Spontaneous fission modes and lifetimes of superheavy elements in the nuclear density functional theory

Background: The reactions with the neutron-rich Ca-48 beam and actinide targets resulted in the detection of new superheavy (SH) nuclides with Z = 104-118. The unambiguous identification of the new isotopes, however, still poses a problem because their alpha-decay chains terminate by spontaneous fission (SF) before reaching the known region of the nuclear chart. The understanding of the competition between alpha-decay and SF channels in SH nuclei is, therefore, of crucial importance for our ability to map the SH region and to assess its extent. Purpose: We perform self-consistent calculations of the competing decay modes of even-even SH isotopes with 108 <= Z <= 126 and 148 <= N <= 188. Methods: We use the state-of-the-art computational framework based on self-consistent symmetry-unrestricted nuclear density functional theory capable of describing the competition between nuclear attraction and electrostatic repulsion. We apply the SkM* Skyrme energy density functional. The collective mass tensor of the fissioning superfluid nucleus is computed by means of the cranking approximation to the adiabatic time-dependent Hartree-Fock-Bogoliubov (HFB) approach. This paper constitutes a systematic self-consistent study of spontaneous fission in the SH region, carried out at a full HFB level, that simultaneously takes into account both triaxiality and reflection asymmetry. Results: Breaking axial symmetry and parity turns out to be crucial for a realistic estimate of collective action; it results in lowering SF lifetimes by more than 7 orders of magnitude in some cases. We predict two competing SF modes: reflection symmetric modes and reflection asymmetric modes. Conclusions: The shortest-lived SH isotopes decay by SF; they are expected to lie in a narrow corridor formed by (28)0Hs, (284)Fl, and (284)(118)Uuo that separates the regions of SH nuclei synthesized in cold-fusion and hot-fusion reactions. The region of long-lived SH nuclei is expected to be centered on (294)Ds with a total half-life of similar to 1.5 days. Our survey provides a solid benchmark for the future improvements of self-consistent SF calculations in the region of SH nuclei. DOI: 10.1103/PhysRevC.87.024320