Extension of the nuclear landscape to hyperheavy nuclei

The properties of hyperheavy nuclei and the extension of nuclear landscape to hyperheavy nuclei are extensively studied within covariant density functional theory. Axial reflection symmetric and reflection asymmetric relativistic Hartree-Bogoliubov (RHB) calculations are carried out. The role of triaxiality is studied within triaxial RHB and triaxial relativistic mean field + BCS frameworks. With increasing proton number beyond Z approximate to 130 the transition from ellipsoidal-like nuclear shapes to toroidal ones takes place. The description of latter shapes requires the basis which is typically significantly larger than the one employed for the description of ellipsoidal-like shapes. Many hyperheavy nuclei with toroidal shapes are expected to be unstable toward multifragmentation. However, three islands of stability of spherical hyperheavy nuclei have been predicted for the first time in Afanasjev et al. [Phys. Lett. B 782, 533 (2018)]. Proton and neutron densities, charge radii, neutron skins, and underlying shell structure of the nuclei located in the centers of these islands have been investigated in detail. Large neutron shell gaps at N = 228, 308, and 406 define approximate centers of these islands in neutron number. On the contrary, large proton gap appear only at Z = 154 in the (Z approximate to 156, N approximate to 310) island. As a result, this is the largest island of stability of spherical hyperheavy nuclei found in the calculations. The calculations indicate the stability of the nuclei in these islands with respect to octupole and triaxial distortions. The shape evolution of toroidal shapes along the fission path and the stability of such shapes with respect to fission have been studied. Fission barriers in neutron-rich superheavy nuclei are studied in triaxial RHB framework; the impact of triaxiality on the heights of fission barriers is substantial in some parts of this region. Based on the results obtained in the present work, the extension of nuclear landscape to hyperheavy nuclei is provided.