At the beginning of the 20th century. Methods for studying the phenomenon of atomic physics were developed and instruments were created that made it possible not only to clarify the basic questions of the structure of atoms, but also to observe the transformations of chemical elements.

The difficulty in creating such devices was that the charged particles used in the experiments are ionized atoms of some elements or, for example, electrons, and the device must register only one particle hitting it or make the trajectory of its movement visible.

As one of the first and simplest devices for detecting particles, a screen coated with a luminescent composition was used. At that point on the screen where a particle with a sufficiently high energy hits, a flash occurs - scintillation (from the Latin “scintillation” - sparkle, flash).

The first basic device for detecting particles was invented in 1908 by G. Geiger. After this device was improved by W. Muller, he could count the number of particles falling into it. The operation of a Geiger-Muller counter is based on the fact that charged particles flying through a gas ionize gas atoms encountered in their path: a negatively charged particle, repelling electrons, knocks them out of the atoms, and a positively charged particle attracts electrons and pulls them out of the atoms.

The meter consists of a hollow metal cylinder, about 3 cm in diameter (Fig. 37.1), with a window made of thin glass or aluminum. A metal thread isolated from the walls runs along the cylinder's surface. The cylinder (chamber) is filled with rarefied gas, for example argon. A voltage of about 1500 V is created between the walls of the cylinder and the filament, which is insufficient for the formation of an independent discharge. The thread is grounded through a large resistanceR. When a high-energy particle enters the chamber, gas atoms in the path of this particle are ionized, and a discharge occurs between the walls and the filament. The discharge current creates a large voltage drop across the resistance R, and the voltage between the filament and the walls is greatly reduced. Therefore, the discharge quickly stops. After the current stops, all the voltage is again concentrated between the walls of the chamber and the thread, and the counter is ready to register a new particle. Voltage with resistance R is supplied to the input of the amplification lamp, in the anode circuit of which the counting mechanism is switched on.

The ability of high-energy particles to ionize gas atoms is also used in one of the most remarkable instruments of modern physics - the cloud chamber. In 1911, the English scientist Charles Wilson built a device with which it was possible to see and photograph the trajectories of charged particles.

The Wilson chamber (Fig. 37.2) consists of a cylinder with a piston; the upper part of the cylinder is made of transparent material. A small amount of water or alcohol is introduced into the chamber, and a mixture of vapor and air is formed inside it. When the piston is quickly lowered, the mixture expands adiabatically and cools, so the air in the chamber becomes supersaturated with vapor.

If the air is cleared of dust particles, then the conversion of excess vapor into liquid is difficult due to the absence of condensation centers. However, ions can also serve as condensation centers. Therefore, if at this time a charged particle flies through the chamber, ionizing air molecules on its way, then vapor condensation occurs on the chain of ions and the trajectory of the particle inside the chamber turns out to be marked by a thread of fog, i.e., it becomes visible. The thermal movement of air quickly blurs the threads of fog, and the trajectories of particles are clearly visible for only about 0.1 s, which, however, is sufficient for photography.

The appearance of the trajectory in a photograph often allows one to judge the nature of the particle and the magnitude of its energy. Thus, alpha particles leave a relatively thick continuous trail, protons leave a thinner trail, and electrons leave a dotted trail. One of the photographs of alpha particles in a cloud chamber is shown in Fig. 37.3.

To prepare the chamber for action and clear it of remaining ions, an electric field is created inside it, attracting ions to the electrodes, where they are neutralized.

As mentioned above, in a cloud chamber, to obtain traces of particles, the condensation of supersaturated vapor is used, i.e., turning it into a liquid. For the same purpose, the opposite phenomenon can be used, i.e., the transformation of liquid into vapor. If a liquid is enclosed in a closed vessel with a piston and using the piston to create increased pressure, and then by sharply moving the piston to reduce the pressure in the liquid, then at the appropriate temperature the liquid may be in a superheated state. If a charged particle flies through such a liquid, then along its trajectory the liquid will boil, since the ions formed in the liquid serve as centers of vaporization. In this case, the trajectory of the particle is marked by a chain of vapor bubbles, i.e., it is made visible. The action of the bubble chamber is based on this principle.

