ISOTOPES

From Big Medical Encyclopedia

ISOTOPES (grech, isos equal, identical + topos the place) — the kinds of one chemical element which are taking the same place in a periodic system of elements of Mendeleyev, i.e. having identical nuclear charge, but differing with the mass of atoms. During the mentioning about And. surely specify what isotope of a chemical element it is. The term «isotope» is used sometimes and in a broader sense — for the description of atoms of various elements. However for designation of any of atoms irrespective of its belonging to this or that element it is accepted to use the term «nuclide».

Accessory And. to a certain element and the main chemical properties are defined by its sequence number Z or number of the protons which are contained in a kernel (respectively and identical number of electrons in a cover of atom), and its nuclear and physical. properties are defined by set and a ratio of number of the protons and neutrons entering it. Each kernel consists of Z protons and N neutrons, and total number of these particles, or nucleons, makes mass number And = Z + N determining nuclear mass. It to the value of mass of this nuclide which is equally rounded to an integer. Any nuclide, thus, is defined by Z and N values though some radioactive nuclides with identical Z and N can be in various nuclear and power states and differ nuclear and physical. properties; such nuclides are called isomers. Nuclides with identical number of protons are called isotopes.

And. are designated by a symbol of the corresponding chemical element with the index A located at the upper left — mass number; sometimes at the left also the number of protons (Z) is below given. E.g., radioactive And. phosphorus with mass numbers 32 and 33 designate: 32 P and 33 P or 32 P and 33 P respectively. At designation I. without indication of a symbol of an element mass number is given after designation of an element, e.g. phosphorus-32, phosphorus-33.

U I. different elements there can be the same mass number. Atoms with various number of protons of Z and neutrons of N, but with identical mass number And are called isobars (e.g., 14 32 Si, 15 32 P, 16 32 S, 17 32 Cl — isobars).

The name «isotope» is offered English scientific F. Soddy. For the first time existence And. it was open in 1906 during the studying of radioactive decay of heavy natural radioelements; in 1913 they were found also in the non-radioactive element of neon, and then the isotope structure of all elements of a periodic system was defined by mass spectrometry. In 1934 I. Zholio-Curie and F. Zholio-Curie for the first time received artificial and radioactive And. nitrogen, silicon and phosphorus, and afterwards by means of various nuclear reactions on neutrons, charged particles and photons of high energy were received radioactive And. all known elements are also synthesized radioactive And. 13 superheavy — transuranic elements (with Z ≥ 93). It is known 280 stable, characterized by stability, and more than 1500 radioactive, i.e. unstable, And., which with this or that speed undergo radioactive transformations. Duration of existence radioactive And. it is characterized half-life (see) — a time term of T 1/2 , during to-rogo quantity of radioactive kernels decreases twice.

In natural mix I. chemical element different And. contain in different quantities. Percentage And. in this chemical element is called their relative prevalence. So, e.g., contains in natural oxygen three stable And.: 16O (99,759%), 17O(0,037 of %) and 18O (0,204%). Many chemical elements have only on one stable And. ( 9 Be, 19 F, 23 Na, 31 P, 89 Y, 127 I, etc.), and some (The CU, Pm, Lu and all elements with Z more than 82) have no stable And.

The isotope structure of natural elements on our planet (and within Solar system) is generally constant, however small fluctuations in prevalence of atoms of light elements are observed. This results from the fact that distinctions in masses them And. are rather big and therefore the isotope structure of these elements changes as a result of various natural processes, as a result of isotopic effects (i.e. distinctions of properties of chemical substances which contain these isotopes). So, the isotope structure of a number of biologically important elements (N, S, N, O, S) is connected, in particular, with existence of the biosphere and life activity of vegetable and animal organisms.

Distinction in structure and structure of atomic kernels And. the same chemical element (different number of neutrons) defines also distinction their nuclear and physical. properties, in particular that one it And. there can be stable, and others — radioactive.

Radioactive transformations. The following types of radioactive transformations are known.

