To nucleic acids include high-polymer compounds that decompose during hydrolysis into purine and pyrimidine bases, pentose and phosphoric acid. Nucleic acids contain carbon, hydrogen, phosphorus, oxygen and nitrogen. There are two classes of nucleic acids: ribonucleic acids (RNA) and deoxyribonucleic acids (DNA).

Structure and functions of DNA

DNA- a polymer whose monomers are deoxyribonucleotides. The model of the spatial structure of the DNA molecule in the form of a double helix was proposed in 1953 by J. Watson and F. Crick (to build this model, they used the work of M. Wilkins, R. Franklin, E. Chargaff).

DNA molecule formed by two polynucleotide chains, spirally twisted around each other and together around an imaginary axis, i.e. is a double helix (exception - some DNA-containing viruses have single-stranded DNA). The diameter of the DNA double helix is ​​2 nm, the distance between adjacent nucleotides is 0.34 nm, and there are 10 pairs of nucleotides per turn of the helix. The length of the molecule can reach several centimeters. Molecular weight - tens and hundreds of millions. The total length of DNA in the human cell nucleus is about 2 m. In eukaryotic cells, DNA forms complexes with proteins and has a specific spatial conformation.

DNA monomer - nucleotide (deoxyribonucleotide)- consists of residues of three substances: 1) a nitrogenous base, 2) a five-carbon monosaccharide (pentose) and 3) phosphoric acid. The nitrogenous bases of nucleic acids belong to the classes of pyrimidines and purines. Pyrimidine bases of DNA(have one ring in their molecule) - thymine, cytosine. Purine bases(have two rings) - adenine and guanine.

The monosaccharide of the DNA nucleotide is represented by deoxyribose.

The name of the nucleotide is derived from the name of the corresponding base. Nucleotides and nitrogenous bases are indicated by capital letters.

A polynucleotide chain is formed as a result of nucleotide condensation reactions. In this case, between the 3 "-carbon of the deoxyribose residue of one nucleotide and the phosphoric acid residue of the other, phosphoether bond(belongs to the category of strong covalent bonds). One end of the polynucleotide chain ends with a 5 "carbon (it is called the 5" end), the other ends with a 3 "carbon (3" end).

Against one chain of nucleotides is a second chain. The arrangement of nucleotides in these two chains is not random, but strictly defined: thymine is always located opposite the adenine of one chain in the other chain, and cytosine is always located opposite guanine, two hydrogen bonds arise between adenine and thymine, three hydrogen bonds between guanine and cytosine. The pattern according to which the nucleotides of different strands of DNA are strictly ordered (adenine - thymine, guanine - cytosine) and selectively combine with each other is called the principle of complementarity. It should be noted that J. Watson and F. Crick came to understand the principle of complementarity after reading the works of E. Chargaff. E. Chargaff, having studied a huge number of samples of tissues and organs of various organisms, found that in any DNA fragment the content of guanine residues always exactly corresponds to the content of cytosine, and adenine to thymine ( "Chargaff's rule"), but he could not explain this fact.

From the principle of complementarity, it follows that the nucleotide sequence of one chain determines the nucleotide sequence of another.

DNA strands are antiparallel (opposite), i.e. nucleotides of different chains are located in opposite directions, and, therefore, opposite the 3 "end of one chain is the 5" end of the other. The DNA molecule is sometimes compared to a spiral staircase. The "railing" of this ladder is the sugar-phosphate backbone (alternating residues of deoxyribose and phosphoric acid); "steps" are complementary nitrogenous bases.

Function of DNA- storage and transmission of hereditary information.

Replication (reduplication) of DNA

- the process of self-doubling, the main property of the DNA molecule. Replication belongs to the category of matrix synthesis reactions and involves enzymes. Under the action of enzymes, the DNA molecule unwinds, and around each strand acting as a template, a new strand is completed according to the principles of complementarity and antiparallelism. Thus, in each daughter DNA, one strand is the parent strand, and the second strand is newly synthesized. This kind of synthesis is called semi-conservative.

The "building material" and source of energy for replication are deoxyribonucleoside triphosphates(ATP, TTP, GTP, CTP) containing three phosphoric acid residues. When deoxyribonucleoside triphosphates are included in the polynucleotide chain, two terminal residues of phosphoric acid are cleaved off, and the released energy is used to form a phosphodiester bond between nucleotides.

