The principle of operation of a geiger counter and modern dosimeters. Geiger-Muller counter could save "radium girls" in America

Geiger-Muller counter

D to determine the level of radiation, a special device is used -. And for such household devices and most professional dosimetric control devices, it is used as a sensitive element geiger counter ... This part of the radiometer allows you to accurately determine the level of radiation.

The history of the Geiger counter

IN the first, a device for determining the intensity of decay of radioactive materials was born in 1908, it was invented by a German physicist Hans Geiger ... Twenty years later, together with another physicist Walter Müller the device was improved, and in honor of these two scientists it was named.

IN During the period of development and formation of nuclear physics in the former Soviet Union, corresponding devices were also created, which were widely used in the armed forces, at nuclear power plants, and in special groups of radiation control of civil defense. The composition of such dosimeters, starting from the seventies of the last century, included a counter based on Geiger principles, namely SBM-20 ... This counter, exactly like its other counterpart STS-5 , is widely used to this day, and is also part of modern means dosimetric control .

Fig. 1. Gas-discharge counter STS-5.

Fig. 2. Gas discharge counter SBM-20.

The principle of operation of the Geiger-Muller counter

AND the registration of radioactive particles proposed by Geiger is relatively simple. It is based on the principle of the appearance of electrical impulses in an inert gas medium under the action of a highly charged radioactive particle or a quantum of electromagnetic oscillations. To dwell in more detail on the mechanism of action of the counter, let us dwell a little on its design and the processes occurring in it when a radioactive particle passes through the sensitive element of the device.

R the recording device is a sealed balloon or container filled with an inert gas, it can be neon, argon, etc. Such a container can be made of metal or glass, and the gas in it is under low pressure, this is done specifically to simplify the process of registering a charged particle. Inside the container there are two electrodes (cathode and anode) to which high DC voltage is supplied through a special load resistor.

Fig. 3. Geiger counter device and circuit.

P when the meter is activated in an inert gas, no discharge occurs on the electrodes due to the high resistance of the medium, but the situation changes if a radioactive particle or a quantum of electromagnetic oscillations enters the chamber of the sensitive element of the device. In this case, a particle with a charge of a sufficiently high energy knocks out a certain number of electrons from the nearest environment, i.e. from the body elements or physically the electrodes themselves. Such electrons, being in an inert gas environment, under the action of a high voltage between the cathode and anode, begin to move towards the anode, ionizing the molecules of this gas along the way. As a result, they knock out secondary electrons from gas molecules, and this process grows on a geometric scale until a breakdown occurs between the electrodes. In the state of discharge, the circuit closes for a very short period of time, and this causes a jump in the current in the load resistor, and it is this jump that makes it possible to register the passage of a particle or quantum through the registration chamber.

T this mechanism makes it possible to register one particle, however, in a medium where ionizing radiation is sufficiently intense, a quick return of the registration chamber to its original position is required to be able to determine new radioactive particle ... This is accomplished by two different ways... The first of them consists in stopping the voltage supply to the electrodes for a short period of time, in this case the ionization of the inert gas stops abruptly, and a new activation of the test chamber allows starting the registration from the very beginning. This type of counter is called non-self-extinguishing dosimeters ... The second type of devices, namely self-extinguishing dosimeters, the principle of their operation is to add special additives to the inert gas medium based on various elements, for example, bromine, iodine, chlorine or alcohol. In this case, their presence automatically leads to the termination of the discharge. With this structure of the test chamber, resistances of sometimes several tens of megohms are used as a load resistor. This allows, during the discharge, to sharply reduce the potential difference at the ends of the cathode and anode, which stops the conductive process and the chamber returns to its original state. It should be noted that the voltage on the electrodes less than 300 volts automatically stops maintaining the discharge.

The entire described mechanism allows registering a huge amount of radioactive particles in a short period of time.

Types of radioactive radiation

H to understand what exactly is being registered geiger - Muller counters , it is worth dwelling on what types of it exist. It should be noted right away that gas-discharge counters, which are part of most modern dosimeters, are only able to register the number of radioactive charged particles or quanta, but cannot determine either their energy characteristics or the type of radiation. For this, dosimeters are made more versatile and targeted, and in order to compare them correctly, one should more accurately understand their capabilities.

P about modern ideas nuclear physics radiation radiation can be divided into two types, the first in the form electromagnetic field , the second in the form particle flow (corpuscular radiation). The first type includes gamma particle flux or x-ray ... Their main feature is the ability to propagate in the form of a wave over very long distances, while they easily pass through various objects and can easily penetrate into the most various materials... For example, if a person needs to hide from the flow of gamma rays due to a nuclear explosion, then hiding in the basement of a house or bomb shelter, provided that it is relatively tight, he will be able to protect himself from this type of radiation only 50 percent.

Fig. 4. X-ray and gamma-ray quanta.

T this type of radiation is pulsed in nature and is characterized by propagation in environment in the form of photons or quanta, i.e. short bursts of electromagnetic radiation. Such radiation can have different energy and frequency characteristics, for example, X-rays have a frequency thousands of times lower than gamma rays. therefore gamma rays are significantly more dangerous for the human body and their impact is much more destructive.

AND radiation based on the corpuscular principle is alpha and beta particles (corpuscles). They arise as a result of a nuclear reaction in which some radioactive isotopes are converted into others with the release of a colossal amount of energy. In this case, beta particles are a stream of electrons, and alpha particles are much larger and more stable formations, consisting of two neutrons and two protons connected to each other. In fact, such a structure has the nucleus of a helium atom, so it can be argued that the flow of alpha particles is a flow of helium nuclei.

