Ununbium

Ununbium, or eka-mercury, is a temporary IUPAC systematic element name for a chemical element in the periodic table that has the temporary symbol Uub and the atomic number 112. Element 112 is one of the superheavy elements. Following periodic trends, one might expect a liquid metal more volatile than mercury. Initial experimental work indicated radon-like properties and theoretical considerations also point to properties more similar to a noble gas than to mercury. . More recent experiments have indicated that element 112 behaves as a typical memeber of group 12, demonstrating properties consistent with a volatile metal.

Discovery
Ununbium was first created on February 9, 1996 at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, Germany. 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 ununbium was produced with a mass number of 277.


 * $$\,^{70}_{30}\mathrm{Zn} + \,^{208}_{82}\mathrm{Pb} \to \,^{278}_{112}\mathrm{Uub} ^{*} \to \,^{277}_{112}\mathrm{Uub} + \,^{1}_{0}\mathrm{n}$$

In May 2000, the GSI successfully repeated the experiment to synthesise a further atom of Uub-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 Joint Working Party (JWP) is currently assessing the validity of the claim of discovery by the GSI team.

Synthesis of Other Isotopes
In 1998, the team at the Flerov Laboratory of Nuclear Research began a research program using Ca-48 nuclei in "warm" fusion reactions leading to superheavy elements (SHE's). In March 1998, they claimed to have synthesised the element (2 atoms) in the reaction:


 * $$\,^{238}_{92}\mathrm{U} + \,^{48}_{20}\mathrm{Ca} \to \,^{286}_{112}\mathrm{Uub} ^{*} \to \,^{283}_{112}\mathrm{Uub} + 3\, ^{1}_{0}\mathrm{n}$$

The product, 283Uub, had a claimed half-life of 5 min, decaying by spontaneous fission (SF). The reaction was successfully repeated by the same team in Jan 2003, confirming the decay mode and half life. However, other teams have failed to repeat this reaction and some confusion has grown surrounding the exact identity of this SF activity. This confusion has cast some doubt on the initial chemical experiments which indicated radon-like properties.

The reaction was repeated in 2003-2004 using a slightly different set-up. This time, 283Uub was found to decay by emission of a 9.53 MeV alpha-particle with a half-life of 4 seconds. 282Uub was also observed in the 4n channel.

In 2006, this decay data was confirmed by a joint PSI-FLNR experiment aimed at probing the chemical properties of ununbium. Two atoms of 283Uub were observed in the decay of the parent 287Uuq nuclei. The experiment indicated that contrary to previous experiments, element 112 behaves as a typical member of group 12, demonstrating properties of a volatile metal.

In an independent experiment, the team at GSI successfully repeated the reaction in May 2005 (1 atom) and in Jan 2007 (3 atoms). Their results fully corroborated the alpha-decay data and further indicated a SF branch for 283Uub.

As such, the 5 min SF activity is still unidentified. It is possible that it refers to a meta-stable isomer, namely 283mUub, whose yield is dependent on the exact production methods.

Element 112 has also been observed as decay products of elements 114, 116 and 118.

As an example, in May 2006, in the JINR synthesis of this element was confirmed by the identification of the isotope 282Uub as a final product of this series of alpha decays:


 * $$\,^{294}_{118}\mathrm{Uuo} \to \,^{290}_{116}\mathrm{Uuh} \to \,^{286}_{114}\mathrm{Uuq} \to \,^{282}_{112}\mathrm{Uub}$$

It was found that the final nucleus undergoes spontaneous fission.

In the synthesis of 289114 and 293116, a 9.15 MeV alpha-decaying activity has been detected with a half-life of 8.9 minutes. Although unconfirmed in recent experiments, it is highly possible that this is associated with a meta-stable isomer, namely 285m112.

Proposed Names
It has been rumoured that scientists at GSI have considered using the names Astrium, Wixhausium (Wi) and Helmholtzium (Hh) for element 112. However, there is no evidence at all in the public domain that either Helmholtzium or Astrium have ever been mentioned by the group. References to Wixhausium also appear to be in error. An article appearing in the 'Darmstadter Echo' (written in German) does mention Wixhausium, but the article actually says that whilst they were celebrating the naming of element 110 as Darmstadtium, it could have been named Wixhausium as this name had been proposed for the element but had ultimately been rejected in favour of the current name. It should be noted that the JWP of IUPAC/IUPAP is currently assessing the priority of claims for discovery of element 112 by the teams from GSI, RIKEN and FLNR. Once the JWP has published it report in PAC, the formal naming process can begin, so it is plausible that the GSI team will not even be allowed to officially name ununbium.