Physical principles of detection of elementary particles. DIY particle detector

2.1. Gas discharge detectors. Geiger-Trost counters, proportional counters, ionization chambers. Scintillation counters.

2.2. Cherenkov counters. Semiconductor counters.

2.3. Track detectors with film recording of information. Cloud chamber, bubble chambers, spark and streamer chambers. Nuclear photo emulsion method.

2.4. Filmless cameras. Proportional and drift chambers. Hodoscopic systems of scintillation and Cherenkov counters.

Methods of measurements and mathematical data processing

3.1. Methods of spectrometric measurements. Magnetic spectrometers. Spectrometric measurement paths with semiconductor and scintillation counters with data output to a computer. Methods for imaging multidimensional spectra.

3.2. Dosimetric measurements. Permissible radiation fluxes. Methods of protection.

3.3. Methods for automatic processing of photographs of tracking devices. Mechanical-optical and electronic scanning systems with data output to a computer.

3.4. Physical installations with automatic data output to a computer. Types of storage devices. The use of different classes of computers for receiving, preliminary processing and accumulation of information, as well as for monitoring and management.

Methods for processing experimental data

4.1. Basic concepts of mathematical statistics. Theory of statistical estimates and hypothesis testing. Maximum likelihood method. Experiment planning.

4.2. Systems mathematical programs processing and analysis of physical results. Geometric reconstruction of particle beams. A system for recognizing a certain class of events. Analysis of physical results.

VIII. Basics
in experimental nuclear physics

Basic properties elementary particles

1.1. Movement of charged particles in electric and magnetic fields; equations of motion.

1.2. Interaction of charged particles with matter. Ionization losses and range of heavy charged particles; the passage of beta particles through matter. Interaction of neutral particles with matter.

1.3. Elementary particles and nuclei. Basic characteristics of kernels. Physical properties particles: charges, mass, spin, parity, isospin. Particle lifetimes.

Methods for recording elementary particles

2.1. Methods for recording charged and neutral particles.

2.2. Gas-filled meters and their types. Ionization chambers. Gas-filled cameras with an optical method of collecting information. Spark and streamer chambers.

2.3. Gas-filled cameras with electronic methods of collecting information. Multi-wire spark, proportional and drift chambers.

2.4. Scintillation and Cherenkov detectors. Photomultipliers.

2.5. Semiconductor detectors. Position-sensitive
detectors.

2.6. Detection of particles using bubble chambers.

Statistical processing of measurement results

3.1. Fundamentals of probability theory. Random variables. Basic laws of distribution of random variables: binomial Poisson distribution, Gaussian distribution.

3.2. Fundamentals of the theory of measurement errors.

3.3. Fundamentals of the theory of miscalculations of recording systems.

IX. General radio electronics and computer technology
(for the technical branch of science)

Methods for calculating electrical circuits and diagrams

1.1. Analysis of linear electrical circuits. Equivalent circuits. Kirchhoff's laws, equivalent generator theorem, nodal potential method, loop current method. Quadrupoles.

1.2. Analysis of electrical signals. Delta function and step function. Fourier transform.

1.3. Transmission of signals through linear systems. Differential equations, describing the processes in electrical circuits. Impulse response linear system. Superposition integral. Coagulation formula. Transfer function. Transient processes in long circuits.

1.4. Basics operational calculus. Laplace transform.

1.5. Fundamentals of algebra logic. Drawing up logical electronic circuits.

Semiconductor devices

2.1.Physical principles of operation of semiconductor devices. Their classification.

2.2. Semiconductor diodes. Operating principle, main characteristics, parameters and operating modes. Types of diodes: pulse diodes, charge storage diodes, tunnel diodes, zener diodes, light emitting diodes, etc. Application examples.

2.3. Bipolar transistors. Operating principle, main characteristics, parameters and operating modes. Switching circuits, equivalent circuits, operation in linear and switching modes. Types of triodes. Examples of their application.

2.4. Field effect transistors. Principle of operation, varieties field effect transistors. Main characteristics, parameters and operating modes. Application examples.

2.5. Other types of semiconductor devices: dinistor, thyristor, unijunction transistor, etc. Their main characteristics and parameters. Application examples.

Integrated circuits

3.1. Hybrid and monolithic integrated circuits. Monolithic integrated circuits based on bipolar and MIS transistors, their features. Technology for manufacturing integrated circuits of various types.

3.2. Analog integrated circuits: differential and operational amplifiers, voltage regulators, code-to-analog and analog-to-code converters. Their main parameters, examples of application.

