Exploring the I = 50-60(Latin small letter h with stroke) domain: Collective and terminating structures in ¹⁵⁶Dy, ¹⁵⁹Er and ¹⁶⁰Er

Very high spin (50-60(Latin small letter h with stroke)) states in transitional 156Dy, 159Er and 160Er nuclei have been studied using the GAMMASPHERE and EUROGAM γ-ray spectrometers. The lowest energy positive-parity bands in 156Dy are found to evolve smoothly towards an oblate shape in contrast to the sudden change observed in the neighbouring 158Er nucleus. In 159Er, the decay path of the positive-parity yrast band splits above Iπ = 85/2+ and favoured multi-particle-hole states are identified in the irregular pattern at 89/2+ and 101/2+. The yrast structure of 160Er is found to remain collective up to and beyond 50(Latin small letter h with stroke) with no sign of an apparent termination.