Alpha decay — the spontaneous transformation of kernels which is followed by emission of alpha particles the, i.e. two protons and two neutrons forming a helium nucleus 2 4 He. As a result the charge Z initial kernels decreases on 2, and total number of nuclides or mass number — by 4 units, e.g.:

88 226 Ra -> 86 222 Ra + 2 4 He

at the same time a motive energy of the taking-off alpha particle is defined by the mass of initial and final kernels (with the mass of the alpha particle) and their power state. If the final kernel is formed in wild spirits, then the motive energy of an alpha particle decreases a little and if the excited kernel breaks up, then energy of an alpha particle respectively increases (at the same time so-called long-range alpha particles are formed). The power range of alpha particles discrete also lies within 4 — 9 MEV approximately for 200 I. heavy elements and 2 — 4,5 MEV for nearly 20 alpha-radioactive And. rare earth elements.

The beta decay — spontaneous transformation of kernels, at Krom a charge Z initial kernels changes on unit, and mass number And remains to the same. the beta decay represents the interconversion of the protons (p) and neutrons (n) which are a part of a kernel which is followed by emission or absorption of electrons (e - ) or positrons (e + ), and also neutrino (v) and antineutrino (v - ). There are three types of a beta decay:

1) an electronic beta decay of n -> p + e - + v - , Z which is followed by increase in a charge at 1 unit, with transformation of one of neutrons of a kernel into a proton, e.g.

2) a positron beta decay of p -> n + e + + v which is followed by reduction of a charge of Z by 1 unit with transformation of one of protons of a kernel into a neutron, e.g.

3) electron capture of p + e - -> n + v with simultaneous transformation of one of protons of a kernel into a neutron, as well as in case of disintegration with emission of a positron, also followed by reduction of a charge by 1 unit, e.g.

Capture of an electron at the same time happens to one of electron shells of atom, most often from the K-cover (K-capture), next to a kernel.

Beta minus disintegration is characteristic of neytronoizbytochny kernels which have a number of neutrons more, than in steady kernels, and beta plus disintegration and, respectively, electron capture — of neytronodefitsitny kernels which have a number of neutrons less, than at steady, or so-called beta and stable, kernels. Disintegration energy is distributed between a beta particle and a neutrino in this connection a beta range not discrete as at alpha particles, and continuous and contains beta particles with energy from close to zero to a nek-swarm of Emax characteristic of each radioactive I. Beta-radioaktivnye I. occur at all elements of a periodic system.

Spontaneous division — autodecomposition of the heavy-nuclei on two (sometimes 3 — 4) a splinter representing kernels of average elements of a periodic system (the phenomenon is open in 1940 the Soviet scientists G. N. Flerov and K. A. Petrzhak).

Gamma radiation — photon radiation with a discrete power range, arises at nuclear transformations, change of a power condition of atomic kernels or at annihilation of particles. Emission of gamma quanta accompanies radioactive transformation when the new kernel is formed in the excited power state. Time of life of such kernels is defined nuclear and physical. properties of maternal and affiliated kernels, in particular increases with reduction of energy of gamma transitions and can reach rather big sizes for cases of metastable excited state. Energy of the gamma radiation which is let out by different P. lies ranging from tens kev to several MEV.

Stability of kernels. At a beta decay there are interconversions of protons and neutrons before achievement of the most energetically favorable ratio of p and n that corresponds to a stable state of a kernel. All nuclides are divided in relation to a beta decay into beta and radioactive and beta and steady kernels. Beta and steady are understood as either stable, or alpha-radioactive nuclides for which the beta decay is energetically impossible. All beta and steady And. at chemical elements with atomic numbers of Z to 83 are stable (with a few exceptions), and at heavy elements stable And. no, and all their beta and steady And. are alpha-radioactive.

