From Big Medical Encyclopedia

TOPOH (outdated synonym radon; Tn, 220Em86) — radioactive light-end product of disintegration 224Ra (ThX); one of isotopes of radon. Half-life makes

54,5 sec.; breaking up, T. forms a number of short-lived affiliated radionuclides.

T. — inodorous colourless monatomic gas with / °pl — 71 ° and * °kip — 61,8 °. T. is in the natural materials containing radionuclides of a number of thorium (see). In air or any other environment T. arrives from toriysoderzhashchy substances.

Receipt of T. in an organism the hl is carried out. obr. through lungs at inhalation of the air containing T. or radionuclides of a thorium row (2:i2Th, 228Ra, 228Th, 224Ra). At the same time T. mixes up with pulmonary air, diffuses in a blood flow and it is carried on an organism; diffusion rate of T. in blood makes about 20% in 1 min. of lungs, and biol. an elimination half-life from blood — 4,5 min.

Existence of T., and also products of its disintegration in air of production rooms harm for the persons (production and processing of toriysoderzhashchy materials, work with the drugs including radio thorium, radium or mesothorium etc.) working in them defines the prof.

The Admissible Concentration (AC) of thoron in air of workrooms — Y0'11 of curie/l.

Complex of actions for decrease in concentration of T. in air includes use of rational ways of preparation and development of thorium fields, effective airing of workrooms (see Ventilation), use of individual protection equipment of a respiratory organs (see Respirators).

In medicine of T. practically it is not used.

Bibliography: Albert R. Tory, Industrial and hygienic aspects, the lane with English, page 93, M., 1971; Pavlov

skaya N. A. and Zeltser M. R. Thorium-232 and products of its disintegration, Biological and hygienic aspects, page 27, M., 1981; Serdyukova A. S. and Kapitanov Yu. T. Isotopes of radon and temporary products of their disintegration in the nature, M., 1969. N. A. Pavlovskaya.