The following enzymes are involved in replication:

1. helicases ("unwind" DNA);
2. destabilizing proteins;
3. DNA topoisomerases (cut DNA);
4. DNA polymerases (select deoxyribonucleoside triphosphates and complementarily attach them to the DNA template chain);
5. RNA primases (form RNA primers, primers);
6. DNA ligases (sew DNA fragments together).

With the help of helicases, DNA is untwisted in certain regions, single-stranded DNA regions are bound by destabilizing proteins, and replication fork. With a discrepancy of 10 pairs of nucleotides (one turn of the helix), the DNA molecule must complete a complete revolution around its axis. To prevent this rotation, DNA topoisomerase cuts one DNA strand, allowing it to rotate around the second strand.

DNA polymerase can only attach a nucleotide to the 3" carbon of the deoxyribose of the previous nucleotide, so this enzyme is able to move along template DNA in only one direction: from the 3" end to the 5" end of this template DNA. Since the chains in maternal DNA are antiparallel , then on its different chains the assembly of the daughter polynucleotide chains occurs in different ways and in opposite directions. On the 3 "-5" chain, the synthesis of the daughter polynucleotide chain proceeds without interruption; this daughter chain will be called leading. On the chain 5 "-3" - intermittently, in fragments ( fragments of Okazaki), which, after completion of replication by DNA ligases, are fused into one strand; this child chain will be called lagging (lagging behind).

A feature of DNA polymerase is that it can start its work only with "seeds" (primer). The role of "seeds" is performed by short RNA sequences formed with the participation of the RNA primase enzyme and paired with template DNA. RNA primers are removed after the completion of the assembly of polynucleotide chains.

Replication proceeds similarly in prokaryotes and eukaryotes. The rate of DNA synthesis in prokaryotes is an order of magnitude higher (1000 nucleotides per second) than in eukaryotes (100 nucleotides per second). Replication begins simultaneously in several regions of the DNA molecule. A piece of DNA from one origin of replication to another forms a unit of replication - replicon.

Replication occurs before cell division. Thanks to this ability of DNA, the transfer of hereditary information from the mother cell to the daughter cells is carried out.

Reparation ("repair")

reparations is the process of repairing damage to the nucleotide sequence of DNA. It is carried out by special enzyme systems of the cell ( repair enzymes). The following steps can be distinguished in the process of DNA structure repair: 1) DNA-repairing nucleases recognize and remove the damaged area, resulting in a gap in the DNA chain; 2) DNA polymerase fills this gap by copying information from the second (“good”) strand; 3) DNA ligase “crosslinks” the nucleotides, completing the repair.

Three repair mechanisms have been studied the most: 1) photoreparation, 2) excise or pre-replicative repair, 3) post-replicative repair.

Changes in the structure of DNA occur constantly in the cell under the influence of reactive metabolites, ultraviolet radiation, heavy metals and their salts, etc. Therefore, defects in repair systems increase the rate of mutation processes and cause hereditary diseases (xeroderma pigmentosa, progeria, etc.).

Structure and functions of RNA

is a polymer whose monomers are ribonucleotides. Unlike DNA, RNA is formed not by two, but by one polynucleotide chain (exception - some RNA-containing viruses have double-stranded RNA). RNA nucleotides are capable of forming hydrogen bonds with each other. RNA chains are much shorter than DNA chains.

RNA monomer - nucleotide (ribonucleotide)- consists of residues of three substances: 1) a nitrogenous base, 2) a five-carbon monosaccharide (pentose) and 3) phosphoric acid. The nitrogenous bases of RNA also belong to the classes of pyrimidines and purines.

The pyrimidine bases of RNA are uracil, cytosine, and the purine bases are adenine and guanine. The RNA nucleotide monosaccharide is represented by ribose.

Allocate three types of RNA: 1) informational(matrix) RNA - mRNA (mRNA), 2) transport RNA - tRNA, 3) ribosomal RNA - rRNA.

All types of RNA are unbranched polynucleotides, have a specific spatial conformation and take part in the processes of protein synthesis. Information about the structure of all types of RNA is stored in DNA. The process of RNA synthesis on a DNA template is called transcription.

