Element 106, seaborgium, has an electron configuration of [Rn] 5f14 6d4 7s2 and a predicted density of 35 g·cm−3. It was first synthesized in 1974 by bombarding a target of californium-249 with oxygen-18 ions, producing seaborgium-263 which decays by alpha emission with a half-life of 0.9 seconds, with its discovery reported by scientists at the Joint Institute for Nuclear Research in Dubna, USSR and the Lawrence Berkeley Laboratory.

1. 106
Seaborgio – Seaborgium
Mass: [269] u
Electron configuration: [Rn] 5f14
6d4
7s2
Melting point: unknown
Boiling point: unknown
Density: 35 (predicted) g·cm−3
Discovery: Scientists working at the Joint Institute for Nuclear Research in
Dubna, USSR reported their discovery of element 106 in June 1974. Synthesis was
also reported in September 1974 at the Super HILAC accelerator at the Lawrence
Berkeley Laboratory by a joint Lawrence Berkeley/Lawrence Livermore collaboration
led by Albert Ghiorso and E. Kenneth Hulet. They produced the new nuclide 263Sg
by bombarding a target of 249Cf with 18O ions. 249Cf + 18O→263Sg. This nuclide
decays by α emission with a half-life of 0.9 ± 0.2 sec.