universe consists only of matter, and there is no antimatter in it, just as there are no or very few stable antiparticles.
Next you should giveclassification of elementary particleswith the division of all particles by mass into classes: leptons, mesons, baryons. When considering and analyzing the table of elementary particles, we pay attention to their characteristics: masses, charges, lifetime. We inform you that the table contains the main particles - stable and relatively stable. Many unstable particles - mesons and baryons, calledresonances, - not included in the table.
Let's discuss particle sizes. According to modern data, photons and leptons do not exhibit extension or internal structure in experiments. In this respect, they can be classified as truly elementary (primary) particles. Mesons and baryons have sizes of the order of 10¯ ¹⁵ m. Experiments on the scattering of very high-energy electrons by them, similar to Rutherford’s experiments, lead to the conclusion about the presence of an internal structure of mesons and baryons. We can say that they are not elementary, but consist of subelementary particles calledquarks.
When studying elementary particles, we do not touch upon the second macroscopic field that exists in nature—gravitational field. It has been theoretically established that at the microlevel it consists of field quanta calledgravitons. These, like photons, are particles without rest mass and charge. However, graviton has not been experimentally detected.
3. Summing up. Reflection
Homework
Goal: To tell students about elementary particles, their basic properties and classifications
During the classes
New material (given in lecture)
Studies of the structure of the atom and the atomic nucleus have shown that the composition of the atom includes electrons, protons, and neutrons. It was customary to call these particles elementary. Photon (), positron (e +) and neutrino (v), which are directly related to the atom and nucleus, also began to be called elementary particles.
According to the original plan, elementary particles are the simplest particles from which the substance (atoms) of the existing world is built.
Elementary particles were initially imagined as something eternal, unchanging, indestructible, and the image of an elementary particle was associated with the image of a grain of sand or a structureless small ball.
Nowadays there is no clear criterion for elementaryness. The concept of "elementary particle" is very complex these days.
Let us briefly list the known elementary particles in the order of their historical discovery.
Methodological notes: Students are asked to fill out the following table at the time of further explanation (Annex 1)
| What type does it belong to? | Particle name | Designation | Opening year | Charge q | Particle mass |
The electron was discovered by J.J. Thomsan in 1897. The masses of other elementary particles are usually expressed through the mass of the electron.
In 1900 M. Planck and especially, in 19005. A. Einstein showed that light consists of separate portions - photons. A photon has no charge, and its rest mass = 0. A photon can only exist in the process of moving at the speed of light.
Rutherford's experiments on particle scattering in 1911. Led to the discovery of the proton. Proton mass=1836m e
Most physicists were confident that they had finally managed to reduce the entire diversity of chemical elements and substances of nature to two simple entities: electrons and protons. The picture drawn by the physicists of those years on the structure of matter instilled a sense of scientific beauty and grace. In the period from 1911 By 1932 Many scientists were filled with a sense of satisfaction that they were able to fulfill the centuries-old dream of scientific research.
However, in 1928 P. Dirac, and subsequently in 1932 K. Anderson discovered such particles, called positrons(e+)
The positron is the first elementary particle predicted theoretically.
In 1932 D. Chadwig discovered a neutron with mass = 1838 m e
A neutron in a free state, unlike a proton, is unstable and decays into a proton and an electron with a half-life T = 1.01 10 3 s. Inside the nucleus, a neutron can exist indefinitely.
In 1931-1933. W. Pauli, analyzing -decay, suggested that during decay, in addition to the proton and electron, another neutral particle with rest mass = 0 is emitted. This particle was called neutrino()
Only in 1956 K. Cowan and his colleagues discovered an antineutrino() produced in a nuclear reactor. It was “caught” when studying the reaction: p+ v n+e + , the neutrino causes the reaction n+p+e - .
In 1937 K. Anderson and S. Nedderman discovered charged particles with a mass of 206.7m e, these particles were called -mesons (+ and -), having a charge of +e and -e. Currently, these particles are called -particles or -muons.