Transfer RNAs usually contain 76 (from 75 to 95) nucleotides; molecular weight - 25,000-30,000. The share of tRNA accounts for about 10% of the total RNA content in the cell. tRNA functions: 1) transport of amino acids to the site of protein synthesis, to ribosomes, 2) translational mediator. About 40 types of tRNA are found in the cell, each of them has a nucleotide sequence characteristic only for it. However, all tRNAs have several intramolecular complementary regions, due to which tRNAs acquire a conformation that resembles a clover leaf in shape. Any tRNA has a loop for contact with the ribosome (1), an anticodon loop (2), a loop for contact with the enzyme (3), an acceptor stem (4), and an anticodon (5). The amino acid is attached to the 3' end of the acceptor stem. Anticodon- three nucleotides that "recognize" the mRNA codon. It should be emphasized that a particular tRNA can transport a strictly defined amino acid corresponding to its anticodon. The specificity of the connection of amino acids and tRNA is achieved due to the properties of the enzyme aminoacyl-tRNA synthetase.

Ribosomal RNA contain 3000-5000 nucleotides; molecular weight - 1,000,000-1,500,000. rRNA accounts for 80-85% of the total RNA content in the cell. In combination with ribosomal proteins, rRNA forms ribosomes - organelles that carry out protein synthesis. In eukaryotic cells, rRNA synthesis occurs in the nucleolus. rRNA functions: 1) a necessary structural component of ribosomes and, thus, ensuring the functioning of ribosomes; 2) ensuring the interaction of the ribosome and tRNA; 3) initial binding of the ribosome and the mRNA initiator codon and determination of the reading frame, 4) formation of the active center of the ribosome.

Information RNA varied in nucleotide content and molecular weight (from 50,000 to 4,000,000). The share of mRNA accounts for up to 5% of the total RNA content in the cell. Functions of mRNA: 1) transfer of genetic information from DNA to ribosomes, 2) a matrix for the synthesis of a protein molecule, 3) determination of the amino acid sequence of the primary structure of a protein molecule.

The structure and functions of ATP

Adenosine triphosphoric acid (ATP) is a universal source and main accumulator of energy in living cells. ATP is found in all plant and animal cells. The amount of ATP averages 0.04% (of the raw mass of the cell), the largest amount of ATP (0.2-0.5%) is found in skeletal muscles.

ATP consists of residues: 1) a nitrogenous base (adenine), 2) a monosaccharide (ribose), 3) three phosphoric acids. Since ATP contains not one, but three residues of phosphoric acid, it belongs to ribonucleoside triphosphates.

For most types of work occurring in cells, the energy of ATP hydrolysis is used. At the same time, when the terminal residue of phosphoric acid is cleaved, ATP is converted into ADP (adenosine diphosphoric acid), when the second phosphoric acid residue is cleaved, it becomes AMP (adenosine monophosphoric acid). The yield of free energy during the elimination of both the terminal and the second residues of phosphoric acid is 30.6 kJ each. Cleavage of the third phosphate group is accompanied by the release of only 13.8 kJ. The bonds between the terminal and the second, second and first residues of phosphoric acid are called macroergic (high-energy).

ATP reserves are constantly replenished. In the cells of all organisms, ATP synthesis occurs in the process of phosphorylation, i.e. addition of phosphoric acid to ADP. Phosphorylation occurs with different intensity during respiration (mitochondria), glycolysis (cytoplasm), photosynthesis (chloroplasts).

ATP is the main link between processes accompanied by the release and accumulation of energy, and processes that require energy. In addition, ATP, along with other ribonucleoside triphosphates (GTP, CTP, UTP), is a substrate for RNA synthesis.

Go to lectures №3“The structure and function of proteins. Enzymes»

Go to lectures number 5"Cell Theory. Types of cellular organization»

For the further development of nuclear physics (in particular, to study the structure of atomic nuclei), special devices were needed with which it would be possible to register nuclei and various particles, as well as to study their interactions.

One of the particle detection methods known to you - the scintillation method - does not provide the necessary accuracy, since the result of counting flashes on the screen to a large extent depends on the visual acuity of the observer. In addition, long-term observation is impossible, as the eye gets tired quickly.

A more advanced device for registering particles is the so-called Geiger counter, invented in 1908 by the German physicist Hans Geiger.