At radioactive transformation there is an allocation of energy corresponding to a ratio of mass of initial and final kernels, weight and energy of the emitted radiation. The possibility of the p-disintegration happening without change of mass number And, depends on a ratio of mass of the corresponding isobars. Isobars with a bigger weight as a result of a beta decay turn into isobars with a smaller weight; at the same time than the mass of an isobar is less, it is closer to those to a P-stable state. The return process by law of conservation of energy cannot go. So, e.g., for the isobars of transformation mentioned above go in the following directions with formation of a stable isotope of sulfur-32:

Kernels of the nuclides steady against a beta decay contain not less than one neutron on each proton (an exception are 1 1 H and 2 3 He), and in process of increase of atomic number a ratio of N/Z increases and reaches value 1,6 for uranium.

With increase in number N the kernel of this element becomes unstable in relation to electronic beta minus disintegration (with transformation >of n-p) therefore neytronoobogashchenny kernels beta are active. Respectively neytronodefitsitny kernels are unstable to positron a beta + - to disintegration or electron capture (with transformation >of p-n), and at heavy-nuclei also alpha decay and spontaneous division is observed.

Division stable and receiving artificial radioisotopes. Division And. — this enrichment of natural mix I. this chemical element separate being its part And. and allocation pure And. from this mix. All methods of division are based on isotopic effects, i.e. on distinctions physical. - chemical properties different And. and the chemical connections (durability of chemical bonds, density, viscosity, heat capacity, temperature of melting, evaporation, diffusion rate etc.) supporting them. Ways of division are also based on distinctions in behavior And. and the connections supporting them in physical. - chemical processes. Electrolysis, centrifuging, gas and thermal diffusion, diffusion in a flow of steam, rectification, chemical and isotope exchanges, electromagnetic division, division by means of the laser, etc. are practically used. If single process gives low effect, i.e. a small fractionation factor And., it is repeatedly repeated before receiving sufficient extent of enrichment. Most effectively there is a division And. light elements in connection with big relative differences of mass of their isotopes. E.g., «heavy water», i.e. the water enriched heavy And. hydrogen — a deuterium, weight to-rogo twice more, in a commercial scale receive on electrolysis installations; highly effectively also allocation of a deuterium low-temperature distillation. Division And. uranium (for receiving nuclear fuel — 235 U) carry out at the gas-diffusion plants. A wide range enriched stable And. receive on electromagnetic dividing installations. In certain cases apply division and enrichment of mix radioactive And., napr, for receiving radioactive And. gland-55 with high specific activity and radionuclide purity.

Artificial and radioactive And. receive as a result of nuclear reactions — interactions of nuclides with each other and with nuclear particles or photons from which formation of other nuclides and particles results. Nuclear reaction is conditionally designated as follows: in the beginning the symbol of initial isotope is specified, and then — formed as a result of this nuclear reaction. In brackets between them it is specified to the first influencing, and behind it — the taking-off particle or quantum of radiation (see the tab., column 2).

The probability of implementation of nuclear reactions is quantitatively characterized by the so-called effective cross-section (or section) reactions designated by the Greek letter about and expressed in barns (10 - 24 cm 2 ). For receiving artificial and radioactive nuclides use nuclear reactors (see. nuclear reactors ) and particle accelerators (see). Many radionuclides applied in biology and medicine receive in the nuclear reactor on nuclear reactions of radiation capture, i.e. capture by a kernel of a neutron with emission of gamma quantum (n, scale) therefore isotope of the same element with mass number, on unit big initial is formed, e.g. 23 Na (n, γ) 24 Na, 31 P (n, γ) 32 R; on reaction (n, γ) with the subsequent disintegration of the received radionuclide and education «affiliated», e.g. 130 Te (n, γ) 131 Te —> 131 I; on reactions with a departure of charged particles (n, p), (n, 2n), (n, α); e.g., 14 N (n, p) 14 C; on secondary reactions with tritons (t, p) and (t, n), e.g. 7 Li (n, α) 3 H and then 16O (t, n) 18 F; on a fission test of U (n, f), e.g. 90 Sr, 133 Xe, etc. (see. Nuclear reactions ).