When studying traces of high-energy particles, a bubble chamber is more convenient than a Wilson chamber, since when moving in a liquid, a particle loses significantly more energy than in a gas. In many cases, this makes it possible to determine the direction of motion of the particle and its energy much more accurately. Currently, there are bubble chambers with a diameter of about 2 m. They are filled with liquid hydrogen. Particle traces in liquid hydrogen are very clear.

The method of thick-layer photographic plates is also used to register particles and obtain their traces. It is based on the fact that particles flying through the photographic emulsion act on the grains of silver bromide, so the trace left by the particles after developing the photographic plate becomes visible (Fig. 37.4) and can be examined using a microscope. To ensure that the trail is long enough, thick layers of photographic emulsion are used.

Sources of elementary particles

To study elementary particles, their sources are required. Before the creation of accelerators, natural radioactive elements and cosmic rays were used as such sources. Cosmic rays contain elementary particles of very different energies, including those that cannot be obtained artificially today. The disadvantage of cosmic rays as a source of high-energy particles is that there are very few such particles. The appearance of a high-energy particle in the field of view of the device is random.

Particle accelerators produce streams of elementary particles that have equally high energy. There are different types of accelerators: betatron, cyclotron, linear accelerator.

Located near Geneva, the European Organization for Nuclear Research (CERN*) has the largest particle accelerator to date, built in a circular tunnel underground at a depth of 100 m. The total length of the tunnel is 27 km. (the ring is approximately 8.6 km in diameter). The super collider was scheduled to launch in 2007. About 4,000 tons of metal would be cooled to just 2 degrees above absolute zero. As a result, a current of 1.8 million amperes will flow through the superconducting cables with almost no loss.

Particle accelerators are such grandiose structures that they are called pyramids of the 20th century.

* The abbreviation CERN comes from the French. Conseil Européen pour la Recherche Nucléaire (European Council for Nuclear Research). In Russian the abbreviation CERN is usually used.

Methods for recording elementary particles

1. Scintillation counters

Initially, luminescent screens were used to register elementary particles - screens coated with a special substance, a phosphor, capable of converting the energy they absorb into light radiation (luminesce). When an elementary particle hits such a screen, it gives a weak flash, so weak that it can only be observed in complete darkness. It was necessary to have a fair amount of patience and attention in order to sit in complete darkness and count for hours the number of flashes noticed.

In a modern scintillation counter, flashes are counted automatically. The counter consists of a scintillator, a photomultiplier and electronic devices for amplification and counting of pulses.

The scintillator converts the particle's energy into visible light quanta.

Light quanta enter a photomultiplier tube, which converts them into current pulses.

The pulses are amplified by an electrical circuit and automatically counted.

2. Chemical methods

Chemical methods are based on the fact that nuclear radiation is a catalyst for certain chemical reactions, that is, it accelerates or creates the possibility of their occurrence.

3. Calorimetric methods

In calorimetric methods, the amount of heat that is released when radiation is absorbed by a substance is recorded. One gram of radium, for example, releases approximately 585 joules per hour. heat.

4. Methods based on the application of the Cherenkov effect

Nothing in nature can travel faster than light. But when we say that, we mean the movement of light in a vacuum. In matter, light travels at a speed where With is the speed of light in vacuum, and n– refractive index of the substance. Consequently, light moves slower in matter than in vacuum. An elementary particle, moving in a substance, can exceed the speed of light in this substance, without exceeding the speed of light in a vacuum. In this case, radiation occurs, which was discovered by Cherenkov in his time. Cherenkov radiation is detected by photomultipliers in the same way as in the scintillation method. The method allows you to register only fast, that is, high-energy, elementary particles.

The following methods not only allow you to register an elementary particle, but also see its trace.

5. Wilson chamber

Invented by Charles Wilson in 1912, he received the Nobel Prize for it in 1927. A cloud chamber is a very complex engineering structure. We present only a simplified diagram.

The working volume of the cloud chamber is filled with gas and contains water or alcohol vapor. When the piston moves down quickly, the gas cools sharply and the steam becomes supersaturated. When a particle flies through this space, creating ions along its path, then droplets of condensed vapor are formed on these ions. A trace of the particle trajectory (track) appears in the chamber in the form of a narrow strip of fog droplets. In strong side lighting, the track can be seen and photographed.

