Gas-discharge geiger counter operating principle briefly. Geiger-Muller counter: operating principle and purpose

Using a modern Geiger counter, you can measure the radiation level of building materials, land plot or apartments, as well as food. It demonstrates almost one hundred percent probability of a charged particle, because only one electron-ion pair is enough to detect it.

The technology on which the modern dosimeter based on the Geiger-Muller counter is created allows you to obtain highly accurate results in a very short period of time. The measurement takes no more than 60 seconds, and all information is displayed in graphical and numerical form on the dosimeter screen.

Device setup

The device has the ability to set a threshold value; when it is exceeded, a sound signal is issued to warn you of danger. Select one of the specified threshold values in the corresponding settings section. The beep can also be turned off. Before taking measurements, it is recommended to individually configure the device, select the brightness of the display, the parameters of the sound signal and batteries.

Measurement procedure

Select the “Measurement” mode, and the device begins to assess the radioactive situation. After approximately 60 seconds, the measurement result appears on its display, after which the next analysis cycle begins. In order to obtain an accurate result, it is recommended to carry out at least 5 measurement cycles. An increase in the number of observations provides more reliable readings.

To measure the background radiation of objects, such as building materials or food products, you need to turn on the “Measurement” mode at a distance of several meters from the object, then bring the device to the object and measure the background as close to it as possible. Compare the readings of the device with data obtained at a distance of several meters from the object. The difference between these readings is the additional radiation background of the object being studied.

If the measurement results exceed the natural background characteristic of the area in which you are located, this indicates radiation contamination of the object being studied. To assess fluid contamination, it is recommended to take measurements above its open surface. To protect the device from moisture, it must be wrapped plastic film, but not more than one layer. If the dosimeter long time was at a temperature below 0°C, before taking measurements it must be kept at room temperature within 2 hours.

Radiation safety and degree of contamination environment did not bother many citizens of the world until catastrophic events occurred that claimed the lives and health of hundreds and thousands of people. The most tragic in terms of radiation pollution were Fukushima, Nagasaki and the Chernobyl disaster. These territories and the stories associated with them are still stored in the memory of every person and are a lesson that, regardless of the foreign policy situation and level financial well-being Radiation safety is always something to worry about. It is necessary to know what particles a Geiger counter is used to register, and what rescue and preventative measures should be taken if a disaster occurs.

What is a Geiger counter used for? In connection with multiple man-made disasters and a critical increase in the level of radiation in the air over the past few decades, humanity has come up with and invented unique and maximum convenient devices for recording particles using a Geiger counter for domestic and industrial use. These devices allow you to measure the level of radiation pollution, as well as statically monitor the pollution situation in the territory or area, taking into account weather, geographical location and climatic changes.

What is the operating principle of a Geiger counter? Today, anyone can purchase a household-type dosimeter and a Geiger counter device. It should be noted that given the fact that radiation can be of both natural and artificial types, a person must constantly monitor the background radiation in his home, and also know exactly what particles are registered by the Geiger counter, about the methods and methods of preventive protection from ionizing substances and. Because radiation cannot be seen or felt by a person without special equipment, many people can be contaminated for a long time without knowing it.

What kind of radiation is needed for a Geiger counter?

It is important to remember that radiation can be different, depending on what charged particles it consists of and how far it has spread from its source. What is a Geiger counter used for? For example, alpha particles of radiation are not considered dangerous and aggressive towards the human body, but with prolonged exposure they can lead to some forms of disease, benign tumors and inflammation. Beta radiation is considered the most dangerous and destructive to human health. It is precisely to measure such particles in the air that the operating principle of a Geiger counter is aimed.

Beta charges can be produced either artificially as a result of the operation of nuclear power plants or chemical laboratories, or naturally, due to volcanic rocks and other underground sources. In certain cases, a high concentration of beta-type ionizing elements in the air can lead to cancer, benign tumors, infections, detachments of the mucous membranes, and disorders of the thyroid gland and bone marrow.