Some radionuclides or cannot be received in the nuclear reactor at all, or such their production is irrational in the medical purposes. On reaction (n, γ) in most cases cannot receive isotopes without carrier; some reactions have too small size of section of a, the irradiated targets — small abundance of initial isotope in natural mix that leads to low exits of reactions, insufficient specific activity of drugs. Therefore many important radionuclides applied in klinich. to radiodiagnosis, receive with sufficient specific activity, using the isotope enriched targets. E.g., for receiving calcium-47 irradiate the target enriched on calcium-46 from 0,003 to 10 — 20% for receiving iron-59 — a target with the iron-58 enriched from 0,31 to 80% for receiving mercury-197 — a target with the mercury-196 enriched from 0,15 to 40%, etc.

In the reactor of hl. obr. many neutrons which are breaking up with a beta mirus_izlucheniyem receive radionuclides. Neytronodefitsitny radionuclides which are formed in nuclear reactions on charged particles (p, d, an alpha) and photons and break up with emission of positrons or by means of electron capture, in most cases receive on cyclotrons, linear accelerators of protons and electrons (in the latter case the bremsstrahlung is used) at energy of accelerating particles about tens and hundreds of MEV. So receive for the medical purposes radionuclides on reactions: 51 V (r, n) 51 Cr, 67 Zn (r, n) 67 Ga, 109 Ag (α, 2n) 111 In, 44 Ca (γ, p) 43 K, 68 Zn (γ, p) 67 Cu, etc. Important advantage of such way of receiving radionuclides is that they, having, as a rule, other chemical nature, than material of the irradiated target, can be allocated from the last without carrier. It allows to receive necessary radiofarm. drugs with high specific activity and radionuclide purity.

For receiving many short-lived radionuclides directly in clinical institutions use the so-called isotope generators containing long-living maternal radionuclide, at disintegration to-rogo the necessary short-lived affiliated radionuclide is formed, e.g. 99m Tc, 87m Sr, 113m In, 132 I. The last can be repeatedly allocated from the generator during time of life of a maternal nuclide (see. Generators of radioisotopes ).

Use of isotopes in biology and medicine. Radioactive and stable And. are widely applied in scientific research. As a tag they are used for preparation of tracers (see. Marked connections ) — the substances and connections having excellent from natural isotope structure. By method of tracers investigate distribution, ways and the nature of movement of labeled substances in various environments and systems, carry out their quantification, study a structure of chemical connections and biologically active agents, mechanisms of various dynamic processes, including their metabolism in an organism of plants, animals and the person (see. Radio isotope research ). By means of a method of tracers conduct researches in biochemistry (studying of a metabolism, structure and mechanism of biosynthesis of proteins, nucleinic to - t, fats and carbohydrates in a live organism, speed of course biochemical, reactions etc.); in physiology (ion migration and various substances, processes of absorption from went. - kish. path of fats and carbohydrates, excretion, blood circulation, behavior and role of microelements etc.); in pharmacology and toxicology (a research of behavior of medicines and toxicants, their absorptions, ways and the speed of accumulation, distribution, removal, the mechanism of action etc.); in microbiology, immunology, virology (studying of biochemistry of microorganisms, mechanisms enzymatic and Immunochemical, reactions, interaction of viruses and a cell, mechanisms of action of antibiotics etc.); in hygiene and ecology (studying of impurity harmful substances and deactivations of productions and environment, ecological chain of various substances, their migrations etc.). And. apply also in others medico-biol. researches (for studying of a pathogeny of various diseases, a research of early changes of a metabolism etc.).

In medical practice radionuclides apply to diagnosis and treatment of various diseases, and also to radiation sterilization of medical materials, products and medicines. Clinics use more than 130 radio diagnostic and 20 radiotherapeutic techniques using opened radiofarm. drugs (RFP) and the closed isotope sources of radiation. For this purpose use St. 60 radionuclides, apprx. 30 of them — most widely (tab.). Radio diagnostic drugs allow to obtain information about funkts, and an anatomic condition of bodies and systems of a human body. In a basis radio isotope diagnosis (see) an opportunity to track for biol, behavior marked radionuclides of chemical substances and connections in a live organism without disturbance of its integrity and change of functions lies. Introduction of the necessary radioisotope of the corresponding element to structure of chemical connection, practically without changing its property, allows to watch his behavior in a live organism by outside detecting of radiation And., in what one of very important advantages of a method of radio isotope diagnosis consists.