The following classification is adopted , alpha particles have the least penetrating ability, in order to protect themselves from them, it is enough for a person and thick cardboardBeta particles have a greater penetrating ability, so that a person can protect himself from the flow of such radiation, he will need metal protection several millimeters thick (for example, an aluminum sheet). There is practically no protection from gamma quanta, and they propagate over considerable distances, attenuating with distance from the epicenter or source, and obeying the laws of propagation of electromagnetic waves.

Fig. 5. Alpha and beta type radioactive particles.

TO the amount of energy possessed by all these three types of radiation is also different, and the largest of them is the flux of alpha particles. For example, the energy possessed by alpha particles is seven thousand times greater than the energy of beta particles , i.e. penetrating power different types radiation, is in the back proportional relationship from their penetrating ability.

D for the human body, the most dangerous type of radioactive radiation is considered gamma quanta , due to the high penetrating power, and then decreasing, beta particles and alpha particles. Therefore, it is quite difficult to determine alpha particles, if it is impossible to tell with an ordinary counter. Geiger - Muller, since almost any object is an obstacle for them, not to mention a glass or metal container. It is possible to determine beta particles with such a counter, but only if their energy is sufficient to pass through the material of the counter container.

For beta particles with low energies, the conventional Geiger-Muller counter is ineffective.

ABOUT fraternal situation with gamma radiation, there is a possibility that they will pass through the container without triggering the ionization reaction. For this, a special screen (made of dense steel or lead) is installed in the counters, which makes it possible to reduce the energy of gamma quanta and thus activate the discharge in the counter chamber.

Basic characteristics and differences of Geiger - Muller counters

FROM it also highlights some of the basic characteristics and differences of different dosimeters equipped with gas-discharge Geiger - Müller counters... To do this, you should compare some of them.

The most common Geiger-Muller counters are equipped with cylindrical or end sensors... Cylindrical are similar to an elongated cylinder in the form of a tube with a small radius. The end ionization chamber has a round or rectangular shape of small size, but with a significant end working surface. Sometimes there are varieties of end chambers with an elongated cylindrical tube with a small entrance window on the end side. Different configurations of counters, namely the cameras themselves, are able to register different types of radiation, or their combinations, (for example, combinations of gamma and beta rays, or the entire spectrum of alpha, beta and gamma). This becomes possible due to the specially developed design of the meter body, as well as the material from which it is made.

E another important component for the targeted use of meters is area of \u200b\u200bthe input sensing element and working area ... In other words, this is the sector through which radioactive particles of interest will enter and register. The larger this area, the more the counter will be able to capture particles, and the stronger will be its sensitivity to radiation. The passport data indicates the area of \u200b\u200bthe working surface, usually in square centimeters.

E another important indicator that is indicated in the characteristics of the dosimeter is noise magnitude (measured in pulses per second). In other words, this indicator can be called the value of its own background. It can be determined in laboratory conditions by placing the device in a well-protected room or chamber, usually with thick lead walls, and recording the level of radiation emitted by the device itself. It is clear that if this level is significant enough, then these induced noises will directly affect the measurement error.

Every professional and radiation has such a characteristic as radiation sensitivity, also measured in pulses per second (imp / s), or in pulses per micro-roentgen (imp / μR). Such a parameter, or rather its use, directly depends on the source of ionizing radiation, to which the counter is adjusted, and by which further measurement will be carried out. Often, tuning is done according to sources that include such radioactive materials as radium - 226, cobalt - 60, cesium - 137, carbon - 14 and others.

E another indicator by which dosimeters should be compared is ion radiation detection efficiency or radioactive particles. The existence of this criterion is due to the fact that not all radioactive particles passed through the sensitive element of the dosimeter will be registered. This can happen when the gamma-ray quantum did not cause ionization in the counter chamber, or the number of particles passed and caused ionization and discharge is so large that the device does not adequately count them, and for some other reason. To accurately determine this characteristic of a particular dosimeter, it is tested using some radioactive sources, for example, plutonium-239 (for alpha particles), or thallium - 204, strontium - 90, yttrium - 90 (beta emitter), as well as others radioactive materials.

FROM the next criterion on which to stop is range of recorded energies ... Any radioactive particle or quantum of radiation has a different energy characteristic. Therefore, dosimeters are designed to measure not only a specific type of radiation, but also their respective energy characteristics. This indicator is measured in megaelectronvolts or kiloelectronvolts, (MeV, KeV). For example, if beta particles do not have sufficient energy, then they will not be able to knock out an electron in the counter chamber, and therefore will not be registered, or only high-energy alpha particles will be able to break through the material of the Geiger-Muller counter body and knock out the electron.

AND proceeding from all of the above, modern manufacturers radiation dosimeters produce a wide range of instruments for various purposes and specific industries. Therefore, it is worth considering specific types of Geiger counters.

Various options for Geiger - Müller counters

P the first version of dosimeters is a device designed to register and detect gamma photons and high-frequency (hard) beta radiation. Almost all of the previously produced and modern ones, both household and professional radiation dosimeters, are designed for this measurement range, for example:. Such radiation has sufficient energy and high penetrating power for the Geiger counter chamber to register them. Such particles and photons easily penetrate through the walls of the counter and cause the ionization process, and this is easily recorded by the corresponding electronic filling of the dosimeter.

D for registration of this type of radiation, popular counters such as SBM-20 having a sensor in the form of a cylindrical tube-balloon with coaxially arranged wire cathode and anode. Moreover, the walls of the sensor tube serve as both a cathode and a housing, and are made of stainless steel. This counter has the following characteristics:

the area of \u200b\u200bthe working area of \u200b\u200bthe sensitive element is 8 square centimeters;
radiation sensitivity to gamma radiation of about 280 imp / s, or 70 imp / μR (testing was carried out for cesium - 137 at 4 μR / s);
the intrinsic background of the dosimeter is about 1 pulse / s;
the sensor is designed to register gamma radiation with an energy in the range from 0.05 MeV to 3 MeV, and beta particles with an energy of 0.3 MeV at the lower boundary.

