EPJ A - Existence of neutron-rich superheavy element 116 confirmed

Details

Published on 10 August 2012

The synthesis of a superheavy element with the proton number Z=116 has been studied at the velocity filter SHIP of GSI in Darmstadt using a ⁴⁸Ca beam on radioactive ²⁴⁸Cm targets. At excitation energies of the compound nuclei of 40.9 MeV, four decay chains were measured, which were assigned to the isotope 292116 produced in 4n channel, and one chain, which was assigned to ²⁹³116 produced in 3n channel. All chains are terminated by spontaneous fission decays of either ²⁷⁷Hs or ²⁸⁴Cn isotopes on the shoreline of the neutron-rich superheavy island.

Measured cross-sections of 3.4 pb and 0.9 pb, respectively, and decay data of the chains confirm with data measured previously at the Flerov Laboratory of Nuclear Reactions (FLNR) in Dubna. As a new result, one alpha-decay chain was measured, which terminates after four alpha decays by spontaneous fission. The alpha energies of the second to fourth decay are considerably higher than those measured for the alpha decays of ²⁸⁹114, ²⁸⁵Cn, and ²⁸¹Ds and the spontaneous fission half-life is significantly longer than that of ²⁷⁷Hs measured in previous experiments.

Possible assignments and role of isomeric states are discussed in the frame of excited quasiparticle states of nuclei populated in the decay chain from ²⁹³116.

The experience gained in this experiment will serve as a basis for future experiments aiming to study still heavier elements at the velocity filter SHIP. For this purpose, related very detailed experimental study of sources of background fission events was also carried out and published in a related article. Here it was shown that such events occur mainly in connection with transfer reactions leading to target-like residues having half-lives similar to the ones of superheavy isotopes from respective fusion reactions.