In 1947 English scientists S. Powell, G. Occhialini and others discovered -mesons (-meson is the primary meson, which, when decaying, gives muons)
The meson has a charge of +e and -e, and a mass of 273.2 m e. Somewhat later than 1950, a neutral -meson (o) was discovered, with a mass of 264.2 m e. Currently, three types of -meson are known: -, o, + , they interact intensively with nucleons and are easily created when nucleons collide with nuclei, i.e. are nuclear active. It is currently believed that -mesons are nuclear field quanta responsible for the bulk of nuclear forces.
From 1949-1950 A literal “invasion” of elementary particles began, their number rapidly increasing.
The newly appeared particles can be divided into two groups:
The first group includes particles with masses of about 966 m e and 974 m e, currently called K-mesons. K + and K - mesons are known with masses of approximately 966.3 m e and electric charges +e and -e. Neutral K-mesons (K o and K o) with masses of 974.5 m e are known.
The second group of particles is called hyperons. The following hyperons are currently known:
In 1955 The antiproton was discovered, and in 1956 the antineutron was discovered.
In recent years, new quasiparticles (resonance states) with an unusually short lifetime, on the order of 10 -22 - 10 -23 sec, have been discovered. In this case, it is not even possible to detect traces of particles and their existence can be judged only from indirect considerations, from analysis behavior of their decomposition products.
In recent years, a second type of neutrino has been discovered, the so-called muon neutrino (antineutrino) and, which is emitted, for example, during the decay of -mesons;
III group- heavy particles, or baryons
This group includes:
- Nucleons and their antiparticles
- Hyperons and their antiparticles
Application of thermonuclear energy using the example of the Tokamak installation
Students are asked to answer the questions:
- What nuclear reaction is called thermonuclear? (oral)
- How can a thermonuclear reaction be carried out?
- Explain the principle of operation of the Tokamak installation. (in writing, using additional literature)
- Explain the principle of operation of a laser installation for thermonuclear fusion" (in writing using additional literature)
To use presentation previews, create a Google account and log in to it: https://accounts.google.com
Slide captions:
Classification of elementary particles Elementary particles (particles that cannot be divided into components) Fundamental (structureless particles) Hadrons (particles with a complex structure) leptons quarks carriers of interactions baryons mesons e-, e+, muon, taon, three types of neutrinos (particles from of which all androns consist) u , c, t , d, s, b 1) electromagnetic: photon 2) strong: gluons 3) weak: intermediate bosons W - , W + neutral boson Z 0 4) gravitational: graviton G (consist of three quarks) p, n, hyperon (consist of two quarks, one of which is an antiquark)
Preview:
Lesson topic : World of elementary particles
Teaching method: lecture
Lesson objectives:
Educational:introduce students to the concept of an elementary particle, with the classification of elementary particles, generalize and consolidate knowledge about fundamental types of interactions,to form a scientific worldview.
Educational: to form a cognitive interest in physics, instilling love and respect for the achievements of science.
Educational: development of curiosity, ability to analyze, independently formulate conclusions, development of speech and thinking.
Equipment: interactive whiteboard (or projector with screen).
During the classes:
Organizational stage
Greeting, checking students' readiness for the lesson.
I. New topic In nature, there are 4 types of fundamental (basic) interactions: gravitational, electromagnetic, strong and weak. According to modern ideas, interaction between bodies is carried out through the fields surrounding these bodies. The field itself in quantum theory is understood as a collection of quanta. Each type of interaction has its own interaction carriers and comes down to the absorption and emission of corresponding light quanta by particles.
Interactions can be long-range (manifest at very long distances) and short-range (manifest at very short distances).
- Gravitational interaction occurs through the exchange of gravitons. They have not been detected experimentally. According to the law discovered in 1687 by the great English scientist Isaac Newton, all bodies, regardless of shape and size, attract each other with a force directly proportional to their mass and inversely proportional to the square of the distance between them. Gravitational interaction always leads to the attraction of bodies.
- Electromagnetic interaction is long-range. Unlike gravitational interaction, electromagnetic interaction can result in both attraction and repulsion. The carriers of electromagnetic interaction are quanta of the electromagnetic field - photons. As a result of the exchange of these particles, electromagnetic interaction arises between charged bodies.
