Po, a radioactive chemical element of Group VI in the Mendeleev periodic table. Atomic number, 84. Polonium was the first element to be discovered by P. Curie and M. Sklo-dowska-Curie because of its radioactive properties (1898); it was named for Poland (Latin Polonid), Mme. Curie’s native land.
There are 25 known radioactive polonium isotopes, with mass numbers ranging from 194 to 218. The longest-lived isotope is the artificially produced α-radioactive 209Po (half-life T½ = 103 yr). Seven polonium isotopes with mass numbers 210–212, 214–216, and 218 occur naturally as members of the radioactive series of uranium, actinouranium, and thorium; α-radioactive 210Po (T½ = 138days) is the most stable of the latter isotopes. Milligram quantities of 210Po may be extracted from natural substances, and also synthesized artificially by the nuclear interaction of neutrons and bismuth. Virtually all data on polonium have been obtained using 210Po.
Polonium is a rare element; the Po content in the earth’s crust is approximately 2 × 10-15 percent. Polonium occurs in free form as a soft, silver-white metal: density, 9.3 g/cm3; melting point, 254°C; boiling point, 1162°C. The configuration of the outer electron shell in the Po atom is 6s2 6p4. Polonium is most similar to tellurium in chemical properties. Like tellurium, polonium has the oxidation states –2, +2, +4, and +6. The known polonium oxides are PoO, PoO2, and PoO3. The volatile hydride P0H2 is formed upon action of Zn on a hydrochloric acid solution of Po; the ions PoO42-, PoO32-, Po4+, and PoO2+ are present in Po solutions. The polonium hydroxide Po(OH)2 is known.
Readily hydrolyzable polonium tetrahalides and sulfates of various compositions are synthesized in weighable quantities. The carrier method, using tellurium, an analogue of polonium, is used in the synthesis of organopolonium compounds, in which Po carbon bonding occurs. For example, polonium diphenyl (C6H5)2Po and polonium diphenyldichloride (C6H5PoCl2 have been obtained. Since polonium is extremely toxic, all work with this element is carried out in special boxes.
The isotope 210Po is used in neutron sources. Energy from the α-particles of 210Po may be transformed into electric power. In particular, small electric “atomic” batteries made with 210Po, which are characterized by a long service life, were used in the satellites Cosmos 84 and Cosmos 89.
S. S. BERDONOSOV.
Polonium-210 (2l0Po). The isotope 210Po is a common constituent of natural radioactive fallout. It passes into plants from the soil through the roots or from the atmosphere through precipitation onto epigeal plant organs. Small quantities of 210Po (10–4 picocurie per g [pc/g]) are found in seawater; the isotope may accumulate in marine organisms (the accumulation coefficient in the algae Porphyra umbilicalis is of the order of 1,000).
Animals and humans ingest 210Po with food. For example, the approximate 210Po content in salt water fish is 20–100 pc/kg; in meat, 2–3 pc/kg; in bread, 1 pc/kg; in groats, 2 pc/kg; and in tea, 500–600 pc/kg. Polonium is relatively evenly distributed among the organs in animals and humans (specific concentration ~4 × 10-5pc/g in raw tissue).
The biological effect of 210Po is determined by α-radiation. Animal experiments have indicated the high toxicity of this radionuclide in large concentrations. For example, 210Po concentrations higher than 0.0003 μc/g liveweight reduced the life span of white rats, altered peripheral blood composition, and induced cirrhosis of the liver; the animals later developed tumors in the kidneys, large intestine, testes, and many other organs. The biological effect of small 210Po concentrations has not been thoroughly studied.
V. A. KAL’CHENKO