M.S. Weiss

Self-consistent study of triaxial deformations: Application to the isotopes of Kr, Sr, Zr and Mo

Abstract Self-consistent mean-field calculations of deformation energy surfaces have been performed for more than 30 exotic isotopes of the Kr, Sr, Zr and Mo elements. Our calculations extend to the proton drip line. We investigate the triaxial stability of the deformed ground states in the deformation regions N ≈ 38 and N ≈ 60. The results are in good agreement with the observed trends.

An improved pairing interaction for mean field calculations using skyrme potentials

Abstract A zero-range interaction is proposed to calculate nuclear pairing at the Fermi surface. The results of Skyrme calculations using the zero range pairing interaction are compared with those using the constant G model for the pairing, as well as with those of a finite-range calculation. Particular attention is paid to the region of superdeformation and fission.

Self-consistent calculation of charge radii of Pb isotopes

Abstract Charge radii of lead isotopes are calculated with the HF plus BCS method, using Skyrme forces (SkM∗, SIII and SGII) for the mean field. When these forces are combined with a seniority pairing force, all of them fail to reproduce the experiment. Neither higher-order corrections, nor ground-state correlations due to the collective modes can resolve the discrepancy. However, by introducing a density-dependent pairing force quenched inside the nucleus, one can explain the odd-even staggering as well as the large kink of charge radii at 208Pb when plotted versus A.

Superdeformation and shape isomerism at zero spin

Abstract Microscopic Hartree-Fock plus BCS calculations in three-dimensional coordinate space are performed to obtain potential energy surfaces in order to analyse shape isomerism in mass regions other than the well-documented fission isomers in the actinides. Many isotopes of platinum, mercury and osmium exhibit a second minimum with a large deformation and are thus candidates for shape isomerism. The same feature also occurs around the 68 Ni nucleus. The most promising candidates for experimental verification are delineated.

Quadrupole collective correlations and the depopulation of the superdeformed bands in mercury

Abstract Fully self-consistent generator coordinate method calculations have been performed on a basis of quadrupole constrained Hartree-Fock plus BCS wave functions for the five even mercury isotopes 190–198 Hg. The gcm results support conclusions drawn from previous HF + BCS calculations. The predicted evolution of superdeformed band head (shape isomer) properties as a function of the neutron number is consistent with the data. Using calculated transition matrix elements, we evaluate in-band versus out-of-band quadrupole decay and explain the sudden termination of the super-deformed band.

Super-deformation and shape isomerism: Mapping the isthmus☆

Abstract An isthmus of shape isomerism is mapped in the region of recently discovered super-deformation by computing well depths and excitation energies for 148 nuclei in fully microscopic, HF-BCS calculations. In all instances in which super deformed isomers have been experimentally observed, our calculations have predicted well deformed second minima with excitation energies and rigid body moments of inertia consistent with the data. Predictions for additional isomers are inferred from the present work.

BULK COMPRESSION DUE TO SURFACE TENSION IN HARTREE-FOCK, THOMAS-FERMI AND DROPLET-MODEL CALCULATIONS*

Hartree-Fock calculations for hypothetical spherical nuclei with N = Z are carried out without the inclusion of Coulomb interactions, spin-orbit terms or pairing in order to study one simple property of such systems: the bulk compression due to surface tension. We find that the behavior expected from Thomas-Fermi and droplet calculations manifests itself for medium and heavy nuclei, and the relation between microscopic and macroscopic descriptions is further illustrated by carrying the calculations to extremely large mass numbers. Deviations of the lighter nuclei from the simplest form of the macroscopic theory are discussed and various improvements are considered.

From ground state to scission: The spinning life of 20Ne

Abstract We solve the cranked Hartree-Fock equations for the nucleus 20 Ne. We follow the yrast line from the ground state to the point where the nucleus fissions. We identify the several configurations which form the yrast line and we also study some excited particle-hole configurations. Quantum effects strongly increase the limiting angular momentum value in comparison with classical estimates. We briefly investigate temperature effects by calculating one isotherm.

GCM calculation of the E2 decay lifetimes of shape isomers

Abstract We apply the generator coordinate method (GCM) in a fully microscopic calculation of the E2 decay lifetime of the isomeric states of 238 U, 230 Thand 232 Th. The basis states have been generated by constrained HFBCS calculations with the potential SkM∗. Triaxial quadrupole deformations have been included. Comparison is made with experiment in the case of 238 U and experimenters are urged to search for the predicted decays in the thorium isotopes.

Nuclear excitation via the motion of electrons in a strong laser field

A method of switching from a nuclear isomeric state to a lasing state is examined. A semi-classical model of laser-electron-nuclear coupling is developed. In it the electrons are treated as free in the external field of the laser, but with initial conditions corresponding to their atomic orbits. Application is made to testing this model in 235U and to the design criteria of a γ-ray laser.