Nature of the Anomalies of the Moment of Inertia at High Spins

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Abstract
Backbending due to the rotational alignment of two i13/2 neutrons oscillates as a function of the neutron number. This is explained in a particle number and angular momentum conserving model. The neutrons in the i13/2-shell are described by shell model wave functions and are weakly coupled to the rotation of the core. It is shown that the alignment is arranged by the nucleus by scattering two i13/2 neutrons mainly from the Ω = 1/2 and Ω = 3/2 i13/2 orbits into the core. The aligned band has therefore in average two neutrons less in the i13/2-shell. Interaction between the valence nucleon and the core is due to the pairing force. It is shown that this interaction has j -3/2 zeros. No interaction between the ground band and the aligned band means strong backbending while a strong interaction means no backbending. In the second part of this contribution we explain the behaviour of the second anomaly of the moment of inertia by the alignment of two h11/2 protons corresponding to the same oscillating behaviour as discussed before. In this way we can explain that for the N = 90 isotones 66156Dy shows no backbending, 68158Er shows upbending and 70160Yb shows a strong second anomaly of the moment of inertia.