High spin states in the ground and β-bands of 156Dy and the band-crossing interpretation of back bending

High spin states have been identified in ¹⁵⁶Dy using (HI, xn) reactions and γ-γ coincidence techniques. The ground state band does not show any “phase change” or “back bending” behaviour up to spin 18⁺. However a second sequence, based on the β-vibrational band, does show back bending at spin 12⁺. The two sequences intersect just below spin 16⁺ with the 16⁺, 18⁺ and 20⁺ members of the β-band sequence becoming yrast levels. Branching ratios have been obtained for transitions above and below the bend at spin 12⁺. The data are discussed in terms of a simple band-crossing model of back bending.