Polonium-210

A naturally radioactive metallic element, occurring in minute quantities as a product of radium disintegration and produced by bombarding bismuth or lead with neutrons. It has 27 isotopes ranging in mass number from 192 to 218, of which Po 210, with a half-life of 138.39 days, is the most readily available. Atomic number 84; melting point 254°C; boiling point 962°C; specific gravity 9.32; valence 2, 4.

A chemical element, Po, atomic number 84. Marie Curie discovered the radioisotope 210Po in pitchblende, and named for her native country, Poland. This isotope is the penultimate member of the radium decay series. All polonium isotopes are radioactive, and all are shortlived except the three ?-emitters, artificially produced 208Po (2.9 years) and 209Po (100 years), and natural 210Po (138.4 days).

Polonium (210Po) is used mainly for the production of neutron sources. It can also be used in static eliminators and, when incorporated in the electrode alloy of spark plugs, is said to improve the cold-starting properties of internal combustion engines.

Most of the chemistry of polonium has been determined using 210Po, 1 curie of which weighs 222.2 micrograms; work with weighable amounts is hazardous, requiring special techniques. Polonium is more metallic than its lower homolog, tellurium. The metal is chemically similar to tellurium, forming the bright red compounds SPoO3 and SePoO3. The metal is soft, and its physical properties resemble those of thallium, lead, and bismuth. Valences of 2 and 4 are well established; there is some evidence of hexavalency. Polonium is positioned between silver and tellurium in the electrochemical series.

Two forms of the dioxide are known: low-temperature, yellow, face-centered cubic (UO2 type), and high-temperature, red, tetragonal. The halides are covalent, volatile compounds, resembling their tellurium analogs.

Polonium is a highly radioactive and toxic element and is dangerous to handle. Even in milligram or microgram amounts, handling polonium-210 is very dangerous and requires special equipment used with strict procedures. Direct damage occurs from energy absorption into tissues from alpha particles.

The maximum allowable body burden for ingested polonium is only 1100 becquerels (0.03 microcurie), which is equivalent to a particle weighing only 6.8 × 10-12 gram. Weight for weight polonium is approximately 2.5 × 1011 times as toxic as hydrocyanic acid. The maximum permissible concentration for airborne soluble polonium compounds is about 7,500 Bq/m3 (2 × 10-11 µCi/cm3).

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