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Dosimeters of ionizing radiation

Ionizing radiation dosimeters are devices designed to measure the magnitude of the dose or dose rate of ionizing radiation. Devices that measure the dose rate of ionizing radiation, also called radiometers. Dosimeters of ionizing radiation are based on taking into account the ionization or luminescent properties of radiation (see Dosimetry). The main component of ionization dosimeters of ionizing radiation are the ionization chamber or gas discharge tube with a limited volume of gas or air. In the wall of the chamber or tube, as well as in the center of their electrodes. In the normal state, the molecules and atoms of the gas are electrically neutral, therefore, when a potential difference is applied to the electrodes, the electric current does not pass through the chamber.


Kit for individual dosimetry control: 1 - charging and measuring unit; 2 - individual ionization chambers; 3 - packing box.
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If such a camera is placed in the zone of action of ionizing radiation, then it will ionize the gas with the formation of positively and negatively charged ions, which, after applying a potential difference, will be directed to the electrodes of the opposite sign. The current resulting from the directional movement of ions in the chamber is called ionization and can be measured by a special device - a galvanometer or a microammeter. Under certain conditions, the ionization current is proportional to the number of ions and depends on the magnitude of the radiation dose absorbed in the chamber. In gas-discharge tubes, in contrast to ionization chambers, electrons produced by exposure to radiation acquire greater energy and, in turn, cause the ionization of other molecules and gas atoms. In this regard, the primary ionization of the gas, due to the effects of radiation, is greatly enhanced and, therefore, it is possible to register very small doses of ionizing radiation.

Dosimeters based on the principle of registration of luminescence that occurs during the transition of an atom from an excited state to a non-excited state when irradiated with certain substances (phosphors) are called luminescent or scintillation. Light flashes in phosphors can be registered with special photomultiplier tubes (PMT). Light flashes in them are converted into electrical impulses, which are recorded by counting devices. Dosimeters of ionizing radiation of all types have, in addition to the sensor (ionization chamber, gas discharge tube or phosphor), the power supply, conversion and recording devices. The sensor can be mounted in one unit with transforming and recording devices. Some sensors are small and are intended for insertion into body cavities, for example, into the cavity of the mouth or bladder. Such sensors are sterilized prior to insertion or enclosed in rubber cylinders.

The power supply device is designed to apply a potential difference across the electrodes. Portable ionizing radiation dosimeters have DC power sources in the form of dry cells. Clinical dosimeters of ionizing radiation are included in the electrical network. Before measurements, it is necessary to warm up the instruments well for 20-30 minutes in order to obtain stable measurements. To measure the radiation dose rate of x-ray or gamma devices, it is necessary to install a sensor in the center of the working radiation beam.

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The transforming device converts the primary radiation effect into electrical impulses. The recording device is a pointer device, graded either in units of dose or in units of dose rate, i.e., in X-rays, milli-roentgens, micro X-rays (r / h, r / min, mr / h, md / sec). Dosimeters of ionizing radiation have several measurement ranges, which are installed immediately before the study. The measurements begin to be made from the maximum range and gradually select the range corresponding to this particular case.

For the intended purpose used in medical practice, dosimeters of ionizing radiation can be divided into four groups.
1. Radiometers. They are intended for measuring therapeutic doses of X-ray and gamma radiation (capacitor dosimeter CD and CMM, radiometers RM-1 and dosimeter integral medical DIM).
2. Micro roentgenometers for measuring the dose rate of radiation at workplaces of personnel (MRM-2) and in adjacent rooms (Sputnik, Kristall).
3. Dosimeters for determining the dose of individual exposure of personnel (KID-2 and ID-2). In fig. The most common ionizing radiation dosimeter for individual dosimetry monitoring is presented.
4. Radiometers to determine the level of radioactive contamination of the room and equipment (TISS and BEAM). These devices are not the dosimeters themselves, but their readings make it possible to determine the dose by calculation.

When working with ionizing radiation dosimeters, the following rules should be observed.
1. Protect from shocks, carry only in packing cases, store in a dry place.
2. Start working with ionizing radiation dosimeters only after a preliminary examination of the instruction manual for the device.
3. Be sure to turn off the device after work.
4. Periodically calibrate the dosimeters of ionizing radiation according to standard standards in special testing laboratories and record the results of graduation in the passport of devices.
5. Use dosimeters of ionizing radiation only for its intended purpose - to measure a certain quality of radiation at certain values ​​of the dose or dose rate.