Dynamic indicators of behavior of marked connection give the chance to estimate funkts, a condition of the studied body or system. So, on a dilution rate of RFP with 24 Na, 42 K, 51 Cr, 52 Fe, 131 I, etc. in fluid mediums determine the volume of the circulating blood, erythrocytes, exchange of albumine, iron, water exchange of electrolytes, etc. On indicators of accumulation, movement and removal of RFP in bodies, systems of an organism or in the center of defeat it is possible to estimate a condition of the central and peripheral hemodynamics, to define function of a liver, kidneys, lungs, to study iodic exchange, etc. of RFP with radioisotopes of iodine and technetium allow to investigate all functions of a thyroid gland. With the help 99 m Tc, 113m In, 123 I, 131 I, 133 Xe can conduct a comprehensive investigation of lungs — to study distribution of a blood-groove, a condition of ventilation of the lungs and bronchial tubes. RFP with 43 K, 86 Rb, 99 m CU, 67 Ga, 131 I, 113m In, 197 Hg, etc. give the chance to define a blood stream and blood supply of a brain, heart, liver, kidneys and other bodies. Radioactive colloid solutions and some iodorganic drugs allow to estimate a condition of polygonal cells and hepatocytes (kupferovsky cells) and anti-toxic function of a liver. By means of radio isotope scanning carry out anatomo-topographical studying and definition of existence, size, a form and the provision of volume damages of a liver, kidneys, marrow, thyroid, parathyroid and the sialadens, easy, limf, nodes; radionuclides 18 F, 67 Ga, 85 Sr, 87M Sr, 99M Tc allow to investigate diseases of a skeleton etc.

In the USSR standards of radiation safety for patients during the use of radioactive materials with the diagnostic purpose which strictly regulate these procedures from the point of view of tolerance levels of radiation are developed and put into operation. Thanks to it, and also the rational choice of methods and equipments for different types of inspections and to use in RFP of whenever possible short-lived radionuclides possessing favorable characteristics of radiation concerning efficiency of their registration at the minimum beam influence beam loads of an organism of the patient at radio isotope diagnostic procedures ah are much lower than the doses received at rentgenol, inspections, and in most cases do not exceed the 100-th and tenth shares is glad.

In the 70th radio isotope drugs became wider than 20 century to be used for the researches in vitro, generally — for the immunochemical analysis. Radio immunochemical methods are based on highly specific immunochemical reaction antigen — an antibody, as a result the cut is formed a steady complex of an antibody and antigen. After separation of the formed complex from not reacted antibodies or antigens carry out quantitative definition by measurement of their radioactivity. Use of antigens or antibodies, marked radioisotopes, e.g. 125 I, increases sensitivity of immunochemical tests in tens and hundreds of times. It is possible to determine content in an organism of hormones, antibodies, antigens, enzymes, enzymes, vitamins and other biologically active agents in concentration to 0,1 mg/ml by these tests. Thus it is possible to define not only various patol, states, but also very small changes reflecting initial stages of a disease. E.g., these techniques successfully apply to early diagnosis of in vitro of a diabetes mellitus, infectious hepatitis, disturbances of carbohydrate metabolism, some allergic and some other diseases. Such radio isotope tests not only it is more sensitive, simpler, but also allow to conduct mass researches and are absolutely safe for patients (see. Radioizotopnaya diagnosis ).

