ELECTRONIC RADIATION

From Big Medical Encyclopedia

ELECTRONIC RADIATION — the corpuscular ionizing radiation consisting of a flow of free electrons. In medicine E. and. use for electronic therapy (see), radio isotope diagnosis (see), and also in medicobiological researches, including carried out with the help submicroscopy (see).

Electron (Greek elektron amber) — a stable elementary particle (see. Elementary particles ), opened by J. J. Thomson in 1897. The electron is the easiest of the particles having the mass of rest. Its mass of rest of m = 9,109·10 - 31 kg that corresponds to energy of 0,511 Mev. Elementary charge e = — 1,602·10 - 19 k, spin (s) in terms of Planck is equal to 1/2 or 1/2 · (h/2π) where to h — constant Planck, equal 6,626·10 - 34 J · sec. Magnetic moment of an electron μe = (e · h) / (4πmc) = 9,274·10 - 24 J · T - 1 , where with — velocity of light.

Electrons are a part of atoms (see. Atom ) and molecules (see. Molecule ), neutralizing positive charge of kernels and forming the electron shells located around them. The structure of electron shells of atom and quantum-mechanical features of the movement of atomic electrons define optical, electric, magnetic, chemical and mechanical characteristics of substance. Sources of free electrons in the nature are space radiation (see), disintegration of nek-ry elementary particles, beta decay (see). Free electrons can be let out also at excitement of atoms of the environment by leading of energy of various nature, e.g. heating (thermionic issue), radiation of the environment by electrons, ions (see) or photons (electronic, ionic and photoelectronic issue, formation of couples of ions).

AA. and., organized in electron beams, receive on particle accelerators (see) various type. The greatest distribution in researches E. and. a wide range of energy (from several megaelectron-volt to ~ 20 Gev) linear accelerators received.

Passing through substance of the environment, electrons interact with its atoms. Refer elastic dispersion and braking in the Coulomb field of a kernel to such processes of interaction, a cut conducts to so-called. to a bremsstrahlung (see); inelastic dispersion on electrons of atoms of the environment and excitement of these atoms (see. Molecule , excited states of molecules); nuclear reactions (see). Elastic dispersion does not change energy primary E. and., however plays an important role in expansion of cross sectional dimensions of an electron beam in process of passing it in Wednesday. The basic processes leading to power loss E. and., inelastic dispersion and excitement of atoms of substance of the environment, and also braking of electrons in the field of atomic nuclei of substance of the environment are. In the field of values of energy E. and. from 0, 1 to ~ 1, 5 Mev ionization losses (in g/cm 2 ) per unit length ways are proportional to the electron density of the environment and are inversely proportional to a square of speed of particles. Linear power transmission (see), that is the mean energy absorbed by the environment in the place of passing of charged particle, referred to unit of its way during the braking of an electron in the field of an atomic nucleus of the environment is proportional to N* Z 2 * T, where T — a motive energy of electronic radiation, Z — effective atomic number of the environment, n — number of atoms in 1 cm 3 Wednesdays.

Energy, at a cut ionization power losss of an electron are equal radiation (power losss on radiation during the braking), is called critical (see. Ionizing radiation). At energy E. and. critical radiation losses give a main type of power loss above. Power losss E. items on ionization and a bremsstrahlung in water (body tissues) make respectively 0, 225 and 0, 0196 kev/micron (T = 10 Mev), 0, 241 and 0, 0475 kev/micron (T = 20 Mev), 0, 264 and 0, 139 kev/micron (T = 50 Mev).

The run of an electron in the environment R (cm) depends on density of the environment r (g/cm 3 ) and energy of an electron (Mev). In the field of energy E. and. from 1,5 to 35 Mev dependence of R on T with a mistake less than ±5% are described by an empirical ratio of PR = 0,51T — 0,26. For a wedge. is more whole important characteristics of spacing of a dose or dosage rate E. and. in the irradiated environment (see the Dozny field) distributions of an absorbed dose in water or biol are. fabrics (see. Izodoza ).

Biol. action E. and. similar to action gamma radiations (see) and a bremsstrahlung of the same energy (see. Ionizing radiation , biological effect).

See also Beta radiation .

Bibliography: Kozlov A. P., etc. Comparison of biological efficiency of electrons of 20 Mev and x-ray emission of 200 kV by training of aberation chromosomes in cells of a tumor of Ehrlich, Radiobiology, t. 14, century 4, page 536, 1974; Experimental nuclear physics, under the editorship of E. Segre, the lane with English, t. 1, page 143, M., 1955; Johns H. E. Cunningham J. R. The physics of radiology, Springfield, 1983; Textbook of radiotherapy, ed. by G. H. Fletcher, Philadelphia, 1980.

A. P. Kozlov.

Яндекс.Метрика