What is a Geiger counter and how does a Geiger counter work? This is the name of a special device that is equipped with dosimeters and radiometers of household and professional types. A Geiger counter is a sensitive element of a dosimeter, which, when set to a certain level of sensitivity, helps to detect the concentration of ionizing substances in the air over a given period of time.

The Geiger counter, the photo of which is shown above, was first invented and tested in practice at the beginning of the twentieth century by scientist Walter Müller. The advantages and disadvantages of the Geiger counter can also be appreciated by current generations. This device is widely used in everyday life and in the industrial sphere to this day. Some craftsmen even make a Geiger counter with their own hands.

Improved dosimeters for radiation

It should be said that from the invention of the Geiger counter and dosimeter to the present day, these universal devices went through many stages of improvement and modernization. Today, such devices can be used not only to check low levels of background radiation in living conditions or in production, but also use more optimized and improved models that help measure radiation levels in nuclear power plants, as well as in warfare.

Modern methods Geiger counter applications make it possible to capture not only the total amount of ionizing substances in the air over a certain period of time, but also respond to their density, degree of charge, type of radiation and the nature of the impact on the surface.

For example, the purpose of Geiger counters for household or personal use does not require the need for upgraded capabilities, since they are usually used for domestic use and are used to check background radiation in the home, on food, clothing or building materials, which could potentially contain a certain level of charge. However, industrial and professional dosimeters are needed to test for more serious and complex radiation exposures and to serve as a permanent way to monitor the radiation field in nuclear power plants, chemical laboratories or nuclear power plants.

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Considering the fact that many modern countries today have powerful nuclear weapons, every person on the planet should have professional dosimeters and Geiger counters, so that in the event of an emergency or disaster they can control the radiation field in a timely manner and save their lives and the lives of their loved ones. It's also a good idea to learn the pros and cons of a Geiger counter beforehand.

It is worth saying that the operating principle of Geiger counters provides a response not only to the intensity of the radiation charge and the number of ionizing particles in the air, but also allows you to separate alpha radiation from beta radiation. Since beta radiation is considered to be the most corrosive and potent in its charge and ion concentration, Geiger counters to test it cover special clamps made of lead or steel in order to filter out unnecessary elements and not damage the equipment during testing.

The ability to screen out and separate various flows of radiation type has allowed many people today to use dosimeters efficiently, to accurately calculate the danger and level of contamination of a particular area with radiation elements of various types.

What does a Geiger counter consist of?

Where is a Geiger counter used? As mentioned above, a Geiger counter is not separate element, but serves to be the leading and main element in the design of the dosimeter. It is necessary for the highest quality and accurate verification of background radiation in a particular area.

It should be said that the Geiger counter has a relatively simple design. In general, its design has the following features.

A Geiger counter is a small container containing an inert gas. Different manufacturers use different elements and substances as gas. Most often, Geiger counters are produced with cylinders filled with argon, neon, or mixtures of these two substances. It is worth mentioning that the gas that fills the meter’s cylinder is under minimal pressure. This is necessary so that there is no voltage between the cathode and the anode and no electrical impulse occurs.

The cathode is the structure of the entire meter. The anode is a wire or metal connection between the cylinder and the main structure of the dosimeter, connected to the sensor. It should be noted that in some cases the anode, which directly reacts to the radiation elements, can be manufactured with a special protective coating, which allows you to control the ions that penetrate the anode and affect the final measurement results.

How does a Geiger counter work?

After we have clarified the main points of the design of the Geiger counter, it is worth briefly describing the principle of operation of the Geiger counter. Considering the simplicity of its arrangement, its operation and functioning are also extremely easy to explain. A Geiger counter works on this principle:

When the dosimeter is switched on, an increased electrical voltage occurs between the cathode and anode using a resistor. However, the voltage cannot drop during operation due to the fact that the meter's cylinder is filled with inert gas.
When a charged ion hits the anode, it begins to mix with an inert gas to ionize. Thus, the radiation element is detected by the sensor and can influence the radiation background in the area being tested. The end of the test is usually signaled by the characteristic sound of a Geiger counter.

