From Big Medical Encyclopedia

ELEMENTARY PARTICLES — primary, further indecomposable particles, from to-rykh as believe, all matter consists. In modern physics the term «elementary particles» is usually used for designation of big group of the most fine particles of matter which are not atoms (see Atom) or atomic kernels (see an atomic nucleus); the exception is an atomic nucleus of hydrogen — a proton.

By 80th 20 century the science knew more than 500 elementary particles, the majority to-rykh is unstable. K E. h belong a proton (p), a neutron (n), an electron (e), a photon (γ), pi mesons (π), muons (μ), heavy leptons (τ + , τ - ), a neutrino of three types — electronic (V e ), muonic (V μ ) and connected with a so-called heavy depton (V τ ), and also «strange» particles (K-mesons and hyperons), various resonances, mesons with the hidden charm, the «fascinated» particles, an upsilon particle (Υ), «beautiful» particles, intermediate vector bosons, etc. There was an independent section of physics — a fieik of elementary particles.

History physicists E. began h since 1897 when by J. J. Thomson the electron (was opened see. Electronic radiation); in 1911 R. Millikan measured the size of his electric charge. The concept «photon» — a light quantum — was entered by Planck (M. Planck) in 1900. The direct experimental evidence of existence of a photon was obtained by R. Millikan (1912 — 1915) and Compton (A. N of Compton, 1922). In the course of studying of an atomic nucleus E. Rutherford opened a proton (see. Proton radiation), and in 1932 Mr. J. Chadwick — a neutron (see. Neutron emission). In 1953 existence of a neutrino was experimentally proved, W. Pauli's cut predicted in 1930

E. divide into three groups h. The first is presented by the only elementary particle — a photon, γ-quantum, or quantum of electromagnetic radiation. The second group is the leptons (grech, leptos small, easy) participating except electromagnetic, also in weak interactions. 6 leptons are known: electron and electronic neutrino, muon and muonic neutrino, heavy τ-lepton and corresponding to a neutrino. A third — a basic group E. make hadrons h (Greek hadros big, strong), to-rye participate in all types of interactions, including and in strong interactions (see below). Particles of two types belong to hadrons: baryons (Greek barys heavy) — particles with half-integer spin and weighing not less than the weight of proton, and mesons (Greek mesos average) — particles with zero or integral spin (see. Electronic paramagnetic resonance). The proton and neutron, hyperons, part of resonances and the «fascinated» particles and nek-ry others E belong to baryons. h. The only stable baryon is the proton, other baryons are unstable (a neutron in a stand-at-ease — an unstable particle, however in the connected state in stable atomic kernels it is stable. Mesons received the name because the mass of the first open mesons — a pi meson and the K-meson — had values, intermediate between the mass of a proton and electron. Later mesons, weight were open to-rykh exceeds the mass of a proton. Hadrons are characterized also by strangeness (S) — zero, positive or negative quantum number. Hadrons with zero strangeness call usual, and with S ≠ 0 — strange. In 1964 G. Zweig and Gell-Mann (M. of Gell-Mann) independently from each other suggested about kvarkovy structure of hadrons. Results of a number of experiments demonstrate that quarks are real material educations in hadrons. Quarks have a number of unusual properties, e.g. fractional electric charge, etc. In a stand-at-ease of quarks did not observe. Believe that all hadrons are formed at the expense of various combinations of quarks.

In the beginning E. h investigated during the studying of radioactive decay (see Radioactivity) and space radiation (see). However since 50th 20 century of a research E. make on particle accelerators h (see), in to-rykh accelerated particles bombard a target or face the particles flying towards. At the same time particles interact among themselves therefore there is their interconversion. Thus the majority E was open. h.

Everyone E. h along with specifics of interactions inherent in it it is described by a set of discrete values of the certain physical quantities expressed by the whole or fractional numbers (quantum numbers). General characteristics of all E. h the weight (m), time of life (t), spin (J) — own moment of number of the movement E are. h, having the quantum nature and not connected with movement of a particle as whole, electric charge (Ω) and magnetic moment (μ). Electric charges studied E. h on absolute value are the whole multiple numbers from elementary charge (e?1,6*10 - 10 к). At known E. h electric charges are equal 0, ±1 and ±2.

In total E. h the corresponding antiparticles, weight and spin have to-rykh are equal to the weight and spin of a particle, and electric charge, magnetic moment and other characteristics are equal on absolute value and are opposite on a sign. E.g., an antiparticle of an electron is the positron — an electron with positive electric charge. AA. h, identical to the antiparticle, the neutron and an antineutron, a neutrino and an antineutrino etc. is called truly neutral, e.g. At interaction of antiparticles with each other there is their annihilation (see).

At hit E. h on material Wednesday they interact with it. Distinguish strong, electromagnetic, weak and gravitational interactions. Strong interaction (is stronger than electromagnetic) arises between E. h, being at distance less than 10 - 15 m (1 Fermi). At distances more than 1,5 Fermi force of interaction between particles is close to zero. Strong interactions between E. provide the exclusive durability of atomic kernels which is the cornerstone of stability of substance in terrestrial conditions h. Idiosyncrasy of strong interaction is its independence of electric charge. To strong interaction hadrons are capable. Strong interactions cause disintegration of short-lived particles (time of life about 10 - 23 — 10 - 24 sec.), to-rye call resonances.

