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Dosimetry

Dosimetry (ionizing radiation) is a section of applied nuclear physics, the subject of research of which is to determine the physical quantities characterizing the effects of ionizing radiation (see Ionizing Radiation) on the environment, and to develop methods and means for measuring these quantities. The range of tasks of dosimetry includes: measuring and calculating doses (see Doses of ionizing radiation) in the fields of radiation sources and in biological objects (tissue dosimetry), measuring the activity of radioactive drugs , etc.

Dosimetry is based on measuring the ionization produced by radiation in air or gas, or on measuring the radiation energy absorbed by the medium.

The negative and positive ions formed during the ionization of the gas medium begin to move in the electric field to the corresponding electrodes, and an electric current arises in the circuit, the value of which is measured by a recording device.

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Methods for measuring the absorbed energy in dense media are based on a number of physical phenomena associated with the passage of radiation through matter. The oldest method for recording ionizing radiation is photographic. This method obtained the first information about a new type of energy. The film can also be used to measure the magnitude of doses, since the degree of blackening of the film is proportional to the absorbed energy. The registration of light flashes (scintillations), which emit atoms and molecules excited by ionizing radiation, is based on a scintillation method. Light flashes are recorded by a photomultiplier tube (see) (PMT), included in the corresponding electronic circuit. The chemical method of dosimetry is to identify irreversible chemical changes that occur under the action of radiation in a substance, most often in aqueous solutions. For these purposes, the reaction of the conversion of bivalent iron to trivalent (in a ferro-sulphate dosimeter) is widely used. Registration of irreversible chemical changes carried out by various physical or chemical methods. Luminescent dosimetry methods are becoming more widespread, because under the action of ionizing radiation in some substances hidden centers of luminescence (luminescence) are formed, which occur during subsequent light (photoluminescence) or thermal (thermoluminescence) effects on irradiated substances. In this case, the luminescence is registered by the PM The use of semiconductors for dosimetry is promising. The most accurate, but technically difficult, method of dosimetry is calorimetric, consisting in the direct measurement of thermal energy into which radiation energy is ultimately converted.

Of particular interest is tissue dosimetry; since direct measurement of absorbed doses in a living organism is impossible, tissue-equivalent phantoms are manufactured (see Dosimetric phantoms) of a human or animal, within which radiation is measured by one of the methods described above.

The determination of the activity of radioactive drugs used to treat tumors, the study of the processes of transfer and metabolism in the body, etc., is done by measuring the number of particles emitted by the preparation per unit of time. This section of dosimetry is called radiometry. See also Dosimetric control, Dosimeters of ionizing radiation, Radioactivity , Counters of nuclear radiation.