To consider the device and the principle of operation of this device, let's turn to Figure 159. The Geiger counter consists of a metal cylinder, which is the cathode (i.e., a negatively charged electrode), and a thin wire stretched along its axis - the anode (i.e., positive electrode). The cathode and anode are connected through resistance R to a high voltage source (of the order of 200-1000 V), due to which a strong electric field arises in the space between the electrodes. Both electrodes are placed in a sealed glass tube filled with a rarefied gas (usually argon).

Rice. 159. Diagram of the device of the Geiger counter

As long as the gas is not ionized, there is no current in the electrical circuit of the voltage source. If, however, some particle capable of ionizing gas atoms flies into the tube through its walls, then a certain amount of electron-ion pairs is formed in the tube. Electrons and ions begin to move towards the corresponding electrodes.

If the electric field strength is high enough, then the electrons on the mean free path (i.e., between collisions with gas molecules) acquire a sufficiently large energy and also ionize gas atoms, forming a new generation of ions and electrons, which can also take part in ionization, and etc. A so-called electron-ion avalanche is formed in the tube, as a result of which there is a short-term and sharp increase in the current strength in the circuit and the voltage across the resistance R. This voltage pulse, indicating that a particle has entered the counter, is recorded by a special device.

Since the resistance R is very high (of the order of 10 9 Ohm), then at the moment of current flow, the main share of the source voltage drops precisely on it, as a result of which the voltage between the cathode and anode decreases sharply and the discharge automatically stops (since this voltage becomes insufficient for the formation of new generations of electron-ion pairs). The device is ready to register the next particle.

The Geiger counter is used mainly for registering electrons, but there are models that are also suitable for registering γ-quanta.

The counter only allows you to register the fact that a particle flies through it. Much greater opportunities for studying the microcosm are given by the device invented by the Scottish physicist Charles Wilson in 1912 and called the cloud chamber.

The cloud chamber (Fig. 160) consists of a low glass cylinder CC with a glass cover LL (the cylinder is shown in section in the figure). Piston P can move inside the cylinder. At the bottom of the chamber is a black cloth FF. Due to the fact that the tissue is moistened with a mixture of water and ethyl alcohol, the air in the chamber is saturated with vapors of these liquids.

Rice. 160. Scheme of the device cloud chamber

With the rapid downward movement of the piston, the air and vapors of liquids in the chamber expand, their internal energy decreases, and the temperature decreases.

Under normal conditions, this would cause vapor condensation (fog). However, this does not happen in the cloud chamber, since the so-called condensation nuclei (dust particles, ions, etc.) are previously removed from it. Therefore, in this case, as the temperature in the chamber decreases, the vapors of liquids become supersaturated, i.e., they pass into an extremely unstable state in which they will easily condense on any condensation nuclei formed in the chamber, for example, on ions.

The studied particles are admitted into the chamber through a thin window (sometimes the particle source is placed inside the chamber). Flying at high speed through the gas, the particles create ions on their way. These ions become condensation nuclei, on which liquid vapors condense in the form of small droplets (water vapor condenses mainly on negative ions, ethyl alcohol vapor on positive ones). Along the entire path of the particle, a thin trace of droplets (track) appears, due to which its trajectory of movement becomes visible.

If you place a cloud chamber in a magnetic field, then the trajectories of charged particles are curved. By the direction of the trace bending, one can judge the sign of the charge of the particle, and by the radius of curvature, one can determine its mass, energy, and charge.

Tracks do not exist in the chamber for long, since the air heats up, receiving heat from the walls of the chamber, and the droplets evaporate. To obtain new traces, it is necessary to remove the existing ions using an electric field, compress the air with a piston, wait until the air in the chamber, heated during compression, cools down, and perform a new expansion.

Usually, particle tracks in a cloud chamber are not only observed, but also photographed. In this case, the chamber is illuminated from the side with a powerful beam of light rays, as shown in Figure 160.

With the cloud chamber, a number of important discoveries were made in the field of nuclear physics and elementary particle physics.

One of the varieties of the cloud chamber is the bubble chamber invented in 1952. It operates on roughly the same principle as a cloud chamber, but instead of supersaturated steam, it uses a liquid superheated above the boiling point (for example, liquid hydrogen). When a charged particle moves in this liquid along its trajectory, a series of vapor bubbles is formed. The bubble chamber is faster than the cloud chamber.