As mentioned above, some anodes for Geiger counters are produced with a special coating. Such measures are necessary to ensure that the counter captures only beta radiation as efficiently as possible and responds to charged particles that are most dangerous to the human body.

In connection with the environmental consequences of human activities related to nuclear energy, as well as industry (including the military) that uses radioactive substances as a component or basis of their products, the study of the basics of radiation safety and radiation dosimetry is becoming quite a relevant topic today. Besides natural sources ionizing radiation Every year more and more places appear that are contaminated with radiation as a result of human activity. Thus, in order to preserve your health and the health of your loved ones, you need to know the degree of contamination of a particular area or objects and food. A dosimeter can help with this - a device for measuring the effective dose or power of ionizing radiation over a certain period of time.

Before you begin manufacturing (or purchasing) this device, you must have an idea of the nature of the parameter being measured. Ionizing radiation (radiation) is a stream of photons, elementary particles or fragments of atomic fission that can ionize matter. Divided into several types. Alpha radiation is a stream of alpha particles - helium-4 nuclei, alpha particles born when radioactive decay, can be easily stopped with a piece of paper, so the danger is mainly if it enters the body. Beta radiation- this is a flow of electrons arising during beta decay; an aluminum plate several millimeters thick is sufficient to protect against beta particles with an energy of up to 1 MeV. Gamma radiation has a much greater penetrating ability, since it consists of high-energy photons that do not have a charge, they are effective for protection heavy elements(lead, etc.) in a layer of several centimeters. The penetrating ability of all types of ionizing radiation depends on energy.

Geiger-Muller counters are mainly used to detect ionizing radiation. It's simple and efficient device Usually it is a metal or glass cylinder metallized from the inside and a thin metal thread stretched along the axis of this cylinder; the cylinder itself is filled with rarefied gas. The operating principle is based on impact ionization. When ionizing radiation hits the walls of the counter, electrons are knocked out of it; electrons, moving in the gas and colliding with gas atoms, knock out electrons from the atoms and create positive ions and free electrons. Electric field between the cathode and anode accelerates electrons to energies at which impact ionization begins. An avalanche of ions occurs, leading to the multiplication of primary carriers. At a sufficiently high field strength, the energy of these ions becomes sufficient to generate secondary avalanches capable of sustaining a self-discharge, causing the current through the counter to increase sharply.

Not all Geiger counters can detect all types of ionizing radiation. They are primarily sensitive to one type of radiation—alpha, beta, or gamma radiation—but can often also detect other radiation to some extent. For example, the SI-8B Geiger counter is designed to register soft beta radiation (yes, depending on the energy of the particles, radiation can be divided into soft and hard), but this sensor is also somewhat sensitive to alpha radiation and gamma radiation. radiation.

However, approaching the design of the article, our task is to make as simple as possible, naturally portable, a Geiger counter, or rather a dosimeter. To make this device, I only managed to get hold of SBM-20. This Geiger counter is designed to detect hard beta and gamma radiation. Like most other meters, SBM-20 operates at a voltage of 400 volts.

Main characteristics of the Geiger-Muller counter SBM-20 (table from the reference book):

This counter has relatively low accuracy in measuring ionizing radiation, but is sufficient to determine if the dose of radiation exceeded the permissible dose for a person. SBM-20 is currently used in many household dosimeters. To improve performance, several tubes are often used at once. And to increase the accuracy of gamma radiation measurement, dosimeters are equipped with beta radiation filters; in this case, the dosimeter registers only gamma radiation, but quite accurately.

When measuring radiation dose, there are several factors to consider that may be important. Even in the complete absence of sources of ionizing radiation, the Geiger counter will produce a certain number of pulses. This is the so-called counter background. This also includes several factors: radioactive contamination of the materials of the counter itself, spontaneous emission of electrons from the cathode of the counter and cosmic radiation. All this gives a certain number of “extra” impulses per unit of time.

