Janusz Skalski

Potential energy and spontaneous-fission half-lives for heavy and superheavy nuclei

Abstract The ground-state potential energy and the spontaneous-fission half-lives are studied in a wide region of even-even nuclei with the proton number Z = 100–130 and the neutron number N = 140–210. The potential energy is calculated by the macroscopic-microscopic method. The fission half-lives are obtained in a static as well as in a dynamic ways.

Non-axial shapes in spontaneous fission of superheavy nuclei

Abstract We test the importance of non-axial nuclear shapes in spontaneous fission of heavy and superheavy even-even nuclei from the region around a hypothetical doubly magic nucleus 298 114. Fission half-lives are calculated by finding dynamical fission paths as dictated by the least WKB action principle with the macroscopic-microscopic energy and the cranking inertial parameters. Results show that the effects of non-axial shapes on the fission process are weakened by the inertia tensor and become important only for the heaviest elements with Z ⩾ 120.

Shape coexistence and low-lying collective states in A ≈ 100 Zr nuclei

Abstract Collective quadrupole and octupole excitations in even 94−00 Zr nuclei are studied within the fully microscopic generator-coordinate method using a basis generated by the selfconsistent Hartree-Fock BCS method. Results with the effective interaction SkM ∗ correctly describe the experimentally observed spherical to deformed shape transition at A = 100. Properties of low-lying O + , 2 + and 3 − states are analysed. The measured B (E3) value of 65 single-particle units in 96 Zr is underestimated in our calculations. Various aspects of our theoretical approach are discussed, including Skyrme force parametrization, treatment of pairing and one- versus two-dimensional description of octupole excitations.

Octupole correlations in superdeformed mercury and lead nuclei: A generator-coordinate method analysis

Abstract Axial and non-axial octupole excitations built on superdeformed states of zero spin in 192,194 Hg and 194 Pb nuclei are studied within the fully microscopic generator-coordinate method using selfconsistent Hartree-Fock BCS states as a basis. Results with the effective interaction SkM ∗ predict vibration energies of 1.9–2.5 MeV, B (E3) values of 15–37 single-particle units and unusually large B (E1) transition rates up to 0.02 W.u. Calculations including both octupole modes with K = 0 and K = 2 indicate that these modes couple weakly.

Antiprotonic studies of nuclear neutron halos

Nuclear capture of antiprotons from atomic states is studied. Partial widths for single-nucleon capture events leading to cold residual nuclei are calculated. Recent CERN experiments that compare the neutron and proton captures are analyzed. Nuclear density distributions at the extreme nuclear surface are calculated and tested against the experimental results. {copyright} {ital 1996 The American Physical Society.}

Properties and decay of actinide and transactinide nuclei

Abstract Recent theoretical results on the properties of the heaviest nuclei are presented and discussed. The main attention is paid to half-lives and to effects of the shell structure of these nuclei on the half-lives.

Nuclear fission with mean-field instantons

We present a description of nuclear spontaneous fission, and generally of quantum tunneling, in terms of instantons, that is, periodic imaginary-time solutions to time-dependent mean-field equations. This description allows comparisons to be made with the more familiar generator coordinate (GCM) and adiabatic time-dependent Hartree-Fock (ATDHF) methods. It is shown that the action functional whose value for the instanton is the quasiclassical estimate of the decay exponent fulfills the minimum principle when additional constraints are imposed on trial fission paths. In analogy with mechanics, these are conditions of energy conservation and the velocity-momentum relations. In the adiabatic limit, the instanton method reduces to the time-odd ATDHF equation, with collective mass including the time-odd Thouless-Valatin term, while the GCM mass completely ignores velocity-momentum relations. This implies that GCM inertia generally overestimates the instanton-related decay rate. The very existence of the minimum principle offers hope for a variational search for instantons. After the inclusion of pairing, the instanton equations and the variational principle can be expressed in terms of the imaginary-time-dependent Hartree-Fock-Bogoliubov (TDHFB) theory. The adiabatic limit of this theory reproduces ATDHFB inertia.

Coupling of the giant dipole resonance to low lying octupole modes - generator coordinate method study

Abstract The effect on the properties of low lying octupole modes of the coupling with the giant dipole resonance is studied within the Generator Coordinate Method. Results are presented for 152 Sm which is deformed in its ground state and for the superdeformed state of 190 Hg. A basis is first generated by Hartree-Fock+BCS calculations with constraints on the octupole and dipole moments. The same Skyrme SkM ∗ effective interaction used in the mean field is then diagonalised by the GCM. For the octupole K = 0 mode, the effect of the coupling is marginal and the dipole properties of low lying states are satisfactorily described by pure octupole calculations. For the K = 1 mode, the dipole-octupole coupling slightly reduces the E1 transition strength.

Mean-field on a 3-dimensional mesh

In this talk we present the main ingredients of the mean-field method based on the Skyrme effective interactions that we have developed in the last years. In particular, we show how the correlations beyond the mean-field approach are introduced. The range of applications of the method is illustrated by the studies of the superdeformed nuclei, the deformed nuclei up to the drip lines and of the influence of the giant dipole resonance on the dipole transitions between the low lying levels in the deformed nuclei.

Properties of the nucleon-nucleon interaction leading to a standing wave instability in symmetric nuclear matter

We examine a recently proposed nucleon-nucleon interaction, claimed by its authors both realistic and leading to a standing wave instability in symmetric nuclear matter. Contrary to these claims, we find that this interaction leads to a serious overbinding of 4He, 16O and 40Ca nuclei when the Hartree-Fock method is properly applied. The resulting nuclear densities contradict the experimental data and all realistic Hartree-Fock results.