From Big Medical Encyclopedia

ALPHA RADIATION — the radiation consisting of alpha particles (atomic nuclei of helium). The alpha particle has positive charge, on absolute value twice big elementary charge. The mass of an alpha particle is approximately four times more than the mass of a proton (see).

And. - and. it is formed at disintegration of some radioactive kernels (see. Alpha decay , Radioactivity ). And. - the N has rather big sizes of energy of particles reaching 2 — 10 Mev. The alpha particles which are usually let out by kernels consist of one or several groups characterized by certain values of energy.

Half-lives of the radioactive kernels which are letting out And. - and., change in very wide limits (from million fractions of a second to many billions of years). At the same time such pattern is observed: the more half-life of isotope, the is less energy and run of the alpha particles which are let out by it and vice versa.

And. - and. can also result from transformations of kernels at their interactions among themselves or with elementary particles. Such transformations are called nuclear reactions. Flows of the accelerated alpha particles can be received in the artificial way by means of particle accelerators (see).

And. - and. is a part of galactic space radiation and solar corpuscular radiation.

During the passing through substance of an alpha particle interact with atoms of the environment generally due to electromagnetic interaction with an electron shell of atoms and molecules. At the same time alpha particles lose a part of the energy on excitement of atoms and molecules of the environment and their ionization.

At collision with atomic nuclei of an alpha particle experience the electromagnetic interactions which are generally leading to dispersion of particles and also the nuclear interactions leading to nuclear reactions. The nuclear reactions caused And. - and., lead to education secondary loaded and uncharged particles.

The ratio of processes electromagnetic and nuclear interaction depends on energy And. - and. and characteristics of the environment. In the range of energy of alpha radiation to several tens megaelectron-volt the main mechanism of power losss are electromagnetic interactions with an electron shell of atoms.

The energy lost by an alpha particle in substance on a unit of length of a way reaches the maximum value in the area 1 Mev, and for water this maximum value makes apprx. 2,3 Mev on 10 microns of a way. Such big power losss And. - and. cause the small size of a run in substance. So, run And. - and. with energy of 4 Mev makes in air 2,5 cm, in aluminum — 16 microns and in biological fabric about 31. At increase in energy up to 10 Mev run increase to the following values: in air — 10,6 cm, in aluminum — 69 microns and in biological fabric — about 130 microns. From these data it is visible that the layer of aluminum thickness apprx. 70 microns and biological fabric apprx. 130 microns completely absorbs And. - and. with energy to 10 Mev. Thus, for protection against external flows And. - and., let out by radioactive materials, only thin coats of substance are necessary.

Biological effect And. - and. it is stronger expressed in comparison with standard x-ray emission that is caused by the bigger size of power losss And. - and. per unit length and respectively bigger density of ionization. It leads to considerable sizes of a factor of quality of the radiation used in calculations of radiation protection. So, if for standard x-ray emission the factor of quality is taken for unit, then for the alpha radiation of its value approximately make: at energy of 40 Mev — 4; 20 Mev — 1; 10 Mev — 10; 6 Mev — 13; 2 Mev less — 20. High biological performance And. - and. it has to be considered during the planning of protective measures.

And. - and. widely apply in medicine — see. Alpha therapy , Radon waters .

E. E. Kovalyov.