With to lay down. the purpose RFP and radionuclide sources of radiation are applied by hl. obr. in oncology, and also at treatment of inflammatory diseases, eczemas, etc. (see. Radiation therapy ). For these purposes are used as the open RFP entered in an organism, in fabrics, serous cavities, cavities of joints, intravenously, vnutriarterialno and in limf, system, and the closed sources of radiation for outside, intracavitary and interstitial therapy. By means of the corresponding RFP, hl. obr. the colloids and suspensions containing 32 P, 90 Y, 131 I, 198 Au and other radionuclides, treat diseases of the hemopoietic system and various tumors, influencing locally on patol, the center. At contact irradiation (Dermatolum, and Ophthalmolum. B-ray applicators) apply 32 P, 90 Sr, 90 Y, 147 Pm, 204 Tl, in remote gamma and therapeutic devices — sources 60 Co or 137 Cs of high activity (hundreds and thousands of curies). For interstitial and intracavitary radiation use needles, granules, a wire and other special types of the closed sources with 60 Co, 137 Cs, 182 Ta, 192 Ir, 198 Au (see. Radioactive drugs ).

Radioactive nuclides are used also for sterilization of materials, products of medical appointment and pharmaceuticals. Practical application of radiation sterilization became possible from 50th when powerful sources of ionizing radiation appeared. In comparison with traditional methods sterilizations (see) the radiation method has a number of advantages. As at the usual sterilizing dose of radiation (2 — 3 Mrad) there is no substantial increase of temperature of the irradiated object, there is possible a radiation sterilization of thermolabile objects, including biol, drugs and products from some types of plastics. Impact of radiation on the irradiated sample happens at the same time in all its volume, and sterilization is carried out with high degree of reliability. At the same time for control use the color indicators of the received dose placed on the surface of packaging of the sterilized object. Medical products and means will be sterilized tekhnol at the end. cycle already in finished form and in hermetic packaging, including and from polymeric materials that excludes need of creation of strictly aseptic conditions of production and guarantees sterility after release of products by the enterprise. Radiation sterilization is especially effective for medical products of one-time use (syringes, needles, catheters, gloves, suture and dressing materials, systems for capture and hemotransfusion, biological products, surgical instruments etc.), not injection pharmaceuticals, tablets and ointments. At radiation sterilization of medicinal solutions it is necessary to reckon with a possibility of their radiation decomposition leading to change of structure and properties (see. Sterilization cold ).

Toxicology of radioisotopes — the section of toxicology studying influence of the incorporated radioactive materials on live organisms. Its main objectives are: establishment of tolerance levels of contents and intake of radionuclides in a human body with air, water and food stuffs, and also degrees of harmlessness of RV entered into an organism at a wedge, radio diagnostic testings; clarification of specifics of defeat by radionuclides depending on the nature of their distribution, energy and a type of radiation, half-life, a dose, ways and a rhythm of receipt and research of effective remedies for prevention of defeat.

Influence on a human body of the radionuclides which are widely used in the industry, a scientific and medical research, and also formed as a result of splitting of nuclear fuel is most deeply investigated.

The toxicology of radioisotopes is integrally connected with radiobiology (see), physics health (see) and medical radiology (see).

Radioactive materials can get into a human body through respiratory tracts, went. - kish. a path, skin, wound surfaces, and at injections — via veins, muscular tissue, joint surfaces. The nature of distribution of radionuclides in an organism depends on the main chemical properties of an element, form of the entered connection, a way of receipt and fiziol, conditions of an organism.

Quite essential distinctions in distribution and ways of removal of separate radionuclides are found. Soluble compounds of Ca, Sr, Wa, Ra, Y, Zr selectively collect in a bone tissue; La, Ce, Pr, Pu, Am, Cm, Cf, Np — in a liver and a bone tissue; K, Cs, Rb — in muscular tissue; Nb, Ru, Te, Po are distributed rather evenly, though tend to accumulation in reticuloendothelial tissue of a spleen, marrow, adrenal glands and limf, nodes; I and At — in a thyroid gland.