6. Bubble chamber(invented by Glaeser in 1952)

The bubble chamber operates similarly to a cloud chamber. Only the working fluid is not supercooled steam, but superheated liquid (propane, liquid hydrogen, nitrogen, ether, xenon, freon...). A superheated liquid, like supercooled steam, is in an unstable state. A particle flying through such a liquid forms ions, on which bubbles immediately form. A liquid bubble chamber is more efficient than a gas cloud chamber. It is important for physicists not only to observe the track of a flying particle. It is important that within the observation region the particle collides with another particle. The picture of particle interaction is much more informative. By flying through a denser fluid, which has a high concentration of protons and electrons, the particle has a much greater chance of experiencing a collision.

7. Emulsion chamber

It was first used by Soviet physicists Mysovsky and Zhdanov. Photographic emulsion is made from gelatin. Moving through dense gelatin, the elementary particle undergoes frequent collisions. Due to this, the path of the particle in the emulsion is often very short and, after developing the photographic emulsion, it is studied under a microscope.

8. Spark chamber (inventor Cranshaw)

In the cell A a system of mesh electrodes is located. These electrodes are supplied with high voltage from the power supply B. When an elementary particle flies through the chamber IN, it creates an ionized trail. A spark jumps along this trail, which makes the particle track visible.

9. Streamer camera

The streamer chamber is similar to the spark chamber, only the distance between the electrodes is greater (up to half a meter). Voltage is applied to the electrodes for a very short time in such a way that a real spark does not have time to develop. Only the rudiments of a spark - streamers - have time to appear.

10. Geiger counter

A Geiger counter is, as a rule, a cylindrical cathode, along the axis of which a wire is stretched - the anode. The system is filled with a gas mixture.

When passing through the counter, a charged particle ionizes the gas. The resulting electrons, moving towards the positive electrode - the filament, entering the region of a strong electric field, are accelerated and in turn ionize gas molecules, which leads to a corona discharge. The signal amplitude reaches several volts and is easily recorded.

A Geiger counter records the fact that a particle passes through the counter, but does not measure the energy of the particle.

Lesson topic: Methods for observing and recording elementary

particles.

The purpose of the lesson: Explain to students the structure and operating principle of installations for recording and studying elementary particles.

Lesson type: A lesson in learning new knowledge.

Epigraph:

“….. nurturing creativity

in a person is based on development

independent thinking"

P.P. Kapitsa

Lesson structure:

Organizational stage.

Greeting students and guests of the seminar. Checking the student’s readiness for the training session

2. Goals and objectives of the lesson. (Preparation of students for work at the main stage)

Declaration of the purpose of the lesson (Today in the lesson you will learn what instruments are used to observe and register charged particles, how they are structured and their principle of operation).

Presentation of new material

First, let's conduct a frontal survey:

What is ionization?

(The process of decay of neutral atoms into ions and electrons)

How to obtain supersaturated steam?

(Answer: Sharply increase the volume of the vessel. At the same time, the temperature

will decrease and the steam will become supersaturated.)

What will happen to supersaturated steam if a particle appears in it? ?

(Answer: It will be the center of condensation, and dew will form on it.)

How does a magnetic field affect the motion of a charged particle?

(Answer: In a field, the speed of a particle changes in direction, but not in

module.)

What is the name of the force with which a magnetic field acts on a charged particle? Where is it headed?

(Answer: This is the Lorentz force; it is directed towards the center of the circle.)

Introductory speech by the teacher

While studying quantum physics, the expressions - atomic nucleus and elementary particles - have already been repeatedly mentioned. However, elementary particles (for example, electrons and ions), as well as atomic nuclei, cannot be seen with any microscope, even an electron one. Therefore, first we will get acquainted with the devices thanks to which the physics of the atomic nucleus and elementary particles arose and began to develop. They are the ones who give people the necessary information about the microworld.

Any device that registers elementary particles is like a loaded gun with the hammer cocked. A small amount of force when pressing the trigger of a gun causes an effect that is not comparable to the effort expended - a shot.

A recording device is a more or less complex macroscopic system that may be in an unstable state. With a small disturbance caused by a passing particle, the process of transition of the system to a new, more stable state begins. This process makes it possible to register a particle. Currently, many different particle detection methods are used.

Depending on the purposes of the experiment and the conditions in which it is carried out, certain recording devices are used, differing from each other in their main characteristics.

