High-spin state spectroscopy of 143Dy

The Dy-143 nucleus has been studied with the Mo-92 (Fe-54, 2pn gamma) reaction at 240 MeV incident energy. A rich variety of structures was observed at high spin. The nearly spherical nuh(11/2) = 11/2 isomer is the basis of a negative parity irregular yrast structure which is observed up to I=51/2. A positive parity band presenting a large dynamic moment of inertia was observed, similar to the deformation enhanced nui(13/2) bands known to exist in this mass region. However, we propose an alternative assignment for this band, namely the triaxial collective minimum with beta =0.2 predicted by total Routhian surface calculations for a N-osc=4 quasineutron excitation coupled to pairs of aligned quasiparticles. Another negative parity structure, with strong M1 and weak E2 crossover transitions, was observed.