3.3. Logic integrated circuits. Their classification according to circuit and technical design. Basic parameters. Speed of circuits. System of logical elements. Trigger types. Application examples.

3.4. Integrated circuits with a medium degree of integration: counters, registers, switches, decoders, adders, etc.

3.5. Integrated circuits with a high degree of integration: complex logical devices, storage devices, microprocessors, etc. Ways to further increase the degree of integration.

Particle detector

The CMS detector, one example of a large particle detector.

Particle detector, ionizing radiation detector in experimental particle physics, a device designed to detect and measure the parameters of high-energy elementary particles, such as cosmic rays or particles produced during nuclear decays or in accelerators.

Main types

List of working or under construction detectors for colliding beam accelerators

Detectors at the LHC collider (CERN)
Detectors at the Tevatron collider
Detectors at electron-positron colliders
- Belle (KEKB collider, KEK)
- BES (BEPC collider, Beijing)
- CLEO (CESR collider)
- KEDR (VEPP-4 collider, Novosibirsk)
- KMD, SND (collider VEPP-2M, VEPP-2000, Novosibirsk)

Application

Besides scientific experiments, elementary particle detectors are also used in applied tasks - in medicine (X-ray machines with a low dose of radiation, tomographs, radiation therapy), materials science (flaw detection), for pre-flight inspection of passengers and baggage at airports.

Literature

K. Group. Detectors of elementary particles. Novosibirsk Siberian Chronograph, 1999.
B. S. Ishkhanov, I. M. Kapitonov, E. I. Kabin, Web publication based on the textbook B. S. Ishkhanov, I. M. Kapitonov, E. I. Kabin. “Particles and nuclei. Experiment”, M.: MSU Publishing House, 2005.
Grupen, C. (June 28-July 10 1999). "Physics of Particle Detection". AIP Conference Proceedings, Instrumentation in Elementary Particle Physics, VIII 536 : 3–34, Istanbul: Dordrecht, D. Reidel Publishing Co.. DOI:10.1063/1.1361756.

Wikimedia Foundation. 2010.

High purity germanium detector
Detelina

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As in any physical experiment, when studying elementary particles you must first put experiment and then register its results. An accelerator is involved in setting up an experiment (collision of particles), and the results of collisions are studied using particle detectors.

In order to reconstruct the picture of the collision, it is necessary not only to find out which particles were born, but also to measure with great accuracy their characteristics, primarily trajectory, momentum and energy. All this is measured using different types of detectors that surround the collision site in concentric layers.

Particle detectors can be divided into two groups: track detectors, which measure the trajectory of particles, and calorimeters, which measure their energies. Track detectors try to follow the movement of particles without introducing any distortion. Calorimeters, on the other hand, must completely absorb a particle in order to measure its energy. The result is a standard layout of a modern detector: several layers of track detectors are located inside, and several layers of calorimeters are located outside, as well as special muon detectors. The general view of a typical modern detector is shown in Fig. 1.

Below we briefly describe the structure and operating principle of the main components of modern detectors. The emphasis is on some of the most general principles detection. For specific detectors operating at the Large Hadron Collider, see the Detectors at the LHC page.

Track detectors

Track detectors reconstruct the particle trajectory. They are usually located in the area magnetic field, and then by the curvature of the particle’s trajectory one can determine its momentum.

The operation of track detectors is based on the fact that a flying charged particle creates an ionization trail - that is, it knocks electrons out of atoms along the path of its movement. In this case, the ionization intensity depends both on the type of particle and on the detector material. Free electrons are collected by electronics, the signal from which reports the coordinates of the particles.

Vertex detector

Vershinny(microvertex, pixel) detector is a multilayer semiconductor detector consisting of individual thin plates with electronics applied directly to them. This is the innermost layer of detectors: it usually starts immediately outside the vacuum tube (sometimes the first layer is mounted directly on the outer wall of the vacuum tube) and occupies the first few centimeters in the radial direction. Silicon is usually chosen as a semiconductor material due to its high radiation resistance (the inner layers of the detector are exposed to huge doses of hard radiation).

Essentially, the vertex detector works in the same way as the matrix of a digital camera. When a charged particle flies through this plate, it leaves a trace in it - a cloud of ionization several tens of microns in size. This ionization is read electronic element directly below the pixel. Having learned the coordinates of the intersection points of a particle with several successive plates of a pixel detector, it is possible to reconstruct the three-dimensional trajectories of the particles and trace them back into the pipe. Through the intersection of such reconstructed trajectories at some point in space, the vertex- the point at which these particles were born.