Fig. 6. Geiger counter SBM-20 device.

Have this counter had various modifications, for example, SBM-20-1 or SBM-20U who have similar characteristics, but differ in the basic design of the contact elements and the measuring circuit. Other modifications of this Geiger - Müller counter, and these are SBM-10, SI29BG, SBM-19, SBM-21, SI24BG have similar parameters, many of them are found in household radiation dosimeters that can be found in stores today.

FROM the next group of radiation dosimeters is designed for registration gamma photons and x-ray ... If we talk about the accuracy of such devices, it should be understood that photon and gamma radiation are quanta of electromagnetic radiation that move at the speed of light (about 300,000 km / s), so registering such an object is a rather difficult task.

The efficiency of such Geiger counters is about one percent.

H to increase it, an increase in the cathode surface is required. In fact, gamma quanta are recorded indirectly, thanks to the electrons knocked out by them, which subsequently participate in the ionization of an inert gas. To maximize this effect, the material and wall thickness of the meter chamber, as well as the dimensions, thickness and material of the cathode, are specially selected. Here, a large thickness and density of the material can reduce the sensitivity of the registration chamber, and too small will allow high-frequency beta radiation to easily enter the camera, and also increase the amount of radiation noise natural for the device, which will drown out the accuracy of the determination of gamma quanta. Naturally, the exact proportions are selected by the manufacturers. In fact, based on this principle, dosimeters are manufactured based on geiger - Muller counters for the direct determination of gamma radiation on the ground, while such a device excludes the possibility of determining any other types of radiation and radioactive exposure, which allows you to accurately determine the radiation contamination and the level negative impact per person only for gamma radiation.

IN domestic dosimeters, which are equipped with cylindrical sensors, the following types are installed: SI22G, SI21G, SI34G, Gamma 1-1, Gamma - 4, Gamma - 5, Gamma - 7ts, Gamma - 8, Gamma - 11 and many others. Moreover, in some types, a special filter is installed on the input, end, sensitive window, which specifically serves to cut off alpha and beta particles, and additionally increases the cathode area for more efficient determination of gamma quanta. These sensors include Beta - 1M, Beta - 2M, Beta - 5M, Gamma - 6, Beta - 6M and others.

H in order to understand more clearly the principle of their operation, it is worth considering in more detail one of these counters. For example, an end counter with a sensor Beta - 2M , which has a rounded working window, which is about 14 square centimeters. In this case, the radiation sensitivity to cobalt - 60 is about 240 imp / μR. This type of meter has very low self-noise values. , which is no more than 1 pulse per second. This is possible due to a thick-walled lead chamber, which, in turn, is designed to register photon radiation with energies in the range from 0.05 MeV to 3 MeV.

Fig. 7. End gamma counter Beta-2M.

To determine gamma radiation, it is quite possible to use counters for gamma-beta pulses, which are designed to register hard (high-frequency and high-energy) beta particles and gamma quanta. For example, model SBM - 20. If in this model of the dosimeter you want to exclude registration of beta particles, then it is enough to install a lead shield, or a shield from any other metal material (lead screen is more efficient). This is the most common method used by most designers to build gamma and X-ray counters.

Registration of "soft" beta radiation.

TO as we have already mentioned, registration of soft beta radiation (radiation with low energy characteristics and relatively low frequency) is a rather difficult task. For this, it is required to provide the possibility of easier penetration into the registration chamber. For these purposes, a special thin working window is made, as a rule, of mica or polymer film, which practically does not hinder the penetration of this type of beta radiation into the ionization chamber. In this case, the sensor body itself can act as the cathode itself, and the anode is a system of linear electrodes, which are uniformly distributed and mounted on insulators. The registration window is made in the end version, and in this case only a thin mica film appears in the path of beta particles. In dosimeters with such counters, gamma radiation is recorded as an application and, in fact, as an additional feature. And if you want to get rid of the registration of gamma quanta, then it is necessary to minimize the cathode surface.

Fig. 8. The device of the end Geiger counter.

FROM it should be noted that counters for the determination of soft beta particles were created quite a long time ago and were successfully used in the second half of the last century. Among them, the most common were sensors of the type SBT10 and SI8B which had thin-walled mica working windows. A more modern version of such a device Beta 5 has a working window area of \u200b\u200babout 37 sq / cm, rectangular made of mica material. For such a size of a sensitive element, the device is able to register about 500 imp / μR, if measured by cobalt - 60. The efficiency of particle detection is up to 80 percent. Other indicators of this device are as follows: intrinsic noise is 2.2 pulses / s, the range of energy determination is from 0.05 to 3 MeV, while the lower threshold for determining soft beta radiation is 0.1 MeV.

Fig. 9. End-face beta-gamma counter Beta-5.

AND naturally worth mentioning geiger - Muller counterscapable of registering alpha particles. If registration of soft beta radiation seems to be a rather difficult task, then fixing an alpha particle, even with high energy parameters, is an even more difficult task. Such a problem can be solved only by a corresponding decrease in the thickness of the working window to a thickness that will be sufficient for the passage of an alpha particle into the registration chamber of the sensor, as well as by an almost complete approach of the input window to the source of radiation of alpha particles. This distance should be 1 mm. It is clear that such a device will automatically register any other types of radiation, and, moreover, with enough high efficiency... This has both a positive and a negative side:

Positive - such a device can be used for the widest range of analysis of radioactive radiation

Negative - due to the increased sensitivity, a significant amount of noise will appear, which will complicate the analysis of the obtained registration data.

