WordNet (r) 3.0 (2006):

roentgenium
    n 1: a radioactive transuranic element [syn: roentgenium,
         Rg, element 111, atomic number 111]

The Elements (07Nov00):

roentgenium
Symbol: Rg
Atomic number: 111
Atmic weight: 280
Roentgenium is placed as the heaviest member of the group 11 (IB)
elements,
although a sufficiently stable isotope is not known at this time that
would
allow its position as a heavier homologue of gold to be confirmed.
Roentgenium was first observed in 1994 and several isotopes have been
synthesized since its first discovery. The most stable known isotope is
280Rg with a half-life of ~4 seconds.
Roentgenium was officially discovered by Peter Armbruster,
Gottfried Münzenberg, and their team working at the Gesellschaft für
Schwerionenforschung (GSI) in Darmstadt, Germany on December 8, 1994.
Only three atoms of it were observed (all 272Rg), by the cold fusion
between
nickel ions and a bismuth target in a linear accelerator.
In 2001, the IUPAC/IUPAP Joint Working Party (JWP) concluded that there
was insufficient evidence for the discovery at that moment in time.
The GSI team repeated their experiment in 2000 and detected a further
3 atoms. In their 2003 report, the JWP decided that the GSI team should
be
acknowledged as the discoverers.
The name roentgenium (Rg) was proposed by the GSI team in honor of the
German physicist Wilhelm Conrad Röntgen, and was accepted as a permanent
name on November 1, 2004. Previously the element was known under the
temporary IUPAC systematic element name unununium, Uuu.