The discovery of element 111 has been officially credited to the GSI laboratory in Darmstadt, Germany, by a joint working party set up by the International Union of Pure and Applied Chemistry (IUPAC) and the sister union for physics (IUPAP). IUPAC has also officially approved a proposal from GSI that element 110 – which was also discovered at the German lab – should be known as darmstadtium (Ds).
Sigurd Hofmann and co-workers first created element 111 in December 1994 by colliding a beam of nickel-64 nuclei with a target made of bismuth-209. The GSI team observed three chains of events that signalled the production and decay of nuclei that contained 111 protons and 161 neutrons.
However IUPAC – the organization that is responsible for assessing such claims – was reluctant to accept this result as conclusive proof for the discovery of a new element because two of the decay chains involved isotopes that were unknown at the time: meitnerium-268, which contains 109 protons, and bohrium-264 (107 protons). The next members of the chain – dubnium-206 (105 protons) and lawrencium-256 (103 protons) – were known but the group was unable to unambiguously measure their decay.
In 2000, the GSI team repeated their experiment with an improved set-up and observed another three decay chains. Moreover, this time Hofmann and co-workers succeeded in detecting isotopes all the way down to lawrencium-256 and the IUPAC-IUPAP working party accepted the new result (P Karol et al. 2003 Pure Appl. Chem. 75 1601).
“IUPAC will now ask us to suggest a name for element 111 and we are in the process of discussing this at GSI,” Hofmann told PhysicsWeb.
However, the working party reported that further results will be needed before credit can be assigned for the discovery of elements 112, 114 and 116. Evidence for these new elements has been seen at GSI and in experiments by Yuri Oganessian’s group at the Dubna Laboratory of Heavy Ion Nuclear Reactions in Russia. Claims by a US team to have created element 118 in 1999 were subsequently retracted after it emerged that the results had been fabricated by one member of the team.