TO in addition, a too thin mica working window, although it increases the capabilities of the counter, however, at the expense of the mechanical strength and tightness of the ionization chamber, especially since the window itself has sufficient large area working surface. For comparison, in the SBT10 and SI8B counters, which we mentioned above, with a working window area of \u200b\u200babout 30 sq / cm, the thickness of the mica layer is 13-17 microns, and with the required thickness for registering alpha particles of 4-5 microns, the input the window can be made only no more than 0.2 sq / cm., we are talking about the SBT9 counter.

ABOUT however, the large thickness of the registration working window can be compensated for by the proximity to the radioactive object, and vice versa, with a relatively small thickness of the mica window, it becomes possible to register an alpha particle at a greater distance than 1–2 mm. It is worth giving an example, with a window thickness of up to 15 microns, the approach to the source of alpha radiation should be less than 2 mm, while the source of alpha particles is understood as a plutonium-239 emitter with a radiation energy of 5 MeV. Let us continue, with the entrance window thickness up to 10 microns, it is possible to register alpha particles at a distance of up to 13 mm, if we make a mica window up to 5 microns thick, then alpha radiation will be recorded at a distance of 24 mm, etc. Another important parameter that directly affects the ability to detect alpha particles is their energy index. If the energy of an alpha particle is greater than 5 MeV, then the distance of its registration for the thickness of the working window of any type will correspondingly increase, and if the energy is less, then the distance must also be reduced, up to the complete impossibility of registering soft alpha radiation.

E another important point to increase the sensitivity of the alpha counter is to reduce the registration ability for gamma radiation. To do this, it is enough to minimize the geometric dimensions of the cathode, and gamma photons will pass through the registration chamber without causing ionization. This measure makes it possible to reduce the effect on the ionization of gamma quanta by a factor of thousands, and even tens of thousands of times. It is no longer possible to eliminate the influence of beta radiation on the registration camera, but there is a fairly simple way out of this situation. First, alpha and beta radiation of the total type is recorded, then a thick paper filter is installed, and a second measurement is made, which will register only beta particles. The value of alpha radiation in this case is calculated as the difference between the total radiation and a separate indicator of the calculation of beta radiation.

For example , it is worth offering the characteristics of a modern Beta-1 counter, which allows registering alpha, beta, gamma radiation. These indicators are:

the area of \u200b\u200bthe working area of \u200b\u200bthe sensitive element is 7 sq / cm;
the thickness of the mica layer is 12 microns, (the distance of effective detection of alpha particles for plutonium is 239, about 9 mm, for cobalt - 60, the radiation sensitivity is reached about 144 imp / μR);
radiation measurement efficiency for alpha particles - 20% (for plutonium - 239), beta particles - 45% (for thallium -204), and gamma quanta - 60% (for strontium composition - 90, yttrium - 90);
the intrinsic background of the dosimeter is about 0.6 pulses / s;
the sensor is designed to register gamma radiation with an energy in the range from 0.05 MeV to 3 MeV, and beta particles with an energy of more than 0.1 MeV at the lower boundary, and alpha particles with an energy of 5 MeV or more.

Fig. 10. End alpha-beta-gamma counter Beta-1.

TO of course, there are still enough wide range counters that are designed for a narrower and professional use... Such devices have a number of additional settings and options (electrical, mechanical, radiometric, climatic, etc.), which include many special terms and capabilities. However, we will not focus on them. Indeed, to understand the basic principles of action geiger - Muller counters , the models described above are quite enough.

IN it is also worth mentioning that there are special subclasses geiger counters which are specially designed to determine different types other radiation. For example, to determine the value ultraviolet radiation, for registration and determination of slow neutrons, which function according to the corona discharge principle, and other options that are not directly related to this topic and will not be considered.

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 the spiral wire electrode, the other electrode is the body of the device.

An additional electronic circuit provides the counter with power supply (as a rule, at least 300), provides, if necessary, discharge extinguishing and counts the number of discharges through the counter.

Geiger counters are divided into non-self-extinguishing and self-extinguishing (not requiring an external circuit for terminating the discharge).

The meter's sensitivity 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 according to historical reasons there was a mismatch between the Russian and english versions of this and subsequent terms:

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

geiger-Muller counter - Geigerio ir Miulerio skaitiklis statusas T sritis fizika atitikmenys: angl. Geiger Müller counter; Geiger Müller counter tube vok. Geiger Müller Zählrohr, n; GM Zählrohr, n rus. Geiger Müller counter, m pranc. compteur de Geiger Müller, m; tube… Fizikos terminų žodynas

discharge Geiger-Muller counter - - Topics Oil and Gas EN electronic pulse height analyzer ... Technical translator's guide

- ... Wikipedia

- (Geiger Müller counter), a gas-discharge detector that is triggered when a charge passes through its volume. h c. The magnitude of the signal (current impulse) does not depend on the energy hc (the device operates in the self-discharge mode). G. s. invented in 1908 by German ... ... Physical encyclopedia

Gas-discharge device for detecting ionizing radiation (a - and b particles, g quanta, light and X-ray quanta, particles of cosmic radiation, etc.). The Geiger-Muller counter is a hermetically sealed glass tube ... Encyclopedia of technology

Geiger counter - Geiger counter GEIGER COUNTER, gas-discharge particle detector. It fires when a particle or g quantum enters its volume. Invented in 1908 by the German physicist H. Geiger and improved by him jointly with the German physicist W. Müller. Geiger ... ... Illustrated Encyclopedic Dictionary

