The structure and principle of operation of the Geiger-Muller counter. The principle of operation of the geiger counter Geiger counter physical principles of operation table

In connection with the environmental consequences of human activities related to nuclear energy, as well as industry (including the military), using radioactive substances as a component or basis of their products, the study of the basics of radiation safety and radiation dosimetry is becoming a fairly relevant topic today. In addition to natural sources of ionizing radiation, every year more and more places appear 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 proceeding with the manufacture (or purchase) of this device, it is necessary to have an idea of the nature of the measured parameter. Ionizing radiation (radiation) is a stream of photons, elementary particles or fission fragments of atoms capable of ionizing a substance. It is divided into several types. alpha radiation is a stream of alpha particles - helium-4 nuclei, alpha particles born during radioactive decay can be easily stopped by a sheet of paper, so it poses a danger mainly when it enters the body. beta radiation- this is the flow of electrons that arise during beta decay, to protect against beta particles with energies up to 1 MeV, an aluminum plate a few millimeters thick is enough. Gamma radiation has a much greater penetrating power, since it consists of high-energy photons that do not have a charge; heavy elements (lead, etc.) with a layer of several centimeters are effective for protection. The penetrating power of all types of ionizing radiation depends on the energy.

To register ionizing radiation, Geiger-Muller counters are mainly used. This simple and effective device is usually 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 principle of operation is based on impact ionization. When ionizing radiation hits the walls of the counter, electrons are knocked out of it, electrons, moving in gas and colliding with gas atoms, knock electrons out of atoms and create positive ions and free electrons. The electric field between the cathode and the anode accelerates the electrons to energies at which impact ionization begins. An avalanche of ions arises, 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 maintaining an independent discharge, as a result of which the current through the counter increases sharply.

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

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

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

This counter has a relatively low accuracy of measuring ionizing radiation, but sufficient to determine the excess of the permissible dose of radiation for humans. 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 measuring gamma radiation, dosimeters are equipped with beta radiation filters; in this case, the dosimeter registers only gamma radiation, but rather 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 give a certain number of pulses. This is the so-called custom 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 amount of "extra" pulses per unit time.

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

I assemble the circuit on a breadboard:

The circuit does not contain scarce parts (except, of course, the meter 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 it is necessary to determine the radiation dose by ear by the number of clicks. This is the classic version. The circuit consists of a voltage converter 9 volts - 400 volts.

A multivibrator is made on the NE555 chip, the frequency of which is approximately 14 kHz. To increase the frequency of operation, you can reduce the value of the resistor R1 to about 2.7 kOhm. This will be useful if the choke you have chosen (or maybe made) will make a squeak - with an increase in the frequency of operation, the squeak will disappear. Inductor L1 is required with a rating of 1000 - 4000 μH. The fastest way to find a suitable choke is in a burned-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 to make pulse transformers. Transistor T1 can use any other field n-channel with a drain-source voltage of at least 400 volts, and preferably more. Such a converter will give only a few milliamps of current at a voltage of 400 volts, but this is enough for a Geiger counter to work several times. After turning off the power from the circuit on the charged capacitor C3, the circuit will work for about another 20-30 seconds, given its small capacitance. The suppressor VD2 limits the voltage at 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, no current flows through resistors R2 - R4 (there are five resistors in the photo on the breadboard, but their total resistance corresponds to the circuit). As soon as the corresponding particle enters the Geiger counter, the gas ionization occurs inside the sensor and its resistance decreases sharply, as a result of which a current pulse occurs. Capacitor C4 cuts off the constant part and passes only a current pulse to the speaker. We hear a click.

In my case, two batteries from old phones are used as a power source (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, occasionally clicks. Now how to use it. The simplest option - it clicks a little - everything is fine, 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 have slightly different numbers. Ideally, laboratory measurements should be made for the selected Geiger counter with reference radiation sources. So for SBM-20, the sensitivity value varies from 60 to 78 pulses / μR according to various sources and reference books. So, we calculated the number of impulses in one minute, then we multiply this number by 60 to approximate the number of impulses in one hour and divide all this by the sensitivity of the sensor, that is, by 60 or 78 or whatever you get closer to reality and as a result we get the value in µR/h. For a more reliable value, it is necessary to take several measurements and calculate the arithmetic mean between them. The upper limit of the safe level of radiation is approximately 20 - 25 microR/h. The permissible level is up to about 50 μR / h. Numbers may vary by country.

