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The operating principle of a Geiger counter and modern dosimeters. Geiger counters. Operating principle Ionization radiation detectors Geiger-Müller counter

Structure and operating principle of a Geiger–Müller counter

IN Lately, attention to radiation safety on the part of ordinary citizens in our country is increasingly increasing. And this is connected not only with the tragic events at the Chernobyl nuclear power plant and its further consequences, but also with various types of incidents that periodically happen 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 have saved many people not only their health, but sometimes their lives, and this applies not only to the territories adjacent to the exclusion zone. Therefore, radiation safety issues are relevant anywhere in our country to this day.

IN All household and almost all professional modern 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, this development was improved by another physicist Walter Muller, and it is the principle of this device that is used to this day.

N Some modern dosimeters have four counters at once, which makes it possible to increase the measurement accuracy and sensitivity of the device, as well as 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 determining high-energy alpha particles. To configure 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.

IN In modern dosimeters for household and professional use, 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; the 20th line of sensors has the following dimensions: 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 camera size, the large quantity radioactive elements will fly through it, and the greater sensitivity and accuracy it has. So, for the 20th series of sensors, dimensions are 8-10 times larger than for the 21st, and we will have a difference in sensitivity in approximately the same proportions.

TO The design of a Geiger counter can be schematically described as follows. A sensor consisting of a cylindrical container into which an inert gas (for example, argon, neon, or mixtures thereof) is pumped under minimal pressure to facilitate the occurrence of an electrical discharge between the cathode and anode. The cathode, most often, is the entire metal body 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 configure the counter to detect only gamma rays.

D For domestic use, currently, end sensors are most often used (for example, Beta-1, Beta-2). Such counters are designed in such a way that they are capable of detecting and registering even alpha particles. Such a counter is a flat cylinder with electrodes located inside and an input (working) window made of mica film only 12 microns thick. This design makes it possible to detect (at close range) high-energy alpha particles and low-energy beta particles. In this case, 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 the Beta-1, it can be used to determine, etc.

E If we talk about the principle of operation of the Geiger counter chamber, it can be briefly described as follows. When activated, a high voltage (about 350 - 475 volts) is applied to the cathode and anode through a load resistor, but no discharge occurs 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, like an avalanche, begins to knock out free electrons from the surrounding inert gas and its ionization occurs, which ultimately leads to a discharge between the electrodes. The circuit is closed, and this fact can be registered using the device’s microcircuit, which is the fact of detection of either a gamma quantum or x-ray radiation. Then the camera comes in the initial state, which allows you to detect the next particle.

H To stop the discharge process in the chamber and prepare the chamber for recording the next particle, there are two ways, 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 process of gas ionization. The second method is based on adding another substance to the inert gas, for example, iodine, alcohol and other substances, and 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 the number of discharges in the meter chamber and one can judge the level of radiation in the measured area or from a specific object.

The Geiger counter is the main sensor for measuring radiation. It detects gamma, alpha, beta radiation and x-rays. It has the highest sensitivity compared to other methods of detecting radiation, for example, ionization chambers. This is the main reason for its widespread use. Other sensors for measuring radiation are used very rarely. Almost all radiation monitoring devices are based on Geiger counters. They are mass produced, and there are devices of various levels: from military-grade dosimeters to Chinese consumer goods. Nowadays, purchasing any device for measuring radiation is not a problem.

Not long ago there was no widespread distribution of dosimetric instruments. So, by 1986, during the Chernobyl accident, it turned out that the population simply did not have any radiation monitoring devices, which, by the way, further aggravated the consequences of the disaster. At the same time, despite the spread of amateur radio and technical creativity circles, Geiger counters were not sold in stores, so making homemade dosimeters was impossible.

How Geiger counters work

This is an electric vacuum device with extremely simple principle work. The radioactive radiation sensor is a metal or glass chamber with metallization, filled with a discharged inert gas. An electrode is placed in the center of the chamber. The outer walls of the chamber are connected to the source high voltage(usually 400 volts). The internal electrode is connected to the sensitive amplifier. Ionizing radiation (radiation) is a stream of particles. They literally transfer electrons from the high voltage cathode to the anode filaments. A voltage is simply induced on it, which can already be measured by connecting it to an amplifier.