Sometimes it turns out that there are several such vertices, and one of them usually lies directly on the axis of collision of oncoming beams (the primary vertex), and the second - at some distance. This usually means that protons collided at the primary vertex and immediately generated several particles, but some of them managed to fly some distance before breaking up into daughter particles.

In modern detectors, the accuracy of vertex reconstruction reaches 10 microns. This makes it possible to reliably record cases when the secondary vertices are 100 microns away from the collision axis. It is precisely at these distances that various metastable hadrons, containing a c- or b-quark (the so-called “charmed” and “lovely” hadrons) fly off. Therefore, the vertex detector is the most important instrument of the LHCb detector, the main task of which will be the study of these hadrons.

Semiconductor devices work on a similar principle. microstrip detectors, in which, instead of small pixels, thin but rather long strips of sensitive material are used. In them, ionization does not settle immediately, but moves along the strip and is read at its end. The strips are designed in such a way that the speed of displacement of the charge cloud along it is constant and so that it does not spread out. Therefore, knowing the moment the charge arrives at the reading element, it is possible to calculate the coordinates of the point where the charged particle pierced the strip. The spatial resolution of microstrip detectors is worse than that of pixel detectors, but they can cover much more O larger area, since they do not require as much large number reading elements.

Drift cameras

Drift cameras- these are gas-filled chambers that are placed outside semiconductor track detectors, where the radiation level is relatively low and the accuracy of determining coordinates is not required as great as with semiconductor detectors.

A classic drift chamber is a gas-filled tube with many very thin wires stretched inside it. It works like a vertex detector, but not on a flat plate, but in a volume. All wires are energized, and their arrangement is chosen in such a way that a uniform electric field. When a charged particle flies through a gas chamber, it leaves a spatial ionization trail. Under the influence electric field ionization (primarily electrons) moves at a constant speed (physicists say “drifts”) along the field lines towards the anode wires. Having reached the edge of the chamber, ionization is immediately absorbed by the electronics, which transmits a signal pulse to the output. Since there are a lot of reading elements, using the signals from them it is possible to reconstruct with good accuracy the coordinates of the flying particle, and therefore the trajectory.

Typically, the amount of ionization created in a gas chamber by a passing particle is small. In order to increase the reliability of charge collection and recording and reduce the error in its measurement, it is necessary to amplify the signal before registering it with electronics. This is done using a special network of anode and cathode wires stretched near the reading equipment. Passing near the anode wire, a cloud of electrons generates an avalanche on it, as a result of which the electronic signal is amplified many times over.

The stronger the magnetic field and the larger the size of the detector itself, the more the particle’s trajectory deviates from a straight line, which means the more reliably its radius of curvature can be measured and the momentum of the particle can be restored from there. Therefore, to study reactions with particles of very high energies, hundreds of GeV and TeV, it is desirable to build larger detectors and use stronger magnetic fields. For purely engineering reasons, it is usually possible to increase only one of these quantities to the detriment of the other. The two largest detectors at the LHC - ATLAS and CMS - differ precisely in which of these quantities is optimized. At the ATLAS detector bigger sizes, but a smaller field, while the CMS detector has a stronger field, but is generally more compact.

Time-projection camera

A special type of drift chamber is the so-called time projection camera(VPK). In fact, the military-industrial complex is one large, several meters in size, cylindrical drift cell. A uniform electric field is created throughout its entire volume along the cylinder axis. The entire swirling ionization trail that particles leave when flying through this chamber uniformly drifts toward the ends of the cylinder, maintaining its spatial shape. The trajectories are, as it were, “projected” onto the ends of the chamber, where a large array of reading elements registers the arrival of a charge. Radial and angular coordinates are determined by the sensor number, and the coordinate along the cylinder axis is determined by the time of signal arrival. Thanks to this, it is possible to restore a three-dimensional picture of the movement of particles.

Among the experiments operating at the LHC, the ALICE detector uses the time-projection camera.

Detectors Roman Pots

There is a special type of semiconductor pixel detectors that work directly inside the vacuum pipe, in close proximity to the beam. They were first proposed in the 1970s by a research group from Rome, and since then they have been given the name Roman Pots(“Roman pots”)

Roman Pots detectors have been designed to detect particles that have been deflected at very small angles during collisions. Conventional detectors located outside the vacuum tube are unsuitable here simply because a particle emitted at a very small angle can fly for many kilometers inside the vacuum tube, turning along with the main beam and not leaving the outside. In order to register such particles, it is necessary to place small detectors inside a vacuum tube across the beam axis, but without touching the beam itself.

