Z. Szymanski

On the nuclear structure and stability of heavy and superheavy elements

Abstract Nuclear potential energy surfaces as a function of deformations are calculated on the basis of a modified oscillator model. In particular, quadrupole ( P 2 ) and hexadecapole ( P 4 ) deformations are considered. The average behavior of the surface is normalized to that of a liquid drop through the employment of a generalized Strutinsky prescription. In this way a synthesis of the single-particle model and the liquid-drop model is obtained. Lowest minima in the potential energy surfaces give the ground state masses and distortions. These results compare extremely well with experimental data. Spontaneous fission half-lives are also obtained. The inertial parameters associated with fission barrier penetration are derived empirically as well as by a microscopic model. Shape (fission) isomeric states are also found. Their N and Z dependence in the present model are discussed and results tabulated. The calculations are extended to the predicted superheavy region around Z = 114 and N = 184. The total overall stability with respect to alpha and beta decay, and spontaneous fission is found to be most favorable in the vicinity of Z = 110 and N = 184. Detailed diagrams and tables are exhibited.

Nuclear shell structure at very high angular momentum

Abstract A cranked modified-oscillator model (with triaxial shape coordinates ϵ and γ) is used to study the nuclear potential-energy surface (based on a Strutinsky type of shell correction method) for very high angular momenta (30 ≦ I ≦ 100). For this region of spin, pair correlation is assumed to have collapsed. The influence of rapid rotation on the shell structure has been studied in the light and heavy rare-earth region as well as the Te-Ba region. Preliminary studies have also been made in the regions of superheavy and light nuclei. The possible occurrence of yrast traps is discussed.

On the spontaneous fission of nuclei with Z near 114 and N near 184

Abstract Theoretical calculations of the potential energy surface as a function of quadrupole and hexadecapole distortion parameters are reported for super-heavy nuclei with Z near 114 and N near 184. Estimates of spontaneous fission half-lives indicate a sizable island of relative stability in the vicinity of these closed-shell nucleon numbers.

Islands of high-spin yrast isomers

Abstract The variation in nuclear deformation with angular momentum is considered in a wide region of nucleides, 34 ≦ Z ≦ 94. Cases of spin trajectories involving rotation around a symmetry axis, oblate or prolate, are surveyed as likely candidates for yrast traps. A few representative yrast spectra are also given and trap mechanisms discussed.

Equilibrium deformations of nuclei in the transuranic region

Abstract The equilibrium deformations and quadrupole moments of even deformed nuclei in the transuranic region are calculated on the basis of wave functions that take into account a pairing interaction through the “superconductivity” formalism. The results obtained theoretically are found to be in reasonable agreement with experiment. The relation between the potential and density deformation parameter is also discussed.

Microscopic calculations of the inertial mass parameter for fissioning nuclei

Abstract Inertia mass parameter B in a fissioning nucleus is calculated. The method of calculation is based on the assumption of adiabatic collective motion in the fission degree of freedom. Resulting values for B are 4 to 11 times larger than those obtained from the liquid-drop model estimates. It turns out that the inertial parameter increases almost linearly with nuclear deformation. It also appears to be a sensitive function of the pairing force strength. Rough estimates of the coupling between quadrupole and hexadecapole modes seem to indicate that it may modify considerably the obtained results. The calculations are extended to the predicted superheavy region connected with Z ≈ 114.

Survey of Collective and Single-Particle Features in the Yrast Domain of the A ∼ 150 Nuclei

Collective properties at low and high spin for nuclei with Z 64 and N 82 are calculated on the basis of deformed single-particle potentials. The calculations are confronted with the available experimental data like low-lying octupole bands, rotational bands of transitional nuclei with N 90 and evidence for collectivity in high-spin single-particle spectra. In the latter collective triaxiality and collective rotation perpendicular to the aligned spin are investigated by cranking and RPA. Predicted regimes of different shapes and shape transitions at high spins are presented. In a gamma cascade calculation, it is shown how the calculated regimes for 152Dy are consistent with the measured inclusive spectrum.

Hexadecapole equilibrium distortions of nuclei

Abstract Theoretical calculations of nuclear deformed shell model equilibrium shapes in the rare earth and actinide regions have yielded hexadecapole distortions in good agreement with recent experimental shapes determined from (α, α′) scattering analysis. Pairing, Coulomb and polarisation effects are included in the calculations.

Search for the yrast traps in neutron deficient rare earth nuclei

Abstract The yrast energies are calculated for some neutron-deficient spherical or oblate rare earch nuclei in the domain of high angular momentum I . Predictions are made for some yrast traps in the region of I ≲ 40.

Particle-hole structure of nuclear isomers at high angular momenta

Abstract Yrast states are calculated for a number of nuclei with 62 ≦ Z ≦ 72 and 80 ≦ N ≦ 90 on the basis of the deformed Woods-Saxon potential. Particular emphasis is put on the search for the yrast traps. Some new traps, mainly around the neutron number N = 86 nuclei are predicted in the light rare earth region. In particular, five high spin isomers are predicted in the nucleus 152 Dy and their magnetic moments are calculated. Calculations are limited to the axially symmetric nuclear deformations.