Message #1

Gas-discharge Geiger counter

The Geiger counter is one of the most important devices. For automatic particle counting. Good counters can register up to 10,000 or more particles per second. The counter consists of a glass tube coated on the inside with a metal layer (cathode) and a thin metal thread running along the axis of the tube (anode).

The tube is filled with gas, usually argon. The counter operates based on impact ionization. A charged particle flying through a gas strips electrons from atoms and creates positive ions and free electrons. The electric field between the anode and cathode (high voltage is applied to them) accelerates the electrons to energies at which impact ionization begins. An avalanche of ions occurs, and the current through the counter increases sharply. In this case, a voltage pulse is formed at the load resistance, which is fed to the recording device.

The Geiger counter is used mainly for recording electrons and y-quanta (high-energy photons). When registering electrons, the efficiency of the counter is about 100%, and when registering y-quanta it is only about 1%. Registration of heavy particles (for example, alpha particles) is difficult, since it is difficult to make a sufficiently thin “window” in the counter that is transparent to these particles.

Addition...
The counter was improved by another German physicist W. Muller, so sometimes this counter is called a Geiger-Muller counter.

Message #2

Wilson chamber

Counters only allow you to register the fact of a particle passing through them and record some of its characteristics. In a cloud chamber, a fast charged particle leaves a trace that can be observed directly or photographed. This device can be called a “window” into the microworld.
A cloud chamber consists of a low glass cylinder with a glass lid. The piston can move inside the cylinder. There is black cloth at the bottom of the chamber. Due to the fact that the fabric is moistened with a mixture of water and alcohol, the air in the chamber is saturated with vapors of these liquids.
The action of the cloud chamber, created in 1912, is based on the condensation of supersaturated steam on ions, formed in the working volume of the chamber along the trajectory of a charged particle.
The particles being studied are introduced into the chamber through a thin window (sometimes the particle source is placed inside the chamber). When the piston is suddenly lowered, caused by a decrease in pressure under the piston, the vapor in the chamber expands. As a result, cooling occurs and the steam becomes supersaturated. If a particle enters the chamber just before or after expansion, the ions it produces will act as nuclei of condensation. The droplets of water that appear on them form a trace of the flying particle - a track. The information that tracks in a cloud chamber provide is much richer than what counters can provide. By the length of the track, you can determine the energy of the particle, and by the number of droplets per unit length of the track, its speed is estimated.

By placing the camera in a uniform magnetic field (method proposed by Soviet physicists P. L. Kapitsa and D. V. Skobeltsin), it is possible to determine the sign of the charge and the charge-to-mass ratio or the momentum of the particle (if its charge is known) from the direction of the trajectory bend and its curvature. .

The 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, and perform a new expansion.

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

Addition...

In addition to being called a window into the microworld, the Wilson chamber was called a “foggy chamber”

In 1932, it was with the help of this camera that Anderson discovered the positron-antielectron.

Message #3

Bubble chamber

In 1952, the American scientist D. Glaser proposed using superheated liquid to detect particle tracks. They consist of a glass cylinder filled with liquid and look a bit like a cloud chamber. In such a liquid based on ions, formed during the movement of a fast charged particle, vapor bubbles appear, giving a visible track. Chambers of this type were called bubble chambers.

In the initial state, the liquid in the chamber is under high pressure, which prevents it from boiling. With a sharp decrease in pressure, the liquid becomes overheated and for a short time it will be in an unstable state. Charged particles flying at precisely this time cause the appearance of tracks consisting of steam bubbles. The liquids used are mainly liquid hydrogen and propane.

Thus, the action of the bubble chamber is based on the boiling of superheated liquid.

The operating cycle of the bubble chamber is short - about 0.1 s. The advantage of the bubble chamber over the Wilson chamber is due to the higher density of the working substance. As a result, the particle paths turn out to be quite short, and particles of even high energies get stuck in the chamber. This allows one to observe a series of successive transformations of a particle and the reactions it causes.

Tracks in a cloud chamber and bubble chamber are one of the main sources of information about the behavior and properties of particles.

Addition...

The dimensions of the bubble chambers range from several tens of centimeters to several meters.

Message #4

Thick film emulsion method

To detect particles, thick-layer photographic emulsions are used along with cloud chambers. This method is done using a photographic plate coated with photoemulsion. The ionizing effect of fast charged particles on the emulsion of a photographic plate allowed the French physicist A. Becquerel to discover in 1896. radioactivity. The photoemulsion method was developed by Soviet physicists L. V. Mysovsky. A. P. Zhdanov and others.