To do this, in a certain section of the accelerator ring, usually at a distance of hundreds of meters from the point of collision of oncoming beams, a special section of a vacuum tube with transverse “sleeves” is inserted. They contain small, several centimeters in size, pixel detectors on moving platforms. When the beam is just injected, it is still unstable and has large transverse vibrations. At this time, the detectors are hidden inside the sleeves in order to avoid damage from a direct hit from the beam. After the beam has stabilized, the platforms extend from their arms and move the sensitive matrices of the Roman Pots detectors into close proximity to the beam, at a distance of 1-2 millimeters. At the end of the next accelerator cycle, before discarding the old beam and injecting a new one, the detectors are retracted into their arms and wait for the next operating session.

The pixel detectors used in Roman Pots differ from conventional vertex detectors in that they maximize the proportion of the wafer surface occupied by sensing elements. In particular, on the edge of the plate that is closest to the beam, there is practically no insensitive “dead” zone ( "edgeless"-technology).

One of the experiments at the Large Hadron Collider, TOTEM, will use several of these detectors. Several more similar projects are in development. The vertex detector of the LHCb experiment also contains some elements of this technology.

You can read more about these detectors in the article Roman pots for the LHC from the CERN Courier magazine or in the technical documentation of the TOTEM experiment.

Calorimeters

Calorimeters measure the energy of elementary particles. To do this, a thick layer of dense substance is placed in the path of the particles (usually heavy metal- lead, iron, brass). A particle in it collides with electrons or atomic nuclei and, as a result, generates a stream of secondary particles - shower. The energy of the original particle is distributed among all the particles of the shower, so that the energy of each individual particle in this shower becomes small. As a result, the shower gets stuck in the thickness of the substance, its particles are absorbed and annihilated, and a certain, well-defined fraction of the energy is released in the form of light. This flash of light is collected at the ends of the calorimeter by photomultipliers, which convert it into an electrical impulse. In addition, the energy of a shower can be measured by collecting ionization with sensitive plates.

Electrons and photons, passing through matter, collide mainly with the electron shells of atoms and generate an electromagnetic shower - a flow of a large number of electrons, positrons and photons. Such showers develop quickly at shallow depths and are usually absorbed in a layer of material several tens of centimeters thick. High-energy hadrons (protons, neutrons, pi-mesons and K-mesons) lose energy primarily through collisions with nuclei. In this case, a hadron shower is generated, which penetrates much deeper into the thickness of matter than the electromagnetic one, and is also wider. Therefore, in order to completely absorb a hadron shower from a very high-energy particle, one to two meters of matter is required.

The difference in characteristics of electromagnetic and hadron showers is used to the maximum in modern detectors. Calorimeters are often made with two layers: inside there are electromagnetic calorimeters, in which electromagnetic showers are absorbed predominantly, and outside - hadronic calorimeters, which can only be reached by hadron showers. Thus, calorimeters not only measure energy, but also determine the “type of energy” - whether it is of electromagnetic or hadronic origin. This is very important for a correct understanding of what happened at the center of the proton collision detector.

To record a shower optically, the calorimeter material must have scintillation properties. IN scintillator Photons of the same wavelength are absorbed very efficiently, leading to excitation of the molecules of the substance, and this excitation is removed by the emission of photons of lower energy. The scintillator is already transparent for the emitted photons, and therefore they can reach the edge of the calorimetric cell. Calorimeters use standard, long-studied scintillators, for which it is well known what part of the energy of the original particle is converted into an optical flash.

To effectively absorb rainfall, it is necessary to use a substance that is as dense as possible. There are two ways to combine this requirement with the requirements for scintillators. First, you can choose very heavy scintillators and fill the calorimeter with them. Secondly, you can make a “puff” of alternating plates of a heavy substance and a light scintillator. There are also more exotic options for constructing calorimeters, for example, “spaghetti” calorimeters, in which many thin quartz optical fibers are embedded in a matrix from a massive absorber. A shower, developing along such a calorimeter, creates Cherenkov light in quartz, which is output through optical fibers to the end of the calorimeter.

The accuracy of particle energy reconstruction in the calorimeter improves with increasing energy. For particles with energies of hundreds of GeV, the error is of the order of a percent for electromagnetic calorimeters and several percent for hadronic calorimeters.