GEYGER COUNTER, gas-discharge particle detector. It fires when a particle or g quantum enters its volume. Invented in 1908 by the German physicist H. Geiger and improved by him jointly with the German physicist W. Müller. Geiger counter apply ... ... Modern encyclopedia

Gas-discharge device for detecting and studying various kinds of radioactive and other ionizing radiation: α and β particles, γ quanta, light and X-ray quanta, high-energy particles in cosmic rays (See Cosmic rays) and ... Great Soviet Encyclopedia

- [by his name. physicists H. Geiger (N. Geiger; 1882 1945) and W. Muller (W. Muller; 1905 79)] gas-discharge detector of radioactive and other ionizing radiation (a and beta particles, quanta, light and x-ray quanta, cosmic particles. radiation ... ... Big Encyclopedic Polytechnic Dictionary

Counter is a device for counting something. Counter (electronics) a device for counting the number of events following each other (eg pulses) by means of continuous summation, or to determine the degree of accumulation which ... ... Wikipedia

Geiger counter - a gas-discharge device for counting the number of ionizing particles passing through it. It is a gas-filled condenser that breaks through when an ionizing particle appears in the gas volume. Geiger counters are quite popular detectors (sensors) of ionizing radiation. Until now, invented at the very beginning of our century for the needs of the nascent nuclear physics, there is, oddly enough, no complete replacement.

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

Usually counters perceive radiation with their entire surface, but there are also those for which a special "window" is provided 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 relative simplicity and low cost of the installation.

Geiger counter connection 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 comes from outside. Primary electrons, accelerating in electric field, ionize "on the way" other molecules of the gaseous medium, generating more and more electrons and ions. Evolving 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 meter, a discharge occurs that is visible (if the balloon is transparent) even with the naked eye.

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

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

Geiger counters are capable of detecting a wide 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 sufficiently thin; for this, mica with a thickness of 3 ... 10 microns is usually used. The balloon of the counter, which 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 counter is made of quartz glass.

Dependence of the count rate on the supply voltage in a Geiger counter

Boron is introduced into the neutron counter, interacting with which the neutron flux is converted into easily detectable a-particles. Photonic radiation - ultraviolet, X-ray, g-radiation - Geiger counters perceive indirectly - through the photoelectric effect, Compton effect, the effect of pairing; in each case, the radiation interacting with the cathode substance is converted into an electron flow.

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

The dependence of the count rate on the degree of radiation exposure of the counter is its main characteristic. The graph of this dependence has an almost linear character and therefore, the radiation sensitivity of the counter is often shown through imp / μR (pulses per microroentgen; this dimension follows from the ratio of the count rate - imp / 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 using another of its also extremely important parameters - its own background. This is the name of the counting rate, the factor of which is two components: external - natural radiation background, and internal - radiation of radionuclides trapped in the very design of the counter, as well as spontaneous electron emission from its cathode.

Dependence of the count rate on the energy of gamma quanta ("move with stiffness") in a Geiger counter

Another essential characteristic of a Geiger counter is the dependence of its radiation sensitivity on the energy ("hardness") of ionizing particles. To what extent this dependence is significant, the graph in the figure shows. "Stroke with stiffness" will obviously affect the accuracy of the measurements.

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

The table provides information on self-extinguishing halogen Geiger counters of domestic production, 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 \u200b\u200blow dependence of the count rate on the supply voltage, V;
3 - counter's own background, imp / s, no more;
4 - radiation sensitivity of the counter, imp / 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.

It has long been not a problem to buy a device with the code name "household dosimeter" (there would have been money - in this sense, Fukushima would screw up radiophobes and radiophiles (TM)), but I think that it would be interesting to make this device with our own hands.

The heart of our device will be a Geiger counter. We know, of course, that this detector has a bunch of shortcomings and, in general, "the device must be scintillation", but the scintillation radiometer is much more complicated and I have the following post conceived for it. Moreover, the Geiger-Muller counter has a number of undeniable advantages.

So, let's begin.

Detector

So, the Geiger-Muller counter. (Fig. 1) The simplest device, consisting of two electrodes placed in a gaseous medium at low pressure - a cathode with a large area, and an anode in the form of a more or less thin wire, which creates a local field of high intensity. in which the process of ion multiplication develops, due to which a single ion pair can cause a powerful ionization avalanche and ignition of a self-sustained discharge.

Figure: 1. Geiger-Muller counter. 1 - anode, 2 - cathode, 3 - balloon, 4 - cathode outlet, 5, 6 - springs that pull the cathode thread.

In fact, the counter works like a thyratron with a cold cathode, only the discharge in it is ignited by ionization caused not by a pulse from the grid, but by a charged particle flying through the gas. After the discharge has ignited, it must be extinguished either by removing the voltage from the anode, or ... Or it will go out by itself. But for this, something must be introduced into the gas environment of the counter, which, under the action of the discharge, will change into a form that will make the gas opaque to ultraviolet radiation and because of this, one of the factors for maintaining a self-sustained discharge, photoelectron emission, will disappear. There are two such additives: alcohol and halogens (chlorine, bromine and iodine). The first in the discharge decomposes, turning, roughly speaking, into soot, and then does not turn back into alcohol, and after a few tens of thousands of pulses, the counter will end. And halogens turn from molecular to atomic, and the process is reversible. They also end up - due to the fact that atomic halogens easily react with anything, including the walls of the counter, but more often they have time to recombine with each other, so halogen counters are much more durable, withstanding billions of pulses. We are primarily interested in halogen meters, because:

A) they are more durable,
b) they work at 400-500 V, and not at one and a half thousand, like alcohol,
c) they are simply the most common.
In Table 1, I have listed several common Geiger counters and their main parameters.