The high sensitivity of the Geiger counter is due to the avalanche effect. The energy that the amplifier detects at the output is not the energy of the source of ionizing radiation. This is the energy of the high-voltage power supply of the dosimeter itself. The penetrating particle only transfers an electron (an energy charge that turns into a current that is detected by the meter). A gas mixture consisting of noble gases: argon, neon is introduced between the electrodes. It is designed to extinguish high-voltage discharges. If such a discharge occurs, it will be a false operation of the counter. Follow-up measuring circuit ignores such emissions. In addition, the high-voltage power supply must also be protected from them.

The power circuit in a Geiger counter provides an output current of several microamps at an output voltage of 400 volts. The exact value of the supply voltage is established for each brand of meter according to its technical specifications.

Geiger counter capabilities, sensitivity, recorded radiation

Using a Geiger counter, gamma and beta radiation can be detected and measured with high accuracy. Unfortunately, the type of radiation cannot be recognized directly. This is done indirectly by installing barriers between the sensor and the object or terrain being examined. Gamma rays are highly transparent and their background does not change. If the dosimeter has detected beta radiation, then installing a separating barrier, even a thin sheet of metal, will almost completely block the flow of beta particles.

The sets of personal dosimeters DP-22 and DP-24, which were common in the past, did not use Geiger counters. Instead, an ionization chamber sensor was used, so the sensitivity was very low. Modern dosimetric instruments using Geiger counters are thousands of times more sensitive. They can be used to record natural changes in solar background radiation.

A notable feature of the Geiger counter is its sensitivity, tens and hundreds of times higher than the required level. If you turn on the counter in a completely protected lead chamber, it will show a huge natural radiation background. These readings are not a design defect of the meter itself, which has been verified by numerous laboratory tests. Such data are a consequence of the natural radiation background in space. The experiment only shows how sensitive the Geiger counter is.

Especially for measuring this parameter in technical specifications The value of the “sensitivity of the imp microsecond counter” (pulses per microsecond) is indicated. The more of these impulses, the greater the sensitivity.

Radiation measurement with a Geiger counter, dosimeter circuit

The dosimeter circuit can be divided into two functional modules: a high-voltage power supply and a measuring circuit. High voltage power supply - analog circuit. The measuring module on digital dosimeters is always digital. This is a pulse counter that displays the corresponding value in the form of numbers on the instrument scale. To measure the radiation dose, it is necessary to count pulses per minute, 10, 15 seconds or other values. The microcontroller converts the number of pulses into a specific value on the dosimeter scale in standard radiation units. Here are the most common ones:

X-ray (usually micro-X-ray is used);
Sievert (microsievert - mSv);
Gray, I'm glad
flux density in microwatts/m2.

The sievert is the most popular unit of measurement for radiation. All norms are related to it; no additional recalculations are required. The rem is a unit for determining the effect of radiation on biological objects.

Comparison of a gas-discharge Geiger counter with a semiconductor radiation sensor

The Geiger counter is a gas-discharge device, and modern trend microelectronics - getting rid of them everywhere. Dozens of versions of semiconductor radiation sensors have been developed. The level of background radiation they record is significantly higher than for Geiger counters. The sensitivity of a semiconductor sensor is worse, but it has another advantage - efficiency. Semiconductors do not require high voltage power. They are well suited for battery-powered portable dosimeters. Another advantage is the registration of alpha particles. The gas volume of the meter is significantly larger than the semiconductor sensor, but its dimensions are still acceptable even for portable equipment.

Measurement of alpha, beta and gamma radiation

Gamma radiation is the easiest to measure. This is electromagnetic radiation, which is a stream of photons (light is also a stream of photons). Unlike light, it has a much higher frequency and a very short wavelength. This allows it to penetrate through atoms. In civil defense, gamma radiation is penetrating radiation. It penetrates through the walls of houses, cars, various structures and is retained only by a layer of earth or concrete of several meters. Registration of gamma quanta is carried out with the calibration of the dosimeter according to the natural gamma radiation of the sun. No radiation sources required. It's a completely different matter with beta and alpha radiation.

If ionizing radiation α (alpha radiation) comes from external objects, then it is almost harmless and represents a stream of nuclei of Helium atoms. The range and permeability of these particles is small - a few micrometers (maximum millimeters) - depending on the permeability of the medium. Due to this feature, it is almost not registered by a Geiger counter. At the same time, recording alpha radiation is important, since these particles are extremely dangerous when they penetrate the body with air, food, or water. Geiger counters are used to a limited extent for their detection. Special semiconductor sensors are more common.