Questions

1. According to Figure 159, tell us about the device and the principle of operation of the Geiger counter.
2. What kind of particles are used in a Geiger counter?
3. According to Figure 160, tell us about the device and the principle of operation of the cloud chamber.
4. What characteristics of particles can be determined using a cloud chamber placed in a magnetic field?
5. What is the advantage of a bubble chamber over a cloud chamber? How are these devices different?

Elementary particles can be observed due to the traces they leave when passing through matter. The nature of the traces makes it possible to judge the sign of the charge of the particle, its energy, and momentum. Charged particles cause ionization of molecules in their path. Neutral particles leave no traces on their way, but they can reveal themselves at the moment of decay into charged particles or at the moment of collision with any nucleus. Therefore, neutral particles are also detected by ionization caused by generated or charged particles.

Gas discharge Geiger counter. A Geiger counter is a device for automatically counting particles. The counter consists of a glass tube covered from the inside with a metal layer (cathode) and a thin metal thread running along the axis of the tube (anode).

The tube is usually filled with an inert gas (argon). The operation of the device is based on impact ionization. A charged particle flying through a gas collides with atoms, resulting in the creation of positive gas ions and electrons. The electric field between the cathode and the anode accelerates the electrons to energies at which impact ionization begins. An avalanche of ions and electrons appears, and the current through the counter increases sharply. In this case, a voltage pulse is formed on the load resistance R, which is fed to the counting device.

The Geiger counter is mainly used to register electrons and -quanta. Registration of heavy particles (for example, -particles) is difficult, since it is difficult to make a sufficiently thin "window" transparent for these particles in the counter.

cloud chamber. In a cloud chamber, built in 1912, a charged particle leaves a trail that can be observed directly or photographed. The operation of the chamber is based on the condensation of supersaturated steam on ions to form water droplets. These ions are created along its trajectory by a moving charged particle. By the length of the trace (track) left by the particle, one can determine the energy of the particle, and by the number of droplets per unit length of the track, one can estimate its speed. Highly charged particles leave a thicker track.

bubble chamber. In 1952 The American scientist D. Glaser suggested using a superheated liquid to detect particle tracks. An ionizing particle flying through the chamber causes a rapid boiling of the liquid, as a result of which the trace of the particle turns out to be indicated by a chain of vapor bubbles - a track is formed.

emulsion chamber. Soviet physicists L.V. Mysovsky and A.P. Zhdanov was the first to use photographic plates to register microparticles. Charged particles have the same effect on photographic emulsion as do photons. Therefore, after the development of the plate in the emulsion, a visible trace (track) of the flying particle is formed. A disadvantage of the photographic plate method was the small thickness of the emulsion layer, as a result of which only tracks of particles lying parallel to the layer plane were completely obtained.

In emulsion chambers, thick packs made up of individual layers of photographic emulsion are exposed to radiation. This method was called the method of thick-layer photographic emulsions.

In this article, we will help prepare for a lesson in physics (grade 9). particle research is not an ordinary topic, but a very interesting and exciting excursion into the world of molecular nuclear science. Civilization was able to achieve such a level of progress quite recently, and scientists are still arguing whether humanity needs such knowledge? After all, if people can repeat the process of an atomic explosion that led to the emergence of the Universe, then maybe not only our planet, but the entire Cosmos will be destroyed.

What particles are we talking about and why to study them

Partial answers to these questions are given by the course of physics. Experimental particle research is a way to see what is inaccessible to humans even with the most powerful microscopes. But first things first.

An elementary particle is a collective term, which refers to such particles that can no longer be split into smaller pieces. In total, more than 350 elementary particles have been discovered by physicists. We are most used to hearing about protons, neurons, electrons, photons, quarks. These are the so-called fundamental particles.

Characteristics of elementary particles

All the smallest particles have the same property: they can mutually transform under the influence of their own influence. Some have strong electromagnetic properties, others have weak gravitational properties. But all elementary particles are characterized by the following parameters:

• Weight.
• Spin is the intrinsic moment of momentum.
• Electric charge.
• Lifetime.
• Parity.
• magnetic moment.
• baryon charge.
• lepton charge.