- Strong interaction is the most powerful of all interactions. It is short-range, the corresponding forces decrease very quickly as the distance between them increases. Nuclear force range 10-13 cm
- The weak interaction occurs at very short distances. The range of action is approximately 1000 times less than that of nuclear forces.
The discovery of radioactivity and the results of Rutherford's experiments convincingly showed that atoms are composed of particles. They have been found to consist of electrons, protons and neutrons. At first, the particles from which atoms are built were considered indivisible. That's why they were called elementary particles. The idea of a “simple” structure of the world was destroyed when in 1932 the antiparticle of the electron was discovered - a particle that had the same mass as the electron, but differed from it in the sign of the electric charge. This positively charged particle was called a positron... according to modern concepts, every particle has an antiparticle. The particle and antiparticle have the same mass, but opposite signs of all charges. If the antiparticle coincides with the particle itself, then such particles are called truly neutral, their charge is 0. For example, a photon. When a particle and antiparticle collide, they annihilate, that is, they disappear, turning into other particles (often these particles are a photon).
Slide (as the story progresses, words appear on the slide).
All elementary particles (which cannot be divided into components) are divided into 2 groups:fundamental(structureless particles, all fundamental particles at this stage of development of physics are considered structureless, that is, they do not consist of other particles) and hadrons (particles with a complex structure).
Fundamental particlesin turn are divided into leptons, quarks and carriers of interactions. Hadrons are divided into baryons and mesons. To leptons include electron, positron, muon, taon, three types of neutrino. They do not participate in strong interactions. TO quarks are the particles that make up all hadrons. Uare often in strong interaction.According to modern concepts, each of the interactions arises as a result of the exchange of particles, calledcarriers of this interaction: photon (particle carryingelectromagnetic interaction), eight gluons (particles carryingstrong interaction), three intermediate vector bosons W + , W − and Z 0 carrying weak interaction, graviton (carrier gravitational interactionI). The existence of gravitons has not yet been proven experimentally.
Hadrons participate in all typesfundamental interactions. They are made of quarks and are divided, in turn, into: baryons , consisting of three quarks, and mesons , consisting of two quarks , one of which is antiquark.
The strongest interaction is the interaction between quarks. A proton consists of 2 u quarks, one d quark, a neutron consists of one u quark and 2 d quarks. It turned out that at very short distances none of the quarks notice their neighbors, and they behave like free particles that do not interact with each other. When quarks move away from each other, an attraction arises between them, which increases with increasing distance. To split hadrons into individual isolated quarks would require a lot of energy. Since there is no such energy, the quarks turn out to be eternal prisoners and forever remain locked inside the hadron. Quarks are held inside the hadron by the gluon field.
III. Consolidation
- Name the main interactions that exist in nature
- What is the difference between a particle and an antiparticle? What do they have in common?
- Which particles participate in gravitational, electromagnetic, strong and weak interactions?
Lesson summary. During the lesson we got acquainted with the particles of the microworld and found out which particles are called elementary.
D/z § 28
Molyanova Nadezhda Mikhailovna ID 011
Topic: The origins of particle physics. Classification of elementary particles.The main content of the educational material:
- Historical stages of development of elementary particles.
- The concept of elementary particles and their classification, mutual transformations.
- Types of interactions of elementary particles.
- Elementary particles in our life.
Lesson type: generalization and systematization.
Lesson format: A lecture with elements of conversation and independent work of students with a textbook and tables. (The tables are on the students’ tables and projected on the screen during the lesson)
The purpose of the lesson:
- Expand students’ understanding of the structure of matter, give a classification of elementary particles, their general properties, and familiarize them with the main stages of development.
- Develop students’ scientific thinking based on ideas about elementary particles and their interactions
During the classes:
1. Organizational moment (1 min.)
2. Learning new material (30 min.)
3. Consolidation of learned knowledge (6 min.)
4. Summing up (2 min.)
5. D/Z (1 min.)
1. Today in the lesson we will talk about the primary, indecomposable particles that make up all matter. You are already more or less familiar with the electron, photon, proton and neutron. But what is an elementary particle?