Beta radiation is perfectly detected by a Geiger counter because a beta particle is an electron. It can fly hundreds of meters in the atmosphere, but is well absorbed by metal surfaces. In this regard, the Geiger counter must have a mica window. The metal chamber is made with a small wall thickness. The composition of the internal gas is selected in such a way as to ensure a small pressure drop. The beta radiation detector is placed on the remote probe. Such dosimeters are not very common in everyday life. These are mainly military products.

Personal dosimeter with Geiger counter

This class of devices is highly sensitive, unlike outdated models with ionization chambers. Reliable models are offered by many domestic manufacturers: Terra, MKS-05, DKR, Radex, RKS. These are all stand-alone devices with data displayed on the screen in standard units of measurement. There is a mode for displaying the accumulated radiation dose and the instantaneous background level.

A promising direction is a household dosimeter-attachment to a smartphone. Such devices are produced foreign manufacturers. They have rich technical capabilities; they have the function of storing readings, calculating, recalculating and summing up radiation over days, weeks, and months. So far, due to low production volumes, the cost of these devices is quite high.

Homemade dosimeters, why are they needed?

The Geiger counter is a specific element of the dosimeter, completely inaccessible to self-made. In addition, it is found only in dosimeters or sold separately in radio stores. If this sensor is available, all other components of the dosimeter can be assembled independently from parts of various consumer electronics: televisions, motherboards, etc. About a dozen designs are now offered on amateur radio sites and forums. It is worth collecting them, since these are the most proven options that have detailed guides for setup and commissioning.

The Geiger counter switching circuit always implies the presence of a high voltage source. Typical operating voltage meter - 400 volts. It is obtained using a blocking generator circuit, and this is the most complex element dosimeter diagrams. The counter output can be connected to a low-frequency amplifier and count the clicks in the speaker. Such a dosimeter is assembled in emergency cases, when there is practically no time for production. Theoretically, the output of a Geiger counter can be connected to the audio input of household equipment, such as a computer.

Homemade dosimeters, suitable for precise measurements, are all assembled on microcontrollers. Programming skills are not needed here, since the program is written ready-made from free access. The difficulties here are typical for home electronic production: obtaining printed circuit board, soldering of radio components, manufacturing of housing. All this is solved in a small workshop. Homemade dosimeters from Geiger counters are made in cases where:

it is not possible to purchase a ready-made dosimeter;
you need a device with special characteristics;
It is necessary to study the process of constructing and setting up a dosimeter.

A homemade dosimeter is calibrated against the natural background using another dosimeter. This completes the construction process.

If you have any questions, leave them in the comments below the article. We or our visitors will be happy to answer them

Whether we like it or not, radiation has firmly entered our lives and is not going to go away. We need to learn to live with this phenomenon, which is both useful and dangerous. Radiation manifests itself as invisible and imperceptible radiations, and without special devices they are impossible to detect.

A little history of radiation

X-rays were discovered in 1895. A year later, the radioactivity of uranium was discovered, also in connection with X-rays. Scientists realized that they were faced with completely new, hitherto unseen natural phenomena. It is interesting that the phenomenon of radiation was noticed several years earlier, but no importance was attached to it, although Nikola Tesla and other workers of the Edison laboratory also received burns from X-rays. Damage to health was attributed to anything, but not to rays, which living things had never encountered in such doses. At the very beginning of the 20th century, articles began to appear about the harmful effects of radiation on animals. This, too, was not given any importance until the sensational story with the “radium girls” - workers of a factory that produced luminous watches. They just wet the brushes with the tip of their tongue. The terrible fate of some of them was not even published, for ethical reasons, and remained a test only for the strong nerves of doctors.

In 1939, physicist Lise Meitner, who, together with Otto Hahn and Fritz Strassmann, belongs to the people who were the first in the world to divide the uranium nucleus, inadvertently blurted out about the possibility of a chain reaction, and from that moment a chain reaction of ideas about creating a bomb began, namely a bomb, and not at all “peaceful atom”, for which the bloodthirsty politicians of the 20th century, of course, would not have given a penny. Those who were “in the know” already knew what this would lead to and the atomic arms race began.

