This device was designed in 1911 by the English physicist Charles Wilson. It is based on the ability of fast-flying particles to ionize molecules of a substance in a vapor state.
The diagram of a cloud chamber is shown in Fig. 22.2.
The working volume of chamber 1 is filled with air or other gas and contains saturated steam of water or alcohol. When piston 2 moves quickly downwards, the steam or gas in volume 1 expands adiabatically and cools, and the steam becomes supersaturated. When a charged particle flies through the volume of the chamber, on its way it creates ions, on which, when volume 1 expands, droplets of condensed vapor are formed. Thus, the particle leaves behind a visible trace (track) in the form of a narrow strip of fog. This track can be observed or photographed.
Alpha particles cause strong ionization of the gas and therefore leave greasy marks in the cloud chamber. Beta particles leave behind very thin tracks (Fig. 22.3). 
Gamma quanta can be detected using a cloud chamber by photoelectrons, which they knock out from gas molecules filling the working volume of the chamber.
A cloud chamber is often placed in a strong magnetic field, which makes it possible to determine the energy and sign of the charge by the curvature of the particle tracks, and the charge and mass of the particles by the thickness of the tracks.
Gas discharge meters
In nuclear physics research, charged particle counters are often used to record individual particles. Let's consider the principle of operation of one of the types of counters - proportional
(Fig. 22.4). 
The meter consists of a gas-filled cylinder 1, into which two electrodes are inserted: anode 3 is a thin metal thread, both ends of which are mounted on insulators. Cathode 2 is made in the form of a conductive metal layer deposited on the inner surface of the cylinder.
A voltage of the order of several hundred volts is applied between the cathode and anode, as a result of which an electric field is created inside the meter. When a particle enters the counter, it ionizes gas molecules and a directed movement of ions occurs in the electric field between the cathode and anode, i.e., a gas discharge occurs. The discharge current creates a large voltage drop across the resistanceR n , and the voltage between the electrodes decreases greatly, so the discharge stops. After the current stops between the cathode and anode, a high voltage is restored again and the counter is ready to register the next particle. Voltage pulse occurring across resistanceR n , is amplified and recorded by a special counting device. Counters are called proportional because the current strength of the gas discharge that occurs after the passage of an ionizing particle is proportional to the number of ions formed by it.
One of the varietiesproportional counters was proposed by E. Rutherford and G. Geiger in 1908. Subsequently, in 1928, the counter was improved by E. Muller and was called the Geiger-Muller counter.
Radioactivity is the emission of various particles by the nuclei of some elements, accompanied by the transition of the nucleus to another state and a change in its parameters.
The phenomenon of radioactivity was experimentally discovered by the French scientist Henri Becquerel in 1896 for uranium salts. Becquerel noticed that uranium salts illuminate photographic paper wrapped in many layers with invisible penetrating radiation.
An atomic device of great importance was the ionization chamber, designed by an English physicist . This famous invention brought Wilson the Nobel Prize in 1937, and the Wilson chamber he created forever immortalized the name of its creator. The camera arose from the observation made in 1897 that ions were nuclei of water vapor. Based on this observation, G. A. Wilson proposed a method for determining the charge of an electron, from which, as we have seen, Millikan's methods developed. Article Charles Thomas Rees Wilson, describing this observation, was entitled "Condensation of water vapor in the presence of dust-free air and other gases." In the history of the Cavendish Laboratory, published in 1910, D. D. Thomson, who was at that time the head of the laboratory, wrote about Wilson’s discovery: “We must now consider the remarkable series of studies by C. T. R. Wilson on the conditions of condensation of water in dust-free gases saturated with water vapor. These studies not only significantly increased our knowledge of the subject under study problem, but also discovered a new and amazing method for studying the properties of ionization gas."
Thomson was right when he called the new method “amazing,” but it is unlikely that at the time he wrote these lines he imagined the full power of this method. In his work in 1897, Wilson showed that the centers of condensation in dust-free air are ions produced by X-rays or Becquerel rays. At the same time, for the formation of droplets on negative ions, a sudden expansion to 1.252 of the initial volume was required, while for the formation of droplets on positive ions, an expansion to 1.375 of the initial volume was required. A year or two after Thomson wrote the lines quoted above, Wilson published a report (1911) in which he described “a method of discovering the paths of ionizing particles in moist gases, based on the condensation of steam on ions immediately after the formation of these ions.”