Muon chambers

A characteristic feature of muons is that they lose energy very slowly as they move through matter. This is due to the fact that, on the one hand, they are very heavy, so they cannot effectively transfer energy to electrons during a collision, and secondly, they do not participate in strong interactions, so they are weakly scattered by nuclei. As a result, muons can fly many meters of matter before they stop, penetrating where no other particles can reach.

This, on the one hand, makes it impossible to measure the energy of muons using calorimeters (after all, a muon cannot be completely absorbed), but on the other hand, it makes it possible to clearly distinguish muons from other particles. In modern detectors muon chambers located in the outermost layers of the detector, often even outside the massive metal yoke that creates the magnetic field in the detector. Such tubes measure not the energy, but the momentum of muons, and it can be assumed with good certainty that these particles are precisely muons, and not anything else. There are several types of muon chambers used for different purposes.

Particle identification

A separate question is particle identification, that is, finding out what kind of particle flew through the detector. This would not be difficult if we knew the mass of the particle, but it is precisely this that we usually do not know. On the one hand, the mass can, in principle, be calculated using the formulas of relativistic kinematics, knowing the energy and momentum of the particle, but, unfortunately, the errors in their measurement are usually so large that they do not allow distinguishing, for example, a pi-meson from a muon due to their proximity wt.

In this situation, there are four main methods for identifying particles:

By response in different types of calorimeters and in muon tubes.
By energy release in track detectors. Different particles produce different amounts of ionization per centimeter of travel, and this can be measured by signal strength from track detectors.
By using Cherenkov counters. If a particle flies through a transparent material with a refractive index n at a speed greater than the speed of light in this material (that is, greater than c/n), then it emits Cherenkov radiation in strictly defined directions. If we take airgel as the detector substance (typical refractive index n= 1.03), then Cherenkov radiation from particles moving at a speed of 0.99 c and 0.995· c, will vary significantly.
By using time-of-flight cameras. In them, using detectors with very high time resolution, the time of passage of a particle over a certain area of the chamber is measured and its speed is calculated from this.

Each of these methods has its own difficulties and uncertainties, so particle identification is usually not guaranteed to be correct. Sometimes a program that processes raw data from a detector may conclude that a muon passed through the detector when in fact it was a pion. It is impossible to completely get rid of such errors. All that remains is to carefully study the detector before operation (for example, using cosmic muons), find out the percentage of cases of incorrect particle identification, and then always take it into account when processing real data.

Requirements for detectors

Modern particle detectors are sometimes called "big brothers" digital cameras. However, it is worth remembering that the operating conditions of the camera and the detector are radically different.

First of all, all detector elements must be very fast and very precisely synchronized with each other. At the Large Hadron Collider, at its peak, bunches will collide 40 million times per second. In each collision, the birth of particles will occur, which will leave their “picture” in the detector, and the detector must not “choke” with this stream of “snapshots”. As a result, in 25 nanoseconds it is necessary to collect all the ionization left by the flying particles, turn it into electrical signals, and also clean the detector, preparing it for the next portion of particles. In 25 nanoseconds, particles fly only 7.5 meters, which is comparable to the size of large detectors. While ionization from flying particles is collecting in the outer layers of the detector, particles from the next collision are already flying through its inner layers!

The second key requirement for a detector is radiation resistance. Elementary particles scattering from the site of collision of clots are real radiation, and very hard at that. For example, the expected absorbed dose of ionizing radiation that the vertex detector will receive during operation is 300 kilograys plus a total neutron flux of 5·10 14 neutrons per cm 2 . Under these conditions, the detector must work for years and still remain in good working order. This applies not only to the materials of the detector itself, but also to the electronics with which it is packed. It took several years to create and test fault-tolerant electronics that will operate in such radiation-harsh conditions.

Another requirement for electronics is low energy dissipation. There is no free space inside multi-meter detectors - every cubic centimeter of volume is filled with useful equipment. The cooling system inevitably takes away the working volume of the detector - after all, if a particle flies directly through the cooling pipe, it simply will not be registered. Therefore, the energy release from the electronics (which means hundreds of thousands of individual boards and wires that collect information from all components of the detector) should be minimal.

Main types [ | ]

Outdated

Detectors for radiation protection

Detectors for nuclear and particle physics

Hodoscopic cameras
Counters
Track detectors
Mass analyzers

Detectors for experiments on colliding beams[ | ]

In particle physics, the concept of “detector” refers not only to various types of sensors for detecting particles, but also to large installations created on their basis and also including the infrastructure to maintain their functionality (cryogenic systems, air conditioning systems, power supplies), electronics for reading and primary data processing, auxiliary systems (for example, superconducting solenoids for creating a magnetic field inside the installation). As a rule, such installations are now created by large international groups.

