Fission instability of nuclei at very high angular momenta

Deformation energy surfaces at high angular momenta ($\text{I ≧ 30?}$) are calculated for different nuclear shapes characterized by the deformation β and a neck parameter r. This parametrization has the advantage that it is a natural extension of the Bohr-Mottelson shape parameters β and γ. This choice allows one to study the neck degree of freedom near the fission instability at high angular momenta and also the sudden change of the nuclear shape from an oblate deformation (β > 0; γ = ?60°) to a prolate one (β > 0, γ = 0°) which gives rise to the so called giant backbending (g.b.b.). The deformation energy surface is calculated using the Strutinsky approach with the rotating liquid-drop model (RLDM) and the shell corrections based on a cranked Saxon-Woods potential. The heights of the first and, if present, the second barrier are studied at γ = 0° as a function of the total angular momentum for even mass rare earth and actinide nuclei. The critical angular momenta at which the fission barriers vanish are often higher than that predicted by the RLDM.