polonium

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. 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. See Table at element.

Century Dictionary and Cyclopedia

1. n. A radioactive substance discovered in pitchblende by M. and Mme. Curie in 1898: named in honor of Poland, the native country Of Mme. Curie. It was found that bismuth precipitated by sulphureted hydrogen from an acid solution of pitchblende carried down with it something possessed of marked radioactivity. The radiation caused electrical conduction in gases, rendered phosphorescent a screen coated with barium platinocyanide, and produced a latent image on a photographic plate protected by a screen opaque to ordinary light The radioactive substance in question was found to resemble bismuth, not only in being thrown down by sulphureted hydrogen, but in furnishing salts soluble in acid but precipitated by water and by ammonia. Partial separation from bismuth was effected, but only to the extent of producing salts of the latter metal of considerably increased radioactivity. Polonium is identical with the radioactive bismuth of Giesel and the radiotellurium of Marckwald. The last-named investigator has gene much farther in the separation of polonium from other substances. By deposition from solution on a plate of metallic bismuth, and by precipitation by stannous chlorid, separating bismuth and in part tellurium, an extremely active product was obtained, but in very small quantity—only 1.5 gram from 2 tons of pitchblende. Afterward, by precipitating all remaining tellurium by hydrazine hydrochlorid, and throwing down the polonium by stannous chlorid, the radioactive substance was obtained in the finally concentrated state as a precipitate weighing only 4 milligrams, or 1 part from 500 million parts of pitchblende. The radioactivity of this final product was, however, extraordinary, one hundredth of a milligram sufficing to render a surface of zinc sulphid phosphorescent so that it could be seen by a large audience. Even in this most concentrated form no directly visible light is given off. The radiation is of the α or non-penetrating type. No gaseous emanation is given off, and activity is not induced on surrounding bodies. The activity of polonium gradually decreases, and falls to half its original value in 143 days. Rutherford has shown that polonium is a disintegration-product of radium and accordingly of uranium. It is the seventh successive product which has been identified as formed from the radium emanation, and is therefore known as radium G.—Polonium rays. See ray.

Wiktionary

1. n. a chemical element (symbol Po) with atomic number 84.

GNU Webster's 1913

1. n. (Chem.) A radioactive chemical element, discovered by M. and MMe. Curie in pitchblende, and originally called radium F. It has atomic number 84 and an atomic weight of 210. It is a very rare natural element, having an abundance in uranium ores only 0.2% that of radium. It is closely related chemically to bismuth. It emits only alpha rays, and has a half-life of 138 days. It is thus more unstable than radium, and a milligram of polonium emits as many alpha particles as 5 grams of radium. Twenty-seven isotopes are known, with atomic masses from 192 to 218. At present a more practical method of preparation than isolation from ores is the preparation by neutron bombardment of bismuth in a nuclear reactor, and it may be obtained commercially by users having an appropriate permit.

WordNet 3.0

1. n. a radioactive metallic element that is similar to tellurium and bismuth; occurs in uranium ores but can be produced by bombarding bismuth with neutrons in a nuclear reactor