Table 1.
Basic parameters of some Geiger-Müller counters.

Notes: 1 - sensitivity to alpha radiation is not regulated; 2 - small-scale counter, data on it are scarce.

Sensitivity

When choosing a Geiger counter for our dosimeter, you must first of all look at its sensitivity. After all, you hardly want a device that will show something only where Kuzkina's mother exploded a couple of hours ago. And, meanwhile, there are plenty of such meters, and for their almost complete uselessness for the average person, they are very cheap. These are all kinds of SI-3BG, SI-13G and other "doomsday counters" that are used in army dosimeters to work at the upper limit of measurements. The more sensitive the counter, the more pulses per second it will give at the same radiation level. The classic counter SBM-20 (aka STS-5 of earlier releases), which was traditionally installed in all perestroika-post-Chernobyl "rattles", gives about 18 pulses per minute with a natural background of 12 μR / h. It is convenient to dance from this figure, counting the sensitivity of the counter in "SBM-20".

What does the counter sensitivity give us? Accuracy and speed of response. The fact is that particles of radioactive radiation arrive at us not on schedule, but as necessary, and the counter will miss some of them, but from some will work (from gamma radiation photons - from about one out of several hundred). So impulses from a Geiger counter (and from any counting radiation detector) go at absolutely random times with unpredictable intervals between them. And counting the number of impulses in one minute, another, a third - we get different meanings... And the standard deviation of these values, that is, the error in determining the count rate, will be proportional to square root from the number of registered impulses. The more impulses there are, the less will be the relative (in percentage of the measured value) their counting error:.
When we have a detector - the aforementioned "reference" SBM-20, and the counting time is 40 seconds (this was done in simple household dosimeters, directly showing the number of counted pulses as the dose rate level in μR / h), against a natural background the number of pulses is ~ 10 pieces. This means that the standard deviation is about three. And the error at 95% confidence level is twice as large, that is, 6 pulses. Thus, we have a sad picture: the readings of a dosimeter of 10 μR / h mean that the dose rate is somewhere from 4 to 16 μR / h. And we will be able to talk about the detection of an anomaly only when the dosimeter shows a deviation of three sigma, that is, more than 20 μR / h ...

To increase the accuracy, you can increase the counting time. If we make it for three minutes, that is, four times more, we will quadruple the number of impulses, which means we will double the accuracy. But then we will lose the response of the device to short bursts of radiation, for example, to the "Your Excellency" who passed by you after scintigraphy or radioiodine therapy, or vice versa, when you pass the clock with SPD at the radio market. And by taking a fourfold more sensitive detector (4 parallel-connected SBM-20, one SBM-19, SBT-10 or SI-8B) and leaving the same measurement time, we will increase the accuracy and maintain the reaction speed.

Alpha, beta, gamma and meter design

Alpha radiation is trapped by a piece of paper. Beta radiation can be shielded by a Plexiglas sheet. And from hard gamma radiation, you need to build a wall of lead bricks. Perhaps everyone knows this. And all this is directly related to Geiger counters: in order for him to feel the radiation, it must at least penetrate inside. And it should not fly right through like a neutrino through the Earth.

The SBM-20 counter (and its older brother SBM-19 and the younger SBM-10 and SBM-21) have a metal case, in which there are no special entrance windows. It follows from this that there is no question of any sensitivity to alpha radiation. He feels beta rays quite well, but only if they are hard enough to penetrate inside. This is somewhere from 300 keV. But he feels gamma radiation, starting from a couple of tens of keV.

And the counters SBT-10 and SI-8B (as well as newfangled and inaccessible because of the scrap prices Beta-1, 2 and 5), instead of a solid steel shell, have an extensive window made of fine mica. Beta particles with energies in excess of 100-150 keV can penetrate through this window, which makes it possible to see carbon-14 pollution, which is completely invisible to steel meters. Also, the mica window allows the counter to sense alpha particles. True, in relation to the latter, one must look at the thickness of the mica of specific counters. So, SBT-10 with its thick mica practically does not see it, and in Beta-1 and 2, the mica is thinner, which gives the detection efficiency of alpha particles of plutonium-239 about 20%. SI-8B is somewhere in between.

And now with regard to the span through and through. The fact is that alpha and beta particles, a Geiger counter registers almost everything that could get inside. But with gamma quanta everything is sad. For a gamma quantum to cause a pulse in the counter, it must knock out an electron from its wall. This electron must overcome the thickness of the metal from the point where the interaction took place to the inner surface, and therefore the "working volume" of the detector, where it interacts with photons of gamma radiation, is the thinnest, several microns, layer of metal. Hence it is clear that the efficiency of the counter for gamma radiation is very low - a hundred or more times less than for beta radiation.

Food

The Geiger counter requires a high voltage power supply to operate. Typical halogen devices of Soviet-Russian production require a voltage of about 400 V, many Western meters are designed for 500 or 900 V. Some meters require a voltage of up to one and a half kilovolts - these are old counters with alcohol quenching, such as MS and VS, X-ray counters for X-ray structural analysis, neutron ... We will not be very interested in them. The power is supplied to the meter through a ballast resistance of several megohms - it limits the current pulse and reduces the voltage on the meter after the pulse has passed, making it easier to damp. The value of this resistance is given in the reference data for a specific device - its too small value shortens the life of the detector, and too large - increases the dead time. Usually it can be taken about 5 megohms.