2. The historical stages of development of elementary particles can be presented in the form of a table.
At the beginning of the 20th century, it was found that all atoms are built from neutrons, protons and electrons. Positrons, neutrinos, photons (gamma quantum) were discovered.
Basic characteristics of the most common elementary particles.
Elementary particles, in the precise sense of the word, are the primary, further indecomposable particles from which all substances are composed.
Currently, this term is used for a large group of microparticles that are NOT atoms or nuclei, with the exception of the proton, which is both an elementary particle and the nucleus of a light hydrogen atom.
Elementary particles are characterized by the following parameters: " rest mass of the particle, spin value, electric charge value, lifetime."
The spin of an elementary particle is equal to the ratio of Planck's constant to 2 n 
Particles having spin, etc. are called bosons ; with half-integer spin - fermions , i.e. all elementary particles are divided into particles and antiparticles. They have the same masses, spins, lifetimes and electric charges of equal magnitude.
The positron was discovered in a cloud chamber in 1928. This particle is an electron, but with a positive charge, the positron was discovered in cosmic rays. Later, during the interaction of gamma quanta with matter and in the reaction of converting a proton into a neutron. 
The process of interaction of an elementary particle with an antiparticle, as a result of which they turn into other particles or quanta of an electromagnetic field, is called annihilation
(disappearance). Annihilation reaction:
The reverse process of annihilation is called birth of a couple
.
Question: Think about what structure antideuterium will have?
Answer: consists of an electron and a nucleus (proton and neutron). An antideuterium atom will consist of an antinucleus (an antiproton and an antineutron) and one positron moving around the antinucleus.
Elementary particles participate in four known fundamental types of interaction:
strong, electromagnetic, weak and gravitational. (see table 3) 
The energies of fundamental interactions are approximately as follows:
Let's look at Table 4
Question: Name the main classes of elementary particles. 
Answer: photons, leptons, mesons, baryons.
Question: Name the main characteristics of elementary particles.
Answer: Mass, charge, spin, lifetime.
Question: How are particles and antiparticles different?
Answer: The signs of the electric charges of the particle and antiparticle are opposite.
Photons– particles participating in electromagnetic and gravitational interactions.
Leptons– particles that do not participate in strong interactions, but are capable of the other three.
Hadrons– particles participating in all types of fundamental interactions. This class includes baryons and mesons. Baryons have half-integer spins, and mesons have integer spins. Belonging to a baryon is marked by assigning a baryon charge - a number equal to +1 for a particle, and -1 for an antiparticle. Hadrons include only part of the mesons (P-meson). Nucleons are classified as baryons. Baryons whose mass is greater than the mass of a nucleon are called hyperons.
Belonging to leptons is marked by assigning a lepton charge to each particle: +1 for particles, -1 for antiparticles.
It has been established that hadrons consist of quarks– six particles having a fractional elementary electric charge. Quarks have not been observed in a free state; only in the very center of the nucleon they are found as independent particles.
In order to penetrate deeper into the microworld, it is necessary to use particles of increasingly higher energies.
It turns out that with the enormous energy existing at temperature, the weak and electromagnetic interactions combine into the electroweak interaction. When all four interactions are combined, it becomes possible to transform particles of physical matter (fermions) into particles that are carriers of interaction (bosons).
Why is information about elementary particles so necessary?
The most important thing for particle physics is the conclusion about the relationship between mass and energy. The energy of a body or system of topics is equal to the mass multiplied by the square of the velocity.
Something to think about!
A neutrino is a particle that appeared at the moment of the birth of the Universe and carries a lot of information, so neutrino telescopes “catch” particles and scientists study them. There is a positron tomograph device. A radioactive element is introduced into the blood of a living organism, emitting positrons, which react with the body’s electrons, annihilate, and emit gamma rays, which are detected by a detector.
In small doses, gamma rays have a certain benefit on living organisms. Field of application: medicine, science, technology.
3.
Using supporting notes, a textbook, tables, answer the questions. 
4. All elementary particles transform into each other, i.e. these mutual transformations are the main factor in their existence. Among the properties of elementary particles, the following can be distinguished: instability, interconvertibility and interaction, the presence of an antiparticle in each particle, complex structure, classification.