The action of this method is based on photochemical reactions.

The photographic emulsion contains a large number of microscopic crystals of silver bromide. A fast charged particle, penetrating, removes electrons from individual bromine atoms. A chain of such crystals forms a latent image. When developed, the metallic content in these crystals is restored. silver, and a chain of silver grains forms a particle track. The length and thickness of the track can be used to estimate the energy and mass of the particle. Due to the high density of the photographic emulsion, the tracks are very short.

The advantage of photographic emulsions is their continuous summing action. This allows rare events to be recorded. It is also important that, due to the high stopping power of photoemulsions, the number of observed interesting reactions between particles and nuclei increases.

Addition...

The thickness of the photoemulsion layer is very small, only 200 microns.

This is the method used on spacecraft to study cosmic rays.

Teacher's addition
In addition to these methods, there are some others:

Spark chamber. In 1959 S. Fukui and S. Miyamoto designed a spark chamber in which the track of a particle is recorded by a spark discharge in neon and argon. Its weight reaches 10 tons.

Scintillation counters. Scintillation is flickering. A charged particle hitting the screen causes a flash of light. Watching the screen through a microscope, the flashes are counted.

Reinforcing the material learned

5 . Summing up the lesson.

So, today we got acquainted with particle registration methods.

We have not talked about all the devices that record elementary particles. Modern instruments for detecting rare and very few living particles are very complex. Hundreds of people take part in their construction.

Now let’s do a test for fixing the material (slides)

1.The operation of a Geiger counter is based on

Impact ionization.

Release of energy by a particle.

2. A device for recording elementary particles, the action of which is based on the formation of steam bubbles in a superheated liquid, is called

Thick film emulsion.

Geiger counter.

Camera.

Wilson chamber.

Bubble chamber.

3. Is it possible to detect uncharged particles using a cloud chamber?

It is possible if they have a small mass (electron)

It is possible if they have a large mass (neutrons)

It is possible if they have a small impulse

Yes, if they have a lot of momentum.

It is forbidden

4. The photoemulsion method for recording charged particles is based on

Impact ionization.

The splitting of molecules by a moving charged particle.

Formation of steam in a superheated liquid.

Condensation of supersaturated vapors.

Release of energy by a particle.

5. A device for recording elementary particles, the action of which is based on the condensation of supersaturated steam, is called

Camera

Wilson chamber

Thick film emulsion

Geiger counter

Bubble chamber

6. What is the Wilson chamber filled with?

Water or alcohol vapor.

Gas, usually argon.

liquid hydrogen or propane heated to almost boiling

Chemical reagents

7.What is a track formed by the thick-layer photographic emulsion method?

Chain of water droplets

Chain of steam bubbles

Avalanche of electrons

Chain of silver grains

6 . Homework.

paragraph 97 laboratory work in physics

Subject: Studying tracks of charged particles using ready-made photographs

Goals: explain the nature of the movement of charged particles

Equipment and materials: photographs of tracks of charged particles obtained in a cloud chamber, bubble chamber and photographic emulsion

Remember, that:

The longer the track length, the higher the energy of the particle and the lower the density of the medium)

The greater the charge of the particle and the lower its speed, the greater the thickness of the track

When a charged particle moves in a magnetic field, its track turns out to be curved, and the radius of curvature of the track is greater, the greater the mass and speed of the particle and the smaller its charge and the magnetic field induction modulus

the particle moved from the end of the track with a large radius to the end of the track with a smaller radius of curvature (the radius of curvature decreases as it moves, since the particle speed decreases due to the resistance of the medium)

Exercise:

I - α-particle tracks, II - α-particle tracks III - electron track

moving in a cloud chamber, in a bubble chamber, in a cloud chamber located in a magnetic field located in a magnetic field

Look at photo I and answer the questions:

In what direction did the α particles move? _________________________________

the lengths of α-particle tracks are approximately the same. What does this mean? _______________ ______________________________________________________________________________

How did the thickness of the track change as the particles moved? ____________________ what follows from this? _____________________________________________________

Determine from photo II:

Why did the radius of curvature and thickness of the tracks change as the α particles moved? _______________________________________________________________________

in which direction did the particles move? _______________________________________

Determine from photo III:

why is the track shaped like a spiral? _________________________________________

what could be the reason that the electron track (III) is much longer than the α-particle tracks (II) ____________________________________________________________

Methods for observing elementary particles

Elementary particles can be observed thanks to the traces they leave as they pass through matter. The nature of the traces allows us to judge the sign of the particle’s charge, its energy, momentum, etc. Charged particles cause ionization of molecules along their path. Neutral particles do not leave traces, 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 the ionization caused by the charged particles they generate.

