How does a personal radiation Dosimeter (meter) work?

Ever since a person began to use the energy contained in an atom, for all mankind, especially in large populated and developed countries, there is a danger ofradiation contamination.

Ever since a person began to use the energy contained in an atom, for all mankind, especially in large populated and developed countries, there is a danger of radiation contamination. And far from examples, there is no need to walk, it is the Chernobyl disaster, the recent incident at the Japanese nuclear power plant Fukushima, and various accidents at enterprises working with radioactive materials, as well as radioactive waste, military tests and so on. In this regard, for ordinary citizens, it becomes necessary to be able to determine the radiation situation by yourself and make the right decision in case of an emergency situation. And here you can very help a special device - a household radiation dosimeter. But for its correct and correct application it is necessary to understand the operating principles of the dosimeter and the measurement procedure.
     In the first household radiation dosimetersappeared only in 1989, they were made by the decision of the National Commission for Radiation Protection, until that time all information on the radiation situation in this or that region was classified. The impetus for such a decision was the events in Chernobyl.
     The first dosimeters were made on the basis of discrete logic chips and an analog interface. Modern radiometers already use microprocessor technologies and use specialized controllers, as well as liquid crystal displays. However, the basis for both is the use of theGeiger counter, Mueller, and what he himself represents is discussed below.
     The Geiger scribe is a sealed chamber made of metal or glass and filled with an inert gas, usually argon or neon, and under low pressure (structure and operating principle). Two electrodes are built into the chamber (anode and cathode). For most domestic dosimeters based on a counter of the SBM-20 type, the cathode is practically the entire casing of the sensitive sensor, and the anode is only a thin wire inside it. And for counters like Beta-1 or Beta-2, a multi-section electrode system and a more complex structure are typical, this allows recording the most diverse types of radiation. For such counters, the thickness of the working window (the area of radiation hit, based on alpha and beta particles) is about 12 μm. Therefore, such end-of-beam dosimeters are able to detect low-energy beta particles, and with properly measured measurements and alpha particles of high energies, this should be measured no more than 1 to 2 mm from the alpha radiation source.
     HTo monitor the dosimeter could detect radioactive particles or gamma-ray quanta, a high voltage of 350 to 475 volts is applied to the electrodes. In the state of rest between the cathode and the anode there is no discharge, since the inert gas serves as a dielectric. However, the situation changes if a radioactive particle enters the chamber, in which case it strikes a free electron from the cathode or the surface of the meter casing, which continues to move and knock electrons out of the gas, causing ionization and an electric discharge between the cathode and the anode. This discharge also fixes the electronics of the device, and also records all radioactive particles that have passed through the working chamber. In the event that it is required to fix and determine alpha particles and beta particles of low energies, then a thin working window from the mica film helps, through it radiation of this type enters the chamber and causes ionization. Read also: how to refine the radiation dosimeter .
     HTo simplify the registration of the radioactive particle passed through the counter, a special load resistor is included in the feeding circuit of the dosimeter, through which changes in the circuit between the cathode and the anode are recorded. In order for ionization in the chamber to cease quickly after discharge, and was ready to fix a new particle, there are two ways to achieve this. The first is based on stopping the voltage supply to the electrodes for a very short period of time, which inhibits further ionization, the second one is based on the addition of alcohol or iodine to the inert gas, as well as a number of other materials. In this case, such an impurity, immediately after discharge, contributes to a sharp decrease in voltage on the cathode and anode, less than 300 volts, which also sharply stops ionization and the counter becomes ready to register the next particle or the radiation quantum.
     The limit of the radiation level is a physical calculation of the microelectronics of the instrument of all radioactive particles passing through the registration chamber, be it beta particles or gamma radiation. Counting such particles for a certain unit of time leads to the result that we can see on the display of the device.
     N ersonalnye dosimeters have the following options radiation calculus, namely Sievert per hour (Sv/h) or roentgens per hour (R/hr). In practice, the data recorded in microroentgen and microSyverts (μR/h, μSv/h) are most often used, since such units of measurement correspond to a normal radiation background. The normal value is the radioactive background value of 0.2 μSv/h or 20 μR/h. Sieverts and X-rays are related to each other by the following ratio: 1 mkSv = 100 mcR.
     To measure beta particles, some modern meters, such as the professional radiometer Dosimeter MKS-05 Terra-p or Dosimeter MKS-05 Terra-pro, determine the beta flux by how many beta particles pass through the window into 1 square centimeter in one minute .
     It should be noted that the accuracy of measurements directly depends on the duration of the measurement, however, a long time for the determination of radioactivity will significantly complicate the use of the device, and in the case of a zone with an increased radiation background, the danger of finding a person doing the measurement. Therefore, many modern household dosimetershave several time modes for conducting radiation measurements. To significantly reduce the time of measurement without loss of accuracy, in some dosimeters several Geiger counters are used, for example, up to 4 pieces. 
     To properly usehome Geiger counter and dosimeter, the above is enough, but we should be interested in the topic, so that a more professional approach in the interpretation of readings and accuracy of the measurements. Although, even a complete lack of understanding of the processes, in case you find the radioactive background significantly above the norm, you should cause alarm in you, with the development of further emergency measures.

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