astatine

[as-tuh-teen, -tin]
noun Chemistry.
a rare element of the halogen family. Symbol: At; atomic number: 85.

Origin:
1945–50; < Greek ástat(os) not steadfast, unstable (see astatic) + -ine2

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World English Dictionary
astatine (ˈæstəˌtiːn, -tɪn)
 
n
a radioactive element of the halogen series: a decay product of uranium and thorium that occurs naturally in minute amounts and is artificially produced by bombarding bismuth with alpha particles. Symbol: At; atomic no: 85; half-life of most stable isotope, 210At: 8.1 hours; probable valency: 1,3,5, or 7; melting pt: 302°C; boiling pt: 337°C (est)
 
[C20: from Greek astatos unstable (see astatic) + -ine²]

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Medical Dictionary

astatine as·ta·tine (ās'tə-tēn', -tĭn)
n.
Symbol At
A radioactive halogen element. Its longest lived isotope has a mass number of 210 and a half-life of 8.1 hours. Atomic number 85; melting point 302°C; boiling point 337°C; valence probably 1, 3, 5, 7.

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Science Dictionary
astatine   (ās'tə-tēn')  Pronunciation Key 
Symbol At
A highly unstable, rare, radioactive element that is the heaviest of the halogen elements. Its most stable isotope has a half-life of 8.3 hours. Atomic number 85; melting point 302°C; boiling point 337°C; valence probably 1, 3, 5, 7. See Periodic Table.
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Encyclopedia Britannica
Encyclopedia

astatine

radioactive chemical element and the heaviest member of the halogen elements, or Group 17 (Group VIIa) of the periodic table. Astatine, which has no stable isotopes, was first synthetically produced (1940) at the University of California by American physicists Dale R. Corson, Kenneth R. MacKenzie, and Emilio Segre, who bombarded bismuth with accelerated alpha particles (helium nuclei) to yield astatine and neutrons. Naturally occurring astatine isotopes have subsequently been found in minute amounts in the three natural radioactive decay series, in which they occur by minor branching (astatine-218 in the uranium series, astatine-216 in the thorium series, and astatine-215 and astatine-219 in the actinium series). Thirty-three isotopes are known; astatine-210, with a half-life of 8.3 hours, is the longest lived.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
One of his major contributions was the observation of the spectra of astatine.
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