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

List of radio elements

Designation	Type of	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	Protective diode	1V5KE400CA	1		To notepad
C1, C2	Capacitor	10 nF	2		To notepad
C3	electrolytic capacitor	2.7uF	1		To notepad
C4	Capacitor	100 nF	1	400V

The structure and principle of operation of the Geiger-Muller counter

AT Recently, the attention to radiation safety on the part of ordinary citizens in our country has been increasingly increasing. And this is due not only to the tragic events at the Chernobyl nuclear power plant and its further consequences, but also to various kinds of incidents that periodically occur in one place or another on the planet. In this regard, at the end of the last century, devices began to appear dosimetric monitoring of radiation for household purposes. And such devices saved many people not only health, but sometimes life, and this applies not only to the territories adjacent to the exclusion zone. Therefore, the issues of radiation safety are relevant in any place of our country to this day.

AT All household and almost all modern professional dosimeters are equipped with . In another way, it can be called the sensitive element of the dosimeter. This device was invented in 1908 by the German physicist Hans Geiger, and twenty years later, another physicist Walter Müller improved this development, and it is the principle of this device that is used at the present time.

H Some modern dosimeters have four counters at once, which makes it possible to increase the accuracy of measurements and the sensitivity of the device, as well as to reduce the measurement time. Most Geiger-Muller counters are capable of detecting gamma radiation, high-energy beta radiation, and X-rays. However, there are special developments for the determination of high-energy alpha particles. To set the dosimeter to detect only gamma radiation, the most dangerous of the three types of radiation, the sensitive chamber is covered with a special casing made of lead or other steel, which makes it possible to cut off the penetration of beta particles into the counter.

AT modern dosimeters for domestic and professional purposes, sensors such as SBM-20, SBM-20-1, SBM-20U, SBM-21, SBM-21-1 are widely used. They differ in the overall dimensions of the camera and other parameters, for the line of 20 sensors the following dimensions are typical, length 110 mm, diameter 11 mm, and for the 21st model, length 20-22 mm with a diameter of 6 mm. It is important to understand that the larger the chamber, the more radioactive elements will fly through it, and the greater the sensitivity and accuracy it has. So, for the 20th series of the sensor, the dimensions are 8-10 times larger than for the 21st, approximately in the same proportions we will have a difference in sensitivity.

To The design of a Geiger counter can be schematically described as follows. A sensor consisting of a cylindrical container filled with an inert gas (eg, argon, neon, or mixtures thereof) at minimal pressure to facilitate the initiation of an electrical discharge between the cathode and anode. The cathode, most often, is the entire metal case of the sensitive sensor, and the anode is a small wire placed on insulators. Sometimes the cathode is additionally wrapped in a protective casing made of stainless steel or lead, this is done to set the counter to detect only gamma rays.

D For domestic use, at present, end-face sensors are most often used (for example, Beta-1, Beta-2). Such counters are designed in such a way that they are able to detect and register even alpha particles. Such a counter is a flat cylinder with electrodes located inside, and an input (working) window made of a mica film with a thickness of only 12 microns. This design makes it possible to detect (at close range) high-energy alpha particles and low-energy beta particles. At the same time, the area of the working window of the Beta-1 and Beta 1-1 counters is 7 sq.cm. The area of the mica working window for the Beta-2 device is 2 times larger than that of Beta-1, it can be used to determine , etc.

E If we talk about the principle of operation of the Geiger counter chamber, then it can be briefly described as follows. When activated, a high voltage (of the order of 350 - 475 volts) is applied to the cathode and anode through a load resistor, but there is no discharge between them due to the inert gas serving as a dielectric. When it enters the chamber, its energy is sufficient to knock out a free electron from the material of the chamber body or cathode, this electron begins to knock out free electrons like an avalanche from the surrounding inert gas and its ionization occurs, which eventually leads to a discharge between the electrodes. The circuit closes, and this fact can be registered using the instrument's microchip, which is the fact of detection of either a gamma or X-ray quantum. The camera then resets, allowing the next particle to be detected.

H In order to stop the discharge process in the chamber and prepare the chamber for registration of the next particle, there are two methods, one of them is based on the fact that the voltage supply to the electrodes is stopped for a very short period of time, which stops the gas ionization process. The second method is based on adding another substance to the inert gas, for example, iodine, alcohol and other substances, while they lead to a decrease in the voltage on the electrodes, which also stops the process of further ionization and the camera becomes able to detect the next radioactive element. This method uses a high capacity load resistor.

P about the number of discharges in the counter chamber and one can judge the level of radiation in the measured area or from a specific object.