The world consists of fundamental particles. Any material body has mass. What is mass? The LHC is a particle accelerator that allows physicists to penetrate deeper into matter than ever before.
The creation of the LHC marks the beginning of future advanced research. Researchers hope for new physical phenomena, such as the elusive Higgs particles, or those that form dark matter, which makes up most of the matter in the Universe. It is impossible to accurately predict the results of the upcoming experiments, but they will definitely have a great impact and not only on particle physics! But the creation of the LHC does not end a page in the history of physics, but rather marks the beginning of future promising research.
5.
Homework (on the board)
Paragraphs 115, 116; reference summary
prepare a report on the progress of research work at the LHC.
Used Books:
Physics 11 G.Ya. Myakishev, B.B. Bukhovtsev. Bustard.
Physics course. Volume 3 K.A. Putilov, V.A. Fabrikant.
Atomic and nuclear physics. OK. Costco.
Lesson developments in physics. Grade 11. V.A.Volkov.
Uroki. Net
Class: 11
Class: 11
Lesson type: lesson of studying and primary consolidation of new knowledge
Teaching Method: lecture
Form of student activity: frontal, collective, individual
The purpose of the lesson: expand students’ understanding of the structure of matter; consider the main stages in the development of elementary particle physics; give the concept of elementary particles and their properties.
Lesson objectives:
- Educational: to introduce students to the concept of an elementary particle, the typology of elementary particles, as well as methods for studying the properties of elementary particles;
- Developmental: to develop the cognitive interest of students, ensuring their feasible involvement in active cognitive activity;
- Educational: education of universal human qualities - awareness of the perception of scientific achievements in the world; developing curiosity and endurance.
Equipment for the lesson:
Didactic materials: textbook material, cards with tests and tables
Visual aids: presentation
1. Organization of the beginning of the lesson.
Teacher's activities: mutual greetings between the teacher and students, fixing students, checking students’ readiness for the lesson. Organization of attention and inclusion of students in the business rhythm of work.
organization of attention and inclusion in the business rhythm of work.
2. Preparation for the main stage of the lesson.
Teacher's activities: Today we will begin to study a new section of “Quantum Physics” - “Elementary Particles”. In this chapter we will talk about the primary, indecomposable particles from which all matter is built, about elementary particles.
Physicists discovered the existence of elementary particles when studying nuclear processes, so until the middle of the 20th century, elementary particle physics was a branch of nuclear physics. Currently, elementary particle physics and nuclear physics are close but independent branches of physics, united by the commonality of many problems considered and the research methods used.
The main task of elementary particle physics is the study of the nature, properties and mutual transformations of elementary particles.
It will also be our main task in studying the physics of elementary particles.
3. Assimilation of new knowledge and methods of action.
Teacher's activities: Lesson topic: "Stages of development of elementary particle physics." In this lesson we will look at the following questions:
- The history of the development of ideas that the world consists of elementary particles
- What are elementary particles?
- How can one obtain an isolated elementary particle and is it possible?
- Typology of particles.
The idea that the world is made of fundamental particles has a long history. Today, there are three stages in the development of elementary particle physics.
Let's open the textbook. Let's get acquainted with the names of the stages and time frames.
Predicted student activity:
Stage 1. From electron to positron: 1897 - 1932.
Stage 2. From positron to quarks: 1932 - 1964.
Stage 3. From the quark hypothesis (1964) to the present day.
Teacher's activities:
Stage 1.
Elementary, i.e. the simplest, further indivisible, this is how the famous ancient Greek scientist Democritus imagined the atom. Let me remind you that the word “atom” in translation means “indivisible”. For the first time, the idea of the existence of tiny, invisible particles that make up all surrounding objects was expressed by Democritus 400 years BC. Science began to use the idea of atoms only at the beginning of the 19th century, when on this basis it was possible to explain a number of chemical phenomena. And at the end of this century the complex structure of the atom was discovered. In 1911, the atomic nucleus was discovered (E. Rutherford) and it was finally proven that atoms have a complex structure.
Let's remember guys: what particles are part of the atom and briefly characterize them?
Predicted student activity:
Teacher's activities: guys, maybe some of you remember: by whom and in what years were the electron, proton and neutron discovered?