Are subject to electromagnetic interaction all loaded E. h, the photons and neutral particles having magnetic moment (e.g., neutrons). Communication with the electromagnetic field is the cornerstone of electromagnetic interactions. Forces of electromagnetic interaction are about 100 times weaker than forces of strong interaction. The main incidence of electromagnetic interaction — atoms and molecules (see the Molecule). Such interaction defines structure of solids, the nature of chemical processes. It is not limited to distance between E. h, therefore the size of atom approximately in 10 4 times more size of an atomic nucleus.

Weak interactions are the cornerstone of extremely slowly proceeding processes with participation of elementary particles. E.g., the neutrinoes possessing weak interaction can freely penetrate thickness of Earth and the Sun. Weak interactions cause also slow disintegrations so-called quasistable E. h, time of life to-rykh is in limits 10 8 — 10 - 10 sec. The elementary particles which are given rise at strong interaction (during 10 - 23 — 10 - 24 sec.), but breaking up slowly (10 - 10 sec.), call strange.

Gravitational interactions between E. give extremely small effects because of negligibility of mass of particles h. This type of interaction is well studied on the macroobjects having big weight.

Variety E. h with different physical characteristics explains difficulty of their systematization. From all E. h only photons, electrons, a neutrino, protons and their antiparticles actually are stable since possess big time of life. These particles represent end products of spontaneous transformation of other elementary particles. Birth E. can result from the first three types of interactions h. For strongly interacting particles a source of the birth are reactions of strong interaction. Leptons that is the most probable, arise at disintegrations of others E. h or are born couples (a particle + an antiparticle) under the influence of photons.

Flows E. create the ionizing radiation (see) causing ionization of neutral molecules of the environment h. Biol. effect E. connect with education in the irradiated fabrics and liquids of an organism of substances with high chemical activity h. Free radicals (see Radicals free), peroxides treat such substances (see) and others. AA. can have also direct effect on bio-molecules and supermolecular structures h, cause a rupture of intramolecular bonds, a depolymerization of high-molecular compounds, etc. A certain value in the nature of action E. h on an organism can have processes of migration of energy and formation of the metastable connections resulting from long preservation of a condition of excitement in nek-ry macromolecular substrates. In cells activity of fermental systems is suppressed or perverted, the structure of cellular membranes and superficial cellular receptors changes that leads to increase in permeability of membranes and change of the diffusion processes which are followed by the phenomena of a denaturation of proteins, dehydrations of fabrics, disturbance of internal environment of a cell. The Porazhayemost of cells substantially depends on intensity of their mitotic division (see the Mitosis) and a metabolism: with increase in this intensity the radioporazhayemost of fabrics increases (see Radiochuvstvitelnost). On this property of flows E. h — the ionizing radiation — their use for radiation therapy is based (see), especially at treatment of malignant new growths. Penetration loaded E. h to a large extent depends on linear power transmission (see), i.e. on the mean energy absorbed by the environment in the place of passing of the charged particle carried to unit of its way.

The damaging action of a flow E. h especially affects stem cells of the hemopoietic fabric, an epithelium of testicles, a small bowel, skin (see. Radial illness, Beam damages). First of all the systems which are in a radiation time in a condition of an active organogenesis and a differentiation are surprised (see. Critical body).

Biological and therapeutic effect E. depends on their type and a dose of radiation h (see Doses of ionizing radiation). So, e.g., at impact of x-ray emission (see the Roentgenotherapy), gamma radiations (see the Gamma therapy) and proton radiation (see. Proton therapy) on all body of the person in a dose apprx. 100 I am glad temporary change of a hemopoiesis is observed; external impact of neutron emission (see. Neutron emission) leads to education in an organism of various radioactive materials, e.g. radionuclides of sodium, phosphorus, etc. At hit in an organism of the radionuclides which are sources of beta particles (electrons or positrons) or gamma quanta there is a so-called internal radiation of an organism (see Incorporation of radioactive materials). Hyzone (3H) and polonium-210 are especially dangerous in this respect quickly rezorbiruyushchiyesya radionuclides with hypodispersion in an organism, e.g.

The radionuclides which are sources E. h and participating in a metabolism, use in radio isotope diagnosis (see).

Bibliography: Akhiyezer A. I. and Rekalo M. P. Biography of elementary particles, Kiev, 1983, bibliogr.; Bogolyubov N. N. and Shirokov D. V. Quantum fields, M., 1980; Bourne M. Atomic physics, the lane with English, M., 1965; Jones of X. Physics of radiology, the lane with English. M, 1965; Krongauz A. N., Lyapidevsky V. K. and Frolova A. V. Physical fundamentals of clinical dosimetry, M., 1969; Radiation therapy by means of an energetic rays, under the editorship of I. Becker and G. Schubert, lane with it., M., 1964; Tyubiana M., etc. Physical bases of radiation therapy and radiobiology, the lane with fr., M., 1969; Shpolsky E. V. Atomic physics, t. 1, M., 1984; Young Ch. Elementary particles, the lane with English. M, 1963.

R. V. Stavntsky.