Regardless of whether we want it or not, but the term "radiation" for a long time wedged into our consciousness and being, and no one can hide from the fact of its presence. People have to learn to live with this somewhat negative phenomenon. The phenomenon of radiation can manifest itself with the help of invisible and imperceptible radiations, and it is almost impossible to reveal it without special equipment.

From the history of the study of radiation

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 face a completely new, hitherto unseen natural phenomenon.

It should be noted that the phenomenon of radiation had already been encountered several years before, 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 the Edison laboratory, were burned with 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 notorious incident in which "radium girls" - workers in a factory that produced luminous watches - suffered.

The factory management told the girls about the harmlessness of radium, and they took lethal doses of radiation: they licked the tips of brushes with radium paint, for fun they painted their nails and even 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 in relation to the rights of some workers who got occupational diseases and sued their employers.

The history of the appearance of the Geiger-Muller counter

The German physicist Hans Geiger, who worked in one of Rutherford's laboratories, in 1908 developed and proposed a schematic diagram of the "charged particle" counter. It was a modification of the already familiar then ionization chamber, which was presented in the form of an electric capacitor filled with gas at low pressure. The camera was 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 1920s, Walter Müller, under the leadership of Geiger, created some types of radiation counters, with 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 Muller had to purposefully work on the creation of such counters that would be sensitive to any of the varieties of radiation of the α, β and γ types identified at that time.

Geiger-Muller counters have proven to be simple, reliable, cheap, and also practical radiation sensors. This despite the fact that they were not the most accurate instruments for studying 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 practical physicists for more accurate measurements in the process of experimentation.

What is ionizing radiation?

For a better understanding of the operation of Geiger-Muller counters, it would not hurt to get acquainted with ionizing radiation as such. It can include everything that causes the ionization of substances that are in a natural state. This will require the presence of some kind of energy. In particular, ultraviolet light or radio waves are not classified as ionizing radiation. The demarcation can begin with the so-called "hard ultraviolet", also called "soft X-ray". This type of flow is called photon radiation. A stream of high-energy photons are gamma quanta.

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. This was later named:

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

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

However, when they hit atomic nuclei with a high potential, they 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 made as hermetic tubes, glass or metal, from which all the air has been evacuated. It is replaced by an 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.

Minuses from constant voltage sources are connected to the cathodes, and pluses from sources with constant voltage are connected to the anodes - using a large constant resistance. From an electrical point of view, a voltage divider comes out. 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 up to several hundred volts.

As the ionizing particles fly through the tubes, the atoms in the inert gas, which are already in a high-intensity electric field, collide with these particles. The energy that was given away by the particles during the collision is considerable, it is enough for the electrons to break away from the atoms of the gas. The resulting secondary order electrons themselves are able to form further collisions, after which a whole electronic and ionic 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 for collisions, in whole or in part (the particles flew through the tube), the ionized gas atoms began to run out.

As soon as the charged particles entered the Geiger-Muller counter, the resistance of the tube dropped by the nascent current, and at the same time the voltage at the central mark of the separator changed, as was indicated earlier. After that, the resistance in the tube, as a result of its growth, resumes, and the voltage level returns to its previous state. As a result, negative voltage pulses are obtained. By counting the pulses, you can set the number of particles that have flown. The greatest 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.

Designs of Geiger-Muller counters

All modern Geiger-Muller counters have two main varieties: "classical" and flat. Classic counters are made of thin-walled corrugated metal tubes. The corrugated surfaces of the meters make the tubes rigid, they will withstand external atmospheric pressure, and will not allow them to wrinkle under any influence. At the ends of the tubes there are glass or plastic hermetic insulators. There are also taps-caps 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 kind 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 delay beta radiation. One such counter can be called a BETA-2 sensor. In all other counters, the determination of their properties is attributed to the materials of their manufacture.

All counters that register gamma radiation have cathodes made of such metals, in which there is a large charge number. Gases are extremely unsatisfactorily ionized by gamma photons. However, gamma photons can knock out a lot of secondary electrons from cathodes if chosen properly. Most Geiger-Muller counters for beta particles 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 have a very good and fast interaction with substances, as a result of which energy is lost.

With alpha particles, things are much worse. For example, despite a fairly decent energy, a few MeV, alpha particles have a very strong interaction with molecules moving along the way and soon losing their energy potential. Ordinary 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 application are often equipped with two counters operating in series. 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 occurs, which is recorded. This is done for the possible determination of neutron radiation, and simple Geiger counters have practically no sensitivity to it.