So, the diagram of a simple dosimeter based on the SBM-20 Geiger counter:

I assemble the circuit on a breadboard:

The circuit does not contain scarce parts (except, of course, the counter itself) and does not contain programmable elements (microcontrollers), which will allow you to assemble the circuit in a short time without much difficulty. However, such a dosimeter does not contain a scale, and the radiation dose must be determined by ear by the number of clicks. Like this classic version. The circuit consists of a voltage converter 9 volts - 400 volts.

The NE555 chip contains a multivibrator whose operating frequency is approximately 14 kHz. To increase the operating frequency, you can reduce the value of resistor R1 to approximately 2.7 kOhm. This will be useful if the choke you have chosen (or maybe the one you have made) makes a squeaking sound - as the operating frequency increases, the squeaking noise will disappear. Inductor L1 is required with a rating of 1000 - 4000 µH. The fastest way to find a suitable inductor is in a burnt-out energy-saving light bulb. Such a choke is used in the circuit; in the photo above it is wound on a core, which is usually used for the manufacture of pulse transformers. Transistor T1 can be used with any other n-channel field-effect transistor with a drain-source voltage of at least 400 volts, and preferably more. Such a converter will produce only a few milliamps of current at a voltage of 400 volts, but this will be enough to operate a Geiger counter several times. After turning off the power from the circuit, the charged capacitor C3 will operate for about another 20-30 seconds, given its small capacitance. The VD2 suppressor limits the voltage to 400 volts. Capacitor C3 must be used for a voltage of at least 400 - 450 volts.

Any piezo speaker or speaker can be used as Ls1. In the absence of ionizing radiation, current does not flow through resistors R2 – R4 (there are five resistors on the breadboard in the photo, but their total resistance corresponds to the circuit). As soon as the corresponding particle hits the Geiger counter, the gas ionizes inside the sensor and its resistance sharply decreases, resulting in a current pulse. Capacitor C4 cuts off the constant part and passes only a current pulse to the speaker. We hear a click.

In my case, two are used as a power source rechargeable batteries from old phones (two, since the required power must be more than 5.5 volts to start the circuit due to the applied element base).

So, the circuit works, it clicks occasionally. Now how to use it. The simplest option is that it clicks a little - everything is good, clicks often or even continuously - bad. Another option is to roughly count the number of pulses per minute and convert the number of clicks to microR/h. To do this, you need to take the sensitivity value of the Geiger counter from the reference book. However, different sources always give slightly different figures. Ideally, it is necessary to carry out laboratory measurements for the selected Geiger counter with reference sources radiation. So for SBM-20 the sensitivity value varies from 60 to 78 pulses/μR according to different sources and reference books. So, we calculated the number of pulses in one minute, then we multiply this number by 60 to approximate the number of pulses in one hour and divide all this by the sensitivity of the sensor, that is, by 60 or 78 or whatever is closer to reality, and in the end we get the value in microR/h. For a more reliable value, it is necessary to take several measurements and calculate the arithmetic mean between them. The upper limit of safe radiation levels is approximately 20 - 25 µR/h. Acceptable level is up to approximately 50 μR/h. IN different countries numbers may vary.

P.S. I was prompted to consider this topic by an article about the concentration of radon gas penetrating into rooms, water, etc. V different regions country and its sources.

List of radioelements

Designation	Type	Denomination	Quantity	Note	My notepad
IC1	Programmable timer and oscillator	NE555	1		To notepad
T1	MOSFET transistor	IRF710	1		To notepad
VD1	Rectifier diode	1N4007	1		To notepad
VD2	Protection diode	1V5KE400CA	1		To notepad
C1, C2	Capacitor	10 nF	2		To notepad
C3	Electrolytic capacitor	2.7 µF	1		To notepad
C4	Capacitor	100 nF	1	400V

Geiger counter

Geiger counter SI-8B (USSR) with a mica window for measuring soft β-radiation. The window is transparent, under it you can see a spiral wire electrode; the other electrode is the body of the device.

Additional electronic circuit provides the counter with power (usually at least 300), provides, if necessary, discharge suppression and counts the number of discharges through the counter.

Geiger counters are divided into non-self-quenching and self-quenching (not requiring an external discharge termination circuit).