Instruments used to register ionizing particles are divided into two groups. The first group includes devices that record the passage of a particle and allow one to judge its energy. The second group consists of track devices, i.e. devices that allow one to observe traces of particles in matter. Recording instruments include ionization chambers and gas-discharge counters. Cherenkov counters and scintillation counters have become widespread.

A charged particle flying through a substance causes not only ionization, but also excitation of atoms. Returning to their normal state, the atoms emit visible light. Substances in which charged particles excite a noticeable flash of light (scintillation) are called phosphors. Phosphorus can be organic or inorganic.

The scintillation counter consists of phosphorus, from which light is supplied through a special light guide to a photomultiplier tube. The pulses obtained at the output of the photomultiplier are counted. The amplitude of the pulses (which is proportional to the intensity of the light flashes) is also determined, which provides additional information about the detected particles.

Counters are often combined into groups and turned on so that only events that are recorded simultaneously by several devices, or only by one of them, are recorded. In the first case, they say that the counters are turned on according to a coincidence scheme, in the second - according to an anti-coincidence scheme.

Tracking instruments include cloud chambers, bubble chambers, spark chambers and emulsion chambers.

Wilson chamber. This is the name of the device created by the English physicist Charles Wilson in 1912. A path of ions laid by a flying charged particle becomes visible in a cloud chamber, because supersaturated vapor of a liquid condenses on the ions. The device does not operate continuously, but in cycles. The relatively short sensitivity time of the camera alternates with a dead time (100-1000 times longer), during which the camera prepares for the next operating cycle. Supersaturation is achieved due to sudden cooling caused by a sharp (adiabatic) expansion of the working mixture consisting of non-condensable gas (helium, nitrogen, argon) and water vapor, ethyl alcohol, etc. At the same moment, stereoscopic (i.e. with several points) photographing the working volume of the camera. Stereo photographs allow you to recreate the spatial picture of a recorded phenomenon. Since the ratio of sensitivity time to dead time is very small, it is sometimes necessary to take tens of thousands of pictures before any event with a small probability is recorded. To increase the likelihood of observing rare events, controlled cloud chambers are used, in which the operation of the expansion mechanism is controlled by particle counters included in an electronic circuit that isolates the desired event.

Bubble chamber. In the bubble chamber invented by D. A. Glezer in 1952, supersaturated vapors are replaced by a transparent superheated liquid (i.e., a liquid under external pressure less than the pressure of its saturated vapors). An ionizing particle flying through the chamber causes a violent boiling of the liquid, as a result of which the trace of the particle is indicated by a chain of vapor bubbles - a track is formed. The bubble chamber, like the Wilson chamber, operates in cycles. The chamber is started by a sharp decrease (relief) in pressure, as a result of which the working fluid passes into a metastable overheated state. Liquid hydrogen is used as a working fluid, which simultaneously serves as a target for particles flying through it (in this case, low temperatures are required).

Spark chambers. In 1957, Cranschau and de Beer designed a device for recording the trajectories of charged particles, called a spark chamber. The device consists of a system of flat electrodes parallel to each other, made in the form of frames with metal foil stretched over them or in the form of metal plates. The electrodes are connected through one. One group of electrodes is grounded, and a short-term (lasting 10 -7 seconds) high-voltage pulse (10-15 kV) is periodically applied to the other. If, at the moment the pulse is applied, an ionizing particle flies through the chamber, its path will be marked by a chain of sparks jumping between the electrodes. The device starts automatically with the help of additional counters switched on according to the coincidence scheme, which record the passage of the particles under study through the working volume of the chamber. In chambers filled with inert gases, the interelectrode distance can reach several centimeters. If the direction of flight of the particle forms an angle with the normal to the electrodes that does not exceed 40°, the discharge in such chambers develops in the direction of the particle track.

