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

• Received 31 May 2000

DOI:https://doi.org/10.1103/PhysRevC.62.064301