The sensitivity of the meter is determined by the composition of the gas, its volume, as well as the material and thickness of its walls.

Note

It should be noted that for historical reasons there has been a discrepancy between Russian and English versions this and subsequent terms:

Russian	English
Geiger counter	Geiger sensor
Geiger tube	Geiger tube
radiometer	Geiger counter
dosimeter	dosimeter

From the history of radiation studies

In 1895, X-rays were discovered. A year later, the phenomenon of uranium radioactivity was discovered, also associated with the discovery and use of X-rays. The researchers had to deal with a completely new, hitherto unseen natural phenomenon.

It should be noted that the phenomenon of radiation had already been encountered several years earlier, but the phenomenon was not given due attention. And this despite the fact that even the famous Nikola Tesla, as well as the working staff in Edison’s laboratory, were burned by X-rays. The deterioration of health was explained by everything they could, but not by radiation.

Later, with the beginning of the 20th century, articles appeared on the harmful effects of radiation on experimental animals. This also went unnoticed until one sensational incident in which the “radium girls”, workers of a factory that produced luminous watches, were injured.

The factory management told the girls about the harmlessness of radium, and they took lethal doses radiation: they licked the tips of brushes with radium paint, and for fun they painted their nails and even their teeth with a luminous substance. Five girls who suffered from such work managed to file a lawsuit against the factory. As a result, a precedent was set regarding the rights of some workers who received occupational diseases and sued their employers.

The history of the Geiger-Muller counter

The German physicist Hans Geiger, who worked in one of Rutherford's laboratories, developed and proposed in 1908 schematic diagram actions of the “charged particles” counter. It was a modification of the then familiar ionization chamber, which was presented in the form of an electric capacitor filled with gas at low pressure. The camera was also used by Pierre Curie when he studied the electrical properties of gases. Geiger came up with the idea of using it to detect ionizing radiation precisely because this radiation had a direct effect on the level of ionization of gases.

At the end of the 20s, Walter Müller, under the leadership of Geiger, created some types of radiation counters, with the help of which it was possible to register a wide variety of ionizing particles. Work on the creation of counters was very necessary, because without them it was impossible to study radioactive materials. Geiger and Müller had to work purposefully to create counters that would be sensitive to any of the types of radiation such as α, β and γ identified at that time.

Geiger-Muller counters have proven to be simple, reliable, cheap, and practical radiation sensors. This despite the fact that they were not the most precision instruments to study radiation or certain particles. But they were very well suited as instruments for general measurements of the saturation of ionizing radiation. In combination with other instruments, they are still used by practicing physicists for more accurate measurements during experimentation.

What is ionizing radiation?

To better understand the operation of Geiger-Muller counters, it would not hurt to become familiar with ionizing radiation as such. It may include everything that causes ionization of substances in their natural state. This will require the presence of some kind of energy. In particular, ultraviolet light or radio waves are not considered ionizing radiation. The distinction can begin with the so-called “hard ultraviolet”, also called “soft x-ray”. This type of flow is called photon radiation. The flow of high energy photons is gamma rays.

For the first time, the division of ionizing radiation into three types was done by Ernst Rutherford. Everything was done on research equipment that involved a magnetic field in empty space. Later all this was called:

α – nuclei of helium atoms;
β – high energy electrons;
γ – gamma quanta (photons).

Later, the discovery of neutrons occurred. Thus, it turned out that alpha particles can be easily retained even with ordinary paper, beta particles have a slightly greater penetrating ability, and gamma rays have the highest. Neutrons are considered the most dangerous, especially at distances of many tens of meters in airspace. Due to their electrical indifference, they do not interact with any electron shell molecules in a substance.

However, when you get into atomic nuclei with high potential lead to their instability and decay, after which radioactive isotopes are formed. And those, further in the process of decay, themselves form the entirety of ionizing radiation.