When the voltage increases from zero, the Geiger counter first works like an ordinary ionization chamber, and then, like a proportional counter: each of the pairs of ions that are formed during the flight of a particle generates a small ion, increasing the ion current hundreds and thousands of times. At the same time, very weak pulses, measured in millivolts, can already be detected at the load resistance in the meter circuit. With increasing voltage, avalanches become more and more, and at some point the strongest of them begin to support themselves, igniting an independent discharge. At this moment, instead of weak, millivolt pulses from avalanches passing through the interelectrode space and disappearing at the electrodes, giant pulses appear with an amplitude of several tens of volts! And their frequency grows rapidly with increasing voltage until the discharge burst begins to cause every avalanche Obviously, with a further increase in voltage, the counting rate should stop increasing. And so it happens: the dependence of sensitivity on voltage is observed plateau.

Nevertheless, an increase in voltage does not leave the counting rate unchanged: a discharge can arise just like that, from spontaneous emission. And with increasing voltage, the probability of such a discharge only increases. Therefore, the plateau turns out to be oblique, and starting from a certain voltage, the counting rate begins to grow rapidly, and then the discharge turns into a continuous one. In this mode, of course, the counter not only fails to fulfill its function, but also quickly fails.

Figure: 2. Dependence of the counting rate of the Geiger counter on the supply voltage.

The presence of the plateau greatly facilitates the power supply of the Geiger counter - it does not require highly stable high voltage sources, which are required for scintillation counters. The length of this plateau for low-voltage meters is 80-100 V. In many Soviet household dosimeters of cooperative origin and in almost all amateur constructions of that time, the meter was powered from a voltage converter based on a blocking generator without any hint of stabilization. The calculation was as follows: with a fresh battery, the voltage at the anode of the meter corresponded to the upper limit of the plateau, so that the lower limit of the plateau, the high voltage reached already with a fairly discharged battery.

Background and dead time

Any detector of any radiation always has some dark signal recorded when no radiation is incident on the detector. The Geiger-Muller counter is no exception. One of the sources of the dark background is the aforementioned spontaneous emission. The second is the radioactivity of the counter itself, which is especially important for counters with a mica window, since natural mica inevitably contains impurities of uranium and thorium. And if the latter practically does not depend on anything and is a constant for a given sample of the detector, then the background from spontaneous emission depends on the magnitude of the high voltage, temperature, "age" of the counter. Because of this, it becomes a bad idea to feed the counter with an unregulated voltage, which we will use mainly when measuring low radiation levels: the counter's own background depends on the supply voltage very significantly.

The count rate from its own background at Geiger counters reaches a level corresponding to 3-10 μR / h, that is, it makes up a noticeable fraction of the count rate under normal radiation conditions. The background is especially high for mica sensors - SBT-10, SI-8B, Beta. So it must be subtracted from the measurement results. But for this you need to know him. The reference book will not help here: only the maximum values \u200b\u200bare given there. To measure your own background, you need a lead "house" with a thickness of at least 5 cm, while inner surface you need to cover with sheets of copper 2-3 mm thick and 5 mm plexiglass. The fact is that the "house" will be under fire from cosmic rays, which make the house itself a source of X-ray radiation, mainly in the characteristic lines of lead. And if you make a protection only from lead, this fluorescent "glow" and "see" the counter - instead of complete "darkness". And plexiglass is needed from electrons knocked out of lead and copper by the same space, the energy of which is also sufficient for detection by a Geiger counter.

When measuring the background, it should be borne in mind that the lead "house" does not have any obstacle for cosmic muons. Their flow is ~ 0.015. For example, 0.12 or 7.2 will pass through the SBM-20 counter with an effective area of \u200b\u200b~ 8. Due to the high energy, the efficiency of registration of cosmic muons by almost any Geiger counter can be taken as 100%, and this value should be subtracted from the dark background.

If the intrinsic background is a source of errors at low levels, then dead time affects at high levels of radiation. The essence of the phenomenon lies in the fact that immediately after the pulse, the counter capacitance has not yet been charged to the initial voltage through the load resistance. In addition, the discharge in the meter only went out - but the quenching additive has not yet had time to return to its original state. Therefore, a counter for 150-200 μs develops a state when it becomes insensitive to the next particle, after which it gradually restores sensitivity. (fig. 3)

Figure: 3. Dead time of the Geiger counter

Dead time correction is found by the formula:

where m and n are the measured and corrected count rates, respectively, and is the dead time.

At very high levels of radiation, many Geiger counters (it also depends on the rest of the circuit) has an unpleasant and dangerous effect: constant ionization prevents the formation of individual pulses. The counter starts to "burn" continuously with a constant discharge and the counting rate drops sharply to a very small value. Instead of going off scale, the dosimeter shows some moderately high, or even almost normal numbers. In the meantime, tens and hundreds of roentgens per hour are shining around and you should run, but you are reassured by the readings of the dosimeter. That is why, in addition to the main sensitive one, army dosimeters almost always have a “doomsday” counter, very insensitive, but capable of digesting thousands of R / h.

From counting rate to dose. Rigidity move and other bad things

Generally speaking, a Geiger counter does not measure dose rate. We get only the counting rate - how many pulses per minute or second the counter gave. To the dose - the energy absorbed in one kilogram of the human body (or something else), this has a very distant relationship. First of all - in connection with the principle of operation: the Geiger counter absolutely does not care about the nature of the particle and its energy. Impulses from photons of any energy, beta particles, muons, positrons, protons - will be the same. But the effectiveness of registration is different.

As I said, the Geiger counter detects beta radiation with an efficiency of tens of percent. And gamma-gamma quanta are only fractions of a percent. And all this resembles the addition of meters with kilograms, and even with arbitrary coefficients. In addition, the counter's sensitivity to gamma radiation is not the same at different energies (Fig. 4). Dose sensitivity to radiation of different energies can differ by almost an order of magnitude. The nature of this phenomenon is clear: low-energy gamma radiation has a much greater chance of being absorbed by a thin layer of matter, therefore, the lower the energy, the higher the efficiency (until absorption in the walls of the counter begins to affect). In the high-energy region, on the contrary: with increasing energy, the detection efficiency increases, which is a rather unusual phenomenon among ionizing radiation detectors.