The first results did not satisfy Wilson, and in 1912 he finally found the design of the device, which later received the name Wilson's chamber.
Here are the first Wilson photographs with his explanations.
"These figures are snapshots from photographs of clouds condensed on ions, which are released when rays of various kinds pass through moist gas. In the following, 1 denotes the density of air before expansion (relative to air saturated with water vapor at 15 ° C and 760 mmHg Art.), 2 - density after expansion, v 2 / v 1 - expansion value, V - potential difference between the lid and bottom of the ionization chamber in volts, M - magnification of the photographic apparatus. In all cases, the chamber lid was positive, so that negative ions moved up and positive ions moved down.
Ionization by α-rays.
The axis of the photographic camera is vertical; horizontal layer with a depth of 2 cm illuminated by a mercury spark.
Rice. 1 (Table I). α-rays of radium. Some of the α particles passed through the air before the expansion, others - after it.
1 = 0.98, v 2 / v 1 = 1.36, 2 = 0.72, V = 40 V, M = 1 / 2.18.
Rice. 2 (Table I). α-rays of radium. All α particles passed through the air after expansion.
1 = 0.97, v 2 / v 1 = 1.33, 2 = 0.73, V = 40 V, M = 1.05.
Rice. 3 (Table I). α-rays of radium. Enlarging part of Fig. 2.
1 = 0.97, v 2 / v 1 = 1.33, 2 = 0.73, V = 40 V, M = 2.57.
Rice. 4 (Table I). α-rays of radium emanation and active sediment.
1 = 1.00, v 2 / v 1 = 1.36, 2 = 0.74, V = 40 V, M = 1 / 124.
Rice. 5 (Table I). The complete path of an α particle ejected by radium emanation.
This amazing and relatively simple device represents one of the earliest methods for detecting the tracks of charged subatomic particles and, accordingly, instruments for studying radiation. It is surprising in that an object of the microworld (an alpha particle, or even an electron) is capable of leaving a trace visible to the naked eye in the macroworld. A kind of bridge between normally poorly intersecting areas of reality.
The principle of operation of a fog camera is quite simple to understand. Supercooled vapor of a volatile substance, preferably with a low melting point (traditionally alcohol, acetone or something similar is used), formed above a surface cooled to the desired temperature, condenses on the ions left by a high-energy charged particle, which as a result leaves a foggy trail (track). A cloud chamber, unlike a fog chamber, operates due to the adiabatic expansion of steam, without forced cooling of the working fluid.
There are several ways to make a fog chamber at home, without the use of complex cryogenic systems, sealed chambers and the like. In general, they come down to two: using cold consumables (dry ice or liquid nitrogen) or thermoelectrically using Peltier elements. Let me remind you that a Peltier element is such a flat square thing that, when a certain current and voltage is applied to it, it begins to heat up on one side and cool down on the other, reaching a temperature difference of 50-70 degrees (different Peltiers depending on operating conditions and quality manufactures work differently).
Since I was too lazy to look for dry ice, and liquid nitrogen would require a rather painstaking dosage to achieve the desired temperature range, Peltier was chosen. In turn, with them there are two ways to achieve the desired temperatures of -50 - -70 * C. The simplest is to connect two elements in series, when one of the elements is placed on the radiator with the hot side, and the cold side cools the hot side of the second. When using water cooling, this method works quite successfully, but I would not recommend it except as an initial test of strength: the fog chamber effects are too unstable. Another way is high-quality cooling of the radiator and the use of a single Peltier element. If you cool its hot side below zero Celsius, for example, using a freon refrigerator, then the desired -60* will be reached on the cold side. Actually, this solution was applied.
Structurally, the fog chamber itself is simply a transparent body with a suspended source of pure alcohol vapor (cleanliness is quite critical) - a cloth soaked in it. At the bottom of the case there is a black-painted Peltier element on a freon-cooled radiator (the design of a freon refrigerator is a topic for another post). A source of alpha particles (in this case, Pu-239 from a radioisotope smoke detector) is located near or near the Peltier. After the system has cooled to operating temperature, when the Pelte surface is illuminated from the side, tracks from alpha particles become visible. Better visibility is achieved when illuminated by a laser laid out in a line with a special attachment, as was done here: such illumination does not illuminate the Peltier surface, but illuminates the foggy tracks, which makes them very contrasty and clearly visible. But a regular flashlight also works quite well.
