Seaborgium-267
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Seaborgium (106Sg) is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized was 263mSg in 1974. There are 12 known radioisotopes from 258Sg to 271Sg and 2 known isomers (261mSg and 263mSg). The longest-lived isotope is 269Sg with a half-life of 3.1 minutes.
This section deals with the synthesis of nuclei of seaborgium by so-called "cold" fusion reactions. These are processes that create compound nuclei at low excitation energy (~10–20 MeV, hence "cold"), leading to a higher probability of survival from fission. The excited nucleus then decays to the ground state via the emission of one or two neutrons only.
The first attempt to synthesise seaborgium in cold fusion reactions was performed in September 1974 by a Soviet team led by G. N. Flerov at the Joint Institute for Nuclear Research at Dubna. They reported producing a 0.48 s spontaneous fission (SF) activity, which they assigned to the isotope 259Sg. Based on later evidence it was suggested that the team most likely measured the decay of 260Sg and its daughter 256Rf. The TWG concluded that, at the time, the results were insufficiently convincing.
The Dubna team revisited this problem in 1983–1984 and were able to detect a 5 ms SF activity assigned directly to 260Sg.
The team at GSI studied this reaction for the first time in 1985 using the improved method of correlation of genetic parent-daughter decays. They were able to detect261Sg (x=1) and 260Sg and measured a partial 1n neutron evaporation excitation function.
In December 2000, the reaction was studied by a team at GANIL, France and were able to detect 10 atoms of 261Sg and 2 atoms of 260Sg to add to previous data on the reaction.
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