Figure: 4. Energy dependence of the dose sensitivity of a Geiger-Muller counter (left) and the result of its compensation using a filter.

Fortunately, at high energies (above 0.5-1 MeV), the Geiger counter's efficiency for gamma radiation is almost proportional to the energy. This means that the energy dependence of the dose sensitivity is not high there. A hump at low energies can be easily removed using a lead filter with a thickness of about 0.5 mm. The filter thickness is selected in such a way that at the energy corresponding to the maximum sensitivity of the detector (this is 50-100 keV, depending on the thickness of the entrance window of the detector), the absorption factor would be the magnitude of this peak. The higher the energy, the lower the absorption in lead, and at 500-1000 keV, where the detector's sensitivity levels itself off, it is almost imperceptible.

A more accurate correction can be achieved using a multi-layer filter made of different metals, which must be matched to a specific meter.

Such a filter reduces the "stroke with stiffness" to 15-20% in the entire range of 50-3000 keV and turns the display meter (well, a search radiometer-indicator) into a dosimeter.

This filter is usually removable because it renders the sensor insensitive to alpha and beta radiation.

***

In general, this is all that a designer of devices based on it needs to know about the Geiger-Muller counter. As you can see, the device is really simple, although there are a number of subtleties. In the next series, we will design something useful on its basis.

Regardless of whether we wish it or not, the term "radiation" has been wedged into our consciousness and being for a long time, 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 radiation, and without special equipment it is almost impossible to detect it.

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. 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 had not received proper attention. And this despite the fact that they burned x-rays even the famous Nikola Tesla, as well as the working staff in Edison's laboratory. The deterioration in health was explained by everything they could, but not by radiation.

Later, at the beginning of the 20th century, an article appeared on the harmful effects of radiation on experimental animals. This also passed unnoticed until one sensational incident, in which the "radium girls" - the workers of the factory that produced the 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. This set a precedent for the rights of some workers who received occupational diseases and sued their employers.

The history of the Geiger-Muller counter

German physicist Hans Geiger, who worked in one of Rutherford's laboratories, in 1908 developed and proposed schematic diagram actions of the counter of "charged particles". 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 used by Pierre Curie when he was studying the electrical properties of gases. Geiger came up with the idea of \u200b\u200busing it to detect ionizing radiation precisely because this radiation had a direct effect on the level of ionization of gases.

In the late 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 investigate radioactive materials. Geiger and Müller had to purposefully work on the creation of such 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 detectors. 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 devices, they are still used by practicing 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 become familiar with ionizing radiation as such. It can include everything that causes the ionization of substances in a natural state. This will require the presence of some kind of energy. In particular, ultraviolet light or radio waves are not counted as ionizing radiation. The delineation can begin with the so-called "hard ultraviolet", also called "soft X-ray". This type of flux is called photon radiation. The high energy photon stream is gamma quanta.

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

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

Later, neutrons were discovered. So, it turned out that alpha particles can be easily retained even with ordinary paper, beta particles have a slightly higher penetrating power, and gamma rays are the highest. The most dangerous are neutrons, 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 molecules in matter.

However, when hitting atomic nuclei with a 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 entire completeness of ionizing radiation.

Geiger-Muller counter devices and principles of operation

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

Cons from DC voltage sources are connected to the cathodes, and to the anodes - using a large constant resistance - pluses from sources with constant voltage... 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. Typically, it can go up to several hundred volts.

During the flight of ionizing particles through the tubes, atoms in an inert gas that are already in a high-intensity electric field collide with these particles. The energy that was given off by the particles during the collision is considerable, it is enough to detach electrons from the gas atoms. 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 hit the Geiger-Muller counter, the resistance of the tube dropped by the incipient current, and at the same time the voltage at the central mark of the separator changes, which was mentioned earlier. After that, the resistance in the tube, as a result of its growth, resumes, and the voltage level again returns to its previous state. As a result, negative voltage pulses are produced. By counting the pulses, you can set the number of particles that flew. 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-Müller counters have two main varieties: "classic" and flat. Classic meters 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 crumple under any influences. At the ends of the tubes there are glass or plastic hermetic insulators. There are also taps-caps to connect to the circuit. 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 mild β-radiation are manufactured differently. Due to the small ranges of β-particles, they are made flat. Mica windows weakly trap beta radiation. One such counter is the BETA-2 sensor. In all other counters, the determination of their properties is referred to the materials of their manufacture.

All counters that register gamma radiation have cathodes made of metals with a high charge number. Gases are extremely poorly ionized by gamma photons. However, gamma photons can knock out many secondary electrons from the cathodes if properly selected. Most Geiger-Müller beta-particle counters are manufactured 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 good and fast, as a result of which energy is lost.

With alpha particles, things are much worse. For example, despite a rather decent energy, a few MeV, alpha particles have a 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 several centimeters.

To make an objective assessment of the level of ionizing radiation, dosimeters on counters with general application are often supplied with two sequentially functioning meters. One may be more sensitive to α-β radiation and the other to γ \u200b\u200bradiation. 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 simple Geiger counters have practically no sensitivity to it.

How Geiger counters are used in practice

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

After the Chernobyl disaster occurred, household dosimeters, previously completely unfamiliar to the population of our country even by name, began to acquire truly nationwide popularity. Many household models began to appear. All of them use Geiger-Müller counters proper as radiation sensors. Typically, household dosimeters have one or two tubes or end counters.