How Geiger counters are used in practice

The Soviet, and now the Russian industry produces many varieties of Geiger-Muller counters. 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 the Chernobyl disaster, household dosimeters, previously completely unfamiliar to the population of our country even by name, began to gain truly nationwide popularity. Many household models began to appear. All of them use their own Geiger-Muller counters as radiation sensors. Usually, one or two tubes or end counters are installed in household dosimeters.

Invented back in 1908 by the German physicist Hans Wilhelm Geiger, a device that can determine is widely used today. The reason for this is the high sensitivity of the device, its ability to register a variety of radiation. Ease of operation and low cost make it possible to buy a Geiger counter for any person who decides to independently measure the level of radiation at any time and in any place. What is this device and how does it work?

The principle of operation of the Geiger counter

Its design is quite simple. A gas mixture consisting of neon and argon is pumped into a sealed container with two electrodes, which is easily ionized. It is supplied to the electrodes (of the order of 400V), which in itself does not cause any discharge phenomena until the very moment when the ionization process begins in the gaseous medium of the device. The appearance of particles coming from outside leads to the fact that the primary electrons, accelerated in the corresponding field, begin to ionize other molecules of the gaseous medium. As a result, under the influence of an electric field, an avalanche-like creation of new electrons and ions occurs, which sharply increase the conductivity of the electron-ion cloud. A discharge occurs in the gaseous medium of the Geiger counter. The number of pulses that occur during a certain period of time is directly proportional to the number of detected particles. This is, in general terms, the principle of operation of the Geiger counter.

The reverse process, as a result of which the gas medium returns to its original state, occurs by itself. Under the influence of halogens (usually bromine or chlorine is used), an intense recombination of charges occurs in this medium. This process is much slower, and therefore the time required to restore the sensitivity of the Geiger counter is a very important passport characteristic of the device.

Despite the fact that the principle of operation of the Geiger counter is quite simple, it is able to respond to ionizing radiation of various types. This is α-, β-, γ-, as well as X-ray, neutron and Everything depends on the design of the device. Thus, the entrance window of a Geiger counter capable of registering α- and soft β-radiation is made of mica with a thickness of 3 to 10 microns. For detection, it is made from beryllium, and ultraviolet - from quartz.

Where is the Geiger counter used?

The principle of operation of the Geiger counter is the basis for the operation of most modern dosimeters. These small, relatively low-cost devices are quite sensitive and can display results in readable units. Their ease of use makes it possible to operate these devices even for those who have a very remote understanding of dosimetry.

According to their capabilities and measurement accuracy, dosimeters are professional and household. With their help, it is possible to timely and effectively determine the existing source of ionized radiation both in open areas and indoors.

These devices, which use the principle of operation of the Geiger counter in their work, can give a timely signal of danger using both visual and sound or vibration signals. So, you can always check food, clothes, examine furniture, equipment, building materials, etc. for the absence of radiation harmful to the human body.

Geiger counter- a gas-discharge device for counting the number of ionizing particles that have passed through it. It is a gas-filled capacitor that breaks through when an ionizing particle appears in the gas volume. Geiger counters are quite popular detectors (sensors) of ionizing radiation. Until now, they, invented at the very beginning of our century for the needs of nascent nuclear physics, do not, oddly enough, have any full-fledged replacement.

The design of the Geiger counter is quite simple. A gas mixture consisting of easily ionizable neon and argon is introduced into a sealed container with two electrodes. The material of the container can be different - glass, metal, etc.

Usually meters perceive radiation with their entire surface, but there are also those that have a special “window” in the cylinder for this. The widespread use of the Geiger-Muller counter is explained by its high sensitivity, the ability to register various radiation, and the comparative simplicity and low cost of installation.

Geiger counter wiring diagram

A high voltage U is applied to the electrodes (see Fig.), which in itself does not cause any discharge phenomena. The counter will remain in this state until an ionization center appears in its gaseous medium - a trace of ions and electrons generated by an ionizing particle that has come from outside. Primary electrons, accelerating in an electric field, ionize "along the way" other molecules of the gaseous medium, generating more and more new electrons and ions. Developing like an avalanche, this process ends with the formation of an electron-ion cloud in the space between the electrodes, which significantly increases its conductivity. In the gas environment of the counter, a discharge occurs, which is visible (if the container is transparent) even with a simple eye.

