From Big Medical Encyclopedia

X-RAY EMISSION (by name it is mute. physics V. Rentgena ) — the kind of quantum (photon) ionizing radiation, energy of photons to-rogo is usually in range from units kev to tens of Mev.

River and. opened in 1895. X-ray, to-ry called this radiation X-beams. X-ray emission is widely used in medicine for diagnosis (see. Radiodiagnosis ) and radiation therapy (see).

Depending on origins of R. and. distinguish brake and characteristic R. and. Brake R. and. arises at change of a motive energy of charged particles as a result of interaction with atoms of the braking substance. Lengths of waves of brake R. and. do not depend on atomic number of the braking substance, and are defined only by energy of the accelerated electrons. Unlike a continuous spectrum of brake R. and. characteristic R. and. has the line spectrum with lengths of waves which are quite determined for this substance. Lengths of waves and intensity of lines of a characteristic range of R. and. are defined by atomic number of an element Z and electronic structure of atoms. Characteristic R. and. arises at change of a power condition of atoms. If one of electrons of an internal cover of atom is beaten out by an electron or a photon, then atom turns into excited state, and the vacant place is filled with an electron from enveloping layers. At the same time atom turns into the normal state and lets out characteristic R.'s quantum and. with the energy equal to a difference of energy at appropriate levels.

R.'s sources and. the X-ray tubes connected to the feeding device are X-ray apparatus (see), targets, in to-rykh braking of the charged particles accelerated in linear or cyclic accelerators and nek-ry radioactive is carried out isotopes (see), at to-rykh disintegration of a kernel changes in power structure of atom result.

Depending on energy of the accelerated electrons or from energy of quanta or lengths of waves of the generated R. and. distinguish short-wave R. and. with energy of quanta St. 50 kev and long-wave R. and. with energy of quanta lower than 50 kev. River and., 5 — 10 kV generated at a tension on a X-ray tube, call boundary or Bukki's beams.

R.'s interaction and. happens to substance by photo-electric absorption, coherent and incoherent dispersion and formation of electronic and positron couples. At R.'s interaction and. with substance there can be Auger's effect when the excited atom spends energy for a departure of own electron. At the same time from atom photoelectrons and Auger's electrons are released, to-rye at interaction with atoms can create secondary electrons and secondary radiation. Such processes of exchange of energy of photons and electrons happen until their energy does not become less binding energy of electrons in atom.

During the passing of a parallel bunch of R. and. intensity of I 0 through a layer of substance thickness Δх R.'s intensity and. decreases by size ΔI, proportional to initial intensity of I 0 and thickness of a layer of substance Δх:

ΔI = — μI 0 Δх

where μ — the linear extinction coefficient depending on lengths of waves of radiation, properties of the environment through to-ruyu it passes, and showing the relative reduction of intensity on unit of thickness of an absorber caused by processes of interaction with substance.

River and., as well as other types ionizing radiation (see), has biological effect. Biol. the processes happening in molecules, cells and an organism in general under the influence of R. and., are caused ionization (see) and excitement of atoms and molecules (see), the becoming reactive and defiant physical. - chemical changes in cells and intercellular substance.

Use of sources of R. and. demands observance of rules radiation safety (see) and antiactinic protection (see).

Bibliography: Baiza To., Henter L. and Holbok Sh. Rentgenotekhnika, the lane with Wenger., Budapest, 1973; Blochin M. A. Physics of X-ray, M., 1957; X-ray, the lane with it., under the editorship of M. A. Blochin, M., 1960; X-ray diagnostic devices, under the editorship of H. N. Blinova, M., 1976; R at d e r-man A. I. and Weinberg M. Sh. Physical bases remote rent-geno-and gamma therapies, M., 1961; The Reference book on a radiology and radiology, under the editorship of G. A. Zedgenidze, page 549, M., 1972; Shmelyov V. K. X-ray apparatus, M., 1973; Richter K., Ap-gerste of in W. u. Steinhart L. Kontgenbildverstarkerphotographie, Lpz., 1980.

A. H. Krongauz.