Multipolarities of prompt transitions in 156Dy and spin-parities of the upper band levels

Abstract The prompt γ-ray and conversion-electron spectra following the 159 Tb(p, 4n) 156 Dy and 156 Gd(α, 4n) 156 Dy reactions have been measured with, respectively, a Ge(Li)-NaI(Tl) Compton suppression device and a mini-orange spectrometer. On the basis of the deduced multipolarities, earlier spin-parity assignments for levels in 156 Dy have been confirmed. Furthermore, the recently reported upper band levels could be divided into a negative-parity band up to 11 − or maybe 13 − , and a positive-parity band with tentative K = 0 character and spins 4 + , 6 + , 8 + , 10 + and maybe 2 + . The negative-parity band is described as an aligned-octupole band; the positive-parity band may possibly represent the low-spin extension of the superband responsible for backbending in the β- and ground-state bands in this nucleus.