For high-quality camera operation, it is very desirable to place a source of static electricity near the working area (or simply a micro-power high-voltage constant source of 10-20 kilovolts). It collects excess ions from the chamber, allowing new particles to form.
Each track corresponds to exactly one particle. Not all particles leave them, but each one left is an undoubted trace of the passage.
This is such a funny toy, a connection between the world of elementary particles and the macrocosm.
Yuri Romanov
“This is the most original and wonderful instrument in the history of science.”
(Ernest Rutherford)
February 14, 1869, 145 years ago, Charles Thomson Rhys Wilson was born on a farm near Edinburgh (Scotland). He studied at one of the private schools in Manchester, then at the university there and dreamed of becoming a doctor. He went to Cambridge to complete his education, and then the vector of his interests sharply changed direction. He became interested in natural sciences.
In the late summer of 1894, Wilson arrived in Scotland and climbed Ben Nevis, the highest of the local mountains. This was not a scientific expedition; Wilson was an athlete, a mountaineer, and decided to take a walk around his native place. From this walk, as we can now judge, Wilson’s new life as a scientist began. There, at the top, he was simply captivated by the magnificent play of light in the clouds surrounding him; he admired the colored halos around the shadows cast by the rocks. In general, there, at the top of Ben Nevis, he desperately wanted to reproduce all the phenomena he had seen in the laboratory. Atmospheric physics is what his new hobby is now called. 
Nobel Prize 1927. Particles in the fog
In 1895, Charles Wilson, as a graduate student in the Cambridge laboratory of J. J. Thompson, began a series of experiments to understand the processes of cloud formation. He comes up with a device in the form of a transparent cylinder, the bottom of which can move. The rapid downward movement of the piston led to an increase in the volume of the chamber and a drop in pressure and temperature in it. At the same time, through the transparent window of the cylinder, Wilson observed thickening fog in the chamber. This phenomenon was already well known: moisture condensed on the smallest particles of dust, nothing new, everything was as usual... Why Wilson decided to repeat this experiment, filling his apparatus with air as clean as possible from dust, is where the mystery lies. Did the scientist’s intuition suggest something? Or did he simply decide to make sure that there would be no condensation in the “dust-free” air, and close this issue?
One way or another, the experiment yielded an unexpected result: fog still forms in clean air. Why? What in this case could be the centers of condensation? Many years later, Wilson described the emotional state in which he was in those days: “I was very excited, because almost immediately I came across something that promised to be much more interesting than the optical phenomena for which I started all this.” Wilson makes the ingenious suggestion that moisture condenses on ions - charged particles that somehow appear in the air.
To test this guess, Wilson borrows one of his precious X-ray tubes from Professor Thompson (he had to constantly fight the fear of damaging or accidentally breaking the device). Thompson was studying the ionizing properties of X-rays at this time, and therefore became an interested participant in the experiments of his graduate student. This is how he described the creative torment of young Wilson: “The creation of a fog chamber [that was the name of this device until it was named after the inventor. - Yu.R.] turned out to be an extremely labor-intensive process. It required several very complex glass parts, which Wilson made himself, having mastered the profession of glass blower. The floor of the laboratory was covered with fragments, the flasks burst again and again. Wilson was not upset, he started all over again, only saying as he attached another flask to the apparatus: “Darling, dear, will you be patient for a little while?”
The device that we know as the “Cloud Chamber” and which would become the most important tool in the arsenal of particle physics for 40 years, was manufactured in 1910. A year later, he manages to take the first photographs of the foggy tracks (traces) of charged particles flying through the camera. In 1959, at the age of 90, he did not forget these events and described them in these words: “I still remember well my admiration for the results obtained. These tracks were great. They looked like hairs or lights appearing here and there... It was amazing.”
In 1927, he was awarded the Nobel Prize in Physics “for his method of visually detecting the trajectories of electrically charged particles by means of vapor condensation.” He did not engage in further improvements to his camera: he was much more interested in problems of atmospheric electrophysics. At the end of his life, he moved with his family to the village of Karlops. Former MP Tam Dalyell, who lived next door to him, remembers his first meeting with Wilson: “It was raining. There was a knock on my door, I opened it. A neighbor was standing on the doorstep and asked if I would like to come over for a cup of tea. While he was working on the kettle, I noticed a photograph on the wall that made me freeze. There were 15 men and one woman. Albert Einstein, Marie Curie and all the great physicists of that time. Among them was a man, he was 40 years younger than now, but it was a neighbor who invited me to tea. I almost fell. It turns out that he is the same great Wilson who helped humanity enter the nuclear age.”
