a superheavy, synthetic radioactive element with a very short half-life. Symbol: Rg; atomic number: 111.
- Formerly u·nu·nun·i·um [uh-nuh-nuhn-ee-uhm], /ə nəˈnʌn i əm/, el·e·ment 111 .
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Scientific definitions for roentgenium
An artificially produced radioactive element with a mass number of 280. Its most stable known isotope has a half-life of 3.6 seconds. Atomic number 111. See Periodic Table.
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