Predicted student activity:
Electron. In 1898, J. Thomson proved the reality of the existence of electrons. In 1909, R. Millikan first measured the charge of an electron.
Proton. In 1919, E. Rutherford, while bombarding nitrogen with particles, discovered a particle whose charge was equal to the charge of an electron, and whose mass was 1836 times greater than the mass of the electron. The particle was named proton.
Neutron. Rutherford also suggested the existence of a chargeless particle whose mass is equal to the mass of a proton.
In 1932, D. Chadwick discovered the particle that Rutherford had suggested and called it the neutron.
Teacher's activities: After the discovery of the proton and neutron, it became clear that the nuclei of atoms, like the atoms themselves, have a complex structure. The proton-neutron theory of the structure of nuclei arose (D. D. Ivanenko and V. Heisenberg).
In the 30s of the 19th century, in the theory of electrolysis developed by M. Faraday, the concept of -ion appeared and the elementary charge was measured. The end of the 19th century - in addition to the discovery of the electron, was marked by the discovery of the phenomenon of radioactivity (A. Becquerel, 1896). In 1905, the idea of electromagnetic field quanta - photons (A. Einstein) arose in physics.
Let's remember: what is a photon?
Predicted student activity: Photon(or quantum of electromagnetic radiation) is an elementary light particle, electrically neutral, devoid of rest mass, but possessing energy and momentum.
Teacher's activities: open particles were considered indivisible and unchangeable primary essences, the basic building blocks of the universe. However, this opinion did not last long.
Stage 2.
In the 1930s, the mutual transformations of protons and neutrons were discovered and studied, and it became clear that these particles are also not the unchanging elementary “building blocks” of nature.
Currently, about 400 subnuclear particles are known (the particles that make up atoms, which are usually called elementary). The vast majority of these particles are unstable (elementary particles transform into each other).
The only exceptions are the photon, electron, proton and neutrino.
The photon, electron, proton and neutrino are stable particles (particles that can exist in a free state indefinitely), but each of them, when interacting with other particles, can turn into other particles.
All other particles, at certain intervals of time, undergo spontaneous transformations into other particles, and this is the main fact of their existence.
I mentioned one more particle - the neutrino. What are the main characteristics of this particle? By whom and when was it discovered?
Predicted activity of the student: Neutrino is a particle devoid of electric charge and its rest mass is 0. The existence of this particle was predicted in 1931 by W. Pauli, and in 1955, the particle was experimentally registered. Manifests itself as a result of neutron decay:
Teacher's activities: Unstable elementary particles differ greatly in their lifetimes.
The longest-lived particle is the neutron. The neutron lifetime is about 15 minutes.
Other particles “live” for a much shorter time.
There are several dozen particles with a lifetime exceeding 10 -17 s. On the scale of the microcosm, this is a significant time. Such particles are called relatively stable .
Majority short-lived elementary particles have lifetimes of the order of 10 -22 -10 -23 s.
The ability for mutual transformations is the most important property of all elementary particles.
Elementary particles are capable of being born and destroyed (emitted and absorbed). This also applies to stable particles, with the only difference being that transformations of stable particles do not occur spontaneously, but through interaction with other particles.
An example would be annihilation (i.e. disappearance) electron and positron, accompanied by the birth of high-energy photons.
A positron is (an antiparticle of an electron) a positively charged particle that has the same mass and the same (in absolute value) charge as an electron. We'll talk about its characteristics in more detail in the next lesson. Let's just say that the existence of the positron was predicted by P. Dirac in 1928, and it was discovered in 1932 in cosmic rays by K. Anderson.
In 1937, particles with a mass of 207 electron masses were discovered in cosmic rays, called muons (-mesons). The average lifetime of a meson is 2.2 * 10 -6 s.
Then in 1947-1950 they opened peonies (i.e. -mesons). The average lifetime of a neutral -meson is 0.87·10 -16 s.
In subsequent years, the number of newly discovered particles began to grow rapidly. This was facilitated by research into cosmic rays, the development of accelerator technology and the study of nuclear reactions.