The reverse process - the restoration of the gaseous medium to its original state in the so-called halogen meters - occurs by itself. Halogens (usually chlorine or bromine), which are contained in a small amount in the gaseous medium, come into play, which contribute to the intensive recombination of charges. But this process is rather slow. The time required to restore the radiation sensitivity of the Geiger counter and actually determines its speed - "dead" time - is its main passport characteristic.

Such meters are designated as halogen self-extinguishing meters. Distinguished by a very low supply voltage, good output signal parameters, and sufficiently high speed, they turned out to be in demand as ionizing radiation sensors in household radiation monitoring devices.

Geiger counters are capable of detecting a variety of types of ionizing radiation - a, b, g, ultraviolet, x-ray, neutron. But the actual spectral sensitivity of the counter is very dependent on its design. Thus, the input window of a counter sensitive to a- and soft b-radiation should be rather thin; for this, mica 3–10 µm thick is usually used. The balloon of a counter that reacts to hard b- and g-radiation usually has the shape of a cylinder with a wall thickness of 0.05 .... 0.06 mm (it also serves as the cathode of the counter). The X-ray counter window is made of beryllium, and the ultraviolet window is made of quartz glass.

The dependence of the counting rate on the supply voltage in the Geiger counter

Boron is introduced into the neutron counter, upon interaction with which the neutron flux is converted into easily detectable a-particles. Photon radiation - ultraviolet, x-ray, g-radiation - Geiger counters perceive indirectly - through the photoelectric effect, the Compton effect, the effect of pair production; in each case, the radiation interacting with the material of the cathode is converted into a stream of electrons.

Each particle detected by the counter forms a short pulse in its output circuit. The number of pulses that appear per unit time - the count rate of the Geiger counter - depends on the level of ionizing radiation and the voltage on its electrodes. The standard plot of the counting rate versus the supply voltage Upit is shown in the figure above. Here Uns is the voltage of the beginning of counting; Ung and Uvg are the lower and upper limits of the working area, the so-called plateau, on which the counting rate is almost independent of the meter supply voltage. The operating voltage Ur is usually chosen in the middle of this section. It corresponds to Nr, the count rate in this mode.

The dependence of the counting rate on the degree of radiation exposure of the counter is its main characteristic. The graph of this dependence is almost linear and therefore often the radiation sensitivity of the counter is shown in terms of pulses / μR (pulses per micro-roentgen; this dimension follows from the ratio of the count rate - pulse / s - to the radiation level - μR / s).

In those cases when it is not indicated, it is necessary to determine the radiation sensitivity of the counter according to its other extremely important parameter - its own background. This is the name of the counting rate, the factor of which is two components: external - the natural radiation background, and internal - the radiation of radionuclides trapped in the counter design itself, as well as the spontaneous electron emission of its cathode.

Dependence of the counting rate on the energy of gamma quanta ("stroke with rigidity") in the Geiger counter

Another essential characteristic of the Geiger counter is the dependence of its radiation sensitivity on the energy ("hardness") of ionizing particles. The extent to which this dependence is significant is shown by the graph in the figure. "Travel with rigidity" will obviously affect the accuracy of the measurements taken.

The fact that the Geiger counter is an avalanche device also has its drawbacks - one cannot judge the root cause of its excitation by the reaction of such a device. The output pulses generated by the Geiger counter under the influence of a-particles, electrons, g-quanta are no different. The particles themselves, their energies completely disappear in the twin avalanches they generate.

The table shows information about self-extinguishing halogen Geiger counters of domestic production, the most suitable for household radiation monitoring devices.

	1	2	3	4	5	6	7
SBM19	400	100	2	310*	50	19x195	1
SBM20	400	100	1	78*	50	11x108	1
SBT9	380	80	0,17	40*	40	12x74	2
SBT10A	390	80	2,2	333*	5	(83x67x37)	2
SBT11	390	80	0,7	50*	10	(55x29x23.5)	3
SI8B	390	80	2	350-500	20	82x31	2
SI14B	400	200	2	300	30	84x26	2
SI22G	390	100	1,3	540*	50	19x220	4
SI23BG	400	100	2	200-400*	—	19x195	1

1 - operating voltage, V;
2 - plateau - area of low dependence of the count rate on the supply voltage, V;
3 — own background of the counter, imp/s, no more;
4 - radiation sensitivity of the counter, pulses/μR (* - for cobalt-60);
5 - amplitude of the output pulse, V, not less;
6 — dimensions, mm — diameter x length (length x width x height);
7.1 - hard b - and g - radiation;
7.2 - the same and soft b - radiation;
7.3 - the same and a - radiation;
7.4 - g - radiation.