An artificially produced, highly unstable, transuranic element with no detectable natural occurrence on Earth. Alpha-alpha correlation, in which the alpha decay of the unknown isotope and that of its alpha decay products are correlated in time, can be used to positively identify short lived isotopes and was used by Ghiorso at the Berkeley Heavy Ion Linear Accelerator in America to identify seaborgium. In 1974, several research groups around the world reported the creation of seaborgium. One group accelerated oxygen-18 ions into a californium-249 target. Seaborgium was created by the reaction ²⁴⁹Cf (¹⁸O , 4n) to give seaborgium-263, which then decayed by alpha emission to rutherfordium, and again to nobelium. The element identified as seaborgium-263 had alpha energies of 9.06 and 9.25MeV with a half-life of 0.9 ±0.2 sec.

Another group of researchers in Russia struck targets of ²⁰⁶Pb, ²⁰⁷Pb and ²⁰⁸Pb with 280MeV ions of ⁵⁴Cr from a cyclotron to produce element 106. It was only named seaborgium in 1994. In 1993 a Russian-American collaboration reported the production seaborgium-265 and -266, which may have halflives up to 30 seconds. The researchers suggest that the unexpectedly long half lives ten times those of other Seaborgium isotopes are due to a recently postulated stabilizing effect of deformed nuclear shells of isotopes with about 162 neutrons and 108 protons. Seaborgium-266 has 160 neutrons, a number expected to make it stable against nuclear fission. They also predict a stable element Z=114 protons with N=184 neutrons and atomic mass A=298, with a filled nuclear shell, with a halflife up to 100 Million years.

The isotope with the longest known halflife of seaborgium is seaborgium-266 with relatively long halflife of between 10 and 30 seconds decaying by alpha decay into rutherfordium-262 which decays by spontaneous fission with a halflife of 47 milliseconds.

Altogether, 5 isotopes of seaborgium are known, all radioactive, and ranging from the alpha/electron capture decaying seaborgium-259 which has a halflife of just 500 milliseconds to the alpha decaying seaborgium-266 with a relatively longish halflife of 20 seconds.

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