Ununquadium

Ununquadium, or eka-lead, is the temporary name of a radioactive chemical element in the periodic table that has the temporary symbol Uuq and has the atomic number 114.

Discovery History
In December 1998, scientists at Dubna (Joint Institute for Nuclear Research) in Russia bombarded a Pu-244 target with Ca-48 ions. A single atom of element 114, decaying by 9.67 MeV alpha-emission with a half-life of 30 s, was produced and assigned to 289114. This observation was subsequently published in January 1999. However, the decay chain observed has not been repeated and the exact identity of this activity is unknown although it is possible that it is due to a meta-stable isomer, namely 289m114.

In March 1999, the same team replaced the Pu-244 target with a Pu-242 one in order to produce other isotopes. This time two atoms of element 114 were produced, decaying by 10.29 MeV alpha-emission with a half-life of 5.5 s. They were assigned as 287114. Once again, this activity has not been seen again and it is unclear what nucleus was produced. It is possible that it was a meta-stable isomer, namely 287m114.

The now-confirmed discovery of element 114 was made in June 1999 when the Dubna team repeated the Pu-244 reaction. This time, two atoms of element 114 were produced decaying by emission of 9.82 MeV alpha particles with a half life of 2.6 s. This activity was initially assigned to 288114 in error, due to the confusion regarding the above observations. Further work in Dec 2002 has allowed a positive reassignment to 289114.


 * $$\,^{244}_{94}\mathrm{Pu} + \,^{48}_{20}\mathrm{Ca} \, \to \,^{292}_{114}\mathrm{Uuq} \,^{*} \to \ ^{289}_{114}\mathrm{Uuq}+ 3 \; ^1_0\mathrm{n} \; $$

Methods of Synthesis
Research in September 2003 demonstrated that element 114 can also be synthesized by bombarding plutonium-242 with calcium-48 ions:


 * $$\,^{242}_{94}\mathrm{Pu} + \,^{48}_{20}\mathrm{Ca} \, \to \,^{290}_{114}\mathrm{Uuq} \,^{*} \to \ ^{288,287,286}\mathrm{Uuq}$$

The isotopes of ununquadium have also been observed in the decay of elements 116 and 118

Chemical Properties
It is expected to be a soft, dense metal that tarnishes in air, with a melting point around 200 degrees Celsius. Experiments aiming at the determination of the chemical properties of element 114 are planned to be undertaken in 2008 by the team at Dubna.

In search for the island of stability - ununquadium-298
According to the island of stability theory, some nuclides around the area of 114 protons and 184 neutrons (i.e. isotope 298114) can be expected to be relatively stable in comparison to the surrounding nuclides. All isotopes of ununquadium synthesized so far are neutron-deficient. This means that they contain significantly fewer neutrons than 184, which is one of the magic number of neutrons that is believed to make the isotope more stable. The isotope 298114 is expected to decay by alpha-emission with a half-life of ~11 minutes.

Difficulty in synthesis
The direct synthesis of ununquadium-298 by a fusion-evaporation pathway is impossible since no known combination of target and projectile can provide 184 neutrons in the compound nucleus.

It has been suggested that such a neutron-rich isotope can be formed by the quasi-fission of a massive nucleus. Such a reaction pathway may occur using the partial fusion of Cm-248 and U-238 nuclei. It may also be possible to generate ununquadium-298, if nuclear transfer reactions can be achieved. One of these reactions may be


 * $$\,^{204}_{80}\mathrm{Hg} + \,^{136}_{54}\mathrm{Xe} \, \to \,^{298}_{114}\mathrm{Uuq} + \,^{40}_{20}\mathrm{Ca} + 2 \; ^1_0\mathrm{n} \; $$