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polonium 音标拼音: [pəl'oniəm] n. 钋 钋 polonium n 1: 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 [ synonym: { polonium}, { Po}, { atomic number 84}] Polonium \ Po* lo" ni* um\ ( p[- o]* l[= o]" n[ i^]*[ u^] m), n. [ NL. So named after Poland, in L. form Polonia, one of the discoverers being a Pole.] ( 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. --[ HBCF61] [ Webster 1913 Suppl. PJC] |
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