Modern accelerators are necessary to carry out the process of creating new particles and studying the properties of elementary particles. The initial particles are accelerated in the accelerator to high energies “on a collision course” and collide with each other in a certain place. If the energy of the particles is high, then during the collision process many new particles are born, usually unstable. These particles, scattering from the point of collision, disintegrate into more stable particles, which are recorded by detectors. For each such act of collision (physicists say: for each event) - and they are recorded in thousands per second! -experimenters as a result determine kinematic variables: the values of the impulses and energies of the “caught” particles, as well as their trajectories (see figure in the textbook). By collecting many events of the same type and studying the distributions of these kinematic quantities, physicists reconstruct how the interaction occurred and what type of particles the resulting particles can be attributed to.
Stage 3.
Elementary particles are combined into three groups: photons , leptons And hadrons (Appendix 2).
Guys, list me the particles belonging to the group of photons.
Predicted student activity: To the group photons refers to a single particle - a photon
Teacher's activities: the next group consists of light particles leptons.
Predicted student activity: this group includes two types of neutrinos (electron and muon), electron and?-meson
Teacher's activities: Leptons also include a number of particles not listed in the table.
The third large group consists of heavy particles called hadrons. This group is divided into two subgroups. Lighter particles form a subgroup mesons .
Predicted student activity: the lightest of them are positively and negatively charged, as well as neutral -mesons. Pions are quanta of the nuclear field.
Teacher's activities: second subgroup - baryons - includes heavier particles. It is the most extensive.
Predicted student activity: The lightest baryons are nucleons - protons and neutrons.
Teacher's activities: they are followed by the so-called hyperons. Omega-minus-hyperon, discovered in 1964, closes the table.
The abundance of discovered and newly discovered hadrons led scientists to believe that they were all built from some other more fundamental particles.
In 1964, the American physicist M. Gell-Man put forward a hypothesis, confirmed by subsequent research, that all heavy fundamental particles - hadrons - are built from more fundamental particles called quarks.
From a structural point of view, the elementary particles that make up atomic nuclei (nucleons), and in general all heavy particles - hadrons (baryons and mesons) - consist of even simpler particles, which are usually called fundamental. In this role of truly fundamental primary elements of matter are quarks, the electric charge of which is equal to +2/3 or -1/3 of the unit positive charge of a proton.
The most common and light quarks are called up and down and are designated, respectively, u (from English up) and d (down). Sometimes they are also called proton and neutron quarks due to the fact that the proton consists of a combination of uud, and the neutron - udd. The top quark has a charge of +2/3; bottom - negative charge -1/3. Since a proton consists of two up and one down, and a neutron consists of one up and two down quarks, you can independently verify that the total charge of the proton and neutron is strictly equal to 1 and 0.
The other two pairs of quarks are part of more exotic particles. Quarks from the second pair are called charmed - c (from charmed) and strange - s (from strange).
The third pair consists of true - t (from truth, or in the English tradition top) and beautiful - b (from beauty, or in the English tradition bottom) quarks.
Almost all particles consisting of various combinations of quarks have already been discovered experimentally
With the acceptance of the quark hypothesis, it was possible to create a harmonious system of elementary particles. Numerous searches for quarks in the free state, carried out at high-energy accelerators and in cosmic rays, have been unsuccessful. Scientists believe that one of the reasons for the unobservability of free quarks is perhaps their very large masses. This prevents the birth of quarks at the energies that are achieved in modern accelerators.
However, in December 2006, a strange message about the discovery of “free top quarks” was broadcast across scientific news agencies and the media.
4. Initial check of understanding.
Teacher's activities: so guys, we've covered:
- main stages in the development of particle physics
- found out which particle is called elementary
- got acquainted with the typology of particles.
In the next lesson we will look at:
- more detailed classification of elementary particles
- types of interactions of elementary particles
- antiparticles.
And now I suggest you take a test to revive in your memory the main points of the material we have studied (Appendix 3).
5. Summing up the lesson.
Teacher's activities: Giving grades to the most active students.
6. Homework
Teacher's activities:
1. pr. 115, p. 347
2. outline of the paragraph according to the plan recorded in the lesson.