How did the Geiger-Müller counter appear?

The German physicist Hans Geiger, who worked in the laboratory of Ernst Rutherford, in 1908 proposed the principle of operation of a “charged particle” counter as a further development of the already known ionization chamber, which was an electric capacitor filled with gas at low pressure. It was used by Pierre Curie in 1895 to study the electrical properties of gases. Geiger had the idea to use it to detect ionizing radiation precisely because these radiations had a direct effect on the degree of ionization of the gas.

In 1928, Walter Müller, under the leadership of Geiger, created several types of radiation counters designed to register various ionizing particles. The creation of counters was a very urgent need, without which it was impossible to continue the study of radioactive materials, since physics, as an experimental science, is unthinkable without measuring instruments. Geiger and Müller purposefully worked to create counters that were sensitive to each of the types of radiation that had been discovered: α, β and γ (neutrons were discovered only in 1932).

The Geiger-Muller counter proved to be a simple, reliable, cheap and practical radiation detector. Although it is not the most accurate instrument for studying specific types of particles or radiation, it is extremely suitable as an instrument for the general measurement of the intensity of ionizing radiation. And in combination with other detectors, it is used by physicists for precise measurements during experiments.

Ionizing radiation

To better understand the operation of a Geiger-Muller counter, it is useful to have an understanding of ionizing radiation in general. By definition, these include anything that can cause ionization of a substance in its normal state. This requires a certain amount of energy. For example, radio waves or even ultraviolet light are not ionizing radiation. The border begins with “hard ultraviolet”, also known as “soft x-ray”. This type is a photon type of radiation. High-energy photons are usually called gamma quanta.

Ernst Rutherford was the first to divide ionizing radiation into three types. This was done in an experimental setup using a magnetic field in a vacuum. It later turned out that this is:

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

Later neutrons were discovered. Alpha particles are easily blocked even by ordinary paper, beta particles have a slightly greater penetrating power, and gamma rays have the highest penetrating power. Neutrons are the most dangerous (at a distance of up to many tens of meters in the air!). Due to their electrical neutrality, they do not interact with the electron shells of the molecules of the substance. But once in atomic nucleus, the probability of which is quite high, lead to its instability and decay, with the formation, as a rule, of radioactive isotopes. And those, in turn, decaying and themselves form the entire “bouquet” of ionizing radiation. The worst thing is that an irradiated object or living organism itself becomes a source of radiation for many hours and days.

The design of a Geiger-Muller counter and its operating principle

A Geiger-Muller gas-discharge counter is usually made in the form of a sealed tube, glass or metal, from which the air is evacuated, and instead an inert gas (neon or argon or a mixture of both) is added under low pressure, with an admixture of halogens or alcohol. A thin wire is stretched along the axis of the tube, and a metal cylinder is located coaxially with it. Both the tube and the wire are electrodes: the tube is the cathode, and the wire is the anode. The minus from the source is connected to the cathode DC voltage, and to the anode - through a large constant resistance - plus from a constant voltage source. Electrically, a voltage divider is obtained, at the middle point of which (the junction of the resistance and the anode of the meter) the voltage is almost equal to the voltage at the source. This is usually several hundred volts.

When an ionizing particle flies through the tube, the atoms of the inert gas, already in electric field high tension, experience collisions with this particle. The energy given off by the particle during a collision is enough to separate electrons from gas atoms. The resulting secondary electrons are themselves capable of forming new collisions and, thus, a whole avalanche of electrons and ions is obtained. Under the influence electric field, electrons are accelerated towards the anode, and positively charged gas ions are accelerated towards the cathode of the tube. Thus, there arises electricity. But since the energy of the particle has already been spent on collisions, fully or partially (the particle flew through the tube), the supply of ionized gas atoms also ends, which is desirable and is ensured by some additional measures, which we will talk about when analyzing the parameters of the counters.

When a charged particle enters a Geiger-Muller counter, due to the resulting current, the resistance of the tube drops, and with it the voltage at the midpoint of the voltage divider, which was discussed above. Then the resistance of the tube, due to an increase in its resistance, is restored, and the voltage again becomes the same. Thus, we get a negative voltage pulse. By counting the impulses, we can estimate the number of passing particles. The electric field strength is especially high near the anode due to its small size, which makes the counter more sensitive.

