Stefan Cwiok

Shell structure of the superheavy elements

Abstract Ground-state properties of the superheavy elements (SHE) with 108 ⩽ Z ⩽ 128 and 150 ⩽ N ⩽ 192 are investigated using both the Skyrem-Hartree-Fock method with a density-independent contact pairing interaction and the macroscopic-microscopic approach with an average Woods-Saxon potential and a monopole pairing interaction. Detailed analysis of binding energies, separation energies, shell effects, single-proton and neutron states, equilibrium deformations, Qα-values, and other observables is given.

Deformed superheavy nuclei

Abstract The study of superheavy nuclei is extended to include deformed nuclei. Even-even nuclei with proton number Z=112−130 and neutron number N=152−210 are considered. The ground-state potential energy, equilibrium deformation, fission barrier, alpha-decay and spontaneous-fission half-lives of the nuclei are studied. It is found that in addition to the “traditional” spherical nuclei, also deformed superheavy nuclei, with half-lives long enough for their detection, are expected to exist.

Shape coexistence and triaxiality in the superheavy nuclei

Superheavy nuclei represent the limit of nuclear mass and charge; they inhabit the remote corner of the nuclear landscape, whose extent is unknown. The discovery of new elements with atomic numbers Z ≥ 110 has brought much excitement to the atomic and nuclear physics communities. The existence of such heavy nuclei hangs on a subtle balance between the attractive nuclear force and the disruptive Coulomb repulsion between protons that favours fission. Here we model the interplay between these forces using self-consistent energy density functional theory; our approach accounts for spontaneous breaking of spherical symmetry through the nuclear Jahn–Teller effect. We predict that the long-lived superheavy elements can exist in a variety of shapes, including spherical, axial and triaxial configurations. In some cases, we anticipate the existence of metastable states and shape isomers that can affect decay properties and hence nuclear half-lives.

Shell corrections of superheavy nuclei in self-consistent calculations

Shell corrections to the nuclear binding energy as a measure of shell effects in superheavy nuclei are studied within the self-consistent Skyrme-Hartree-Fock and relativistic mean-field theories. As a result of the presence of a low-lying proton continuum resulting in a free particle gas, special attention is paid to the treatment of the single-particle level density. To cure the pathological behavior of the shell correction around the particle threshold, a method based on the Greens function approach has been adopted. It is demonstrated that for the vast majority of Skyrme interactions commonly employed in nuclear structure calculations, the strongest shell stabilization appears for Z=124 and 126, and for N=184. On the other hand, in the relativistic approaches the strongest spherical shell effect appears systematically for Z=120 and N=172. This difference probably has its roots in the spin-orbit potential. We have also shown that, in contrast to shell corrections which are fairly independent of the force, macroscopic energies extracted from self-consistent calculations strongly depend on the actual force parametrization used. That is, the A and Z dependence of the mass surface when extrapolating to unknown superheavy nuclei is prone to significant theoretical uncertainties. (c) 2000 The American Physical Society.

Shell structure of the heaviest elements

Abstract The status of experimental and theoretical studies of the heaviest elements is reviewed. The single-particle structure of the heaviest nuclei with 95⩽ Z ⩽111 and 149⩽ N ⩽162 is investigated using the Nilsson-Strutinsky approach with an average Woods-Saxon potential and a monopole pairing residual interaction. Detailed analysis of shell effects, single-proton and -neutron states, equilibrium deformations, binding energies, and Q α -values, is given.

Hyperdeformations and clustering in the actinide nuclei

Abstract Hyperdeformed minima in the actinide nuclei are discussed with the shell correction approach. Calculations are carried out in a large deformation space which makes it possible to provide a realistic description of very elongated shapes up to the fission saddle point. It is shown that the density distribution at the third, hyperdeformed minimum resembles a di-nucleus consisting of a nearly-spherical nucleus around the doubly-magic nucleus 132Sn, and a well-deformed fragment from the neutron-rich A ≈ 100 region.

Structure of superdeformed states in AuRa nuclei

Abstract Energies of superdeformed states in nuclei around 192 Hg are calculated using the Strulinsky shell correction method with an average Woods-Saxon potential and a monopole pairing force. The influence of various terms in the model hamiltonian on the excitation energy of the superdeformed minimum is analysed. The systematics of calculated excitation energies of shape-isomeric minima and barrier heights in even-even HgRa nuclei are given together with predictions for one-quasiparticle band-head energies in odd-A Au, Hg, Tl, Pb and Bi nuclei. Possible occurrence of hyperdeformed states in very neutron-deficient PoRa isotopes is investigated. It is shown that the presence of these exotic configurations is strongly related to the magnitude of pairing correlations at strongly elongated shapes. Finally, the role played by reflection-asymmetric deformations at superdeformed shapes is discussed.

Study of the potential energy of “octupole”-deformed nuclei in a multidimensional deformation space

Abstract The collective potential energy of even-even “octupule”-deformed nuclei is studied in a multidimensional deformation space in both radium and barium regions. This energy is calculated by the macroscopic-microscopic method, with the Yukawa-plus-exponential model taken for the macroscopic part and the Strutinski shell correction (based on the Woods-Saxon single-particle potential) used for the microscopic part of the energy. The deformations βλ of all multipolarity degrees: λ = 2, 3, …, 7 (or even 8) are treated as independent variables. The multipolarities: λ = 5, 6 and 7, usually omitted or treated in an average way up to now, are found to be important for the properties of the nuclei.

Two Fission Modes of the Heavy Fermium Isotopes

The collective potential energy of even-even heavy isotopes of fermium is studied. The energy is calculated using the macroscopic-microscopic method. The Yukawa-plus-exponential model is used for the macroscopic part of the energy and the Strutinski shell correction, based on the Woods-Saxon single-particle potential, is taken as the microscopic part. The energy is analyzed in the five-dimensional deformation space, described by the usual deformation parameters: βλ(λ = 2, 3, 4, 5, 6). The results explain in a natural way the simultaneous appearance of both fission modes (with a low and high total kinetic energy of the fragments), observed recently for 258Fm. The important role of the reflection-asymmetric deformations of the nucleus in this explanation is stressed.

Do the superheavy nuclei really form an island

Abstract The spontaneous-fission and alpha-decay half-lives are calculated for even-even nuclei with Z = 104−110. Rather large values of the lifetimes are obtained, indicating that the usual peninsula of relatively long-lived nuclides may extend further than has been believed. Due to this, the region of hypothetical superheavy nuclei (around the nucleus 298 114) may constitute a part of the peninsula, rather than form an island separated from it by a region of deep instability.