Rotation of nuclei around a prolate symmetry axis at very high spin states

Abstract

Classically one expects that nuclei rotate at very high spins (30 < I _< 80) around an oblate symmetry axis. It is shown that strong shell correction energies yield for some nuclei at the end of the rare earth region and in the Pb-region yrast states for a rotation around a prolate symmetry axis. Like for the rotation around an oblate symmetry axis one expects also here yrast traps. The deformation energy surfaces for very high spin states are calculated by the Strutinsky method using a Saxon-Woods potential and by a microscopic method built on constraint Nilsson functions. Both methods agree qualitatively. Yrast traps are studied for these nuclei. It is shown that the MONA (Maximisation of the Overlap of Nuclear wave functions by Alignment) effect prefers at high spin rotation around the symmetry axis of a negative deformed shape at the beginning of the shell and of positive deformation at the end of the shell.

Angular momentum and energy dependence of fission andn, p,4He emission from194Hg compound nucleus

“…The aim of the extensive calculations of the potential energy and the shell correction maps [1][2][3] at very high angular momenta were to study the shape changes and the nuclear stability. Unfortunately, details hidden in the DES calculated either microscopically [-13] or by means of the Strutinsky approach [-1-3] cannot be directly compared with the experimental data.…”

“…Such a description is consistent with the classical picture of the heavy ion reaction visualizing nuclei as liquid drops or Fermi gas bubbles. One knows, however, from extensive studies of nuclear properties, hidden in deformation energy surfaces (DES) at high spins [1][2][3] that shell effects change the classical picture significantly in many instances. The rotating liquid drop model (RLDM) which is successfull in pointing out general tendencies [4], fails for rare-earth and actinide nuclei to describe shape changes, ICRIT at which the giant back-bending occurs as well as the fission instability [5].…”