Photoemulsion method. Soviet physicists L.V. Mysovsky and A.P. Zhdanov were the first to use photographic plates to record elementary particles. A charged particle passing through a photographic emulsion causes the same effect as photons. Therefore, after developing the plate in the emulsion, a visible trace (track) of the flying particle is formed. The disadvantage of the photographic plate method was the small thickness of the emulsion layer, as a result of which only tracks of particles flying parallel to the plane of the layer were obtained. In emulsion chambers, thick packs (weighing up to several tens of kilograms), composed of individual layers of photographic emulsion (without a substrate), are exposed to irradiation. After irradiation, the pack is disassembled into layers, each of which is developed and viewed under a microscope. In order to be able to trace the path of a particle as it passes from one layer to another, before disassembling the pack, the same coordinate grid is applied to all layers using X-rays.

Atomistic concept of the structure of the world

The quantum model of the atom assumes that the nucleus of an atom consists of positively charged protons and neutrons, which have no charge. The nucleus is also surrounded by electrons, which in turn have a negative charge...

The simplest form of this APPJ source consists of a dielectric tube with two tubular metal electrodes and some noble gas (He, Ar) flowing through it. To demonstrate that...

High energy vacuum plasma technology

There are not many methods for performing APP (atmospheric pressure plasma) diagnostics. One very powerful tool is the ICCD (intensified interconnect device load) camera...

Study of the processes of evaporation and condensation of liquid droplets

Individual particles are characterized by so-called morphological characteristics: size, density, shape, structure, chemical composition...

The search for dark matter particles

Acoustic detection of massive charged dark matter particles in experiments on satellites To detect charged massive dark matter particles, it is proposed to use radiation acoustics methods...

Development of laboratory work "Brownian motion"

2.1 Analysis of works on Brownian motion The article “Brownian motion through the “eyes” of a digital microscope” was published in the newspaper “September 1” Physics No. 16/08. In it, the author /Tsarkov I.S./ talks about the experience of Municipal Educational Institution Secondary School No. 29 in the city of Podolsk...

Action potential phases. Radioactive radiation

Various recording devices make it possible to study mainly charged particles that cause ionization of the medium, i.e. upon collision, they tear out an electron from the atoms of the particles of the medium, imparting to it the ionization energy Ei. However, uncharged particles...

Physical foundations of cosmology and astrophysics

The abundance of types of elementary particles has raised difficult questions for physicists: what underlies the structure of matter, is there any general scheme, systematics...

Elementary particles

Elementary particles

Elementary particles are understood as microparticles whose internal structure, at the current level of development of physics, cannot be imagined as a combination of other particles...

Elementary particles

In order to understand what led scientists to the idea that hadrons consist of quarks, you must first understand what binds protons and neutrons into the nucleus of an atom, and go with them on their way into the depths of matter...

Elementary particles

Nuclear forces

In 1932, a positron was discovered in cosmic radiation, the existence of which was predicted by Dirac’s theory back in 1929. This fact was very important not only for confirming the correctness of Dirac’s theory, but also because...

