BETA RADIATION

From Big Medical Encyclopedia

BETA RADIATION (beta beams) — a flow of the loaded beta particles (electrons or positrons) which are let out at radioactive transformations of kernels.

Beta particles are formed at intranuclear transformations of neutrons or protons (see. Beta decay ). Emission of an electron happens at transformation of one of the neutrons which are a part of a kernel into a proton. At the same time nuclear charge increases by unit, and its mass number does not change. E.g., at disintegration of an atomic nucleus of sverkhtyazhe-ly hydrogen — the hyzone consisting of one proton and two neutrons (nuclear charge is equal +1, mass number — 3), there is a transformation of a neutron into a proton and an electron (see. atomic nucleus ). The new kernel consists of two protons and one neutron and helium-3 is a kernel of isotope (nuclear charge is equal +2, mass number — 3). The electron arising at such transformation takes off from a kernel and is called a beta particle. Emission of a positron, i.e. positively charged electron, happens at transformation of one of the protons which are a part of a kernel into a neutron. Nuclear charge at the same time decreases by unit, and mass number does not change. Energy of beta particles at disintegration can be various.

Passing through substance, B. - and. interacts with atoms of the environment and causes ionization. The ionizing B.'s ability - and. it is possible to characterize quantity steam of ions created on each centimeter of a way of particles in substance. In air under normal conditions B. - and. creates on average several cells of couples of ions on centimeter of a way.

Owing to power losss on ionization of a particle of B. - and. are gradually slowed down in substance. Length of a way in substance before dead stop is called B.'s run - and. Run B. - and. depend on energy of particles and characteristics of atoms of substance of the environment. They change for this reason over a wide range. E.g., B. - and. with energy of 1 Mev gets into water or biological fabric on depth to 4 mm, in organic glass — to 3,5 mm, in aluminum — to 1,5 mm and in lead — to 0,3 mm. At energy 3 Mei run make: in water (fabric) — 1,5 cm, in organic glass — 1,25 cm, in aluminum — 5,3 mm and in lead — 1,3 mm.

Run B. - and. strongly increase with reduction of density of substance. In air B.'s run - and. reach 3,7 m at energy of 1 Mev and 13 m at energy of 3 Mev. Thus, dense materials are more effective in B.'s braking - and. It, however, does not mean that they represent the best protection against B. - and. During the braking of electrons in dense substances it is formed so-called. bremsstrahlung (see), creating additional radiation hazard. Intensity of a bremsstrahlung is proportional to a square of atomic number of an element of the environment and depends on energy of beta particles.

The best substances for protection against B. - and. to big energy serves elements with small atomic numbers. Among them the most suitable material is the aluminum rather light on weight having good constructive properties.

B. - and., consisting of positrons, B. extends in substance in the same way, as well as - and., consisting of electrons, except for some features connected with positive charge of a positron.

The positron has ability to annihilate at interaction with electrons of the environment, forming annihilation radiation (see. Annihilation ). Therefore time of life of a positron is rather short, and its run in substance it is slightly less, than at electrons of identical energy.

Electronic B.'s sources - and. natural radioactive materials serve. Positron B.'s sources - and. serve artificial radioak-tivnye isotopes.

The beta radiating isotopes widely are used at radio isotope research (see), in particular at beta diagnosis (see), and radiation therapy (see). Most often apply isotopes — 14 With, 32 P, 35 S, 89 Sr, 90 Sr, 99 Tc, 141 Ce, 144 Ce, etc.

See also Ionizing radiation , biological effect.


Bibliography: Moiseyev A. A. and Ivanov V. I. Reference book on dosimetry and physics health, M., 1974; Hurst G. S. a. Turner I. E. Elementary radiation physics, N. Y. a. o., 1970.

E. E. Kovalyov.

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