Adam Sobiczewski

Ground-state properties of the heaviest nuclei analyzed in a multidimensional deformation space

Abstract Ground-state properties of the heaviest nuclei are analyzed in the three-dimentional deformation space {βλ}, γ = 2, 4, 6. Effects of using even larger spaces are explored. Deformation, mass, alpha-decay energy and half-life of even-even nuclei with proton number Z = 90−114 and neutron number N = 136−168 are studied. The ground-state energy of the nuclei is treated in the macroscopic-microscopic approach. It is found that the use of a larger deformation space (in particular, a proper inclusion of the deformation β6 in this space) significantly improves the description of experimental results and, also significantly, changes the predictions for nuclei not yet observed.

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.

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.

Shell effects in the properties of the heaviest nuclei

Abstract Shell effects are extracted in the following experimental quantities: mass, alpha-decay energy and half-life, spontaneous-fission barrier and lifetime. The heaviest even-even nuclei known experimentally, with Z = 92–108 are considered. This extraction is based on the Yukawa-plus-exponential model, used for the description of the macroscopic part of nuclear mass. The effects are found to be large; e.g. they increase the spontaneous-fission half-life of some nuclei by about 15 orders of magnitude. The sensitivity of these effects to changing the macroscopic model is discussed.

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.

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.

PROPERTIES OF NUCLEI AT THE THIRD-MINIMUM DEFORMATION*

Abstract Potential-energy surfaces of heavy nuclei in the Ra-Th region are calculated by the macroscopic-microscopic method using the modified oscillator potential. A rather large region of nuclei with a third minimum along the fission trajectory is found. This minimum appears at a very large quadrupole deformation, e 2 ∼ 0.9, and has a stable octupole deformation with e 3 ∼ 0.2. It is found that in addition to the deformation parameters e 2 , e 3 , e 4 and e 5 it is important to include also e 6 . Particular attention is paid to the Th-isotopes, for which experimental evidence for the existence of a third minimum in the fission barrier has been found. Properties like the moment of inertia, the decoupling parameter and the energy splitting between positive- and negative-parity rotational bands are studied.

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.

THE MOMENT OF INERTIA AND THE ENERGY GAP OF FISSION ISOMERS

Abstract The moments of inertia and the energy gaps of protons and neutrons have been calculated within the pairing formalism with Nilsson wave functions for different prolate shapes of doubly even nucleides from radium to curium. Two different assumptions — a constant pairing strength G = const, and one that increases proportionally to the surface area G ∝ S — are investigated. The results are compared to available data for the ordinary ground-state shapes and for the shapes of the second minimum associated with fission isomers. The calculations account for the experimental results in the second minimum as well or even better than for the ground-state minimum. They support the theoretical description of the isomers as prolate shapes with a ratio of axes of about 1:2. The experimental data are not sufficiently accurate or numerous to decide which of the two assumptions about the pairing strength is the most realistic one.