While studying the effect of luminescent substances on photographic film, French physicist Antoine Becquerel discovered unknown radiation. He developed a photographic plate on which a copper cross coated with uranium salt was located in the dark for some time. The photographic plate produced an image in the form of a distinct shadow of a cross. This meant that the uranium salt spontaneously radiates. For his discovery of the phenomenon of natural radioactivity, Becquerel was awarded the Nobel Prize in 1903. RADIOACTIVITY is the ability of some atomic nuclei to spontaneously transform into other nuclei, emitting various particles: Any spontaneous radioactive decay is exothermic, that is, it occurs with the release of heat.
ALPHA PARTICLE(a-particle) – the nucleus of a helium atom. Contains two protons and two neutrons. The emission of a-particles is accompanied by one of the radioactive transformations (alpha decay of nuclei) of some chemical elements.
BETA PARTICLE –electron emitted during beta decay. A stream of beta particles is a type of radioactive radiation with a penetrating power greater than that of alpha particles, but less than that of gamma radiation. GAMMA RADIATION (gamma quanta) is short-wave electromagnetic radiation with a wavelength less than 2 × 10–10 m. Due to the short wavelength, the wave properties of gamma radiation are weakly manifested, and corpuscular properties come to the fore, and therefore its represented as a stream of gamma quanta (photons). The time during which half of the initial number of radioactive atoms decays is called the half-life. During this time, the activity of the radioactive substance is halved. The half-life is determined only by the type of substance and can take different values ​​- from several minutes to several billion years. ISOTOPES- these are varieties of a given chemical element, differing in the mass number of their nuclei. The nuclei of isotopes of the same element contain the same number of protons, but a different number of neutrons. Having the same structure of electron shells, isotopes have almost identical chemical properties. However, isotopes can differ quite dramatically in their physical properties. All three components of radioactive radiation, passing through the medium, interact with the atoms of the medium. The result of this interaction is the excitation or even ionization of atoms of the medium, which in turn initiates the occurrence of various chemical reactions. Therefore, radioactive radiation has a chemical effect. If the cells of a living organism are exposed to radioactive radiation, then the occurrence of reactions initiated by radioactive radiation can lead to the formation of substances that are harmful to the given organism and, ultimately, to tissue destruction. For this reason, the effect of radioactive radiation on living organisms is destructive. Large doses of radiation can cause serious illness or even death. 3. Nuclear reactions
NUCLEAR REACTIONS are transformations of atomic nuclei as a result of interaction with each other or with any elementary particles. To carry out a nuclear reaction, it is necessary that the colliding particles approach each other at a distance of about 10–15 m. Nuclear reactions obey the laws of conservation of energy, momentum, electric and baryon charges. Nuclear reactions can occur with both release and absorption of kinetic energy, and this energy is approximately 106 times greater than the energy absorbed or released during chemical reactions.

Discovery of the neutron by D. Chadwick in 1932

In 1932, German physicist W. Heisenberg and Soviet physicist D.D. Ivanenko was offered proton-neutron model of the atomic nucleus. According to this model, atomic nuclei consist of elementary particles - protons and neutrons.

Nuclear forces are very powerful, but decrease very quickly with increasing distance. They are a manifestation of the so-called strong interaction. A special feature of nuclear forces is their short-range nature: they manifest themselves at distances on the order of the size of the nucleus itself. Physicists jokingly call nuclear forces “a hero with short arms.” The minimum energy required to completely split a nucleus into individual nucleons is called the nuclear binding energy. This energy is equal to the difference between the total energy of free nucleons and the total energy of the nucleus. Thus, the total energy of free nucleons is greater than the total energy of the nucleus consisting of these nucleons. Very precise measurements made it possible to record the fact that the rest mass of a nucleus is always less than the sum of the rest masses of its constituent parts. slopes by a certain amount, called mass defect. Specific binding energy characterizes the stability of nuclei. Specific binding energy is equal to the ratio of binding energy to mass number and characterizes the stability of the nucleus. The higher the specific binding energy, the more stable the nucleus is. The plot of the dependence of the specific binding energy on the number of nucleons in the nucleus has a weak maximum in the range from 50 to 60. This suggests that nuclei with average mass numbers, such as iron, are the most stable. Light nuclei tend to fuse, while heavy ones tend to separate.

Examples of nuclear reactions.

Nuclear chain reactions. Thermonuclear reactions are nuclear reactions between light atomic nuclei that occur at very high temperatures (~108 K and above). In this case, the substance is in a state of completely ionized plasma. The need for high temperatures is explained by the fact that for the fusion of nuclei in a thermonuclear reaction, it is necessary that they come close to a very small distance and fall within the sphere of action of nuclear forces. This approach is prevented by the Coulomb repulsive forces acting between like-charged nuclei. To overcome them, the nuclei must have very high kinetic energy. After the thermonuclear reaction begins, all the energy spent on heating the mixture is compensated by the energy released during the reaction.
4. Nuclear energy. The use of nuclear energy is an important scientific and practical task. A device that allows a controlled nuclear reaction to occur is called a nuclear reactor. The neutron multiplication factor in the reactor is maintained equal to unity by introducing or removing control rods from the reactor. These rods are made of a substance that absorbs neutrons well - cadmium, boron or graphite.
The main elements of a nuclear reactor are: – nuclear fuel: uranium-235, plutonium-239; – neutron moderator: heavy water or graphite; – coolant for removing the released energy; – nuclear reaction rate regulator: a substance that absorbs neutrons (boron, graphite, cadmium).