Geiger-Muller counter designs

Modern Geiger-Muller counters are available in two main versions: “classic” and flat. The classic counter is made of a thin-walled metal tube with corrugation. The corrugated surface of the meter makes the tube rigid, resistant to external atmospheric pressure and does not allow it to wrinkle under its influence. At the ends of the tube there are sealing insulators made of glass or thermosetting plastic. They also contain terminal caps for connecting to the device circuit. The tube is marked and coated with a durable insulating varnish, not counting, of course, its terminals. The polarity of the terminals is also indicated. This is a universal counter for all types of ionizing radiation, especially beta and gamma.

Counters sensitive to soft β-radiation are made differently. Due to the short range of beta particles, they have to be made flat, with a mica window that weakly blocks beta radiation; one of the options for such a counter is a radiation sensor BETA-2. All other properties of the meters are determined by the materials from which they are made.

Counters designed to record gamma radiation contain a cathode made of metals with a high charge number, or are coated with such metals. Gas is extremely poorly ionized by gamma photons. But gamma photons are capable of knocking out many secondary electrons from the cathode if it is chosen appropriately. Geiger-Muller counters for beta particles are made with thin windows to better transmit the particles, since they are ordinary electrons that have just received more energy. They interact with matter very well and quickly lose this energy.

In the case of alpha particles the situation is even worse. So, despite a very decent energy, on the order of several MeV, alpha particles interact very strongly with molecules in their path and quickly lose energy. If matter is compared to a forest, and an electron is compared to a bullet, then alpha particles will have to be compared to a tank crashing through a forest. However, a conventional counter responds well to α-radiation, but only at a distance of up to several centimeters.

For an objective assessment of the level of ionizing radiation dosimeters General purpose meters are often equipped with two counters operating in parallel. One is more sensitive to α and β radiation, and the second to γ rays. This scheme of using two counters is implemented in a dosimeter RADEX RD1008 and in a dosimeter-radiometer RADEKS MKS-1009, in which the counter is installed BETA-2 And BETA-2M. Sometimes a bar or plate of an alloy containing an admixture of cadmium is placed between the counters. When neutrons hit such a bar, γ-radiation is generated, which is recorded. This is done to be able to detect neutron radiation, to which simple Geiger counters are practically insensitive. Another method is to coat the housing (cathode) with impurities that can impart sensitivity to neutrons.

Halogens (chlorine, bromine) are added to the gas to quickly extinguish the discharge. Alcohol vapor also serves the same purpose, although alcohol in this case is short-lived (this is generally a feature of alcohol) and the “sobered up” meter constantly begins to “ring”, that is, it cannot work in the intended mode. This happens somewhere after 1e9 pulses (a billion) have been detected, which is not that much. Meters with halogens are much more durable.

Parameters and operating modes of Geiger counters

Sensitivity of Geiger counters.

The sensitivity of the counter is estimated by the ratio of the number of microroentgens from the reference source to the number of pulses caused by this radiation. Since Geiger counters are not designed to measure particle energy, accurate estimation is difficult. The counters are calibrated using reference isotope sources. It should be noted that this parameter at different types counters can vary greatly, below are the parameters of the most common Geiger-Müller counters:

Geiger-Muller counter Beta-2- 160 ÷ 240 imp/µR

Geiger-Muller counter Beta-1- 96 ÷ 144 imp/µR

Geiger-Muller counter SBM-20- 60 ÷ 75 imp/µR

Geiger-Muller counter SBM-21- 6.5 ÷ 9.5 imp/µR

Geiger-Muller counter SBM-10- 9.6 ÷ 10.8 imp/µR

Entrance window area or work area

The area of the radiation sensor through which radioactive particles fly. This characteristic is directly related to the dimensions of the sensor. The larger the area, the more particles the Geiger-Muller counter will catch. Typically this parameter is indicated in square centimeters.

Geiger-Muller counter Beta-2- 13.8 cm 2

Geiger-Muller counter Beta-1- 7 cm 2

This voltage corresponds approximately to the middle performance characteristics. The operating characteristic is the flat part of the dependence of the number of recorded pulses on the voltage, which is why it is also called the “plateau”. At this point the highest operating speed is achieved ( upper limit measurements). Typical value is 400 V.

