| 释义 |
WordReference Random House Learner's Dictionary of American English © 2024ra•don /ˈreɪdɑn/USA pronunciation n. [uncountable]- Chemistryan element that is a heavy, odorless inert, radioactive gas;
produced by the decay of radium, it is harmful in high concentrations.
WordReference Random House Unabridged Dictionary of American English © 2024ra•don (rā′don),USA pronunciation n. [Chem.]- Chemistrya chemically inert, radioactive gaseous element produced by the decay of radium: emissions produced by outgassing of rock, brick, etc. are a health hazard. Symbol: Rn;
at. no.: 86;
at. wt.: 222.
Collins Concise English Dictionary © HarperCollins Publishers:: radon /ˈreɪdɒn/ n - a colourless radioactive element of the rare gas group, the most stable isotope of which, radon-222, is a decay product of radium. It is used as an alpha particle source in radiotherapy. Symbol: Rn; atomic no: 86; half-life of 222Rn: 3.82 days; valency: 0; density: 9.73 kg/m³; melting pt: –71°C; boiling pt: –61.7°C
Etymology: 20th Century: from radium + -on |