Anomalous rotational energies and transition probabilities at high spin in the ground-state band in 159Ho

Abstract

Levels with spin values up to 35 2 in the ground-state band of 159Ho are populated when a 159Tb target is bombarded with 49 MeV α-particles. The observed pattern of rotational energies is discussed within a model where a quasiparticle is coupled to a rotor with a variable moment of inertia. The analysis suggests that the core exhibits back-bending similar to the behaviour in 160Er and 158Dy. However, the angular velocity giving back-bending is larger than in the adjacent even nucleides uless the introduced ad hoc attenuation of the Coriolis force disappears at high spin, or more likely, unless the matrix elements of j 2 are also reduced. This uncertainty associated with the motion of the odd particle precludes the analysis of small effects on the back-bending mechanism due to the blocking of an h 11 2 orbital. The relative γ-ray intensities support the notion that g R decreases with increasing values of spin. Furthermore, in the region of back-bending an additional drop of the E2/M1 branching ratio suggests that the B(E2) values are here reduced by about 50%.