Nobel Prize 1948. The fog is under control
Patrick Maynard Stewart Baron Blackett succeeded in fundamentally improving the Wilson chamber. A career Navy officer, he saw action in World War I in the Falkland Islands and Jutland. After the war he retired and took up physics under Ernest Rutherford at Cambridge.
Later he would achieve remarkable scientific results and make several outstanding discoveries, but all this is a topic for another discussion. Something else is important now. In 1932, working with the young Italian physicist Giuseppe Occialini (pictured below), he developed an elegant combination of a cloud chamber and two Geiger-Muller counters, one placed above the camera and the other below it. A special electronic circuit started the cloud chamber into operation only if both counters were triggered simultaneously.
Thanks to Blackett's invention, the cloud chamber acquired a "directional pattern"; it could now be configured to capture particles arriving from a given direction. Moreover, by setting the triggering threshold of Geiger counters, it turned out to be possible to filter the observed particles by energy. Both of these factors have led to tremendous progress in cosmic ray research, astrophysics, and particle physics in general. In 1948, Blackett was awarded the Nobel Prize in Physics "for his improvements in the cloud chamber method and the resulting discoveries in nuclear physics and cosmic radiation."
Nobel Prize 1960. Bubbles and fog
If in a cloud chamber tracks of charged particles were formed due to the condensation of supercooled vapor on ions, then in the device, which was invented in 1953 and called a “bubble chamber” by Donald Arthur Glaser, traces of particles appeared in a superheated liquid as the pressure decreased. In this case, a kind of “reverse fog” arose: as the particles moved in the liquid, chains of bubbles filled with steam were formed.
Glaser conducted many experiments with various liquids, including even beer (at first he claimed that the very idea of a bubble chamber came to his mind when he observed the “boiling” of beer when uncorking a bottle; he later admitted that there was no “beer inspiration”, but it is a fact The fact remains: he poured light beer into the first models of the bubble chamber, and the chamber worked perfectly!)
Glaser's bubble chamber turned out to be such a successful device that since the 60s it has completely replaced Wilson chambers. And the 1960 Nobel Prize in Physics went to Donald Glaser “for the invention of the bubble chamber.” Experiments at accelerators around the world are beginning to be carried out using increasingly large cryogenic bubble chambers, which turn into complex engineering complexes stuffed with electronics.
Now the “era of fog and vapor” in experimental particle physics is ending, and new types of detectors are replacing bubble chambers. But that's a completely different story...
Purpose of the device
Wilson camera - one of the first devices in history for recording traces (tracks) of charged particles. A cloud chamber can be called a “window” into the microworld. It is a hermetically sealed vessel filled with water vapor or alcohols close to saturation.
Inventor of the device
An important step in the technique of observing particle tracks was the creation of a cloud chamber
(1912). It was invented by Charles Wilson in 1912. For this invention Ch. Wilson in 1927
Nobel Prize awarded.
Charles Wilson
Wilson chamber.
Glass plate
Device.
Glass
Glass
Black fabric
Saturated
Device.
Wilson chamber. A container with a glass lid and a piston at the bottom is filled with saturated vapors of water, alcohol or ether. When the piston is lowered, due to adiabatic expansion the vapors cool and become supersaturated. A charged particle passing through the chamber leaves a chain of ions in its path. The vapor condenses on the ions, making the particle's trail visible.
Robot principle
The operating principle of a cloud chamber is based on the condensation of supersaturated vapor and the formation of visible drops of liquid on ions along the trail of a charged particle flying through the chamber. supersaturated steam To create supersaturated steam, rapid adiabatic expansion of the gas occurs using a mechanical piston. After photographing the track, the gas in the chamber is compressed again, and the droplets on the ions evaporate. The electric field in the chamber serves to “clean” the chamber of ions formed during the previous ionization of Wilson gas, based on the condensation of supersaturated vapor and the formation of visible drops of liquid on the ions along the trail of a charged particle flying through the chamber. After photographing the track, the gas in the chamber is compressed again, and the droplets on the ions evaporate. The electric field in the chamber serves to “clean” the chamber of ions formed during the previous ionization of the gas
which resulted in the formation of an oxygen nucleus and