A brief excursion into the theory of the structure of matter

Any substance consists of atoms, which in turn have a nucleus and electrons. Electrons, like the planets in the solar system, move around the nucleus, each on its own axis. The distance between them is very large, on an atomic scale. The nucleus consists of protons and neurons, the connection between them is so strong that it is impossible to separate them in any way known to science. This is the essence of experimental methods for studying particles (briefly).

It is hard for us to imagine this, but nuclear communication surpasses all forces known on earth by millions of times. We know chemical, nuclear explosion. But what holds the protons and neurons together is something else. Perhaps this is the key to unraveling the mystery of the origin of the universe. That is why it is so important to study experimental methods for studying particles.

Numerous experiments led scientists to the idea that neurons are made up of even smaller units and called them quarks. What is inside them is not yet known. But quarks are inseparable units. That is, there is no way to single out one. If scientists use particle experimentation to extract one quark, no matter how many attempts they make, at least two quarks are always released. This once again confirms the indestructible strength of the nuclear potential.

What are the methods of studying particles

Let us proceed directly to the experimental methods for studying particles (Table 1).

Method name		Operating principle
	Glow (luminescence)	The radioactive drug emits waves, due to which the particles collide and individual glows can be observed.
	Ionization of gas molecules by fast charged particles	It lowers the piston at high speed, which leads to strong cooling of the steam, which becomes supersaturated. Droplets of condensate indicate the trajectories of the chain of ions.
bubble chamber	Liquid ionization	The volume of the working space is filled with hot liquid hydrogen or propane, which is acted upon under pressure. Bring the state to overheated and sharply reduce the pressure. Charged particles, acting with even more energy, cause hydrogen or propane to boil. On the trajectory along which the particle moved, vapor droplets are formed.
Scintillation method (Spinthariscope)	Glow (luminescence)	When gas molecules are ionized, a large number of electron-ion pairs are produced. The greater the tension, the more free pairs arise until it reaches a peak and there is not a single free ion left. At this moment, the counter registers the particle. This is one of the first experimental methods for studying charged particles, and was invented five years later than the Geiger counter - in 1912. The structure is simple: a glass cylinder, inside - a piston. Below is a black cloth soaked in water and alcohol, so that the air in the chamber is saturated with their vapors. The piston begins to lower and raise, creating pressure, causing the gas to cool. Condensation should form, but it does not exist, since there is no condensation center (ion or dust grain) in the chamber. After that, the flask is raised to get particles - ions or dust. The particle begins to move and condensate forms along its trajectory, which can be seen. The path that a particle travels is called a track. The disadvantage of this method is that the range of particles is too small. This led to a more progressive theory based on a device with a denser medium. bubble chamber The following experimental method for studying particles has a similar principle of operation of a cloud chamber - Only instead of a saturated gas, there is a liquid in a glass flask. The basis of the theory is that under high pressure, a liquid cannot begin to boil above the boiling point. But as soon as a charged particle appears, the liquid begins to boil along the track of its movement, turning into a vapor state. The droplets of this process are captured by a camera. Method of thick-layer photographic emulsions Let's return to the table in physics "Experimental Methods for Investigating Particles". In it, along with the cloud chamber and the bubble method, a method for detecting particles using a thick-layer photographic emulsion was considered. The experiment was first staged by Soviet physicists L.V. Mysovsky and A.P. Zhdanov in 1928. The idea is very simple. For experiments, a plate covered with a thick layer of photographic emulsions is used. This photographic emulsion consists of silver bromide crystals. When a charged particle penetrates a crystal, it separates electrons from the atom, which form a hidden chain. It can be seen by developing the film. The resulting image allows you to calculate the energy and mass of the particle. In fact, the track is very short and microscopically small. But the method is good because the developed picture can be enlarged an infinite number of times, thereby studying it better. Scintillation Method It was first held by Rutherford in 1911, although the idea arose a little earlier from another scientist, W. Krupe. Despite the fact that the difference was 8 years, the device had to be improved during this time. The basic principle is that a screen coated with a luminescent substance will display flashes of light as a charged particle passes through. Atoms of a substance are excited when exposed to a particle with a powerful energy. At the moment of collision, a flash occurs, which is observed under a microscope. This method is very unpopular among physicists. It has several disadvantages. First, the accuracy of the results obtained depends very much on the visual acuity of the person. If you blink, you can miss a very important moment. The second is that with prolonged observation, the eyes get tired very quickly, and therefore, the study of atoms becomes impossible. conclusions There are several experimental methods for studying charged particles. Since the atoms of matter are so small that they are difficult to see even with the most powerful microscope, scientists have to experiment to understand what is in the middle of the center. At this stage in the development of civilization, a long way has been made and the most inaccessible elements have been studied. Perhaps it is in them that the secrets of the universe lie.