Width of the counter operating characteristic.

This is the difference between the spark breakdown voltage and the output voltage on the flat part of the characteristic. Typical value is 100 V.

Slope of the meter operating characteristic.

The slope is measured as a percentage of pulses per volt. It characterizes the statistical error of measurements (counting the number of pulses). Typical value is 0.15%.

Permissible operating temperature of the meter.

For general purpose meters -50 ... +70 degrees Celsius. This is a very important parameter if the meter operates in chambers, channels, and other places of complex equipment: accelerators, reactors, etc.

Working resource of the counter.

The total number of pulses that the meter registers before its readings begin to become incorrect. For devices with organic additives, self-quenching is usually 1e9 (ten to the ninth power, or one billion). The resource is counted only if operating voltage is applied to the meter. If the counter is simply stored, this resource is not consumed.

Counter dead time.

This is the time (recovery time) during which the counter conducts current after being triggered by a passing particle. The existence of such a time means that there is an upper limit to the pulse frequency and this limits the measurement range. A typical value is 1e-4 s, which is ten microseconds.

It should be noted that due to dead time, the sensor may be “off scale” and remain silent at the most dangerous moment (for example, a spontaneous chain reaction in production). Such cases have happened, and to combat them, lead screens are used to cover part of the sensors of emergency alarm systems.

Custom counter background.

Measured in thick-walled lead chambers to assess the quality of meters. Typical value is 1 ... 2 pulses per minute.

Practical application of Geiger counters

Soviet and now Russian industry produces many types of Geiger-Muller counters. Here are some common brands: STS-6, SBM-20, SI-1G, SI21G, SI22G, SI34G, meters of the Gamma series, end counters of the series Beta"and there are many more. All of them are used for monitoring and measuring radiation: at nuclear industry facilities, in scientific and educational institutions, in civil defense, medicine, and even in everyday life. After the Chernobyl accident, household dosimeters, previously unknown to the population even by name, have become very popular. Many brands of household dosimeters have appeared. All of them use a Geiger-Muller counter as a radiation sensor. In household dosimeters, one to two tubes or end counters are installed.

UNITS OF MEASUREMENT OF RADIATION QUANTITIES

For a long time, the unit of measurement P (roentgen) was common. However, when moving to the SI system, other units appear. An x-ray is a unit of exposure dose, a "quantity of radiation", which is expressed as the number of ions produced in dry air. With a dose of 1 R in 1 cm3 of air, 2.082e9 pairs of ions are formed (which corresponds to 1 unit of charge of the SGSE). In the SI system, exposure dose is expressed in coulombs per kilogram, and with x-rays this is related to the equation:

1 C/kg = 3876 R

The absorbed dose of radiation is measured in joules per kilogram and is called Gray. This is a replacement for the outdated rad unit. The absorbed dose rate is measured in grays per second. Exposure dose rate (EDR), formerly measured in roentgens per second, is now measured in amperes per kilogram. The equivalent radiation dose at which the absorbed dose is 1 Gy (gray) and the radiation quality factor is 1 is called Sievert. The rem (biological equivalent of an x-ray) is a hundredth of a sievert, now considered obsolete. Nevertheless, even today all outdated units are very actively used.

The main concepts in radiation measurements are dose and power. Dose is the number of elementary charges in the process of ionization of a substance, and power is the rate of dose formation per unit time. And in what units this is expressed is a matter of taste and convenience.

Even a minimal dose is dangerous in terms of long-term consequences for the body. Calculating the danger is quite simple. For example, your dosimeter shows 300 milliroentgen per hour. If you stay in this place for a day, you will receive a dose of 24 * 0.3 = 7.2 roentgens. This is dangerous and you need to leave here as soon as possible. In general, if you detect even weak radiation, you need to move away from it and check it even from a distance. If she “follows you”, you can be “congratulated”, you have been hit by neutrons. But not every dosimeter can respond to them.

For radiation sources, a quantity characterizing the number of decays per unit of time is used; it is called activity and is also measured by many different units: curie, becquerel, rutherford and some others. The amount of activity, measured twice with a sufficient separation in time, if it decreases, makes it possible to calculate the time, according to the law of radioactive decay, when the source becomes sufficiently safe.

Geiger counter

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

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

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

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

Note

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

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