Fission barriers and saddle-point shapes

The energy of rare-earth and heavy fissile nuclei is calculated as a function of quadrupole, octupole, and hexadecapole deformations. The liquid-drop model is used with shell corrections according to a method proposed by Strutinsky. The liquid-drop part of the deformation energy is treated exactly by numerical integration. In the shell-model part we used potentials of the Saxon-Woods type as well as harmonic oscillator potentials. Though the latter can more easily be treated numerically, certain ambiguities arise from the various parameters entering in their definition. These are investigated by comparison with the results obtained with use of the Saxon-Woods potential. The symmetry energy and charge radius parameters in the liquid-drop part of the binding energy were taken from Seeger's work. The geometrical parameters defining the single-particle potential and the spin orbit coupling strength were fitted to the energy-level sequence near the Fermi surface or to nucleon scattering data analysed within the optical model. The pairing strength is chosen to reproduce the region of deformed nuclei correctly and to give the over-all trend of odd-even mass differences. The ground-state deformations, fission-barrier heights and locations, and the excitation energy of shape isomers are calculated for various nuclei of the rare-earth and actinide region. (author)