Since building a large installation requires significant financial investment and human effort, in most cases it is used not for one specific task, but for a whole range of different measurements. The main requirements for a modern detector for accelerator experiments are:

For specific problems, additional requirements may be required, for example, for experiments measuring CP violation in a system of B-mesons, the coordinate resolution in the beam interaction region plays an important role.

Conventional image of a multilayer universal detector for an accelerator using colliding beams.

The need to fulfill these conditions leads to the design of a universal multilayer detector that is typical today. In English-language literature, such a scheme is usually compared to an onion-like structure. In the direction from the center (the region of interaction of the beams) to the periphery, a typical detector for a colliding beam accelerator consists of the following systems:

Track system[ | ]

The tracking system is designed to record the trajectory of a charged particle: coordinates of the interaction area, departure angles. In most detectors, the tracking system is placed in a magnetic field, which leads to curvature of the trajectories of charged particles and makes it possible to determine their momentum and charge sign.

The tracking system is usually based on semiconductor silicon detectors.

Identification system[ | ]

The identification system allows you to separate various types charged particles. The operating principle of identification systems most often consists of measuring the speed of passage of a particle in one of three ways:

Together with measuring the momentum of the particle in the tracking system, this provides information about the mass, and, consequently, about the type of particle.

Calorimeter [ | ]

List of working or under construction detectors for colliding beam accelerators[ | ]

Application[ | ]

In addition to scientific experiments, elementary particle detectors are also used in applied tasks - in medicine (X-ray machines with a low radiation dose,

Every second, tens of thousands of elementary particles from space fly through our body - muons, electrons, neutrinos, and so on. We don't feel or see them, but that doesn't mean they don't exist. And this does not mean that they cannot be recorded. We offer readers N+1 build a device with your own hands that will allow you to “see” this continuous cosmic rain.

“Real” particle detectors, such as those at the Large Hadron Collider, cost millions of dollars and weigh hundreds of tons, but we will try to get by on a much more modest budget.

We will need:

dry ice (about 80 rubles per kilogram, it is advisable to buy a foam thermal container for another 300 rubles - otherwise everything you bought will evaporate too quickly). You don’t need a lot of dry ice, a kilogram is enough;
isopropyl alcohol (costs 370 rubles per 0.5 liter, sold in radio stores);
a piece of felt (sewing store, about 150 rubles);
glue to glue the felt to the bottom of the container (“Moment”, 150 rubles);
a transparent container, for example a plastic aquarium with a lid (we bought a food container made of hard plastic for 1.5 thousand rubles);
a stand for dry ice, this could be a photographic cuvette (found in the editorial kitchen);
flashlight.

So let's get started. First you need to glue a piece of felt to the bottom of the container and wait a few hours for the glue to dry. After this, the felt needs to be soaked in isopropyl alcohol (be careful not to get the alcohol in your eyes!). It is advisable that the felt is completely saturated with alcohol, the remainder of which must then be drained off. Then you need to pour dry ice into the bottom of the cuvette, close the container with a lid and place it in the dry ice with the lid down. Now you need to wait until the air inside the chamber is saturated with alcohol vapor.

The principle of operation of a cloud chamber (also known as a “fog chamber”) is that even a very weak impact causes saturated alcohol vapor to condense. As a result, even the impact of cosmic particles causes the steam to condense, and chains of microscopic droplets - tracks - are formed in the chamber.

You can watch the experiment in our video:

A few notes from experience: you shouldn’t buy too much dry ice - it will evaporate completely in less than a day, even from a thermal container, and you are unlikely to find an industrial refrigerator. The lid of the transparent container needs to be black, for example, you can close it from the bottom with black glass. The tracks will be better visible on a black background. You need to look exactly at the bottom of the container, a characteristic fog will form there, similar to drizzling rain. It is in this fog that particle tracks arise.

What tracks can you see:

Symmetry Magazine

These are not cosmic particles. The short, thick tracks are traces of alpha particles emitted by atoms of the radioactive gas radon, which continuously leaks from the bowels of the Earth (and accumulates in unventilated areas).

Symmetry Magazine

Long, narrow tracks are left by muons, heavy (and short-lived) relatives of electrons. They are produced in large numbers in the upper atmosphere when high-energy particles collide with atoms and produce particle showers, mostly consisting of muons.