flerovium, artificially produced radioactive chemical element; symbol Fl; at. no. 114; mass number of most stable isotope 289; m.p., b.p., sp. gr., and valence unknown. Situated in Group 14 of the periodic table, it is expected to have properties similar to those of lead and tin.

Late in Dec., 1998, using plutonium-244 and calcium-48 isotopes provided by the Lawrence Livermore National Laboratory in Calif., Russian scientists employed a cyclotron at the Joint Institute for Nuclear Research in Dubna to produce an atom of element 114 with a mass number of 289. After a surprisingly long existence of 30 sec, the flerovium atom broke down successively into copernicium (element 112), darmstadtium (element 110), and hassium (element 108). The Dubna team created a second isotope of flerovium, Fl-287, with a half-life measured in milliseconds, three months later. In 2011 the International Union of Pure and Applied Chemistry (IUPAC) confirmed the element's synthesis, but the confirmation was based on 2004 Dubna-Livermore work involving collisions of plutonium-242 and calcium-48, which produced Fl-287. The most stable isotope that has been confirmed is flerovium-289 with a half-life of approximately 2.6 sec. The name flerovium, after the Flerov Laboratory of Nuclear Reactions in Dubna, was proposed for the element in 2011 and was adopted by the International Union of Pure and Applied Chemistry (IUPAC) in 2012.

Flerovium is the first element of what might be an "island of stability" among heavy nuclei. Synthetic elements heavier than uranium are generally unstable. Scientists have for some time thought that elements number 114 and above might possess a very stable configuration of neutrons and protons because the nucleus would have a full complement of protons and neutrons making for longer life. The Dubna and Berkeley results seem to be evidence for this, since each isotope having an increasing number of neutrons (toward the optimum 184) has a longer half-life.

See also synthetic elements; transactinide elements; transuranium elements.