CAESIUM

From Big Medical Encyclopedia

CAESIUM (Caesium, Cs) radioactive — chemical element

of 1 group of a periodic system of D. I. Mendeleyev. Sequence number 55, atomic weight (weight) 132,905. Caesium is a rare element from group of alkali metals. It is present at tissues of animals and plants. Its average content in a human body about 1,5 mg. In the nature it meets hl. obr. in a scattered state, in minerals — lepidolite, kornelite, berilla, and also forms independent minerals — pollu-tion and rhodizite. Its content in crust makes 7*10_4% on weight.

C. — soft, viscous metal of silver-white color, its density

of 1,903 g! cm3 at 20 °, * °PL 28,5 °, / °kip 705 °. In all connections C. odnovalenten. It has high reactivity, connects to oxygen with instant recovery, with water reacts with explosion, violently reacts with to-tami.

At natural C. there is one stable nuclide with mass number 133. Also 30 radioisotopes C are known. with mass numbers from 116 to 146, five of to-rykh have nuclear isomers (see the Isomerism, an isomerism of atomic kernels). Majority of radionuclides C. short-lived with second and minute half-lives; half-lives of several of them from 1 to 13 days, two radioisotopes long-living — 134Cs (TV2 = 2,062 years) and 137Cs (Ti/2 = 30,18 years). 137Cs can come to the environment during the testing of nuclear weapon and as a result of emissions of radioactive waste in the atmosphere and reservoirs by the enterprises of the atomic industry and nuclear power, and also vessels with nuclear power stations. By estimates of UN committee on action of atomic radiation, by 1970 as a result of all the tests of nuclear weapon which are carried out till this time in the soil, water and air collected apprx. 25 Mkyuri 137Cs. Physicochemical properties C. cause high mobility 137Cs in ecological chains of the biosphere (see the Radioecology) and its concoction in separate links of these chains, including a human body. From arrived with foodstuff 137Cs apprx. 80% it is found in muscles and apprx. 8% — in bones. Due to rather short biological period on-luvyvedeniya 137Cs from a human body in comparison with half-life of this radionuclide (elimination half-lives of the separate fractions containing 137Cs fluctuate of several days to two hundred) concentration 137Cs in an organism changes according to its contents in a diet.

Radioisotopes of C. are applied in chemical researches, in gamma-radiography of various industrial products (see Defectoscopy), in radiation technology, in radiobiol. experiments. In medicine found practical application 137Cs, used as a source of gamma radiation for contact and remote radiation therapy (see), and also for radiation sterilization (see).

137Cs is one of cleavage products of heavy elements. Industrial receiving 137Cs for needs of the national economy and medicine carry out it allocation from mix of fragmental products by various methods (extraction, coprecipitation, adsorption), usually in the form of the dry CsCl placed then in hermetic capsules. The domestic industry releases sources with 137Cs more than 30 types with various face values of activity.

137Cs Er2 = 1173,4 kev (5,2%), with E^ mean energy = 179 kev and the accompanying gamma radiation with Е^ = = 661,662 kev (85,3%), belonging to the short-lived isomer of barium 1z7tva which is formed at the same time breaks up with emission of a two-component beta range with boundary energy of its components of Er1 = 511,7 kev (94,8%). There is also characteristic x-ray emission of barium with the energy its Clinium lying ranging from 32 to 36,5 kev (total intensity of 7%).

According to standards of radiation safety (NRB-76) on radio toxicity radionuclides 131Cs and 137Cs concern respectively to groups G and B, i.e. their open drugs with activity to 100 mkkyura (3,7 MBK) and 10 mkkyur (0,37 MBK) can be in a workplace without the permission of a sanepidsluzhba.

Admissible concentration 137Cs in water of open reservoirs 1,5 * • 10'8 curies! l (555 Bq/l), in air of a working zone — 1,4-10 "11 curies! l

(~ 0,52 Bq/l), in free air 4,9 * 10“ 13 curies! l (~ 0,02 Bq/l).

See also Isotopes, Radionuclide sources of radiation (t. 25,

additional materials).

Bibliography: L e in and V. I N. Receiving radioisotopes, M., 1972; Moisey in A. A, and Ramzayev P. V. Caesium-137 in the biosphere, M., 1975; Standards of radiation safety of NRB-76, M., 1978; Holnov Yu. V. and d river. Characteristics of radiations of the radioactive nuclides applied in the national economy, M., 1980; Anger R. T. a. S about d d V. J. Dosimetry of 129Cs and 13lCs, Phys. in Med. Biol., v. 16, p. 698, 1971; Radioactive pharmaceuticals, ed. by G. A. Andrews a. o., p. 619, Oak Ridge, 1966. V. V. Bochkaryov.

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