Distribution in an organism of the elements relating to a certain Mendeleyev's group has much in common. Elements of the first basic group (Li, Na, To, Rb, Cs) are completely soaked up from intestines, rather evenly distributed on bodies and allocated preferential with urine. Elements of the second basic group (Ca, Sr, Ba, Ra) are well soaked up from intestines, selectively postponed in a skeleton, allocated in a little large numbers with a stake. Elements of the third of the main and the fourth collateral groups, including easy lanthanides, actinides and transuranic elements, are practically not soaked up from intestines, as a rule, selectively postponed in a liver and in a smaller measure in a skeleton, allocated preferential with a stake. Elements the fifth and sixth main of groups of a periodic system, except for Ro, are rather well soaked up from intestines and removed almost only with urine within the first days thanks to what in bodies are found in rather small amounts.

Adjournment of radionuclides in pulmonary fabric at inhalation depends on the size of the inhaled particles and their solubility. The aerosols are larger, the their big share is late in a nasopharynx and smaller gets into lungs. Slowly leave easy low solubility connections. High concentration of such radionuclides often is found in limf, nodes of roots of lungs. The oxide of hyzone, soluble compounds of alkaline and alkaline earth elements are very quickly soaked up in lungs. Cm and other heavy metals are slowly soaked up in easy Pu, Am, Xie.

The Standard of Radiation Safety (SRS) regulate receipt and content of radionuclides in an organism of persons whose work is connected with profvrednost, and individuals from the population, and also the population in general, admissible concentration of radionuclides in free air and water, food stuffs. These norms are based on sizes of the marginal doses (MD) of radiation established for four groups of critical bodies and fabrics (see. Critical body , Marginal doses ).

For the persons working in the conditions of profvrednost, the accepted size traffic regulations of radiation of all body, gonads and red marrow is equal 5 rem/year, muscular and fatty fabrics, a liver, kidneys, a spleen, went. - kish. a path, lungs, a crystalline lens of eyes — 15 rem/year, a bone tissue, a thyroid gland and skin — 30 rem/year, hands, forearms, anklebones and feet — 75 rem/year.

Norms for individuals from the population are recommended 10 times below, than for the persons working in the conditions of profvrednost. Radiation of all population is regulated by genetically significant dose, edges shall not exceed 5 rem in 30 years. The possible exposure doses caused by medical procedures and natural background radiation do not enter this dose.

The size of annual marginal receipt of soluble and insoluble compounds (mkki / year) through a respiratory organs for personnel, a limit of annual intake of radionuclides through a respiratory organs and digestion for individuals from the population, the annual average admissible concentration (AAAC) of radionuclides in free air and water (curie/l) for individuals from the population, and also the content of radionuclides in critical body corresponding to the marginal level of receipt (mkka) for personnel are given in standards.

During the calculation of tolerance levels of intake of radionuclides in an organism also quite often found uneven nature of distribution of radionuclides in separate bodies and fabrics is considered. The uneven distribution of radionuclides leading to creation of high local doses is the cornerstone of high toxicity of alpha emitters that is promoted in no small measure by lack of recovery processes and almost full summation of the damages caused by this type of radiation.

See also Doses of ionizing radiation , Ionizing radiation .


Table. The RADIOISOTOPES which are MOST WIDELY APPLIED IN CLINICAL PRACTICE, the MAIN REACTIONS of THEIR RECEIVING AND SOME PHYSICAL CHARACTERISTICS

Designations: β-— beta radiation; β + — positron radiation; n — a neutron; p — a proton; d — a deuteron; t — a triton; α — an alpha particle; E.Z. — disintegration by capture of an electron; γ — gamma radiation (as a rule, only the main lines of a γ-range are given); Nominative — isomeric transition; U (n, f) — fission test of uranium. The specified isotope is emitted from mix of cleavage products; 90 Sr-> 90 Y — receiving a daughter isotope ( 90 Y) as a result of disintegration maternal ( 90 Sr), including by means of the isotope generator.


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V. V. Bochkaryov; Yu. I. Moskalyov (current.), author of the tab. V. V. Bochkaryov.

Яндекс.Метрика