Geiger-Muller counter devices and operating principles

Gas-discharge Geiger-Muller counters are mainly designed as sealed tubes, glass or metal, from which all air has been pumped out. It is replaced by added inert gas (neon or argon or a mixture thereof) at low pressure, with halogen or alcohol impurities. Thin wires are stretched along the axes of the tubes, and metal cylinders are located coaxially with them. Both tubes and wires are electrodes: tubes are cathodes, and wires are anodes.

The negatives from constant voltage sources are connected to the cathodes, and the positives from constant voltage sources are connected to the anodes using a large constant resistance. From an electrical point of view, the output is a voltage divider. and in the middle of it the voltage level is almost the same as the voltage at the source. As a rule, it can reach several hundred volts.

As ionizing particles fly through the tubes, atoms in the inert gas, which are already in a high-intensity electric field, collide with these particles. The energy that was given up by the particles during the collision is considerable; it is enough to tear electrons away from gas atoms. The resulting secondary order electrons are themselves able to form further collisions, after which a whole electron and ion cascade emerges.

When exposed to an electric field, electrons are accelerated towards the anodes, and positively charged gas ions – towards the cathodes of the tubes. As a result, an electric current is generated. Since the energy of the particles had already been used up in collisions, either in whole or in part (the particles flew through the tube), the ionized atoms of the gas began to run out.

As soon as the charged particles entered the Geiger-Muller counter, the resistance of the tube dropped through the incipient current, and at the same time the voltage at the central mark of the separator changed, as mentioned earlier. After this, the resistance in the tube resumes as a result of its increase, and the voltage level returns to its previous state. As a result, negative voltage pulses are obtained. By counting the pulses, you can determine the number of particles that flew by. The highest intensity of the electric field is observed near the anode, due to its small size, as a result of which the counters become more sensitive.

Geiger-Muller counter designs

All modern Geiger-Muller counters have two main types: “classical” and flat. Classic meters are made of thin-walled corrugated metal tubes. The corrugated surfaces of the counters make the tubes rigid and will withstand external atmospheric pressure, and will not allow them to wrinkle under any influence. There are glass or plastic seals at the ends of the tubes. There are also cap taps to connect to the circuit. The tubes are marked and coated with a durable insulating varnish indicating the polarity of the taps. In general, these are universal counters for any type of ionizing radiation, especially for beta-gamma radiation.

Counters that may be sensitive to soft β radiation are manufactured differently. Due to the small ranges of β-particles, they are made flat. Mica windows weakly block beta radiation. One such counter can be called the BETA-2 sensor. In all other meters, the determination of their properties is related to the materials of their manufacture.

All counters that register gamma radiation have cathodes made of metals that have a high charge number. Gases are extremely poorly ionized by gamma photons. However, gamma-ray photons can knock out many secondary electrons from cathodes if chosen appropriately. Most Geiger-Muller beta particle counters are made to have thin windows. This is done to improve the permeability of the particles, because they are just ordinary electrons that have received more energy. They interact with substances very well and quickly, as a result of which energy is lost.

With alpha particles things are much worse. For example, despite quite a decent energy, several MeV, alpha particles experience very strong interaction with molecules moving along the way and soon losing their energy potential. Conventional counters respond well to α-radiation, but only at a distance of a few centimeters.

To make an objective assessment of the level of ionizing radiation, dosimeters on counters with general use often equipped with two sequentially functioning meters. One may be more sensitive to α-β radiation, and the other to γ radiation. Sometimes bars or plates made of alloys containing cadmium impurities are placed among the counters. When neutrons hit such bars, γ-radiation is generated, which is recorded. This is done for the possible determination of neutron radiation, and to it simple counters Geiger has virtually no sensitivity.

How Geiger counters are used in practice

Soviet, and now Russian industry There are many types of Geiger-Muller counters available. Such devices are mainly used by people who have something to do with nuclear industry facilities, scientific or educational institutions, civil defense, and medical diagnostics.

After it happened Chernobyl disaster, household dosimeters, previously completely unfamiliar to the population of our country even by name, began to gain truly nationwide popularity. Many models for household use began to appear. All of them use Geiger-Muller counters themselves as radiation sensors. Typically, household dosimeters have one or two tubes or end counters installed.