Production of the Heaviest Elements 107 to 109, Limitations, and Prospects to go Beyond

Abstract

In recent years isotopes of the elements 107 to 109 were discovered. Together with studies on the isotopes of the elements 104–106 it was established that beyond element 105 the main decay mode for isotopes with (N–Z) = (47–49) is α-decay. The trend of strongly increasing instability against spontaneous fission for the heaviest elements is broken. The isotope^{260, 106} has a partial halflife against spontaneous fission of about 7 ms, which is to be compared to a halflife of 8 ms for^{256, 104}. The long α-chains detected allow to determine the absolute masses. Together with macroscopic mass values the shell correction energies are obtained. It is shown that the fission barrier for the (N–Z) = 48-isotopes of the heaviest elements stay constant at a value of about 6 MeV, in spite of vanishing macroscopic fission barriers. From an analysis of the mass values and the spontaneous fission halflives it follows, that the heaviest isotopes detected are protected against spontaneous fission by a single humped narrow fission barrier, which is due to shell corrections, e.g. the isotope²⁶⁰ 106 is shell stabilized by 15 orders of magnitude in its halflife against spontaneous fission. Paskevich et al. and Møller et al. independently predict the nuclei to be deformed and to have a strong negative ß4 deformation (sausage-like). The isotopes investigated are shell stabilized isotopes of superheavy elements (SHE), in the sense that SHE are elements unstable within macroscopic models but stabilized by shell effects to halflives long enough to be detected still.