THORIUM (Thorium, Th) — radioactive chemical element III of group of a periodic system of D. I. Mendeleyev; belongs to group of actinoids (see). Sequence number 90, at. weight 232,038. Silver-white metal, density is 11,72 g/cm3, * °pl 1690-1750 °, * °kip 3500 — 4200 °.
Half-life 232Th makes apprx. 1,4-1010 years. 232Th, breaking up, forms a number of the radioelements which are isotopes of radium (see), lead, bismuth, polonium, actinium, thallium, thorium and radioactive gas of radon (see). Nek-rye from 13 known isotopes T. — 232Th, 228Th (radio thorium), 234Th (uranium of Hkh) and 230Th (ionium) — are applied in the industry (radnoli electrotechnical, metallurgy, nuclear power etc.) and can constitute health hazard. During the work with T. and its connections it is necessary to follow rules of radiation safety (see).
T. and products of its disintegration are eurysynusic in the nature, are a part of top coats of crust; their average content in a granite layer makes 1,3*10 ~ 3%, and in a sedimentary cover 1,8 • 10 ~ 3% (on weight). T. is a part of many fabrics of plants and animals; the hl is absorbed. obr. lungs, liver, spleen, bone tissue. Daily receipt of T. with food and water at the person makes apprx. 3 mkg. It is brought out of an organism generally with a stake. Decomposition products T. are removed quicker, than T.
Neposredstvenno in medicine of T. and its connections in the USSR ceased to apply, and medical value T. and products of its disintegration the hl is defined. obr. their natural radioactivity (see). Besides, thorium as radioelement is one of sources of a radioactive background (see background radiation).
Occupational health. During the receiving ii use of T. and its connections extent of their adverse effect on a human body is defined physical. - chemical properties of connection, its solubility, half-life of isotope, a look and radiant energy, and also kind of work and the equipment used at the same time.
Under production conditions aerosols of T can come to air of workrooms. and products of its disintegration, to-rye are formed during the crushing, packaging, drying, evaporation and other operations. The majority of decomposition products 232Th belongs to the ss-radiating elements (radionuclides) with high energy (see Alpha radiation).
During the work with T. comes to air a Torah (see). Its allocation depends by nature and reduction ratioes of the materials containing T. During the work with large numbers of T. and waste of its production perhaps raised 'at - radiation, napr, at decomposition of a monocyte (the main industrial source of T.) during processing of T., and also in places of allocation of one of short-lived isotopes T. — mesothorium and work with it.
Receiving and use of T. can be followed by pollution of integuments and clothes of service personnel, the surfaces of the equipment and building constructions and - and p-active products. T. and its decomposition products occluded by various surfaces are additional sources in air of thoron and radioactive aerosols.
During the work with metal T. and additional danger because of their ability to self-ignition and explosions arises its hydride in a powdery state.
T. and decomposition products can come to an organism through a respiratory organs, digestion, partially through skin and to accumulate in various bodies and fabrics. Long delay of T. and its connections brings in an organism to and - to about-spearing of fabrics. In spite of the fact that T. chemically malotoksichen, it has harmful effect on the hemopoietic, nervous and reticuloendothelial systems. Functional and pathological changes in a pulmonary, bone tissue and parenchymatous bodies are observed. The changes characteristic for hron can develop in later terms. a radial illness (see), development of new growths is possible.
Maximum allowable concentration of thorium in air of a working zone — 0,05 mg/m3; AC (admissible concentration) makes 1,7-10 ~ 15 curies! l. Minimum significant activity (i.e. the greatest activity of a source which is not demanding registration or obtaining permission of bodies of the State sanitary inspection) in a workplace for T. makes 100 mkkyur.
Preventive m of ER about N r and I am t and I during the work with T. are directed to the prevention of receipt in air of aerosols and light-end products of disintegration of T. and on an exception of pollution of a body by them. Receiving and use of large numbers of T. demand mechanization of production, placement of the equipment in shelters, its sealing, use of means of distance steering; raw materials, waste, tests should be stored in special rooms. It is necessary to provide sufficient air exchange by the device of local and general ventilation in all cases (see). The deleted air is subject to cleaning with a wet way. All equipment before repair needs to be subjected to cleaning of T. Receiving metal T. and its hydride by crushing it is reasonable to carry out in the atmosphere of inert gases (nitrogen or helium).
At contact with T. and its connections it is necessary to follow strictly rules of personal hygiene, to use individualn ym both to means and protection (ShM.) respiratory organs and integuments. The device a dignity is required. propusknik with control of levels of pollution of a body and clothes. Control of maintenance of T is necessary. and its connections in air of the place of work and storage of materials and waste, and also control of level at - radiations (see. Radiation control). Carrying out preliminary and periodic (1 time in 12 months) the medical surveys working is important (see. Medical examination). Special attention should be paid on a condition of lungs, peripheral blood, bone structures and parenchymatous bodies, to carry out control measurements of content of thoron in expired air and to Calais or measurement of ionizing radiation of a body by means of special counters (see Dosimetry of ionizing radiation).
Bibliography: Albert R. Tory, Industrial and hygienic aspects, the lane with English, M., 1971; Harmful substances in the industry, under the editorship of N. V. Lazarev and I. D. Gadaskina, t. 3, page 584, L., 1977; Standards of radiation safety of NRB-76, M., 1978; Pavlovsk N. A. and Zeltser M. R. Thorium-232 and products of its disintegration, Biological and hygienic aspects, M., 1981, bibliogr.; Tarasenko N. Yu. Occupational health during the work with thorium, M., 1963, bibliogr.; Distribution, retention and late effects of thorium dioxide, ed. bv R. L. Swarm, N. Y.,
H. A. Pavlovskaya; H. Yu. Tarasenko (gigabyte).