Copernicium is a synthetic radioactive chemical element with the
symbol Cn and atomic number 112. The element was previously known
by the IUPAC systematic element name ununbium, with the symbol Uub.
It was first created in 1996 by the Gesellschaft für
Schwerionenforschung (GSI). It is named after the astronomer
Nicolaus Copernicus.
Copernicium is currently the highest-numbered element to be
officially recognized by the International Union of Pure and
Applied Chemistry (IUPAC). The most stable isotope discovered to
date is 285Cn with a half-life of ˜30 s, although
evidence exists that 285Cn may have a nuclear isomer
with a much longer half-life of 8.9 min. In total, about 75 atoms
of copernicium have been detected using various nuclear reactions.
Recent experiments suggest that copernicium behaves as a typical
member of group 12, demonstrating properties consistent with a
volatile metal.
Copernicium was first created on February 9, 1996, at the
Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, Germany
by Sigurd Hofmann, Victor Ninov et al. This element was created by
firing accelerated zinc-70 nuclei at a target made of lead-208
nuclei in a heavy ion accelerator. A single atom (the second has
subsequently been dismissed) of copernicium was produced with a
mass number of 277.
In May 2000, the GSI successfully repeated the experiment to
synthesise a further atom of Cn-277. This reaction was repeated at
RIKEN using the GARIS set-up in 2004 to synthesise two further
atoms and confirm the decay data reported by the GSI team. The
IUPAC/IUPAP Joint Working Party (JWP) assessed the claim of
discovery by the GSI team in 2001 and 2003. In both cases, they
found that there was insufficient evidence to support their claim.
This was primarily related to the contradicting decay data for the
known isotope 261Rf. However, between 2001 and 2005, the
GSI team studied the reaction
248Cm(26Mg,5n)269Hs, and were able
to confirm the decay data for 269Hs and
261Rf. It was found that the existing data on
261Rf was for an isomer, now designated
261aRf. In May 2009, the JWP reported on the claims of
discovery of element 112 again and officially recognized the GSI
team as the discoverers of element 112. This decision was based on
recent confirmation of the decay properties of daughter nuclei as
well as the confirmatory experiments at RIKEN