Author: Fomicheva S.E., teacher of physics MBOU "Secondary School No. 27" of the city of Kirov Methods for registration and observation of elementary particles Geiger counter Wilson chamber Bubble chamber Photo emulsion method Scintillation method Spark chamber (1908) Designed for automatic counting of particles. Allows you to register up to 10,000 or more particles per second. Registers almost every electron (100%) and 1 in 100 gamma rays (1%) Registration of heavy particles is difficult Hans Wilhelm Geiger 1882-1945 Device: 2. Cathode - a thin metal layer 3. Anode - a thin metal thread 1. Glass tube, filled with argon 4. Recording device To detect a γ-quantum, the inner wall of the tube is covered with a material from which γ-quanta extract electrons. Principle of action: The action is based on impact ionization. A charged particle flying through a gas removes electrons from atoms. There is an avalanche of electrons and ions. The current through the counter increases sharply. A voltage pulse is formed across the resistor R, which is recorded by a counting device. The voltage between the anode and cathode decreases sharply. The discharge stops, the counter is ready for operation again (1912). Designed to observe and obtain information about particles. When a particle passes, it leaves a trace - a track that can be observed directly or photographed. Only charged particles are fixed, neutral ones do not cause ionization of the atom, their presence is judged by secondary effects. Charles Thomson Reese Wilson 1869-1959 Device: 7. Chamber filled with water vapor and alcohol 1. Particle source 2. Quartz glass 3. Electrodes to create an electric field 6. Tracks 5. Piston 4. Fan Operating principle: Operation is based on the use of an unstable state environment. The vapor in the chamber is close to saturation. When the piston is lowered, an adiabatic expansion occurs and the steam becomes supersaturated. Water droplets form tracks. The flying particle ionizes the atoms, on which the vapor, which is in an unstable state, condenses. The piston rises, the droplets evaporate, the electric field removes the ions and the chamber is ready to receive the next particle. by the number of drops per unit length - about the speed (the more N, the v); According to the thickness of the track - about the magnitude of the charge (the more d, the more q) According to the curvature of the track in a magnetic field, about the ratio of the charge of the particle to its mass (the more R, the more m and v, the more q); In the direction of the bend about the sign of the charge of the particle. (1952) Designed to observe and obtain information about particles. Tracks are studied, but, unlike the cloud chamber, it allows studying particles with high energies. It has a shorter duty cycle - about 0.1 s. Allows you to observe the decay of particles and the reactions it causes. Donald Arthur Glaser 1926-2013 Arrangement: Similar to a cloud chamber, but liquid hydrogen or propane is used instead of vapor. The liquid is under high pressure at a temperature above the boiling point. The piston descends, the pressure drops and the fluid is in an unstable, overheated state. Vapor bubbles form tracks. The flying particle ionizes the atoms, which become the centers of vaporization. The piston rises, the steam condenses, the electric field removes the ions and the chamber is ready to receive the next particle (1895). The plate is covered with an emulsion containing a large number of silver bromide crystals. Flying, the particle tears off electrons from bromine atoms, a chain of such crystals forms a latent image. When developed in these crystals, metallic silver is restored. A chain of silver grains forms a track. Antoine Henri Becquerel This method makes it possible to register rare phenomena between particles and nuclei. 1. Aluminum foil 4. Dynode 5. Anode 3. Photocathode 2. Scintillator The scintillation method consists in counting tiny flashes of light when alpha particles hit a screen coated with zinc sulfide. It is a combination of a scintillator and a photomultiplier. All particles and 100% of gamma quanta are registered. Allows you to determine the energy of the particles. Represents a system of parallel metal electrodes, the space between which is filled with an inert gas. The distance between the plates is from 1 to 10 cm. Discharge sparks are strictly localized. They arise where there are free charges. Spark chambers can have dimensions on the order of several meters. When a particle passes between the plates, a spark breaks through, creating a fiery track. The advantage is that the registration process is manageable.