Spin ∼60 ℏ in 156Dy: competition between collective and terminating structures at very high-spin

Abstract

The highest-spin discrete states ( I∼60 ℏ and E x ∼30 MeV) in normal deformed nuclei have been observed in the rare-earth isotope 156Dy using the 124Sn( 36S,4n) reaction in conjunction with the GAMMASPHERE spectrometer. The positive parity yrast sequence appears to evolve smoothly from a prolate (collective) towards an oblate (non-collective) shape, in contrast to the sudden shape change observed in the isotone 158Er. Terminating states are identified in the negative parity sequences at I π =52 − and 53 − and specific multi-particle-hole configurations are assigned by comparison with cranked Nilsson-Strutinsky calculations. An order of magnitude increase in the interaction strength between close lying high-spin weakly collective structures is determined compared with that found in the lower-spin strongly collective domain. These results give valuable insight into the interplay between collective and terminating structures, and their competition for yrast status in the 40−60 ℏ spin range.